Jaw gaping in Spinosaurus hinges on modern birds

A north African spinosaurine, with obvious nods to recent work suggesting some of these animals might've had short legs and a semi-aquatic lifestyle. The pterosaurs are azhdarchids, which are known to coexist with some African spinosaurines.

Honestly, I don't intend to cover every new paper which comes out on Spinosaurus. This fourth blog post, covering the third successive paper on this animal since 2014, is not the latest instalment of a stealthily-implemented new blog feature (check out this, this and this for previous non-instalments). Rather, north African spinosaurs are simply 'in' right now, hard to miss on palaeontological social media and the topic of widespread conversation - the dinosaur equivalent of skinny jeans, adult colouring books or whatever ITV runs on a Saturday night nowadays.

The latest paper on these animals is that of Christophe Hendrickx et al. (2016), a piece which provides another interpretation on Moroccan spinosaurine diversity based on isolated quadrate bones. These are elements from the back of the skull which, among other things, articulate with the lower jaw. I don't really want to go into the ins and outs of their primarily descriptive and systematic assessment as the paper is a) a bit of a beast and b) we've spoken a lot about spinosaurine taxonomy of late and I'm desiring fresh topics. It will suffice to summarise that Hendrickx et al. (2016) provide compelling evidence for at least two spinosaurines being present in the Moroccan Kem Kem Beds, one of which is Sigilmassasaurus brevicollis and the other is - in their interpretation - Spinosaurus aegyptiacus. These results are not exactly the same as those presented in the recent Evers et al. (2015) paper, as Hendrickx et al. shuffle and deal north African spinsosaurid fossils among named taxa in another unique way. However, it certainly adds further evidence against the concept of a single spinosaurine species ruling Late Cretaceous north Africa proposed by Ibrahim et al. (2014). And yes, for those interested in scientific responses to the famous quadrupedal Spinosaurus reconstruction publicised in 2014, Hendrickx et al. (2016) specifically comment on the likelihood of it being a chimera of animals from across time and space. There's lots more in the paper - spinosaur skull morphology, body size, ontogeny, loads of illustrations and it's 100% open access - interested parties should definitely check it out.

The pelican-like foraging anatomy of Spinosaurus, as illustrated in Hendricks et al. (2016).

Moving on to fresh, but still spinosaurine-filled waters, let's talk about something more fun - functional morphology that is*! One of the neater parts of the Hendrickx et al. analysis is that they pay a lot of attention to the jaw articulation of spinosaurines, providing detailed descriptions of how it may have influenced jaw operation and prey capture (above). Some readers may be aware that spinosaurids have 'helical' or 'asymmetric' jaw articulations, in which the quadrate condyles force the jaw somewhat outwards as it opens. Hendrickx et al. quantify this, noting that the lateral displacement is somewhere in the region of 20% of the quadrate width when the jaw is opened 45°. This equates to approximately 20 mm of motion on each side of the jaw in a c. 1 m long skull. As a rule, non-avian theropods do not have these helical joints, although they do occur in some pterodactyloid pterosaurs and, perhaps more famously, modern pelicans. Hendrickx et al. (2016) also note that the anterior connection between spinosaurid mandibular rami - the mandibular symphysis - has a fibrous texture indicative of being somewhat loose and flexible, enhancing the pelecanid comparisons further.

*It's OK, my shame about that pun is worse than any punishment you could deliver.

In both the paper and news outlets (example), these perceived similarities between spinosaurid and pelican jaws are being stated as evidence of spinosaurs feeding in a pelican-like fashion, splaying their jaws to enhance food capture and swallow larger prey. Regular readers may recall that Darren Naish and I published research on similar claims for pterosaurs in 2013 (although the paper was not 'officially' published until last year - Witton and Naish 2015), countering suggestions that some pterosaurs fed like pelicans because of their helical quadrate articulations (Averianov 2013). This background made me surprised that another group of fossil animals was being labelled as pelican-like, as much of our discussion on pterosaurs is applicable to non-avian theropods and we're even cited in the Hendrickx et al. paper! I thought it might be of interest to explain some of my reservations about this idea here**.

**I want to note that I feel a bit awkward writing this commentary in light of recent controversies on palaeontology blogs, so-called 'Post Publication Peer Review' and so on. I hope that it's clear that this article, as with all the writings here, are meant as constructive, well-meaning expressions of opinion from someone with an interest in these topics and experience in a similar research field. My disagreement with the functional analogy proposed by Hendrickx et al. and their PR work is a polite one, and doesn't mean I disrespect them as scientists or want to undermine the significance of their paper.

We should begin by familiarising ourselves with the jaws of some relevant modern birds. Quite a bit of research has been done into pelican jaw anatomy (Schreiber et al. 1975; Meyers and Myers 2005; Field et al. 2011), an unsurprising fact given how awesomely and specifically adapted their jaws are to their unusual foraging method. Researchers have identified a number of adaptations critical to pelicans being able to splay their jaws so widely. They include reduced mineralisation at the middle part of the lower jaw to make a long 'bending zone', and even further reduction of mineral content (down to 20%) adjacent to the mandibular symphysis. This makes a 'hinge' for the mandibular rami to swing outwards on despite the fact there is no articulation or joint in the jaw at this point. The mandibular symphyses are so short that virtually all the jaw length is permitted to splay. At the other end of the jaw, the tongue is similarly reduced so as not to get in the way when the mouth is opened. The connection between the dentary bone (forming the jaw anterior) and the complex of bones of the posterior jaw is long, loosely connected and obliquely oriented so as to aid motion when the mandible spreads outwards. Even the horny tissues of the beak are specialised, being very thin (described as 'skin-like' by some authors) so as not to impede jaw flexion.

Contrastingly, little mention is made of helical jaw joints when talking about pelican foraging strategies. Zusi (1993) mentions that jaw spreading at the joints may be important to this effect, but more recent literature states that the precise mechanic responsible for bowing pelican mandibles is not really understood (Meyers and Myers 2005). Three hypotheses are currently thought viable: forces and weight of water acting on the jaw (known to be only part of the solution, as pelicans can splay their jaws on land too), contraction of muscles in the gular pouch (pulling the chin backwards, pushing the jaw rami out) or twisting of the lower jaw by the pterygoideus jaw musculature (Meyers and Myers 2005 and references therein). I guess it's possible that lateral displacement of the jaws has some role too, but it's interesting that the pelican guys aren't championing it's role as essential to manibular bowing. It's always risky using negative evidence in this way, but it might be telling given how intensively studied pelican skulls are.

Mandibular bowing in modern birds, as illustrated by Zusi (1993). a, herring gull (Larus argentatus) with relaxed and bowed mandibles; b, common potoo (Nyctibius griseus) skull and mandible (arrows show zones of flexion; c, tawny frogmouth (Podargus strigoides), a potoo incapable of mandibular kinesis. Note contrasting morphology between the potoo mandibles - even as a fossil taxon, there would be no doubt that N. griseus was capable of mandibular flexion.

