Flying Volaticothere Developments
Updated depictions of Argentoconodon, Triconolestes and Ichthyoconodon (Ceri Thomas and Dylan Bajda, respectively), and a fictional species for the Speculative Dinosaur Project by Tim Morris.
So a while ago I made some posts on whereas a group of Mesozoic mammals, the volaticotheres, were capable of true powered flight. There have been relatively few responses since then, other than the expected “take this with a grain of salt” (which is fair; it’s an outrageous hypothesis), and even fewer addressals to the points I provided. I had a conversation with paleofail-explained on Julio Lacerda’s commission, but it was abandoned quickly. A more successful counter-argument was made by fezraptor, which I will address below.
In the past few months there have been relatively few papers involving eutriconodont mammals, and none of them involving volaticothere taxa. Thus, for now, things remain as they remain.
However, I previously did miss an important study, which deals with the dietary ranges of Mesozoic mammals and their relation to angiosperm diversity. Here, both Argentoconodon and Volaticotherium are present, firmly within the animalivorous range, with the former ranking more with carnivorous taxa and the latter with insectivorous taxa. Animalivorous mammals are shown to have declined substantially during the mid-Cretaceous; both points strengthen the arguments for volaticotheres being specialised animalivores, and thus unlikely to have been gliders.
Now, unto for the addressal:
The manus of Volaticotherium is actually sufficiently preserved to show that it is smaller than the pes (barring the presence of unprecedentedly weird distal phalanges), precluding it looking bat-like.
The appendix for Meng 2003 describes the manus as “poorly preserved”, and doesn’t mention size. Granted, the fact that the metacarpals don’t seem to be particularly specialised in relation to those in the foot makes a bat-like wing less likely, but the aforementioned elongated phalanges might suggest an atypical wing structure.
Ichthyoconodon is actually outside of the clade that preserves any evidence of adaptations for gliding, so kenbrasai’s reasons for why Ichthyoconodon would be atypical for a glider actually strike me as evidence it wasn’t volant at all.
True, though it’s worth to note that Ichthyoconodon‘s exclusive status from this clade is based on one character less (Gaetano et al 2011). In any case Ichthyconodon‘s molars are less recurved than those in Volaticotherium and Argentoconodon, and as these taxa are already disparate in their jaw morphology it could mean that Ichthyoconodon was functionally very different. We do have evidence of truly aquatic eutriconodonts, after all.
I do stand by my hypothesis, however, as it is still a rare taxon, so an aquatic lifestyle seems less likely.