Chinlestegophis

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Chinlestegophis
Temporal range: Late Triassic, 221–206  Ma
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Order:
†Temnospondyli
Suborder:
†Stereospondyli
Superfamily:
† Metoposauroidea?
Genus:
†Chinlestegophis

Pardo et al., 2017
Binomial name
†Chinlestegophis jenkinsi
Pardo et al., 2017

Chinlestegophis is a diminutive Late Triassic stereospondyl that has been interpreted as a putative stem caecilian, a living group of legless burrowing amphibians. [1] If Chinlestegophis is indeed both an advanced stereospondyl and a relative of caecilians, this means that stereospondyls (in the form of caecilians) survived to the present day; historically the group was thought to have gone extinct by the early Cretaceous. [2] Chinlestegophis jenkinsi, the type and only species, is known from two partial skulls discovered in the Chinle Formation in Colorado.

Contents

History of study

Chinlestegophis was described in 2017 by Jason Pardo, Adam Huttenlocker, and Bryan Small based on two specimens collected in the late 1990s by Small. [1] The genus name is derived from the name of the formation (Chinle), the Greek root stego- ('roof' or 'cover'), and the Greek root -ophis ('serpent'). The species name honors Farish Jenkins, the longtime curator of the Museum of Comparative Zoology at Harvard University who described Eocaecilia , the oldest known caecilian. The taxon is readily diagnosed by numerous features given its distinctive small size and consequent diverging morphology from many contemporaneous stereospondyls; Pardo et al. noted numerous features shared between Chinlestegophis and brachyopoids (e.g., lacrimal-maxilla fusion), Rileymillerus (e.g., lateral exposure of the palate), and caecilians (e.g., double tooth row on the lower jaw).

Relationships

The phylogenetic positions of many small-bodied temnospondyls have often been controversial, including that of the closely related Rileymillerus cosgriffi from the Late Triassic of Texas. [3] The analysis by Pardo et al. (2017) used a modified matrix from Schoch (2013), which looked at the relationships of all temnospondyls. [4] In addition to recovering Chinlestegophis as the sister taxon to Rileymillerus, the authors also recovered these taxa as the closest relatives of brachyopoids, another clade of stereospondyl that were the last non-lissamphibian temnospondyls to survive in the Mesozoic. In turn, the analysis recovered Chinlestegophis as the closest relative to Eocaecilia , the oldest known caecilian. As such, these results form the basis for a fourth major hypothesis regarding lissamphibian origins, namely that all lissamphibians are derived from temnospondyls, but that batrachians (frogs and salamanders) are descended from dissorophoids, whereas caecilians came from Chinlestegophis-like taxa nested among the stereospondyls.

Other workers have disputed the interpretation of Chinlestegophis as a stem caecilian on various grounds. For example, Marjanović & Laurin (2019) note that the original study reported only a Bayesian consensus and a majority-rule consensus tree of the main data matrix, and while both support the claimed caecilian affinities of Chinlestegophis jenkinsi, the strict parsimony consensus tree does not, given that it is compatible with lissamphibian monophyly (indeed, this topology is found in some of the most parsimonious trees); those workers generally favor and recover support for a monophyletic origin of lissamphibians from lepospondyls. [5] Criticism of the use of the majority-rule consensus has also been published by Serra Silva & Wilkinson (2021). [6] The use of a modified version of the Pardo et al. matrix by Daza et al. (2020) and Schoch et al. (2020) recovered a single origin of all lissamphibians from dissorophoids, consistent with the historic "temnospondyl hypothesis"; [7] [8] further analysis in the description of the unequivocal Late Triassic gymnophionomorph Funcusvermis gilmorei also recovered the traditional "temnospondyl hypothesis." [9] The characters that have been used to support gymnophionan affinities of Chinlestegophis have also been criticized. [10] [11] No other studies to date have independently supported the hypothesis of relationships proposed by Pardo et al.

Related Research Articles

<span class="mw-page-title-main">Lissamphibia</span> Subclass of amphibians

The Lissamphibia is a group of tetrapods that includes all modern amphibians. Lissamphibians consist of three living groups: the Salientia, the Caudata, and the Gymnophiona.

<span class="mw-page-title-main">Caecilian</span> Order of amphibians

Caecilians are a group of limbless, vermiform (worm-shaped) or serpentine (snake-shaped) amphibians with small or sometimes nonexistent eyes. They mostly live hidden in soil or in streambeds, and this cryptic lifestyle renders caecilians among the least familiar amphibians. Modern caecilians live in the tropics of South and Central America, Africa, and southern Asia. Caecilians feed on small subterranean creatures such as earthworms. The body is cylindrical and often darkly coloured, and the skull is bullet-shaped and strongly built. Caecilian heads have several unique adaptations, including fused cranial and jaw bones, a two-part system of jaw muscles, and a chemosensory tentacle in front of the eye. The skin is slimy and bears ringlike markings or grooves and may contain scales.

