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Ichnogenus Anomoepus morphological variation



From: Ben Creisler
bcreisler@gmail.com


A new paper:


Sebastian G. Dalman and Robert E. Weems (2013)
A New Look at Morphological Variation in the Ichnogenus Anomoepus,
with Special Reference to Material from the Lower Jurassic Newark
Supergroup: Implications for Ichnotaxonomy and Ichnodiversity.
Bulletin of the Peabody Museum of Natural History 54(1):67-124
doi: http://dx.doi.org/10.3374/014.054.0104
http://www.bioone.org/doi/abs/10.3374/014.054.0104



Numerous new trackways of the small, ornithischian dinosaurs
ichnogenus Anomoepus were discovered in the Lower Jurassic
(Hettangian) East Berlin Formation in Holyoke, Massachusetts. This new
material consists of 16 trackways, on two bedding surfaces 1.5 cm
apart, all in close proximity to each other. The abundant pedal and
manual impressions have well-preserved digital pad impressions, and
claw marks are often discernible also. An Osteometric analysis allows
reconstruction of the pedal digits and weight-bearing portions of the
metatarsals. On the basis of their small size, as well as distinctive
features and proportions of both the manus and pes impressions, these
prints are assigned to the ichnospecies Anomoepus lacertoideus (comb.
nov.). Three ichnospecies of Anomoepus can be recognized in the Lower
Jurassic of the Newark Supergroup: A. lacertoideus, A. scambus and A.
crassus. The A. lacertoideus footprints described herein provide
evidence that this small, ornithischian track maker engaged in a
variety of locomotion-related behaviors. Trackways mostly consist of
digitigrade pes prints, reflecting bipedal locomotion, but intervals
of quadrupedal progression also are documented by metatarsal and manus
imprints in seven trackways. The longest trackways, each consisting of
10 to 15 pes impressions, vary in morphology as a result of the
presence or absence of an impression of the distal parts of
metatarsals II and IV. The manus prints show two distinct digital
divarication angles, 120° and 180°, depending on whether the animal
was walking normally or stopping. Variations in substrate consistency
influenced locomotor behavior, as shown by the variable pattern of
body weight distributions on the pedal digits. Such differences are
especially apparent in the longest trackways, which vary in stride and
pace lengths. The trends of the abundant trackways at this site also
suggest group behavior in Anomoepus, something previously unrecorded
for this ichnogenus in the Connecticut River Valley. Evidence from the
East Berlin Formation suggests that ichnogenus Anomoepus is not
monospecific as some authors have suggested.