[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Deltopectoral Crests and Condyles on the Humeri



Hello everyone. Well, I've been reading the archives since the mid 90's and finally decided to join up. And yes, I'll admit right now, that being able to post something on the Dinosaur Mailing List and actually get a reply back from many of its members is like a physicist being able to talk to Einstein. Just me engaging in a bit of hero worship :-)

OK, now that I've got that off my chest, I have a question about the deltopectoral crest in avian and non-avian dinosaurs.  A friend has been doing some investigation into the osteology and he's noticed that in birds it is at a sort of 45 degree angle to the humerus. As far as I can tell, it is about the same in dromaeosaurs. Now, my question is do we know when it went from pointing forwards to bent to the side in that manner??? What animals show the change? On a side note, when you take a look at _Bambiraptor's_ you really have to sit and say to yourself that boy oh boy is there one heck of an angle, just like a bird's. (Go figure.)

He was also looking at the location of the condyles on the humeri of certain animals, not just dinosaurs. In a way, he was being a bit prejudice because of the bones he was using. All of the bones he was looking at had the condyles on the cranial surface of the humeri, but this is not the norm. See, he was looking at cats, opossums, squirrels and so on. They all are tree climbers. Is the movement of the condyles to the cranial position a sign of a tree climber??? I ask only because, and this is the interesting part, basal theropods have their condyles on the distal surface. Dromaeosaurs do not. I'm sure one can blame this situation on grasping and killing in both cats and maniraptors, but it's the squirrels, opossums, and monkeys having the same setup that is confusing me a bit. Is there just some sort of illusion going on here? Does the cat and the maniraptor condyle angle mean tree climbing trait first? I know that the first "cats" are thought to have been tree dweller! s,! ! so this makes sense in my mind's eye. Only later in their evolution did they venture to the ground. Now, much to the delight of many (and me I might add), it appears with _Microraptor_ and NGCM 91, and even _Archaeopteryx_ for that matter, that we have a highly suggestive situation here that says that your basal dromaeosaurs were arboreal. This gels nicely with the position of their cranial surface condyles, and also fits with the idea I mentioned about their presence being kept to aid with grasping prey and what not. And yes, I'm sure it flashes like a neon sign in Las Vegas, I've been a Secondarily Flightless Theropod Hypothesis nut since it's inception by Gregory S. Paul in 1988. "Predatory Dinosaurs of the World".... wonderful book. (Now, if only that second book of his will get published!) Oh, I have to say that it's amusing that Ostrom mentioned, in just a little sentence at the end of his 1976 paper on _Archaeopteryx_ , that the gripping on the hands could be pointin! g ! ! to tree climbing.... "Quadrupedal tree climbers." Hehehehehe.

Just some ideas and questions to toss around. I hope I didn't sound too ridiculous. I'm sure I'm repeating things that have been discussed already on the message board, so, I apologize in advance.

And that's about it.

Kris