Perhaps a factor in ornithologists not paying much attention to pelican jaw joints is that helical quadrate articulations are not unique to them. In addition to pelicans, pterosaurs and spinosaurids, numerous bird groups are equipped with asymmetric quadrate condyles. These including herons, shoebills, certain hummingbirds and seed-eating songbirds, potoos and others. In all these species, the effect is the same - lateral displacement of the posterior jaws when the mouth is opened. Because these animals have very different diets, foraging strategies and lifestyles, their convergence on a similar jaw anatomy reflects a basic functional requirement: apprehending or swallowing large food (Zusi 1993). However, not all these species bow their anterior mandible regions in a significant way. To perform this trick, many non-pelecanid birds have mandibles with hinged regions (above). Some species, like certain potoos, are remarkable in this regard, perhaps surpassing pelicans in their ability to expand and even twist their throats into wide basins. It is not only specialised taxa which have remarkable lower jaws: the likes of seagulls can also bow their mandibles to an impressive extent. In these birds, a combination of the pull of the pterygoideus muscle and osteological specialisations allow the jaws to bulge sideways and large food items to enter the throat. The message here seems to be that helical jaw joints might have nothing to do with pelican-like jaw bowing, whereas other features - the development of pronounced mandibular hinges and specialised musculature - might be.

Modern birds give us a pretty good idea of what sort of features we're looking for in a pelican-like dinosaur. In doing so, as might already be obvious, they suggest major issues with the pelican-spinosaur analogy. Firstly, we need to acknowledge that helical jaw joints are not a special pelican feature. We could also call spinosaurid mandibular joints 'heron-like', 'potoo-like', or even 'hummingbird-like'. It seems more precise to suggest spinosaurid jaw joints are similar to those of several modern bird lineages and not over-emphasise anything to do with pelicans.

Our mandibular bowing experiments with pterosaurs and pelicans illustrated. Even when stretching the pterosaur jaws beyond the limits of their jaw joints, their area increase was negligible compared to that of a lazy pelican. From Witton and Naish 2015.

Secondly, given how ecologically variable modern birds with helical jaw joints are, and that there is no obvious correlation between asymmetric quadrate condyles and mandibular bowing, we need to treat them as part of a 'functional package' - a recipe of functional elements considered simultaneously to assess their overall effect on behaviour and lifestyle. The attempt here is to see the bigger picture of how such joints work with the rest of the jaw - do they function in a pelican-like fashion? It doesn't seem so. The amount of mandibular movement in spinosaurids is pretty negligible compared to what we see in modern birds. As noted above, quantification of of jaw motion by Hendrickx et al. suggests the lower jaws move only a tiny amount, each jaw splaying 20 mm from a skull approaching 1000 mm long. It's likely this motion would not even be noticeable in life. I'm reminded of the calculations Darren and I predicted for pterosaur jaw expansion (above) where we found pterosaur helical jaw joints boost jaw area, at most, by a few 10s of percent, but anterior jaw bowing in pelicans increases area by hundreds of percent (Witton and Naish 2015). These calculations seem to agree with current research that bowing of the anterior mandible is the most important agent in having widely distending jaws. No spinosaurid jaw yet known has adaptations for anterior mandible motion akin to those of pelicans, or even other birds capable of mandibular bowing. Many readers will know that we can, and have, assessed the kinetic potential of fossil animal skulls, including those of fossil pelicans (Louchart et al. 2011). we should be able to detect bowing mandibles in non-avian dinosaurs and other fossil reptiles, should they occur.

My points here might be countered by the observation that the mandibular symphyses of some spinosaurids are quite fibrous, perhaps indicating a loose and mobile connection between them (Hendrickx et al. 2016). This might be the case, but Hendrickx et al. also note that some spinosaurid symphyses are longer than those of other theropods, thus actually having a greater degree of anterior attachment between each lower jaw. Based on our understanding of modern bird jaws, surely this is the opposite of what we'd expect in an extinct pelican-analogue? Even if I'm wrong on that, a slightly spongy symphysis and helical jaw joints are several functional miles off the flexibility afforded by avian jaws - especially those with the most extreme adaptations for mandibular bowing, like pelicans.

In all, then, I'm not convinced on the idea that spinosaurids were pelican-like in their foraging habits. Rather, the adaptations outlined by Hendrickx et al. suggest a somewhat bird-like ability to increase gape for swallowing slightly larger food than usual. In actuality, spinosaurid jaw functionality contrasts so markedly with that of pelicans that it might be misleading to tout pelicans as spinosaur analogues. After all, the spinosaurid ability to bulge their jaws slightly is not especially pronounced or even rare, whereas what pelicans do is really both those things: an extreme and marked adaptation, and almost unique in nature. I come back to a point I've made about other instances of 'extreme' modern animals being used as analogues for extinct ones: we need to be as thorough as possible in our functional assessments before pointing to highly specialised and extremely adapted modern species as suitable analogues for long dead taxa.

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The artwork and words you see here are supported by Patreon, the service which allows you to directly support artists and authors with monthly payments. You can support this blog from $1 a month and, in exchange, get access to bonus content and rewards - the more you pledge, you more bonuses you receive. For this post, I'll be explaining the rationale behind the spinosaurine depicted at the top of this post - it's not Spinosaurus 2014, not a 'classic' reconstruction - what's going on?

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References

• Averianov, A. O. (2013). Reconstruction of the neck of Azhdarcho lancicollis and lifestyle of azhdarchids (Pterosauria, Azhdarchidae). Paleontological Journal, 47(2), 203-209.
• Field, D. J., Lin, S. C., Ben‐Zvi, M., Goldbogen, J. A., & Shadwick, R. E. (2011). Convergent evolution driven by similar feeding mechanics in balaenopterid whales and pelicans. The Anatomical Record, 294(8), 1273-1282.
• Hendrickx, C., Mateus, O., & Buffetaut, E. (2016). Morphofunctional Analysis of the Quadrate of Spinosauridae (Dinosauria: Theropoda) and the Presence of Spinosaurus and a Second Spinosaurine Taxon in the Cenomanian of North Africa. PloS one, 11(1), e0144695.
• Ibrahim, N., Sereno, P. C., Dal Sasso, C., Maganuco, S., Fabbri, M., Martill, D. M., Zouhri, S. Myhrvold, N. & Iurino, D. A. (2014). Semiaquatic adaptations in a giant predatory dinosaur. Science, 1258750.
• Louchart, A., Tourment, N., & Carrier, J. (2011). The earliest known pelican reveals 30 million years of evolutionary stasis in beak morphology. Journal of Ornithology, 152(1), 15-20.
• Meyers, R. A., & Myers, R. P. (2005). Mandibular bowing and mineralization in brown pelicans. The Condor, 107(2), 445-449.
• Schreiber, R. W., Woolfenden, G. E. & Curtsinger, W. E. (1975). Prey capture by the Brown Pelican. The Auk, 92(4), 649-654.
• Witton, M. P. and Naish, D. (2015) Azhdarchid pterosaurs: water-trawling pelican mimics or "terrestrial stalkers"? Acta Palaeontologica Polonica 60, 651-660.
• Zusi, R. L. (1993). Patterns of diversity in the avian skull. The skull, 2, 391-437.

The Spinosaurus saga continues

A year after the 'Spinosaurus reboot' as a small-legged, early whale-mimicking aquatic quadruped, experts remain divided over fundamental aspects of Spinosaurus palaeobiology. This depiction shows Spinosaurus aegyptiacus as generally imagined prior to 2014.

The long, tragic and occasionally controversial research history of the giant, enigmatic theropod Spinosaurus aegyptiacus will be familiar to many readers of this blog*. First named and described in the early 20th century by Ernst Stromer from remains found in Late Cretaceous strata of Egypt, our principle Spinosaurus material fell victim to Allied bombing raids in World War II and was completely destroyed. Stromer's detailed illustrations and descriptions are all that remains of this material, and these have formed a variably interpreted foundation of all subsequent Spinosaurus research. For much of the 20th century the life appearance of Spinosaurus remained mysterious. Depicted as a nondescript sailed giant theropod early on, discovery of well represented spinosaurids like Baryonyx and Suchomimus, as well as fragments of new Spinosaurus material, permitted more confident interpretations of Spinosaurus size and form as we approached the new millennium. By the 2010s, Spinosaurus was recognised as a gigantic, derived and perhaps semi-aquatic spinosaurid, adapted for feeding on large aquatic prey (above). Much of this interpretation relied on new Spinosaurus remains from multiple locations in northern Africa, including the famous Moroccan Kem Kem Beds, an expanse of Late Cretaceous rocks roughly contemporaneous with those Egyptian deposits yielding the original, destroyed Spinosaurus remains.

