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Late Cretaceous marine ecosystems saw a major adaptive radiation of mosasaurids, which evolved highly disparate jaw and tooth morphologies to feed on different prey. A striking pattern seen in mosasaurids was a high diversity of durophagous forms. Durophagy likely evolved several times independently in the mosasaurine genera Globidens, Prognathodon, and Carinodens. Carinodens is unusual in having low, rectangular, laterally compressed teeth. The genus is known from around the world, with the species Carinodens minalmamar and C. belgicus previously reported from the Maastrichtian Phosphates of Morocco. Here, we report a new species of Carinodens, C. acrodon, from the same Maastrichtian Phosphates. It is characterized by teeth with tall crowns, triangular apices, and broad bases. Many of the diagnostic features of this species appear to be plesiomorphies, suggesting the persistence of a primitive species of Carinodens into the latest Maastrichtian alongside the more derived C. minalmamar and C. belgicus. The new species contributes to an emerging pattern of mosasaurid hyperdiversity in the late Maastrichtian of Morocco. A revised faunal list, including stratigraphic range extensions of Khinjaria and Stelladens into the latest Maastrichtian of upper Couche III of the Phosphates of Morocco, suggests at least 16 species of mosasauroid coexisted here. [ABSTRACT FROM AUTHOR]

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The study of new finds of mosasaurids from the Izhberda locality (Southern Urals, Orenburg Region) has made it possible to record for the first time the presence of mosasaurs from the subfamilies Mosasaurinae, Tylosaurinae, and Plioplatecarpinae from the Upper Cretaceous of the Orenburg Region, including representatives of the genera Mosasaurus, Prognathodon, and Clidastes, which are known from the Upper Cretaceous of North America and Western Europe. Of interest is the discovery of the tylosaurine Taniwhasaurus, previously known from New Zealand, Antarctica, South Africa, and Japan. Therefore, the Campanian mosasaurid fauna of the Southern Urals is intermediate and includes North American–European and Asia–Pacific taxa. However, all the finds of mosasaurs from the Izhberda locality can only be identified in open nomenclature, which makes detailed comparisons of the faunas difficult. Revision of the type series of mosasaur Liodon rhipaeus Bogolyubov, 1910 from the Southern Urals has allowed us to conclude that, in addition to the three mosasaurian vertebrae, it includes the ischium and posterior fragment of the mandible of a plesiosaur. Liodon rhipaeus is clearly a nomen dubium and the vertebrae of its type series cannot be identified more precisely than Tylosaurinae indet. [ABSTRACT FROM AUTHOR]

Isolated mosasaur teeth and vertebrae recovered from beds of the Guadalupe Group of central Boyacá, Colombia, are reported. A partial tooth crown identified as Globidens sp., found in the Labor-Tierna Formation (Maastrichtian), represents the first report of this genus from northern South America and its most equatorial occurrence. A tooth crown recovered from the Plaeners Formation (upper Campanian–lower Maastrichtian), represents the youngest record of the subfamily Plioplatecarpinae in Colombia. These occurrences collectively constitute the youngest record of the family Mosasauridae in Colombia and expand both the taxonomic diversity and biogeography of mosasaurids in northern South America. [ABSTRACT FROM AUTHOR]

Here we describe new marine vertebrate remains, mainly isolated teeth, from the Upper Cretaceous (Coniacian-Santonian) of near Mardin, SE Turkey. This is the first report in this area of ptychodontid sharks (elasmobranchs), enchodontid teleosts (actinopterygians) and mosasaurid squamates (reptiles). The respective taxa Ptychodus cf. mortoni, Enchodus sp., Platecarpus sp. and Mosasaurinae indet. are described. These new data improve our knowledge on early Late Cretaceous marine vertebrate faunas from the Arabic Platform, classically known previously mostly from the Maastrichtian outcrops of Middle-East and Northwestern Africa, and extend the palaeobiogeographical distribution of these taxa into the western part of the Mediterranean Tethys, confirming their cosmopolitan status. [ABSTRACT FROM AUTHOR]

