Hybodont sharks from the lower Cretaceous Khok Kruat Formation of Thailand, and hybodont diversity during the Early Cretaceous
Published:January 01, 2008
G. Cuny, V. Suteethorn, S. Kamha, E. Buffetaut, 2008. "Hybodont sharks from the lower Cretaceous Khok Kruat Formation of Thailand, and hybodont diversity during the Early Cretaceous", Fishes and the Break-up of Pangaea, L. Cavin, A. Longbottom, M. Richter
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Isolated teeth of five hybodont species are described from the Khok Kruat Formation (Aptian): Hybodus aequitridentatus nov. sp., Heteroptychodus steinmanni, Thaiodus ruchae, Khoratodus foreyi nov. gen. et nov. sp., and Acrorhizodus khoratensis. A new family, Thaiodontidae is also erected for Thaiodus and Khoratodus. Two species are recognized inside the genus Heteroptychodus, H. steinmanni and H. chuvalovi nov. comb. These sharks show a wide range of diet and many of them appear to be restricted to a freshwater environment and thus are probably endemic to the Khorat Plateau. However, Thaiodus and Heteroptychodus are also found in deltaic and/or marine environments outside Thailand, but are nevertheless restricted to the Asian continent. It seems that the appearance of three different palaeobiogeographical provinces (Europe, Asia and Africa–South America) around the Tethys during the Early Cretaceous led to the highest diversity at the generic level in the history of hybodont sharks.
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Fishes and the Break-up of Pangaea
This volume, in honour of Peter L. Forey, is about fishes as palaeobiogeographic indicators in the Mesozoic and Cenozoic. The last 250 million years in the history of Earth have witnessed the break-up of Pangaea, affecting the biogeography of organisms. Fishes occupy almost all freshwater and marine environments, making them a good tool to assess palaeogeographic models.
The volume begins with studies of Triassic chondrichthyans and lungfishes, with reflections on Triassic palaeogeography. Phylogeny and distribution of Late Jurassic neoselachians and basal teleosts are broached, and are followed by five papers about the Cretaceous, dealing with SE Asian sharks, South American ray-finned fishes and coelacanths, European characiforms, and global fish palaeogeography. Then six papers cover Tertiary subjects, such as bony tongues, eels, cypriniforms and coelacanths.
There is generally a good fit between fish phylogenies and the evolution of the palaeogeographical pattern, although a few discrepancies question details of current palaeogeographic models and/or some aspects of fish phylogeny.