Monday 5 January 2015

Babified Allosaurus and prehistoric sphenodontians

A curious juvenile Allosaurus is told to get off the lawn owned by a grumpy Opisthias. Prints are available. 
With Christmas 2014 fading into memory, I can start sharing pieces of artwork commissioned for presents by various clients without fear of spoiling any surprises. I have several of these to reveal, and the first of which is above, showing an alsatian-sized Allosaurus and a feisty Jurassic sphenodontian, Opisthias. The Allosaurus in this image is based on one of the smallest Allosaurus specimens known, the partial skeleton SDSM 30510. This specimen, described by John Foster and Daniel Chure in 2006. is notable for not only its small size but also its proportions: it seems that very young Allosaurus had relatively longer legs than their parents, which is interpreted as them being more sprightly and cursorial than larger Allosaurus individuals (Foster and Chure 2006). I tried to capture these proportions accurately in the image, not the least because it was commissioned as a Christmas present for John Foster, the chap who discovered and assessed the significance of the specimen (I hear from my commissioner, ReBecca Hunt-Foster (@paleochick), that it's got the seal of approval). It must be stressed, however, that much of the reconstruction is speculative because many details of tiny Allosaurus anatomy remain unknown. Thus, a lot of the anatomy here reflects 'babification' of larger Allosaurus specimens. 

Allosaurus is joined in this image by the small sphenodontian Opisthias rarus. As with many small Mesozoic herps, Opisthias is not well known and much of what you see here as goes appearance and anatomy is based on the modern tuatara. It would be nice to know what Mesozoic sphenodonts really looked like rather than just trotting out variants of the Sphenodon bauplan again and again. Until better fossils are known, I guess this remains the most sensible option, however, as tired as it is. At least have good skull material for Opisthias and, from this, we can see it wasn't a straight replicate of the Sphenodon condition: the snout is longer, the temporal region rather shorter, and the teeth are generally more bulbous without pronounced anterior fangs. I attempted to further differentiate my Opisthias from Sphenodon with a green and red colour scheme, although its behaviour - an open mouth 'push up' pose - is a classic sphenodon threat display, a nod to the aggressive nature of modern male tuataras.

As is becoming tradition around these parts, I tweeted some in-progress images of this painting.

Coming soon: Deinonychus! The pterosaur formally known as 'Phobetor'! Comic-style Carnotaurus!


  • Foster, J. R., & Chure, D. J. (2006). Hindlimb allometry in the Late Jurassic theropod dinosaur Allosaurus, with comments on its abundance and distribution. New Mexico Museum of Natural History and Science Bulletin, 36, 119-122.

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