Three big crocs: Dyrosaurus, Sarcosuchus and Gryphosuchus, enter the LRT

A few days ago
the gharial, Gavialis, entered the large reptile tree (LRT, 1885+ taxa; subset Fig. 4) at an unexpected, but often compared node: at the base of the pre-sea crocs: the teleosaurids and the sea crocs, the thalattosuchids (= metriorhynchids).

Salas-Gismondi et al. 2016 wrote:
“Numerous unresolved issues hinder understanding of the origin, time of divergence, and patterns of adaptive radiation of gavialoid crocodylians. Whereas molecular data sets favor a close relationship and an Eocene or even Neogene divergence between the Indian gharial Gavialis gangeticus and the Indonesian false gharial Tomistoma schlegelii, morphological phylogenies suggest that:

1) these two extant longirostrine species are much more distantly related,
2) their elongated skulls evolved convergently, and
3) the oldest fossil gavialoid dates back to the Cretaceous Period in North America, Europe, and Africa.

In fact, analyses of extant Gavialis and its nearest fossil relatives do not provide strong support for their phylogenetic affinities with any other crocodylian clade, probably as part of what Clark 1994 called the “longirostrine problem”.

According to results recovered by the LRT
(subset Fig. 4) Gavialis and Tomistoma are indeed:
1) distantly related,
2) their elongated skulls evolved convergently, and unexpectedly
3) their last common ancestor, Dyoplax, is from the Late Triassic.

Let’s add three more longirostrine taxa
(Figs. 1–3) to see what happens to the LRT.

Number 1 big croc
When a Miocene gavialoid, Gryphosuchus (Fig. 1) was added to the LRT it nested predictably with Gavialis without moving Gavialis from the base of the pre-sea crocs, the teleosaurids and the flippered sea crocs, in the Thalattosuchia. This clade has a rather consistent upper temporal fenestra larger than the orbit. Gryposuchus pachakamue (Gurich 1912, Salas-Gismondi et al. 2016; Miocene, 70mya; MUSM 987) is from the Amazon of South America. Some members of this genus are among the largest crocodylomorphs on record.

Number 2 big croc
gigantic, Early Cretaceous, Sarcosuchus (Fig. 2) nested in the LRT with Gryphosuchus (Fig. 1) and Gavialis. Sarcosuchus imperator (de Broin and Taquet 1966, Sereno et al. 2001; 9m est length) is from North Africa. Note the overhanging and laterally expanded premaxilla.

Number 3 big croc
Odd, Early Eocene, Dyrosaurus (Fig. 3) nested in the LRT basal to both the Gavialis clade and the sea-croc clade. Dyrosaurus has a long list of traits that make it unique (so far) among tested croc taxa in the LRT. Dyrosaurus phosphaticus (Thomas 1893; Early Eocene; 6m in length) is basal to Gavialis and the sea crocs, derived from Dyoplax in the LRT. Tall neural spines and a crazy double-layered postorbital distinguish this taxon. The mandible lacks a fenestra and the retroarticular processes are the largest in the Tetrapoda. The scapula is dorsally expanded.

In the LRT Early Jurassic Pelagosaurus
(Fig. 5) is moving further away from other thalattosuchians with each of these additions. According to Wikipedia, “The systematic taxonomy of Pelagosaurus has been fiercely disputed over the years, and was assigned to Thalattosuchia after its systematics within Teleosauridae were disputed.” Perhaps that is so because Pelagosaurus is closer to Gavialis than to Teleosaurus, according to the LRT.

The LRT is starting
to provide one solution to “the longirostrine problem.” Perhaps more taxa are needed, but the previous solution to the nesting of Gavialis is holding without shifting. Whether this novel hypothesis of interrelationships becomes accepted or not is up to others who test it on their own. Readers should note, it is difficult to find any two peer-reviewed published croc cladograms that are identical to one another if they were created independently, rather than borrowed.

References
Brochu CA 1997. Morphology, fossils, divergence timing, and the phylogenetic relationships of Gavialis. Systematic Biology 46(3):479–522.
de Broin F and Taquet P 1966. Découverte d’un Crocodilien nouveau dans le Crétacé inférieur du Sahara. C. R. Acad. Sci. Paris (in French). 262.
Bronn HG 1841. Über die fossilen Gaviale der Lias-Formation und der Oolithe. Archiv für Naturgeschichte, Berlin 8:77–82.
Fraas O 1867. Dyoplax arenaceus, ein neuer Stuttgarter Keuper-Saurier. Jh. Verein vaterländ. Naturk. Württemberg 23:108-112; Stuttgart.
Gmelin JF 1789. Amphibia – Pisces. In: Gmelin J.F. (Ed.) Caroli a Linnaei Systema Naturae per Regna Tria Naturae, Ed. 13. Tome 1(3). G.E. Beer, Lipsiae [Leipzig]. pp. 1033-1516.
Lucas SG, Wild R, Hunt AP 1998. Dyoplax O. Fraas, a Triassic sphenosuchian from Germany. Stuttgarter Beiträge zur Naturkunde, B. 263: 1–13.
Maisch MW, Matzke AT and Rathgeber T 2013. Re-evaluation of the enigmatic archosaur Dyoplax arenaceus O. Fraas, 1867 from the Schilfsandstein (Stuttgart Formation, lower Carnian, Upper Triassic) of Stuttgart, Germany. Neues Jahrbuch für Geologie und Paläontologie – Abhandlungen. 267 (3): 353–362.
Salas-Gismondi R, Flynn JJ, Baby P, Tejada-Lara JV, ClaudeJ and Antoine P-O 2016. A New 13 Million Year Old Gavialoid Crocodylian from Proto- Amazonian Mega-Wetlands Reveals Parallel Evolutionary Trends in Skull Shape Linked to Longirostry. PLoS ONE 11(4): e0152453. doi:10.1371/journal.pone.0152453
Sereno PC, Larson, HCE, Sidor CA and Gado B 2001. The Giant Crocodyliform Sarcosuchus from the Cretaceous of Africa. Science. 294(5546):1516–9.
Steel R 1973. Crocodylia. Handbuch der Paläoherpetologie, Teil 16. Stuttgart: Gustav Fischer Verlag, 116 pp.

wiki/Gryposuchus
wiki/Sarcosuchus
wiki/Dyrosaurus