Ophidia

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Ophidians
Temporal range:
Middle Jurassic – Holocene, [1]
170–0  Ma
Coast Garter Snake.jpg
Coast garter snake,
Thamnophis elegans terrestris
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Clade: Toxicofera
Clade: Ophidia
Latreille, 1804
Subgroups

Ophidia /oʊˈfɪdiə/ (also known as Pan-Serpentes [2] ) 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 ancestor of Pachyrhachis and Serpentes (modern snakes), and all its descendants" by Lee and Caldwell (1998: 1551). [3] The latter author has used Ophidia in a manner inconsistent with this definition, using it to incorporate other more basal stem-snakes, such as the Late Cretaceous Najash rionegrina or the Jurassic Diablophis and Portugalophis[ citation needed ].

The clade name Ophidia derives from the Ancient Greek word ὀφίδιον (ophídion), meaning "small snake". [4] [5]

Evolution

Modern snakes are thought to have evolved from either burrowing or aquatic lizards during the mid-Cretaceous period, and the earliest known fossils date to around 112 Ma ago. However, the relationship between modern snake and more primitive snake ancestors, many of which retained hind limbs, is less clear. While many of these "stem-snakes" are known from Mesozoic fossils, some of them may be descendants of the earliest true snakes rather than more primitive lineages. Below is a cladogram modified from a study by Wilson et al. (2010), which found many stem-snakes of other studies to be true snakes instead. [6]

Serpentes  (modern snakes)

Below is different phylogenetic overview of ophidians, following the study by Caldwell et al. 2015. [1]

Ophidia

The fossil record of snakes is relatively poor because snake skeletons are typically small and fragile, making fossilization uncommon. Fossils readily identifiable as snakes (though often retaining hind limbs) first appear in the fossil record during the Cretaceous period. [7] The earliest known snake fossils come from sites in Utah and Algeria, represented by the genera Coniophis and Lapparentophis , respectively. These fossil sites have been tentatively dated to the Albian or Cenomanian age of the late Cretaceous, between 112 and 94 Ma ago. However, an even greater age has been suggested for one of the Algerian sites, which may be as old as the Aptian, 125 to 112 Ma ago. [8]

Based on comparative anatomy, there is consensus that snakes descended from lizards. [9] : 11  [10] Pythons and boas—primitive groups among modern snakes—have vestigial hind limbs: tiny, clawed digits known as anal spurs, which are used to grasp during mating. [9] : 11  [11] The Leptotyphlopidae and Typhlopidae groups also possess remnants of the pelvic girdle, sometimes appearing as horny projections when visible.

Front limbs are nonexistent in all known snakes. This is caused by the evolution of Hox genes, controlling limb morphogenesis. The axial skeleton of the snakes' common ancestor, like most other tetrapods, had regional specializations consisting of cervical (neck), thoracic (chest), lumbar (lower back), sacral (pelvic), and caudal (tail) vertebrae. Early in snake evolution, the Hox gene expression in the axial skeleton responsible for the development of the thorax became dominant. As a result, the vertebrae anterior to the hindlimb buds (when present) all have the same thoracic-like identity (except from the atlas, axis, and 1–3 neck vertebrae). In other words, most of a snake's skeleton is an extremely extended thorax. Ribs are found exclusively on the thoracic vertebrae. Neck, lumbar and pelvic vertebrae are very reduced in number (only 2–10 lumbar and pelvic vertebrae are present), while only a short tail remains of the caudal vertebrae. However, the tail is still long enough to be of important use in many species, and is modified in some aquatic and tree-dwelling species.

Modern snakes greatly diversified during the Paleocene. This occurred alongside the adaptive radiation of mammals, following the extinction of (non-avian) dinosaurs. The colubrids, one of the more common snake groups, became particularly diverse due to preying on rodents, an especially successful mammal group.

Origins

The origin of snakes remains an unresolved issue. There are two main hypotheses competing for acceptance.

