If you wondered why I love some peculiar Triassic tetrapods like Longisquama or Sharovipteryx, it’s probably due to the high diversity and degree of questions you can ask about them, and some even provide curious answers.
So here’s the answer to the riddle above:
I mean, look at that. The megalancosaurid drepanosaur Megalancosaurus preonensis is one helluva animal.
A large triangular head with huge, forward-facing orbits suggests a key arboreal adaptation for prey acquisition. But unlike even most early birds, the jaws are equipped with small teeth all the way to the tip of the jaws, and extending behind the eye.
The forelimbs have hands with three digits extending in one direction and two in the other, effectively “zygodactyle” in the manner of chameleons and several groups of birds, useful for gripping narrow or semi-vertical substrates. Indeed, the arms appear to have been kept flexed at the elbow, and a lateral-facing humeral glenoid suggests a semi-sprawling posture.
The hindlimbs don’t have the chameleon-like feet, which is further weird, but instead have a large, blunted “big toe” or pollex, which diverges medially and may have been prehensile, as in non-hominoid primates but especially some xenarthrans. Again, this suggests an arboreal habit!
And finally, the tail is deep and narrow, but wide at the base, with haemal arches (chevrons) fused to their respective vertebrae, looking for all intents a relatively immobile tail. Yet, this tail terminates in a small triangular “claw”-like bone, which may resemble the fused caudal vertebrae of many different groups of sauropsids, principally ankylosaurids, some sauropods, oviraptorosaurs, and birds. The immediate comparison is to prehensile tails in arboreal primates, but here, the tail lacks the mobility of such tails, and such tails lack the expanded neural spines, chevrons.
There have been suggestions that Meglancosaurus was arboreal, fossorial, or even suspensorial (a form of arboreality), in which the chameleon-hands or anteater-feet or monkey-tail were all useful in creating a highly mobile, arboreal predator. Albeit one with unusual bones.
As I said, many questions!
Calzavara, M., Muscio, G. & Wild, R. 1980. Megalancosaurus preonensis, n. g., n. sp., a new reptile from the Norian of Friuli. Gortania 2: 49-63.