Arizonasaurus(?) (poposaur) tracks from Middle Triassic of Germany

[Ben Creisler <bcreisler@gmail.com>]

Ben Creisler
bcreisler@gmail.com


A new paper:

Cajus Diedrich (2015)
Isochirotherium trackways, their possible trackmakers
(?Arizonasaurus): intercontinental giant archosaur migrations in the
Middle Triassic tsunami-influenced carbonate intertidal mud flats of
the European Germanic Basin.
Carbonates and Evaporates (advance online publication)
DOI: 10.1007/s13146-014-0228-z
http://link.springer.com/article/10.1007/s13146-014-0228-z

A remarkable Middle Triassic (Pelsonian, Anisian) fossil track site at
Bernburg in Central Germany permits reconstruction of a tetrapod fauna
at the point of recovery when early poposaur quadruped dinosaurs
diversificated globally. The site has yielded numerous tetrapod and
thousands of arthropod horseshoecrab tracks from several levels in
intertidal biolaminites with intercalated storm and seismic-influenced
carbonates. The tetrapod tracks, Procolophonichnium, Rhynchosauroides,
Chirotherium, and Isochirotherium, are assigned to smaller
Archosauromorpha and large Archosauria. The largest chirotheroid
tracks Isochirotherium herculis (Egerton in Proc Geol Soc London
3:14–15, 1838) reach up to 350-mm-long pes sizes and 120-mm-long manus
imprints. Those were most probably made by a 5-m-long poposauroid
archosaur like Arizonasaurus, based on matching skeleton anatomy and
trackways including a new three-dimensional model of those giants in
locomotion. A first German poposauroid bone record is added herein
with a scapula from shallow marine carbonates of similar Pelsonian
ages. These crurotarsan archosaurs were at the top of their food
chains globally, and fed most probably on smaller tetrapods
(Hescheleria, Macrocnemus), the latter also represented well by long
behavioural escaping Rhynchosauroides trackways. The smaller reptiles
may have fed especially on “Millions” of horseshoecrab eggs in those
arthropod reproduction seasons in the intertidal carbonate mud flats.
Such tidal flats and sabkhas extended over hundreds of square
kilometres surrounding the Germanic Basin in Central Europe in the
Middle Triassic, representing a drastic change in the
palaeoenvironment of central Pangaea, and a possible trigger for
continuing diversification of archosauromorphs and eventually
dinosaurs. The horseshoecrab reproduction seasons seem to have caused
a food chain reaction along the southern Pangaean (northern Tethys)
coast in carbonate mud flats between Northern America, Africa, Europe
and China, with possibly long-distance migrations of poposauroids such
as Arizonasaurus, whose bones were found in terrestrial to shallow
marine carbonate deposits in terrest to coastal context.