Cutting the Gordian knot: a historical and taxonomic revision of the Jurassic crocodylomorphMetriorhynchus

Abstract

Metriorhynchidae was a clade of extinct crocodylomorphs that adapted to a pelagic lifestyle, becoming a key component of Mesozoic lagoonal and coastal marine ecosystems. The type genus Metriorhynchus is one of the best-known genera of Mesozoic crocodylomorphs, and since the mid-19th century, the ‘concept’ of Metriorhynchus has become associated with the referred species Me. superciliosus. Historically Metriorhynchus has been the most species-rich genus in Metriorhynchidae, with most Middle Jurassic species and many Late Jurassic species referred to the genus at some point in their history. However, the type species Me. geoffroyii has largely been omitted in the literature. Its type series is a chimera of multiple metriorhynchid species, and a type specimen has never been designated. Moreover, phylogenetic analyses have repeatedly shown that the 19th–20th century concept of Metriorhynchus is not monophyletic – to the point where only referring every metriorhynchid species, and some basal metriorhynchoids, to the genus would render it monophyletic. Herein we designate a lectotype for Me. geoffroyii, re-describe it and restrict the genus Metriorhynchus to the type species. We also establish the new genus Thalattosuchus for Me. superciliosus, thereby cutting the ‘Gordian knot’ of Metriorhynchus with Th. superciliosus.

A new species of Cricosaurus (Thalattosuchia, Metriorhynchidae) based upon a remarkably well-preserved skeleton from the Upper Jurassic of Germany

“…Overall, the strict consensus topology recovered here (Figure 8; Table 1) is very similar to the one presented in Young et al (2020aYoung et al ( , 2020b and Herrera et al (2021aHerrera et al ( , 2021b. Note, herein we will solely focus on the internal relationships of Metriorhynchinae.…”

“…The character changes made herein has had no impact on the position of Cricosaurus albersdoerferi (BMMS-BK 1-2), previously referred to as 'the Solnhofen Cricosaurus' in the phylogenetic analyses of Young et al (2020aYoung et al ( , 2020b. It is consistently recovered within Cricosaurus 'subclade A'.…”

“…A, unweighted topology; B, strongly down-weighted topology (k=1); C, all other weighting analyses topology (k=3, 7, 10, 20, and 50). results and those of Young et al (2020b) are the removal of the two Cuban metriorhynchine metriorhynchids. Overall, their removal has led to more consistent results for the internal relationships of Metriorhynchinae, with three differing topologies recovered.…”

“…The dataset employed forms part of the ongoing Crocodylomorph Super-Matrix Project and is the phylogenetic framework for the Edinburgh-based CrocTransition Project. This dataset (referred to as the Hastings + Young matrix, or HY matrix) is continually being revised (e.g., Ristevski et al, 2018;Ősi et al, 2018Ősi et al, , Foffa et al 2019Sachs et al 2019;Young et al 2020aYoung et al , 2020bJohnson et al 2020), and herein we revise the most recent version in Young et al (2020b). This revision consisted of the following: we added seven new craniomandibular pneumatic characters, moved a character from the braincase region of the dataset to the pneumaticity section, revised the metriorhynchid salt gland character, altered character 440 from a binary to an ordered multistate character, and removed the tail fluke character that was apomorphic for Cricosaurus albersdoerferi as that region of the tail is reconstructed.…”

The braincase and inner ear of ‘Metriorhynchus’ cf. ‘M.’ brachyrhynchus – implications for aquatic sensory adaptations in crocodylomorphs

“…While Lydekker (1888:96) initially referred NHMUK PV OR 32617 to Metriorhynchus superciliosus (now referred to the genus Thalattosuchus; Young et al, 2020), we refer it to 'M.' cf.…”