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Friday, 22 February 2019

How to spot palaeontological crankery

Pterosaurs, such as the newly described Jurassic species Klobiodon rochei, are magnets for palaeontological cranks: those individuals who harbour and promote idiosyncratic and problematic ideas about palaeobiological topics. Some cranks are a genuine nuisance for educators, but they are easy enough to spot and avoid if you know their characteristics. Say, that sounds like a good idea for a blog post.
Like many popular sciences, palaeontology attracts individuals harbouring what can kindly be called ‘alternative’ or ‘fringe’ ideas: interpretations of evolutionary relationships, animal biomechanics or other facets of palaeobiology that contrast with ‘mainstream’ science. Such individuals are generally referred to as "cranks" - a term defined at Wikipedia as "a person who holds an unshakable belief that most of his or her contemporaries consider to be false". While most crank palaeontology is confined to obscure literature or forgotten corners of the internet, and is therefore pretty harmless, some cranks are major sources of misinformation thanks to their prominent, professional-looking websites, deals with mainstream book publishers, or careers in public outreach exercises.

Cranks are thus a real issue for palaeontological educators and science communicators. Students, teachers and naive members of the public are all potential victims of crankery, and many of us have witnessed crank media being embraced or shared by well-meaning individuals. Among those of us interested in science and outreach, cranks are a semi-regular topic of conversation: how do we combat their miseducation? Ignore them? Engage them on social media? Take them on in public debates? I don't know that there's a right answer, but one approach we can use is helping less experienced individuals recognise crankery when they find it. As with most peddlers of alternative ideas and pseudoscience, palaeontological cranks have characteristic behaviours and interests that stand out quickly once you learn what they are, and this can only help us avoid being hoodwinked by their unique brand of miseducation.

This, then, is my attempt to prime readers for recognising palaeontological crankery. In the interests of making this article as accessible as possible I've attempted to use easily understood, plain-English throughout. I'm dividing the post in two: first, we'll outline the commonest subjects of palaeontological crankery, so as to let readers know when to be extra alert for crank output; and in the second section, we'll look at some crank red flags which should set our sceptical systems to maximum alert. It's worth noting before we dive in that I'm only concerned with 'true' palaeontological cranks here, and will not be tackling young earth creationism, evolution deniers or palaeo-themed cryptozoology. Those are all worthy topics but are well beyond our scope today. I'm also going to generally avoid naming and linking to specific cranks or sources in this article, on grounds that any publicity is good publicity.

The favoured subjects of palaeontological cranks


Claims of remarkable fossil discoveries
Probably the commonest form of palaeontological crankery is the claim of having a significant fossil discovery, yet to be recognised by science. This might be an amazing new fossil, such as a complete pterosaur head in amber, or it could be the identification of overlooked extra bones, soft-tissues or other features on an existing specimen. Cranks making these claims vary as to whether or not they've actually seen the specimens they're discussing, and sometimes they work only from images found in papers, books or on websites. These 'discoveries' are often the crux of all subsequent output from that individual, whether they are simply showing off their specimens on a website or using them to inform ideas about evolution and biomechanics.

Most fossils don't escape some damage en route to discovery by humans: cracks, breaks, distortion of other kinds are common, as shown here on the broken holotype skull of the pterosaur Lacusovagus magnificens. But some individuals will not see these as artefacts of preservation and instead assume that they represent overlooked structures such as teeth, bone divisions or vestigial elements. Given that this work is often based on photos alone, this implies that the experts who spent hours or days studying the actual specimens have missed obvious structures, but that the crank is able to see them without difficulty in a photograph.
A phrase tossed about lots when talking about these claims is 'pareidolia' - the phenomenon of seeing significant patterns or forms in what is actually random visual data. Like perceiving a face on Mars or Jesus on a slice of toast, these individuals 'find' significance in rock structures, cracks on fossils, detritus in amber, or even artefacts of image reproduction. Overwhelmingly, the response from people who've experienced the fossils in question is that these claims represent major over-interpretation of specimens.

Rearranging evolutionary trees
Most would agree that determining the relationships of species with one another is a challenging endeavour, but that generations of anatomical and genetic-based investigations have created a reasonable insight into the broad outline of life's evolution. Not so, according to many cranks, several of whom argue that major branches of evolution (mostly certain charismatic tetrapods) are misplaced in 'mainstream' takes on life's evolutionary tree. Oddly, few cranks agree on exactly which relationships are incorrect. Are birds pterosaurs? Are mammals archosauromorphs? Are pangolins late-surviving stegosaurs? There are lots of alternatives out there, leaving only a smattering of die-hard BAND ("Birds Are Not Dinosaurs") supporters agreeing over where we've got our interpretation wrong.

These contrary opinions are mostly informed by nothing but intuition or cherry-picked data. On rare occasions, actual phylogenetic software is used to predict non-standard evolutionary trees, but it's well documented that these analyses are so broken and misinformed by problematic anatomical data that their results are meaningless. Darren Naish's article on the claims made at the infamous website ReptileEvolution.com offers a great insight into a particularly egregious example of this, and is recommended reading for anyone researching paleontological subjects online.

Amazingly, there are still people out there who doubt the bird-dinosaur link, despite the literal thousands of fossils and hundreds of studies that evidence the origin of birds among theropod dinosaurs. Even relatively non-birdy theropods, like Gorgosaurus libratus, shown here, have skeletons littered with features that are otherwise only seen in bird-line tetrapods.
The lifestyles of fossil reptiles
The great size and peculiar anatomy of many fossil animals - but especially certain Mesozoic reptiles - draws crank attention when they don't buy into accepted modern interpretations of their lifestyles. How could large dinosaurs support their great weight on land? How did plane-sized pterosaurs fly? How could an animal the size and shape of a giant theropod be hidden from prey? Rather than deriving answers from disciplines that have a genuine bearing on these issues, such as biomechanics, fossil trackways, palaeoenvironmental interpretations, or the ecology of living predators, cranks instead propose radical solutions. Perhaps all dinosaurs were aquatic? Maybe Earth's atmosphere was thicker, or gravity was radically different from how we know it today?

Each of these 'solutions' is actually a rabbit hole of problems, errors and logical fallacies that we could disappear into for some time. It's common for cranks to cite something from their background that makes them uniquely able to see biomechanical problems where others can't. My favourite example is a high-school physics teacher who argues that they understand giant dinosaurs and pterosaurs better than anyone because of a particularly formidable understanding of square-cube law. What we're really seeing in these cases is Dunning-Kruger effect: a cognitive bias where individuals rank their cognition of a topic much higher than anyone else, even if they have only a slight or even problematic understanding of the subject in question. I can give no better example of this than the recent and public debate over Too Big to Walk, a book by microbiologist Brian Ford (published in 2018) which proposes that dinosaurs were incapable of supporting themselves on land and must have been confined to aquatic habits. Ford's thesis is outlined here and in other articles online, with responses by palaeontologist and dinosaur specialist Darren Naish here, here and here. All palaeontological crankery is reliant on Dunning-Kruger to a certain extent, but crank arguments about the lifestyles or biomechanics of prehistoric reptiles are particularly good examples.

10 Red flags and pointers for spotting crank palaeontology

If these are the current hot topics in palaeontolgical crankery, how do we distinguish genuine scientific discussions of these matters from crank nonsense? Given that most cranks seem to regard themselves as somehow 'special' - being of unique abilities and insight, or at least due respect for authoring some critical scientific breakthrough - it must pain them to learn that they are actually extremely similar and predictable in how they present their work, talk about themselves and interact with others. This is to our benefit, as it gives us excellent means to guauge the general reliability of whatever it is we're reading or listening to. Some of these checks and tells are listed below. This list is not exhaustive, but if an article, presentation or book hits a number of these marks you probably want to treat their content with extra scepticism.

1. The creation of a problem to solve
Our first red flag is the prediction of cranks to manufacture problems that need solving. They confidently make grand claims like "scientists have never explained this" or "subject X has never been satisfactorily investigated". Such statements are an essential foundation of crank thinking because if these 'problems' didn't exist, the crank would have nothing to 'solve'. While many palaeontologically savvy readers will smell these rats immediately, such claims stand a chance of duping naive readers. Be cautious when reading any sweeping, unreferenced suggestion that we're entirely wrong or misinformed about a particular facet of palaeontology. It's actually very difficult to think of a major palaeontological area where all previous work is totally useless, and such claims are more likely to be someone sidestepping science in order to create space for a pseudoscientific approach.

2. Avoidance of conflicting data or fields of study
A sure-fire crank giveaway is the dismissal of data contradicting with their ideas, even if that means rejecting an entire scientific discipline. Science works by testing ideas using different methods, not through cherry picking the results and methods that best support our preferred ideas. If someone states that DNA-based methods for reconstructing evolutionary trees are bogus, or that fossil footprints have no bearing on the habitat preferences of giant extinct animals, there's a good chance that they're attempting to deflect data that conflicts with their ideas.

