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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


  • Bickelmann, C., Müller, J., & Reisz, R. R. (2009). The enigmatic diapsid Acerosodontosaurus piveteaui (Reptilia: Neodiapsida) from the Upper Permian of Madagascar and the paraphyly of “younginiform” reptiles. Canadian Journal of Earth Sciences, 46(9), 651-661.
  • Chen, X. H., Motani, R., Cheng, L., Jiang, D. Y., & Rieppel, O. (2014). The enigmatic marine reptile Nanchangosaurus from the Lower Triassic of Hubei, China and the phylogenetic affinities of Hupehsuchia. PLoS One, 9(7), e102361.
  • Cheng, L., Chen, X. H., Shang, Q. H., & Wu, X. C. (2014). A new marine reptile from the Triassic of China, with a highly specialized feeding adaptation. Naturwissenschaften, 101(3), 251-259.
  • Ezcurra, M. D., Scheyer, T. M., & Butler, R. J. (2014). The origin and early evolution of Sauria: reassessing the Permian saurian fossil record and the timing of the crocodile-lizard divergence. PLoS One, 9(2), e89165.
  • Kuhn-Schnyder, E. (1974). Die Triasfauna der Tessiner Kalkalpen. Neues Jahrbuch der Naturforschenden Gesellschaft in Zürich, 176, 1–119
  • Li, C., Rieppel, O., Wu, X. C., Zhao, L. J., & Wang, L. T. (2011). A new Triassic marine reptile from southwestern China. Journal of Vertebrate Paleontology, 31(2), 303-312.
  • Li, C., Jiang, D. Y., Cheng, L., Wu, X. C., & Rieppel, O. (2014). A new species of Largocephalosaurus (Diapsida: Saurosphargidae), with implications for the morphological diversity and phylogeny of the group. Geological Magazine, 151(1), 100-120.
  • Motani, R., Ji, C., Tomita, T., Kelley, N., Maxwell, E., Jiang, D. Y., & Sander, P. M. (2013). Absence of suction feeding ichthyosaurs and its implications for Triassic mesopelagic paleoecology. PLoS One, 8(12), e66075.
  • Müller, J. (2004). The relationships among diapsid reptiles and the influence of taxon selection. In G. Arratia, M. V. H. Wilson & R. Cloutier (eds.): Recent advances in the origin and early radiation of vertebrates, 379-408.
  • Naish, D. (2004). Fossils explained 48: Placodonts. Geology Today, 20(4), 153-158.
  • Neenan, J. M., Klein, N., & Scheyer, T. M. (2013). European origin of placodont marine reptiles and the evolution of crushing dentition in Placodontia. Nature Communications, 4, 1621.
  • Ősi, A. (2011). Feeding‐related characters in basal pterosaurs: implications for jaw mechanism, dental function and diet. Lethaia, 44(2), 136-152.
  • Peyer, R. (1955). Die Triasfauna der Tessiner Kalkalpen. XVIII. Helveticosaurus zollingeri, n. g. n. sp. Schweizerische Palaeontologische Abhandlungen, 72, 1–50.
  • Rieppel, O. (1989). Helveticosaurus zollingeri Peyer (Reptilia, Diapsida) skeletal paedomorphosis, functional anatomy and systematic affinities. Palaeontographica Abteilung A, 123-152.
  • Scheyer, T. M., Neenan, J. M., Bodogan, T., Furrer, H., Obrist, C., & Plamondon, M. (2017). A new, exceptionally preserved juvenile specimen of Eusaurosphargis dalsassoi (Diapsida) and implications for Mesozoic marine diapsid phylogeny. Scientific reports, 7(1), 4406.
  • Sues, H. D. (1987). On the skull of Placodus gigas and the relationships of the Placodontia. Journal of Vertebrate Paleontology, 7(2), 138-144.

Tuesday, 23 October 2018

An interview with Katrina van Grouw, author and artist of The Unfeathered Bird and Unnatural Selection

If you're the sort of person who's interested in cool stuff like anatomy, evolution and functional morphology, you can't have missed two incredible books published in recent years by author and artist Katrina van Grouw: The Unfeathered Bird (2013) and Unnatural Selection (2018). Although tackling different topics, they are united by their exceptional illustrations of animals in various states of dissection (though mostly skeletonised), lavish design, great production quality and highly detailed yet accessible text. The Unfeathered Bird, which focuses on bird skeletal anatomy and functional morphology, caused ripples in the palaeontological community upon release for being a book which looks at modern birds the way we look at fossil animals. As a monumental book - huge, comprehensive, scholarly and aesthetically spectacular - I'm sure we would all have been happy with more of the same for Katrina's follow up project (The Unfuzzy Mammal, The Unscaled Reptile, The Un... er... skinned Amphibian?) but her latest book, Unnatural Selection, is even more ambitious in scope, detailing how human-controlled animal breeding - the titular 'unnatural selection' - offers a window into the mechanics of biological evolution.

Katrina's new book, Unnatural Selection, available now from Princeton University Press, all the usual online retailers and good book shops.
To celebrate the release of Unnatural Selection a few months ago, I invited Katrina to give an interview about her new book, her art, and her future projects. I do this as a certified van Grouw fan: the Disacknowledgement and I have three van Grouw artworks on our wall in addition to her books on our shelves. Katrina has always skirted the line between author, scientist and artist and, before The Unfeathered Bird, she already had a background in fine art, museum curation (bird skin curation at the Natural History Museum) and book writing. I will fully confess to finding her skills and knowledge intimidating, and was a little frightened of meeting her at the 2015 TetZooCon. After all, if anyone was ever going to expose my work for the hack job it is, it would be this Baroness van Grouw, dual master of detailed anatomy and artistry (lightning flashes, thunder rumbles)*. It turns out that it's actually impossible to be scared of Katrina once you talk to her however, and we remain close friends today.

