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Enantiornithine Questions

Hi All -

        There's been some discussion of enantiornithine birds on ther list
lately.  First, the question of the number of enantiornithine genera:  As
far as I can tell, there are presently many genera known throughout the
Cretaceous, and several occurrences of unnamed (or indeterminate) forms. 
Although there have been many phylogenetic (and some
less-than-phylogenetic) analyses of their intrarelationships and
interrelationships within the Aves (Avialae of some).  Regardless of the
phylogenetic definition of the Enantiornithes, there are very few
diagnostic characters that multiple authors agree on for the group -- thus,
many fragmentary finds attributed to the group may be incorrect, while
other fragments may belong to the group but go unrecognized at present. 
Furthermore, some specimens have been placed within the Enantiornithes in
one analysis, based on one author's set of characters, when the same
specimen isn't considered an enantiornithine in another author's analysis.

        The original list of diagnostic characters for the group is, of

Walker, C.A.  1981.  New subclass of birds from the Cretaceous of South
America.  _Nature_ 292:  51-53.

        Some of the most comprehensive, _published_ analyses of the group

Chiappe, L.M.  1993.  Enantiornithine (Aves) tarsometatarsi from the
Cretaceous Lecho Formation of northwestern Argentina.  _American Museum
Novitates) 3083:  1-27.

Martin, L.D.  1995.  The Enantiornithes:  terrestrial birds of the
Cretaceous, pp. 23-36 in Peters, D.S. (ed.)  _Acta Palaeorntihologica_. 
_Courier Forschungsinstitut Senckenberg_ 181.

Kurochkin, E.N.  1996.  A new enantiornithid of the Mongolian Late
Cretaceous, and a general appraisal of the Infraclass Enantiornithes
(Aves).  _Russian Academy of Sciences, Paleontological Institute_ Special
Issue:  1-50.

        Other useful references are:

Chiappe, L.M.  1995.  The first 85 million years of avian evolution. 
_Nature_ 378:  349-355.

______  1996.  Late Cretaceous birds of southern South America:  anatomy
and systematics of Enantiornithes and _Patagopteryx deferrariisi_. _
Münchner Geowissenschaften Abhandlungen_ 30:  203-244.

Padian, K. and Chiappe, L.M.  1998.  The origin and early evolution of
birds.  _Biological Review_ 73:  1-42.

Martin, L.D.  1983.  The origin and early radiation of birds, pp. 291-338
in Brush, A.H. and Clark, G.A., Jr.  (eds.)  _Perspectives in Ornithology: 
Essays presented for the Centennial of the American Ornithological Union_. 
Cambridge:  Cambridge University Press.

Kurochkin, E.N.  1995.  Synopsis of Mesozoic birds and early evolution of
class Aves.  _Archaeopteryx_ 13:  47-66.

        Diagnostic characters of the group that most authors seem to agree
on are:

* the articulation between the scapula and coracoid involves a process on
the coracoid which articulates with a facet on the scapula (this is the
opposite situation of Ornithurine birds, in which a process on the scapula
articulates with a facet on the coracoid)

* the medial condyle of the tibiotarsus is bulbous and significantly larger
than the lateral condyle

* coracoid has a broad, deep, triangular fossa on the dorsal surface

* metatarsal IV is reduced with respect to metatarsals II and III

Characters less agreed upon (probably in part due to the fragmentary nature
of many specimens, rendering the utility of the characters dubious, and
partly due to our present lack of information on the overall diversity and
evolution of the group) are:

* humeral head concave cranially and convex caudally

* dorsal (lateral) humeral condyle oriented transversely

* radius with a longitudinal groove on the caudoventral surface

* tibiotarsal cnemial crest indistinct

and, surprisingly,

* tarsometatarsus fused only proximally, not distally.  (This is surprising
because it is the most oft-quoted diagnostic character of the
Enantiornithes, and, along with the shoulder, is the reason for the
"opposite" designation of the birds.  Martin and Kurochkin believe
_Archaeopteryx_ has this feature, and it is thus diagnostic not only for
the Enantiornithes, but also for their Sauriurae.)

        Two characters specifically contemplated on this list, involving
the hand:

* carpometacarpus fused proximally but not distally

* metacarpal III extends further distally than metacarpal II (where manual
digital formula is 1-2-3)

are used by Martin and Kurochkin as diagnostic characters of the
Enantiornithes.  I haven't seen these particular characters addressed by
Chiappe or others, but I'm sure that new papers in the Ostrom festschrift
volume will do so.

        As for the possibility of penguin-like, diving enantiornithines, a
marine occurrence of a North American enantiornithine was addressed in:

Lamb, J.P., Chiappe, L.M., and Erickson, P.G.P.  1993.  A marine
enantiornithine from the Cretaceous of Alabama.  _Journal of Vertebrate
Paleontology_ 13 (suppl. 3):  45A.

although this abstract doesn't specifically address whether this form was a
diver or just a marine occurrence of a volant form (it co-occurs in the
Mooreville Chalk with _Ichthyornis_ fossils).

        Hope this is helpful!

           ____/_\,)                     ..  _   
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                     Jerry D. Harris
                 Fossil Preparation Lab
          New Mexico Museum of Natural History
                   1801 Mountain Rd NW
               Albuquerque  NM  87104-1375
                 Phone:  (505) 899-2809
                  Fax: ; (505) 841-2866