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Early Triassic theropod footprints
The latest issue of the Australian paleo journal _Alcheringa_ has the
Retallick G.J. (1996) Early Triassic theropod footprints from the Sydney
Basin, Australia. Alcheringa, 20:301-314.
A large rock slab collected in 1913 from the roof of the Bellambi Colliery
in the southern Sydney Basin bears fossil tracks that are now known from
radiometric and chemostratigraphic dating to be earliest Triassic, rather
than latest Permian in age. The tracks show two distinctive features of
reptiles: scale impressions and claw marks. Both manus and pes are
pentadactyl, ectaxonic, semidigitigrade and have an outer interdigital
angle (digits IV-V) greater than the inner interdigital angles. Digit
proportions are consistent with a phalangeal formula of 23333. The fossil
tracks are refered to the ichnospecies _Dycnodontipus bellambiensis_ sp.
nov. They are similar to the kinds of tracks thought to be produced by
_Lystrosaurus_ species. Given the abundance of these species in Early
Triassic faunas of low diversity and the occurrence of members of the
_Lystrosaurus_ fauna in Queensland and Antarctica, chances are good that
this is indeed a trackway of _Lystrosaurus_. If considered to be made by
an animal of that type, the trackway was produced using the primitive
alternate gait, rather than the mammalian amble, by an animal about 84 cm
long and some 22 cms high. Preservation of bones of these creatures would
not be expected given the non-calcareous nature of associated fossil soils
in the Sydney Basin Triassic. Herbaceous lycopods, locally common in these
and other Early Triassic strata worldwide, are among the most likely foods
of these tusked, low-browsing herbivores.
Many say it was a mistake to come down from the trees, some say
the move out of the oceans was a bad idea. Me, I say the stiffening
of the notochord in the Cambrian was where it all went wrong,
it was all downhill from there.