*Note that Katrina's status as a Baroness is a product of my over-active imagination, not reality. 

There's lots to like about Katrina's books, and I mean no disrespect when saying that they're some of my favourite books simply to look at. Katrina's illustrations - drawn in pencil and then tinted to sepia tones digitally - are truly world class, and her subjects are frequently drawn in lively, life-appropriate poses so that, even when skeletonised or half-dissected, they look very much alive. But it's not only the drawings which make her books exceptional to behold: their size, ivory-coloured pages, font hues and text layouts recall a romanticised age of 19th century museums and scholarship. It's impossible not to think of exhibition halls filled with wooden cabinets, animal bones, taxidermy specimens, curiosities in jars and stuffy formalwear when reading these books. They evoke the atmosphere of a classic age of learning and exploration on every page. It must be stressed how, for their size and quality, both The Unfeathered Bird and Unnatural Selection are exceptionally good value for money ($45-50 cover price, but being sold at £20-25 at Amazon UK, and equivalent in the US). I can only wonder what Mephistophelian deal Princeton University Press has made to to sell these fantastic books at such low costs and, to the poor production editors suffering in the afterlife for making such a deal, know that it was really worth it: I can't think of many books published in recent years that are anywhere near as splendid to look at in this price bracket. For next-level book quality I can only think of tomes like the considerably more expensive (but ultimately disappointingPaleoart: Visions of the Prehistoric Past (Lescaze 2017), with a cover price twice that of Katrina's books.

Fans of The Unfeathered Bird will be intimately familiar with Katrina's skeletonised birds. Unnatural Selection offers a greater proportion of art devoted to living individuals, including this jungle fowl, the ancestral species of chickens. © Katrina van Grouw.
But to only look at The Unfeathered Bird or Unnatural Selection would be a huge disservice to their scholarly content. The academic merits of The Unfeathered Bird are widely known and I won't rehash them here - suffice to say that, if you're a regular reader of this blog, you'll want a copy. Although much newer, the amazingness of Unnatural Selection has already been sung in several reviews and previews (hereherehere, here and here) and I want to quickly add my own endorsement of Katrina's latest book before we delve into the interview.

Unnatural Selection is genuinely a fascinating and thought provoking insight into a side of evolutionary mechanics that we often ignore or stigmatise. Like many people - including other scientists - I've often thought that human-bred animals have little to tell us about evolution because they're somehow 'artificial', and that the genetic interplay that underlies their development somehow doesn't compare to what happens in 'real' natural selection. But Unnatural Selection shows the folly of this view, exploring how animal breeding reveals much about the ease and frequency of trait development, how our breeding choices are analogous to splitting and extintinguishing evolutionary lineages, the mechanisms behind expressing certain phenotypes, and evolutionary rates. Human-led breeding might be shaping animals towards a pre-ordained goal of our choosing, but it's still evolution. Ignoring it severs a wealth of insight and knowledge pertaining to evolutionary processes of any sort, human-led or otherwise. 

The strangely deformed skull of a King Charles spaniel. We view this sort of anatomical modification as extreme, and certainly there are welfare issues to consider with many domestic breeds (and not just dogs, as is most widely reported). But many of the extreme (and healthy) breeds we've created are no more bizarre than what we see in nature. In response to questions about pushing animal anatomy too far, Unnatural Selection responds "...look at what nature has done to the sword-billed hummingbird!". However we feel about the ethics of breeding bizarrely proportioned animals, we're not the only evolutionary force behind their creation. From Unnatural Selection, © Katrina van Grouw.
It's worth stressing that this is not a book about the ethics of purebreds or pedigree lineages: Unnatural Selection is book about evolutionary science viewed through the lens of domesticated species, and it leaves the politics and ethics of animal welfare at the door. Some may find the lack of ethical discussion a little peculiar given that any mention of animal fancy is so often presented hand-in-hand with animal welfare, but I can understand why this was left out: a good scientist presents their work objectively for society to implement as it sees fit, they don't present science to support their own opinions on a subject, no matter how strongly they personally feel about it. As an animal owner herself, Katrina is on record as being just as concerned with the health of animal breeds as anyone, but she didn't feel her book was the place to share her opinions - I can respect this.

So yes, Unnatural Selection is a fascinating, unique and spectacular book that I heartily endorse. But that's enough preamble, over to its author and artist. I've included, with Katrina's help, a selection of artwork from The Unfeathered Bird, Unnatural Selection and some rarely-seen earlier works. All artwork in this post is Katrina's, and used with her permission.

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MW. Much of Unnatural Selection discusses the prolonged challenge of having artificial selection viewed as having useful insights on 'natural' evolution. As you argue, this seems peculiar - a bit like a physicist arguing that experiments done on atomic particles in the lab have no bearing on 'naturally occurring' particles. Why do you think this issue has persisted for as long as it has?

KvG. I honestly have no idea. I too used to be what I call a ‘wild animal snob’ i.e. I considered domesticated animals as something man-made and irrelevant, though I’ve come to revise my opinions significantly!

It’s always said that Darwin drew up his analogy between natural and artificial selection specifically in order to introduce to the Victorian public the frightening concept that all the diversity of life could have come about without the need for a divine creator. Like the spoon full of sugar that makes the medicine go down. I suspect, as Darwin later maintained in his revised autobiography, that artificial selection was indeed highly influential in the formulation of his theory.

However, even Darwin had problems accepting that certain radical traits (like achondroplasia, or disproportionate dwarfism, discussed in the next question) could be successful in the evolution of wild animals, so he drew a line between them.

Richard Goldschmidt in the 1940s also made macro mutations appear ridiculous as a result of his ‘hopeful monster’ theory, which may have caused scientists to dismiss selective breeding as useless in comparison with evolution in nature. As you’ll be able to see from the next question, and especially in the book itself, there is actually very strong evidence that the same traits not only occur in wild animals, but may be favoured by natural selection.

