[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
a while back somebody posted this link-
http://home.stlnet.com./~azero/Megalancosaurid.html - it's dave peter's
illos of the megalancosaurs, you can get an idea of how weird they are and
pick up some refs.
There is a lot of argument over these guys. Megalancosaurus was
possibly arboreal, there was an article in JVP a few years back on this and
it's really stunning- almost as if someone took a whole bunch of different
climbing taxa from all over tetrapoda and threw them together (nature
really does tend to repeat good ideas). Weird weird weird. The foot has a
weird pollex that looks like that of some tree-climbing marsupials. The
hands have two digits opposing three, something like in koalas and
chameleons (I don't know about chameleons, but in koalas it's two "thumbs",
while megalancosaurus appears to have three "thumbs" against the remaining
two digits). The digits are all mostly same length more or less, pretty
common in graspers I think, some of them also have elongate penultimate
phalanges which indicates grasping function (seen especially in the
raptorial digits of theropods, or predatory and tree-climbing birds). The
tail has massive chevrons curving downwards, and fused onto the centra,
presumably these functioned as levers to ventroflex the tail and allow it
to be curvled, chameleon style, around a branch. the tail, and especially
its distalmost part, has a distinct curve, apparently for going around
branches. I think Renesto is the guy who did the JVP article and suggested
that Megalancosaurus darted out it's long neck to snatch insects off of
branches. Seems at least plausible. Re: digging it is possible (heck,
groundhogs get into trees, why not climbers into the ground) but they don't
look too well-designed for it. The arms are long which reduces their
leverage, and relatively slender such that their bending resistance would
be pretty poor- not like in, say, a mole or an armadillo which is made for
busting through some serious earth; diggers also have huge processes and
tuberosities sticking out all over the limb bones to attach muscles and
give them leverage, in particularly they almost invariably have a really
big olecranon to improve forelimb extension.
Drepanosaurus lacks some of the above features, but has other weird
stuff- for one, it's got a "claw" on the end of the tail (it looks like a
scorpion), apparently a climbing hook (no distal tail in megalancosaurus).
The knuckles on the feet all align with each other, allowing the digits to
flex and extend in parallel, as in some climbers (you can see this to a
certain extent in our own hands).The weirdest thing is the massive manual
claw. The animal sort of reminds me of an arboreal anteater but the claw
profile is wrong, it looks more like the thumb claws of some bats, in my
opinion- just really, really big. But it is a really weird forelimb. Again,
the humerus seems slender compared to any digger.
No, it's not an april fool's joke- take a look at the pictures.
Both look like the hindlimbs are powerful enough to support the
entire animal, either alone or with the tail. This would be handy for
climbing- the animal could hold on with its feet and then reach out to a
branch and latch on, like arboreal anteaters do.
There has also been the idea that these things were aquatic,
neither of them really shows anything that would indicate this except for
the sheer depth of the tail, however. Various anti-dinosaur camps like to
interpret these guys as being potential bird relatives. Ruben has
interpreted Megalancosaurus as a glider but I don't see any osteological
correlates to gliding present, if one can even find osteological correlates
to gliding (if there are I'd love to know).