Here we determine the individual age of a basal mosasaur (subfamily Halisaurinae) using zygapophyseal skeletochronology. This study is based on the cervical vertebra from the Late Cretaceous Beloe Ozero locality (Saratov Region). By of counting the zygapophyseal growth rings on the right prezygapophysis, it has been revealed that the age of the animal to which this vertebra belonged was at least 11 years. The absence of drastic reduction in the distance between the zygapophyseal growth rings is indicative of the fact that in the first 11 years of life, until the moment of death, the animal grew rapidly and evenly and reached a length of about 6 meters. [ABSTRACT FROM AUTHOR]

Mosasaurid squamates were the dominant amniote predators in marine ecosystems during most of the Late Cretaceous. Here, we use a suite of biomechanically rooted, functionally descriptive ratios in a framework adapted from population ecology to investigate how the morphofunctional disparity of mosasaurids evolved prior to the Cretaceous–Palaeogene (K/Pg) mass extinction. Our results suggest that taxonomic turnover in mosasaurid community composition from Campanian to Maastrichtian is reflected by a notable global increase in morphofunctional disparity, especially driving the North American record. Ecomorphospace occupation becomes polarized during the late Maastrichtian, with morphofunctional disparity plateauing in the Southern Hemisphere and decreasing in the Northern Hemisphere. We show that these changes are not strongly associated with mosasaurid size, but rather with the functional capacities of their skulls. Our novel approach indicates that mosasaurid morphofunctional disparity was in decline in multiple provincial communities before the K/Pg mass extinction, highlighting region-specific patterns of disparity evolution and the importance of assessing vertebrate extinctions both globally and locally. Ecomorphological differentiation in mosasaurid communities, coupled with declines in other formerly abundant marine reptile groups, indicates widespread restructuring of higher trophic levels in marine food webs was well underway when the K/Pg mass extinction took place. [ABSTRACT FROM AUTHOR]

Mosasauroid squamates were abundant and had a worldwide distribution during the Late Cretaceous, but records from Sub-Saharan Africa are comparatively scanty and based mainly on fragmentary and isolated material. Here new mosasaur remains from the Maastrichtian (Upper Cretaceous) of Dakhla Oasis in the South-Western Desert of Egypt are recorded, including: a small, fragmentary right dentary of an indeterminate mosasaurine with a single tooth preserved in situ and an isolated tooth crown of the genus Globidens. This material stems from fossiliferous, calcareous sandstones with intercalated shales that form the lower portion of the Dakhla Formation, known to be an intertidal to subtidal deposit. Previously recorded mosasaur remains from the Eastern Desert in Egypt included Globidens phosphaticus , Platecarpus sp., and Igdamanosaurus aegyptiacus. In Africa, mosasaurs of the Maastrichtian age have been recorded from Morocco, Nigeria, Angola, the Democratic Republic of Congo, and Niger. The newly collected material from Dakhla Oasis currently constitutes the youngest record of mosasaurs in Egypt. [ABSTRACT FROM AUTHOR]

Mosasaurs were large, globally distributed aquatic lizards that lived during the Late Cretaceous. Despite numerous specimens of varying maturity, a detailed growth series has not been proposed for any mosasaur taxon. Two taxa—Tylosaurus proriger and T. kansasensis/nepaeolicus—have robust fossil records with specimens spanning a wide range of sizes and are thus ideal for studying mosasaur ontogeny. Tylosaurus is a genus of particularly large mosasaurs with long, edentulous anterior extensions of the premaxilla and dentary that lived in Europe and North America during the Late Cretaceous. An analysis of growth in Tylosaurus provides an opportunity to test hypotheses of the synonymy of T. kansasensis with T. nepaeolicus, sexual dimorphism, anagenesis, and heterochrony. Fifty-nine hypothetical growth characters were identified, including size-dependent, size-independent, and phylogenetic characters, and quantitative cladistic analysis was used to recover growth series for the two taxa. The results supported the synonymy of T. kansasensis with T. nepaeolicus and that T. kansasensis represent juveniles of T. nepaeolicus. A Spearman rank-order correlation test resulted in a significant correlation between two measures of size (total skull length and quadrate height) and maturity. Eleven growth changes were shared across both species, neither of the ontogram topologies showed evidence of skeletal sexual dimorphism, and a previous hypothesis of paedomorphy in T. proriger was not rejected. Finally, a novel hypothesis of anagenesis in Western Interior Seaway Tylosaurus species, driven by peramorphy, is proposed here.