Four-winged dinosaurs have evolved a number of times, including at the hands of pigeon breeders (pigeon hindwing, or 'muff' foot, shown at the base of the image). Understanding the genetic changes behind the development of such traits may help us understand the mechanisms through which these evolved in nature, something of obvious interest to palaeontologists interested in development of stem birds and avian flight. From Unnatural Selection, © Katrina van Grouw.
Every so often geneticists make a so-called breakthrough revealing some trend in domesticated animals that sheds light on evolutionary biology, and invariably these ‘discoveries’ have been known already to generations of animal fanciers who breed them. Feathered feet in pigeons are a good example. Every pigeon fancier knows that the wing-like ‘muff’ feet (palaeo-people will know these as ‘hind wings’) are produced by combining two very different foot feather types. Geneticists would do well to pay attention to the knowledge of animal fanciers instead of constantly re-inventing the wheel.

Whereas in past centuries scientists had eclectic interests and would happily turn to the products of horticulture as to botany, or to animal breeding as to wild animals, it seems that the more knowledge that’s available the more blinkered and over-specialised scientists become. I even know molecular geneticists who don’t fully understand Mendelian principles.

Sadly for too many of us, even though the subject of domestication is currently very popular in scientific circles, selective breeding is viewed either with derision or contempt. Fit only for children or eccentric losers, or an emotive subject to stir up the wrath of animal welfare crusaders.

I hope that my book will do something to redress the balance.

Unnatural Selection draws attention to the rapidity of evolutionary modification, specifically how animal form can be dramatically modified in a generation thanks to single genetic changes. You somewhat playfully speculate that this may have had a role in the evolution of some groups - such as the short limbs of mustelids: would you care to suggest - speculatively or otherwise - if any other groups may have benefited from these rapid changes?

That’s right. Though it’s important to stress that the most significant evolutionary change is the result of an accumulation of tiny steps – ‘natura non facit saltus’, as Darwin was fond of saying: ‘nature does not make leaps’. But there are plenty of traits that are single step, all or nothing, changes. Think of the spiralling direction of shells, or horns, for example. Colour aberrations too can result in major phenotypic changes just by the addition or subtraction of a pigment. (Colour ‘aberrations’ are only aberrant when they’re in low numbers in a population, but if they prove to be advantageous, or if they’re isolated in a small gene pool, these aberrations of today can be the colour morphs, races, or even species of tomorrow.)

Vertebral counts are considered a big deal in vertebrate palaeontology, often being used to distinguish different species. It turns out that gaining additional vertebrae is not particularly difficult and is not just the remit of weirdos with extreme numbers of axial elements, like snakes. We've emphasised this trait among species that we harvest for meat, such as landrace pigs, which have several more vertebrae than other breeds. From Unnatural Selection, © Katrina van Grouw.
However, I’m deviating in my preamble. There are lots, and lots, of other examples, besides the short limbs of mustelids, where you can suggest, speculatively, that the evolution of wild animal groups may have been given a ‘leg up’ (no pun intended!) by a single major mutation. The naked neck trait in chickens is a good one - the heat-reducing naked necks of marabou storks, ostriches, and vultures is comparable and is probably caused by the same genetic process. Henny feathering in chickens (where the male has the same plumage as the female with no loss of virility) possibly has a connection with the seasonal eclipse plumage in waterfowl. Mutations that cause winglessness in chickens may sound pretty gross, but moas were totally wingless too, and there’s no fossil evidence to suggest that they ever went through a gradual evolution towards winglessness. Rex fur in rabbits may seem like just a fancy coat type for the show bench, but a similar coat (without directional guards hairs) allows moles to move freely backwards and forwards in their burrows.

The exact same mutations are equally likely to occur in wild as domesticated animals and their success is all down to whether or not they find themselves in an environment that’s favourable. The ‘right’ environment can come in many forms, and it can change, but traits that might not be successful in the wild for whatever reason might just appeal to the whims of fanciers. There are only a finite number of possible traits that will ever be viable, and the same things tend to occur across a wide range of animal groups, albeit expressed differently. Meaning that speculative zoologists would do well to pay more attention to domesticated animals and the traits they exhibit. This is variation in its most likely forms and a very accurate suggestion of the possible directions evolution might take in the future. Again, the initial mutation only needs to be a start. After that, natural selection can refine it further and fine tune it over millions of years to each particular environment.

Both The Unfeathered Bird and Unnatural Selection are simply stunning to look at, but not all your readers will know how instrumental you were to their design, not only creating the text and illustrations, but also having tight control over the page layouts and overall aesthetics. I gather this level of control is not typical in publishing, and it very much makes these your books. Can you tell us a little about your design decisions? 

I’m glad you asked that; indeed, most people assume that the publisher designed the books, which is the more normal arrangement. I’m exceedingly lucky to have a publisher that has so much faith in me.

After nearly two decades of trying to find a publisher for The Unfeathered Bird, I was painfully aware that many people associate anatomy with greyscale diagrams in academic textbooks. I wanted it to be as much a work of art as of science, so changing the colour of the finished pencil drawings to a sepia brown colour, and printing onto ivory-coloured paper was a deliberate attempt to make the book softer and more accessible and to be suggestive of the beautiful historical natural history illustrations of past centuries. This particularly suited the historical theme of both books: The Unfeathered Bird references Linnaeus (this was a clever way to discuss adaptations through convergence rather than adhering to actual phylogenetic relationships) and Unnatural Selection is all about Darwin and Mendel.

