Atoposauridae Gervais 1871

Bajor, Daniel, Alarcón Muñoz, Jhonatan, Lizama Catalán, Álvaro & Rubilar Rogers, David, 2022, An Isolated Mesoeucrocodylian Tooth Crown From The Lower Cretaceous Cerro La Isla Pterosaur Site In The Atacama Region, Northern Chile, Boletín del Museo Nacional de Historia Natural, Chile 71 (2), pp. 5-22 : 13-14

Atoposauridae Gervais 1871

Atoposaurids were small-bodied terrestrial to semi-aquatic neosuchians with heterodont dentition (Tennant et al. 2016; Young et al. 2016). Although some atoposaurids (e.g., Alligatorellus Gervais 1871 and Theriosuchus Owen 1878 ) possess pseudo-caniniform teeth with apicobasal ridges in the anteriormost region of their jaws, their similarity with SGO.PV.1160 is only superficial (Tennant and Mannion 2014; Tennant et al. 2016). In addition, though Tennant et al. (2016) restricted the group to include only three genera, thereby reducing the biostratigraphic range of Atoposauridae to the Upper Jurassic of western Europe; even prior to this revision, the only tentative records from Gondwana were from Africa and Madagascar (Young et al. 2016) and no atoposaurid fossils have ever been discovered in South America. Therefore, SGO.PV.1160 belongs to a different crocodyliform taxon.

Thalattosuchia

Thalattosuchia Fraas 1901 (sensu Young and Andrade 2009) are marine crocodyliforms that lived during the Sinemurian (Lower Jurassic)-Barremian (Lower Cretaceous) interval (Gasparini et al. 2000; Jouve et al. 2016; Cortes et al. 2019). The phylogenetic affinities of the group are uncertain; though most recent analyses have recovered Thalattosuchia as non-eusuchian neosuchians (e.g., Pol et al. 2014; Leardi et al. 2015; Dal Sasso et al. 2017; Ristevski et al. 2018; Arribas et al. 2019; Fernández Dumont et al. 2020; Novas et al. 2021). Thalattosuchia comprises two groups, the Teleosauroidea Geoffroy Saint-Hilaire 1831 (sensu Young and Andrade 2009) and the Metriorhynchoidea Fitzinger 1843 (sensu Young and Andrade 2009). Based on their similar morphology to extant crocodylians, teleosauroids are considered to have been relatively unspecialized to their marine ecology (e.g., Young et al. 2010; Wilberg 2015; Ősi et al. 2018). Though they predominantly inhabited coastal areas, lagoons and brackish estuarine waters, a few teleosauroids have been reported from Asian continental freshwater environments (e.g., Young 1948; Martin et al. 2019). The presence of the group in South America has been recently confirmed by the discovery of the partial postcranial skeleton of a large indeterminate teleosauroid from the upper Barremian (Lower Cretaceous) of Colombia ( Cortes et al. 2019). Regarding their dentition, possessing teeth with apicobasal ridges is a teleosauroid synapomorphy (Johnson et al. 2020). Johnson et al. (2020) separated Teleosauroidea into two families: Teleosauridae and Machimosauridae. Teleosauridae are characterized by their smaller body size and distribution restricted to Laurasia. Machimosauridae were considerably larger and more widely distributed, being present in what is now western Europe as well as northern and eastern Africa (Johnson et al. 2020). So far, only the genus Machimosaurus von Meyer 1837 is known to have survived into the Lower Cretaceous (Jouve et al. 2016), while all other taxa seem to have disappeared in the Kimmeridgian (Upper Jurassic) (Johnson et al. 2020). Due to its large size and Lower Cretaceous age, the teleosauroid specimen from Colombia is likely a representative of the tribe Machimosaurini (Jouve et al. 2016; Cortes et al. 2019). The comparatively wider distribution of Machimosauridae is also consistent with where it was discovered. Machimosaurins were large-bodied macro/durophagous teleosauroids, characterized by possessing blunt, bicarinate tooth crowns with serrated carinae (Jouve et al. 2016; Johnson et al. 2020). Based on our current knowledge of the teleosauroid fossil record, the tooth from Cerro La Isla could only belong to a machimosaurin. However, the dental morphology of this group differs so much from that of SGO.PV.1160 that we discard this possibility.

Regarding Metriorhynchoidea, at least four (SÉon et al. 2020) and possibly six (Sachs et al. 2020) lineages survived into the Lower Cretaceous, the most recent currently known fossil being an isolated tooth crown from the lowermost Aptian of Sicily ( Chiarenza et al. 2015). However, these lineages are all represented by derived forms (i.e., metriorhynchids) with a battery of adaptations to their pelagic ecology (such as a hydrodynamic body plan, paddle-like limbs, a hypocercal tail fin and hypertrophied nasal exocrine salt glands; Young et al. 2010; Wilberg 2015; Ősi et al. 2018; SÉon et al. 2020; Young et al. 2020), whose presence in a continental setting approximately 20-50 km inland is too unlikely to be considered. Therefore, SGO.PV.1160 is not a metriorhynchoid tooth crown.