Euthecodon

Euthecodon is an extinct genus of long-snouted crocodyline crocodilians. It was common throughout much of Africa during the Neogene, with fossils being especially common in Kenya. It existed from the Early Miocene to the Early Pleistocene.

Euthecodon
Temporal range: Miocene—Pleistocene, 23.03–0.781 Ma
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Crocodilia
Family: Crocodylidae
Subfamily: Crocodylinae
Genus: †Euthecodon
Fourtau, 1920
Type species
†Euthecodon nitriae
Fourtau, 1920
Species
  • †E. nitriae Fourtau, 1920
  • †E. brumpti Joleaud, 1920
  • †E. arambourgi Ginsburg and Buffetaut, 1978

Description
Scale diagram showing the size of E. brumpti (orange)

Euthecodon was large for a crocodilian. One specimen, LT 26306, found from the Turkana Basin, was estimated by skull length to have been around 10 m long.[1] It had a narrow rostrum that was unusually elongate with deeply scalloped dorsal margins. The skull table, however, was proportionally small and is almost square in shape. The jaws were lined with isodont, or slender, similarly sized and shaped, teeth. Unlike nearly all other crocodilians, Euthecodon possessed only four premaxillary teeth. Because they are sharp and bicarinate, they are believed to have been an adaptation for a piscivorous feeding habit, or a diet that included fish.

Discovery and species

Collected material now known to be from Euthecodon was initially placed in the genus Tomistoma, of which the modern false gharial is a member. These specimens were described from the Pliocene Omo Group in Ethiopia.[2] The genus Euthecodon was first named in 1920 on the basis of material found from Wadi Natrun, Egypt. This material was believed to have belonged to the same species as the specimens from Ethiopia, yet it appeared to be distinct from the genus Tomistoma. As a result, the material from Ethiopia was reassigned to the new genus along with the material from Egypt, with the species being named E. nitriae.[3]

A new species, named E. brumpti, was found from Lothagam, Kenya and can be distinguished from E. nitriae by skull and rostral proportions as well as tooth count.[4][5][6] E. brumpti is one of the most common fossil crocodylians found in the Turkana Basin, along with Crocodylus. A complete articulated skull and mandible referrable to E. brumpti was found in situ from the Kaiyumung Member of the Nachukui Formation in Lothagam in 1992.[7]

A shorter snouted species named E. arambourgi has been found from early Miocene deposits in Gebel Zelten, Libya.[8][9][10] Classification of specimens from several localities across Africa are indeterminant at the species level, with material being found from the Sahabi Formation in Libya of early Pliocene age,[11] the Victoria Basin strata of Rusinga Island of early Miocene age,[12] early Miocene deposits in Ombo, Kenya,[13] and possibly the Albertine Rift sediments of the Congo of early Miocene age.[14][15]

Phylogeny

Euthecodon was originally considered a tomistomine crocodilian. It has even been suggested to be a direct offshoot of Eogavialis.[16][17] However, it is now thought to be a crocodylid, having been allied with Rimasuchus, Osteolaemus, and Voay in the past.[18][19]

References
  1. Storrs, G. W. (2003). Late Miocene-Early Pliocene crocodilian fauna of Lothagam, southwest Turkana Basin, Kenya. In: Lothagam: The Dawn of Humanity in Eastern Africa pp. 137–159. New York. Columbia University Press. ISBN 0-231-11870-8.
  2. Joleaud, L. (1920). Sur la présence d'un Gavialide du genre Tomistoma dans le Pliocène d'eau douce de l'Ethiopie. Comptes Rendus de l'Académie des Sciences 70:816-818.
  3. Forteau, R., ed. (1920). Contribution à l'étude de vertébrés Miocènes de l'Egypt. Cairo. Government Press.
  4. Ginsburg, L. E. and Buffetaut, E. (1978). Euthecodon arambourgi n. sp. et l'évolution du genera Euthecodon, crocodilien du Néogène d'Afrique. Géologie Méditerranéenne 5:291-302.
  5. Kälin, J. (1955). Crocodilia. In: J. Piveteau, ed., Traité de paléontologie 5:695-784. Paris: Masson.
  6. Steel, R. (1973). Crocodylia. In: O. Kuhn, ed., Handbuch der Paläoherpetologie 16:1-116. Stuttgart. Fischer.
  7. Leakey, M. G. and Harris, J. M. (2003). "Introduction". Lothagam: The Dawn of Humanity in Eastern Africa. Columbia University Press. New York. p. 6. ISBN 0-231-11870-8
  8. Arambourg, C. and Magnier, P. (1961). Gisement de vértébres dans le bassin tertiare de Syrte (Lybie). Comptes Rendus de l'Académie des Sciences 252:1181-1183.
  9. Buffetaut, E. (1985). Zoogeographical history of African crocodilians since the Triassic. In: Karl L. Schuchmann, ed., Proceedings of the International Symposium on African Vertebrates: Systematics, Phylogeny and Evolutionary Ecology. pp. 453-469. Bonn. Zoologisches Forschunginstitut und Museum Alexander Koening.
  10. Ginsburg, L. and Buffetaut, E. (1978). Euthecodon arambourgi n. sp. et l'évolution du genre Euthecodon, crocodilien du Néogène d'Afrique. Géologie Méditerranéenne 5:291-302.
  11. Hecht, M. K. (1987). Fossil snakes and crocodilians from the Sahabi Formation of Libya. In: N. T. Boaz, A. El-Arnauti, A. W. Gaziry, J. de Heinzelin, and D. D. Boaz, eds., Neogene Paleontology and Geology of Sahabi. pp. 101-106. New York. Liss.
  12. Tchernov, E. and Van Couvering, J. (1978). New crocodiles from the Early Miocene of Kenya. Palaeontology 21:857-867.
  13. Buffetaut, E. (1979). Présence du crocodilien Euthecodon dans le Miocène inférieur d'Ombo (golfe de Kavirondo, Kenya). Bulletin de la Société Géologique de France 21:321-322
  14. Aoki, R. (1992). Fossil crocodilians from the Late Tertiary strata in the Sinda Basin, eastern Zaire. African Study Monographs, Supplementary issue 17:67-85.
  15. Pickford, M. (1994). Late Cenozoic crocodiles (Reptilia:Crocodylidae) from the Western Rift, Uganda. In: B. Senut and M. Pickford, eds., Geology and Paleobiology of the Albertine Rift Valley, Uganda-Zaire. Paleobiology/Paléobiologie 2(29):137-155. Orléans. Centre International pour la Formation et les Echanges Géologiques.
  16. Tchernov, E. (1976). Crocodylidae from the Pliocene/Pleistocene formations of the Rudolf Basin. In: Y. Coppens, F. C. Howell, G. L. Isaac and R. E. Leakey, eds., Earliest Man and Environments in the Lake Rudolf Basin: Stratigraphy, Paleoecology, and Evolution, pp. 370-378. Chicago. University of Chicago Press.
  17. Tchernov, E. (1986). Evolution of the Crocodiles in East and North Africa. Cahiers de Paléontologie. Paris. Centre National pour la Formation et les Echanges Géologiques.
  18. Brochu, C. (1997). Morphology, fossils, divergence timing, and the phylogenetic relationships of Gavialis. Systematic Biology 46:479-522.
  19. Brochu, C. and Storrs, G. W. (1995). The giant dwarf crocodile: A reappraisal of "Crocodylus" robustus from the Quaternary of Madagascar. In: B. D. Patterson, S. M. Goodman, and J. L. Sedlock, eds., Environmental Change in Madagascar. pp. 6. Chicago. Field Museum.
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