*For succinct overviews of Spinosaurus research prior to 2014, check out posts at Tetrapod Zoology and Laelaps.

Famously, last year saw Spinosaurus reinvented again, this time as a quadrupedal, knuckle-walking, long-bodied, tiny-legged dinosaurian take on a crocodile or early whale (below). The authors of this widely publicised study, Nizar Ibrahim and colleagues (2014), synthesised existing and new data on African spinosaurids to create this reconstruction, synonymising several taxa into S. aegyptiacus and presenting new Spinosaurus remains obtained from the Kem Kem beds. The most significant of these was a set of associated vertebrae, pelvic and hindlimb remains which were proposed as a neotype specimen for Spinosaurus (a specimen to hold the Spinosaurus name now that the original material is lost to science). That this neotype represents Spinosaurus was bolstered by it bearing similar hindlimb and vertebral proportions to 'Spinosaurus B', a collection of Egyptian spinosaurid specimens described by Stromer, considered referable to Sp. aegyptiacus by Ibrahim and colleagues. Spinosaurus B is also now lost, also being destroyed in WWII. The Ibrahim et al. study provided a lot of new data on Spinosaurus and has helped cement the concept of it being a semi-aquatic animal, but several aspects of the paper didn't meet the warmest reception from a number of academics. Specific issues were scaling of the skeletal components, how sensible it was to lump so much north African spinosaurid material into one species, and uncertainty about the provenance of the neotype specimen. Some of these concerns were diffused by the authors, but we await a promised monograph for answers to all the questions raised by their first paper. In the mean time, the 2014 Spinosaurus interpretation remains a debated topic among those interested in dinosaur palaeontology.

The Ibrahim et al. (2014) take on Spinosaurus aegyptiacus. Different colours represent different specimens: red is the neotype; brown is the original Spinosaurus material; yellow is referred, isolated Spinosaurus remains; green bones are borrowed from other spinosaurids, and blue bones are crafted to fit the skeleton based on neighbouring elements. Image borrowed from Smithsonian.com.

One year later...

This week, the Spinosaurus tale has taken another twist with publication of a mammoth (open access) paper penned by a team of European spinosaurid experts, led by Serjoscha Evers. Evers et al. have reappraised the affinities of Moroccan specimens seemingly related to Spinosaurus: Sigilmassasaurus brevicollis and Spinosaurus maroccanus. These animals, known only from vertebrae, were subsumed into Sp. aegyptiacus by Ibrahim et al. (2014) as part of their trans-African Spinosaurus concept, and that decision is a core focus of the Evers et al. paper. Their work contains extensive commentary on the detailed anatomy of Moroccan spinosaur material and what it might mean for recent interpretations of Spinosaurus form and lifestyle. Given the wide interest in Spinosaurus and the 2014 reconstruction, I thought it might be of interest to summarise some of what they outline here.

Firstly, taxonomic revisions proposed by Evers et al. present a very different picture of what fossils we can identify as belonging to Spinosaurus. Their work on Si. brevicollis and Sp. maroccanus suggests these species are probably one and the same (the latter being sunk into the former), and that Sigilmassasaurus should be considered distinct from Sp. aegyptiacus. They go on to suggest that other Kem Kem vertebrae hint at a second spinosaurid species in the Kem Kem fauna, and outline several reasons why the Ibrahim et al. 'neotype' specimen cannot be referred to Spinosaurus. For one, the neotype is anatomically quite different from Stromer's Egyptian 'Spinosaurus B' specimen. Ibrahim et al. considered Spinosaurus B as representing Sp. aegyptiacus, but Evers and colleagues argue that Spinosaurus B is anatomically more similar to Sigilmassasaurus than Spinosaurus. Spinosaurus B therefore might have no use for linking any specimens specifically to Sp. aegyptiacus, including that all-important neotype.

In addition to these morphological objections, Evers et al, also raise palaeobiogeographic issues with the 'neotype' referral. Evidence for Egyptian dinosaur species being present in Morocco is scant at best, most data indicating little mixing of eastern and western African dinosaur species during the Late Cretaceous. It would be unusual, then, to find the Egyptian species Sp. aegyptiacus in Morocco. Palaeobiogeography is not a deal clincher for taxonomy of course - careful examination of the neotype and genuine Spinosaurus remains will be the deciding factor here - but it is another stick in the mud for the neotype proposal. Although the exact identity of the 'neotype' specimen is left in the air by Evers et al. - ongoing descriptive work on the specimen needs to be completed to truly assess this - they reject the proposal of the Kem Kem specimen as a Sp. aegyptiacus neotype, and leave Spinosaurus characterised by features in Stromer's illustrations. This is obviously quite a shake up of the suggestions made last year: Spinosaurus 2014 might be a mix of at least two named species, incorporate material of under-appreciated taxonomic importance, and substantial, newly published material might have little, if anything, to do with Spinosaurus.

The proposed Spinosaurus neotype. Image borrowed from Andrea Cau's excellent Theropoda blog.

Moving on, Evers et al. also raise concerns about interpretations of Spinosaurus in context of Kem Kem fossil collecting practises. Museum exhibitions and PR exercises suggest that the Kem Kem yields complete skeletons of dinosaurs and other fossil vertebrates, but the reality is quite the opposite. Kem Kem vertebrates are typically preserved as isolated, often broken bones in multitaxic bone beds (that is, bone beds comprising many species). Associated skeletons of single individuals do occur, but they're relatively rare and rely on precise collecting documentation to prove their authenticity. Unfortunately, historic and recent records of Spinosaurus occurrences and excavation are often poor. We might chalk a lack of historic documentation to the practises and technological limitations of bygone times, but recent issues are caused primarily by the commercial value of Kem Kem fossils. The greater majority of Kem Kem fossils, including dinosaurs, are collected without extensive documentation and then sold by private dealers. Even if localities are recorded, ambiguity often surrounds association of fossil material prior to excavation. Several alleged associated Spinosaurus specimens are meant to have come from single localities, but being from the same place is really only half the battle if they stemmed from multitaxic assemblages. Concordant size of bones might suggest genuine association, but this is not always certain either: Evers et al. report practises where collectors sort loose material from disparate locations into type and size categories before sale - nefarious individuals making fossil skeletons more substantial with unassociated elements is a real problem the world over. It's sad but true that the monetary value associated with substantial vertebrate fossils makes ascertaining their authenticity crucial for subsequent credible interpretation.

Unfortunately, Evers et al. report these factors as affecting virtually all associated Spinosaurus material, including the 'neotype' and the other specimen key to the 2014 reconstruction, Spinosaurus B. In the case of the latter, all we have to go on to establish association are Stromer's notes, which are not quite as detailed as we might like. For the neotype, we know some of the specimen was directly collected in the field, and that other bits were purchased from dealers by two academic institutions over a two year period - exact documentation of this remains to be presented (hopefully it will in the 'neotype' monograph). Without strict certainty over how many individuals these specimens might represent, Evers et al. suggest some of the odd proportions in recent Spinosaurus reconstructions may reflect the marrying of mismatched bones to one another. That's not a certainty, of course, but it's also something which shouldn't be casually ignored.