Burrowing lizard hypothesis

There is fossil evidence to suggest that snakes may have evolved from burrowing lizards, such as the varanids (or a similar group) during the Cretaceous Period. [12] An early fossil snake, Najash rionegrina , was a two-legged burrowing animal with a sacrum, and was fully terrestrial. [13] One extant analog of these putative ancestors is the earless monitor Lanthanotus of Borneo (though it also is semiaquatic). [14] Subterranean species evolved bodies streamlined for burrowing, and eventually lost their limbs. [14] According to this hypothesis, features such as the transparent, fused eyelids (brille) and loss of external ears evolved to cope with fossorial difficulties, such as scratched corneas and dirt in the ears. [12] [14] Some primitive snakes are known to have possessed hindlimbs, but their pelvic bones lacked a direct connection to the vertebrae. These include fossil species like Haasiophis , Pachyrhachis and Eupodophis , which are slightly older than Najash . [11]

Fossil of Archaeophis proavus. Naturkundemuseum Berlin - Archaeophis proavus Massalongo - Monte Bolca.jpg
Fossil of Archaeophis proavus.

Aquatic lizard hypothesis

Many researchers believe that snakes share a common marine ancestry with mosasaurs, a suggestion advanced in 1869 by Edward Drinker Cope, who coined the term Pythonomorpha to unite them. The idea lay dormant for more than a century, to be revived in the 1990s. [15] [16] The mosasaurs were aquatic varanid [17] lizards from the Cretaceous—which in turn are derived from Aigialosaurids. [10] [18] According to this hypothesis, the fused, transparent eyelids of snakes are thought to have evolved to combat marine conditions (corneal water loss through osmosis), and the external ears were lost through disuse in an aquatic environment. This ultimately led to an animal similar to today's sea snakes. In the Late Cretaceous, snakes recolonized land, and continued to diversify into today's snakes. Fossilized snake remains are known from early Late Cretaceous marine sediments, which is consistent with this hypothesis; particularly so, as they are older than the terrestrial Najash rionegrina. Similar skull structure, reduced or absent limbs, and other anatomical features found in both mosasaurs and snakes led to a positive cladistical correlation, and some of these features are shared with varanids.[ clarification needed ]

The cladogram below, based on Palci and Caldwell (2010), suggests that snakes are more closely related to Dolichosaurids than mosasaurs proper. [19] [20] placing the Dolichosauridae as a sister group to modern snakes and their closest ancestors.

Related Research Articles

<span class="mw-page-title-main">Snake</span> Limbless, scaly, elongate reptile

Snakes are elongated, limbless, carnivorous reptiles of the suborder Serpentes. Like all other squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales. Many species of snakes have skulls with several more joints than their lizard ancestors, enabling them to swallow prey much larger than their heads. To accommodate their narrow bodies, snakes' paired organs appear one in front of the other instead of side by side, and most have only one functional lung. Some species retain a pelvic girdle with a pair of vestigial claws on either side of the cloaca. Lizards have independently evolved elongate bodies without limbs or with greatly reduced limbs at least twenty-five times via convergent evolution, leading to many lineages of legless lizards. These resemble snakes, but several common groups of legless lizards have eyelids and external ears, which snakes lack, although this rule is not universal.

<span class="mw-page-title-main">Mosasaur</span> Extinct marine lizards of the Late Cretaceous

Mosasaurs are an extinct group of large aquatic reptiles within the family Mosasauridae that lived during the Late Cretaceous. Their first fossil remains were discovered in a limestone quarry at Maastricht on the Meuse in 1764. They belong to the order Squamata, which includes lizards and snakes.

Tylosaurus is a genus of mosasaur, a large, predatory marine reptile closely related to modern monitor lizards and snakes, from the Late Cretaceous.

<span class="mw-page-title-main">Pythonomorpha</span> Clade of lizards

Pythonomorpha was originally proposed by paleontologist Edward Drinker Cope (1869) as a reptilian order comprising mosasaurs, which he believed to be close relatives of Ophidia (snakes). The etymology of the term Pythonomorpha comes from the Greek Python 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 ophidian part of their affinities, I have called this order Pythonomorpha." Cope incorporated two families, the Clidastidae and the Mosasauridae.