The many faces of exhibition homing pigeons, an example of one of the full page spreads from Unnatural Selection. I can't be the only one thinking the Exhibition Homer resembles a certain piece of Therizinosaurus artwork. © Katrina van Grouw.
Personally designing the books sort of happened by accident – I preferred to prepare the digital image files because I was reluctant to allow the original drawings out of my care. Also, I knew exactly how the different images on the page should be arranged in relation to one another. The drawings are all done on separate pieces of paper, so putting them together digitally myself seemed to make more sense than trying to explain where they should go. After that I discovered that my publishers were also happy to let me choose the fonts, guide the positioning of text, and even design the entire jacket, all of which I loved doing.

I had a lot of fun designing the page layouts, especially the chapter opening pages in Unnatural Selection where I’ve shown historical museum specimens against antiquated-looking background paper. And the three coloured images in the book where I discuss pigment changes. The ‘let’s colour a Gouldian finch!’ page was based on Andy Warhol’s Marilyn Monroe prints, with more than a passing nod towards Edward Lear’s coloured birds. This pleased me immensely as John Gould treated Edward Lear very badly in life, so it seemed like justice for Lear!

I'm curious about the poses of many of your subjects. Where you have control over this aspect of their illustration, what helped you decide to pose them a certain way, other than the simple practicalities of "I want to show this feature"?

Many of my decisions were indeed guided by ‘I want to show this feature’. The Unfeathered Bird is all about adaptations, so it was important to show the features that I describe in the text as being particularly adapted to specific behaviour. So it made sense from a scientific and aesthetic point of view to show skeletons actually engaged in that behaviour. Husband put together the majority of the skeletons so it seemed fair to give him an input into the choice of positions. We had endless pleasure discussing the behaviour of birds and arguing (in a friendly way) about which position to choose.

Of course it’s not just the position of the actual skeleton, but the viewpoint I select to draw it from. The diver in the surface swimming position may be fairly straightforward, but I decided on a fish’s-eye view, looking up at it from below, as this was the viewpoint that most clearly showed the boat-like sternum, sideways-angled hind-limbs, and razor-thin legs.

A budgie skeleton passes the mirror test, from The Unfeathered Bird. © Katrina van Grouw.
Some of the poses, although superficially just for fun, are for practical as well as aesthetic reasons. The budgie skeleton looking at itself in a mirror in The Unfeathered Bird was a way of showing both sides of the skull in the same drawing (while making it crystal clear that it’s a budgie!). I did the same thing with the reflection in the water under the porpoising penguin.

I enjoyed playing around with visual references, for example I deliberately showed the avocet in the same position as the RSPB logo; the red grouse was modelled on the whisky label, and the robin on the spade handle was modelled on 90% of the Christmas cards ever printed!

For all the major bird groups I included a page showing the feather tracts, musculature and skeleton of a species all together and for these it made sense to show them like an actual group of birds interacting. So I made up little tableaus: three rooks rushing to get a worm that’s just disappearing underground, or a pigeon’s frantic pouting courtship ritual being completely ignored by the other pigeons only intent on eating.

The skeleton of the mighty auroch, one of my favourite pieces from Unnatural Selection. Katrina didn't pose this individual (it's based on a museum mount) but has really captured its implied energy and mass. We might be looking at a skeleton, but you can almost see the muscles rippling as the animal moves. From Unnatural Selection, © Katrina van Grouw.

I can't look at your anatomical work without wondering how you could translate your skill into palaeoart, and I must not be the only person imagining that a van Grouw restoration of a fossil bird or (based on some of the amazing work in Unnatural Selection) a fossil mammal would be spectacular. Will we ever see a life restoration of a Gastornis, entelodont or Microraptor emerge from your pencils? And can I have a copy if it happens? I'll be your best friend.

Proof, as if it were needed, that Katrina knows her way around skeletons and musculature as well as the best palaeoartists: a parade of cow bottoms. Note the 'double muscle' individual at the end of the row. From Unnatural Selection, © Katrina van Grouw.
Haha, if it happens I promise you you’ll be the first to know! Probably because I’ll need your help to get it right and won’t be brave enough to show it to anyone until you’ve given it your seal of approval! I’m not adverse to the idea, but at the present moment I can’t envisage how it would fit into the planned book projects which, for the foreseeable future, will be purely anatomical.

It’s not entirely impossible though. With the right incentive (for example, producing commissioned illustrations for someone else’s book) I could probably be persuaded.

Katrina's take on Pomarine skuas. I can't be the only person wanting to see this anatomical expertise and style applied to fossil animals. © Katrina van Grouw.

Before your recent books you were best known for your work illustrating fantastic cliffs and seabird colonies. These are amazing images and I understand a number of folks were sad to hear you declare that this part of your artistic life is behind you. Is the door completely closed to this sort of wildlife art, or will it reinvent itself in some form? And if not, what lies ahead? 

When I finished The Unfeathered Bird I was fully intending to return to those sorts of pictures and to being a fine artist again, but I found that I’d moved on. It’s not that I refuse to do the same work; it’s because my heart is somewhere else now. You can’t force it – it has to come from genuine passion. Ever had a persistent ex who tries to convince you that you can fall in love with them again, while you know damned well it ain’t ever gonna happen? It’s a bit like that.

One of Katrina's pre-Unfeathered Bird cliffscapes, St. Abbs Head, Scotland. © Katrina van Grouw.
To be brutally honest I have nothing but contempt people who find it sad that I no longer do the same old work. It shows a lack of respect for my artistic integrity. It wouldn’t be so bad if these were faithful collectors and patrons from my past, but they’re not. Most, in fact, are creative people too so they should understand that creative development is a one-way process and not a matter of personal choice.

Before the rocks/seabird colony drawings I did images of big dramatic birds doing exciting things: fighting and chasing each other and stuff. Then I had a… I guess you’d call it an epiphany, on the cliffs of Hermaness in Shetland, and my work changed to the rocks overnight. And yep, you’ve guessed it, loads of people expressed regret that I wasn’t still doing the same bird pictures…

The important thing to remember is that the illustrations in my books are just that – illustrations. The book’s aren’t art books showcasing my anatomical art; they’re science books – albeit very beautiful ones. Each illustration is just a means to an end and a very small part of the whole. To me the creation of the book – the entire book, from conception to design - is the creative process. What can possibly be finer than bringing into existence an entirely original and very beautiful book?! It ticks all the boxes for me at every creative and intellectual level.