Collectively, Evers et al. use these points to provide an alternative take on Spinosaurus to that presented in 2014. Ibrahim et al. argued that their new material helped simplify and integrate different interpretations of African spinosaurid material, but Evers et al. argue the opposite: they emphasise how poorly known Spinosaurus and kin are, and how interpreting fossils of north African spinosaurids is getting increasingly complex. Spinosaurus fossils remain very fragmentary to the point where most cannot be directly compared, they seem to hint at, but don't really crystalise, an apparent high species diversity, and are often of uncertain association or exact origin. At face value, that doesn't leave us with a lot to be confident about, although we'll have to see how this more despondent view goes down with other spinosaurid researchers. More complete and well documented discoveries will soon help smooth out bumps in our knowledge, but it seems likely that a lot of work and discussion remains to sort out what is really going on with north African, Late Cretaceous spinosaurids.

What does this mean for 'the Spinosaurus reboot'?

That's not quite the end of our discussion, however. It might be assumed that the points outlined above sound the death knell for the strangely proportioned 2014 Spinosaurus reconstruction, and that we should go back to our traditional interpretation of this animal. That might not be quite right, for two reasons. Firstly, given how distinctive many 'Spinosaurus' remains now seem to be, it's actually questionable what specimens should be considered Sp. aegyptiacus at all, other than the first specimen described by Stromer. A lot of referred isolated Spinosaurus specimens have been incorporated into our 'traditional' reconstructions in recent years, and we might need to think hard about their role in our interpretations of this animal. What we've become typically used to thinking of as Spinosaurus may not entirely be Spinosaurus!

Secondly, while some aspects of the 2014 interpretation of Spinosaurus have clearly been challenged by the Evers et al. paper, not all proportional aspects of the recent Spinosaurus reinvention are obviously erroneous. Last year, Ibrahim et al. noted that both Spinosaurus B and the 'neotype' have reduced hindlimbs with respect to their associated vertebrae, and used this fact as support for the diminutive legs in their reconstruction. Although arguing that there is no longer evidence for short hindlimbs in Spinosaurus itself, Evers et al. don't completely dismiss the notion of some African spinosaurids being short legged. The hindlimb proportions of those specimens is very similar despite the vagaries surrounding fossilisation and exhumation of ancient animal remains, maybe more similar than you'd expect from chance alone. If it is coincidence, it's certainly a startling one.

Stromer's 'Spinosaurus B' material: proportionally similar to the 'neotype' specimen, but does that tell us anything about spinosaurid proportions? Another image borrowed from Theropoda.

However, Evers et al. also attach some important caveats to this point. Stromer's notes clearly state that he did not consider the 'Spinosaurus B' material to represent one individual, and his testimony is the closest thing we have to a report on the excavation of the material. He specifically comments on the hindlimb being too small and slender to match the vertebrae, and thus interpreted them as representing a second individual. Other workers have agreed that this material must represent multiple animals or even several types of dinosaur (discussions about the possibly chimeric nature of Stromer's spinosaur specimens are not new - e.g. Rauhut 2003; Novas et al. 2005). Interpretation of the Spinosaurus B material as representing one animal is thus against some current thought and, of course, Stromer's original declaration. While the 'neotype' specimen might make a case for Stromer being mistaken, we really need to know more about the collection history to ascertain that. We're left with an intriguing set of measurements hinting at the reduced hindlimbs proposed by Ibrahim et al., but little in the way of objective information to explain their significance. The discovery of new specimens is needed to establish whether some spinosaurids were really short-legged, or if confusion of specimen inventories just made it look that way. In short, and no-doubt to the disdain of people who lose sleep about 'what science has done' to one of their favourite theropods, there's still something to play for with these short-legged spinosaurids.

So that's the latest chapter of research in Spinosaurus, then: I don't doubt that it's going to cause a lot of discussion in popular and academic circles. My personal take-home is that we seem to know less about Spinosaurus than might have been recently suggested, or at least that some issues need to be ironed out before we can develop a clear picture of what Spinosaurus is, and what sort of lifestyle it led. I don't know that any recent proposals about this animal have been shot down entirely yet, although clear gauntlets have been established for some of the more extreme ideas suggested in the last few years. It's going to be very interesting to see how others interpret these latest developments in the ongoing Spinosaurus saga, and where our understanding of this animal moves to next.

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References

• Evers, S. W., Rauhut, O. W. M, Milner, A. C, McFeeters, B, & Allain R. (2015) A reappraisal of the morphology and systematic position of the theropod dinosaur Sigilmassasaurus from the “middle” Cretaceous of Morocco. PeerJ 3:e1323
• Ibrahim, N., Sereno, P. C., Dal Sasso, C., Maganuco, S., Fabbri, M., Martill, D. M., & Zouhri, S., Myhrvold, N. and Iurino, D. A. (2014). Semiaquatic adaptations in a giant predatory dinosaur. Science, 345(6204), 1613-1616.
• Novas, F., Dalla Vecchia, F., & Pais, D. (2005). Theropod pedal unguals from the Late Cretaceous (Cenomanian) of Morocco, Africa. Revista del Museo Argentino de Ciencias Naturales nueva serie, 7(2), 167-175.
• Rauhut, O. W. M. (2003). Special Papers in Palaeontology, The Interrelationships and Evolution of Basal Theropod Dinosaurs (No. 69). Blackwell Publishing.

New takes on the Wealden Supergroup palaeobiota, part 2: Baryonyx, freshwater plesiosaurs, ornithomimosaurs and others

Last week we took a look at some new art of animals from the Wealden Supergroup, the intensively studied, historically important Lower Cretaceous rocks of Southern Britain. We all know the Wealden for celebrity dinosaurs like Iguanodon and Baryonyx, but there's a heap of other interesting animals in there which get relatively little publicity. It's mostly these we're focusing on here, in the second (and final) part of these 'picture of the day'-style posts. 

As before, if you like anything here, remember that you can buy prints of them all from my shop (the Wealden section might be relevant) and its new Facebook outlet. Indeed, if you like my work and are on Facebook, why not 'like' the new Mark Witton Palaeoart page? It's the best place to see when new prints and finished pictures are available.

Baryonyx walkeri: king of the fishers, redux

Baryonyx walkeri, off for a stroll among the crocodyliforms and pterosaurs.

Let's break this post in with a familiar animal: spinosaurid Baryonyx. It's hard to appreciate now how weird this animal seemed back in the 1980s and 1990s. At this point, other spinosaur material was only very poorly known, and laymen and scientists alike found this weird, superficially-crocodile like animal fascinating. Ironically, it's recently turned out that we first collected Wealden spinosaur material centuries ago, but struggled to recognise its significance until more complete remains were unearthed in the 1980s. We now know that Baryonyx can be found throughout a good chunk of upper Wealden stratigraphy and teeth referable to it - or another spinosaurid - are fairly common, at least as Wealden dinosaur fossils go. Baryonyx provided the basic template we'd recognise for all spinosaurid anatomy until last year when, famously, some spinosaurs were proposed to be rather different. It's clear that, whatever is going on with Spinosaurus, Baryonyx retains more conventional hindlimb and pelvic proportions, and may not have been so aquatically adapted as true spinosaurines. In this updated image, B. walkeri is splashing into a body of water while goniopholidid crocodyliforms and gnathosaurine pterosaurs go about their business around it. Note how much larger Baryonyx is compared to the crocs: Baryonyx is the largest theropod in the Wealden Supergroup, by a good margin.

