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Euthecodon is an extinct genus of long-snouted crocodile. It was common throughout much of Africa during the Neogene, with being especially common in Kenya, Ethiopia, and Libya. Although superficially resembling that of gharials, the long snout was a trait developed independently from that of other crocodilians and suggests a diet of primarily fish. Euthecodon coexisted with a wide range of other crocodiles in the areas it inhabited before eventually going extinct during the Pleistocene.
Some estimates suggest Euthecodon to be among the largest Cenozoic crocodilians, if not one of the largest , with one specimen (LT 26306), found in Lothagam in the Lake Turkana, being estimated to have reached a total body length of up to . This specimen's skull alone would have measured . Other specimens indicate smaller sizes however. In particular specimen KNM-ER 757 from the Koobi Fora Formation, a skull measuring , was calculated to yield a length of , accounting for a change in proportion in large sized crocodiles. Brochu and Storrs however note that this estimate was achieved by using the proportions of nile crocodile and saltwater crocodiles, which differ significantly in skull to body ration when compared to longirostrine taxa. Subsequently, these estimates may be exaggerating the actual size of Euthecodon in the absence of described postcranial remains.
Other remains of Euthecodon are known from the Miocene Beglia Formation (Tunisia), Early Miocene Rusinga Island (Lake Victoria), the Albertine Rift (Congo),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.Aoki, R. (1992). Fossil crocodilians from the Late Tertiary strata in the Sinda Basin, eastern Zaire. African Study Monographs, Supplementary issue 17:67-85. Ombo (Kenya) 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 and the Messinian to Zanclean Sahabi Formation (Libya). Despite this abundance in northern Africa around the Mediterranean, no fossils of Euthecodon have ever been found outside Africa.
Among the three recognized species, Ginsburg and Buffetaut note a clear evolutionary series from the oldest to youngest species. According to their research, Euthecodon shows a series of adaptations present in E. arambourgi and progressively exaggerated in E. nitriae, reaching their peak with E. brumpti. These adaptations include the gradual loss of the second premaxillary tooth, development of additional maxillary teeth, continued lengthening and narrowing of the skull, the exaggeration of a pre-orbital boss spanning the nasal, lacrimal, prefrontal and frontal bones, the raising of the external nares and the prominence of the lacrimal crest. The eyes also face more forward in later species than they do in E. arambourgi. The authors do, however, note that certain traits do not conform to such a direct evolutionary series, and instead appear most prominent in the intermediate E. nitriae. One such example is that in E. nitriae the prefrontals overflow the orbits, giving them a more circular appearance compared to that of E. brumpti. Ginsburg and Buffetaut suggests that this could be evidence for two possible hypothesis. The first holds on to a continuous lineage, suggesting that the continued rise of the nasal to frontal boss caused a complete reshaping of the region around the orbits, effectively undoing adaptations seen in earlier forms. Their second hypothesis proposes that Euthecodon split into two lineages, both evolving increasingly longirostral forms but doing so in different ways. This latter interpretation is favored by the fact that Euthecodon was clearly already present in East Africa by the early Miocene, as indicated by the remains from Ombo and Rusinga Island.
Restricting the analysis to morphological data alone removes Mecistops from Osteolaeminae and brings Voay into the family. In this tree Euthecodon clusters with Brochuchus.
Euthecodon was just one of several species within the diverse Crocodilian fauna of Miocene to Pliocene Africa, mirroring similar conditions observed elsewhere during the Miocene (South Americas Pebas Megawetlands and Australia's Riversleigh). In Lothagam, in the southwestern part of the Turkana Basin, Euthecodon brumpti coexisted with as many as four different species of crocodiles, including the earliest records of Mecistops, the gharial Eogavialis and two species of Crocodylus: C. checchiai and C. thorbjarnarsoni. Of these, Euthecodon and Eogavialis are heavily specialised for a piscivorous diet, specialising in preying on smaller fish. Mecistops cataphractus, the modern slender-snouted crocodile, also shows a longirostrine snout morphology, but is more generalist, feeding on amphibians, crustaceans and birds in addition to fish. Such a high number of taxa all coexisting indicates a high degree of niche partitioning supported by favorable environmental conditions and a rich selection of prey items. Fish fossils from Lothagam indicate the presence of Nile perch, bichir, African lungfish and Gymnarchus.
