Enantiornithine Bird from the Upper Cretaceous La Colonia Formation of Patagonia, Argentina

[Ben Creisler <bcreisler@gmail.com>]

From: Ben Creisler
bcreisler@gmail.com


A 2011 paper that apparently has not been mentioned yet on the DML.
Based on the abstract, the taxon is apparently unnamed.




Daniel R. Lawver, Aj M. Debee, Julia A. Clarke and Guillermo W. Rougier (2011)
A New Enantiornithine Bird from the Upper Cretaceous La Colonia
Formation of Patagonia, Argentina.
Annals of Carnegie Museum 80(1):35-42
doi: http://dx.doi.org/10.2992/007.080.0104
http://www.bioone.org/doi/abs/10.2992/007.080.0104



Enantiornithes is a diverse clade of Mesozoic birds first recognized
from the Upper Cretaceous sediments of a South American locality in
northern Argentina. Extensive discoveries of Mesozoic birds have since
been made globally, and three other South American localities have
subsequently produced enantiornithine material. Here, we report an
enantiornithine specimen from a new locality in the Upper Cretaceous
La Colonia Formation of Patagonia, Argentina. Although mammals and
other vertebrate fossils have been reported from the site, this new
specimen is the first bird. The specimen, from deposits assessed to be
Maastrichtian in age, is the uncrushed distal end of a right humerus
with well-preserved muscle scars. The following characters support its
referral to Enantiornithes: (1) weakly developed distal condyles; (2)
anteroposterior distal compression and transverse expansion of the
humerus; and (3) distal projection of the ventral epicondyle. The
specimen is differentiated from most other Enantiornithes by the
development of a ridge on the dorsodistal edge of the ventral condyle
and by a thin crest on the ventral margin of the humerus, which is
interpreted as bordering a ventrally displaced area of origin for m.
brachialis. The ridge present on the edge of the ventral condyle is
proposed to be possibly synapomorphic of a previously unrecognized
enantiornithine subclade with a Laurasian and Gondwanan distribution,
while the thin crest on the ventral margin of the humerus is
recognized as a potential autapomorphy of this specimen. The presence
of a dorsal supracondylar tubercle, like that in the new specimen and
other avialans, is shown not to be an indicator of wading ecology as
had been previously proposed. In sum, the new specimen expands our
understanding of South American diversity in Avialae and morphological
diversity in Enantiornithes. Further material will elucidate the
phylogenetic relationships and taxonomic status of the new fossil.