Can it be? Even more non-dinosaurian epipophyses? Yes, and this time they’re non-ornithodiran!
February 8, 2015
Here, for example, is the basal archosauriform Vancleavea. (Thanks to Mickey Mortimer, whose a comment on an earlier post put us onto this, and various other candidate epipohysis-bearers which we’ll see below.)
Here is a pair of Vancleavea cervical vertebrae:
No ambiguity here: the epipophysis is even labelled.
But we can find epipophyses even outside Archosauriformes. Here, for example, is the the rhynchosaur Mesosuchus:
Check out the rightmost vertebra (C7), clicking through for the full resolution if necessary. There is a definite eminence above the postzyg, separated from it by a distinct groove. Unless the drawing is wildly misleading, that is a definite epipophysis, right there.
But even more basal archosauromorphs have epipophyses. Check out Teraterpeton, described by Hans-Dieter Sues in 2003:
This is another one where the epipophysis is labelled (though not recognised as such — it’s just designated an “accessory process”).
Can we go yet more basal? Yes we can! Here are cervicals 2 and 3 of the trilophosaur Trilophosaurus (in an image that I rearranged and rescaled from the published original for clarity):
The parts of this image to focus on (and you can click through for a much better resolution) are the postzyg at top right of the left-lateral view, which has a distinct groove separating the zygapophyseal facet below from the epipohysis above; and the posterior view, which also shows clear separation on both sides between these two structures.
While we’re playing with trilophosaurs here’s here’s another one (probably), Spinosuchus:
Again, the groove separating postzygapophyseal facet from epipophysis (at top right in the image) is clear.
But there’s more! Even the protorosaurs, pretty much the most basal of all archosauromorphs, have convincing epipophyses. Here are two that I found in Dave Peters’ post from two years ago, which I only discovered recently. [Here I must insert the obligatory disclaimer: while Dave Peters is a fine artist and has put together a really useful website, his ideas about pterosaur origins are, to put it mildly, extremely heterodox, and nothing that he says about phylogeny on that site should be taken as gospel. See Darren’s write-up on Tet Zoo for more details.]
Dave shows some probable, but not super-convincing epipophyses in the protorosaur Macrocnemus (shaded purple here) …
… and some much more convincing epipophyses in the better known and more spectacular protorosaur Tanystropheus:
Frustratingly, Dave doesn’t attribute these images, so I don’t know where they’re originally from (unless they’re his own artwork). Can anyone enlighten me? There’s a nice illustration in figure 57 of Nosotti’s (2007) epic Tanystropheus monograph that is at least highly suggestive of epipophyses:
But it’s not as good as the one Peters used, as that one shows a distinct notch between postzyg and epipophysis, so I’d like to track that down if I can.
With this, I believe I am done on cataloguing and illustrating epipophyses, unless something dramatic turns up. (For example, this commenter thinks that nothosaurs have epipophyses, but I’ve not been able to verify that.) Here’s what we’ve found — noting that we’ve illustrated epipophyses on every taxon on this tree except Crocodylia:
So it seems that epipophyses may well be primitive at least for Archosauromorpha — which implies that they were secondarily lost somewhere on the line to modern crocs.
With this lengthy multi-part digression complete, hopefully, we’ll get back to sauropods next time!
- Dilkes, David W. 1998. The Early Triassic rhynchosaur Mesosuchus browni and the interrelationships of basal archosauromorph reptiles. Philosophical Transactions of the Royal Society of London B 353:501-541.
- Kellner, Alexander W. A., and Yukimitsu Tomida. 2000. Description of a new species of Anhangueridae (Pterodactyloidea) with comments on the pterosaur fauna from the Santana Formation (Aptian-Albian), Northeastern Brazil. National Science Museum monographs, Tokyo, 17. 135 pages.
- Nesbitt, Sterling J., Michelle R. Stocker, Bryan J. Small and Alex Downs. 2009. The osteology and relationships of Vancleavea campi (Reptilia: Archosauriformes). Zoological Journal of the Linnean Society 157:814-864.
- Nosotti, Stefania. 2007. Tanystropheus longobardicus (Reptilia, Protorosauria): re-interpretations of the anatomy based on new specimens from the Middle Triassic of Besano (Lombardy, Northern Italy). Memorie della Societa Italiana di Scienze Naturali e del Museo Civico di Storia Naturale di Milano 35(III). 88pp.
- Spielmann, Justin A., Spencer G. Lucas, Larry F. Rinehart and Andrew B. Heckert. 2008. The Late Triassic Archosauromorph Trilophosaurus. New Mexico Museum of Natural History and Science Bulletin 43.
- Justin A. Spielmann, Spencer G. Lucas, Andrew B. Heckert, Larry F. Rinehart and H. Robin Richards III. 2009. Redescription of Spinosuchus caseanus (Archosauromorpha: Trilophosauridae) from the Upper Triassic of North America. Palaeodiversity 2:283-313.
- Sues, Hans-Dieter. 2003. An unusual new archosauromorph reptile from the Upper Triassic Wolfville Formation of Nova Scotia. Canadian Journal of Earth Science 40:635-649.