The carbon stable isotope composition (δ13C) of tooth enamel in mosasaurid squamates reflects aspects of their diet and diving behaviour. Here we present new δ13C data for such marine squamates from the Maastrichtian of Denmark and compare these with results obtained in previous studies from the lower-latitude type area of the Maastrichtian Stage (latest Cretaceous; 72.1-66.0 Ma) in the south-east Netherlands and north-east Belgium. For the Danish samples, there is a weak correlation between mosasaur body size and δ13C values, with larger-sized taxa having lower δ13C values, comparable to what has previously been observed for mosasaurs from the Maastrichtian type area. [ABSTRACT FROM AUTHOR]

Plotosaurus is a highly aquatically adapted mosasaur, which is supposed to inhabit the deep ocean basin. The geographic occurrence of this genus has been limited only to the west coast of North America. In this study, two Plotosaurus‐type mosasaur caudal vertebrae derived from the Upper Cretaceous Nakaminato Group in Ibaraki Prefecture, Japan, are described with discussion on the paleobiogeographic significance of the Late Cretaceous mosasaur fauna in the Northwestern Pacific region. The two specimens are an intermediate caudal vertebra found in a beach cobble, which presumably originated from the Hiraiso Formation (upper Campanian), and a terminal caudal vertebra found in situ in the lower Isoai Formation (lower Maastrichtian). Because their relative centrum lengths (ratio of centrum length/centrum height, ~0.7) are very close to that of Plotosaurus, the specimens are referred to cf. Plotosaurus sp. The two specimens provide the first evidence that highly specialized Plotosaurus‐type mosasaurs inhabited the Northwestern Pacific Ocean, suggesting that such forms had a wider distribution than previously recognized and might have existed since the late Campanian in the Northwestern Pacific Ocean. [ABSTRACT FROM AUTHOR]

Mosasaurus lemonnieri is a mosasaurine mosasaurid first unearthed from the lower Maastrichtian of the Mons Basin, southern Belgium. Even though numerous well-preserved specimens have been attributed to the taxon, the knowledge of its anatomy is surprisingly poor and merely limited to some general characteristics. Here I describe the morphology of the marginal dentition of M. lemonnieri based on the holotype and 14 referred individuals originating from the upper Campanian and Maastrichtian of Belgium. The dental variability is assessed through linear discriminant analyses aimed to appraise the tooth crown distinguishability between (1) individuals, (2) tooth-bearing elements (premaxillae, maxillae, and dentaries), and (3) within particular jaw regions (anterior, middle, and posterior). The overall dental distinguishability between individuals was, expectedly, poor though the rates of correctly classified teeth differed for particular specimens, which can have taxonomic implications. The premaxillary and maxillary teeth were inferred to be more distinguishable than the dentary teeth. The dental distinguishability of M. lemonnieri is further compared to that of other sympatric and potentially sympatric taxa. The use of mosasaurid dental measurements substantially facilitates the comparisons of mosasaurid teeth on both inter- and intraspecific scale, increasing the accuracy of the studies appraising the patterns of mosasaurid dental evolution. [ABSTRACT FROM AUTHOR]

Upper Cretaceous coastal marine deposits are widespread in the Southern Urals with a number of marine vertebrates previously reported from this region. However, previous studies on the vertebrate faunas in this region often lack detailed taxonomic descriptions and illustrations, rendering comparisons to other faunal assemblages difficult. A new diverse vertebrate assemblage comprising cartilaginous and bony fishes, as well as marine reptiles, is described here from the Orenburg region near Akkermanovka (Southern Urals, Russia). Thirty five taxa are identified, including three holocephalans (Elasmodus sp., Ischyodus yans c hini , Chimaeroid indet.), two hybodontiform sharks (Meristodonoides sp., cf. Polyacrodus sp.), 17 neoselachians (Paraorthacodus cf. andersoni , Paraorthacodus sp., Synechodus sp., Cederstroemia nilsi , Acrolamna acuminata , Archaeolamna ex gr. kopingensis , Cretalamna sarcoportheta , Cretoxyrhina mantelli , Eostriatolamia segedini , E. venusta , Hispidaspis horridus , H. cf. gigas , Pseudocorax laevis , Pseudoscapanorhynchus compressidens , Scapanorhynchus rhaphiodon , Squalicorax kaupi , Ptychodus rugosus), a holostean (Lepisosteidae indet.), nine teleosts (Protosphyraena sp., Saurodontidae indet., cf. Pachyrhizodus sp., Pachyrhizodontidae indet., Enchodus petrosus , E. ferox , E. cf. gladiolus , E. spp., Alepisauroidei indet.), two plesiosaurs (Polycotylidae indet., Plesiosauria indet.), and one mosasaurid (Tylosaurinae indet.). Based on the faunal assemblage, a Santonian–?early Campanian age is proposed. Lamniform sharks are the best represented group in terms of taxic diversity and relative abundance, probably reflecting the peak in diversity this group experienced following the Cenomanian radiation in the Late Cretaceous. The faunal assemblage of Akkermanovka exhibits significant taxonomic overlaps with assemblages reported from Asia and North America, but not from Southern Hemisphere continents, indicating east–west dispersal of several marine taxa during the Late Cretaceous. [ABSTRACT FROM AUTHOR]

