Dolichosauridae (from Latin, dolichos = "long" and Greek sauros= lizard) is a family of Cretaceous aquatic lizards. They are widely considered to be the earliest and most primitive members of Mosasauria, though some researchers have recovered them as more closely related to snakes.[5]
| Dolichosauridae | |
|---|---|
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| Fossil skeleton of Pontosaurus | |
Scientific classification 
| |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Order: | Squamata |
| Clade: | Toxicofera |
| Family: | †Dolichosauridae Gervais, 1852 |
| Genera | |
Description
editDolichosaurus was a small marine squamate at about 0.5 to 1 meter in total length.[6] Coniasaurus was similarly sized at about 0.5 meters in length.[7] They were elongated (especially apparent in the neck) marine lizards with reduced limbs and small, thin heads. Dolichosaurs may have occupied a niche similar to the earlier nothosaurs and modern sea snakes, in using their thin heads to feed in crevices and narrow spaces along coral reefs and rocky shores.[6] One of the earliest dolichosaurs, Kaganaias from Barremian,[1][2][4] probably lived in freshwater environment unlike other members in the family.[3] Despite their aquatic nature, fluctuations in sea level did not appear to have any significant effects on dolichosaurid evolution during the Cenomanian and Turonian.[8]
The degree to which the limbs were reduced suggest that the dolichosaurs would have been unable to generate any significant movement on land, and they thus likely spent most of their time underwater.[6] Though the reduction of the limbs have no obvious evolutionary advantage, it is an adaptation that might be shared with early snakes.[9]
History of discovery
editBoth of the genera routinely referred to the Dolichosauridae, Dolichosaurus and Coniasaurus, were described by Richard Owen in 1850 based on specimens of Cenomanian age collected from the Lower Chalk of southeastern England.[10] The unusually large number of dorsal and cervical vertebrae present in Dolichosaurus prompted it to be named as a new genus and Coniasaurus could be distinguished from known Cretaceous lizards by dental characteristics.[10] Nopcsa (1908)[11] restudied the specimens discovered by Owen and described several new specimens of Coniasaurus and Dolichosaurus.
Classification
editMany authors have suggested the dolichosaurs to be a paraphyletic group.[5]
Both known species of Coniasaurus, C. gracilodens and C. crassidens, are known from disarticulated skulls with isolated vertebral elements. In contrast, Dolichosaurus longicollis, the only species of Dolichosaurus, is known from postcranial skeletons with only very fragmentary skulls and no teeth. This has made the exact nature of their relation difficult to determine.[6]
Coniasaurus and Dolichosaurus are generally considered to be either nested within basal mosasauroids as a third group alongside mosasaurs and aigialosaurs,[11] or as the sister group to the mosasauroids.[12] The difficulties in establishing more certain relationships not only between the Dolichosauridae and the Mosasauroidea, but also between Dolichosaurus and Coniasaurus, arise from the nature of the fossil remains referred to the genera. With Coniasaurus largely lacking postcranial material and Dolichosaurus largely lacking cranial material, they are difficult to compare with each other.[6]
Studies that propose a close relation between snakes and mosasauroids in a group dubbed Pythonomorpha demonstrate the importance of Dolichosaurus, Coniasaurus and other Late Cretaceous marine squamates in squamate phylogeny and evolutionary history.[12] The hypothesis suggesting that snakes, mosasaurs, aigialosaurs and dolichosaurs share a common aquatic ancestor is not universally accepted and stands in stark contrast with the previously widespread hypothesis of snakes having a fossorial origin.[6]
The cladogram below is based on Palci and Caldwell (2010a), Caldwell and Palci (2010b),[13][14] placing the Dolichosauridae as a sister group to modern snakes and their closest ancestors.
Other authors have disagreed with this hypothesis, instead placing dolichosaurs at the base of Mosasauria, with Mosasauria unrelated to snakes.[5]
Cladogram following Augusta et al. (2022):[5]
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Ophidia (snakes) | |
References
edit- ^ a b c d Ilaria Paparella; Alessandro Palci; Umberto Nicosia; Michael W. Caldwell (2018). "A new fossil marine lizard with soft tissues from the Late Cretaceous of southern Italy". Royal Society Open Science. 5 (6): 172411. doi:10.1098/rsos.172411. PMC 6030324. PMID 30110414.
- ^ a b c d Michael W. Caldwell; Tiago R. Simões; Alessandro Palci; Fernando F. Garberoglio; Robert R. Reisz; Michael S. Y. Lee; Randall L. Nydam (2021). "Tetrapodophis amplectus is not a snake: re-assessment of the osteology, phylogeny and functional morphology of an Early Cretaceous dolichosaurid lizard". Society of Vertebrate Paleontology, Latest Articles. 19 (13): 893–952. doi:10.1080/14772019.2021.1983044. S2CID 244414151.
