Reisz and Fröbisch 2014
considered Eocasea martini (Late Pennsylvanian, Fig. 1) the basalmost caseid, despite its long slender appearance and small size.
Figure 1. Eocasea in situ with anterior skull imagined based on phylogenetic bracketing. This long, low taxa does not nest with large, big-bellied caseasaurs but with more similar sister, including Delorhynchus. These are not wide dorsal ribs, but belong to a specimen with a standard, narrow torso.
And at the time (2 years ago), I wrote in ReptileEvolution.com,
“[Eocasea] had a long narrow torso and short legs. Note the resemblance to millerettids like Australothyris and Oedaleops.”
Reisz and Fröbisch did not include those two
in their phylogenetic analysis because they were so sure they had a caseasaur. They also did not include Eunotosaurus, Acleistorhinus, Microleter, Delorhynchus, or Feeserpeton for the same reason.
But they should have done so, because
that’s where Eocasea nests in the large reptile tree (Fig. 2) close to, but not with caseasaurs.
Figure 2. Eocasea nests between Feeserpeton + Australothyris and Delorhynchus in this subset of the large reptile tree, not close to Casea.
The problems with the Reisz and Fröbish data set
is that it was too small. The authors presumed Eocasea would be a caseasaur and so included only the following taxa: Reptilia, Diadectes, Limnoscelis, Mycterosaurus, Varanops, Oromycter, Casea, Cotylorhynchus, Angelosaurus, Ennatosaurus and Eocasea. As you can imagine, providing scores to a clade named, “Reptilia” is inappropriate and, frankly, dangerous, whether cherry-picking traits or scoring all zeroes. Diadectes, Limnoscelis, Mycterosaurus, Varanops are not related to each other or to caseasaurs. Reisz and Fröbisch were making guesses without having a large gamut study from which to draw subsets.
Reisz and Fröbisch report,
“Eocasea changes significantly our understanding of the evolutionary history of both caseids and caseasaurs.” Not with the current nesting. “The discovery of Eocasea extends the fossil record of Caseasauria and Caseidae significantly, well into the Pennsylvanian, in line with the fossil record of other early synapsid clades, indicating that the initial stages of synapsid diversification were well under way by this time.” Eocasea is not a caseid and caseids are not synapsids, so it doesn’t extend anything related to Caseidae.
“More significantly, Eocasea also allows us to re-evaluate the origin and evolution of herbivory within this clade, and terrestrial vertebrates in general.” It’s not an herby and it’s not a clade member. “Thus, we can identify Paleozoic herbivores because their rib cages are typically significantly wider and more capacious than those of their closest insectivorous or carnivorous relatives. Not in Eocasea. “Nevertheless, it is likely that the ability to process this kind of plant matter precedes the skeletal correlates that can be found in the fossil record.” This is an unsupported supposition in light of the new nesting. “It is therefore possible that we are underestimating the extent of herbivory that existed in the Paleozoic, but this does not invalidate our results because the clades of herbivores that we examine here are widely separated by successive clades of non herbivorous vertebrates.” There is no ‘therefore’ when the setup if invalid.
To their credit,
Reisz and Fröbisch did not nest Edaphosaurus or Protorothyris as outgroup taxa to the Caseasauria (Eothyris at its base). Perhaps that is so because they did not include these taxa! And I wonder why? But they did nest the unrelated Varanops and Mycterosaurus as caseasaur outgroups. Both nest about twenty nodes away on the other major branch of the Reptilia, the new Archosauromorpha.The Reisz and Fröbisch tree is bogus because their outgroup taxon list was based not on testing, but on tradition.
If you’re looking for
osteological evidence for herbivory in the ancestry of the Caseasauria, you won’t find big bellies and flat teeth, but you will find several herbivores arising from Milleretta (late Permian late survivor of a Carboniferous radiation) in the clade Lepidosauromorpha. These include diadectids and their allies bolosaurids (post-crania unknown) and procolophonids, pareiasaurs and their allies turtles, along with caseasaurs.
Working on their ‘wish list’
Reisz and Fröbisch continue with their hypothesis: “Whereas other caseids also show dental specializations, with leaf-like large serrations being present in the marginal dentition, Eocasea, Oromycter, and the undescribed Bromacker Quarry caseid lack these serrations. Interestingly, both Oromycter, and the Bromacker caseid show skeletal evidence for herbivory, raising the possibility that oral processing in the form of puncturing vegetation may have evolved within Caseidae after the acquisition of herbivory.” Only the latter two are indeed caseasaurids. Eocasea definitely is not one. You can’t derive homolog conclusions from unrelated taxa.
Reisz and Fröbisch continue
“Late Pennsylvanian and Early Permian diadectids also show convincing evidence of dental and skeletal adaptations for herbivory. These enigmatic [not any more] Paleozoic forms are part of Diadectomorpha, a sister group to crown Amniota [not any more]. A preliminary phylogeny of diadectids indicates that Ambedus, a small diadectid from the Early Permian, tentatively identified as omnivorous because of its labiolingually expanded cheek teeth (but no evidence of dental wear) is the sister taxon to all other diadectids. Ambedus may not be a diadectid as noted here. However, the oldest known diadectid from the late Pennsylvanian of Oklahoma is already clearly an herbivore and older than the edaphosaur Edaphosaurus novomexicanus. As is the case with the caseid and edaphosaur synapsids, the sister taxon of Diadectidae, the Early Permian Tseajaia from New Mexico, was faunivorous.” That oldest known diadectid is not identified.
Reisz and Fröbisch add to their unsupported hypothesis with,
“Although the holotype of Eocasea certainly represents a juvenile individual [actually, and you can check this, it is the same size as sister taxa, but smaller than basal and other caseasaurs], it is diminutive, with an estimated snout-vent length of 125 mm. In contrast, the smallest known herbivorous caseid with a comparable ontogenetic age, based on level of ossification of the vertebrae and pedal elements, is a basal, undescribed form from Germany and has an estimated snout-vent length of 400 mm.” Not sure which specimen this is…
If Reisz and Fröbisch had just
increased the size of their taxon list, they would/could have correctly nested Eocasea, and avoided making the many subsequent mistakes based on that bad nesting, including the unfortunate and inappropriate naming of the taxon and the bogus headline that got tacked to the article and all the PR that attended it.
We don’t have a name yet
for the enanticaseasaurs or paracaseasaurs (Fig. 2), but we need one!
Reisz R and Fröbisch J 2014. The oldest caseid synapsid from the Late Pennsylvanian of Kansas, and the evolution of herbivory in terrestrial vertebrates. PLoS ONE 9(4): e94518. doi:10.1371/journal.pone.0094518