Metriorhynchinae Fitzinger, 1843

Young, Mark T., Wilberg, Eric W., Johnson, Michela M., Herrera, Yanina, Brandalise, Marco de Andrade, Brignon, Arnaud, Sachs, Sven, Abel, Pascal, Foffa, Davide, Fernández, Marta S., Vignaud, Patrick, Cowgill, Thomas & Brusatte, Stephen L., 2024, The history, systematics, and nomenclature of Thalattosuchia (Archosauria: Crocodylomorpha), Zoological Journal of the Linnean Society 200 (2), pp. 547-617 : 600

Metriorhynchinae Fitzinger, 1843 (Zoological Code)

Metriorhynchinae Lydekker 1888 A: 91, converted clade name (PhyloCode)

RegNum registration number1018. Type genus: Metriorhynchus von Meyer, 1832 .

Etymology

‘Pertaining to Metriorhynchus ’. The stem Metriorhynch - is based on the genus Metriorhynchus . - inae, is a Latin feminine plural suffix for ‘pertaining to’. Under Article 29.2 of the Zoological Code, the suffix - inae denotes a subfamily rank within the family-group.

Geological range

Middle Jurassic (middle Callovian) to Early Cretaceous (early Valanginian) ( Andrews 1913, Young et al. 2010, Sachs et al. 2020).

PhyloCode phylogenetic definition

The smallest clade within Metriorhynchidae containing Rhacheosaurus gracilis von Meyer, 1831 , Metriorhynchus brevirostris ( Holl 1829) , and Gracilineustes leedsi ( Andrews 1913) .

Reference phylogeny

Fig. 3 .

Zoological Code diagnosis and PhyloCode diagnostic apomorphies

Metriorhynchid crocodylomorphs with the following unique combination of characters (4): reduction in external ornamentation on the maxilla (shared with the South American ‘ Metriorhynchus ’ species, Torvoneustes , the ‘E’-clade, Plesiosuchus , Geosaurus , and Dakosaurus andiniensis ) (18.0–2); lack of ornamentation on the intertemporal bar (shared with Torvoneustes , Geosaurus , and Dakosaurus ) (24.1); posterodorsal retraction of the posterior margin of the narial fossa (shared with Torvoneustes and the ‘E’-clade) (104.2–6); the humerus is shorter than the scapula (749.2).

Composition

Gracilineustes , Maledictosuchus , Metriorhynchus , and the subclade Rhacheosaurini .

Comments

Authorship: While the nomen Metriorhynchinae was first used by Lydekker (1888a), under the Zoological Code Fitzinger 1843 is the nominal authority. The nominal author of a family-group is the author who first erected a family-group taxon that is valid (in fulfilment of Article 11), and in accordance with the Zoological Code Principle of Coordination applied to family-group names (Article 36.1). Under the PhyloCode, the nominal authority is Lydekker (1888a).

Prior phylogenetic definition: Young and Andrade (2009) defined Metriorhynchinae as the most inclusive clade including Metriorhynchus geoffroyii von Meyer, 1832 , but not Geosaurus giganteus ( von Sömmerring 1816) . Here we have decided to choose a more stable clade to attach the nomen Metriorhynchinae to, to ensure future ergotaxonomic and nomenclatural stability. In some datasets Thalattosuchus superciliosus is the basalmost member of Metriorhynchinae (e.g. Young et al. 2021), whereas in other datasets Thalattosuchus falls outside of Metriorhynchidae sensu Young and Andrade (2009) (see: Wilberg 2015 b, Wilberg et al. 2023). Given the instability of Thalattosuchus , and how well supported the Gracilineustes + Rhacheosaurini clade is, we have decided to make the latter Metriorhynchinae .

Discussion: The most recent list of characters used to diagnose Metriorhynchinae comes from Young and Andrade (2009). However, our knowledge of thalattosuchians has expanded since then, and only three of those characters can define a clade: atlas intercentrum subequal in length to atlas centrum (675.1); posterior cervical vertebra centra length is less than centrum height (697.2); tibia being shorter than the femur (less than 40%) (805.4). Unfortunately, these characters are not well sampled, and the final character also unites Neustosaurus with Metriorhynchinae . The Valanginian genera Enaliosuchus and Neustosaurus are extremely poorly understood ( Raspail 1842, Koken 1883, Piveteau 1928, Sachs et al. 2020) and them being a clade of early diverging metriorhynchines creates a ghost lineage spanning from the Valanginian into the Bathonian. Moreover, the position of Thalattosuchus superciliosus is unstable between different datasets. Sometimes Thalattosuchus is recovered as the first early diverging metriorhynchine (e.g. Young et al. 2021), whereas in other datasets Thalattosuchus is the sister-taxon to Metriorhynchinae + Geosaurinae ( Wilberg 2015 b, Wilberg et al. 2023). Given the instability of Thalattosuchus , and how well supported the Gracilineustes + Rhacheosaurini clade is, we have decided to make the latter clade Metriorhynchinae .

Figures

Figure 3. The equal weights, no constraints strict consensus topology (C0). Length = 4164, CI = 0.303, RI = 0.831, RC = 0.251, HI = 0.697, number of most parsimonious cladograms hit the hold limit.Phylogeny pruned to highlight Thalattosuchia (see Supporting Information, Appendix S2, Fig. S1 for the entire topology). A, Crocodylomorpha; B, Crocodyliformes; C, Thalattosuchia; D, Neothalattosuchia; E, Teleosauridae; F, Teleosaurinae; G, Aeolodontini; H, Machimosauridae; I, Machimosaurinae; J, Machimosaurini; K, Euthalattosuchia; L, Metriorhynchidae; M, Metriorhynchinae; N, Rhacheosaurini; O, Geosaurinae; P, Geosaurini. Green lines highlight non-neothalattosuchian thalattosuchians, orange lines highlight teleosauroid thalattosuchians, and blue lines highlight metriorhynchoid thalattosuchians.Images from PhyloPics.org, with the teleosauroid by Scott Hartman, and the metriorhynchid by Dmitry Bogdanov (vectorized by T. Michael Keesey), the only change made was to their colouration, and their license is: https://creativecommons.org/licenses/by/3.0/.