3. Over-confidence
One of the most defining features of cranks is their confidence. Genuine palaeontologists, like all scientists, learn early in their careers to be careful about overstating certainty. Outside of describing raw data (e.g. reporting measurements or the outcomes of analyses) they use cautious phraseology like "this infers", "our findings indicate", and "we were unable to replicate Author X's findings". This accepts that interpreting fossil life is always a work in progress and that our work is rarely the last word on a given topic. Cranks, on the other hand, tend to write boldly and without reserve: "this is", "I have shown" and "Author X is blinkered and wrong". This level of confidence is not only misplaced (cranks revise their ideas as often as legitimate scientists, often without documenting why) but characterises a dangerous level of self-belief for someone purporting to conduct legitimate science.

Cranks are drawn to large dinosaurs like Dreadnoughtus schrani when they cannot, or will not, accept that they were capable of walking on land, which leads to ideas of dinosaurs living largely in water, in denser atmospheres, or under reduced gravity. Huge swathes of data from anatomy, geology and dinosaur trackways show that none of these concepts are correct. It also seems lost on cranks that plenty of non-dinosaurian Mesozoic organisms would struggle to live in denser atmospheres, low gravity or waterlogged habitats. It's almost like these ideas are not well thought through.
4. An embarrassment of scientific riches
It's rare for cranks to make one bold claim. Instead, they frequently have a slew of amazing, game-changing discoveries. They don't have one amazing fossil, they have many. Palaeontologists have not got the anatomy of one species wrong, they've overlooked major anatomical characteristics across huge groups. And it's common for cranks to suggest that their work has a significant bearing on all manner of palaeontological mysteries: that their idea on dinosaur locomotion also explains giant pterosaur flight, that their anatomical criteria for understanding the evolution of reptiles can be applied, without modification, to mammals or birds. It's a hallmark of crankery to have all the answers - or at least more answers than 'mainstream' scientists.

Claims for so many ground-breaking discoveries should immediately trigger our scepticism. Yes, there are skilled and prolific scientists who make numerous significant contributions to our collective knowledge, but they do not make them every week. Good science takes time: time to collect and analyse data, time to document and report the findings, time for peers to check the work, and time to publish it in a suitable venue. While the crank may view their churning out of game-changing revelations as the inevitable consequence of a self-led scientific revolution, they're actually exposing their lack of rigour, willingness or ability to have their work vetted by relevant experts.

5. An abundance of self-citation
Does the article you're reading extensively cite the work of the author, and almost always in an affirming light? It would be wrong to say that genuine scientists do not self-cite, or even that some do not over cite their own work (scientists have egos too, many have rather big ones), but if you're reading a work that is extensively citing and complementing the author's own work, be wary: this is often a sign of crankery. This red flag flies especially high if the author is demeaning the work of others while holding their own work in high regard (see below).

6. Knowing your authors
In science, what is said matters more than who says it, but when a questionable claim is made the integrity of the author can be a useful indicator of credibility. Whether we like it or not, reputation matters. We should be extra sceptical with proposals made by those with a history of quackery or no background in the field they're claiming expertise in. This is not to say that amateur or non-professional individuals can't or won't have insights on palaeontolgical matters overlooked by experienced researchers, but folks without experience or training in a relevant field are more prone to making mistakes and overlooking data. It’s quite easy to research scientists and educators nowadays by simply Googling their names, or by asking around in the right internet venues. Sometimes this very quickly reveals whether you should be taking that individual seriously, or if you need to take a more cautious approach to their ideas.

7. Misleading credentials and other trickery
While some cranks decry academic titles, others flaunt their credentials to add support to their claims. But simply having a high-level qualification does not make someone an expert in all subjects. If someone is making questionable claims, check out what their qualifications are actually in: having a postgraduate qualification in microbiology or graphic design does not automatically equate to an equivalent understanding of dinosaurian biomechanics. Similarly, be wary of cranks making up official-sounding institutions as their place of research. There's no restriction on naming your own institution or society so cranks can create 'scientific' or 'educational' bodies as easily as I can call my garden shed the "Mark Witton Institute of Natural History". A quick round of Googling will quickly expose these institutions and credentials for what they really are. Needless to say, if someone is distorting their credentials in order to seem more authoritative, you've got an excellent reason to question pretty much everything they say.

That most cranks have only a superficial knowledge of palaeontology is demonstrated by their focus on well-known and charismatic species such as big dinosaurs and pterosaurs. It's rare to see cranks applying their ideas to more routine, less exciting species like extinct fish, invertebrates or even crocodyliforms like Hulkeopholis willetti. My hunch is that most cranks learn about palaeontology largely through popular media and if so, this explains why their ideas are so easily dismissed. Even basic training in palaeontology is enough to expose major holes in their ideas.
8. A predilection for criticism and personal attacks of scientists
Because cranks believe they have a superior scientific insight they are often extremely critical of other researchers. This seems to get worse as the crank gets older and has faced long-term rejection from the scientific community, and it can manifest itself in particularly nasty and underhand ways: obsessive and ultra-detailed 'criticisms' of published works; personal attacks and harassment of scientists; accusations of institutions being dogmatic, blinkered or even fundamentalist in their adherence to 'mainstream' views; and even attempts to dissuade prospective PhD students from legitimate postgraduate programmes. You don't see comments like this in legitimate research because genuine science is concerned with hypotheses and ideas, not venting frustrations at individuals or institutions. Crank hostility can be especially obvious if they have a comment field on their websites: when challenged, they are often quick to vent their frustrations.

9. The Galileo Gambit
Another major red flag common to all cranks is their frequent comparison between themselves and scientists who received establishment pushback against their ideas - Wegner, Galileo, Darwin and so on. The folly of the Galileo Gambit is well established and we needn't outline it in detail here, it will suffice to point out that invoking these big names is clear evidence of self-belief in their own abilities against overwhelming evidence to the contrary. Note that scientists making genuine research contributions never use this defence when proposing ideas they know will cause upset or controversy. If you see someone comparing themselves in this way to a historically persecuted scientific figure, there's a very good chance they're a dyed-in-the-wool crank.

10. Beware of Big Palaeo!
Saving the best until last: yes, unbelievable as it is, there are individuals who suggest mainstream scientists are somehow organising against them to suppress their work. While maybe not imagining something as sinister as the Big Pharma conspiracy, some cranks infer that palaeontology is governed by individuals who dictate what is and what isn't acceptable science, and who forbid the publication of work that challenges the status quo. The plot thickens with universities not simply training scientists, but actually indoctrinating them into this way of thinking. This casts PhDs not as experts in their subject, but as brainwashed members of the Big Palaeo cult. In controlling the ebb and flow of palaeontological science these individuals are able to maintain lofty academic positions and secure grant money. In my experience, this claim tends to follow the crank's papers being rejected from academic journals or finding that no palaeontologists will agree with their interpretation of an (allegedly) amazing fossil.

As someone with academic experience myself, I find this mindset genuinely fascinating. It gives a real insight into how some cranks see the world: so convinced are they of their own findings and significance that their rejection from academia can only reflect a global, organised conspiracy. In reality, their lack of academic recognition reflects the fact that any average scientist can spot fatal errors in their proposals. Moreover, the idea that palaeontologists, or any scientists, suppress controversial new ideas is ludicrous. Within the well-publicised realm of dinosaur science, just some recently published contentious ideas include the recovery of soft, unlithified proteinaceous tissues in 80 million year old fossil bones (Schweitzer et al. 2005), that Spinosaurus was a weirdly proportioned, archaeocete-like quadruped (Ibrahim et al. 2014), and that major branches of the dinosaur evolutionary tree have been incorrectly arranged for a century (Baron et al. 2017). These are bold claims that remain debated, but they were published nonetheless. The difference between these papers and crank ideas is simply the evidence and methodologies used to justify their conclusions - that's all there is to it. We could write a whole essay on how flawed the idea of a Big Palaeo conspiracy is but, in short, if you encounter anybody claiming their work is being silenced by a conspiracy of palaeontologists they are, without doubt, an embittered crank of the highest order.

These are just a few giveaways that you're dealing with a palaeontological crank, hopefully they're of use to folks less familiar with the more questionable parts of palaeontological outreach. Some readers may have identified some parts of the above list as common hallmarks of more general crankery, and that's no coincidence: as mentioned above, although crank subjects change, their behaviour and public presentation is remarkably consistent. There are longer, more detailed discussions of crank detection available online, but what we've outlined here should be enough to equip most readers with an early warning system for crankery. We've not, of course, answered the question about what to do with cranks when we identify them. Should we ignore them? Alert others about them? Contact them about their bad science? That's another long discussion (and a much murkier one) however, so that'll have to wait for another time.