<i>Najash</i> Extinct genus of snakes

Najash is an extinct genus of basal snake from the Late Cretaceous Candeleros Formation of Patagonia. Like a number of other Cretaceous and living snakes it retained hindlimbs, but Najash is unusual in having well-developed legs that extend outside the rib cage, and a pelvis connected to the spine.

Haasiophis, consisting of the sole species Haasiophis terrasanctus, is an extinct genus of snakes with hind limbs. It is one of three genera of Cenomanian snakes known to have possessed hindlimbs.

Pachyrhachis is an extinct genus of snake with well developed hind legs known from fossils discovered in Ein Yabrud, near Ramallah, in the central West Bank. It is a relatively small snake, measuring more than 1.5 metres (4.9 ft) long at maximum. Pachyrhachis appears to have been an ancient marine snake; the fossils occur in a marine limestone deposit, and the thickened bone of the ribs and vertebrae would have functioned as ballast to decrease the buoyancy of the animal, allowing it to dive beneath the ancient Cretaceous seas that it once inhabited.

<span class="mw-page-title-main">Pelvic spur</span> Modified reptilian appendages

Pelvic spurs are external protrusions found around the cloaca in certain superfamilies of snakes belonging to the greater infraorder Alethinophidia. These spurs are made up of the remnants of the femur bone, which is then covered by a corneal spur, or claw-like structure. This femur derives from ancestral hind limbs found in the most recent common ancestor of modern snakes and the other reptiles of the clade Toxicofera, many of which have fully functional front and hind limbs. Due to the fact that the spurs derive from the ancestral state of functional legs, but are no longer functional for locomotion specifically, these structures do meet the criteria for being considered vestigial. Nonetheless, uses for the structures have been thoroughly documented. Species that have external spurs have corresponding muscles, neurological structures, and vascularization to allow for independent movement. The spurs are more pronounced and visible in male specimens and have been observed in use during courtship behavior. The spurs are specifically used in the clasping and stimulation of females by males during courtship and mating. In certain species, males will also use their spurs to engage in combat with one another.

<span class="mw-page-title-main">Madtsoiidae</span> Extinct family of snakes

Madtsoiidae is an extinct family of mostly Gondwanan snakes with a fossil record extending from early Cenomanian to late Pleistocene strata located in South America, Africa, India, Australia and Southern Europe. Madtsoiidae include very primitive snakes, which like extant boas and pythons would likely dispatch their prey by constriction. Genera include some of the longest snakes known such as Vasuki, measuring at least 11–15 metres (36–49 ft) long, and the Australian Wonambi and Yurlunggur. As a grouping of basal forms the composition and even the validity of Madtsoiidae is in a state of flux as new pertinent finds are described, with more recent evidence suggesting that it is paraphyletic as previously defined.

<i>Adriosaurus</i> Extinct genus of lizards

Adriosaurus is an extinct genus of squamate which lived in what is now Slovenia and other parts of Europe during the Late Cretaceous. It was small, snake-like reptile, with type species measuring up to 30 cm (12 in) in length. This is the first fossil record of vestigial limbs in lizards. It lost its manus and forearm completely in order to elongate its axial skeleton. These unique anatomical features led to discussions of the evolutionary patterns of limb reduction in Squamata.

<i>Kaganaias</i> Extinct genus of lizards

Kaganaias is an extinct genus of basal and oldest dolichosaur that lived in what is now Japan during the Early Cretaceous. Kaganaias was semi-aquatic and is the only known aquatic squamate known from before the Cenomanian stage of the Cretaceous. It is also the first to be found in an inland area, instead of on the coast where aquatic squamates are commonly found. Its generic name is derived from Kaga Province, the old name for the Ishikawa Prefecture where the specimens were found, while the species name hakusanensis comes from the mountain that gives its name to Hakusan the city near its find site. The geological formation in which the specimens were found, the Kuwajima Formation, stands alongside the Tetori River and has been the site of numerous other finds including molluscs, dinosaurs, fish, and pterosaurs.

<i>Eupodophis</i> Extinct genus of snakes

Eupodophis is an extinct genus of snake from the Late Cretaceous period. It has two small hind legs and is considered a transitional form between Cretaceous lizards and limbless snakes. The feature, described as vestigial, was most likely useless to Eupodophis. The type species Eupodophis descouensi was named in 2000 and resides now in the paleontology section of the Mim Museum in Beirut, Lebanon. The specific name is dedicated to the French naturalist Didier Descouens.

