Geese are bastards, and this is an objective truth. I live in Canada, so I live with one of the biggest bastards of the geese family (it's family Anatidae if you're interested): the Canada Goose. It is rumoured that Canadians are so nice because the geese soak up all the mean vibes. I don't blog about geese or birds in general, but there is a temnospondyl out there whose name, for reasons entirely known to me, invokes the Greek root for 'goose' - up this week on the edopoid rotation is Chenoprosopus.
AnatomyAs I noted last week, Cochleosaurus and Chenoprosopus have pretty similar-looking skulls, although some proportions and shapes of cranial elements are distinctly different. As a result, there aren't really any clear-cut autapomorphies of Chenoprosopus but instead a variety of features that largely separate it from Cochleosaurus, such as the presence of a vomerine depression and the obvious absence of postparietal lappets. It's possible that there might be differences in the postcrania, but none are apparent because there is no unequivocal postcrania of Chenoprosopus milleri. Mehl (1913) described and figured a vertebra that had been smashed into the palate of the holotype and noted how similar it was to that of Diadectes...which is probably because it does belong to a diadectid. Some postcrania was described for C. lewisi, including the girdles and some limb material (see below), but comparisons are complicated by the possible interpretation of this taxon as simply a juvenile. Langston (1953) suggested that perhaps some vertebrae of another temnospondyl such as Eryops had been mistakenly identified and were actually Chenoprosopus, but this has never been proven since. RelationshipsIt may be considered surprising that Chenoprosopus and Edops are not recovered as closely related within Edopoidea; intuitively, taxa from the same geographic region that live at the same approximate time would be expected to be more closely related than ones from more disparate time or place. Regardless of where Nigerpeton goes, Cochleosaurus and Chenoprosopus are typically recovered as highly nested edopoids compared to Edops, Adamanterpeton, or Procochleosaurus. Indeed, much of the phylogeny is at odds with the stratigraphic and geographic position of various edopoids, which suggests long ghost lineages where earlier representatives are unknown (e.g., Carboniferous edopids) and morphological stasis over long time intervals. If the division between the monotaxic Edopidae and the Cochleosauridae (the rest of the edopoids) is true, then their divergence would have been way back in the Carboniferous, possibly dozens of millions of years before Edops appeared. One key point is that a number of cochleosaurids are only known from small skulls - Adamanerpeton and Procochleosaurus, and these taxa have distinctly shorter skulls as would be predicted for the primitive condition and that are more similar in some proportions to Edops. However, these taxa might have turned into more Cochleosaurus-type animals as adults if indeed the presently largest specimens are only juveniles, thereby indicating that the phylogeny captures at least a misleading, if not exaggerated, morphological disparity. More on that in the future perhaps... Up next week to close out the month of edopoids is Nigerpeton. Refs
David Marjanović
1/22/2020 02:00:23 pm
Métôpon is "the space between the eyes, brow, forehead"; prósôpon is "face" (and metaphorical extensions like "front" and "person"), say the dictionaries at perseus.tufts.edu, and I think I once read it's the part of the face in front of the eyes – nose and mouth basically. Comments are closed.
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