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Wednesday, 25 March 2015

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.

Sunday, 22 March 2015

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.

Thursday, 19 March 2015

Short-necked azhdarchid pterosaurs - say what?

LPV (FGGUB) R.2395, our unnamed short-necked azhdarchid from Maastrichtian deposits of the Hațeg basin. Prints of this chap are available.

Odds are that most regular readers of this blog are familiar with azhdarchid pterosaurs, the toothless, often gigantic flying reptiles which increasingly dominated pterosaur evolution in the Cretaceous. With a better fossil record than most pterosaur lineages, they are among the best understood and most researched of all flying reptiles. In recent years our understanding of their anatomy, distribution and palaeobiology has advanced considerably.

Since azhdarchids were recognised as a group in the 1980s it has been realised that their most striking and characteristic features pertain to their neck anatomy. In both relative and absolute terms they have the longest necks of any pterosaurs, stretching their mid-series cervical vertebrae to long tubes with reduced features. Cervicals IV - VI are especially long and tubular, with the mid-portions of the neural spines reduced to such a degree that they are effectively split into anterior and posterior sections. The only significantly developed features of these cervicals are bulbous zygopophyses and condyles, which nestle together so snugly that neck articulation seems limited. Regular readers will know that this has considerable bearing on the likely habits of these animals, probably precluding strenuous lifestyles such as skim-feeding or pelican-like scooping. The extremes of their neck bones - cervicals I - III, and the somewhat 'dorsalised' VIII - IX - are less modified, although some azhdarchid weirdness infects these too in terms of length, neural spine shape, or both.

With azhdarchid cervicals being so diagnostic, they can be identified when found in isolation and even when only poorly preserved. Indeed, many azhdarchid occurrences are represented by isolated cervicals - they compete with jaw tips for the most common type of azhdarchid fossil. In recent years, the complete neck osteology of the Santonian, central Asian azhdarchid Azhdarcho lancicollis has been documented in some detail (Averianov 2010), permitting some insight into which specific part of the neck sequence isolated neck bones represent. It can be a little tough to tell a cervical IV and V apart - they seem very similar, except that V is invariably the longer of the two (indeed, the longest of the entire neck) - but we can now at least tentatively identify bones from the rest of the sequence. This is a major breakthrough, meaning that isolated cervicals can tell us a lot more than just where an azhdarchid was preserved: their potential for taxonomic and biomechanical studies has been increased considerably.

Eyes to Romania

A lot of new azhdarchid material, including said isolated cervicals, has recently been emerging from various Maastrichtian deposits of Romania. These sediments represent the rivers and lakes which once ran through Hațeg island, an ancient setting famous for its dwarf dinosaurs and the enormous azhdarchid Hatzegopteryx thambema. The Hațeg pterosaurs, and their neighbours from Transylvania, have been the focus of a number of recent pterosaur papers and, this week, a team of researchers (including Mátyás Vremir, myself, Darren Naish, Gareth Dyke, Stephen Brusatte, Mark Norell, and Radu Totoianu) published another in American Museum Novitates (Vremir et al. 2015). It reports the discovery of just one bone* - the near-complete azhdarchid cervical LPV (FGGUB) R.2395, from Hațeg Basin red beds - but it's enough to cast new light on these otherwise familiar azhdarchid fossils, as well as the general evolution of azhdarchids themselves.

*So yes, the picture at the top is 1% fossil data, 99% palaeoart polyfiller.


Line drawing of LPV (FGGUB) R.2395, isolated azhdarchid cervical IV or V. It don't look like much, but it's got it where it counts. From Vremir et al. 2015.
R.2395 (above) is not a large vertebra, being an estimated 100 mm long and 44 mm across the prezygapophyses when complete (it's missing the posterior portion, including most of the condyle and postzygagpophyses, as well as the left prezygapophysis). Our paper provides a long discussion about the likely portion of the neck represented by R.2395, concluding that it is probably a cervical IV or V. In azhdarchids, these vertebrae are among the longest of all, sometimes being eight times longer than wide. R.2395 was clearly a lot stouter than this however, barely being twice longer than broad. This proportion is unique among azhdarchid CIV and Vs, and there was some discussion among our team as to whether or not this was sufficient to erect a new taxon. In the end we decided the material was too scant to support a name of its own, but it is almost certainly a new species.

