Not Arizonasaurus, but Postosuchus, made the giant Isochirotherium tracks

A recent paper by Diedrich (2015) purported to match the Arizonasaurus to giant Isochirotherium tracks from the Middle Triassic of Germany (Fig. 1).

The problem is,
no manus or pes are known for Arizonasaurus. Furthermore, all related taxa in the large reptile tree have digit 3 the longest, and all digits are elongate. The giant Isochirotherium tracks indicate that both digits 2 and 3 are the longest, and they are short. So matching candidates have to be found elsewhere, not close to Arizonoasaurus (although the size and time are right!).

Among the 504 taxa in the large reptile tree that are possible candidates with digits 2 and 3 the longest are Erythrosuchus (Fig. 1), Shansisuchus, Lotosaurus and the Postosuchus alisonae (Peyer 2008, Fig. 1). It turns out that only the latter is the best match when scaled up to the size of P. kirkpatrchicki (Chatterjee 1985, Fig. 1).

Figure 1. Giant Isochirotherium tracks matched to Postosuchus alisonae scaled up to the size of P. kirkpatrcki.

Figure 1. Giant Isochirotherium tracks matched to Postosuchus alisonae scaled up to the size of P. kirkpatrcki. Click to enlarge. This taxon was not considered originally because it is Late Triassic and the tracks are Middle Triassic.

Postosuchus was not mentioned in the text
because Diedrich (recent email) knew Postosuchus was Late Triassic, not Middle Triassic. He did not accept the idea that between the origin, radiation and extinction of Postosuchus there might have been a Middle Triassic relative.

Diedrich also saw the small manus tracks and assumed they were produced by a large poposaurid. Unfortunately, Arizonasaurus does not nest with poposaurids either. And poposaurids, other than Lotosaurus, do not match the track morphology.

It would have been helpful,
I suppose, to do what I did and make a list of possible candidates from a large list, AND THEN delete the possible candidates one by one as bad matches. Other than that phylogenetic bracketing mismatch, Diedrich does good work with excellent graphics. It took a leap of faith, I suppose to match tracks to a taxon for which no manus or foot is known.

C. Diedrich writes:
“Watch my ARTE docu – there you see Arizonasaurus (Ticinosuchus and Macrocnemus) walking in my point of view combining trak/sleketal records”:

Chatterjee S 1985. Postosuchus, a new Thecodontian reptile from the Triassic of Texas and the origin of Tyrannosaurs. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences 309 (1139): 395–460. doi:10.1098/rstb.1985.0092.
Diedrich C 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 Evaporites  DOI 10.1007/s13146-014-0228-z
Novak SE 2004. A new specimen of Postosuchus from the Late Triassic Coelophysis Quarry, siltstone member, Chinle Formation, Ghost Ranch, New Mexico. M.S. thesis, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina.
Peyer K Carter, JG, Sues H-D, Novak SE, and Olsen PE 2008. A new Suchian Archosaur from the Upper Triassic of North Carolina. Journal of Vertebrate Paleontology 28 (2): 363–381. doi:10.1671/0272-4634(2008)28[363:ANSAFT]2.0.CO;2.


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