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References

  • Baron, M. G., Norman, D. B., & Barrett, P. M. (2017). A new hypothesis of dinosaur relationships and early dinosaur evolution. Nature, 543(7646), 501.
  • Ford, B. J. (2018). Too Big to Walk: The New Science of Dinosaurs. HarperCollins UK.
  • Ibrahim, N., Sereno, P. C., Dal Sasso, C., Maganuco, S., Fabbri, M., Martill, D. M., ... & Iurino, D. A. (2014). Semiaquatic adaptations in a giant predatory dinosaur. Science, 345(6204), 1613-1616.
  • Schweitzer, M. H., Wittmeyer, J. L., Horner, J. R., & Toporski, J. K. (2005). Soft-tissue vessels and cellular preservation in Tyrannosaurus rex. Science, 307(5717), 1952-1955.

Friday, 25 January 2019

Plesiosaurs on the rocks: the terrestrial capabilities of four-flippered marine reptiles

Maurice Wilson's charming c. 1958 painting of plesiosaurs coming ashore, from the Daily Mail Boys Annual (note "boys": girls aren't allowed to be interested in prehistory. Get out of our tree house!). Such depictions were commonplace until a few decades ago, but are all but extinct now. So what's happened to the idea that plesiosaurs could venture onto land?
Until comparatively recently it was not uncommon to see depictions of plesiosaurians* on rocks and beaches as if they had hauled themselves from the sea like breeding sea turtles or basking pinnipeds. Such restorations have a long history. Some of the earliest marine reptile palaeoart shows plesiosaurians on beaches or very shallow water, and we've even seen land-based plesiosaurians in feature films and documentaries, including notable sequences in When Dinosaurs Roamed the Earth (1969) and Walking with Dinosaurs (1999, below).

*Why 'plesiosaurians' rather than 'plesiosaurs'? Though a common vernacular, the term 'plesiosaurs' is potentially confusing as it could either refer to a number of marine reptile clades (e.g. plesiosauroids, plesiosaurids) or body plans (plesiosauromorphs). 'Plesiosauria' has a less ambiguous meaning as it specifically refers to the clade encompassing rhomaleosaurids, pliosauroids and plesiosauroids, so it might be a preferable catch-all term this marine reptile clade.

Today, it's much rarer to see plesiosaurians depicted outside of the aquatic realm. For... reasons, I'm restoring a number of marine reptiles at the moment, so I've been wondering if it would be acceptable to revive artwork of these creatures on rocky shores, beaches and other coastlines, if only to bring some variation to my marine scenes. As usual, this inquiry began with a literature crawl. Because 19th century palaeoart suggests palaeontologists once imagined these animals as routinely emerging from the waves, I expected marine reptile papers to be full of discussion about the terrestrial prospects of plesiosaurians, perhaps with an in-depth analysis of the concept bringing an end to the artistic tradition of depicting them on land. The transition from imagining plesiosaurians as semi-aquatic to fully aquatic seems to have happened organically, however: if there's a watershed paper or significant debate behind this, I've missed it. Richard Ellis' 2003 book Sea Dragons - perhaps the closest thing we have to an all-encompassing introductory review of marine reptiles - seems to confirm my independent findings, portraying plesiosaur terrestrial abilities as highly doubtful, but also a question without a firm answer in scientific literature.

Jurassic plesiosaur Cryptocleidus sits around the coasts of the Oxford Clay Sea in 1999's Walking with Dinosaurs. Uploaded to Youtube by user MARTINEZZZ365.

The idea of plesiosaurians leaving water has been strongly tied to historic uncertainty about their reproductive habits. It stands to reason that, if plesiosaurians laid eggs, they must have somehow dragged their way out of the sea to construct their nests (Taylor 1981, 1986). The notion that plesiosaurians could have given birth to live young is pretty old (e.g. Seeley 1896) but scant evidence of their reproductive strategies prevented dismissal of land-based nesting habits until relatively recently. We now have evidence of live birth in plesiosaurian relatives (nothosauroids, Sander 1988; Renesto et al. 2003; Cheng et al. 2004) as well as a true plesiosaurian (a polycotylid, O'Keefe and Chiappe 2011), and so we needn't imagine plesiosaurians hauling out onto beaches to lay eggs, turtle-style.

But I'm going to keep pulling at this thread. While their capacity to give birth to live offspring eliminates the behavioural necessity for leaving water, it does not, in itself, demonstrate that plesiosaurian anatomy was functionally incapable of land-based locomotion, or that they did not leave the sea to find refuge or seize prey - orca style - from shorelines. After all, viviparity does not mean that seals, sea otters or even manatees have committed to a fully aquatic life (a voluntarily beached manatee deserves a citation - see Motani et al. 2015). Is there a cogent functional argument for why plesiosaurians might struggle out of water that will let me (and others) escape painting nothing but blue and green pictures?

How plesiosaurians might have moved on land

Our discussion will be aided by first outlining what we might realistically expect of a walking or crawling plesiosaurian. No one, for instance, predicts that plesiosaurians could stride around like sea lions or the plesiosaur in When Dinosaurs Roamed the Earth. Their flipper skeletons were essentially inflexible so they were incapable of being articulated into a walking limb. This precludes walking on their hands and feet in the way that eared seals can. They were also likely incapable of bouncing along in the manner of true seals, where the flexibility of the spine is used to 'hump' their way forward while powerful, gripping claws pull and steer them around. Plesiosaurian bodies were pretty rigid - their robust gastralia and ribs are sometimes superficially compared to turtle shells - and likely incapable of the twisting and bending necessary to bounce their way over shorelines. And in lacking claws, the only contribution their flippers could make to crawling would be crude pushing and lifting actions.

True seals, such as the grey seal (Halichoerus grypus), are far less terrestrially proficient than the eared seals (sea lions, fur seals etc.) and have to bounce or drag themselves around when ashore. Large claws on their flippers help in this activity (and are also useful for scratching). Grey seal cow photo by Georgia Witton-Maclean.
If plesiosaurians could leave the water at all, we have to imagine something more akin to turtle locomotion: using their flippers to push and pull themselves along while lying on their bellies. Their weight and a likely inability to clear their bodies entirely from the ground predicts that much of their energy would go into overcoming drag incurred by their wide bodies and tails. Terrestrial plesiosaurians would need to make full use of their powerful flipper downstroke muscles (soundly evidenced by the enormous muscles of their chest and the underside of their hips; see Carpenter et al. 2010; Araújo and Correia 2015) to lift their bodies and propel themselves forward. The exact motion of their flippers remains controversial, but is likely to have been a wingbeat-like action (Taylor 1986; Carpenter et al. 2010; Liu et al. 2015; Muscutt et al. 2017) that may have been enough to shove plesiosaurians over shorelines. The picture we're building here is of a slow and laborious means of locomotion. If plesiosaurians did intentionally leave water, they almost certainly visited locations inaccessible to terrestrial predators.

Polycotylid Dolichorhynchops bonneri demonstrating a fairly typical plesiosaurian torso and flipper construction. At face value, the retention of four limbs and stout limb girdles looks like terrestrial locomotion shouldn't be too hard for these guys - they certainly look more terrestrially capable than many other marine tetrapods. From Carpenter et al. (2010). Scale bar is 1 m.
I also think we should rule out raw body size as a compelling reason to doubt land-based locomotion in plesiosaurians. There's no reason to regard plesiosaurians as atypically heavy compared to other marine animals (Everhart 2000, Henderson 2006) and, indeed, their general lack of pachyostosic skeletons might make them lightweight compared to some other aquatic tetrapods (e.g. Street and O'Keefe 2010). Many species were probably within the mass ranges of living species known to transition between land and sea. The known maximum limit for this lifestyle is set by bull elephant seals which, according to Wikipedia, reach 3,000 - 4,000 kg. We don't have many plesiosaurian mass estimates to compare this figure to, but a few noteworthy values are Everhart's (2000) predicted mass of 2.8 tonnes for a 9 m long plesiosauroid, and Henderson's (2006) 217 kg 3 m Cryptocleidus. Truly giant plesiosaurians - 10 and 11 m long individuals - are beyond the masses of big elephant seals (Henderson 2006), but this still leaves plenty of small and mid-sized species at or below the mass threshold of marine species that we know can venture onto land, assuming they have the right adaptations. For me, our question is most appropriately addressed through assessment of anatomy and functional morphology, not a priori judgements about size.

Scrutinising the model

The bar we've set for plesiosaurian terrestrial locomotion is thus pretty low: even if they can only shamble up a beach we could consider our conditions met. But how feasible is even this laborious means of getting around on land? To cut to the chase: not very. There are multiple aspects of plesiosaurian anatomy that probably precluded even very basic terrestrial capabilities.

