"Maniraptorans are the most diverse clade of
http://www.geol.umd.edu/~tholtz/G104/lectures/104coelur.html
MANIRAPTORA"Maniraptorans show numerous specializations:
- Elongated forelimb
- Large bony sternum for attachment of the muscles that pull the arms inwards
One possible problematic shared derived feature of Maniraptora is a backwards-pointing pubis. Most coelurosaurs (and saurischians in generally) have a vertically-oriented or anteriorly-oriented pubis. In therizinosauroids, alvarezsaurids, the basal troodontid Sinovenator, dromaeosaurids, Archaeopteryx, and avialians the pubis points backwards; in the basal therizinosaur Falcarius, oviraptorosaurs, and troodontids other than Sinovenator it points vertically or anteriorly. So it is difficult to say which condition is found in the concestor of Maniraptora.
- Semilunate carpal: a pully-shaped block of wrist bone that allowed greater folding motion while sacrificing motion in any other plane
Changes in the muscle attachments in the hindlimbs of maniraptorans show a switch from the femur-and-tail power stroke found in other dinosaurs (inherited from the early diapsids) to one where the flexion of the knee is more important.
Maniraptorans are the most diverse clade of dinosaurs. Noneretain[have] a basal theropod form: indeed, very fewretain[have] the ancestral carnivorous condition. Major groups include Oviraptorosauria, and Eumaniraptora [Paraves]"
BOTTOM LINE
The bottom line is that pterosaurs are very similar to birds while as we see from the quote above, dinosaurs are not similar at all.
Possessing derived characteristics doesn't mean that a clade couldn't be descended from something without those characteristics, especially if the derived trait is a modification of an already existent structure, for example, tetrapods are united by their possession of four legs and feet (hence the name), and a bunch of other things, but this doesn't mean that they didn't evolve from "fish".
ReplyDeleteElogated forelimb: Yes, most members of maniraptoriformes possess them, but there are many exceptions; alvarezsaurs, mahakala, etc. Xuanhanosaurus also has very long arms, and it's either a basal tetanuran or a basal megalosauroid, so it isn't unreasonable that this maniraptorans could have evolved this trait from more basal theropods (I mean basal coelurosaurs) too.
Almost none of the characteristics you have listed are shared with pterosaurs. Even if maniraptorans weren't dinosaurs, this wouldn't automatically make them pterosaur descendants, this isn't an "if not A then B" kind of deal
You have said:
ReplyDelete"Almost none of the characteristics you have listed are shared with pterosaurs."
Which of these characteristics are not shared with pterosaurs?
Please provide links for whatever you claim.
That would be very helpful.
Semilunate carpal, backwards pointing pubis (in pterosaurs, the pubis is fused to the ischium, and there is a prepubic bone), "Changes in the muscle attachments in the hindlimbs of maniraptorans show a switch from the femur-and-tail power stroke found in other dinosaurs (inherited from the early diapsids) to one where the flexion of the knee is more important." (most pterosaurs were probably quadrupedal), etc.
ReplyDeleteDjango, I asked you to provide reference links for whatever you claim.
ReplyDeleteYou did not do that.