Mystriosuchus planirostris (Meyer, 1863)

Sues, Hans-Dieter & Schoch, Rainer R., 2025, Synopsis of the Triassic reptiles from Germany, Fossil Record 28 (2), pp. 411-483 : 411-483

Mystriosuchus planirostris (Meyer, 1863)

Lectotype.

MCZ VPRA-1018 , part of the antorbital region of the cranium ( Hunt and Lucas 1989).

Type locality.

Neuhaus near Aixheim, Schwarzwald district, Baden-Württemberg.

Type horizon.

Middle Stubensandstein (S 2), Löwenstein Formation (equivalent of Arnstadt Formation), Middle Keuper Subgroup. Age: Late Triassic (Norian: Alaunian).

Referred material.

Hunt and Lucas (1989) also identified a series of rostral fragments in the MCZ collection ( MCZ VPRA-1019 A-C ; MCZ VPRA-1022 A-B ) as paralectotypes. See Hungerbühler (1997). Referred specimens include SMNS 9134 , which includes a complete skull (Fig. 16 A ) first illustrated by E. Fraas (1896).

Diagnosis.

Diagnosed by the following combination of features: rostrum greatly elongated; ratio of rostral to narial plus postnarial length exceeding 2.2; interpremaxillary fossa slit-like; skull roof and narial region with sculpturing of deep pits and blunt ridges (Fig. 16 B ); antorbital depression crescent-shaped; anterior margin of supratemporal fenestra raised; parietosquamosal bar dorsoventrally thick posteriorly with triangular cross-section; squamosal with distinct, overhanging lateral ridge; posterior process of squamosal small; and posttemporal fenestra very small ( Hungerbühler 1997, 2002).

Comments.

Hungerbühler and Hunt (2000) named a second species, Mystriosuchus westphali , which they distinguished from Mystriosuchus planirostris by the greater robusticity of its skull, a massive and shorter snout, the presence of a premaxillary crest, and a possibly more differentiated dentition. Its holotype is a complete cranium ( GPIT-PV -31397 ) from the Middle Stubensandstein (S 2) of the former “ Untere Mühle ” Quarry in Trossingen. This specimen was first reported as Belodon plieningeri by F. Huene (1911). We concur with Kimmig and Spielmann (2011) who argued that Mystriosuchus planirostris and M. westphali likely represent an example of sexual dimorphism rather than distinct species. Zeigler et al. (2003) found a similar situation in the co-occurrence of two species of “ Pseudopalatus ” (now Machaeroprosopus ) in strata of the Upper Triassic (Norian) Chinle Formation exposed in the Canjilon Quarry in New Mexico. One, Machaeroprosopus buceros , has a distinct prenarial crest whereas the other, M. pristinus , lacks this feature. Zeigler et al. (2003) plausibly interpreted this difference as sexual dimorphism. Hungerbühler et al. (2013) disagreed with Kimmig and Spielmann. One of their arguments concerned the relative abundance of the two morphotypes, but their assumption of a 1: 1 sex ratio is questionable because extant crocodylians are known to show sex-biased sex ratios in some populations. The two ‘ species’ of Mystriosuchus have always been recovered as sister-taxa in phylogenetic analyses (e. g., Jones and Butler 2018).

References.

F. Huene (1911, 1922), Westphal (1963), Hungerbühler (1997, 2002), Hunt and Lucas (1989), Hunt and Hungerbühler (2000), Kimmig and Spielmann (2011).

Figures

Figure 16. A. Mystriosuchine parasuchid Mystriosuchus planirostris (SMNS 9134), skull in dorsal view. Scale bar: 10 cm. Courtesy of R. J. Butler. B. Mystriosuchine parasuchid Mystriosuchus planirostris (SMNS 9900), posterior portion of skull in lateral view. Scale bar: 3 cm. Courtesy of R. J. Butler. C. Mystriosuchine parasuchid Nicrosaurus kapffi, cranium (SMNS 5726) and mandible (SMNS 5730) in oblique lateral view. Scale bar: 10 cm.