Rediagnosis and redescription of Mosasaurus hoffmannii (Squamata: Mosasauridae) and an assessment of species assigned to the genus Mosasaurus

Abstract

-The large Late Cretaceous marine reptile Mosasaurus has remained poorly defined, in part owing to the unorthodox (by today's nomenclatural standards) manner in which the name was erected. The lack of a diagnosis accompanying the first use of either the genus or species names allowed the genus to become a catchall taxon, and subsequent diagnoses did little to refine the concept of Mosasaurus. We herein present emended diagnoses for both Mosasaurus and the type species M. hoffmannii, based solely on personal examination of the holotype, and a description of the type species based on personal examination of many specimens. Mosasaurus exhibits a premaxilla with a short, conical edentulous rostrum, a maxilla with little to no dorsal excavation for the external naris, posteromedial processes of the frontal that deeply invade the parietal, a quadrate taller than long with a short suprastapedial process and the stapedial pit dorsal to the mid-height of the shaft, an angular that is laterally visible for only a short length of the post-dentary unit, a very tall surangular, a humerus with the postglenoid process robust and offset and a distal width greater than the length, and a pubis with an anteriorly projecting tubercle. M. hoffmannii is distinguished from other species assignable to the genus by the anteroventral corner formed on the tympanic rim of the quadrate, the asymmetric carinae of the anterior marginal teeth dividing the tooth circumference into short labial and long lingual segments, and the proximal and distal expansion of the femur.

Inferring ‘weak spots’ in phylogenetic trees: application to mosasauroid nomenclature

“…The inference of the structure of the mosasaurine phylogenetic tree appears to be difficult especially due to the unstable positions of the taxa attributed to Prognathodon (e.g., Leblanc, Caldwell & Bardet, 2012 ; Simões et al, 2017 ; our study). Nevertheless, numerous derived mosasaurines are currently under revision as is apparent from Street & Caldwell (2017) that provided detailed reappraisal of Mosasaurus hoffmannii , preliminary discussion of some other taxa traditionally assigned to Mosasaurus , and reported on an ongoing research. Together with reconsideration of some species traditionally attributed to Prognathodon , the resolution of the mosasaurines might benefit from addition of some presumably rootward mosasaurine taxa that have not been included in previous ‘complete’ versions of the Bell’s data set (i.e., when the aim was to assess the interrelationships within all major clades of mosasauroids).…”

“…Furthermore, once set as ordered to reflect the homology among nested state-transitions, the character defined this way leads to inflating the phylogenetic importance of a feature that may be merely size-related and individually variable among the same taxon. For instance, Mosasaurus hoffmannii is often reported as having 14 dentary teeth (e.g., Street & Caldwell, 2017 ). However, some specimens have 15 dentary teeth (e.g., CAMSM F22228, IRSNB R 0303; D Madzia, pers.…”

Mosasauroid phylogeny under multiple phylogenetic methods provides new insights on the evolution of aquatic adaptations in the group

“…According to recent revisions [51–53], Mosasaurus maximus is a junior synonym of M . hoffmannii , and this synonymization is incorporated in our dataset by exclusion of the M .…”

The iliosacral joint in lizards: an osteological and histological analysis

“…A similar condition is also found in Aigialosaurus dalmaticus (Dutchak & Caldwell, ), and aigialosaurs and dolichosaurs are hypothesized to share a common ancestor (Lee & Caldwell, ; Caldwell, ; Conrad, ; Paparella et al ). In fact, in obligatory aquatic forms such as mosasauroids, where the ilium, ischium and pubis do not fuse during ontogeny, the preacetabular process is either reduced or completely lost (IP personal observation; Bardet et al ; Konishi et al ; Makádi et al ; Street & Caldwell, ; Jiménez‐Huidobro et al ).…”