Plesiosaurian flippers, for instance, seem poorly suited for use on coastal substrates. Semi-aquatic species such as turtles, seals and terrestrially-roaming fish have a degree of jointing or articulation in their forelimbs which transforms them from flippers or paddles into walking limbs (Mazouchova et al. 2013, also see this post on the potentially amphibious ichthyosaur Cartorhynchus). A jointed limb performs considerably better on loose substrates (such as those common on beaches, mudflats and other shoreline locations) because it enables greater control of force distribution as animals move. Immobile flippers tend to skim over or dig into sand or mud, while jointed limbs can respond to yielding substrates to maximise lift and propulsive forces. Where substrates have already been disturbed, fixed-shape flippers can struggle to get any purchase at all (Mazouchova et al. 2013).

The evolution of the plesiosaurian flipper - represented here with early sauropterygians (A - B) and true plesiosaurians (C - D) involves the development of tightly fitting bones and removal of joint mobility. This makes for a superior flipper for an underwater flier, but compromises their terrestrial capacity. Image and caption from Storrs (1993).
Assuming these findings apply to plesiosaurians - and there's no reason they shouldn't - their effectively immobile flippers present a major barrier to terrestrial activity. Plesiosaurian flippers lack both obvious bony joints or significant cartilaginous regions that would allow them to flex, so they best fit those modelled flippers which skid around or dig into the substrates they're meant to traverse. We must consider that their flippers are married to animals that are already encumbered by large size and weight, as well as the additional difficulty of drag forces operating on their bodies as they moved forward. The it hard not to imagine a beached plesiosaurian like a heavy vehicle stuck in sand, spinning its wheels as it tries to move forward.

The issues with plesiosaurian limbs do not stop there as their limb girdles are also ill-equipped for supporting their weight on land. While augmented ventrally to accommodate big downstroke muscles, the upper regions of plesiosaurian shoulder and pelvic girdles are only weakly developed. This isn't unusual for aquatic species as a major role of expanded upper limb girdles - specifically the scapulae of the shoulder, and ilium in the hips - is stabilisation of the limb girdles during terrestrial locomotion (some readers may recall us discussing this recently in context of another marine reptile, Helveticosaurus). But while adequate for life at sea, on land these small girdle elements provide only weak girdle support and thus impede locomotion, and this was probably true for plesiosaurians. Though retaining a connection between the ilia and sacral vertebrae, the articulation is weak and ligamentous, and thus unsuited to weight-bearing (O'Keefe and Chiappe 2011). Similarly, their small scapulae leave little space for muscles associated with stabilising the shoulder against the body, and the shoulder is poorly braced for terrestrial locomotion (see Rieppel 1989 for discussion, also Araújo and Correia 2015). We thus have flippers ill-suited to land-based locomotion attached to limb girdles which are maladapted to weight-bearing. These are not the features of animals that are regularly hauling themselves onto shorelines.

Pelvis of Brancasaurus brancai in lateral (A) and medial (B) view, from Carpenter et al. (2010). Note the extremely narrow ilium: this structure articulates with the vertebrae overlying the hip to act as an important brace for the pelvic girdle during terrestrial locomotion, so its small size does not bode well for the prospects of plesiosaurs leaving water.
And there are further impacts from the reduction of the scapula to be explored. The muscles that elevate our heads and necks are anchored to our scapulae as well as our vertebrae, so the size of bones making up our shoulders dictates how large muscles important to neck elevation and control (e.g. the trapezius, levator scapulae) can be. Plesiosaurians famously have large necks and/or heads, but lack the weight-saving adaptations of similarly proportioned land animals such as pneumatic tissues and reduction or displacement of neck musculature towards the body (e.g. Taylor and Wedel 2013, also see this discussion of the lifestyle of Tanystropheus). Their necks and heads must have thus been heavy compared to those of large necked or big headed terrestrial reptiles**, so we might expect substantial shoulder bones to anchor massive neck elevators if they were routinely leaving water. This casts their tiny scapulae as the exact opposite of what we might expect if these animals were routinely crawling around on land.

**To put some numbers on this, Henderson (2006), modelled plesiosaurian heads and necks with tissue densities of 1.05 g/l, about 1.5 times heavier than a value we assume for a bird or bird-like dinosaur.

The pectoral region and musculature of Rhomaleosaurus, modified from Araújo and Correia (2015). While the humerus is well muscled, the scapula is proportionally tiny compared to the chest, which has implications for shoulder stability and carriage of the head and neck.
Plesiosaurians could have developed an alternative approach to supporting the weight of their heads and necks out of water, such as bulking up the muscles surrounding their neck vertebrae. If so, we could predict structures equivalent to withers (elevated vertebral spines over the shoulders related to expanded neck musculature) in species with particularly large heads and necks. Such structures are not to be found plesiosaurians however, so I don't think this idea is compelling. This being so, it looks like neither the shoulders or anterior trunk vertebrae provide sufficient space for the powerful neck muscles needed to elevate their necks and heads on land for sustained periods. The impact of struggling to lift their heads for long intervals could include further impedance to their locomotion (additional drag, difficulty overcoming obstacles) as well as exposing their facial tissues to abrasion and other damage.

Ventral view of rhomaelosaurid Meyerasaurus victor, as figured by Smith and Vincent (2010). Note that the extensive bones of the chest, hips and gastric regions are entirely unfused: like many secondarily marine animals, plesiosaurian skeletons were likely far more cartilaginous than their terrestrial ancestors. Scale bar is 1 m.
A final, but no less significant, consideration for our inquiry is the high volume of cartilage associated with the plesiosaurian skeleton. A glut of unfused bones and loosely fitting contours between closely associated elements betrays a skeletal system held together primarily through extensive amounts of cartilage tissue. This includes areas of relevance to land-based locomotion, such as the shoulder and hip joints, the limb girdles and the region between the gastralia and ribs. In water, these softer connections wouldn't cause any issue, but on land the flexibility and softness of cartilage might weakens skeletal support and strength. The hypothesis outlined above posits that land-based plesiosaurians are essentially moving around with brute force, shoving their large masses around with motions of their flippers against large drag forces. Under this scenario, a relatively rigid and uncompromising skeletal frame would be ideal, whereas one with large volumes of cartilage would make movement less efficient.

What about small-bodied plesiosaurians?

With ,any aspects of plesiosaurian anatomy looking incompatible with terrestrial activity, we might need to play a biomechanical get-out-of-jail-free card to prevent abandonment of this concept altogether: small body size. Inescapable rules of scaling mean that a given bauplan, expressed at smaller size, can perform biomechanical feats impossible for bigger individuals. Might small plesiosaurian species or juveniles exploit greater relative tissue strength ratios, lower body masses and improved muscle power:weight ratios to haul themselves onto land, leaving only larger plesiosaurians confined to water?

The pliosaurid Thalassiodracon hawkinsi is one of the smallest plesiosaurians known at c. 2 m long, and yet it bears all the same hallmarks of incompetent terrestrial abilities as its larger relatives. Are the virtues of small size enough to justify thinking animals of this size could leave the water? Photo from Wikipedia, by the paleobear, CC BY 2.0.
I must admit that I'm skeptical even here. Anatomically speaking, small plesiosaurians have the same terrestrially-inhibited anatomy as their larger relatives: inflexible flippers, high cartilage volumes, and low weight bearing capabilities for the body, head and neck. Smaller size could make all the difference, but size alone is of ambiguous significance to predictions of extinct animal behaviour. It's clearly a factor in what fossil species could and couldn't do, but it should not overshadow better established relationships between form and function when considering extinct animal lifestyles (see also: flight in giant pterosaurs). So while small size theoretically makes terrestrial locomotion more achievable for an aquatic animal, it's ultimately circumstantial evidence for this behaviour and not an especially compelling counterargument.

And as a final, closing thought on this, it's also worth considering that plesiosaurians were generally large bodied creatures. Genuinely small species (such as the c. 2 m long Thalassiodracon hawkinsi) are rare and even their offspring were large (e.g. 1.5 m calf lengths in 4.7 m long mothers - O'Keefe and Chiappe 2011). Mesozoic shorelines were probably not swarming with small plesiosaurians even if they did have superior terrestrial capabilities, because by and large plesiosaurians weren't small creatures.

Bring on the blue paints

So, should palaeoartists get back to painting plesiosaurs out of water? Sadly, no. Any notion that plesiosaurians were capable of hauling themselves onto land is not only unnecessary in light of what we know of their reproductive biology, but also contradicts much of what we understand about the functional morphology of semi-aquatic animals. Their four-flipped construction looks a little more terrestrially-apt than the bodies of a whale or ichthyosaur, but I suspect an accidentally beached plesiosaurian would be in just as much trouble as these more classically-shaped marine forms. History shows that we can make beached plesiosaurians look half convincing in art, but it's a hollow victory: the science is not on our side.

