Il sito italiano sugli squali

Gli squali fossili


Ginsu mako
Upper Cretaceous
Ordine Famiglia
Lamniformes BERG 1958 Cretoxyrhinidae GLIKMAN 1958

Cretoxyrhina is a Cenomanian to lower Campanian genus present in the fossil faunas of Africa, Europe and the Americas. In North America, it is represented by Cretoxyrhina mantelli (AGASSIZ 1843), common in Upper Cretaceous sediments of the Western Interior Seaway.

The teeth of this genus are large, triangular and very similar in appearance to those of the modern mako shark (Isurus oxyrinchus). The crowns are broadly based and moderately high, with a strong distal inclination in all but the most anterior teeth. They have razor-like (non-serrated) mesial and distal cutting edges. A single pair of cusplets may occur in a few teeth, especially those from the lateral and posterior portions of the jaw. The cutting edge of the tooth extends from crown to root. There is a broad lingual dental band present. The roots are strongly bilobate and rounded, with a prominent lingual protuberance in the anterior teeth. A nutrient groove is never present, and the central lingual foramen is small when present.

Fig. 1 - Cretoxyrhina mantelli
Smoky Hill Chalk, Niobrara Formation, Kansas

In Kansas, Cretoxyrhina mantelli is found in the Carlile Shale (middle Turonian), Fort Hays Limestone (lower through middle Coniacian) and Smoky Hill Chalk (upper Coniacian through lower Campanian). C. mantelli is the most common shark from the family Cretoxyrhinidae in the Smoky Hill chalk. It is found from the base of the chalk upwards, but becomes extinct during early Campanian time. Cretoxyrhina teeth have not been found in the last few meters of this formation. Studies have shown a general increase in size in Cretoxyrhina teeth through time, but fieldwork by the author indicates that the species reaches its largest size by the end of the Coniacian. In the Smoky Hill chalk, the largest teeth have crown heights in the 52-54 mm range. Welton and Farish (1993) cite a 63 mm Cretoxyrhina tooth from gravels derived from the Coniacian / Santonian Austin group in Texas. The Smoky Hill chalk of Kansas has been the source of several well preserved and nearly intact shark "mummies", with complete dentitions, dermal scales, vertebral columns, stomach contents, and fossilized cartilage. This shark probably reached lengths of 6 meters or more in the Western Interior Seaway during the late Cretaceous.

Fig. 2 - Cretoxyrhina mantelli
Smoky Hill Chalk, Niobrara Formation, Kansas
Fig. 3 - Cretoxyrhina mantelli
Smoky Hill Chalk, Niobrara Formation, Kansas
Anterior 33.0 x 21.0 mm, Lateral 27.0 x 30.5 mm

Fig. 4
Fig. 5

Fig. 4 - 5 - 6: Cretoxyrhina mantelli
Sternberg Museum (FHSU VP-2187)
largest tooth 52 mm
Smoky Hill Chalk, Niobrara Formation, Kansas

Shimada, Kenshu, 1997. Stratigraphic Record of the Late Cretaceous Lamniform Shark, Cretoxyrhina mantelli (Agassiz), in Kansas, Trans. Kansas Academy of Science, 100(3-4), pp 139-149

Shimada, Kenshu, 1997. Paleoecological Relationships of the Late Cretaceous Lamniform Shark, Cretoxyrhina mantelli (Agassiz), J. Paleontology, 71(5), pp. 926-933

Shimada, Kenshu, 1997. Dentition of the Late Cretaceous Lamniform Shark Cretoxyrhina mantelli, from the Niobrara chalk of Kansas, Journal of Vertebrate Paleontology, 17(2):269-279.

Shimada, Kenshu, 1997. Periodic Marker Bands in Vertebral Centra of the Lamniform Shark, Cretoxyrhina mantelli, Copea, pp 233-235

Shimada, Kenshu, 1997. Gigantic Lamnoid Shark Vertebra from the Lower Cretaceous Kiowa Shale of Kansas, J. Paleontology, 7(13), pp 522-524

Siverson, Mikael, 1992. Biology, Dental Morphology and Taxonomy of Lamniform Sharks from the Campanian of the Kristianstad Basin, Sweden, Paleontology, Vol. 35, Part 3, pp 519-554

Siverson, Mikael, 1996. Lamniform Sharks of the Mid Cretaceous Alinga Formation and Beedagong Claystone, Western Australia, Paleontology, Vol. 39, Part 4, pp 813-849

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