The important thing is to bring all this stuff – pictures or books or whatever - into the world, and the fact that it can’t be relied upon to be repeated forever is what makes it precious. I don’t know what lies ahead, of course, but I think it highly unlikely that I’ll ever return to being a fine artist. But if I do develop in an unexpected direction, promise me you won’t say it’s sad that I no longer produce books!

Katrina's terrifically moody albatross piece, a big dramatic bird doing an exciting thing. A skeletonised version of this image graces the opening of The Unfeathered Bird. © Katrina van Grouw.

In some respects we have arrived at a similar career path from opposing directions: I became an author/illustrator through training as a scientist, while you trained as an artist before authoring science books. You mention in Unnatural Selection that this professional path was not without its struggles, and I can entirely empathise with this. You have to become equally skilled in two, sometimes very different fields and practical issues mean it's not easy to be highly trained in both. Despite these challenges, you've produced two spectacular and very well received books. How have you dealt with the challenge of transitioning from artist to author who does art?

To be fair to myself, although I was deprived of the opportunity of a formal science education, my world before The Unfeathered Bird wasn’t entirely devoid of science, though it was practical rather than theoretical. I was a passionate birder from childhood, and my interests led me to train as a bird ringer in my early 20’s. I took part in long term ringing expeditions to Senegal and Ecuador and was particularly interested in moult and other physiological indicators that ringers use to age and sex birds. Around this time I taught myself taxidermy and began to assemble my own bird skin collection, and also prepared bird skins for museums. The personal project that let to me to make an in-depth study of bird anatomy (beginning with a dead duck I christened Amy) has been told many times already. Ironically, many of these elements are not things that science undergraduates are taught. I know plenty of lettered biologists who have never even touched a scalpel. That was all back in the late 1980’s so the transition into science hasn’t been a sudden recent change.

Anyone can educate themselves. The difficulties lie in the lack of opportunity for discussion with peers and tutors, and the difficulty of accessing academic texts, but it’s certainly not impossible. Harder to throw off is the bias based on your actual qualifications.

A disproportionately dwarfed "ancon" sheep, an example of a single-step evolution. Such sheep are more common than we may expect, and we have to wonder how often such radical changes occur naturally. It's conceivable that major, single-step changes in animal form could be selected for under some natural circumstances, and may have even played a role in 'natural' animal evolution. From Unnatural Selection, © Katrina van Grouw.
What I find most difficult, and personally infuriating, is people’s preconceptions; the tendency to put two and two together to make five. Many people find it difficult to accept that someone with an art background can have a genuinely scientific interest in something. They’ll assume that my anatomical interests have an artistic root – as though I’m inspired by textures and shapes and all that. And of course I do enjoy drawing this sort of thing, but it’s not the reason for it. I try to explain that if I wasn’t producing books, I wouldn’t be drawing skeletons, but no-one wants to hear that. Even on my book tour this year I sometimes had to really fight to be described as an author and not an artist. One venue insisted on advertising my talk: ‘Katrina van Grouw’s evolutionary illustrations’. It was humiliating.

The most damaging element of all this, and one that I find deeply painful, is the assumption that I must rely on Husband to help me with the science in my books, because I’m an artist (‘only’ an artist is the unspoken word here). In fact neither of us have an academic science background, and both of us formerly shared a career as curator of the bird collections at the Natural History Museum. Husband is indeed useful for mounting skeletons, and for his knowledge of domesticated animals, but I’m the one with the interest in evolutionary biology.

All in all it seems to be a lot easier for a scientist to be respected as a self-taught artist than the other way around.

Being self-taught does have its plus side however. Having to learn science the hard way means that I know a lot of the pitfalls and barriers to grasping each subject, so I’m in a good place to explain difficult concepts to others in a clear way. It’s made me a really good science communicator.

Given that this is primarily a palaeontology-led blog, I feel we should end with the news that The Unfeathered Bird will be making a return at some point in future, and will have a significant palaeo-themed component this time. Can you give any hints as to what to expect?

Yep, that’s right. I actually signed the contract to do a second edition of The Unfeathered Bird last spring, but I haven’t quite gotten into gear with it yet due to all the work of production and publicity for Unnatural Selection.

It’ll have an extra 96 pages, making a total of 400. You’ll remember that the first edition is divided into two sections: ‘generic’ – talking about birds in general - and ‘specific’ – talking about particular bird groups. The new material will mostly go into the generic section, looking at the definition of what makes a bird, what birds are and aren’t, and of course a whole load of stuff about bird evolution.

Red throated diver skeleton, from The Unfeathered Bird. A new edition will be with us one day! © Katrina van Grouw.

Bird wings will be compared with bats and pterosaurs (and Yi qi?). There’ll be stuff about feather evolution (maybe I can get a palaeo reconstruction in here somewhere...), lots of stuff about the loss of digits, the rotation of the wrist, shortening of tails, lengthening of necks, and the orientation of thighs. And you can expect a few active maniraptoran skeletons doing maniraptoran things.

In addition to this I’ll be replacing some of the drawings in the ‘specific section’; adding some more and giving the existing ones a good polish. I’ll be completely re-writing all the text and replacing the short family sections with entire chapters. The total word count is estimated to be around 110,000 words, in comparison with the 46,000 of the first edition. The science will be better, though still easily accessible. There’ll probably be a new jacket design, but almost certainly still showing peacocks. And I’m guessing the original title will be followed by a subtitle (suggestions on a postcard, please).

