Xenodens calminechari gen. et sp. nov., a bizarre mosasaurid (Mosasauridae, Squamata) with shark-like cutting teeth from the upper Maastrichtian of Morocco, North Africa

The mosasaurids (Mosasauridae) were a group of lizards that became highly specialized for marine life in the mid-Cretaceous. By the end of the Cretaceous, they had undergone an adaptive radiation, and showed a wide range of body sizes, locomotor styles, and diets. Their ranks included piscivores, apex predators, and durophages. Here, we report a new taxon, Xenodens calminechari gen. et sp. nov., from the upper Maastrichtian phosphates of Morocco, with dental specializations unlike those of any known reptile. Teeth form a unique dental battery in which short, laterally compressed and hooked teeth formed a saw-like blade. Unique features of tooth structure and implantation suggest affinities with the durophagous Carinodens. The tooth arrangement seen in Xenodens not only expands known disparity of mosasaurids, but is unique among Squamata, or even Tetrapoda. The specialized dentition implies a previously unknown feeding strategy, likely involving a cutting motion used to carve pieces out of large prey, or in scavenging. This novel dental specialization adds to the already considerable disparity and functional diversity of the late Maastrichtian mosasaurids and marine reptiles. This provides further evidence for a diverse marine fauna just prior to the K-Pg extinction

The Mosasaur Fossil Record Through the Lens of Fossil Completeness

The quality of the fossil record is essential for interpreting the significance of macroevolutionary patterns. Palaeodiversity is filtered through geological and human processes, and efforts to correct for these biases are part of a debate concerning the role of sampling proxies and standardisation in models of biodiversity. Here, we analyse the fossil record of mosasaurs in terms of fossil completeness as a measure of fossil quality, using three novel metrics of fossil completeness for a compilation of 4,083 specimens. All metrics correlate with each other. A new qualitative measure of character completeness (QCM), correlates with the phylogenetic character completeness metric. Mean completeness by species decreases with specimen count, and average completeness by substage varies significantly. Mean specimen completeness is higher for species-named fossils than those identified to genus and family. The effect of tooth-only specimens is analysed. Importantly, we find that completeness of species does not correlate with completeness of specimens. Completeness varies by palaeogeography, North American specimens showing higher completeness than those from Eurasia and Gondwana. These metrics can be used to identify exceptional preservation, with specimen completeness varying significantly by both formation and lithology. The Belgian Ciply Formation displays the highest completeness, and clay lithologies show higher completeness values than others. Neither species diversity nor sea level correlates significantly with fossil completeness. A GLS analysis using multiple variables agrees with this result. However, GLS shows that two variables have significant predictive value for modelling averaged diversity, namely sea level and mosasaur- and plesiosaur-bearing formations, the latter of which is shown to be redundant with diversity. Mosasaur completeness is not driven by sea level, nor is completeness limiting the diversity signal in the mosasaur record

Bevarat maginnehåll hos mosasaurier

Relationen mellan bytesdjur och rovdjur i forntida ekosystem kan rekonstrueras med hjälp av olika fossil som t.ex. kololiter, det vill säga förstenat mag- och tarminnehåll. Mosasaurier (familjen Mosasauridae) är en grupp marina ödlor med världsvid utbredning under sen krittid. De var generellt opportunistiska i sina födoval, men några arter som specialiserat sig på skalförsedda djur förekommer också. Bevarat maginnehåll från mosasaurier är känt från flera släkten och utgörs av fisk, bläckfisk, mollusker, sköldpaddor, fåglar, andra mosasaurier samt svanödlor. Denna studie beskriver ett skelettfynd som påträffades under revbenen på en individ av släktet Mosasaurus. Fyndet utgörs av sex benfragment med tydlig ytkorrosion och tolkas här som bevarat maginnehåll. Benfragmenten anses tillhöra en sköldpadda och skalplåtarnas ytstruktur är karaktäristisk för familjen Trionychidae. Tillsammans med benbitarna påträffades även metalliska noduler. Deras kemiska sammansättning och homogena inre struktur tyder på att de inte är del av maginnehållet. I stället rör det sig troligtvis om diagenetiskt bildade noduler.Relationships between prey and predator in ancient ecosystems can be reconstructed by interpreting fossil remains such as kololites (fossilized stomach and intestinal contents). They function as a direct evidence of food ingested and thus provide insights into the diet and digestive system of extinct animals. Mosasaurs (family Mosasauridae) are a cosmopolitan group of extinct marine lizards that evolved and eventually perished durng the Late Cretaceous. The variety of prey items suggests that mosasaurs were an opportunistic group in their choice of food, although some specialized species did exist. Preserved stomach contents are known from several genera and include fish, cephalopods, bivalves, turtles, birds, other mosasaurs and plesiosaurs. This study describes stomach content that was found underneath the ribcage of a Mosasaurus. Six bone fragments with signs of corrosion are interpreted as the remains of gastric content. Furthermore, the bones are identified as turtle bones, and certain surface structures are characteristic of the family Trionychidae. Metallic nodules were also found in association with the bone fragments. The chemical composition and homogenous internal structure do not indicate that they are remnants of undigested stomach content. On the contrary, it is likely that they were diagenetically formed

Testando padrões macroevolutivos em tetrápodes com recurso a redes de ossos cranianos

The vertebrates’ skull houses the brain and important sensory organs. This anatomic structure has suffered various changes and specializations that recapitulate the evolutionary process. This variability, its complexity and easy preservation makes it one of the standard characteristics used in comparative anatomy and evolutive biology for instance in the classification of vertebrates and phylogenetic reconstruction. A total of 25 species were considered: Acanthostega gunnari; 14 species within Mammalia including the groups Sirenia, Hyracoidea, Carnivora, Cetartiodactyla and Primates and 10 Reptilia from Crocodylia, Neotheropoda, Rhynchocephalia, Squamata and Testudines. All the collected data was analyzed through three different softwares: PAUP, for phylogenetic analysis, Gephi to build networks of contacts from the skull and Rstudio for statistics. In this study we show how phylogeny of an animal can be inferred to Class level using exclusively information regarding skull bone contacts but there is not enough information contained on the skull alone to recreate phylogenetic paths to build complete phylogeny.No corpo dos vertebrados o crânio aloja o cérebro e diversos órgãos sensoriais importantes. Esta estrutura anatómica passou por várias modificações e especializações que recapitulam o processo evolutivo. O facto de ser muito variável, complexo e de fácil preservação torna-o uma estrutura comummente utilizada em anatomia comparada e em estudos de biologia evolutiva, nomeadamente para a classificação de vertebrados e reconstruções filogenéticas. Na análise aqui apresentada consideramos um total de 25 espécies: Acanthostega gunnari; 14 espécies dos Mammalia incluindo os grupos Sirenia, Hyracoidea, Carnivora, Cetartiodactyla e Primatas e 10 Reptilia distribuídos entre Crocodylia, Neotheropoda, Squamata, Rhynchocephalia e Testudines. Todos os dados recolhidos foram analisados em três softwares diferentes: PAUP, para uma análise filogenética, Gephi para construir redes de contactos dos ossos do crânio e Rstudio para aferir dados estatísticos. No presente trabalho mostramos que a filogenia de um animal pode ser inferida até ao nível da classe usando somente dados de contactos cranianos, no entanto, não é suficiente para reconstruir árvores filogenéticas.Mestrado em Ecologia Aplicad