Globidens ("Globe tooth") is anextinctgenus ofmosasaurid oceaniclizard classified as part of theGlobidensini tribe in theMosasaurinae subfamily.Globidens belongs to the familyMosasauridae, which consists of several genera of predatory marine lizards of various sizes that were prevalent during theLate Cretaceous. Specimens ofGlobidens have been discovered inAngola,Brazil,Colombia,Morocco,Syria and theUnited States.[1] Among mosasaurs,Globidens is probably most well known for the highly rounded, globe-like teeth that give it its name.
Globidens alabamaensis was the first species ofGlobidens described, in a publication byCharles W. Gilmore (1912). It is used as thetype specimen forGlobidens.
Globidens was a relatively medium-sized mosasaur, measuring about 5–6 metres (16–20 ft) long.[2] It was similar in appearance to other mosasaurs, with its streamlined body,flippers, a laterally flattenedtail, and powerfuljaws. Theteeth ofGlobidens differed from those of other mosasaurs in being rounded or “globular”, giving rise to its generic name. Most mosasaurs had sharp teeth evolved to grab soft, slippery prey likefish,squid, plesiosaurs, and other mosasaurs. In some later mosasaur species, their teeth were modified to rend flesh as well. While many other mosasaurs were capable of crushing the shells of ammonites or turtles, none were as specialized for dealing with armored prey asGlobidens.Globidens had semispherical teeth with rounded points suited for crushing tough, armored prey, includingturtles,ammonites,nautili, andbivalves. Like its larger relative,Mosasaurus,Globidens had a robustly built skull with tightly-articulating jaws and a strong bite that played a large role in the animal’s ability to penetrate the armor of its shelled prey.
Gilmore's initial assessment ofGlobidens, based on an incomplete specimen ofG. alabamaensis, made note of characteristics observable in parts of the skull, the teeth, and one of thecervical vertebrae. He made note of a long snout with a largemaxilla, a large, sturdyfrontal bone, and the characteristic globular teeth with finely wrinkled enamel. Gilmore concluded that the skull characters were similar toPlatecarpus or, more closely, toBrachysaurus (which is currentlyPrognathodon).
Reconstructed skull ofG. dakotensis
Studies since Gilmore's assessment establish more specific and more complete lists of diagnostic features. Gilmore correctly inferred thatGlobidens had a stout, powerfully built skull. In addition, a few of its notable skull characteristics include a small parietal foramen located entirely within the parietal, tuberosities present on thejugal, a longitudinal crest present on the dorsal surface of the frontal, and apremaxilla with a rostrum anterior to the premaxillary teeth.[3] The rounded teeth with finely wrinkled enamel seen inGlobidens are characteristic of Globidensini. However, the degree of rounding on individual teeth may be indicative of genus or even species. Marginal teeth inGlobidens become most subspherical toward the center of the jaws. Additionally,Globidens had thirteen maxillary teeth and either lacked or showed only rudimentarypterygoid teeth on the roof of its mouth.[3]
Globidens was first described in 1912 byCharles W. Gilmore. Using an incomplete specimen made of only of a partial skull with several teeth, a single cervical vertebra, and numerous fragments, Gilmore identifiedGlobidens as a new genus and named his type specimenGlobidens alabamaensis. The genus name was based on the globular structure of the specimen's teeth and the species name on the location in which it was discovered:Alabama. However, it may be noted that the original location from which the specimen was taken is not precisely known, as Gilmore was examining a specimen that had been collected earlier.[4]
Since Gilmore's identification ofGlobidens, several other species have been identified, includingG. dakotensis (Russell 1975), which is sometimes used as a secondary type specimen alongsideG. alabamaensis. Some specimens previously thought to be new species ofGlobidens have since been reassigned to other taxa, such asPrognathodon, or placed in a new taxa, such asG. aegypticus, which is now a type specimen forIgdamanosaurus.[5]
Globidens alabamaensis Gilmore, 1912 - (Generic type) The height of the tooth crown is less than the greatest tooth crown diameter behind the seventh maxillary tooth. The crown length is greater than the crown width in front of the tenth maxillary tooth. The maxilla is long and the frontal is narrow. The frontal bone slightly enters the orbits dorsally.[3]
G. dakotaensis Russell, 1975 - The height of the tooth crown is less than the greatest tooth crown diameter behind the fourth maxillary tooth. The crown length is greater than the crown width in front of the tenth maxillary tooth. The maxilla is long and the frontal is broad. The frontal bone does not enter the orbits dorsally.[3]