Mosasaurids were highly diverse and dominant as predators in late Cretaceous marine ecosystems. In the Maastrichtian, the Halisaurinae, a clade of relatively small-bodied mosasaurids, became common, especially in North Africa. Here, we report a new species of halisaurine from the lower Maastrichtian Dakhla Shale of the Western Desert of Egypt. Halisaurus hebae sp. nov. resembles Halisaurus platyspondylus and H. arambourgi in the shape of the frontal, suggesting close affinity with those species. A revised halisaurine phylogeny shows a cluster of species characterized by modification of the orbital bones to accommodate large eyes, suggesting a shift towards the use of visual cues to find prey, perhaps in low light conditions. The abundance and diversity of halisaurines in Africa contrasts with their relative rarity elsewhere in the world, emphasizing the regionalization of marine reptile faunas in the Maastrichtian. [ABSTRACT FROM AUTHOR]

The Mosasauridae underwent a major radiation early in the Late Cretaceous, with the subfamilies Plioplatecarpini and Tylosaurini appearing in the Turonian. Here we report an almost complete mosasaur skull assigned to the plioplatecarpine genus Yaguarasaurus. The specimen was discovered southwest of Vallecillo in the northeastern Mexico state of Nuevo Leon, about 80 km north of Monterrey, in a laminated limestone layer of the upper member of the Agua Nueva Formation (Upper Turonian - ?Lower Coniacian). The specimen is referred to as a new species, Y. regiomontanus. This is the first report of Yaguarasaurus from Mexico and the most complete of the Americas. At roughly 5 m in length, it is one of the earliest large mosasaurids. Along with Yaguarasaurus columbianus , Russellosaurus coheni , and an unnamed plioplatecarpine from Texas, it documents the rapid diversification and expansion of plioplatecarpines in the marine realm in the Turonian. • The Highlight of the paper is that is a new species of mosasaurus described for Mexico. [ABSTRACT FROM AUTHOR]

Ontogeny—the growth and development of an organism—is among the more poorly understood aspects of the life history of mosasaurs, largely owing to a dearth of fossil material from young individuals. We describe the partial and complete skulls of two subadult individuals of the mosasaurid Tylosaurus proriger from the upper Smoky Hills Chalk Member of the Niobrara Formation in Kansas. We include the more complete of the two specimens in an allometric analysis to better understand proportional changes of the skull through growth. Although our small sample size produces several instances of ‘soft isometry’, we recover the length of the edentulous rostrum as significantly negatively allometric, and quadrate height as significantly positively allometric. In light of our findings, we go on to consider the question of whether T. kansasensis represents an immature ontogimorph of T. nepaeolicus, but find no convincing evidence that this is the case.