The width of R.2395 suggests the neck owner was not a tiny animal. It's difficult to get a size estimate from a single neck bone, especially with cervical length varying so much taxonomically across Pterosauria, as well as ontogenetically. However, vertebral width is a little more stable with respect to overall body size, and that of R.2395 indicates an animal on the small size for an azhdarchid - an arm-wavy wingspan estimate of 3 m seems about right. When we plugged the length of R.2395 into a database of near-complete azhdarchid necks, we found the estimated CIII - CVIII length was a paltry 352–419 mm (the range depends on whether it represents a CIV or CV): 23-41% shorter than the estimated neck length of the similarly-sized Transylvanian azhdarchid Eurazhdarcho, langendorfensis and notably shorter than neck of the smaller (2.5 m wingspan) Chinese azhdarchid Zhejiangopterus linhaiensis  (measured neck length 502 mm). It seems R.2395 did indeed have a short, robust neck for an azhdarchid of its size.

The possibility that R.2395 represents a short-necked juvenile of a long-necked species was something we looked into. After all, pterosaur necks seem to increase in length disproportionately to body size, and a 3 m wingspan would leave a lot of growing room for several azhdarchid species. However, the bone texture of R.2395 is characteristically 'polished' and avascular where well preserved, which has been suggested for some pterosaurs as an indicator of skeletal maturity. This observation is bolstered by the sharply ossified anatomy of R.2395: young pterosaur skeleltons tend to have rounded, poorly defined features, but our vertebra shows a surprising amount of sharply-defined detail in its superficially simple form. We don't know how old R.2395 was when it died, but it did seem to have a very well-ossified skeleton: it was likely at, or very near to, full size, and further neck growth seems unlikely. 

What does it mean to find short necks in a clade thought to be defined by long necks? We have no idea how this plugs into azhdarchid evolution, although the retention of all azhdarchid cervical features apart from the enhanced length is of interest there. We might also conclude that suggestions azhdarchids were all anatomically similar (e.g. Witton and Naish 2008) are questionable. There are doubtless some functional and palaeoecological implications of this discovery as well - we speculate that neck mechanics and strength likely differed between long- and short-necked azhdarchids - but further remains are clearly needed to say anything substantial about specific functionality. And... in truth, I'm biting my tongue here: there's tons to say about this, but I don't want to scoop other papers which are in prep and review. Both myself and Darren Naish have been hinting at some of this short-necked azhdarchid stuff for a while now, and heavily implying that we have things to say about Haztegopteryx as well as this much smaller animal. Some readers may, therefore, be wondering why there's no discussion of giant pterosaurs here. We were both hoping that this would be out by now as well, but it turns out that this parallel-running project has been published first - that's just how these things work out sometimes! Further details on these finds is coming, with other publications in states of progress which will add to this picture. Watch this space, in other words.

To end on a less cagey note, it is worth briefly mentioning why the seemingly maximum size of R.2395 is rather interesting. It is often said that small pterosaurs are absent from the upper Cretaceous, a fact sometimes controversially attributed to competition with birds. If R.2395 really is an adult, it joins Eurazhdarcho and the 2.5 m wingspan Montanazhdarcho in suggesting that smaller pterosaurs were not absent, and perhaps even not uncommon, in the latest Cretaceous. Granted, these species are not as small as some pre-Cretaceous pterosaurs, but they are certainly size-consistent with taxa found in Lower Cretaceous Lagerstätten of China and Brazil. I do wonder if the lack of sites of exceptional preservation in the Late Cretaceous has resulted in under-sampling of smaller pterosaur species in Late Cretaceous rocks, and that drawing conclusions about the Cretaceous decline of diminutive pterosaurs, and associated competition with birds, is premature. An elephant in the room here is the scarcity of small, Late Cretaceous juvenile pterosaurs: we know they had to exist, and yet they are exceptionally rare fossils. There is clearly a preservation bias against these small individuals - can we rule out that the same bias was not acting against small adults, too? That might be nonsense, but I do wonder if  we sometimes take the - knowingly poor - fossil record of pterosaurs a bit too literally.

