Friday, October 7, 2011

Flightless Birds


    Flightless birds
    • Pterosaur -->
    • Primitive flightless birds -->
    • Modern ratites - Ostrich (Struthio), Rhea (Rheidae), Cassowary, Emu (Casuariidae), Kiwi (Apteryx) 





Plucked ostrich
"Ostrom compared Deinonychus to the ostrich and cassowary. He noted that the bird species can inflict serious injury with the large claw on the second toe.[1]"
Avimimus meaning "bird mimic", was a genus of bird-like maniraptoran dinosaur [Oviraptor] that lived in the late Cretaceous in what is now Mongolia, around 70 million years ago.

A cassowary's three-toed feet have sharp clawsThe second toe, the inner one in the medial position, sports a dagger-like claw that is 125 millimetres (5 in) long.[6] This claw is particularly fearsome since cassowaries sometimes kick humans and animals with their enormously powerful legs.

See here also concerning neotony:

See also here for more info:

Some general info:
"Maniraptora is the only dinosaur group known to have included flying members, though how far back in this lineage flight extends is controversial. Powered and/or gliding flight is believed to have been present in some types of dromaeosaurid, such as Rahonavis and Microraptor.[5] Other groups, like the Oviraptorosauria, are not known to have been capable of flight, but some scientists have suggested that they could be descended from ancestors which flew. Paul has suggested that this might be the case. Paul has gone as far as to propose that Therizinosauria, Alvarezsauroidea, and the non-maniraptoran group Ornithomimosauria descended from flying ancestors as well.[6]"

Oviraptors as flightless birds:
"Analyses like those of Osmólska et al. (2004) suggest that they [Oviraptors] may in fact represent primitive flightless birds".[2]
"Evidence for feathered oviraptorosaurs exists in several forms. Most directly, four species of primitive oviraptorosaurs (in the genera Caudipteryx, Protarchaeopteryx, and Similicaudipteryx) have been found with impressions of well developed feathers, most notably on the wings and tail, suggesting that they functioned at least partially for display. Secondly, at least two oviraptorosaur specimens (Nomingia and Similicaudipteryx) preserved tails ending in something like a pygostyle, a bony structure at the end of the tail that, in modern birds, is used to support a fan of feathers.[5] Similarly, quill knobs (anchor points for wing feathers on the ulna) have been reported in the oviraptorosaurian species Avimimus portentosus.[7] Additionally, a number of oviraptorid specimens have famously been discovered in a nesting position similar to that of modern birds. The arms of these specimens are positioned in such a way that they could perfectly cover their eggs if they had small wings and a substantial covering of feathers.[8]""

Concerning alvarezsaurs a case could be made that they are flightless birds:
"... assignments of alvarezsaurs to birds were caused primarily by features that are strikingly, or even uniquely, avian. The sternum, for example, is elongated and deeply keeled for an enlarged pectoralis muscle, as it is in neognathous birds and volant ratites. One bone in the skull of Shuvuuia appeared to be an ectethmoid fused to a prefrontal. The ectethmoid is an ossification known only in Neornithes. Other birdlike characters included the palatine, foramen magnum, cervical and caudal vertebrae, and many others".[9]

Also see these links:

It is interesting to analyze the dromaeosaurids and the troodontids.
Let's begin with the dromaeosaurids.
The dromaeosuarids fall into two groups. One group includesdeinonychusmicroraptorgraciliraptor and utahraptor etc. This group dates to around 125 mya. If we look at the characteristics of this group we find flying bird characteristics such as aerodynamic flight (asymmetric) feathers.
The other group of dromaeosuarids includes dromaeosaurus,saurornitholestesbambiraptormahakalaunenlagia andvelociraptor etc. This group dates to around 75 mya. In this second group we find flightless bird characteristics, such as only symmetric feathers.
Turning to troodontids we see the same pattern.
We find anchiornissinovenatormei, and sinornithoides etc from around 125 mya with flying bird characteristics.
And we find troodon and saurornithoides etc from around 75 mya with flightless bird characteristics.
The fossil record (even if incomplete) tells a clear story. Flying birds were from very early on, with flightless birds later (closer to today).

No comments:

Post a Comment