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Re: Bird Question



On 96-02-02 15:59:07 EST, Nick Pharris wrote:

<<On Fri, 2 Feb 1996 Dinogeorge@aol.com wrote:>>

<<The second is the Cretaceous bird radiation, which witnessed
the spread of enantiornithine birds around the world. These seem
to have gone extinct in the Cretaceous extinction along with the
dinosaurs. Inasmuch as enantiornithines were essentially unknown
until 1981, we still have a lot to learn about this radiation. It
is very telling that nearly all the known Cretaceous bird
skeletons are of enantiornithine birds.>>

<<Out of curiosity, how do you define an "enantiornithine"?>>

<<Many birds I've seen described as "enantiornithines" appear to
be just a serially derived bunch of outgroups between
_Archaeopteryx_ and modern birds.>>

Our own Dave Peters (DPterosaur) has obligingly listed 17
enantiornithan (not necessarily enantiornithine) synapomorphies
(MAPS Digest 17(4) EXPO XVI Edition, 1994: 30, where they're
only numbered 1-16). Print and save:

(1) Metatarsal IV splintlike or more slender that II or III
(2) Tubercle on front of metatarsal II (except _Concornis_)
(3) Trochlea of metatarsal II broader than that of III
(4) Tarsometatarsus ossifies proximally to distally, with sutures
remaining visible (unlike extant birds, in which the TM ossifies
distally to proximally, and the sutures are largely obliterated)
(5) Bulbous medial distal condyle, narrow lateral distal condyle
of tibiotarsus
(6) Cnemial area of tibiotarsus lacks flanges
(7) 9 sacral vertebrae
(8) Pygostyle often with a dorsal shelf
(9) Rear of sternum deeply notched, with distal expansions on
lateral processes
(10) Sternum keel ossified back-to-front (unlike extant birds, in
which the keel ossifies front-to-back)
(11) Pubis sub-circular in cross section (not flattened as in
extant birds)
(12) Humerus with prominent bicipital crest
(13) Humeral head flat or concave
(14) Coracoid with convex posterior margin (margin straight in
living birds)
(15) Scapula with facet and coracoid with corresponding boss
(unlike extant birds, where the boss is on the coracoid and the
facet is on the scapula; this is the ultimate source of the term
Enantiornithans: "opposite birds")
(16) Furcula articulates with scapula
(17) Glenoid directed posteriorly

As you can see, lots of minor characters. Enantiornithan birds
would have looked much like extant birds to the casual observer,
though perhaps with more "tail." Most enantiornithan specimens
are too incomplete for all the above characters to be identified in
them. But usually the metatarsus is enough.

Discussions of enantiornithans and enantiornithines are hampered by
the lack of a good description of the type genus _Enantiornis_ and its
family, order, etc.