We describe and name a new mosasaur taxon, Sarabosaurus dahli gen. et sp. nov., from the lower Turonian part of the Tropic Shale in Utah, USA. The holotype specimen preserves significant portions of the skull and axial postcranial skeleton. It was found in the upper part of the Watinoceras devonense Ammonite Zone, bounded by radioisotopic dates above and below, and is thus about 93.7 Ma, the oldest mosasaurid taxon known from the Western Interior Seaway. The new taxon possesses a vascular pattern of the basisphenoid heretofore only seen in late diverging plioplatecarpine mosasaurids. Reevaluation of the morphology of the basisphenoid of previously described Turonian mosasaurs using μCT techniques reveals the derived condition is also present in Yaguasaurus and the incipient condition in Tethysaurus and Russellosaurus. In these two taxa, the canals enter the basisphenoid, but do not pass into the basioccipital. Instead, they exit only high on the posterior wall of the sella turcica, in a position similar to the basilar artery of other lizards. This vascular pattern, both in its incipient and derived states, is unique among squamates and supports inclusion of the aforementioned taxa in a monophyletic Plioplatecarpinae, for which we provide an emended diagnosis. Phylogenetic analysis recovers Sarabosaurus dahli gen. et sp. nov. as the sister taxon to Yaguarasaurus and all other later diverging plioplatecarpines, with Russellosaurus and Tethysaurus as successive sister taxa. Tylosaurine mosasaurids retain the primitive condition of the basisphenoid vascularization pattern and implies a tylosaurine-plioplatecarpine divergence in the late Cenomanian or earliest Turonian. [ABSTRACT FROM AUTHOR]

Squamates present a unique challenge to our understanding of dental evolution in amniotes because they are the only extant tooth-bearing group for which a ligamentous tooth attachment is considered to be absent. This has led to the assumption that mammals and crocodilians have convergently evolved a ligamentous tooth attachment, composed of root cementum, periodontal ligament, and alveolar bone, whereas squamates are thought to possess a single bone of attachment tissue that fuses teeth to the jaws. The identity and homology of tooth attachment tissues between squamates, crocodilians, and mammals have thus been a focal point of debate for decades. We provide a novel interpretation of the mineralized attachment tissues in two focal taxa in this debate, mosasaurids and snakes, and compare dental tissue histology with that of the extant crocodilian Caiman sclerops. We identify a periodontal ligament in these squamates that usually exists temporarily as a soft connective tissue anchoring each tooth to the alveolar bone. We also identify two instances where complete calcification of the periodontal ligament does not occur: in a durophagous mosasaur, and in the hinged teeth of fossil and modern snakes. We propose that the periodontal ligament rapidly calcifies in the majority of mosasaurids and snakes, ankylosing the tooth to the jaw. This gives the appearance of a single, bone-like tissue fusing the tooth to the jaw in ankylosed teeth, but is simply the end stage of dental tissue ontogeny in most snakes and mosasaurids. [ABSTRACT FROM AUTHOR]

Aunque el genero de mosasaurio Prognathodon esta conocido mundialmente durante el Cretácico final (Campaniense-Maastrichtiense), damos a conocer su primera occurencia en el Levante Español. Previamente ya se conocía en niveles contemporáneos del País Vasco. El especimen de Castalla corresponde a un diente del pterigoides. Aunque no se puede identificar a nivel especifico, el diente pertenece a una especie de Prognathodon con dientes 'delgados' como P. compressidens, P. sectorius y P. mosasauroides, del Campaniense-Maastrichtiense de Europa, o P. kianda del Maastrichtiense de Angola.

Un diente aislado de mosasaurio procedente del Campaniense de Álava (País Vasco), previamente asignado a cf. Mosasaurus sp., se atribuye en este trabajo a un tilosaurino. Podría pertenecer a Tylosaurus, un género cuasi cosmopolita del Santoniense-Maastrichtiense. Es la primera cita de un mosasáurido tilosaurino en la Península Ibérica. Además, se trata del registro más meridional de este clado en el margen norte del Tetis mediterráneo. Los Tylosaurinae están representados por fósiles en Norteamérica, Europa, Nueva Zelanda, Antártida, África y Asia, pero carecen de registro en el margen sur del Tetis mediterráneo y en paleolatitudes tropicales.