Button-toothed crocs, redux

Bernissartid Koumpiodontosuchus aprosdokiti foraging for molluscs. It's eating a mud snail, Viviparus cariniferus, while tiny (6 mm long) physid gastropods Prophysa crawl over pond scum in the lower left of the image. Dragonflies provide scale, and unnamed tetanurans prowl around the background.

Last year I was lucky enough to provide the first restoration of Kompiodontosuchus aprosdokiti, a small neosuchian crocodyliform common to the Wessex Formation, and perhaps other parts of the Wealden sequence. Koumpiodontosuchus is a bernissartid, a group of small-bodied crocodyliforms with robust, shell-cracking teeth at the back of their jaws. As you'll know if you read my write up last year, these were likely employed in smashing molluscs and insects. The tetanuran theropods in this image are unnamed, but are not thought to be referable to any existing Wealden taxa. We probably need more material of them to consider them nameable, however: recognising that they are different from other Wealden theropods is only half the battle. Modern students of Wealden fossils famously do their best to preserve historic names based on fragmentary bones, but there seems to be an effort to 'future proof' Wealden taxonomy against confusion by only naming well-represented, characteristic animals. I guess I could have chosen one of the better known theropods to play the 'This was the Age of Dinosaurs' card for this PR image, but I think it's good to show that not all large theropods in the Wessex palaeobiota were Neovenator, Baryonyx or Eotyrannus. 

Welcoming the new Wealden ornithomimosaurs

A flock of Wessex Formation ornithomimosaurs forage in a marshland, while istiodactylid pterosaurs skulk about behind them.

Those keeping their ears to the ground will know that the newest arrivals to the Wealden dinosaur palaeobiota are ornithomimosaurs, commonly known as ostrich dinosaurs. Two specimens show that these animals were present in both the Weald and Wessex basins of the broader Wealden succession, and one of these fossils represents a historic taxon named in 1889: Valdoraptor oweni. Key to identifying ostrich dinosaurs in the Wealden was the discovery of abundant ornithomimosaur remains in France, many of which are so reminiscent of Valdoraptor and other Wealden theropod material that they may represent the same taxon. If you want to know more about these and their relationship to the complex story of Wealden theropods, check out Darren Naish's post on this at Tetrapod Zoology.

The above new painting shows a group of (nameless) Wessex Formation ornithomimosaurs in a well-vegetated marshland, in the rainy season, while istiodactylid pterosaurs mosey about in the background. The abundance of ostrich dinosaurs and juveniles in the middle-right are nods to the frequent recovery of abundant specimens of different levels of maturity at many ostrich dinosaur sites, including the new, French 'Angeac ornithomimosaur'. Note that the wings of the running foreround animal are somewhat swept back: I don't think the more common way of reconstructing ornithomimosaurs with 'dangly arms' looks right. They look like they should be holding shopping bags or something.

Valdosaurus in the forest, redux

Two Wealden dryosaurids Valdosaurus canaliculatus, and a stubborn avialan.

Ornithomimosaurs weren't the only fast runners in Wealden landscapes. Dryosaurids, like Valdosaurus canaliculatus were also fleet-footed animals with powerful, well-muscled hindlimbs, and tiny bodies attached to the front. In this reworked image, two of these 3-4 m long animals are taking it slow through a Wealden woodland. Although Wealden climates were quite warm and arid, leaving much of the landscape looking quite chaparral-like, some relatively upland parts seem to have been more vegetated: it's here that this picture is set. In my mind, these animals always walked with the stooping posture of the foreground animal - as noted last time, I like the idea that prehistoric animals had characteristic postures varying slightly from those we consistently restore in skeletal restorations. Note the avialan on the left of the image, which is a nod to the recovery of bird teeth from Wealden deposits. Anyone who's ever been forced to walk around a stubborn reclined mallard will recognise the situation now facing the Valdosaurus.

Barilium dawsomi in leathers, redux

Barilium dawsoni, a large and very robust iguanodont from Sussex. A flock of 'Ashdown maniraptorans' add scale.

Last time we featured Iguanodon bernissartensis: now it's the turn of the 'other' big Wealden iguanodont, the stratigraphically older, and osteologically chunkier Barilium dawsoni. In this redone painting, I've tried to make the Barilium skin more interesting than just plain old scales, covering the back in small, horny ossicles and creasing the flanks as if the skin is particularly thick, leathery and folded. I think we should be rendering more interesting skin regularly in scaly dinosaur palaeoart, as it seems most extensive dinosaur skin remains show unexpected features - strangle scales, wattles, folds and that sort of thing - which small skin patches mostly cannot record adequately. It's interesting to contrast these skin impressions with homogeneous restorations of scaly dinosaur appearance presented by some, where every species is covered in smooth hide following perfect contours of the underlying tissues: I'm not sure that's what fossils are telling us. As before, the 'Ashdown maniraptoran' provides scale to the bulk of Barilium. For the uninitiated, the Ashdown maniraptoran is seriously small for a Mesozoic dinosaur - maybe about 30-50 cm long. If you find big iguanodonts exciting, be sure to check out this previous post.

Polacanthus redux, again

A Wealden tree vies for attention with Polacanthus foxii, and some tiny birds.

OK, I'm cheating a bit with this one. This redone version of a much older painting has been posted fairly recently, but it seemed a bit remiss to skip this ankylosaur in this run down of recently produced Wealden palaeoart. Polacanthus foxii is, of course, the Wealden's sacral-shield-bearing nodosaurid, shown here strolling around a Cretaceous hillock with some birds for company. Having scratched the completist itch, let's move on, because we've seen this all before.

Accidentally sinister Leptocleidus, redux 

Mother and calf Leptocleidus superstes, a freshwater leptocleidid plesiosaur, explore a river inlet in Lower Cretaceous Sussex. 

Our final stop is in Wealden rivers and estuaries, where Leptocleidus superstes and other species of freshwater leptocleidid plesiosaurs roamed. The new version of this image has added a lot of detail on top of the original, which has inadvertently made the mother and calf Leptocleidus look more sinister than intended - hey, it's not my fault their teeth stick out like that. Back in the original post on these animals I mentioned that pliosaurs may also have been present in Wealden lakes and rivers, but note that this is no longer certain: the Hastanectes valdensis remains once provisionally considered pliosauroid have been placed in Leptocleididae in more recent analyses. That does make for a neater story - it means that leptocleidids retain their dominant role as 'near-shore-or-freshwater' animals, but perhaps a slightly less interesting one.

And that's all for now - I hope you've enjoyed this jaunt back to the ancient Wealden and these revised artworks. I'm sure we'll visit the Wealden again in time. Coming next, probably: walking with non-pterodactyloid pterosaurs.

Tyrannosaurus and Triceratops - friends at last?

Tyrannosaurus and Triceratops, not locked in mortal combat. Something must be wrong.  Cretaceous interspecies adoption concept, mimicking similar behaviours seen in modern mammals and birds, by Chidumebi Browne. Prints are available here.

Is there a more iconic palaeontological scene than Tyrannosaurus facing down Triceratops? The artistic association of these taxa has existed since at least 1906 when the very first, highly influential restoration of Tyrannosaurus (by Charles Knight, of course) pictured these animals alongside each other (Glut 2008). This idea flowed into aspects the first dinosaur movies - The Ghost of Slumber Mountain (1918) and The Lost World (1925) (unsurprisingly, given how much these films are indebted to Knight) - and, by 1928, the year Knight completed the famous Field Museum mural of Tyrannosaurus and Triceratops, their adversarial relationship was truly cemented. Book illustrations, TV shows and films have so perpetually shown encounters between these species that it's difficult to think of a new angle on this scene. At least, that's what I thought until being contacted by Chidumebi Browne, who asked me about working up a second Tyrannosaurus picture for him, this time co-starring Triceratops. Instead of combat however, he wondered about likelihood of a juvenile Triceratops being 'adopted' by the tyrant, as some animals make the headlines for doing so today (see below). Clearly I liked the idea enough to carry out the commission (I try to avoid things I feel are too unreasonable), but is this pure speculation, playing on gaps in our knowledge, or is there something credible to this idea? Could Triceratops and Tyrannosaurus, after more than a century of conflict, learn to be friends?