The Unfeathered Bird NEEDS a palaeo-themed component. It’s incomplete without it, and any reviewer who wanted blood could easily and justifiably have torn the first edition into shreds. But that didn’t happen. Instead the palaeo-world received us with open arms and heaped praise upon us. It was possibly the most humbling experience of my life. This new edition is my way of expressing my gratitude.

--

Thanks very much to Katrina for the interview, and please leave your suggestions for the subtitle of the next edition of The Unfeathered Bird in the comment field below. Personally, I'm thinking Unfeathered Bird II: The Birdening; UB2: Judgement Day; Unfeathered Bird: First Blood Part 2; or The Return of the Unfeathered Bird: Rave to the Grave. Alternatively, use those same seconds to grab yourself a copy of Unnatural Selection and The Unfeathered Bird, both available now from Princeton University Press and all good bookstores.

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Thursday, 16 August 2018

Those terrific pelagornithids

Miocene pelagornithid Pelagornis chilensis parents and chicks, what fantastic animals they must have been. Note the lack of pseudoteeth on the chicks, recent work suggests they didn't develop until the cusp of adulthood. Not that I drew them in and removed them at the last minute when researching this post, of course.
Given how often I've written about giant pterosaurs, it's peculiar that I've never thought to cover the only flying animals which have ever come close to challenging their size, the pelagornithids: long-winged, often gigantic birds which attained wingspans exceeding 6 m. And yes, a 6 m wingspan is a metric that many pterosaurs - not even just the big azhdarchids - would find endearingly cute, but it's the largest wingspread of any bird and well above the size of any living flying animal. In public engagement pelagornithids are mostly wheeled out to gawk at their size and weird pseudoteeth before being put away again, but there's lots of fascinating anatomy under those big wings, and they deserve a longer period in the spotlight.

Pelagornithids - which are sometimes called (the now defunct name) "pseudodontorns" - were a long-lived and globally distributed group, their fossils ranging from Palaeocene - Pliocene rocks of Eurasia, both Americas, Africa, Antarctica and New Zealand (Mayr and Rubilar-Rogers 2010; Bourdon and Cappetta 2012). They were a group of large-bodied pelagic soarers, seemingly adapted for extended periods of flight over seas and oceans. Most of their fossils are - as is typical for birds - pretty fragmentary, but a number of species are are relatively well represented, especially members of the genus Pelagornis. Their soft-tissue anatomy is virtually unknown, save for primary wing feather impressions associated with the holotype of P. orri (Howard 1957).

Many pelagornithids are known from single bones or a few pieces of skeletal shrapnel. In having good cranial and limb material, the Oligocene taxon Pelagornis sandersi is among the better known species. Note the difference in size of the humerus (e-f) vs. the hindlimb bones (j-q; femur is j-k, tibiotarsus is l-m, and carpometatatsus is o-p). From Ksepka (2014).
Much uncertainty and confusion surrounds the composition of pelagornithid taxa with numerous genera being considered invalid or synonymous with others. This problem is rooted in over-enthusiastic naming of undiagnostic, often crushed scraps of bone as well as a lack of comparable anatomies between holotypes. Evaluation of Neogene pelagornithid material has suggested that most genera are weakly supported, leading Mayr and Rubilar-Rogers (2010) to suggest that all Miocene and Pliocene taxa (which includes Osteodontornis, Pseudodontornis, Neodontornis and possibly Cyphornis) should be sunk into Pelagornis. It's a little difficult to say how speciose Pelagornithidae is given the fluidity of their taxonomy but, as a rough figure, it seems to be composed of a little over a half-dozen Neogene Pelagornis species and a handful of Palaeogene representatives. All pelagornithids share the same basic "long-winged and pseudotoothed" bauplan, but the characteristic anatomies and proportions of the group are most expressed in later taxa, such as Pelagornis.

The confusion over pelagornithid systematics is not confined to generic relationships. Their placement among other birds has been the source of much discussion and controversy, and it's perhaps best to regard their affinities as currently uncertain. Initially regarded as possible relatives of Pelecaniformes (classically thought to contain pelicans, cormorants, gannets and so on - the situation has changed since then), Procellariiformes (tube-nosed birds, including albatrosses) or Ciconiiformes (storks and allies), Bourdon (2005) found stronger evidence linking pelagornithids with Anseriformes - the same group that includes ducks, geese and screamers. Numerous features of the skull and forelimb support this affinity, as do some features of skull development (Louchart et al. 2013). An affinity with waterfowl might seem bizarre for these ocean-going giants but Anseriformes have a long and varied evolutionary history: this is the same branch of avian evolution that (probably) begat the giant, flightless gastornithids and mihirungs, as well as the wader-like Presbyornis. Viewed from a geological perspective instead of a modern one, Anseriformes are not just birds that honk and quack.

But while an anseriform affinity for pelagornithids has not being dismissed out of hand, the idea is not without critics. Some pelagornithid anatomies - such as their sterna - are not anseriform like (Mayr et al. 2008), and other features imply a position outside the anseriform-galliform clade (Galloanserae: crudely, the duck-chicken group) without qualifying for entry into Neoaves (all living birds but ratites and galloanserans) (Mayr and Rubilar-Rogers 2010; Mayr 2011). So while these studies broadly agree that pelagornithids emerged from fairly rootward stock among Aves, and that they are not closely related to any modern soaring birds, further work, and maybe more fossils, are needed to clarify their actual phylogenetic position.

Pelagornithid primary wing feather impressions associated with the holotype of Pelagornis orri. It's not known is these represent the longest feathers of the wing, but they still have a useful role to play in reconstructing pelagornithid wingspans. From Howard (1957).