I still find it odd that there isn't a more detailed discussion of plesiosaurian - or maybe broader sauropterygian - terrestrial capability in marine reptile literature. After all, many clades generally regarded as relatives or even ancestral to plesiosaurians are regarded as semi-aquatic (e.g. nothosaurs, Helveticosaurus) and there has to be an interesting story there regarding the progressive abandonment of land. Hopefully studies along these lines will be performed before we're much older. But for the time being, I'll be restoring all my plesiosaurians in water, where they almost certainly belonged. I'll leave you with this painting of Pliosaurus kevani in their rightful habitat.

Pliosaurus kevani large and small, at home in the sea. Junior is particularly happy that it doesn't have to venture out onto land, probably because it's always freezing cold getting out of the water, and pliosaurids were surprisingly wimpy about that sort of thing. #palaeofact

Enjoy monthly insights into palaeoart, fossil animal biology and occasional reviews of palaeo media? Support this blog for $1 a month and get free stuff!

This blog is sponsored through Patreon, the site where you can help online content creators make a living. If you enjoy my content, please consider donating $1 a month to help fund my work. $1 might seem a meaningless amount, but if every reader pitched that amount I could work on these articles and their artwork full time. In return, you'll get access to my exclusive Patreon content: regular updates on research papers, books and paintings, including numerous advance previews of two palaeoart-heavy books (one of which is the first ever comprehensive guide to palaeoart processes). Plus, you get free stuff - prints, high quality images for printing, books, competitions - as my way of thanking you for your support. As always, huge thanks to everyone who already sponsors my work!

References

  • Carpenter, K., Sanders, F., Reed, B., Reed, J., & Larson, P. (2010). Plesiosaur swimming as interpreted from skeletal analysis and experimental results. Transactions of the Kansas Academy of Science, 1-34.
  • Cheng, Y. N., Wu, X. C., & Ji, Q. (2004). Triassic marine reptiles gave birth to live young. Nature, 432(7015), 383.
  • Ellis, R. (2003). Sea dragons: predators of the prehistoric oceans. University Press of Kansas.
  • Everhart, M. J. (2000). Gastroliths associated with plesiosaur remains in the Sharon Springs Member of the Pierre Shale (Late Cretaceous), western Kansas. Transactions of the Kansas Academy of Science (1903), 64-75.
  • Henderson, D. M. (2006). Floating point: a computational study of buoyancy, equilibrium, and gastroliths in plesiosaurs. Lethaia, 39(3), 227-244.
  • Liu, S., Smith, A. S., Gu, Y., Tan, J., Liu, C. K., & Turk, G. (2015). Computer simulations imply forelimb-dominated underwater flight in plesiosaurs. PLoS computational biology, 11(12), e1004605.
  • Mazouchova, N., Umbanhowar, P. B., & Goldman, D. I. (2013). Flipper-driven terrestrial locomotion of a sea turtle-inspired robot. Bioinspiration & biomimetics, 8(2), 026007.
  • Motani, R., Jiang, D. Y., Chen, G. B., Tintori, A., Rieppel, O., Ji, C., & Huang, J. D. (2015). A basal ichthyosauriform with a short snout from the Lower Triassic of China. Nature, 517(7535), 485.
  • Muscutt, L. E., Dyke, G., Weymouth, G. D., Naish, D., Palmer, C., & Ganapathisubramani, B. (2017). The four-flipper swimming method of plesiosaurs enabled efficient and effective locomotion. Proc. R. Soc. B, 284(1861), 20170951.
  • O’Keefe, F. R., & Chiappe, L. M. (2011). Viviparity and K-selected life history in a Mesozoic marine plesiosaur (Reptilia, Sauropterygia). Science, 333(6044), 870-873.
  • Renesto, S., Lombardo, C., Tintori, A., & Danini, G. (2003). Nothosaurid embryos from the Middle Triassic of northern Italy: an insight into the viviparity of nothosaurs? Journal of Vertebrate Paleontology, 23(4), 957-960.
  • Rieppel, O. (1989). Helveticosaurus zollingeri Peyer (Reptilia, Diapsida) skeletal paedomorphosis, functional anatomy and systematic affinities. Palaeontographica Abteilung A, 123-152.
  • Sander, P. M. (1988). A fossil reptile embryo from the Middle Triassic of the Alps. Science, 239(4841), 780-783.
  • Seeley, H.G. (1896) On a pyritous concretion from the Lias of Whitby. Annual Report of the Yorkshire Philosophical Society, 1895, 20–9.
  • Storrs, G. W. (1993). Function and phylogeny in sauropterygian (Diapsida) evolution. American Journal of Science, 293(A), 63.
  • Street, H. P., & O'Keefe, F. R. (2010). Evidence of pachyostosis in the cryptocleidoid plesiosaur Tatenectes laramiensis from the Sundance Formation of Wyoming. Journal of Vertebrate Paleontology, 30(4), 1279-1282.
  • Taylor, M. A. (1981). Plesiosaurs-rigging and ballasting. Nature, 290, 628-629.
  • Taylor, M. A. (1986). Marine reptiles: Lifestyle of plesiosaurs. Nature, 319(6050), 179-179.
  • Taylor, M. P., & Wedel, M. J. (2013). Why sauropods had long necks; and why giraffes have short necks. PeerJ, 1, e36.

Sunday, 23 December 2018

No, Cretaceous sharks did not leap from water to eat flying pterosaurs

How the heavy hitters covered Hone et al. 2018: a short, open-access and easy-to-read paper about a shark tooth preserved with Pteranodon. The Sun gets bonus stupid points for making their own graphic. 
Sigh.

Major news outlets have been reporting this week that a new study evidences prehistoric sharks predating pterosaurs by leaping from the water to snatch them in mid-air. It would be an awesome discovery, if it were true. In reality, these headlines are nothing but a construct by journalists based on a misread palaeoart image, ignorance of some basic facts of animal biology, and lazy science reporting. I'm particularly angry because the study being misreported, and the art being misread, stems from a paper that I recently published with with my friends and colleagues Dave Hone and Mike Habib (Hone et al. 2018). The paper is in PeerJ, and is thus open-access. Anyone - including our dear media - can fact check what we have to say without hitting a paywall.

The nature of modern news is that stories can spread like wildfire, and it's effectively impossible to correct major gaffes once a story gains momentum. With that in mind, the best I can do is outline here what our new paper actually says, what our artwork actually shows, and hope that readers link to this post wherever they see this ridiculous press story being shared. It must be said that a number our outlets are reporting the story more accurately, but enough have mangled our findings that I feel I need to do something. I genuinely care about the accurate conveyance of science, and I've found this distortion of our work and my painting very distressing.

What our paper actually says

OK, first up: a summary of our paper. Mike, Dave and I have documented a series of neck vertebrae from the famous Late Cretaceous pterosaur Pteranodon associated with the tooth of a lamniform shark, Cretoxyrhina mantelli. The vertebrae and their teeth were found in 1965 but our records about their discovery are confused and we don't know whether they were part of a larger discovery of bones, or just a few isolated remains. There are hints that they may have been part of a more impressive skeleton, but it's pretty hard to tell. In any case, today this string of vertebrae is on display at the Los Angeles County Museum as part of a composite skeleton.

Vertebrae are not diagnostic for different Pteranodon species so we refrain from identifying the pterosaur beyond Pteranodon sp. The specimen was found in Niobrara Formation rocks that traditionally yield P. longiceps however, and this is probably the likely species identity- we just can't verify it*. The identification of the shark is better constrained as the tooth is a perfect match for C. mantelli. Indeed, we can even tell which part of the mouth it came from thanks to Cretoxyrhina mantelli being exceptionally well known: even complete skulls and skeletons have been found. This allows us to roughly gauge the size of the Cretoxyrhina as c. 2.5 m long, which makes it a small individual compared to the 6-7 m specimens known from other remains. Our Pteranodon was on the small size as well at c. 5 m across the wings. This is within the upper size range of Pteranodon fossils, but still 1-2 m off the full wingspread of this species.

*If anyone's wondering, yes, we follow the traditional Bennettian concept of Pteranodon taxonomy. It was actually writing the manuscript for this paper that prompted my blog post on Pteranodon taxonomy.

Pteranodon sp. specimen LACM 50926 as mounted as part of a composite skeleton in the Los Angeles County Museum, and in more detail with their hitchhiking Cretoxyrhina mantelli tooth (arrowed). Scale bar is 50 mm. From Hone et al. 2018.
The Cretoxyrhina tooth does not actually penetrate the pterosaur bone, but is wedged beneath a vertebral process in a complex, intimate manner. We assume this evidences the shark biting into the pterosaur neck and shedding a tooth into its soft-tissues. An alternative - that the specimens became associated through actions of currents or storms - is less plausible given the strange position of the tooth, its tightness to the specimen, as well as the gentle, low-energy marine conditions of the Niobrara Formation.

