Abstract
an order of late Paleozoic freshwater sharks in the superorder Euselachii; formerly called Pleuracanthodii. Eellike and as long as 13 feet, the Xenacanthida are distinguished by two-pronged teeth and a large serrated spine extending backward from the rear of the braincase. They appeared in the Carboniferous and spread worldwide in the Permian, but only a few genera survived the Permian extinctions before disappearing in the Middle Triassic.
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Carlton, R.L. (2019). X. In: A Concise Dictionary of Paleontology. Springer, Cham. https://doi.org/10.1007/978-3-030-25586-2_24
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DOI: https://doi.org/10.1007/978-3-030-25586-2_24
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