G. phosphaticus Bardet et al. 2005[6] from Morocco and Angola.[1]
G. schurmanni Martin, 2007.
G. hisaensis Kaddumi, 2009 from central Jordan.[7]
G. simplex LeBlancet al. 2019 from Morocco. A complete mandible and partial skull was recovered, showing large jaw adductor musculature attachment points indicative of hard shelled prey. A shortened dentary with respect to the Posterior Mandibular Unit relative to other globidensine mosasaurs supports this as well. Postcranial remains were also recovered and histological analysis of one rib showed increased bone compactness reminiscent of conditions seen in early stages of marine tetrapod evolution, suggesting increased ability to stay submerged for long periods along the sea floor.[8]
Globidens resides within the subfamilyMosasaurinae, which includes several mosasaur lineages, and within that, the TribeGlobidensini, which also includes the genusCarinodens.[3]Carinodens is thus regarded as a sister taxon ofGlobidens.
Placement ofGlobidens and, to an extent, Mosasauridae in a phylogenetic tree is somewhat unclear and specific placement of genera varies between many morphological and molecular tests. It is generally agreed that Mosasauridae is a sister group to Pythonomorpha, which includes all snakes.[13] Within Mosasauridae,Globidens is generally placed nearPrognathodon, although some placements ofPrognathodon specimens are questionable.[14]
Below is acladogram of mosasaurs and related taxa modified from Aaron R. H. Leblanc, Michael W. Caldwell and Nathalie Bardet, 2012:[14]
Lateral and oblique, medial view of the left maxilla ofG. alabamaensis
Globidens was uniquely adapted to take advantage of hard-shelled prey in comparison to other mosasaurs. In addition to a generally robust skull,[3] its teeth are adapted for crushing rather than piercing or tearing. It is believed thatGlobidens was a durophagous predator, eating hard-shelledmollusks such asbivalves andammonites.[15] Stomach contents of a specimen found in South Dakota support prior assumptions, showing the crushed shells ofinoceramid clams.[16]
Globidens, like other mosasaurs, lived in the warm, shallow seas of the Late Cretaceous, such as theWestern Interior Seaway of North America. So far,Globidens has been discovered primarily in North America and in parts of northern and western Africa, such as Morocco and Angola, although specimens from the Middle East and eastern South America have been found as well.[6][17]
^abPolcyn, Michael J.; Jacobs, Louis L.; Schulp, Anne S.; Mateus, Octávio (1 March 2010). "The North African Mosasaur Globidens phosphaticus from the Maastrichtian of Angola".Historical Biology.22 (1–3):175–185.doi:10.1080/08912961003754978.
^Cooper, S.L.A.; Marson, K.J.; Smith, R.E.; Martill, D. (2022). "Contrasting preservation in pycnodont fishes reveals first record of regurgitalites from the Upper Cretaceous (Maastrichtian) Moroccan phosphate deposits".Cretaceous Research.131 (4). 105111.doi:10.1016/j.cretres.2021.105111.
^abcdefRussell, Dale (1975). "A new species ofGlobidens from South Dakota, and a review of globidentine mosasaurs".Fieldiana Geology.33 (13):235–256.