The literature on animal adoption is vast, with something like 270 species of mammal and bird known to adopt juveniles of their own species (via kidnapping, accidental inheritance or other means - Riedman 1982; Avital et al. 1998). Interspecific adoption is far rarer however, and most records pertain to animals housed in zoos or wildlife park. These adoptions can work both ways: juveniles can 'recruit' surrogate parents as readily as parents adopt surrogate offspring (for instance, the bond between Owen, a young hippo, and Mzee, a century-old giant Aldabran tortoise, seems to mostly reflect efforts of the hippo). There is relatively little documentation of interspecies adoption in wild animals, however. The example everyone knows is the Kenyan lioness Kamunyak, who has become something of a sensation for her habit of adopting young oryx. She adopted at least six calves before she was last sighted in 2004, defending them from others - including predators, humans seeking to intervene, and oyrx mothers - as if they were her own cubs. At least one species of monkey, as well as wading, raptorial and passerine birds have also adopted and reared the juveniles of other species (Izar et al. 2006; Literak and Mraz 2011; Oswald et al. 2013). Brood parasitism - the offloading of parental duties to other species - clearly exploits this behaviour (Riedman 1982), and famously occurs in cuckoos, certain ducks and geese, cowbirds, fish and bees.

The significance and evolutionary purpose of these interspecific relationships remains mysterious in many cases. Of course, the internet is awash with suggestions that these species have become 'friends', typically accompanied by heavily-edited video footage showing two different species at their squeeful snugglywugilinest. If they feature predators engaging in joyful play or nurturing behaviour with usual prey species, all the better. According to those sagest of human beings - internet commenters - these examples of natural harmony show us - spiteful, war-making human beings - to be the real animals. Truly, we are awful.

In the real world, the causes of these relationships are considerably less fluffy. The fact that most interspecies adoptions develop in captivity is not surprising, likely resulting from the close quarters contact between individuals and the deficient of conspecifics. Desires for parents, mates or group behaviours in some animals may be so strong in some species that they become blinded to the clear differences between themselves and the only other individuals they know. It's difficult to know whether these examples provide good models for interspecific adoption in natural circumstances.

Pictured: trouble in the neighbourhood.

The rarity of wild cases of interspecies adoption makes it hard to draw any firm conclusions about its adaptive significance, if it even has any (Izar et al. 2006). Although juvenile animals may receive some benefit from being adopted (especially if the alternative is not having parents at all), most biologists consider interspecific adoption a mistake - 'misdirected parenting' from confused adults. For some instances of bird adoption, this might reflect the similar appearance of chicks within certain lineages: adults simply can't tell them apart (Oswald et al. 2013). The circumstances surrounding some 'adoptions' are truly bizarre, where adoptees are ex-prey items which have become surrogate offspring. This has certainly happened with sea eagles where, having brought local buzzard chicks back to their own nest, presumably to eat, they started rearing them instead (Literak and Mraz 2011). It is assumed that the appearance of a raptor chick in their nest overrode any feeding impulses of these eagles, and they successfully reared several buzzards in this fashion (Literak and Mraz 2011). The idea that these parenting 'misfires' reflect recognition errors is supported by at least one instance where Caspian terns, rearing Ring-billed gulls, dropped their degree of parenting as juveniles outgrew resemblance to typical tern offspring (Oswald et al. 2013).

It is less easy to explain adoption across taxonomic and ecological boundaries so wide that even passing resemblance is unlikely. It must be said here that peer reviewed literature on these cases is hard to find, at least in my experience, so much of what is reported online is found in documentaries and news stories - not the most ideal venues for discussing complex, unusual animal behaviour (this is not a sleight against the experts featured in such outlets, just that these things are highly-edited and narrative-hungry, which often leads to embellishment and distortion of facts). As an example of how highly selective these reports can be, some stories of lions 'adopting' prey animals result from 45 minutes of observation, receiving justified scepticism from biologists. 45 minutes of coexistence does not equal a clear case of adoption, especially in species renowned for toying with easily overpowered prey.

Where these cases carry more reliability - such as the widely verified case of Kamunyak and her oryx calves - behavioural factors remain unclear. It seems unlikely that a lioness would visually confuse an oryx calf was her own, except for the possibility that her eyesight was very poor. I see explanations that possible recent, traumatic loss of her (genetic) offspring as premature on the available evidence, most likely spurred on by a desire to project human values into a simplified narrative. The fact that Kamunyak ended up eating the starved carcass of one of her adoptees, and became a serial adoptee suggests her condition might be more complex and deeper-seated than a response to one recent event. Moreover, if cub death is the catalyst for this behaviour, would it not be more common in other lions? As far as I'm aware, cub death is a pretty frequent occurrence. It also strikes me that lots of medical conditions - head trauma, brain tumours, organ malfunction leading to hormone imbalances, even certain diseases - can drastically alter animal behaviour. As far as I'm aware, no assessment of Kamunyak's health was made before she disappeared. I wonder if an illness of some kind is a more parsimonious explanation of Kamunyak's condition than complex, psychological trauma.

Let's bring all this back to Chidumebi's concept: could extinct dinosaurs have engaged in inter-species adoption, especially species as different as Triceratops and Tyrannosaurus? We certainly know that modern animals can establish these weird relationships even between animals as different as large predators and tiny prey. We also know that dinosaurs are capable of inter-species adoption, because modern birds engage in this behaviour. On these analogies, a Tyrannosaurus adopting a Triceratops is not too far fetched. We might assume that their morphological distinctions are so great that the tyrant is not misidentifying the ceratopsid for offspring of its own, and thus must be a 'behaviourally abnormal' tyrannosaur: a Cretaceous Kamunyak, if you like. The background tyrants are meant to be behaviourally 'normal', and have sighted the Triceratops calf - I expect, as is reported for many of Kamunyak's adoptions, that the Triceratops infant would not last long.

So... is this the first picture of an obviously slightly unhinged tyrannosaur?

This exercise is hampered ultimately by a lack of knowledge about the parentage of fossil dinosaurs however, and particularly that of tyrannosaurs. Despite the relative wealth of knowledge on tyrant dinosaur palaeobiology (they are extremely well studied compared to other fossil groups), we still know very little, if anything, about tyrannosaur parental behaviour. Parenting is so varied among reptiles and birds that even phylogenetic brackets are of questionable use here. Strong parental instincts seem like a prerequisite for interspecific adoption, and the evidence is equivocal for such instincts in Tyrannosaurus. Until we know more about this, the likelihood of the scene above remains questionable. Of course, that doesn't mean the image composition is without merit: there are scenarios where predators and baby prey individuals coexist peacefully, such as when adult prey animals have run off and juveniles, being slower, have hidden instead. Indeed, such scenarios likely explain some hastily dubbed predator-prey 'adoptions' reported in the media. At least that provides a partial answer to our question, then: could Tyrannosaurus and baby Triceratops get along? Probably - at least until the former got hungry.