But what sort of circumstances brought these animals together? It's here that our questions go beyond what the fossils can tell us. There's only so much a single tooth and string of vertebrae can objectively reveal about an ancient animal interaction, and we conclude that either a predatory and scavenging act could have produced the association - there's just no way to tell. While a scavenging story explains itself (short version: pterosaur dies over water; shark gets a meal), we explored how a predatory scenario may have played out given the known fish-eating habits of Pteranodon and hypotheses that this pterosaur regularly dived or swam to catch its prey (e.g. Bennett 2001; Hone and Henderson 2014; Witton 2013, 2018). Swimming pterosaurs are a new idea to many but substantiated by several lines of evidence, including swimming tracks, modelling of their aquatic launch strategy, and studies of their floating capability (Lockley et al. 2003; Habib and Cunningham 2010; Hone and Henderson 2014). We propose that if Pteranodon was a regular swimmer it would be vulnerable to sharks and other large predators, and its flight muscles would surely be a decent meal for many carnivores. Pterosaurs were probably pretty sinewy across their limbs, but there'd be some sizeable steaks to carve from their shoulders and chests. As big, powerful predators, it seems entirely plausible that even a half-size Cretoxyrhina would be capable of subduing a large Pteranodon, assuming they could catch one.

And that is as far as we go in our paper - it's pretty conservative stuff. You can read another summary of the paper at Dave Hone's Archosaur Musings.

The illustration

Rocket shark eats flying pterosaur? No. Artwork of a small Cretoxyrhina mantelli attacking a group of floating Pteranondon longiceps, erupting from the sea with one in its jaws. Note the other swimming pterosaurs in this picture - it's almost like pterosaurs weren't always flying, or something. From Hone et al. 2018.
Mike, Dave and I are palaeoart fans and we all - perhaps myself especially - enjoy well-illustrated papers, so we decided to include a reconstruction of Cretoxyrhina vs. Pteranodon in our paper (above). Having recently drawn an image of Pteranodon being hounded by another Cretaceous shark, Squalicorax, at the water surface, I wanted to do something different with this illustration and decided on a more exciting breaching scene: a shark leaping from the water with a Pteranodon in its mouth. Anyone who's watched even a few wildlife documentaries will know this behaviour is far from speculative: it's a widely-filmed, photographed and documented behaviour of South African white sharks (see Planet Earth excerpt from BBC Earth, below). These sharks strike floating prey with such speed that they leap entirely from the water. It's very dramatic, very awesome and seemed like great inspiration for a palaeoartwork. And sure, we have no idea that Cretoxyrhina did this, but a breaching attack is no more or less speculative than any other means of depicting a shark tooth lodging in a Pteranodon neck. I won't bore you with some additional practical factors that influenced the composition (in short, this image is being featured in an upcoming book where I have some firm ideas about visual narrative, and this strongly influenced choices of posture and colour).

In my mind, shark breaching is a widely known, instantly recognisable behaviour that shouldn't be foreign to folks writing science articles. It's routinely covered in major documentary programmes like Planet Earth, as shown here in this YouTube clip from BBC Earth. It's weird to me that folks are assuming my artwork has to be something more awesome than this, just because a pterosaur is involved.

A number of swimming and water-launching pterosaurs were added in the background of the image to make it clear that the Pteranodon was caught from a floating position. In my mind, the image shows a flock of pterosaurs busying themselves in the sea before Cretoxyrhina crashes their party - you can invent your own reasons for all the Pteranodon milling about. Maybe they're foraging, maybe they're congregating for another reason - it doesn't matter too much, what matters is that the sea has six or so Pteranodon either floating or launching from the water. Also note that water is shedding from the main pterosaur's wings, as if it's just left the water along with the shark. I carefully referenced how much water should be flying about using footage and photos of breaching sharks around the peak of their arcs: we often overdo water dynamics in palaeoart, and I was keen to make this image grounded in spite of its spectacular action.

So what's gone wrong?

What we've ended up with, then, is a pretty simple, conservative paper with an illustration that is pretty bleeding edge in terms of pterosaur science (flying reptiles as swimmers) and radical in terms of shark behaviour (breaching). But the two are entirely compatible with one another and the image is appropriately grounded in zoology and palaeontology. It looks extreme, but it's not ridiculous compared to what happens in modern natural history.

Unfortunately, this broader face of our project has been neglected in the media. Instead, our artwork - or rather a knee-jerk, lunkhead interpretation of it - has become the media story and we now have 'science-endorsed' headlines stating that sharks shot out of the water to grab pterosaurs (or even 'flying dinosaurs' in several articles) when they soared overhead. As I've outlined here, this is entirely false, and not representative of our ideas at all. Any hope that our paper could be used to broadly communicate some cool ideas about pterosaur ecology, the role of sharks as important predators throughout the Mesozoic, or even the simple fact that pterosaurs could likely swim has been lost behind ridiculous headlines based on erroneous readings of my picture.

So that's basically that - this is essentially a tale of how quickly false information can spread when it's attached to a pretty image, and why we shouldn't believe everything we read. Perhaps there's a lesson here in the power of imagery, and I am certainly now wondering if I erred in my reconstruction being too complex (to my defence, I did not contribute to the PR campaign for this and did not get the opportunity to sign off on an appropriate description for the picture). Perhaps we're looking at the reality of naive audiences assuming that anything to do with sharks or prehistoric creatures must automatically be the most awesome, badass thing. Maybe I erred in my assumption that people would be familiar with the basics of breaching shark behaviour.

But what this hits home hardest for me is the reality of science reporting in our digital, content-fuelled age. Anyone who led with the stupid shark vs. flying pterosaur headline went nowhere near our actual paper to check what we said, even though it was literally just a link click away. They simply parroted one another to make sure their outlets have the same stories as everyone else. Only a few thought to double check what our conclusions were, and I find that distressing. Remember folks, these are the same guys who're reporting news about far more important things than pterosaurs: vaccinations, climate change, health and environmental issues, and so on: these pterosaur-devouring rocket sharks are stark reminders of how they work. If you've seen accurately reported examples of this story (and they do exist) then add those news services to your bookmarks: they are rare examples of media outlets that aren't jumping our shark.

If understanding pterosaur ecology through fossil associations is of interest, be sure to check out this series of three blog posts: part 1, part 2, and part 3.

Enjoy monthly insights into palaeoart, fossil animal biology and occasional reviews of palaeo media? Support this blog for $1 a month and get free stuff!

This blog is sponsored through Patreon, the site where you can help online content creators make a living. If you enjoy my content, please consider donating $1 a month to help fund my work. $1 might seem a meaningless amount, but if every reader pitched that amount I could work on these articles and their artwork full time. In return, you'll get access to my exclusive Patreon content: regular updates on research papers, books and paintings, including numerous advance previews of two palaeoart-heavy books (one of which is the first ever comprehensive guide to palaeoart processes). Plus, you get free stuff - prints, high quality images for printing, books, competitions - as my way of thanking you for your support. As always, huge thanks to everyone who already sponsors my work!

References

  • Bennett, S. C. (2001). The Osteology and Functional Morphology of the Late Cretaceous Pterosaur Pteranodon Part II. Size and Functional Morphology. Palaeontographica Abteilung A, 113-153.
  • Habib, M. B., & Cunningham, J. (2010). Capacity for water launch in Anhanguera and Quetzalcoatlus. Acta Geoscientica Sinica, 31, 24-25.
  • Hone, D. W., & Henderson, D. M. (2014). The posture of floating pterosaurs: ecological implications for inhabiting marine and freshwater habitats. Palaeogeography, Palaeoclimatology, Palaeoecology, 394, 89-98.
  • Hone, D. W., Witton, M. P., & Habib, M. B. (2018). Evidence for the Cretaceous shark Cretoxyrhina mantelli feeding on the pterosaur Pteranodon from the Niobrara Formation. PeerJ, 6, e6031.
  • Lockley, M. G., & Wright, J. L. (2003). Pterosaur swim tracks and other ichnological evidence of behaviour and ecology. Geological Society, London, Special Publications, 217(1), 297-313.
  • Witton, M. P. (2013). Pterosaurs: natural history, evolution, anatomy. Princeton University Press.
  • Witton, M. P. (2018). Pterosaurs in Mesozoic food webs: a review of fossil evidence. Geological Society, London, Special Publications, 455(1), 7-23.