Size-off: Pelagornithids vs. Argentatvis

All pelagornithids are characterised by large size with even the earliest, smallest taxa being comparable to big albatrosses in wingspan (Bourdon 2005). But how big did they get? I know several readers are already sharpening their comment knives about my introduction suggesting that pelagornithids are avian wingspan record holders, thinking I've forgotten about the giant, 7 m wingspan Miocene teratorn Argentavis magnificens. But that's not a mistake: pelagornithids really should be considered the record holders for avian wingspans, and Argentavis isn't as big as most people imagine.

Classic image of teratorn researcher Kenneth E. Campbell posing with a 25ft wingspan (7.62 m) silhouette model of Argentavis magnificens at the National History Museum of Los Angeles. Alas, Argentavis wasn't quite as big as depicted here. From Campbell (1980).
Some giant pelagornithids, such as Pelagornis chilensis, are unusual among giant fossil fliers in being represented by relatively good skeletal material and their feathered wingspan estimates of 6 m or more can be considered trustworthy, reliable figures. Giant Argentavis magnificens, on the other hand, are known from fragmentary remains and some degree of uncertainty surrounds their wingspans: estimates have ranged from 5.7 to 8.3 m (e.g. Campbell and Tonni 1983; Chatterjee et al. 2007). Recent workers have suggested that the lower range of these estimates is more likely. When describing P. chilensis, Mayr and Rubilar-Rogers (2010) noted that the 82 cm long humerus of their pelagornithid was vastly bigger than the 57 cm long Argentavis humerus, and that scaling the latter to proportions seen in smaller teratorns yields a wing skeleton length of 183 cm. If so, the bony wing spread of the largest Argentavis might have struggled to reach 4 m, and this is before assuming any flex in the wing bone joints. And no, the addition of feathers does not bring Argentavis into record-breaking territory. Ksepka (2014) predicted that the primary feathers of Argentavis would need to be about 1.5 m long to reach a 7-8 m wingspan, a length that would exceed the primary feather: wingspan ratio of all living birds as well as contradict the observation that primaries tend to scale with negative allometry against wingspan. Accordingly, Ksepka (2014) suggested Argentavis was more reliably sized at a 5.09 - 6.07 m wingspan, with estimates at the lower end of that range being predicted in most models. In contrast, the wing skeletons alone of P. chilensis and P. sandersi easily exceed wingspans of 4-5 m, and the addition of conservatively estimated feather lengths easily raise these wingspans into the 6-7 m range.

Skeletal reconstructions of giant pelagornithids: the holotype of Pelagornis chilensis (ventral view) and P. sandersi (dorsal view). That bird to the right of the image is a little thing called the wandering albatross, which has the largest wingspan of any extant flying bird. Pelagornithids must have been amazing to see in life. Images from Mayr and Rubilar-Rogers (2010) and Ksepka (2014).
Despite their size, pelagornithids were not heavy animals. Mass estimates for giant pelagornithids are in the region of 16–29 kg for P. chilensis and 21.9–40.1 kg for P. sandersi (Mayr and Rubilar-Rogers 2010; Ksepka 2014). Given that these birds are twice the size of albatrosses, the fact that their predicted masses match, or only double, the maximum masses of extant flying birds are surprising. Remember that mass increases by a factor of eight for every doubling of a linear dimension so, if we scaled wandering albatross (using masses given at Wikipedia) to Pelagornis proportions we’d expect a mass of 50-96 kg - well above those predicted figures. The pelagornithid weight-watching secret seems to lie in their unique wing proportions: even more than albatross, pelagornithids have extremely long wings compared to the rest of their bodies, and can thus attain giant wingspans while keeping their masses low. Similar tactics were also exploited by giant pterosaurs: maximising wing area while keeping the body small is a great way to maintain volancy at large size. Extremely thin walled bones also helped pelagornithids maintain low masses (and also explains why so many pelagornithid fossils look like they've been hit with a bulldozer).

Biological sailplanes

The largest pelagornithids were of a size which exceeds some theoretical flight limits for albatross-like birds (e.g. Sato et al. 2009), though the plainly obvious flight adaptations of their skeletons suggest this problem lies with our calculations and not the concept of pelagornithid flight itself. Indeed, glide analyses of P. sandersi indicate a supreme soaring capability with a very low sink rate (the rate at which altitude is lost during gliding) and high glide speeds, a combination that would facilitate extremely wide-ranging, energy efficient flight (Ksepka 2014). Their flight performance seems generally more akin to that of albatross than other pelagic birds, so reconstructions of pelagornithids riding air currents between waves, buzzing along the water surface and cruising on ocean winds seems sound. Reduced hindlimb proportions indicate that pelagornithids were probably not capable walkers or runners however, and we might envisage them only landing infrequently, perhaps most commonly when nesting. Curiously flattened and wide toe bones recall those of birds which use their feet as air brakes when landing (Mayr and Rubilar-Rogers 2010; Mayr et al. 2013), and may also have aided stabilisation on land (Mayr et al. 2013).

Predictions of glide ability and lift:drag ratios in P. sandersi from Ksepka (2014). Note how both models compare very well to albatross flight (black), but less well with frigate bird (red) or raptor flight (green).
Maintaining flight is a relatively easy part of aerial locomotion: how pelagornithids became airborne is trickier to fathom. This is mostly because of several indications of a limited flapping ability in the largest Neogene species, which are also the ones that would struggle the most with launch. Scaling of muscle energy availability predisposes all large flying animals to a relatively limited flapping capability and, like all fliers operating at the upper limit of their respective bauplan, pelagornithids likely relied on short-lived bouts of powerful anaerobic muscle activity to perform flapping (Ksepka 2014). But there is some question over whether they could flap their wings at all: several osteological features suggest pelagornithids had reduced shoulder/humeral motion (including a lack of rotatory capability) and lessened downstroke musculature (Mayr et al. 2008). A lack of dynamism is also seen elsewhere on the wing in that the articulation for the alulua was weakly developed, prohibiting spread of this structure during takeoff and landing (Mayr and Rubilar-Rogers 2010). The alula, when extended, allows the wing to function at higher angles of attack (the angle of the wing relative to the direction of airflow) and is thus very useful in initiating flight, controlling landing and general aerial manoeuvrability. Its immobility in pelagornithids would have impacted their range of flight dynamics quite considerably.