References

• Avital, E., Jablonka, E., & Lachmann, M. (1998). Adopting adoption. Animal Behaviour, 55(6), 1451-1459.
• Glut, D. (2008). Tyrannosaurus rex: a century of celebrity. In: Larson, P. and Carpenter, K. (eds) Tyrannosaurus rex, the tyrant king. Indiana University Press. 398-427
• Izar, P., Verderane, M. P., Visalberghi, E., Ottoni, E. B., Gomes De Oliveira, M., Shirley, J., & Fragaszy, D. (2006). Cross‐genus adoption of a marmoset (Callithrix jacchus) by wild capuchin monkeys (Cebus libidinosus): case report. American Journal of Primatology, 68(7), 692-700.
• Literak I, & Mraz J. (2011). Adoptions of young Common Buzzards in White-tailed Sea Eagle nests. The Wilson Journal of Ornithology 123(1), 174-176.
• Oswald, S. A., Wails, C. N., Morey, B. E., & Arnold, J. M. (2013). Caspian Terns (Hydroprogne caspia) Fledge a Ring-billed Gull (Larus delawarensis) Chick: Successful Waterbird Adoption Across Taxonomic Families. Waterbirds, 36(3), 385-389.
• Riedman, M. L. (1982). The evolution of alloparental care and adoption in mammals and birds. Quarterly Review of Biology, 405-435.

More new-old art: Therizinosaurus, superpigeon, and Polacanthus, walking coffee table

Two Therizinosaurus cheliformis hanging out in Late Cretaceous Mongolia. The guy on the left thinks he's all that: she doesn't. Prints are available from my online store.

Time for more new takes on old pictures. First up, above, is a reworking of my 2013 image of two Therizinosaurus cheloniformis, giant therizinosaurids from Maastrichtian deposits of Mongolia. Before we knew just how bizarre Deinocheirus was, these pot-bellied, small-headed and scythe-clawed animals held the title of least expected anatomy in a non-avian theropod. The metre-long claws on their hands suggest they were dangerous, ferocious animals, and they are often restored with long arms and claws ready to lash out at passers by. I don't doubt that being clobbered by a Therizinosaurus would be an experience best avoided, but, being herbivores, they probably spent far more of their time eating and digesting that they did swatting other animals. For me, Therizinosaurus was figuratively 'de-clawed' for good in John Conway's restoration of them as squatting, shaggy 'feather mountains' harvesting leaves from trees. Since then, restorations of keen-eyed, 'scythe weilding' therizinosaurs have seen especially silly, even among other 'slasher pose' artwork.

My own restoration of these animals sides with the idea of Therizinosaurus being a large herbivore largely disinterested in the world around it. A clear source of reference for this painting were pigeons, specially the wood pigeon Columba palumbus. I find the proportions of these birds - tubby bodies, small feet, small heads - reminiscent of the anatomy of large therizinosaurs, and I thought it might be fun to mix the two together. The male animal on the left of the image is engaged in pigeon-like display behaviour, strutting around with a cocked head, inflated chest and making noises best described as 'übercoos'. The female, right, like most female pigeons presented with courting, couldn't be less interested (although, to be honest, it's hard to tell what pigeons find interesting: they always seem a bit confused to me. They're like avian Dougal McGuires).

Much as I normally try to avoid painting ancient animals in the clothes of modern species, I quite like the spin the pigeon-appearance puts on these animals. All too often Mesozoic dinosaurs are considered embodiments of savage natural selection and intense, often violent competition. There are few modern animals with characters further from this concept than pigeons, which succeed despite their apparent tendencies for confusion, pratfallery, and seemingly simple behaviour*. Transferring these qualities to the Mesozoic seems to put a different spin on ancient dinosaur lifestyles ecology.

*I say this with fondness: I find watching pigeons really interesting. I'm sure they're a lot more sophisticated than they often appear.

Wealden ankylosaur Polacanthus foxii and tiny feathered friends. Prints are available from my store.

Next up is another reworked 2013 piece, the large ankylosaur Polacanthus foxii on a Wealden hillock, with some speculative avians hitchikers. I was lucky enough to have a quick glimpse at some new Polacanthus material being worked on at the University of Southampton a few years back, including lots of limb and hip elements. The size of the specimens was really impressive (an impression helped, I guess, by the fact I'm used to working on much smaller, more gracile pterosaur bones) and it definitely seems that, like other ankylosaurs, Polacanthus was a 'walking coffee table': a low slung creature with a flattish back. The broad sacral shield of was probably an excellent place to put drinks, and experts have recently predicted that Polacanthus had very strict 'use a coaster' policy.

There are two species of birds show here: a flock of small, grey forms leaving the tree, and a suite of smaller brown birds hanging out on the Polacanthus itself. These animals are speculative additions to this Wealden scene as, while possible avialan teeth have from one Wealden formation (the Wessex) have been mentioned, I don't think they've been described or analysed in detail just yet. However, a diverse suite of small birds have been found in Lower Cretaceous deposits elsewhere in the world (including Wealden-equivalent deposits of Spain, and famously in China), so it's not a huge stretch to embellish a painting with such animals.

Torvosaurus tanneri and the progressiveness of Knight and Burian

Mother Torvosaurus tanneri, reclining in Late Jurassic North America, wondering when her life became all about the kids. See the original version of this painting here, and check out my store to buy a print.

Regular readers will know that I've been overhauling some of my favourite bits of artwork recently. It's a process I recommend to any digital artist attempting to better themselves. Rather than starting from scratch, modifying older work provides a foundation to critique and expand on, as well as revealing the the results of new techniques or styles relatively quickly. I've found it not only helps generate get old bits of work to higher standards, but that it helps produce stronger work more rapidly when starting fresh images.

My latest revisions are to an image of a nesting Torvosaurus tanneri, first published in 2013 atop my post on daleks, xenomorphs and palaeoart. The initial inspiration for this piece was the then-recent discovery of Torvosaurus eggs and embryos in Portugal (Araújo et al. 2013), and the misfiring palaeoart accompanying publication of the discovery (Jurassic Park Velociraptors stood in for Torvosaurus, which - even though the art was well produced - still constitutes a major palaeoart fail). In 2013, and moreso in this 2015 revamp, I attempted to render the nest-guarding Torvosaurus as obviously scaly and 'reptilian'. There are lots of spikes, folds, bumpy textures and sags of skin - sort of like some modern monitors and iguanas. This is a deliberate nod to both the fact that not all theropods would have looked like overgrown birds, and that some dinosaurs were indeed scaly, but also to the work of classic palaeoartists: Zdenek Burian and Charles Knight. Both, of course, worked under the impression that dinosaurs were fully-reptilian animals (as opposed to stem birds combining classically 'avian' and 'reptilian' characteristics) and it's clear that modern reptiles were primary references for their work, maybe even moreso than the underlying skeletons! Their dinosaurs are frequently adorned with all manner of wattles, dewlaps, frills, skin folds, and elaborate scales, and make for striking, memorable takes on many extinct species. I think their highly detailed dinosaur integuments were a big part of their success as palaeoartists.  As much as we look at their work as scientifically dated now, Knight and Brian really knew how to make their subjects look like real animals of unique, interesting and characteristic appearance.