Friday, 30 November 2018

Helveticosaurus: the small-headed, long-armed Triassic marine reptile that just wants to be your friend :(

Helveticosaurus zollingeri, one of those strange Triassic marine reptiles that no-one ever talks about, wrestling in a coastal swamp. Not everything about being a marine tetrapod takes place in the sea.
The fossil record is full of fascinating, relatively well-represented species that, on paper, seem like they should be widely known and featured in all sorts of palaeontological media, and yet in reality are almost entirely overlooked in popular literature, documentaries and games. Triassic marine reptiles are definitely among these animals. Many are distinctive, unusual and well-researched species that are just as interesting (if not more so) than many more familiar Triassic animals, and yet their popular coverage is frequently dire: even their Wikipedia pages are little more than footnotes.

In interests of trying to correct this injustice even a little, it's time to talk about a Triassic marine reptile with a criminally poor popular coverage/deserved interest ratio: Helveticosaurus zollingeri. Discovered in Middle Triassic rocks of Switzerland in 1933 and described some years later (Peyer 1955), this small-headed, long-armed marine reptile represents a unique anatomical experiment among aquatic tetrapods: a sort of lizard-seal thing with a skull from an '80s supernatural horror film. Its basic bauplan is well demonstrated thanks to a mostly complete and reasonably preserved holotype, missing only the end of the tail and some parts of the limbs. Alas, some especially informative aspects of its anatomy are poorly represented, including the skull, distal limbs and pelvis. Though all are present, they are disarticulated and difficult to interpret. Additional Helveticosaurus specimens are known (Kuhn-Schnyder 1974), but are not as well preserved or complete as the holotype and don't add much to our knowledge of this species (Rieppel 1989). Though attracting reasonable scientific interest in the last half century, much about its lifestyle and evolutionary relationships remain unexplored or contentious.

The Helveticosaurus zollingeri holotype, as illustrated by Kuhn-Schnyder (1974). Although a little jumbled, a good portion of the skeleton is preserved. It's unfortunate the skull is such a mess. Check out Wikipedia for a photo of the actual specimen.
Much of our modern take on this animal has been informed by Olivier Rieppel's 1989 paper on its anatomy and function, and the following overview is largely based on this assessment. Helveticosaurus was a small-headed creature with a short neck, long body and a tail of unknown length. The preserved portion of the tail comprises large, well developed vertebrae and it doesn't seem unreasonable to assume it was much longer when complete. If we had a more secure idea of the phylogenetic position of Helveticosaurus we might take a stab at estimating the tail length, but this doesn't seem possible at the moment.

Tail proportions are not the only issue confusing predictions of the overall body length of this animal. When preparing this post I found that the total length estimates of Helveticosaurus provided in modern papers are at odds with measurements of skeletal elements within the holotype, to the effect that we might be significantly underestimating its overall size. Recent papers give a total predicted length of c. 2 m for the holotype animal (e.g. Rieppel 1989; Cheng et al. 2014), while also reporting that the lower jaw of the same specimen is 250 mm long, and the humerus as 205 mm (Rieppel 1989; Cheng et al. 2014). Even just eyeballing images of the holotype suggests some sort of miscalculation here: there's no way the entire animal - including the missing tail - is just 10 times the length of these bones. Using a line drawing of the holotype from Khun-Schnyder (1974) and the reported mandible and humerus measurements, I found that 2.1 - 2.8 m better describes the length of the preserved skeleton (see calculations in the image below, note that the reported 45 mm difference between the humerus and mandible length is not obvious in the drawing I used, resulting in two different body length estimates. Scaling from photos or illustrations is not a substitute for measuring actual specimens). This is back-of-the-envelope stuff, but it's enough to convince me that Helveticosaurus wasn't a 2 m long animal. I wonder if the figures reported by Khun-Schnyder (1974) are more plausible: he reported a 2.5 m length for the preserved holotype skeleton, and an estimated total length of 3.6 m. That would add another metre onto the holotype, which seems quite plausible - maybe even conservative - to me.

Just how big was Helveticosaurus? It's hard to say without a complete specimen, but the individual represented by the holotype skeleton clearly exceeded the oft-cited 2 m body length. Perhaps other published estimates of 3.6 m are more reasonable?
One of the most interesting features of Helveticosaurus is its short, c. 25 cm long skull. Alas, the best Helveticosaurus skull remains we have look as if they were hit by a truck before fossilisation: scattered, broken, and with many unidentifiable parts (Rieppel 1989). Enough is known to allow for a tentative reconstruction but a confident picture of the face of Helveticosaurus awaits better preserved material. The front of the upper jaw was abbreviated, blunt and tall, creating a skull profile that might have been somewhat box-like in lateral aspect. The orbital and temporal regions are poorly known, but they seem to hint at the presence of an upper and lower temporal fenestrae and a large eye socket. A number of oversize conical teeth line each jaw. The exact number of teeth is unknown, but a notable feature is the large 'canine' in the upper jaw. Neither the size of the temporal region or the lower jaw (the latter being one of the best preserved cranial elements) imply an especially large set of jaw muscles, though the mandible has an expanded retroarticular process - a prong of bone at the back of the jaw associated with opening the mouth. This likely has implications for the feeding style of Helveticosaurus, although I'm unaware of any studies into its function. The aberrant size of the Helveticosaurus skull is peculiar for a marine reptile lacking a long neck, and perhaps only challenged in proportion by the Triassic marine vacuum cleaner Atopodentatus (Cheng et al. 2014). Distinct anatomy make it clear that these animals were very different ecologically however, and it's possible that their diminutive skulls reflect very different adaptive regimes.

Tentative Helveticosaurus skull reconstruction, from Rieppel (1989). The jaws remain the best known elements, and some question exists over the arrangement of the rest of the skull. Scale bar represents 50 mm.
The body of Helveticosaurus is similar, at least superficially, to many other Triassic marine reptiles, especially early sauropterygians. It's torso was long, with well-developed and high-spined vertebrae, stout ribs and an extensive set of gastralia (belly ribs). Differentiation between the vertebral spines at the front and back of the body hint at some functional distinction, perhaps related to larger muscles associated with the shoulder region (Rieppel 1989). As is assumed for plesiosaurs, the combination of stout ribs and gastralia likely reduced the flexibility of the torso and may have improved swimming efficiency. The tail, so much as it is known, bears the same high neural spines as the trunk vertebrae, as well as caudal ribs. These features indicate it was likely well-muscled for use in sculling propulsion, although the chevrons are not particularly large. Assuming these anchored the caudofemoralis muscle, as they do in most reptiles, I wonder if this indicates diminished musculature associated with hindlimb retraction.

After the peculiar head, the forelimbs of Helveticosaurus are perhaps its most unusual feature. They anchored to an atypically well-developed pectoral girdle which - unlike most marine reptiles - has a long, robust scapula. Marine reptile shoulder blades are often extremely reduced, little more than bony nubbins that create a shoulder joint. But here, the scapulae are long enough to create a deep, U-shaped shoulder girdle that would not look out of place on a terrestrial animal (Rieppel 1989). The forelimb itself is proportionally elongate, both with respect to the body and in comparison to the hindlimb. It's exact length remains uncertain because the bones of the hand are scattered, but the major limb bones are each 10% longer than their counterparts in the hindlimb. The humerus in particular is very long for a marine reptile, and maintains hallmarks of functionality beyond just being the top of an stiffened flipper (Rieppel 1989). The fingers are hyperphalangic (i.e. they have an enhanced number of finger bones) in a fashion typical of marine tetrapods, and - in contrast to several Helveticosaurus palaeoartistic reconstructions (all five of them that exist) - they lack claws. The arrangement of the fingers requires some reconstruction but their slender bones and arrangement in the holotype implies more of a broad, rounded paddle than a narrow ichthyosaur or plesiosaur-like flipper.

Helveticosaurus forelimb, as illustrated by Rieppel (1989). Some ribs and gastralia have been removed for clarity. Note the elongate scapulae and long forelimb elements - this is not a typical marine reptile arm. Scale bar represents 100 mm.
The hindlimb shares some general characteristics with the forelimb - relatively elongate limb bones for a marine form, hyperphalangy, spreading, unclawed digits - but is shorter, noticeably more gracile and probably more cartilaginous than the forelimb. The pelvis is poorly known, but it also appears to have been at least partly cartilaginous, the joints of the pelvic bones being insufficient to contact one another around the hip joint without some additional skeletal material (Rieppel 1989). These features imply that the hindlimb was structurally weaker than the forelimb.

