Geosaurini Bonaparte 1845

Geosaurini Bonaparte, 1845 (Zoological Code)

Geosaurini Cau and Fanti 2011: 551, converted clade name (PhyloCode)

RegNum registration number 1021.

Type genus: Geosaurus Cuvier 1824.

Etymology

‘Pertaining to Geosaurus ’. The stem Geosaur - is based on the genus Geosaurus. - ini is a Latin masculine plural suffix for ‘pertaining to’. Under Article 29.2 of the Zoological Code, the suffix - ini denotes a tribe rank within the family-group.

Geological range

Middle Jurassic (early Callovian) to Early Cretaceous (earliest Aptian) (Young et al. 2013, 2023 a, Chiarenza et al. 2015, Foffa et al. 2018, Sachs et al. 2020).

PhyloCode phylogenetic definition

The smallest clade within Metriorhynchidae containing Tyrannoneustes lythrodectikos Young et al., 2013, Geosaurus giganteus (von Sömmerring 1816), Torvoneustes carpenteri (Wilkinson et al. 2008), and Dakosaurus maximus (Plieninger 1846).

Reference phylogeny

Fig. 3.

Zoological Code diagnosis and PhyloCode diagnostic apomorphies

Metriorhynchid crocodylomorphs with the following unique combination of characters (4): prefrontal lateral border is a continuous convex curve, with an inflexion point of approximately 60–70° from the anteroposterior axis of the skull (209.1); coronoid process ventral to both the retroarticular process and glenoid process (488.1); deeply excavated surangulodentary groove (529.2); enlargement of the anterior maxillary tooth crowns (626.1–2).

Composition

Tyrannoneustes, Purranisaurus, Torvoneustes, the subclade Geosaurina, the subclade Plesiosuchina, the subclade Dakosaurina, and multiple taxa that do not have a valid generic assignment.

Comments

Authorship: The nomen Geosaurini was first used by Cau and Fanti (2011), however, under the Zoological Code Bonaparte 1845 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, Cau and Fanti (2011) is the nominal authority.

Prior phylogenetic definition: Cau and Fanti (2011) defined Geosaurini as the least inclusive clade, including Geosaurus giganteus (von Sömmerring 1816), Torvoneustes carpenteri (Wilkinson et al. 2008), and Dakosaurus maximus (Plieninger 1846). Here we have added Tyrannoneustes lythrodectikos to the list of internal specifiers.

Characteristics: Many of the tooth crown characters (including those relating to the reduction in number, increase in crown size, and those scoring for contiguous denticles) independently evolved in lineages within Geosaurini rather than at the base of the clade (e.g. see: Foffa et al. 2018). The discovery that the geosaurin lineages originated in the Middle Jurassic (e.g. Foffa et al. 2018) and the discovery of Tyrannoneustes (Young et al. 2013, Foffa and Young 2014) have altered character polarity at the base of the clade.

Cau and Fanti (2011: 551) listed the following characters as being diagnostic for Geosaurini: the presence of prefrontal with the inflexion point directed caudally at an angle of less than 70° from the rostrocaudal axis of the skull; the presence of a very narrow (close to 45°) angle between the medial and the caudolateral processes of the frontal; by the caudal expansion of the supratemporal fossa beyond the parietal; the reduction of the basal tubera; the elongation of the maxillary tooth crowns; and the reduction of the humerus. Two out of five of those characters still define the clade Dakosaurus + Plesiosuchus + Torvoneustes.