<span class="mw-page-title-main">Batrachia</span> Clade of amphibians

The Batrachia are a clade of amphibians that includes frogs and salamanders, but not caecilians nor the extinct allocaudates. The name Batrachia was first used by French zoologist Pierre André Latreille in 1800 to refer to frogs, but has more recently been defined in a phylogenetic sense as a node-based taxon that includes the last common ancestor of frogs and salamanders and all of its descendants. The idea that frogs and salamanders are more closely related to each other than either is to caecilians is strongly supported by morphological and molecular evidence; they are, for instance, the only vertebrates able to raise and lower their eyes. However, an alternative hypothesis exists in which salamanders and caecilians are each other's closest relatives as part of a clade called the Procera, with frogs positioned as the sister taxon of this group.

<span class="mw-page-title-main">Labyrinthodontia</span> Paraphyletic group of tetrapodomorphs

"Labyrinthodontia" is an informal grouping of extinct predatory amphibians which were major components of ecosystems in the late Paleozoic and early Mesozoic eras. Traditionally considered a subclass of the class Amphibia, modern classification systems recognize that labyrinthodonts are not a formal natural group (clade) exclusive of other tetrapods. Instead, they consistute an evolutionary grade, ancestral to living tetrapods such as lissamphibians and amniotes. "Labyrinthodont"-grade vertebrates evolved from lobe-finned fishes in the Devonian, though a formal boundary between fish and amphibian is difficult to define at this point in time.

<span class="mw-page-title-main">Lepospondyli</span> Polyphyletic group of tetrapodomorphs

Lepospondyli is a diverse taxon of early tetrapods. With the exception of one late-surviving lepospondyl from the Late Permian of Morocco, lepospondyls lived from the Early Carboniferous (Mississippian) to the Early Permian and were geographically restricted to what is now Europe and North America. Five major groups of lepospondyls are known: Adelospondyli; Aïstopoda; Lysorophia; Microsauria; and Nectridea. Lepospondyls have a diverse range of body forms and include species with newt-like, eel- or snake-like, and lizard-like forms. Various species were aquatic, semiaquatic, or terrestrial. None were large, and they are assumed to have lived in specialized ecological niches not taken by the more numerous temnospondyl amphibians that coexisted with them in the Paleozoic. Lepospondyli was named in 1888 by Karl Alfred von Zittel, who coined the name to include some tetrapods from the Paleozoic that shared some specific characteristics in the notochord and teeth. Lepospondyls have sometimes been considered to be either related or ancestral to modern amphibians or to Amniota. It has been suggested that the grouping is polyphyletic, with aïstopods being primitive stem-tetrapods, while recumbirostran microsaurs are primitive reptiles.

<span class="mw-page-title-main">Dissorophoidea</span> Extinct superfamily of amphibians

Dissorophoidea is a clade of medium-sized, temnospondyl amphibians that appeared during the Moscovian in Euramerica, and continued through to the Late Permian and the Early Triassic of Gondwana. They are distinguished by various details of the skull, and many species seem to have been well adapted for life on land.

<span class="mw-page-title-main">Temnospondyli</span> Ancestors of modern amphibians adapted to life on land

Temnospondyli or temnospondyls is a diverse ancient order of small to giant tetrapods—often considered primitive amphibians—that flourished worldwide during the Carboniferous, Permian and Triassic periods, with fossils being found on every continent. A few species continued into the Jurassic and Early Cretaceous periods, but all had gone extinct by the Late Cretaceous. During about 210 million years of evolutionary history, they adapted to a wide range of habitats, including freshwater, terrestrial, and even coastal marine environments. Their life history is well understood, with fossils known from the larval stage, metamorphosis and maturity. Most temnospondyls were semiaquatic, although some were almost fully terrestrial, returning to the water only to breed. These temnospondyls were some of the first vertebrates fully adapted to life on land. Although temnospondyls are amphibians, many had characteristics such as scales and armour-like bony plates that distinguish them from the modern soft-bodied lissamphibians.

<span class="mw-page-title-main">Stereospondyli</span> Extinct suborder of amphibians

The Stereospondyli are a group of extinct temnospondyl amphibians that existed primarily during the Mesozoic period. They are known from all seven continents and were common components of many Triassic ecosystems, likely filling a similar ecological niche to modern crocodilians prior to the diversification of pseudosuchian archosaurs.