<i>Carsosaurus</i> Extinct genus of lizards

Carsosaurus is a genus of extinct amphibious reptiles, in the mosasaur superfamily, containing only the species Carsosaurus marchesetti. It is known from a single individual that lived during the Upper Cretaceous in what is now Slovenia. The specimen is well-preserved, containing many different bones as well as some skin impressions and sternal cartilage. While more remains are needed to be certain, it is generally thought to belong to the Aigialosauridae. In life, it was an amphibious creature that spent most of its time on land, although its later relatives would become fully aquatic.

Parviraptor is a genus of squamate containing one species, Parviraptor estesi, from the Late Jurassic (Tithonian) or Early Cretaceous (Berriasian) Purbeck Limestone Formation of Dorset, England. A second species, Parviraptor gilmorei, was described from the Late Jurassic Morrison Formation of Western North America; it was present in stratigraphic zone 4. However, the second species was subsequently transferred to a separate genus Diablophis. An indeterminate species is known from the Bathonian aged Kirtlington Mammal Bed.

Acteosaurus is an extinct genus of aquatic lizard that lived in the upper Cretaceous period. Its species, A. tommasinii and A. crassicostatus, were described in 1860 and 1993. Though A. crassicostatus is probably a junior synonym for Adriosaurus suessi, A. tommasinii was found to be similar to coniasaurs, mosasauroids, and a sister taxon to modern snakes in 2010.

<i>Tetrapodophis</i> Extinct genus of lizard

Tetrapodophis is an extinct genus of lizard from the Early Cretaceous (Aptian) aged Crato Formation of Brazil. It has an elongate snake-like body, with four limbs. Tetrapodophis has been considered by some authors to be one of the oldest members of Ophidia. However, this classification has been disputed by some other authors, who identify Tetrapodophis as a dolichosaurid much less closely related to snakes.

<i>Pachyophis</i> Extinct genus of snakes

Pachyophis is an extinct genus of Simoliophiidae snakes that were extant during the Cenomanian stage of the Late Cretaceous period. More specifically, it was found to be from the Cenomanian Age about 93.9-100.5 million years ago in the suburb area of Bileca, Herzegovina.

<span class="mw-page-title-main">Dolichosauridae</span> Extinct family of lizards

Dolichosauridae 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.

<span class="mw-page-title-main">Ophidiomorpha</span> Clade of lizards

Ophidiomorpha is a proposed clade composed of snakes and a number of extinct squamate groups. The clade was defined by Placi and Caldwell (2007) as a node-based clade containing the most recent common ancestor of dolichosaurs, adriosaurs, Aphanizocnemus, and fossil and extant Ophidia and all of its descendants.

<span class="mw-page-title-main">Mosasauria</span> Extinct squamates of the Cretaceous period

Mosasauria is a clade of aquatic and semiaquatic squamates that lived during the Cretaceous period. Fossils belonging to the group have been found in all continents around the world. Early mosasaurians like dolichosaurs were small long-bodied lizards that inhabited nearshore coastal and freshwater environments; the Late Cretaceous saw the rise of large marine forms, the mosasaurids, which are the clade's best-known members.

