''Carinodens'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

marine lizard belonging to the

mosasaur Mosasaurs (from Latin ''Mosa'' meaning the 'Meuse', and Ancient Greek, Greek ' meaning 'lizard') are an extinct group of large aquatic reptiles within the family Mosasauridae that lived during the Late Cretaceous. Their first fossil remains wer ...

family. "''Carinodens''" means "keel teeth" and was named in 1969 as a replacement name for ''Compressidens'', "compressed teeth", which was already in use for a

gadilida Gadilida is an order of very small tusk shells, marine scaphopod molluscs. The species within the Gadilida are usually very much smaller than those within the other order of scaphopods, the Dentaliida. Families Families within the order Gadil ...

scaphopod Scaphopoda (plural scaphopods , from Ancient Greek σκᾰ́φης ''skáphē'' "boat" and πούς ''poús'' "foot"), whose members are also known as tusk shells or tooth shells, are a class (biology), class of shelled Marine life, marine inve ...

mollusk. ''Carinodens'' is widely considered a

sister taxon In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

to '' Globidens'' classified within the tribe

Globidensini The Globidensini or Globidentatini are a tribe of mosasaurine mosasaurs, a diverse group of Late Cretaceous marine squamates. Members of the tribe, known as "globidensins" or "globidensine mosasaurs", have been recovered from North America, Eur ...

. Like its close relative, ''Carinodens'' also possesses distinctive round, blunt teeth for crushing primitive clams and oysters. Most of the cranial elements known from the genus have been recovered from deposits in the

Netherlands , Terminology of the Low Countries, informally Holland, is a country in Northwestern Europe, with Caribbean Netherlands, overseas territories in the Caribbean. It is the largest of the four constituent countries of the Kingdom of the Nether ...

and

Belgium Belgium, officially the Kingdom of Belgium, is a country in Northwestern Europe. Situated in a coastal lowland region known as the Low Countries, it is bordered by the Netherlands to the north, Germany to the east, Luxembourg to the southeas ...

, with the only known

postcrania The postcranium ("behind the cranium"; plural: postcrania) or postcranial skeleton in zoology and vertebrate paleontology is the skeleton apart from the skull. The postcranium encompasses the axial skeleton, which includes the entirety of the verte ...

l material being known from deposits of latest

Maastrichtian The Maastrichtian ( ) is, in the International Commission on Stratigraphy (ICS) geologic timescale, the latest age (geology), age (uppermost stage (stratigraphy), stage) of the Late Cretaceous epoch (geology), Epoch or Upper Cretaceous series (s ...

age in

Jordan Jordan, officially the Hashemite Kingdom of Jordan, is a country in the Southern Levant region of West Asia. Jordan is bordered by Syria to the north, Iraq to the east, Saudi Arabia to the south, and Israel and the occupied Palestinian ter ...

. Other materials have been discovered in

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

and

North Africa North Africa (sometimes Northern Africa) is a region encompassing the northern portion of the African continent. There is no singularly accepted scope for the region. However, it is sometimes defined as stretching from the Atlantic shores of t ...

Description

''Carinodens'' measured about in length and is one of the smallest known mosasaurs. It was closely related to '' Globidens'', though is scantly known in comparison. The holotype specimen consists of an incomplete right

dentary In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone ...

and most subsequently referred fossils are isolated teeth. The holotype dentary only preserves the posteriormost teeth, meaning that until recently when more comprehensive material was recovered, most of the dentition of the genus (its most distinctive feature) was unknown. ''Carinodens'' can easily be distinguished from the closely related ''Globidens'' by the compressed nature of its teeth and its relatively delicate dentary. Russell (1967) offered a brief diagnosis (due to the fragmentary nature of the fossils) of the genus, then known as ''Compressidens'': "Small projection of dentary anterior to first dentary tooth. Median dentary teeth bilaterally compressed, bicarinate, subrectangular in lateral view and with pointed apices. Anterior teeth circular in cross-section with strongly recurved pointed apices".

Dentition

By mosasaur standards, the teeth of ''Carinodens'' are unusually

heterodont In anatomy, a heterodont (from Greek, meaning 'different teeth') is an animal which possesses more than a single tooth morphology. Human dentition is heterodont and diphyodont as an example. In vertebrates, heterodont pertains to animals wher ...

, both in morphology and size. The alveoli show a marked size decrease between teeth #8 and #7, and the teeth themselves change dramatically in both size and morphology between #8 and #7. This is similar to the maxillary teeth of '' Globidens dakotensis'' (between positions #5 and #6, though this is less pronounced than in ''Carinodens'') and in '' Globidens alabamaensis''.

Diet

''Carinodens'', like the related '' Globidens'', is considered to have been a durophagous mosasaur. Because the anteriormost part of the dentary of ''Carinodens'' is relatively slender with small pointed tooth crowns, only the posteriormost five teeth actually functioned for crushing food. The anteriormost portion of the dentary was thus likely used for acquiring and handling food rather than crushing it, an idea already suggested by Dollo (1913) during the description of the type species. The maxilla of ''Carinodens'' is unknown, which hinders knowledge on the interaction between the lower and upper jaw. Dollo (1913, 1924) suggested a diet dominated by

echinoderm An echinoderm () is any animal of the phylum Echinodermata (), which includes starfish, brittle stars, sea urchins, sand dollars and sea cucumbers, as well as the sessile sea lilies or "stone lilies". While bilaterally symmetrical as ...

s, whereas Lingham-Soliar (1990, 1999) listed a wide array of potential prey items, including

belemnites Belemnites may refer to: *Belemnitida, an extinct order of cephalopods commonly known as "belemnites" *Belemnites (genus), ''Belemnites'' (genus), a belemnite genus from the Early Jurassic {{disambiguation ...