In northern Africa conditions appear similar, with Euthecodon arambourgi appearing alongside a cast of other crocodilians including the brevirostrine Rimasuchus and Crocodylus checchiai and the longirostrine Tomistoma lusitanicum in both Egypt and Libya. Both Moghara and Gebel Zelten preserve fluvio-marine environments yielding fossils of sharks, dolphins and sawfish alongside catfish, anthracotheres, carnivorans, proboscideans and primates. Gebel Zelten is especially well understood, the environment being reconstructed as rivers banked by tropical forests coming from the south and feeding into a large lagoon, while the intermediate areas are covered by savanna. Although some crocodilians of the area ( Crocodylus, Tomistoma and possibly Gavialosuchus) have been found on both sides of the Mediterranean, Euthecodon seemingly never ventured outside of Africa. This may be connected to its specialised lifestyle, preventing it from venturing too far out into saltwater and restricting it to the riverbanks further up river. By the time of Euthecodon brumpti, crocodilian diversity had diminished in East Africa compared to that in the older Pliocene records. In Ethiopia Euthecodon appeared alongside only two other crocodiles, the modern Nile crocodile and the slender-snouted crocodile. Eventually, increased aridification, increased salinity and conditions favoring more temporary bodies of water may have all contributed to the disappearance of the highly specialised Euthecodon, incapable of sustaining itself or traveling over great enough distances to other bodies of water like the generalist Nile crocodile.
Species
Phylogeny
Although the genus was considered to be a tomistomine gavialoid or even a direct descendant of EogavialisTchernov, 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.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. by early research due to its elongated skull, later research has repeatedly shown this to be merely be the result of convergent evolution, instead placing it much deeper within the Crocodylidae. For instance, Euthecodon differs from gavialids and most tomistomines in its small supratemporal fossae and the relatively gradual narrowing of the rostrum (something much more abrupt in gharials). Most current analyses place it in Osteolaeminae, a family consisting of the extant dwarf crocodile and the extinct Rimasuchus, Brochuchus as well as possible Voay and the slender-snouted crocodile.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.Brochu, C. (1997). Morphology, fossils, divergence timing, and the phylogenetic relationships of Gavialis. Systematic Biology 46:479-522. Phylogenetic analysis utilizing molecular (DNA sequencing), stratigraphic (fossil age) and morphological data recovers Osteolaeminae, as shown below, with Mecistops as a close relative of Euthecodon. Voay was recovered as closer to the genus Crocodylus.
Paleoecology
Although Euthecodon superficially resembles gharials and likely inhabited a similar Ecological niche, its the functional morphology shows some clear differences. Throughout their evolutionary history, many Pseudosuchian groups that evolved elongated skulls (Thalattosuchia, Tethysuchia and many gavialoids) also show enlarged supratemporal fossae. Contrary to this connection between fossa size and snout length, however, Euthecodon has notably small supratemporal fossae, creating only a weak insertion point for the jaw musculature (adductor mandibulae externus profundus muscle). The unique alveolar sleeves likely evolved to at least partly compensate for this, allowing the bodies of the teeth to be much narrower than in other longirostrine taxa. Despite this, however, Euthecodon would have likely still had a relatively weak bite. The eyes also show clear convergence with gavialoids through different means. To elevate their eyes above the rostrum, derived gharials have increased the circumference of the orbits and enlarged orbital rims, while in Euthecodon similar results are achieved by raising the entire orbital region. The extremely elongated yet fragile rostrum, trap-like interlocking teeth and raised nares and orbits all indicate a piscivorous diet and aquatic lifestyle, perfected by the Pliocene to Pleistocene Euthecodon brumpti.
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