A quick plug for a good cause

Finally, some readers will know that I like to bang drums about Supporting Original Palaeoart, and that it's often independent artists who're providing some of the more interesting and creative palaeoart projects out there. One of these comes from David and Jennie Orr (David is perhaps best known around these parts for founding Love in the Time of Chasmosaurs, as well as a his unique, stylish artwork), who have launched an Indiegogo campaign to fund their book Mammoth is Mopey. It's a wonderfully illustrated book for younger readers showing a different prehistoric animal for each letter of the alphabet. The animals in question aren't the same tried-and-tested taxa we see in every kids book however: they're the likes of Brontomerus, Jeholopterus, Gorgonops and so on, and each is wonderfully illustrated in David's Bézier-curve-loving style. It looks great, and I've already pledged enough for two copies: one for my nephew, and another for me (hey, you're never too old to have an alphabet refresher, right?). An example image from the book is below - I can't wait to see the rest.

Artistic Ankylosaurus is artistic. From Mammoth is Mopey, which you can support here. Illustration by David Orr.

References

  • Averianov, A. O. (2010). The osteology of Azhdarcho lancicollis Nessov, 1984 (Pterosauria, Azhdarchidae) from the late Cretaceous of Uzbekistan. Proceedings of the Zoological Institute RAS, 314(3), 264-317.
  • Witton, M. P., & Naish, D. (2008). A reappraisal of azhdarchid pterosaur functional morphology and paleoecology. PLoS One, 3(5), e2271.
  • Vremir, M., Witton, M., Naish, D., Dyke, G., Brusatte, S. L., Norell, M. & Totoianu, R. 2015. A medium-sized robust-necked azhdarchid pterosaur (Pterodactyloidea: Azhdarchidae) from the Maastrichtian of Pui (Haţeg Basin, Transylvania, Romania). American Museum Novitates 3827, 1-16. 

Monday, 9 March 2015

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.

Saturday, 7 March 2015

How Ornithocheirus simus and other pterosaurs took to the air... from water?

Aquatically-adapted ornithocheiroid Ornithocheirus simus takes off using aquatic quad launch, as hypothesised by Habib and Cunningham (2010). Prints of this painting - which might be the first illustration of this launch strategy - are available from my shop.

Many pterosaur lineages seem to have close ties with marine environments, as evidenced by biases in their fossil and taphonomic records and indications of frequent interactions with marine fish. It stands to reason that these animals would find themselves in water on occasion, and trackways made by swimming pterosaurs indicate they may have been quite at home in this medium. Recent studies by Dave Hone and Donald Henderson have cast doubt on the swimming ability of pterosaurs because their floating postures seem rather awkward, which they suggest might have impeded breathing while swimming (Hone and Henderson 2014). Their studies found that, rather than sitting atop the water with arcing necks like birds, front-heavy pterosaur bodies collapse the head and necks into the water, bringing the mouth and nostrils close to the water surface. Although initially sceptical of this idea, I must admit to at least agreeing that avian-like postures may be difficult for pterosaurs. Our expectation that they floated in a bird-like fashion - which I've illustrated several times (Witton 2013 and elsewhere) - is actually quite silly given their proportions and differences with bird morphology. Pterosaurs lack the well-muscled hindlimbs which depress the back end of bird bodies into water, as well as the flexible necks and small heads required to attain duck or gull like floating postures. Indeed, birds seem unique in their floating posture, whereas pterosaurs seem to have floated in a manner more typical of other animals. Does the proximity of their nostrils or mouths to the water surface impede their swimming ability? Maybe not, given that virtually all non-avian animals I can think of  - including aquatic species like otters, crocodylians, swimming rodents, etc. - float and swim with their nostrils close to the water. As long as they have enough control over their swimming ability to clear their nostrils for respiration, they were probably fine. I see no clear reason to think pterosaurs were less competent in water than other animals, and maintain the view that some - for functional reasons - probably needed to swim to obtain the pelagic prey they did/likely did consume (Witton 2013).

But what did pterosaurs do when they needed to leave the water? Could they fly from the water surface or did they have to seek land to take off from? Anyone who knows anything about current pterosaur research knows that the leading hypothesis on pterosaur takeoff is quadrupedal launching, where the hindlimbs mostly serve to provide forward momentum, and vertical heft was provided by the forelimbs (Habib 2008) - many species of bats including vampires molossids and some mystacinids use a similar mechanism. It's worth stressing that this idea is not only supported by anatomical characteristics and positive results from biomechanical studies, but also by the fact that the hindlimbs were too weak to launch sensibly-massed pterosaurs into the air. All studies favouring bipedal launch have had to circumvent this somehow, typically by under-estimating pterosaur masses by, probably, as much as 60%. This makes bipedal launch a real no-go, whereas quad-launch has, to my knowledge, has meet all tests and predictions. We typically discuss quad-launch in terrestrial contexts, but can it work on water?

