Sutekhsuchus

Sutekhsuchus Temporal range: Early Miocene
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Order:	Crocodilia
Family:	Gavialidae
Subfamily:	Gavialinae
Genus:	Sutekhsuchus Burke et al., 2024
Type species
Sutekhsuchus dowsoni Fourtau, 1920

Sutekhsuchus (formerly known as Tomistoma dowsoni) is a species of gavialine crocodilian from the Miocene of Libya and Egypt. While this species was originally described as a species of the genus Tomistoma, which includes the modern false gharial, later studies have shown that it was actually a much more derived gavialoid closely related to the Kenyan Eogavialis andrewsi.

History and naming

The species Tomistoma dowsoni was coined in 1920 by René Fourtau on the basis of assorted fragments including a lower jaw and the tip of the snout recovered from the Moghra Formation at Wadi Moghra in Egypt. However, Fourtau did not provide an actual holotype nor did he provide specimen numbers and his material is now thought to be lost. By 1973 a second specimen (NHMUK PV R 4769) had been discovered at the nearby Siwa Oasis and was referred to T. dowsoni by William Roger Hamilton. While multiple studies went on to use this much more complete specimen as a stand in for the holotype of T. dowsoni in phylogenetic analysis, the referral to the species was never questioned throughout most its history. However, many of these studies generally agreed that though originally referred to Tomistoma, T. dowsoni did not directly clade with the modern false gharial. In the year 2000 Christopher Brochu and Philip D. Gingerich published a paper that argued that all tomistomines of the Miocene Mediterranean represented a single taxon, Tomistoma lusitanica. Llinás Agrasar followed this conclusion when describing fossils (MNHN LBE 300–302) from the Maradah Formation at Gebel Zelten, Libya, in 2004, but did note that the animal closely resembled the specimens previously known as Tomistoma dowsoni. In 2015 Stephane Jouve and colleagues once again suggested that T. dowsoni was a valid and distinct species, citing differences between Hamilton's specimen and T. lusitanica. In 2024 Burke and colleagues eventually published a study describing the skull of T. dowsoni in detail as well as evaluating the material referred to the species. In accordance with phylogenetic analysis consistently recovering T. dowsoni as only distantly related to the modern false gharial, a new name was coined: Sutekhsuchus.

The name Sutekhsuchus derives from the Egyptian deities Sutekh, better known as Set, and Sobek. Sobek is the root of the Latin "suchus", which means crocodile and has been used as a suffix in the scientific names of many crocodilians. The reference to Sutekh/Set meanwhile is rooted in the fact that Sutekh is known as the "god of deception", which is paralleled with the fact that Sutekhsuchus was initially taken to be a species of Tomistoma.

Phylogeny

In the 2024 study by Burke and colleagues, both the referred Hamilton skull and the original syntype material was used to determine the relation between Sutekhsuchus and other gavialoids. In this study, the analysis was conducted both with equal weighting of the phylogenetic characters and with implied weighting of phylogenetic characters, meaning that in one version all traits were regarded as equal while in the other some were assumed to be of greater importance. As a consequence, both trees share their general layout, but differ in some of the details. Under equal weighting, the modern false gharial clades with gavialoids from the Eocene of Northern Africa and Europe, forming a monophyletic group outside of Gavialinae that does not include many of the species once assigned to it (most of which instead were found to be relatives of Gavialosuchus and Thecachampsa. Sutekhsuchus was found to be much more derived than these forms and appears to have split off from other gavialoids after the East Asian clade formed by Toyotamaphimeia and Hanyusuchus as well as the largely Cretaceous thoracosaurs. This particular analysis suggests that Sutekhsuchus was most closely related to Eogavialis, specifically E. africanum and E. andrewsi, with the latter as the sister taxon to Sutekhsuchus. Under implied weighting the results are slightly changed. For example, the modern false gharial stands on its own with no close relatives as the basal-most offshoot of Gavialinae, after which the East Asian clade splits off from the subfamily followed by the taxa clustering around Gavialosuchus and Thecachampsa, the opposite order of what is seen under equal weighting, thoracosaurs remain similar in their position relative to Sutekhsuchus, though the clade is much larger. Under implied weighting Sutekhsuchus continues to be recovered as the closest relative of Eogavialis andrewsi, however, E. africanum was found to diverge after the two, making it more closely related to modern gharials. In both analysis the most crown-ward gavialines are those of Neogene South America (gryposuchines) and the genus Gavialis itself. Both phylogenetic trees are shown below.

Gavialoidea †Maomingosuchus Gavialidae †Paratomistoma Tomistoma schlegelii (false gharial) †Dollosuchoides †Kentisuchus †Maroccosuchus Gavialinae †Gavialosuchus †"Tomistoma" calaritanum †"Tomistoma" gaudense †"Tomistoma" lusitanica †Melitosaurus †Thecachampsa †Toyotamaphimeia †Hanyusuchus †Penghusuchus †Eosuchus †"Tomistoma" cairense †Thoracosaurus isorhynchus †Eothoracosaurus †Portugalosuchus †Thoracosaurus neocesariensis †Eogavialis africanum †Eogavialis andrewsi †Sutekhsuchus dowsoni †Aktiogavialis †Argochampsa †Dadagavialis †Piscogavialis †Ikanogavialis †Siquisiquesuchus †Gryposuchus pachakamue †Gryposuchus colombianus †Gryposuchus neogaeus †Gryposuchus croizati †Gavialis lewisi †Gavialis browni Gavialis gangeticus (Indian gharial)

Gavialoidea †Maroccosuchus †Kentisuchus †Dollosuchoides Gavialidae †Maomingosuchus Gavialinae Tomistoma schlegelii (false gharial) †Penghusuchus †Toyotamaphimeia †Hanyusuchus †Melitosaurus †Gavialosuchus †Thecachampsa †"Tomistoma" lusitanica †"Tomistoma" calaritanum †"Tomistoma" gaudense †Paratomistoma †"Tomistoma" cairense †Thoracosaurus isorhynchus †Eosuchus †Eothoracosaurus †Portugalosuchus †Thoracosaurus neocesariensis †Eogavialis andrewsi †Sutekhsuchus dowsoni †Eogavialis africanum †Aktiogavialis †Argochampsa †Piscogavialis †Siquisiquesuchus †Ikanogavialis †Gryposuchus colombianus †Dadagavialis †Gryposuchus pachakamue †Gryposuchus neogaeus †Gryposuchus croizati †Gavialis lewisi †Gavialis browni Gavialis gangeticus (Indian gharial)