^LeBlanc, Aaron; Mohr, Sydney; Caldwell, Michael (2019). "Insights into the anatomy and functional morphology of durophagous mosasaurines (Squamata: Mosasauridae) from a new species of Globidens from Morocco".Zoological Journal of the Linnean Society.doi:10.1093/zoolinnean/zlz008.
^Zdansky, O. 1935. The occurrence of mosasaurs in Egypt and in Africa in general. Bulletin de l’Institut d’Egypte 17: 83-94.
^Schulp, Anne S.; Jagt, John W. M.; Fonken, Frans (2004-09-10). "New material of the mosasaur Carinodens belgicus from the Upper Cretaceous of the Netherlands".Journal of Vertebrate Paleontology.24 (3):744–747.doi:10.1671/0272-4634(2004)024[0744:NMOTMC]2.0.CO;2.ISSN0272-4634.
^Eric W.A. Mulder; John W.M. Jagt (2019). "Globidens(?) timorensis E. VON HUENE, 1935: not a durophagous mosasaur, but an enigmatic Triassic ichthyosaur".Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen.293 (1):107–116.doi:10.1127/njgpa/2019/0835.
^Kruytzer, E.M. 1961. "Een nieuwe Mosasaurier voor ons land.Globidens belgicus (Woodward 1891).Natuurhistorisch Maandblad50 (7-8): 72-73
^Caldwell, M. W. 1999. Squamate phylogeny and the relationships of snakes and mosasauroids. Zoological Journal of the Linnean Society, 125(1):115-147
^abAaron R. H. Leblanc, Michael W. Caldwell and Nathalie Bardet (2012). "A new mosasaurine from the Maastrichtian (Upper Cretaceous) phosphates of Morocco and its implications for mosasaurine systematics".Journal of Vertebrate Paleontology.32 (1):82–104.doi:10.1080/02724634.2012.624145.
^Massare, J. A. 1987. Tooth Morphology and Prey Preference of Mesozoic Marine Reptiles. Journal of Vertebrate Paleontology, 7(2):121-137.
^Martin, J. E. and Fox, J. E. 2007. Stomach contents ofGlobidens, a shell-crushing mosasaur (Squamata), from the Late Cretaceous Pierre Shale Group, Big Bend area of the Missouri River, central South Dakota. Geological Society of America Special Papers, 427:167-176.doi:10.1130/2007.2427(12)
^Polcyn, M. J., Jacobs, L. L., Schulp, A. S., and Mateus, O. 2010. The North African MosasaurGlobidens phosphaticus from the Maastrichtian of Angola. Historical Biology, 22(3):175-185.
Everhart, M.J. 2008. Rare occurrence of aGlobidens sp. (Reptilia; Mosasauridae) dentary in the Sharon Springs Member of the Pierre Shale (Middle Campanian) of Western Kansas. p. 23-29 in Farley G. H. and Choate, J.R. (eds.), Unlocking the Unknown; Papers Honoring Dr. Richard Zakrzewski, Fort Hays Studies, Special Issue No. 2, 153 p., Fort Hays State University, Hays, KS.[page needed]
Huene, E. von. 1935. Mosasaurier-Zähne von Timor. Zentralblatt für Mineralogie, Geologie und Palaeontologie; in Verbindung mit den Neuen Jahrbuch für Mineralogie, Geologie und Palaeontologie. Stuttgart. Abt. B 10 412-416, 3 figs. (in German)
Martin, J. E. 2007. A new species of the durophagous mosasaur,Globidens (Squamata: Mosasauridae) from the Late Cretaceous Pierre Shale Group of central South Dakota, USA. Pages 167-176 in Martin, J. E. and Parris D. C. (eds.), The Geology and Paleontology of the Late Cretaceous Marine Deposits of the Dakotas. Geological Society of America, Special Paper 427. (Globidens schurmanni)
Russell, Dale A. 1975. A new species ofGlobidens from South Dakota. Fieldiana Geology, 33(13): 235-256. (Field Museum of Natural History)
