Hyperossified megafrogs of the Oxford University Museum of Natural History
September 25, 2012
Another extraordinary specimen from the wonderful Oxford University Museum of Natural History: the skeleton of a goliath frog Conraua goliath, the largest extant anuran, which comfortably exceeds 30 cm and 3 kg in life:
As noted by sometime SV-POW!sketeer Darren Naish over on Tetrapod Zoology, frogs have stupidly weird skeletons — surely the most derived of any tetrapod, despite their lowly, early diverging “amphibian” status. Rather than describe all the oddities myself, I’ll just quote Darren’s article:
Anurans have (at most) nine presacral vertebrae, and some have as few as five; ribs are either highly reduced or absent; the radius and ulna are fused (forming the radioulna); the bones of the pectoral girdle are highly reduced and complimented by an assortment of new weird bits; the pelvis consists of a rod-like central unit (the urostyle) surrounded by two super-long, shaft-like ilia; and in their (generally) elongate hindlimbs, the tibia and fibula are fused (forming the tibiofibula) while the ankle bones are elongated to form a long ‘extra’ limb segment.
That’s a pretty astonishing list; and, sure enough, frog skeletons weird me out every time I see them. (Of all the dead animals I’d like to get hold of in decent condition, to extract the bones from, frogs miss the top of the list only to bats, crocs and turtles. And maybe raptors.)
This particular species of frog has another skeletal oddity that caught my eye:
As you can see, the humerus is perforated: there is a distinct foramen running down it just behind the anterior edge. Is the anterior bar a partially detached deltopectoral crest? Or is it a completely novel ossification that has become partially fused to the humerus?
For what it’s worth, this feature doesn’t seem to be consistently present in goliath frogs. A bit of googling shows that it’s present in this skeleton, but not in this one from Bone Clones. The humerus of the latter does have a distinctly protruding deltopectoral crest, but it lacks the perforation. So I guess that is evidence against the Novel Ossification hypothesis.
Does anyone know more about this odd feature? Does it develop through ontogeny? Is it found in other frogs? What is its mechanical significance?