, nautilids,

bivalves Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed by a calcified exoskeleton consis ...

gastropods Gastropods (), commonly known as slugs and snails, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, freshwater, and from the land. Ther ...

scaphopods Scaphopoda (plural scaphopods , from Ancient Greek σκᾰ́φης ''skáphē'' "boat" and πούς ''poús'' "foot"), whose members are also known as tusk shells or tooth shells, are a class of shelled marine invertebrates belonging to the ph ...

brachiopod Brachiopods (), phylum (biology), phylum Brachiopoda, are a phylum of animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear e ...

s, echinoderms and

arthropod Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...

s. These groups were abundant in the late Cretaceous seas around

Maastricht Maastricht ( , , ; ; ; ) is a city and a Municipalities of the Netherlands, municipality in the southeastern Netherlands. It is the capital city, capital and largest city of the province of Limburg (Netherlands), Limburg. Maastricht is loca ...

, meaning that their population numbers cannot explain the rarity of ''Carinodens''. It is possible that ''Carinodens'' spent most of its life in deep waters, only rarely swimming in shallow seas. Dental wear evidence strongly suggests that ''C. belgicus'' ate hard-shelled benthic invertebrates.

Classification

''Carinodens fraasi'' was first described and illustrated by Louis Dollo in 1913 as "'' Globidens fraasi''". Dollo later erected a separate genus, "''Compressidens''" for the species in 1924, recognising the more compressed nature of the teeth in comparison to those of ''Globidens''. Dollo also assigned '' Bottosaurus belgicus'', previously misinterpreted as a species of crocodilian, to the genus as ''Compressidens belgicus''. With the name ''Compressidens'' being preoccupied by a

mollusk, Thurmond (1969) proposed the substitute name ''Carinodens''. ''Carinodens'' is most frequently recovered as a sister taxon to ''Globidens'' within the

tribe in the

Mosasaurinae The Mosasaurinae are a subfamily of mosasaurs, a diverse group of Late Cretaceous marine Squamata, squamates. Members of the subfamily are informally and collectively known as "mosasaurines" and their fossils have been recovered from every contin ...

. The cladogram below, covering the Globidensini, is based upon a summary of evolutionary adaptations in the Globidensini featured in Schulp et al. (2004), who saw ''C. belgicus'' as being identical to ''C. fraasi'' and having priority:Kuypers, M.M.M., J.W.M. Jagt, H.H.G. Peeters, and D.Th. de Graaf. 1998. "Laat-kretaceische mosasauriërs uit Luik-Limburg: nieuwe vondsten leiden tot nieuwe inzichten". ''Publicaties van het Natuurhistorisch Genootschap in Limburg'' 41: 5–48 The primary feature distinguishing the two recognised species, ''C. fraasi'' and ''C. belgicus'' is found in their dentition. The teeth of ''C. fraasi'' are unicuspid and the teeth of ''C. belgicus'' are tricuspid. ''Carinodens'' fossils from

, consisting of an almost complete skull with at least 24 teeth still occupying their natural locations, a complete neck

vertebra Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spina ...

l series as well as several back vertebrae, and front paddles were reported by Kaddumi (2009). In addition to the

maxilla In vertebrates, the maxilla (: maxillae ) is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The two maxil ...

ry, and

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammals h ...

ry teeth, several small

pterygoid Pterygoid, from the Greek for 'winglike', may refer to: * Pterygoid bone, a bone of the palate of many vertebrates * Pterygoid processes of the sphenoid bone ** Lateral pterygoid plate ** Medial pterygoid plate * Lateral pterygoid muscle * Medial ...

teeth were also recovered from the same specimen. Kaddumi (2009) fully described the remains and referred them to a new species of ''Carinodens'', ''C. palistinicus''. Based on the remarkable dental

y exhibited in ''C. palistinicus'', several previously not considered prey items may be postulated for ''Carinodens'' (Kaddumi 2009). Sharpe et al. (2024) found that the holotype of ''

Xenodens ''Xenodens'' (from Greek language, Greek and Latin for "strange tooth") is a potentially Nomen dubium, dubious extinct genus of marine lizard belonging to the mosasaur family. It contains a single species, ''X. calminechari'' (From Arabic کال� ...

'' could not differentiate that genus from being an earlier ontogenetic stage of the ''Carinodens'' dental morph. They also argued that the limited diagnostic potential of mosasaur teeth should render taxa diagnosed strictly based on teeth ''nomina dubia'', such as most species of ''Carinodens'', with the possible exception of ''C. palistinicus'' which is known from a relatively complete cranial material and partial postcranial material.

References

{{Taxonbar, from=Q1622418 Mosasaurines Mosasaurs of Europe Mosasaurs of Asia Fossil taxa described in 1969