Based on its uniquely inset tooth row
(Figs. 1–3) Erpetosuchus (Newton 1894; Late Carnian, Late Triassic) has been a traditional enigma taxon.
According to Wikipedia,
“The relationship of Erpetosuchus to other archosaurs is uncertain. In 2000 and 2002, it was considered a close relative of the group Crocodylomorpha, which includes living crocodylians and many extinct relatives. However, this relationship was questioned in a 2012 analysis that found the phylogenetic placement of Erpetosuchus to be very uncertain.”
“Benton and Walker (2002) found the same sister-group relationship and proposed the name Bathyotica for the clade containing Erpetosuchus and Crocodylomorpha.”
“Nesbitt and Butler (2012) included Erpetosuchus within a more comprehensive phylogenetic analysis and found it to group with the archosaur Parringtonia (Fig. 1) from the Middle Triassic of Tanzania. Both were part of the clade Erpetosuchidae. Nesbitt and Butler did not find support for the sister-group relationship between Erpetosuchus and Crocodylomorpha. Instead, erpetosuchids formed a polytomy or unresolved evolutionary relationship at the base of Archosauria along with several other groups. It could take many positions within Archosauria, but none were as a sister taxon of Crocodylomorpha.”
A recent review of the Crocodylomorpha
subset of the large reptile tree (LRT, 1660+ taxa; Fig. 4) knocked Erpetosuchus out of the Crocodylomorpha and out of the Archosauria. Erpetosuchus and other members assigned to the Erpetosuchidae (Pagosvenator, Parringtonia, Tarjadia (Figs. 2-3), but not the basal marine crocodile Dyoplax, at least not yet) now nest with Decuriasuchus (Figs. 2–3) in the LRT. This clade nests between Rauisuchia and Poposauria + Archosauria (Fig. 4).
The small size of Erpetosuchus
(Fig. 3) is a derived trait, following several much larger ancestors. Alas, as far as we know, Erpetosuchus was a terminal taxon, leaving no descendants.
Why was Erpetosuchus traditionally considered ‘crocodile-like’?
The extreme anterior lean of the quadrate and quadratojugal are typical crocodile traits shared by convergence with members of the clade Erpetosuchidae (including Decuriasuchus).
Eagle-eyed readers may note
a few other changes in the Crocodylomorpha subset of the LRT (Fig. 4). We’ll deal with these in future blogposts.
Benton MJ and Walker AD 2002. Erpetosuchus, a crocodile-like basal archosaur from the Late Triassic of Elgin, Scotland, Zoological Journal of the Linnean Society 136:25-47.
Nesbitt SJ and Butler RJ 2012. Redescription of the archosaur Parringtonia gracilis from the Middle Triassic Manda beds of Tanzania, and the antiquity of Erpetosuchidae. Geological Magazine: 1. doi:10.1017/S0016756812000362
Nesbitt SJ, Stocker MR, Parke WGr, Wood TA, Sidor CA and Angielczy KD 2018. The braincase and endocast of Parringtonia gracilis, a Middle Triassic suchian (Archosaur: Pseudosuchia) Journal of Vertebrate Paleontology 37, Memoir 17: Vertebrate and Climatic Evolution in the Triassic Rift Basins of Tanzania and Zambia.
Newton TE 1894. Reptiles from the Elgin Sandstone—Description of two new genera. Philosophical Transactions of the Royal Society of London, B, 185:573–607.