Pythonomorpha was originally proposed by

paleontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...

Edward Drinker Cope (1869) as a reptilian order comprising

mosasaurs Mosasaurs (from Latin ''Mosa'' meaning the 'Meuse', and Greek ' meaning 'lizard') comprise a group of extinct, large marine reptiles from the Late Cretaceous. Their first fossil remains were discovered in a limestone quarry at Maastricht on th ...

, which he believed to be close relatives of

Ophidia __FORCETOC__ Ophidia (also known as Pan-Serpentes) is a group of squamate reptiles including modern snakes and reptiles more closely related to snakes than to other living groups of lizards. Ophidia was defined as the "most recent common ancest ...

( snakes). The etymology of the term Pythonomorpha comes from the

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

''Python'' (a monstrous snake from

Greek mythology A major branch of classical mythology, Greek mythology is the body of myths originally told by the ancient Greeks, and a genre of Ancient Greek folklore. These stories concern the origin and nature of the world, the lives and activities ...

) and ''morphe'' ("form"), and refers to the generally serpentine body plan of members of the group. Cope wrote, "In the mosasauroids, we almost realize the fictions of snake-like dragons and sea-serpents, in which men have been ever prone to indulge. On account of the

ophidia __FORCETOC__ Ophidia (also known as Pan-Serpentes) is a group of squamate reptiles including modern snakes and reptiles more closely related to snakes than to other living groups of lizards. Ophidia was defined as the "most recent common ancest ...

n part of their affinities, I have called this order Pythonomorpha." Cope incorporated two families, the Clidastidae (now defunct but including only ''

Clidastes ''Clidastes'' is an extinct genus of marine lizard belonging to the mosasaur family. It is classified as part of the Mosasaurinae subfamily, alongside genera like ''Mosasaurus'' and ''Prognathodon''. ''Clidastes'' is known from deposits ranging i ...

'') and the Mosasauridae (including ''Macrosaurus'' ''Tylosaurus''.html"_;"title="Tylosaurus.html"_;"title="=Tylosaurus">''Tylosaurus''">Tylosaurus.html"_;"title="=Tylosaurus">''Tylosaurus''_''Mosasaurus.html" ;"title="Tylosaurus">''Tylosaurus''.html" ;"title="Tylosaurus.html" ;"title="=Tylosaurus">''Tylosaurus''">Tylosaurus.html" ;"title="=Tylosaurus">''Tylosaurus'' ''Mosasaurus">Tylosaurus">''Tylosaurus''.html" ;"title="Tylosaurus.html" ;"title="=Tylosaurus">''Tylosaurus''">Tylosaurus.html" ;"title="=Tylosaurus">''Tylosaurus'' ''Mosasaurus'', and ''Platecarpus''). However, a close relationship between mosasaurs and snakes was rejected by most 20th-century herpetologists and paleontologists, who sought, instead, to demonstrate a close relationship between mosasaurs and varanid (monitor) lizards and who generally considered snakes to have evolved from

terrestrial Terrestrial refers to things related to land or the planet Earth. Terrestrial may also refer to: * Terrestrial animal, an animal that lives on land opposed to living in water, or sometimes an animal that lives on or near the ground, as opposed to ...

, burrowing lizards (see, for example, Russell, 1967). Cope's Pythonomorpha was later resurrected by a number of paleontologists (Lee, 1997; Caldwell et Lee, 1997) who had conducted

cladistic Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived char ...

analyses that seemed to show that snakes and mosasaurs may have been more closely related to one another than either were to the varanid lizards, and that snakes more likely arose from aquatic ancestors. As redefined by Lee (1997), the monophyletic Pythonomorpha consists of "the most recent common ancestor of mosasauroids and snakes, and all its descendants." This would include the aigialosaurs, dolichosaurs, coniasaurs, mosasaurs, and all snakes. Lee (1997) was able to show no less than 38 synapomorphies supporting Pythonomorpha. If Pythonomorpha is valid, it contains not only mosasauroids but the Ophidiomorpha, which was defined as a node-based clade containing the most recent common ancestor of dolichosaurs, adriosaurs, '' Aphanizocnemus'', and fossil and extant

and all of its descendants. However, the validity of Pythonomorpha is still debated; indeed, there is no consensus about the relationships of snakes or mosasaurs to each other, or to the rest of the lizards. An analysis by Conrad (2008) placed mosasaurs with varanoid lizards, and snakes with skinks, while an analysis by Gauthier et al. (2012) suggested that mosasaurs are more primitive than either snakes or varanoids. However, a combined morphological and molecular analysis by Reeder et al. (2015) recovered Mosasauria and Serpentes as sisters, consistent with Pythonomorpha.

References

* Caldwell, M. W., Carroll, R. L. et Kaiser, H. 1995: The pectoral girdle and forelimb of ''Carsosaurus marchesetti'' (Aegialosauridae), with a preliminary phylogenetic analysis of Mosasauroids and varanoids. ''Journal of Vertebrate Paleontology'' 15(3): 516-531. * Caldwell, M. W. et Lee, M. S. Y. 1997. A snake with legs from the marine Cretaceous of the Middle East. ''Nature'' 386:705-709. * Caldwell, M. W. 1999. Squamate phylogeny and the relationships of snakes and mosasauroids. ''Zoological Journal of the Linnean Society'' 125:115-147. * Cope, E. D. 1869. On the reptilian orders Pythonomorpha and Streptosauria. ''Proceedings of the Boston Society of Natural History'' 12:250–266. * Lee, M. S. Y. 1997. The phylogeny of varanoid lizards and the affinities of snakes. ''Philosophical Transactions of the Royal Society of London B'' 352:53-91. * Lee, M. S. Y. et Caldwell, M. W.. 2000. ''Adriosaurus'' and the affinities of mosasaurs, dolichosaurs, and snakes. ''Journal of Paleontology'' 74(5):915-937. * Russell, D. A., 1967. Systematics and morphology of American mosasaurs. Peabody Museum of Natural History, Yale University, Bulletin 23. * Gauthier, J. A., Kearney, M., Maisano, J.A., Rieppel, O. et Behkke, A. D. B. 2012: Assembling the Squamate Tree of Life: Perspectives from the Phenotype and the Fossil Record. ''Bulletin of the Peabody Museum of Natural History'' 53(1):3-308. {{Taxonbar, from=Q4180380 Anguimorpha Bajocian first appearances Extant Middle Jurassic first appearances Taxa named by Edward Drinker Cope

References

Further reading