Schematic of water-hopping quad-launch strategy, from Witton 2013. The floating posture in panel 1 might be incorrect, but the general thrust of the image is OK.

It turns out, probably yes. According to work by Habib and Cunningham (2010), a version of quad-launch works just fine in aquatic settings. It seems that many folks have difficulty imagining how this works, but it's really not too dissimilar to terrestrial quad-launching. As with any takeoff mechanism, the the trick to water-launching is a leap providing sufficient height and speed to facilitate wing use (flapping alone doesn't really get you anywhere, and is especially ineffective at larger sizes). In this respect, it is just like terrestrial launch. An added complication of water launch is escaping surface tension, the cohesive force operating at air-water interfaces. This is where differences between terrestrial and aquatic launch become apparent, because it seems most pterosaurs were incapable of overcoming surface tension from a 'standing' (er... stationary floating) start. Their half-submerged posture and the fluid nature of the medium they are pushing against likely prohibited generation of sufficient energy for a standing launch. The solution to this is a series of hops across the water surface (above), each one providing further water clearance and velocity than the last. These were achieved, as on land, by the combined efforts of both the legs and arms. The wings are not fully deployed at this point, although the arm motion is probably showing some similarities to a flight stroke. The early stage of this takeoff might  look a little like swimming with a particularly powerful butterfly-stroke, albeit one where the swimmer is emphasising vertical motion rather than horizontal. Eventually, the pterosaur is leaping across - not through - the water and is clear enough to push off fully from the water surface. For this final push, the wing is opened and flapping can start. It seems that some pterosaurs - principally ornithocheiroids - were very well adapted for these manoeuvres, showing the shoulder reinforcement, upper-arm strength and distal-limb adaptations you'd predict for water-hopping quad launchers (Habib and Cunningham 2010, Witton 2013).

Some especially powerful pterosaurs, however, probably didn't need to worry about water hops. Giant azhdarchids, which experts predict were not only fuelled by muscle, but raw awesomeness sucked out of the universe itself, were probably powerful enough to water launch without hopping (Habib and Cunningham 2010). Some also ducks have sufficient power to do this - check out the launches in this video for cracking, slow-mo examples (the second is best, at 20 seconds in. Hat tip to Mike Habib for the link).


Recently, palaeoblogosphere regular Mike Traynor commissioned me to paint pterosaur water quad-launch - I think for the first time (if anyone knows different, please let me know). The results, a 6 m wingspan Ornithocheirus simus at the apex of the launch cycle, are above and, for fun, shown in progress from my Twitter feed below. If you'd like to own a copy of this image, you can: point your internet mobile at this page.





We're not done with aquatically-adapted animals just yet. Coming soon: the surprising aquatic adaptations of our own Mesozoic relatives.

References

  • Habib, M. B. (2008). Comparative evidence for quadrupedal launch in pterosaurs. Zitteliana, B28, 159-166.
  • Habib, M., & Cunningham, J., (2010). Capacity for water launch in Anhanguera and
  • Quetzalcoatlus. Acta Geosci. Sin. 31, 24–25.
  • Hone, D. W., & Henderson, D. M. (2014). The posture of floating pterosaurs: Ecological implications for inhabiting marine and freshwater habitats. Palaeogeography, Palaeoclimatology, Palaeoecology, 394, 89-98.
  • Witton, M. P. (2013). Pterosaurs: natural history, evolution, anatomy. Princeton University Press.

Friday, 20 February 2015

Deinonychus, Parasaurolophus, Dreadnoughtus and Carnotaurus welcome in the MarkWitton.com print store

Since launching a limited print buying service at the close of last year I've had enough interest to warrant investing more resources into print sales. The result is an online print store over at the new slightly revamped MarkWitton.com where you can buy prints at a range of sizes and prices with just a few mouse clicks. Payment goes through Paypal, and delivery should be within a week or so for UK customers, and 2-3 weeks for international orders. There's a catalogue of recent artworks to choose from, which I'll expand over time, but I'm also happy to take orders for artwork not hosted there yet. If you would like a print of an older, unhosted piece, let me know.

