Ichthyoconodon jaworowskorum by Dylan Bajda (sheather888.deviantart.com)
Like many Mesozoic mammals, it is known only from a couple of teeth. That happened to be in what was once a sea bed. Barely eroded, implying that it didn’t die far away…
Now, this was originally taken to be that it was a sea mammal, one of the first in fact. But, while they do look vaguely similar, eutriconodont molars are not functionally similar to those of piscivorous mammals: seals and cetaceans grasp, eutriconodonts, like carnivoran mammals, sheath.
Recently, studies aligned it with gliding eutriconodonts, Volaticotherium and Argentoconodon. This could suggest that, rather than a sea mammal, Ichthyoconodon was instead aerial; rather than the first sea mammal, it was probably the earliest mammalian aeronaut, predating bats by at least 93 million years.
Its worth to note that Volaticotherium’s hand is noted as “poorly preserved”, with only a few metacarpals being known…
Either way, besides the wing finger or styliforme bone, most of what you see is true to volaticotherine mammals: a large patagia, sprawing hindlimbs, a deep, almost gorgonopsid-like snout and the presence of tarsal spurs (here incorporated into the uropatagia).
In life, flying or not, Ichthyoconodon would have been a carnivore, since it was fairly large by Mesozoic mammal standards (comparable to the closely related Jugulator, weighting over 700 g), large canines and its meat-slicing molars discussed above. I asked Dylan to give it a falcon-like colour scheme, to hint at its nefarious lifestyle.