A specimen of a halisaurine mosasaur is reported from Japan for the first time, closing the pre-existing biogeographical gap between the Middle East and the eastern Pacific.Phosphorosaurus ponpeteleganssp. nov., from the lowermost Maastrichtian of Hokkaido, has been assigned to the genusPhosphorosaurusfor sharing the following suite of major cranial characters withP.ortliebi, the type species from Belgium: apex of posterodorsal triangular plateau on frontal reaching level of interorbital constriction; frontal lateral border forming a step-like junction between interorbital and preorbital segments of frontal; preorbital segment of frontal sloping anteroventrally; and stapedial meatus parallel-sided in latero-medial view. Potential autapomorphies that distinguishP.ponpetelegansfrom other members of Halisaurinae include: postorbitofrontal jugal process elongate and stalk-like, projecting laterally; this process distally bearing a ventrally facing depression for jugal articulation; and lateral surangular–articular suture angular rather than round. The long and laterally projecting jugal processes, when combined with a depressed as well as narrow snout, provide compelling evidence for well-developed binocular vision for the new mosasaur, with an estimated binocular field of view (BFoV) of 35°. This value is unusually high for non-ophidian squamates that typically exhibit a BFoV of 10—20°, and is higher than those of other measured mosasaur taxa by at least 5°. Among colubrid snakes, nocturnal species exhibit greater BFoV than diurnal ones in both arboreal and terrestrial taxa. Known also from the Maastrichtian of Hokkaido are fossils of lantern fish (myctophids) and 10-armed cephalopods (coleoids), both of which are typically bioluminescent today. It is hence proposed that the exceptionally large, forward-facing eyes ofP.ponpetelegansmay well have been a special adaptation for a nocturnal lifestyle, where they hunted small, bioluminescent prey at night while avoiding direct competition with larger, more piscine mosasaurine taxa such asMosasaurus hobetsuensisthat co-existed withP.ponpetelegans. http://zoobank.org/urn:lsid:zoobank.org:pub:3EF73BE7-B3FE-4441-BA5E-29C5D5FCCBC9 [ABSTRACT FROM PUBLISHER]

The Upper Cretaceous of Africa has produced a diverse fauna of mosasaurs, including the highly specialized, long-jawed Pluridens. The type of Pluridens walkeri comes from the Maastrichtian Farin-Doutchi Formation of Niger, with a second, referred specimen coming from the Campanian section of the Campanian-Maastrichtian Nkporo Shale near Calabar, in southern Nigeria. Comparisons of this referred specimen with the holotype suggest that it represents a distinct and more primitive species. The Calabar jaw resembles P. walkeri in being long and narrow anteriorly with a shallow subdental shelf, and in having small, numerous, recurved teeth with medially positioned replacement pits. However, it lacks many of the derived features that characterize Pluridens walkeri , such as the extremely long and straight jaw, the extreme lateral protrusion and subcircular section of the dentary, strong transverse expansion of the dental thecae, and extreme reduction and increase in number of the teeth. The Calabar Pluridens is therefore referred to a new species, Pluridens calabaria. Following recent studies, Pluridens is considered to represent a highly derived member of the Halisaurinae. The marked differences between the Campanian and Maastrichtian species of the genus underscore the rapid pace of mosasaur evolution during the Cretaceous. [ABSTRACT FROM AUTHOR]

Erupting teeth are some of the oldest witnesses of developmental processes in the vertebrate fossil record and provide an important resource for vertebrate cladistics. Here, we have examined a mosasaur jaw fragment from central Texas using ultrathin ground section histology and 3D tomographic imaging to assess features critical for the cladistic placement of mosasaurs among varanoids vs. snakes: (i) the orientation of replacement teeth compared to the major tooth axis, (ii) the occurrence of resorption pits, and (iii) the mode of tooth implantation/attachment to the tooth bearing element (TBE). The replacement tooth studied here developed in an inclined position slightly distal of the deciduous parent tooth, similar to another varanoid squamate, the Gila monster Heloderma suspectum. Ground sections and tomographs also demonstrated that the replacement tooth attachment apparatus was entirely intact and that there was no evidence of mechanical deformation. Sections and tomographs further illustrated that the replacement tooth was located within a bony crypt and the inclination of the crypt matched the inclination of the replacement tooth. These preparations also revealed the presence of a resorption pit within the boundaries of the deciduous tooth that surrounded the developing replacement tooth. This finding suggests that developing mosasaur teeth developed within the walls of resorption pits similar to varanoid tooth germs and unlike developing snake teeth which are surrounded by fibrous connective tissue integuments. Finally, mosasaurs featured pseudo-thecodont tooth implantation with teeth anchored within a socket of mineralized tissue by means of a mineralized periodontal ligament. Together, these data indicate that the moderate inclination of the erupting mosasaur tooth studied here is neither a result of postmortem displacement nor a character representative of snakes, but rather a shared character between Mosasaurs and other varanoids such as Heloderma. In conjunction with the presence of resorption pits and the evidence for pseudothecodont tooth implantation, the tooth eruption and implantation characters described in the present study either place mosasaurs among the varanoids or suggest convergent evolution mechanisms between both clades, with mosasaurs evolving somewhat independently from a common varanoid ancestor. [ABSTRACT FROM AUTHOR]