To celebrate the launch of the store, I thought it would be cool to show four of my favourite new pieces of art generated within the last few months. These all represent private commissions which I have permission to post and sell as prints. If you want your own copy, you know where to go...

Dreadnoughtus dwarfs Talenkauen, is happy

"Oh, you say you're a medium-sized dinosaur? Sorry, it's hard to hear you with my head all the way above the trees here." Experts predict Dreadnoughtus schrani was jerk it was to other, smaller species like the iguanodont Talenkauen santacruensis. Print.

First up is Chris Wummer's commission of giant, latest Cretaceous titanosaur Dreadnoughtus schrani, an animal which needs little introduction after the publicity of its discovery last year. Dreadnoughtus was publicised as the most massive terrestrial animal of all time at 59 tonnes, but regular readers of the palaeoblogosphere may know that sauropod guru Matt Wedel questioned this over at SVPOW! through rough volumetric estimates of mass and, later, when considering the restored Dreadnoughtus trunk as too long. Palaeoartist Greg Paul has also provided contrary comment on the 59 tonne estimates and restored proportions (although I'm not really sure what context that article is presented in - it looks like an unpublished MS). Estimating the mass of any extinct animal is difficult and especially so at the extreme sizes represented by giant titanosaurs, but there seems good reason to think the Dreadnoughtus holotype individual achieved a mass of 30-40 tonnes. That's still very big of course, but within fairly 'typical' ranges for giant titanosaurs.

There are two versions of the Dreadnoughtus image shown here. Chris wanted the picture to have personal relevance and so asked for his house to be included. That choice was inspired by his residence in Philadelphia, the city were Dreadnoughtus was studied and unveiled to the world. Switching between the version with familiar modern objects and a completely 'natural' scene reinforced how difficult it is to show absolute prehistoric animal size without a frame of reference: Dreadnoughtus looks a lot smaller when its head isn't clearing a rooftop. Two ornithopods - the 4 m long iguanodont Talenkauen santacrucensis - were added to this version to help stress the size of the sauropod. It's still difficult to appreciate a precise size of the sauropod in this image, but hopefully it at least looks very big, which might be the best we can hope for in images without obvious scale references.

Deinonychus pair in the swamps

Two Deinonychus antirrhopus either taking a moment to drink, or looking at something really interesting at the bottom of that pool. Print.

Next up is Patrick Murphy's pair of Deinonychus antirrhopus. The Early Cretaceous dromaeosaur Deinonychus has been restored so many times that it's difficult to come at it from a fresh angle. I thought one way to do that was to not show it on open plains, but in a backswamp. Deinonychus is known from two geological units, the Cloverly and Antlers formations, both of which represent sediments deposited by ancient, subtropical rivers and their floods. Some sediments in the Antlers Formation represent large (10 m wide or more) abandoned river channels, complete with evidence of soils, low velocity or still water, and ancient vegetation (Hobday et al. 1981). The depicted animals are meant to have recently eaten something - their muzzles are still read with blood - and popped down to their local swamp for a drink and some shade. I imagine that these guys are set to sit down and digest after this, waiting until they get hungry enough to chase prey again.

The arms of the foreground animal are pressed tight to the body in the manner proposed by palaeoartistic Queen of the maniraptorans, Emily Willoughby, rather than held half-folded as we're more used to seeing them. As Emily explains, there is good reason to think the 'arms out' postures we're used to is nonsensical - animals just don't carry themselves like that (including ourselves: our arms don't just hang limp - we fold, stow and hold them when they're not in use).

These guys were a lot of fun to paint: Deinonychus has an appealing character - a sort of mash up of a wolf and a raptorial bird - which is fun to try to capture. My thought is that Deinonychus should always look like an animal which we would admire and revere, but would purposely avoid close proximity with.

Parasaurolophus, alone with other dinosaurs

Parasaurolophus walkeri, wondering where his friends are. Print.
Delano DuGarm's Parasaurolophus walkeri brings us back to the Late Cretaceous, specifically the Campanian. Delano's brief was for a fairly minimalist scene, which I think matches one part of the 'Campanian story' quite well. By this time some of the fauna and flora we think of as epitomising the Mesozoic were already gone or showing clear evidence of decline, including ichthyosaurs, some dinosaurs, pterosaurs and ammonites. Although some taxa were doing fine in this interval, and even radiating, seeds of change were already being sown for Cretaceous biospheres. We have to wonder how long many 'classic' Mesozoic groups would have lasted even without the global catastrophes occurring at 66 million years ago: even without them, the post-Mesozoic world might have been quite different.