<i>Gerobatrachus</i> Extinct genus of amphibians

Gerobatrachus is an extinct genus of amphibamid temnospondyl that lived in the Early Permian, approximately 290 million years ago (Ma), in the area that is now Baylor County, Texas. When it was first described in 2008, Gerobatrachus was announced to be the closest relative of Batrachia, the group that includes modern frogs and salamanders. It possesses a mixture of characteristics from both groups, including a large frog-like head and a salamander-like tail. These features have led to it being dubbed a frogamander by the press. Some more recent studies place Gerobatrachus as the closest relative of Lissamphibia, the group that contains all modern amphibians including frogs, salamanders, and caecilians, or place modern amphibians far from Gerobatrachus within a group called Lepospondyli.

<span class="mw-page-title-main">Albanerpetontidae</span> Family of amphibians

The Albanerpetontidae are an extinct family of small amphibians, native to the Northern Hemisphere during the Mesozoic and Cenozoic. The only members of the order Allocaudata, they are thought to be allied with living amphibians belonging to Lissamphibia. Despite a superficially salamander-like bodyform, their anatomy is strongly divergent from modern amphibians in numerous aspects. The fossil record of albanerpetontids spans over 160 million years from the Middle Jurassic to the beginning of the Pleistocene, about 2.13–2 million years ago.

<span class="mw-page-title-main">Lapillopsidae</span> Extinct family of temnospondyls

Lapillopsidae is an extinct family of temnospondyls.

<span class="mw-page-title-main">Stereospondylomorpha</span> Extinct clade of temnospondyls

Stereospondylomorpha is a clade of temnospondyls. It includes the superfamily Archegosauroidea and the more diverse group Stereospondyli. Stereospondylomorpha was first proposed by Yates and Warren (2000), who found Archegosauroidea and Stereospondyli to be sister taxa in their phylogenetic analysis. A similar clade is Archegosauriformes, named by Schoch and Milner (2000), which includes Stereospondyli and some Permian temnospondyls that are similar in appearance to stereospondyls, including the archegosauroids. However, according to Schoch and Milner's phylogeny, Archegosauroidea is a paraphyletic group of taxa that are successively basal to Stereospondyli, rather than a monophyletic sister taxon.

<span class="mw-page-title-main">Limnarchia</span> Extinct clade of temnospondyls

Limnarchia is a clade of temnospondyls. It includes the mostly Carboniferous-Permian age Dvinosauria and the mostly Permian-Triassic age Stereospondylomorpha. The clade was named in a 2000 phylogenetic analysis of stereospondyls and their relatives. Limnarchia means "lake rulers" in Greek, in reference to their aquatic lifestyles and long existence over a span of approximately 200 million years from the Late Carboniferous to the Early Cretaceous. In phylogenetic terms, Limnarchia is a stem-based taxon including all temnospondyls more closely related to Parotosuchus than to Eryops. It is the sister group of the clade Euskelia, which is all temnospondyls more closely related to Eryops than to Parotosuchus. Limnarchians represent an evolutionary radiation of temnospondyls into aquatic environments, while euskelians represent a radiation into terrestrial environments. While many euskelians were adapted to life on land with strong limbs and bony scutes, most limnarchians were better adapted for the water with poorly developed limbs and lateral line sensory systems in their skulls.

<i>Lapillopsis</i> Extinct genus of temnospondyls

Lapillopsis is an extinct genus of stereospondyl temnospondyl within the family Lapillopsidae. Fossils belonging to the genus have been found in the Arcadia Formation of Queensland, Australia.

Rileymillerus is an extinct genus of temnospondyl amphibian from the Late Triassic Post Quarry in the Dockum Group of Texas that was described by John Bolt and Sankar Chatterjee in 2000. The holotype, a nearly complete skull with articulated jaws, is housed at the Museum of Texas Tech University. The genus is named for Riley Miller, who allowed Chatterjee to work on the Post Quarry, and the species is named for the paleontologist John Cosgriff.

<span class="mw-page-title-main">Salientia</span> Order of amphibians

The Salientia are a total group of amphibians that includes the order Anura, the frogs and toads, and various extinct proto-frogs that are more closely related to the frogs than they are to the Urodela, the salamanders and newts. The oldest fossil "proto-frog" appeared in the early Triassic of Madagascar, but molecular clock dating suggests their origins may extend further back to the Permian, 265 million years ago.

<span class="mw-page-title-main">Amphibamidae</span> Extinct family of temnospondyls

The Amphibamidae are an ancient family of dissorophoid temnospondyls known from Late Carboniferous-Early Permian strata in the United States.

The Micropholidae are an extinct family of dissorophoid temnospondyls known from Late Carboniferous to Early Triassic strata in the United States and South Africa.