References

  1. 1 2 Caldwell, M. W.; Nydam, R. L.; Palci, A.; Apesteguía, S. N. [in Spanish] (2015). "The oldest known snakes from the Middle Jurassic-Lower Cretaceous provide insights on snake evolution". Nature Communications . 6: 5996. Bibcode:2015NatCo...6.5996C. doi: 10.1038/ncomms6996 . hdl: 11336/37995 . PMID   25625704.
  2. ↑ Hsiang, A. Y.; Field, D. J.; Webster, T. H.; Behlke, A. D.; Davis, M. B.; Racicot, R. A.; Gauthier, J. A. (2015). "The origin of snakes: Revealing the ecology, behavior, and evolutionary history of early snakes using genomics, phenomics, and the fossil record". BMC Evolutionary Biology. 15: 87. doi: 10.1186/s12862-015-0358-5 . PMC   4438441 . PMID   25989795.
  3. ↑ Lee, M. S. Y. (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. PMC   1692386 .
  4. ↑ Bailly, Anatole (1981-01-01). Abrégé du dictionnaire grec français. Paris: Hachette. ISBN   978-2010035289. OCLC   461974285.
  5. ↑ Bailly, Anatole. "Greek-french dictionary online". www.tabularium.be. Retrieved January 7, 2019.
  6. ↑ Wilson, J.A.; Mohabey, D.M.; Peters, S.E.; Head, J.J. (2010). Benton, Michael J. (ed.). "Predation upon Hatchling Dinosaurs by a New Snake from the Late Cretaceous of India". PLOS Biology . 8 (3): e1000322. doi: 10.1371/journal.pbio.1000322 . PMC   2830453 . PMID   20209142.
  7. ↑ Durand, J.F. (2004). "The origin of snakes". Geoscience Africa 2004. Abstract Volume, University of the Witwatersrand, Johannesburg, South Africa, pp. 187.
  8. ↑ Vidal, N.; Rage, J.-C.; Couloux, A.; Hedges, S.B. (2009). "Snakes (Serpentes)". In Hedges, S.B.; Kumar, S. (eds.). The Timetree of Life. Oxford University Press. pp. 390–397.
  9. 1 2 Mehrtens, JM (1987). Living Snakes of the World in Color. New York: Sterling Publishers. p. 480. ISBN   0-8069-6460-X.
  10. 1 2 Sanchez, Alejandro. "Diapsids III: Snakes". Father Sanchez's Web Site of West Indian Natural History. Retrieved 2007-11-26.
  11. 1 2 "New Fossil Snake With Legs". UNEP WCMC Database. Washington, D.C.: American Association for the Advancement of Science. Archived from the original on 2007-12-25. Retrieved 2007-11-29.
  12. 1 2 Mc Dowell, Samuel (1972). "The Evolution of the Tongue of Snakes, and its Bearing on Snake Origins". Evolutionary Biology. Vol. 6. pp. 191–273. doi:10.1007/978-1-4684-9063-3_8. ISBN   978-1-4684-9065-7.
  13. ↑ Apesteguía, Sebastián [in Spanish]; Zaher, Hussam (April 2006). "A Cretaceous terrestrial snake with robust hindlimbs and a sacrum". Nature . 440 (7087): 1037–1040. Bibcode:2006Natur.440.1037A. doi:10.1038/nature04413. PMID   16625194. S2CID   4417196 . Retrieved 2007-11-29.
  14. 1 2 3 Mertens, Robert (1961). "Lanthanotus: an important lizard in evolution". Sarawak Museum Journal. 10: 320–322.
  15. ↑ "Palaeos Vertebrates Squamata: Pythonomorpha". palaeos.com. 2012. Retrieved 25 November 2014.
  16. ↑ Everhart, M. J. (2000). "Mosasaurs: Last of the Great Marine Reptiles". Prehistoric Times (44): 29–31. Retrieved 25 November 2014.
  17. ↑ Lindgren, J.; Caldwell, M.W.; Konishi, T.; Chiappe, L.M. (2010). Farke, Andrew Allen (ed.). "Convergent Evolution in Aquatic Tetrapods: Insights from an Exceptional Fossil Mosasaur". PLOS One . 5 (8): e11998. Bibcode:2010PLoSO...511998L. doi: 10.1371/journal.pone.0011998 . PMC   2918493 . PMID   20711249.
  18. ↑ Wilf, P.; Reeder, T. W.; Townsend, T. M.; Mulcahy, D. G.; Noonan, B. P.; Wood, P. L.; Sites, J. W.; Wiens, J. J. (2015). "Integrated Analyses Resolve Conflicts over Squamate Reptile Phylogeny and Reveal Unexpected Placements for Fossil Taxa". PLOS One . 10 (3): e0118199. Bibcode:2015PLoSO..1018199R. doi: 10.1371/journal.pone.0118199 . PMC   4372529 . PMID   25803280.
  19. ↑ 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.
  20. ↑ 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.
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