Living in water imposes severe constraints on the evolution of the vertebrate body. As a result of these constraints, numerous extant and extinct aquatic vertebrate groups evolved convergent osteological and soft-tissue adaptations. However, one important suite of adaptations is still poorly understood: dermal cover morphologies and how they influence surface fluid dynamics. This is especially true for fossil aquatic vertebrates where the soft tissue of the dermis is rarely preserved. Recent studies have suggested that the keeled scales of mosasaurids (pelagic lizards that lived during the Late Cretaceous) aided in surface frictional drag reduction in a manner analogous to the riblets on shark placoid scales. However, here we demonstrate that mosasaurid scales were over an order of magnitude too large to have this effect. More likely they increased the frictional drag of the body and may have played a role in controlling flow separation by acting as surface roughness that turbulated the boundary layer. Such a role could have reduced pressure drag and enhanced manoeuvrability. We caution those studying fossil aquatic vertebrates from positing the presence of surface drag reducing morphologies, because as we show herein, to be effective such features need to have a spacing of approximately 0.1 mm or less.

The Cretaceous–Paleogene (K–Pg) transition saw mass extinctions in terrestrial and marine ecosystems. Terrestrial vertebrate diversity patterns across the K–Pg boundary have seen extensive study, but less is known about marine vertebrates. We describe a new mosasaurid from the latest Maastrichtian phosphatic beds of Morocco, showing how mosasaurids evolved to become apex predators in the latest Cretaceous. Thalassotitan atrox gen. et sp. nov., from the Oulad Abdoun Basin of Khouribga Province, Morocco is characterized by large size, a broad skull, massive jaws, and reduced cranial kinesis, suggesting it was highly adapted for carnivory. Teeth resemble those of killer whales in their robust, conical shape, and show heavy wear and damage. Phylogenetic analysis recovers Thalassotitan as a close relative of Prognathodon currii and P. saturator within the Prognathodontini. Among the associated fauna, three genera of mosasaurids, elasmosaurid plesiosaur, chelonioid turtle, and enchodontid fish show acid damage, and could be prey ingested by mosasaurids, likely Thalassotitan. Thalassotitan shows mosasaurids evolved to fill the marine apex predator niche, a niche occupied by orcas and white sharks today. Mosasaurs continued to diversify and fill new niches until their extinction at the end of the Cretaceous. [ABSTRACT FROM AUTHOR]

Halisaurinae is a subfamily of enigmatic, small- to medium-sized mosasauroids, which retain a mosaic of primitive and derived features. The first record of a South American Halisaurus with precise stratigraphic information includes a quadrate carrying a tympanic disc together with twelve vertebrae, collected in the Late Maastrichtian of Jagüel Formation in northern Patagonia (Argentina). The preservation of a tympanic disc allows exploring and discussing the mechanisms of sound transmission in these mosasauroids. The location of the tympanic disc resembles that one formed by the extracolumella of aquatic turtles and at least one extant lizard. Based on morphological comparison of the middle ear we discuss previous hypotheses on the modification of the tympanic middle ear system of mosasauroids for underwater hearing, in a manner similar to that observed in aquatic turtles. [ABSTRACT FROM AUTHOR]

Mosasaurid squamates are the most numerically abundant, and taxonomically/ecologically diverse clade of marine amniotes represented in the Maastrichtian Phosphates of Morocco. With few exceptions, they are faunally typical of the Southern Mediterranean Tethys Margin (around palaeolatitude 25°N) and range from the base to the top of the stage. The Moroccan assemblages include at least 7 genera and 10 species representing a broad spectrum of sizes and morphologies that illustrate several ecological trends. Noteworthy is the predominance of Mosasaurinae which are widespread in contemporaneous outcrops worldwide and constitute 80% and 70% of the total genus/species number respectively. In contrast, Halisauromorpha and Russellosaurina (plioplatecarpines) are scarce and tylosaurines are presently unknown. All of the Moroccan mosasaurids exhibit characteristic tooth morphologies and can be placed into resource partitioning morphoguilds indicative of adaptations for piercing, crushing or cutting. Medium to large predators are found to distribute along the ‘Crush’–‘Cut’ axis of the morphoguild projection, and a new ‘Crush–Cut’ guild, previously unrecognised amongst Mesozoic marine amniotes, accommodates several Prognathodon species. Also of importance is the lack of mosasaurids along the ‘Pierce’–‘Crush’ axis, potentially inferring that these ecological niches were occupied by other marine vertebrates such as selachians and plesiosaurians. In addition, the relative abundance of mosasaurids throughout the Maastrichtian series of the Gantour Basin evidences direct ecological competition or predation phenomena. [ABSTRACT FROM AUTHOR]

