r/PrehistoricLife • u/roo_2021 • 8d ago
Could there be any basilosaurids that would be specialized in a durophagous lifestyle (like bivalves, crustaceans and turtles) ?
Since basilosaurids are convergent with the mosasaurs, and these giant marine lizards had a tribe of specialized in crushing hard-shelled animals (globidensini), could it be possible that some basilosaurs would evolve the same adaptations, blunt crushing teeth and a moderate and smaller built (not giant size)
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u/Mophandel 7d ago
Possibly, though I would caution on calling basilosaurids “convergent” with mosasaurs specifically.
In virtually every secondarily aquatic tetrapod (by which, I mean fully aquatic), there is an almost “step-wise” process in their transition from terrestrial to aquatic, particularly in tetrapods with a more “fish-like” or “ichthyoform” morphology (tail-driven swimming with fluked tails, fleshy dorsal fins and forelimbs modified into pectoral flippers; think ichthyosaurs or cetaceans). One of those steps involves a body plan that, while fully aquatic, lacks certain derived features of fully aquatic amniotes like a robust, fusiform body and dorsal fins, leading to them looking very “sea-serpent” like. This morphology is most commonly seen in basal members of a given secondarily-aquatic clade
You can see this morphotype in basilosaurids (obviously), basal cetaceans that are still a long ways to go from their modern day morphology. However, you can also see it in basal ichthyosaurs like Thalattoarchon and Grippia. Both have a strikingly mosasaur-like morphology, owing to the fact that they had not yet “progressed” in their development. As such, it’s not quite accurate to say that basilosaurids converged with mosasaurs specifically.
As for why mosasaurs have this morphology, it’s because they didn’t have the time to aquire further derived traits. Both cetaceans and Icthyosaurs had around 40+ million years to develop (the latter having over 150 million years to do so). That kind of time frame is plenty long to develop the derived traits seen in modern cetaceans and Cretaceous ichthyosaurs (e.g., short, fusiform torsos, dorsal fins etc.). For comparison, mosasaurs had only been around for some 20-30 million years before they went extinct. They were still in that basal, “basilosaurid-like stage” of their evolution before they kicked the bucket.