Dyoplax skull under DGS

Today,
the benefits of better data are presented.

Earlier
we nested the sole example of a traditional enigma croc, Dyoplax (Figs, 1, 2; Fraas 1867), in the large reptile tree (LRT 1559 taxa) based on a 19th century drawing (Fig. 1). With that sketchy data, Dyoplax nested basal to the clade(s) of marine crocodiles.

Figure 1. Dyoplax arenaceus Fraas 1867 is a mold fossil recently considered to be a sphenosuchian crocodylomorph. Here it nests as a basal metriorhynchid (sea crocodile) in the Late Triassic.

Figure 1. Dyoplax arenaceus Fraas 1867 is a mold fossil recently considered to be a sphenosuchian crocodylomorph. Here it nests as a basal metriorhynchid (sea crocodile) in the Late Triassic.

Maisch et al. 2013
provided a closeup photo and interpretive drawing of the skull (Fig. 2). Their interpretation and analysis tentatively put Dyoplax close to another traditional enigma, the croc with indented jaw margins, Erepetoscuchus. No cladogram was presented. Rather a list of shared traits was proposed by them and by prior authors. Yes, by listing traits, they were ‘Pulling a Larry Martin.’  The keywords ‘Dibothrosuchus‘, ‘Thalattosuchia’ and ‘marine’ were not found in the pdf text. So, yes, evidently they were excluding taxa.

By contrast,
using the new data from the skull published in Maisch et al., together with DGS and the LRT all work together to keep Dyoplax at the base of the marine crocodiles, far from Erpetosuchus. Dibothrosuchus remains the outgroup taxon for the sea crocs + river crocs.

Figure 3. Added 08/09/19 from Maisch et al. 2013. DGS sutures do not match sutures found by Maisch et al. (drawing) Hypothetical missing parts based on phylogenetic bracketing ghosted on in color

Figure 3. Added 08/09/19 from Maisch et al. 2013. DGS sutures do not match sutures found by Maisch et al. (drawing) Hypothetical missing parts based on phylogenetic bracketing ghosted on in color

Sea crocs have a longer rostrum
with maxillae that contact one another dorsally. The nares merge. 

Figure 7. Dibothrosuchus nests basal to all later quadrupedal crocs, including marine crocs, in the LRT.

Figure 4. Dibothrosuchus nests basal to all later quadrupedal crocs, including marine crocs, in the LRT. The hind limbs are unknown.

Subtext to this blogpost:
Several mistakes (using the old etching) need not misdirect the software as it employs hundreds of traits to nest hundreds of taxa. I have employed less than optimal data (Fig. 1) often enough. Taxon inclusion remains the key to understanding systematics. Without relevant taxa, enigmas and apparently unique taxa are more difficult to nest.


References
Fraas O 1867. Dyoplax arenaceus, ein neuer Stuttgarter Keuper-Saurier. Jh. Verein vaterländ. Naturk. Württemberg 23:108-112; Stuttgart.
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.

wiki/Dyoplax

 

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