Delano's lone Parasaurolophus painting gave a good opportunity to hint at this changing world. The left of the painting features a few (speculative) wading birds and two bird flocks leaving the trees - these, of course, are the 'new dinosaurs' that will live on through the late Cretaceous troubles. The Parasaurolophus on the right looks a bit big and cumbersome by contrast, sort of like an old design which can't compete with new technologies. Aiding this comparison is the relative chunkiness of the Parasaurolophus skeleton: hadrosaurs are hardly a svelte bunch, but the bones of Parasaurolophus are especially big and robust, with expanded areas for muscle attachment. As far as I'm aware, the significance of this is unknown (but let me know otherwise in a comment below!).

Carnotaurus with a difference

Azhdarchids > theropods, as demonstrated by this lousy predation attempt by Carnotaurus sasteri. Print.

Finally, we're popping back to Maastrichtian South America for Chris Tait's Carnotaurus sasteri vs. azhdarchids image. An obvious artistic departure from the rest, this is an attempt to achieve a comic-book style in line with Chris' intention to give this to his son as a present. I've tampered with minimalist, comic-book styles before and quite enjoy it. Comic-book palaeoart - especially Ricardo Delgado's Age of Reptiles graphic novels - has influenced my work since the age of nine because of the energy, character and personality infused into the animals. Of course, you have to try hard not to find character in animals like Carnotaurus which, with its strange proportions and anatomy, looks almost like work of comic book fiction already (must... resist comment... about fictional theropod design and Jurassic World...). Carnotaurus, like other abelisaurs, was adapted for speed more than manoeuvrability, and this attempt to grab a passing pterosaur snack is an example of how nimble, agile prey might easily evade one. The pterosaurs shown here are quite small, which might seem odd for very late Cretaceous azhdarchids - aren't the small pterosaurs meant to be gone by then? Fragments of pterosaur jaw from Late Cretaceous Hungary indicate that some azhdarchid species retained small absolute body sizes even when most of the group represented medium-giant species (Prondvai et al. 2014). The discovery of these smaller Late Cretaceous pterosaurs does not buck the overall trend of average pterosaur size increase throughout the Mesozoic of course, but it does show that there were some exceptions to this wider trend.

Yes yes yes... but how are the bees doing?


Regular readers will know that I'm donating all funds from February sales of one print to the Bumblebee Conservation Trust. The good news is that I'm now up to a donation of £130, and there's still eight days left to get your order in. I'm really happy to have sold enough of these to break £100 - huge thanks to everyone who's bought one - and exceeding £150 is my new goal. 

It's now easier than ever to buy a copy of the bee-charity print, so you can get yourself a copy and help our struggling wildlife with just a few mouse clicks. Prices start at £20 (+shipping), and I'm giving as much as I can from each sale to the trust. 

References

  • Hobday, D. K., Woodruff, CM, Jr., McBride, MW. (1981), Paleotopographic and structural controls on non-marine sedimentation of the Lower Cretaceous Antlers Formation and correlatives, north Texas and southeastern Oklahoma. Recent and ancient nonmarine depositional environments, 71-87.
  • Prondvai, E., Bodor, E. R., & Ősi, A. (2014). Does morphology reflect osteohistology-based ontogeny? A case study of Late Cretaceous pterosaur jaw symphyses from Hungary reveals hidden taxonomic diversity. Paleobiology, 40(2), 288-321.

Sunday, 8 February 2015

Controversial ceratopsids revisited: woolly Pachyrhinosaurus and scavenging Styracosaurus

Spurned on by a print request, I've spent free time this week revising two images of ceratopsids which may be familiar to long-term readers: my woolly Pachyrhinosaurus perotorum and scavenging Styracosaurus albertensis. The former is now just over two years old, and the latter a whopping eight years old - wow, have I really been messing about with internet palaeoart for that long?

Maastrichtian Alaska was quite chilly, but woolly Pachyrhinosaurus perotorum doesn't care. See this post for the original image and exploration of the concept shown here. Prints are available.
Because I appreciate some folks are fond of my original paintings, I haven't deviated too far from the original compositions and instead just added more detail, tweaked colour values and tidied up some sketchy areas. I'm very conscious of not 'pulling a Lucas' on my old work. Most importantly, the science has been improved/corrected: the cranial morphology of Pachyrhinosaurus perotorum is now correct to that species (like a doofus, I based the morphology in the original image on a different Pachyrhinosaurus species) and the tyrannosaur in the scavenging scene is appropriately filamentous. Thanks to Darren Naish, Zachary Miller and Christian Kammerer for discussions of Styracosaurus horn shape.

