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re: Endothermic Crocs in Nature

David Peters wrote:

<Considering that early crocs are hard to distinguish from early dinos (witness
Macelognathus, Scleromochlus, etc.), especially when just their bits and pieces
are known,

To be fair, and as you allude to, the original material for _Macelognathus_ was very scrappy. As Gohlich et al. (2005) say: "_Macelognathus vagans_ was described by O.C. Marsh in 1884, based on a mandibular symphysis... New material of this species from the Morrison Formation of western Colorado demonstrates its affinities with basal crocodylomorphs ..." Marsh and his successors could be forgiven for not knowing the precise identity of _Macelognathus_.

_Scleromochlus_ is neither dinosaurian nor crocodylomorph, AFAIK. Here the problem is not so much the lack of material (we have several specimens), but the difficulty in discerning characters in these specimens, which are all natural casts in coarse-grained sandstone, and very small to boot. (Not that I'm advocating anybody booting lil' _Scleromochlus_ ...)

As Greg Paul has noted earlier, apparently the easiest
time for a taxon to revert is when it is only a few steps into the next level.

Greg cites this in support of "neoflightlessness" in early birds. This "rule" makes a great deal of intuitive sense; but I have yet to see any hard evidence (e.g., similar reversions of incipient or nascent ecomorphologies in other lineages). For example, I know of no "neoflightless" insects, nor "neoamphibious" proto-cetaceans.