The large size of pelagornithids means that a very limited, maybe absent flapping ability may not be as detrimental as we intuitively predict. Flapping motions - both frequency and amplitude - reduce against increasing wing area and flight speed (the latter being predicted as high for any giant flier) so, as the largest flying birds of all time, pelagornithids may not have missed flapping as much as you'd think. But nonetheless, a significantly reduced flapping capacity and limited alula motion may have demanded fairly specialised launch and landing behaviour. Pelagornithids may have been limited to launching by simply extending their wings and using running, gravity or headwinds to find sufficient glide velocity. Landing, by contrast, may have involved low-angle approaches, slowing as much as possible (a dangerous game, as slower gliding also brings higher sink rates) and ditching to the ground. I can entirely believe that undignified semi-crash landings were common in this group.

If our understanding of pelagornithid flight is accurate, typical seabird behaviours like cliff-nesting - demonstrated here by northern gannets (Morus bassanus) - can be ruled out. Long winged seabirds are not the most agile fliers, but many still have enough control over their initiation and cessation of flight to land on small ledges. Pelagornithids trying this may have ended up splattered, Wile E. Coyote-style, on the side of a cliff. Photo by Georgia Witton-Maclean.
Being so light relative to wingspan would assist in both takeoff and landing, but nevertheless question marks hang over their ability to achieve flight in some conditions, such as escaping water (Ksepka 2014). Perhaps, like frigate birds, pelagornithids avoided entering water (though the former struggle with water escape because of waterlogged feathers rather than restricted flapping kinematics). I wonder if this is the case however, it being historically proposed that (unrealistically lightweight) giant pterosaurs could achieve flight from water by simply spreading their wings and catching wind (e.g. Bramwell and Whitfield 1974). The predicted pterosaur masses, wingspans and wing area models used in these old pterosaur studies are not far off those modelled today for giant Pelagornis: if so, could pelagornithids have escaped water with the same wing-spreading trick? It would be interesting to see this modelled biomechanically for a pelagornithid-specific model. On land, we may assume that pelagornithids favoured open space that permitted full 6-7 m wing spreads for launching and landing, and it would not be surprising if they favoured windy, elevated coastal regions that provided environmental launch assistance. I'm not sure what their prospects for flight in continental habits are, but it probably wasn't good: they almost certainly stuck to oceanic soaring, as suggested by the skew of their fossils to marine sediments.

They're only pseudoteeth, but I like them

We’ve made it all the way through this post without discussing the other characteristic anatomy of pelagornithids: their ‘pseudoteeth’. These structures are bony outgrowths of the jaw bones which strongly resemble actual dentition, though histological studies have verified that they lack all tissues associated with true teeth (Howard 1957; Louchart et al. 2013). It’s thought that pseudoteeth compensated for a well-developed hinge in the lower jaw that permitted wide horizontal bowing during feeding. This allowed for large prey to be swallowed, but compromised overall jaw integrity and potentially risked the loss of slippery seafood prey. A set of variably sized spikes along the margins of the beak is a great way to ensure snagged foodstuffs - thought to be mainly surface-seized fish or squid - did not slip from their beaks. Though many of the spikes are hollow, jaw bone surficial textures indicate that the entire jaw - pseudoteeth and all - was covered with a cornified sheath typical of other bird beaks (Louchart et al. 2013). As we discussed when looking at mammal horns, that’s a pretty potent combination for maximising lightness with strength, though the bone forming the pseudoteeth was mechanically weak and, despite their ferocious appearance, they were not adapted for tackling large, formidable prey (Louchart et al. 2013).

Holotype skull of P. chilensis in lateral view: check out those pseudoteeth. From Mayr and Rubilar-Rogers (2010).
That pelagornithid teeth functioned well as fish-grabs is suggested in their similarity in size and distribution to the dentition of other fish eaters, including certain crocodylians, large predatory fish, pterosaurs and temnospondyls. Quite how pelagornithids caught their prey is not well understood: if they could enter the water, they may have foraged from the water surface or dived; if not, they may have snatched prey from the water surface or stole it from other birds. Further research into pelagornithid flight capabilities and launch kinematics would narrow down this range of possibilities.

Recent studies have shown that pseudoteeth erupted from the jaw relatively late in pelagornithid growth (Louchart et al. 2013), meaning juvenile Pelagornis would have looked like regular, cute baby birds before developing their toothy smiles as adults. This has several interesting implications for pelagornithid growth and ecology. The first is that the cornified beak tissue covering their jaws must not have hardened until after the teeth had fully developed (recall from a previous post that cornified sheaths, on account of being inert, dead tissue, can’t be easily modified once deposited). This characteristic is not common among birds, but occurs in a number of Anseriformes. This observation is not a deal clincher for the pelagornithid-anseriform phylogenetic hypothesis, but it's an interesting connection nonetheless. Secondly, studies show that the emerging pseudoteeth were relatively delicate and potentially unable to withstand stresses imparted by thrashing fish or squid until late in development. This being the case, Louchart et al. (2013) proposed that pelagornithids might have been altricial, feeding regurgitated food to their offspring until they were fully grown and able to forage for themselves; or else that the juveniles were foraging on different foodstuffs. Altriciality would be unusual behaviour for a stem-neoavian as most bird species of this grade have precocial offspring that feed themselves straight after hatching. Insight into these hypotheses would be provided by fossils of juvenile pelagornithids but these remain extremely rare. I wonder if these animals were like living pelagic birds and nested atop cliffs in isolated offshore settings? If so, I wouldn’t hold your breath waiting for fossils of their hatchlings.

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