Have these depictions have been supported or refuted by any new discoveries? As far as I'm aware, skin impressions still remain elusive for Pachyrhinosaurus, although new data has emerged on the facial integument of juveniles (Fiorillo and Tykoski 2013). The 2014 discovery of Kulinadromeus and its assortment of filament-like scales, true filaments and other integumentary oddities (Godefroit et al. 2014) might indirectly add credence to the idea of shaggy ceratopsids, however. Along with Psittacosaurus and Tianyulong, Kulindadromeus shows that the evolution of ornithischian integument was complex, that single animals can bear a suite of different integument types, and that the assumption of dinosaur skin being ancestrally scaly is uncertain. The weird scales in (unpublished) skin impressions of Triceratops are further evidence that 'one skin fits all' approaches to reconstructing these animals are likely flawed, and that even clades with relatively limited anatomical disparity - like ceratopsids - had diverse integuments. Thus, the idea that some members of Dinosauria may have looked very different to our traditional interpretations is being strengthened by genuine data, and shaggy arctic ceratopsids remain a fun extrapolation of that concept. For further discussion on these points, check out my discussion of version one of the woollysaur painting.

The Campanian centrosaurine Styracosaurus albertensis scavenges the remains of a tyrannosaurid. He was going for warpaint on his face, but he ended up at 'Tonto'. For fun, the original 2007 version can be seen here. Prints are available.
What of scavenging ceratopsids, as in the reworked 2007 image of a tyrannosaurid-eating Styracosaurus? Ceratopsid omnivory has yet to be explored in the technical literature and, to my knowledge, remains best represented by a short paragraph in Paul (1991). More recently, Mallon and Anderson (2013) provided reasoning for why ceratopsids were not predatory animals, although their discussion seems to consider 'carnivory' synonymous with 'predation': opportunistic scavenging or omnivory are not explored. This leaves most discussion of ceratopsid scavenging online, and several famous denizens of the online palaeontological community seem to support it. Back in 2007 I wrote a long essay substantiating the idea. That essay is no longer online*, but the argument is pretty straightforward:

*After eight years, I figured it's time to archive my old Flickr stream. The bulk of the content there is not representative of modern science or a good representation of my work, so it's been taken offline. I won't pretend I'm not a bit sad to do so, but there's obviously reason for bringing internet searches to my best, most recent work, not images I created when first learning how to paint.