How might this mix of anatomies have functioned? A qualified assessment by Rieppel (1989) makes some sensible interpretations of Helveticosaurus locomotion. On the whole, the animal is mostly adapted for life in water, with aquatic adaptations being especially obvious on the limbs, pelvis and tail. Although the tail is missing, its robust, high-spined and complex vertebrae are consistent with features of sculling animals and we might envisage Helveticosaurus propelling itself with powerful motions of its tail when swimming, akin to marine iguanas or crocodylians. The weak pelvis and hindlimb indicate the rear limbs contributed less to propulsion. Rieppel proposes that, like swimming lizards, they may have been pulled against the body when swimming save for the occasional action to help with steering or thrust. The forelimbs were evidently strong and likely useful in swimming, though the configuration of the shoulder girdle does not imply any rigid kinematics for underwater flight in the manner of a penguin or turtle. They might have functioned more like the foreflippers of otariid seals (the eared seal group: sealions, fur seals etc.) in providing some thrust, but also playing important roles in steering and breaking (Rieppel 1989). While the shoulder girdle does not seem optimised for powerful downstrokes, the large size of the arm, and implied articulation of at least some parts of the limb (see below), suggest it was a dynamic steering aid. Helveticosaurus may have been quite an agile swimmer.

But where Helvetiosaurus becomes especially interesting is out of the water. Even in the Middle Triassic many marine reptiles had wholly committed themselves to aquatic lifestyles, but Helveticosaurus appears to have remained some terrestrial capabilities. Why it did this remains uncertain: did it still lay eggs? Did it have a complex life history involving both land and sea phases? Did it live in settings where periodic escapes from the sea were advantageous? We don't have insights into any of this yet, but we can predict how Helveticosaurus might have moved around on land. Supporting limbs during terrestrial gaits is not simply a matter of having strong limb bones, it's also necessary to have a robust and stable limb girdle. For shoulders, this requires support and control exerted by muscles attached to the torso and neck, as well as having a big enough scapula for these to act on. The robust shoulder girdle of Helveticosaurus seems to meet these criteria. It not only provides space for the necessary muscle to support and move the forelimb on land but also - with particular reference to the relatively big scapula - is sufficiently developed to brace the shoulder against the body skeleton (Rieppel 1989). The length and robustness of the forelimb is also notable, as are the retention of humeral features associated with flexing the lower limb. Marine reptile limbs are often immobile south of the shoulder or hip, and readers with good memories might recall that this makes terrestrial locomotion difficult. The articulations of the Helveticosaurus limb are not well preserved - they seem to have been highly cartilaginous - so we don't know the full extent of its forelimb mobility, but muscle attachment scars hint at abilities to flex the wrist and fingers (Rieppel 1989). Any flexible jointing would enhance its terrestrial potential, so this is another tick in the box for relatively proficient land locomotion. The hindlimb, in being less developed and more cartilaginous, probably contributed little to terrestrial locomotion. Helveticosaurus may have therefore crawled and flopped around more like a seal than a lizard, using its arms to drag and push itself around, maybe occassionally assisted by its legs and thrashing motions of the tail to propel itself faster. It must have been pretty neat to see a reptile move like this: a sort of creeping, lolopping reptile-mermaid topped off with the face of the Engineer from Hellraiser.

When Helveticosaurus collide. In the image illustrating this article, I've assumed that the terrestrial capabilities of Helveticosaurus were sufficient to bring them into terrestrial coastal habitats, perhaps for mating, nesting or some other reason. We have no evidence of this happening, but analogous behaviours are seen today in turtles and seals, some of which travel kilometres inland despite their limited terrestrial abilities. Maybe some Mesozoic marine reptiles did the same.
We can't go this far into discussion of Helveticosaurus without questioning its ecology. I'm not aware of any analyses that address this issue, so this paragraph is shot from the hip based on what others have said about its functional morphology and a basic form-function reading of Helveticosaurus anatomy - take it with an appropriate pinch of salt. As already noted, the skull of Helveticosaurus is too poorly preserved to say much about specifics of foraging, but its long, slender teeth clearly betray a predatory lifestyle. Worn tooth tips indicate that it did not eat entirely soft, fleshy prey, but the teeth are not robust enough to suggest a tough diet. I'm aware that a similar suite of dental features occur in pterosaurs that are assumed to small fish, squid and other diminutive swimming creatures (Ősi 2010), and I wonder if a similar diet might apply here. The skull of Helveticosaurus is also too small to suggest it routinely ate large prey, though I guess scavenging carcasses is difficult to rule out. The enlarged retroarticular process is of interest because such features are often seen in suction feeders - aquatic animals which rapidly open their mouths to suck up prey within a pressure gradient. Short faces often characterise suction feeders too, but we need knowledge of other anatomies - such as the bones of the throat - to reliably infer such foraging strategies (Motani et al. 2014). We also have to acknowledge that a short jaw and specifics of the posterior mandible can be related to other functions. A small head capable of fitting between rocks and other obstacles would be useful if Helveticosaurus sought benthic or demersal prey, for instance. The combination of a swimming tail and large limbs may have made Helveticosaurus relatively agile, a useful trait when chasing small prey. In all, I wonder if the seal analogy applied to some aspects of Helveticosaurus anatomy and locomotion might extend to its lifestyle. It would be great to see this looked into with a dedicated study.

Bringing this post back to firmer scientific ground, it's finally time to ask: just what the heck is Helveticosaurus? Initially interpreted as a placodont (Peyer 1955), Helveticosaurus has since jumped all over the reptile tree as different teams use different approaches to resolve its placement. There are probably several reasons for our inability to pin down the evolutionary home of Helveticosaurus. Firstly, the anatomy of Helveticosaurus confuses character distribution in phylogenetic trees, it having features of enough groups to scramble easy reading of homologies and convergences (Ezcurra et al. 2014). This makes Helveticosaurus very sensitive to taxon and character choices used in our evolutionary calculations, and prone to shifting in position dramatically from one cladogram to the next (e.g. Chen et al. 2014). Helveticosaurus is far from the only marine reptile to present such a problem, and there are debates among researchers about how to deal with what some regard as a problematic amount of convergence between aquatic Mesozoic reptiles (see, for recent takes, Chen et al. 2014 vs. Scheyer et al. 2017). A third issue concerns the ongoing controversy over the origins of marine reptiles generally. The relationships of even well-supported groups like ichthyosauromorphs, turtles and sauropterygians to other reptiles remain contested, and these clades have major 'pull' in phylogenies when they move about, hauling possible relatives like Helveticosaurus around as tree topologies change.

We don't know of any species quite like Helveticosaurus, but the Triassic diapsid Eusaurosphargis dalsassoi - here represented by an excellent fossil of a juvenile skeleton - has been recovered as a near relative in several recent analyses. Intriguingly, it also seems well adapted for terrestrial locomotion, implying that such abilities may have been common to their branch of marine reptile evolution. Image from Scheyer et al. (2017).
Perhaps for this reason, it's not uncommon to see many authors sidestepping classifying Helveticosaurus altogether, instead simply labelling it an 'enigmatic diapsid' and moving on. But others have tackled the issue more head on and, while it would be premature to say we know what Helveticosaurus is, some clarity is emerging about which branch of reptile evolution it belongs to (even if the position of that branch is a more open question). The placodont affinity for Helveticosaurus has been questioned on grounds of very limited shared anatomies (Sues 1987; Rieppel 1989) and this identification has not been supported in recent analyses. Other ideas - a tentative interpretation as some sort of archosauromorph (Rieppel 1989; Naish 2004) or a near relative of lepidosaurs (Chen et al. 2014) - have also not found much traction. But a large number of authors have recovered Helveticosaurus as a close relative of Sauropterygia (Müller 2004; Bickelmann et al. 2009; Li et al. 2011, 2014; Neenan et al. 2013; Chen et al. 2014; Scheyer et al. 2017), and it's looking like this is the best horse to back concerning the phylogenetic position of this historically enigmatic animal.

Alas, this is not the neat end of the story we might think it is, as the origins of Sauropterygia itself remain poorly understood. In at least some analyses Helveticosaurus and Sauropterygia is part of a marine reptile 'superclade', a huge, unnamed group containing ichthyosaurs, sauropterygians and a number of Triassic lineages that have long struggled to find homes. Another Swiss Triassic reptile, the possibly mostly terrestrial Eusaurosphargis dalsassoi (above), has been postulated as a close relative of Helveticosaurus several times (e.g. Scheyer et al. 2017). Sauropterygians are deeply nested in this 'superclade' and the position of the terrestrially-enabled Helveticosaurus and Eusaurosphargis is interesting with respect to the evolution of aquatic lifestyles in Triassic marine reptiles. Given that more rootward lineages in the 'superclade' are entirely aquatic forms, might genera like Helveticosaurus and Eusaurosphargis represent animals that returned to land from swimming ancestors, or are they representatives of a more basic semiaquatic ancestral bauplan that remains underrepresented in other lineages? At the risk of ending on an old palaeontological cliche, we need more specimens, more data and more investigations to answer these questions.

It turns out that marine reptiles are a pretty fun group, I think you'll be seeing more art and reading more about them here in the coming months. If all goes to plan, we'll be walking (or not) with plesiosaurs and meeting some giant ichthyosaurs before too long.

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References


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