<span class="mw-page-title-main">Amphibamiformes</span> Extinct clade of temnospondyls

Amphibamiformes is an unranked clade with Dissorophoidea created by Schoch (2018). It encompasses all of the taxa traditionally considered to be "amphibamids", branchiosaurids, and hypothetically lissamphibians under the traditional temnospondyl hypothesis of lissamphibian origins. These taxa are typically small-bodied dissorophoids and form the sister group to Olsoniformes, which comprises dissorophids and trematopids.

<i>Funcusvermis</i> Extinct genus of amphibians

Funcusvermis is an extinct genus of stem-caecilian from the Late Triassic of Arizona. It is based on a large sample of jaws and other skull and postcranial fragments, discovered in an approximately 220 million years old layer of rock in the Blue Mesa Member of the Chinle Formation at Petrified Forest National Park. There is a single species, called Funcusvermis gilmorei.

References

  1. 1 2 Pardo, Jason D.; Small, Bryan J.; Huttenlocker, Adam K. (2017-07-03). "Stem caecilian from the Triassic of Colorado sheds light on the origins of Lissamphibia". Proceedings of the National Academy of Sciences. 114 (27): E5389–E5395. doi: 10.1073/pnas.1706752114 . ISSN   0027-8424. PMC   5502650 . PMID   28630337.
  2. ↑ Warren, Anne; Rich, Thomas H.; Vickers-Rich, Patricia (1997). "The last labyrinthodonts". Palaeontographica Abteilung A. 247: 1–24.
  3. ↑ Bolt, John R.; Chatterjee, Sankar (2000). "A new temnospondyl amphibian from the Late Triassic of Texas". Journal of Paleontology. 74 (4): 670–683. doi:10.1017/s0022336000032790. ISSN   0022-3360.
  4. ↑ Schoch, Rainer R. (2013). "The evolution of major temnospondyl clades: an inclusive phylogenetic analysis". Journal of Systematic Palaeontology. 11 (6): 673–705. doi:10.1080/14772019.2012.699006. ISSN   1477-2019. S2CID   83906628.
  5. ↑ Marjanović, David; Laurin, Michel (2019). "Phylogeny of Paleozoic limbed vertebrates reassessed through revision and expansion of the largest published relevant data matrix". PeerJ. 6 (e5565): e5565. doi: 10.7717/peerj.5565 . PMC   6322490 . PMID   30631641.
  6. ↑ Silva, Ana Serra; Wilkinson, Mark (2021-03-22). "On Defining and Finding Islands of Trees and Mitigating Large Island Bias". Systematic Biology. 70 (6): 1282–1294. doi:10.1093/sysbio/syab015. hdl: 1983/ce7732e1-3dd9-4e61-b60e-2b7700fece9e . ISSN   1063-5157.
  7. ↑ Daza, Juan D.; Stanley, Edward L.; Bolet, Arnau; Bauer, Aaron M.; Arias, J. Salvador; Čerňanský, Andrej; Bevitt, Joseph J.; Wagner, Philipp; Evans, Susan E. (2020-11-06). "Enigmatic amphibians in mid-Cretaceous amber were chameleon-like ballistic feeders". Science. 370 (6517): 687–691. doi:10.1126/science.abb6005. ISSN   0036-8075.
  8. ↑ Schoch, Rainer R.; Werneburg, Ralf; Voigt, Sebastian (2020-05-11). "A Triassic stem-salamander from Kyrgyzstan and the origin of salamanders". Proceedings of the National Academy of Sciences. 117 (21): 11584–11588. doi:10.1073/pnas.2001424117. ISSN   0027-8424. PMC   7261083 . PMID   32393623.
  9. ↑ Kligman, Ben T.; Gee, Bryan M.; Marsh, Adam D.; Nesbitt, Sterling J.; Smith, Matthew E.; Parker, William G.; Stocker, Michelle R. (2023-01-25). "Triassic stem caecilian supports dissorophoid origin of living amphibians". Nature. 614 (7946): 102–107. doi:10.1038/s41586-022-05646-5. hdl: 10919/113568 . ISSN   0028-0836.
  10. ↑ Santos, Rodolfo Otávio; Laurin, Michel; Zaher, Hussam (2020). "A review of the fossil record of caecilians (Lissamphibia; Gymnophionomorpha) with comments on its use to calibrate molecular timetrees". Biological Journal of the Linnean Society. 131 (4): 737–755. doi: 10.1093/biolinnean/blaa148 .
  11. ↑ Marjanović, David; Maddin, Hillary C.; Olori, Jennifer C.; Laurin, Michel (2024-01-04). "The new problem of Chinlestegophis and the origin of caecilians (Amphibia, Gymnophionomorpha) is highly sensitive to old problems of sampling and character construction". Fossil Record. 27 (1): 55–94.
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