  1. As is well-known, a number of modern herbivores eat animal remains on occasion. This may reflect nutrient stress (thought to explain carrion use by hippos, which is not as common as 'common knowledge' might suggest) or else a method of supplementing a mineral-deficient diet (as in deer, cows, giraffes and a host of other hoofed mammals - Hutson et al. 2013). Remarkably, some cases of hippo carnivory involve the hippos killing animals first, and they will also scare other carnivores from kills to obtain carcass access (Dudley 1998). Of further interest is that entire herds of hippos will chew on carcasses when available - these are not the acts of rogue, aggressive or aberrant individuals (Dudley 1998). Note that studies on the carnivorous tendancies of generally herbivorous animals are in their infancy, and it may be that this behaviour is more common and opportunistic than we currently realise.
  2. Other species, such as pigs, ingest animal matter as part of their normal diets. Studies on some pigs suggest 28% of their diet is derived from animals, either being invertebrates or carrion (e.g. Thomson, and Challies 1988). There is no reason to think that large extinct animals were incapable of comparable omnivory, but we restrict most discussion of it to smaller dinosaurs and pterosaurs. We can predict that such animals should have jaws mostly adapted for herbivory (e.g. teeth suited to browsing and grazing, long 'cheek' toothrows, vertically displaced jaw joints etc.) but would also have some means to process animal remains (e.g. crushing teeth to break bones, caniform teeth or sharp beaks for ripping meat etc.).
  3. Ceratopsid jaws certainly belonged to primarily herbivorous species capable of chewing their food, but their approach to herbivory was unusual. Their teeth and jaws, unlike other herbivorous dinosaurs and mammals, were incapable of grinding plant matter. Instead, they sliced food into pieces, their teeth sliding vertically past one other like scissors. Ceratopsid beaks are also unusually deep and narrow compared to other dinosaurian herbivores, and recall the beaks of parrots in many respects. The beaks of these birds are famously powerful, enabling their owners to access a range of nuts, seeds and animal matter (e.g. Greene 1999). The diet of of ceratopsids has been questioned by palaeontologists because chopping plant matter is not common among modern herbivores. To the contrary, most food slicers are carnivores - meat is easier to chop and slice into easily digested chunks than it is to grind into a paste. One sensible suggestion is that ceratopsids ingested particularly fibrous, woody plant matter (see Mallon and Anderson 2013 and references therein). We might imagine them devastating Cretaceous shrubs, removing entire chunks of tree - leaves, branches and bark - with each bite, or overturning plants with their huge heads to access their roots and tubers. However, it is odd that their jaws aren't more convergent with those of other herbivores, as grinding mechanisms have developed so many times in multiple tetrapod lineage and might be considered optimal for breaking down plant matter. So, maybe ceratopsid jaws were used for more than simply eating plants, and their shearing teeth and hooked beaks are the traits of omnivory we mentioned above, equally capable of slicing plants and animal remains. Opening carcasses, snapping smaller bones and slicing meat was almost certainly possible with their jaws and beaks, and we might imagine ceratopids as Mesozoic variants of pigs: largely herbivorous species with opportunistic carnivorous tendencies, and certainly capable of competing with strict carnivores for carcass access. The possibility that they could occasionally kill other animals for food, as demonstrated by the aforementioned hippos, is not unreasonable.
Back in 2007 I mentioned a possible smoking gun for this idea - a rumoured Psittacosaurus specimen with bony gut content. Since then, it's become apparent that that specimen either doesn't exist, has disappeared or has otherwise been forgotten about - it's best to consider that an unsubstantiated rumour for now. Despite this, I still think the concept of ceratopsian omnivory has legs: maybe a technical paper on the topic would be worthwhile.

Bumblebee Conservation Trust charity prints: an update

In my last post I mentioned you can buy a print of my Tyrannosaurus vs. bees painting and donate money to the Bumblebee Conservation Trust. I'm happy to say £55 has been raised in the last week for this cause, and thanks to those who've bought in. It would be great to make even more money however: if you'd like to contribute, find out more here.

Of course, prints are available for all my other work too, including the ceratopsid pieces above. Contact me at wittonprints@gmail.com to order one, and check out this page for prices and other details.


References


  • Dudley, J. P. (1998). Reports of carnivory by the common hippo Hippopotamus amphibius: short communication. South African Journal of Wildlife Research, 28(2), 58-59.
  • Fiorillo, A. R., & Tykoski, R. S. (2013). An immature Pachyrhinosaurus perotorum (Dinosauria: Ceratopsidae) nasal reveals unexpected complexity of craniofacial ontogeny and integument in Pachyrhinosaurus. PloS one, 8(6), e65802.
  • Godefroit, P., Sinitsa, S. M., Dhouailly, D., Bolotsky, Y. L., Sizov, A. V., McNamara, M. E. & Spagna, P. (2014). A Jurassic ornithischian dinosaur from Siberia with both feathers and scales. Science, 345(6195), 451-455.
  • Greene, T. C. (1995). Aspects of the ecology of Antipodes Island Parakeet (Cyanoramphus unicolor) and Reischek's Parakeet (C. novaezelandiae hochstetten) on Antipodes Island, October-November 1995. Notornis 46: 301-31
  • Hutson, J. M., Burke, C. C., & Haynes, G. (2013). Osteophagia and bone modifications by giraffe and other large ungulates. Journal of Archaeological Science, 40(12), 4139-4149.
  • Mallon, J. C., & Anderson, J. S. (2014). The functional and palaeoecological implications of tooth morphology and wear for the megaherbivorous dinosaurs from the Dinosaur Park Formation (upper Campanian) of Alberta, Canada. PloS one, 9(6), e98605.
  • Paul, G.S. (1991). The many myths, some old, some new, of dinosaurology. Modern Geology, 16: 69-99
  • Thomson, C., & Challies, C. N. (1988). Diet of feral pigs in the podocarp-tawa forests of the Urewera Ranges. New Zealand journal of ecology, 11, 73-78.