Re: New alvarezsaurid

["Matthew Troutman" <m_troutman@hotmail.com>]

>Imagine the arboreal, flying ancestral forms as having most if not all 
of the
>different avian characters that have been noted in "theropods," then 
>losing<
>some of them--randomly (particularly forelimb/pectoral characters, as 
the
>wings vestigialize)--in each different lineage of their ground-dwelling
>descendants. It would create a bunch of lineages, each sporting its own
>distinct random selection of avian features, some modified from 
subsequent
>evolution, some not so modified. This is what is seen in the fossil 
record of
>"theropods."
>

   First of all this is not documented in flightless birds to the extent 
you propose here. Though kiwis are flightless, they do not differ much 
from their Paracathartes lithornithid ancestors. No major characters are 
lost and there is a gap of 55 million years. The only place where kiwis 
differ much from other related, but volant birds ( such as the tinamou 
), is in their physiology. They have a slower metabolism and have two 
functional ovaries. This, though, is an adaptation for survival and 
protection against predators. Other flightless birds, such as 
Thambetochen ( the flightless, extinct Hawaiian goose ) show no major 
differences in basic anatomy from its ancestors. Though the trends like 
the degeneration of the flight apparatus are present, you can still 
trace ancestry and there is a consistent pattern of what is lost 
( the flight apparatus). A volant lineage such as birds with all the 
typical adaptations of the goup ( reduced postorbital, jugal bar, 
squasmol-quatrojugal bar lost, three tympanic recesses, opisthopubic 
pubis, loss of obtutator process, etc.) that goes flightless, still has 
the basic adaptations of the group. If some theropods did descend from 
early birds, then you would expect _all_ the diagnostic features still 
to be present. 


MattTroutman



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