In revisiting some Knight and Burian work recently, it struck me that their depictions of dinosaur skin were actually quite progressive. Pre-Paulian palaeoartists are often viewed as presenting inaccurate, over-conservative depictions of extinct animals. That observation is not entirely without merit, but at least the integuments of these 20th century depictions show this work was not devoid of elaborations and speculations on extinct life. Some of their portrayals of dinosaurs include heavy armour, elaborate frills and spines, as well as smooth or wrinkled skin without any indication these structures existed - Knight's 'Agathaumus' or Burian's Chasmosaurus are classic examples of such reconstructions. The skin is so striking that it is just as memorable and interesting as the animal itself and, if such animals existed today, their skin would be a talking point or namesake. We can only assume that Knight and Burian based these integuments on those of modern animals while also avoiding contradicting fossil data about the life appearance of these animals known to them or their advisers. It's difficult not to view this as reasoned speculation within the data limits of their respective eras and, in this respect, these outlandish integuments might represent early embodiment of the speculative, progressive attitudes now lauded in modern palaeoart and All Yesterdays. 

Indeed, there's a discussion to be had about whether later 20th century Paulian palaeoart, which might be summarised as using quite literal interpretations of fossil data, was a step backwards in this regard. As much as Paulian art promoted a much-needed emphasis on fossil data and meticulous reconstruction methodologies, and produced some classic art in it's own right, its over-reliance on the fossil record is a known problem. The fossil record is not only full of gaps, but also presents a very selective, distorted view of even well-known species. Perhaps this is why some pre-Paulian artworks still look, for all their scientific flaws, like renderings of real animals, whereas some Paulian-era pieces look less convincing, even when the artworks are excellent themselves. Again, I find myself returning to well-trodden thoughts about the fossil record not capturing everything an artist needs to portray extinct animals with the same conviction as modern species. If that's true for us now, it was even truer for Knight and Burian, who were working with a far less complete picture of extinct life than we currently enjoy. Perhaps they deserve praise for not only being excellent artists and influential figures within palaeoart, but also for the ways they speculated and experimented - even if only a little - to make their restorations as compelling as they are.

Wrinkly old Torvosaurus 2015, in detail. 

As is par for the course now, prints of the Torvosaurus painting can be bought from my store along with a bunch of other recent work. If you enjoy seeing my work and articles online, buying prints is a great way to ensure more content follows!

Reference

• Araújo, R., Castanhinha, R., Martins, R. M., Mateus, O., Hendrickx, C., Beckmann, F., Schnell, N, & Alves, L. C. (2013). Filling the gaps of dinosaur eggshell phylogeny: Late Jurassic theropod clutch with embryos from Portugal. Scientific reports, 3.

Does Deinonychus really have one of the most powerful bites of all dinosaurs?

Quick sketch of Deinonychus antirrhopus with expanded, bone-puncturing jaw muscles, a requirement of having a bite as strong as a modern alligator. Say what? Read on...

There's a part in Michael Crichton's Jurassic Park novel where Velociraptor attempt to bite through bars to reach a people-shaped lunch. Presumably, they're meant to give readers something to rally behind seeing as one person in the line of fire is Ian Sodding Malcolm - I'd be chewing through steel too if it meant we could enjoy a few moments without another preachy monologue. Crichton describes them as hyena-like in their ability to bite through steel, delivering thousands of pounds of pressure per square inch and gnawing their way through thick metal bars in 15 minutes.

Dromaeosaurids biting through steel bars - heck, any animal biting through steel bars, including hyenas - intuitively sounds like crazy talk*. But was Crichton at least right about the strong bites of dromaeosaurids? I've been doing some investigating on dromaeosaur jaw muscles for a new palaeoart commission, but I've come unstuck. Here's why.

*Is there any substance to claims about modern animals biting through steel? Given that tooth enamel is only very slightly harder than straight steel, I wonder how long teeth would last when gnawing through anything but the thinnest metal sheet.

Recently, Gignac et al. (2010) presented a suite of bite marks on Tenontosaurus bones argued to show Deinonychus as capable of deeply puncturing bone with powerful bites. The tooth gouges match those of large Deinonychus in many aspects (bite mark size, shape, correspondence with dental arcade) and broken teeth associated with the same Tenontosaurus corroborate suggestions that Deinonychus fed from the carcass. Other teeth, not from Deinonychus, were also at the site, but their owner does not seem to have left any other obvious traces. Experiments with modern cow bones suggest Deinonychus needed a whopping 8200 N to puncture Tenontosaurus bones to the degree seen in the fossil remains. This value puts Deinonychus bites on par with those of adult alligators and leaves hyenas in the biomechanical dust. It also grants Deinonychus one of the highest estimated bite forces of any dinosaur, even greater than animals of much larger size. The tooth marks only match the largest known Deinonychus individuals, possibly indicating that juveniles were incapable of delivering such bite forces. Because Deinonychus puncture wounds are rare, Gignac et al. argue that puncturing bones was not common in Deinonychus, and that their powerful bites were primarily used for aggressive behaviours instead.

Bitemarks in the radius of Tenontosaurus specimen FMNH PR 2261, below, compared to the dental arcade of Deinonychus antirrhopus, above. This is one of many pathologies on FMNH PR 2261, almost all of which have been attributed to Deinonychus feeding behaviour. From Gignac et al. 2010.

For artists, Gignac et al.'s paper has important implications. Generating 8000 N of bite force requires a lot of muscle, so we might predict that Deinonychus jaws had the same swollen jaw muscles of modern crocodiles to generate all those bone-smashing newtons. This is at odds with other reconstructions of Deinonychus, where the jaw muscles do not atypically alter the contours of the face. I don't know how visible expanded, crocodile-like jaw muscles would be on deeply feathered maniraptorans, but reconstructions with sparse or naked faces would certainly need to take this on board. I've had a quick play about with this concept in the conservatively feathered Deinonychus above.

Problem is, Gignac et al.'s conclusions are not uncontested. Biomechanical assessments of Deinonychus jaws have found they were mechanically weak and ill-suited to delivering powerful bites (Therrien et al. 2005; Sakamoto 2010; Fowler et al. 2011). Therrien et al. (2005) estimated Deinonychus bite force at a relatively wimpy 15.7% of alligator jaw power, which Gignac et al. translate into 1450 N. This isn't unimpressive - as strong as that of a 30 kg wolf - but a far cry from an alligator-like bite, and certainly deflates our reconstructed jaw muscles to their traditional size. On the face of it, I certainly find the arguments for weak jaws more convincing. Hyenas and alligators have robust, wide and solidly-built skulls with generous room for jaw muscle placement, whereas the skull of Deinonychus is full of holes, is relatively narrow and slender, and with comparatively little room spaces jaw for muscles.

So, what to do? Jaws with relatively small muscles have been the norm in Deinonychus palaeoart since its discovery, but is it time we changed that? Were their jaws actually visibly and powerfully muscled as inferred by their trace feeding evidence, or is there something missing here? Is it significant that lower estimates of their bite forces match those of animals which can also puncture bone (wolves - see Haynes 1982)? If anyone has anything to add, please let me know...

References

• Fowler, D. W., Freedman, E. A., Scannella, J. B., & Kambic, R. E. (2011). The predatory ecology of Deinonychus and the origin of flapping in birds. PLoS One, 6(12), e28964.
• Gignac, P. M., Makovicky, P. J., Erickson, G. M., & Walsh, R. P. (2010). A description of Deinonychus antirrhopus bite marks and estimates of bite force using tooth indentation simulations. Journal of Vertebrate Paleontology, 30(4), 1169-1177.
• Haynes, G. (1982). Utilization and skeletal disturbances of North American prey carcasses. Arctic, 266-281.
• Sakamoto, M. (2010). Jaw biomechanics and the evolution of biting performance in theropod dinosaurs. Proceedings of the Royal Society B: Biological Sciences, 277(1698), 3327-3333.
• Therrien, F., Henderson, D. M., & Ruff, C. B. (2005). Bite me: biomechanical models of theropod mandibles and implications for feeding behavior. The carnivorous dinosaurs, 179-237.