- ^ a b Evans, Susan E.; Manabe, Makoto; Noro, Miyuki; Isaji, Shinji; Yamaguchi, Mikiko (2006). "A Long-Bodied Lizard from the Lower Cretaceous of Japan". Palaeontology. 49 (6): 1143–1165. doi:10.1111/j.1475-4983.2006.00598.x. ISSN 0031-0239. S2CID 129356719.
- ^ a b Amiot, Romain; Kusuhashi, Nao; Saegusa, Haruo; Shibata, Masateru; Ikegami, Naoki; Shimojima, Shizuo; Sonoda, Teppei; Fourel, François; Ikeda, Tadahiro; Lécuyer, Christophe; Philippe, Marc (2021-01-01). "Paleoclimate and ecology of Cretaceous continental ecosystems of Japan inferred from the stable oxygen and carbon isotope compositions of vertebrate bioapatite". Journal of Asian Earth Sciences. 205: 104602. doi:10.1016/j.jseaes.2020.104602. ISSN 1367-9120.
- ^ a b c d Augusta, Bruno G.; Zaher, Hussam; Polcyn, Michael J.; Fiorillo, Anthony R.; Jacobs, Louis L. (2022-08-11), Gower, David J.; Zaher, Hussam (eds.), "A Review of Non-Mosasaurid (Dolichosaur and Aigialosaur) Mosasaurians and Their Relationships to Snakes", The Origin and Early Evolutionary History of Snakes (1 ed.), Cambridge University Press, pp. 157–179, doi:10.1017/9781108938891.011, ISBN 978-1-108-93889-1, retrieved 2024-01-30
- ^ a b c d e f Caldwell, Michael W. (2000-12-01). "On the aquatic squamate dolichosaurus longicollis (cenomanian, upper cretaceous), and the evolution of elongate necks in squamates". Journal of Vertebrate Paleontology. 20 (4): 720–735. doi:10.1671/0272-4634(2000)020[0720:OTASDL]2.0.CO;2. ISSN 0272-4634. S2CID 86163923.
- ^ Caldwell M.W. & Cooper J.A. (1999). "Redescription, palaeobiogeography and palaeoecology of Coniasaurus crassidens Owen, 1850 (Squamata) from the Lower Chalk (Cretaceous; Cenomanian) of SE England" (PDF). Zoological Journal of the Linnean Society. 127 (4): 423–452. doi:10.1111/j.1096-3642.1999.tb01380.x.
- ^ Jacobs, L. L.; Ferguson, K.; Polcyn, M. J.; Rennison, C. (1 April 2016). "Cretaceous δ13C stratigraphy and the age of dolichosaurs and early mosasaurs". Netherlands Journal of Geosciences. 84 (3): 257–268. doi:10.1017/S0016774600021041. Retrieved 13 March 2023.
- ^ Lee, Michael S. Y.; Caldwell, Michael W. (29 October 1998). "Anatomy and relationships of Pachyrhachis problematicus, a primitive snake with hindlimbs". Philosophical Transactions of the Royal Society B: Biological Sciences. 353 (1375): 1521–1552. doi:10.1098/rstb.1998.0308. ISSN 0962-8436. PMC 1692386.
- ^ a b Owen, R. 1850. Description of the Fossil Reptiles of the Chalk Formation; pp. 378–404 in F. Dixon (ed.), The Geology and Fossils of the Tertiary and Cretaceous Formations.
- ^ a b Nopcsa, F. 1908. Zur kenntnis der fossilen Eidechsen. Beitra¨ge zur Pala¨ontologie und Geologie O¨sterreich-Ungarns und des Orients 21: 33–62.
- ^ a b Caldwell, M. (1999-01-01). "Squamate phylogeny and the relationships of snakes and mosasauroids". Zoological Journal of the Linnean Society. 125 (1): 115–147. doi:10.1006/zjls.1997.0144. ISSN 0024-4082.
- ^ Alessandro Palci & Michael W. Caldwell (2010a). "Redescription of Acteosaurus tommasinii von Meyer, 1860, and a discussion of evolutionary trends within the clade Ophidiomorpha". Journal of Vertebrate Paleontology. 30 (1): 94–108. doi:10.1080/02724630903409139. S2CID 85217455.
- ^ Caldwell, Michael W.; Palci, Alessandro (2010). "A new species of marine ophidiomorph lizard,Adriosaurus skrbinensis, from the Upper Cretaceous of Slovenia". Journal of Vertebrate Paleontology. 30 (3): 747–755. doi:10.1080/02724631003762963. S2CID 85570665.