ABSTRACT—The first described genus of mosasaur,Mosasaurus hoffmannii, has been coarsely diagnosed and defined since its creation, with numerous specimens and new species being assigned to the genus with little or no reference to, and thus few real similarities with, the generic type specimen. One of the earliest examples of a weakly defined and diagnosed species assigned to the genus isMosasaurus gracilis. Location and examination of the various assigned specimens and the holotype indicate thatM. gracilisshares more characters, such as a short rostrum on the dentary anterior to the first teeth, with russellosaurine mosasaurs. In addition,M. gracilisis known from Turonian deposits, whereas other species belonging toMosasaurusare upper Campanian–Maastrichtian in age. Based on the evidence of shared characters and contemporaneity, we suggest thatM. gracilisbe removed fromMosasaurusbecause it shares more affinities with members of the Russellosaurina. This represents the first step in the very necessary process of untangling the alpha taxonomy, and subsequently the complete systematics, of the genusMosasaurus hoffmannii. [ABSTRACT FROM AUTHOR]

A new, exquisitely preserved specimen of a small mosasaur, referable toMosasaurus missouriensis, is reported from the Bearpaw Formation (ca. 75 Ma, upper Campanian) of southern Alberta, Canada. Many calcified cartilaginous elements, including tracheal rings and the sternum, are preserved. The sternum most closely resembles that ofClidastes propython, bearing five shallow sternal rib facets on each side. Our comparative study of the new material with the holotype, referred material, and the genotypeM.hoffmanniiis congruent with the preexisting hypothesis thatM.missouriensisandM.hoffmanniiare phylogenetically more closely related to each other than to the other congeners, in spite of a temporal gap of nearly 10 million years between them. Also preserved with the mosasaur, inside its ribcage and around the specimen, are well-preserved aulopiform fish bones, including a skull. The fish skull is punctured and its centra truncated, suggesting macrophagy was employed byM.missouriensisdespite the apparent lack of tooth wear. A sympatric specimen ofPrognathodon overtoniis known to have consumed a sea turtle as well as fishes, and consistently exhibits apical wear across marginal teeth. We hypothesize that coexistence of these apex predators in the Bearpaw Sea was possible because of niche partitioning. Finally, the mosasaur carcass was likely scavenged by at least three lamniform sharks, based on their shed teeth and a series of truncated transverse processes on the mosasaur tail. [ABSTRACT FROM AUTHOR]

A review of the remains of mosasaurine mosasaurs from the upper Campanian–Maastrichtian of Italy is provided. The first discoveries of mosasaur material from Italy are represented by a series of isolated teeth from the Scaglia Rossa Formation north of Vittorio Veneto (late Campanian). These teeth show some similarities toPrognathodon,Liodon, andEremiasaurus, but are not identical and probably represent a new taxon. A partial mosasaur skull found south of Reggio Emilia in 1886 is potentially a new species ofMosasaurus, although more material is needed to support this possibility. This specimen is temporarily referred toM. cf.hoffmanni. A second fragmentary mosasaur skull was accidentally discovered in 1892 north of Verona during the demolition of a school (inside one of the building stones). Based on its general morphology, size, and dentition, this second specimen can be considered as very closely related toM. hoffmanni, but its older age (early–middle Maastrichtian) suggests that it likely represents a new species ofMosasaurus. We refrain from erecting new taxonomic names for these specimens pending the discovery of new, more complete material upon which satisfactory diagnoses can be based. The paleobiogeographic distribution ofMosasaurus hoffmanni,M. cf.hoffmanni,M. beaugei,Liodon, andPrognathodonis reviewed briefly. SUPPLEMENTAL DATA—Supplemental materials are available for this article for free athttp://www.tandfonline.com/UJVP. [ABSTRACT FROM PUBLISHER]