Bird-like tracks from Late Triassic (new Nature issue)

[bh480@scn.org]

The new issue of Nature has the following article of 
interest:
MELCHOR, RICARDO N., SILVINA DE VALAIS & JORGE F. GENISE, 
2002. Bird-like fossil footprints from the Late Triassic. 
Nature 417, 936 - 938 (2002).
The paper describes:
"well-preserved and abundant footprints with clearly avian 
characters from a Late Triassic redbed sequence of 
Argentina, at least 55 Myr before the first known skeletal 
record of birds. These footprints document the activities, 
in an environment interpreted as small ponds associated 
with ephemeral rivers, of an unknown group of Late 
Triassic theropods having some avian characters.....
"(1) an overall similarity to modern bird footprints; (2) 
footprints that are wider than they are long (not 
considering the hallux) and of small size; (3) slender 
digit impressions; (4) a wide angle between digits II and 
IV; (5) a posterior or posteromedial hallux impression, 
visible both in shallow and deep tracks; (6) slender claws 
showing distal curvature of lateral and medial claws away 
from the foot axis; and (7) a sole or metatarsal-
phalangeal impression is visible in some footprints, where 
digits II to IV converge. Additional indications of an 
avian affinity are afforded by comparison with tracks of 
modern waterbirds and waders.
"Whatever the ichnotaxonomic affinities of these 
footprints, their producers are unknown from Late Triassic 
skeletal remains. In particular, the Late Triassic 
theropodan record is sparse and no theropod shows evidence 
of an avian-like reversed hallux. Consequently, these bird-
like footprints can only be attributed to an unknown group 
of theropods showing some avian characters."