Rhineceps

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Rhineceps
Temporal range: Lopingian
Rhineceps nyasaensis.jpg
Restoration
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Order: Temnospondyli
Suborder: Stereospondyli
Family: Rhinesuchidae
Genus: Rhineceps
Watson, 1962
Type species
Rhinesuchus nyasaensis
(Haughton, 1927)

Rhineceps is an extinct genus of temnospondyl amphibian in the family Rhinesuchidae. [1] Rhineceps was found in Northern Malawi (formerly Nyasaland) in Southern Africa known only from its type species R. nyasaensis. Rhineceps was a late Permian (256-258 Mya) semi-aquatic carnivore that lived in streams, rivers, lakes or lagoons. [2] [3] [4] Rhineceps is an early divergent Stereopondyl within the family Rhinesuchidae, which only existed in the late Permian (Lopingian) and failed to survive the Permian-Triassic extinction unlike other stereospondyl families. [1]

Contents

History

Rhineceps was originally discovered in the “Upper Bone Beds” of the Chiweta Beds, North Waller Area in Northern Malawi. [5] [6] The fossil was first described and named by Haughton in 1926, whereby he described the fossil of a left mandibular ramus of R. nyasaensis as within the genus Rhinesuchus due to its similarity with the fossils of Rhinesuchus whaitsi. [6] Watson later determined in a letter to Parrington that the original fossil was actually the anterior end of a right ramus and not a left ramus. [5] Watson in 1962 described fossils newly found from the same locality collected by Parrington as fossils of R. nyasaensis and determined they were from the same individual. [5]   Watson also placed R. nyasaensis as part of a new genus Rhineceps that is distinct from other Rhinesuchus species. [5]

Classification

Rhineceps belongs to the family Rhinesuchidae, which is within the clade Stereospondyli (a Temnospondyl clade). Until recently, both morphology, historical placement and phylogenetic analysis has placed Rhineceps as a sister group to Rhinesuchus within Rhinesuchinae, an early diverging group of Rhinesuchidae. [6] [7]

Rhinesuchidae
Rhinesuchinae

Rhineceps

Rhinesuchus

Rhinesuchus broomianus

Rhinesuchus whaitsi

Uranocentrodon senskalensis

Australerpetinae

Broomistega putterelli

Australerpeton

Serra de Cadeado short-snouted

Laccosaurus watsoni

BP-1-4473

‘Rhinesuchus’ capensis

Rhinesuchoides tenuiceps

[7]

In 2017, Marsicano et al. created a new phylogeny that places Rhineceps as a sister group to Uranocentrodon rather than within Rhinesuchinae (which is no longer a monophyletic group). [1]

Rhinesuchidae

Australerpeton

Rhinesuchoides

Rhinesuchoides capensis

Rhinesuchoides tenuiceps

[1]

This discrepancy in clearly describing phylogenetic relationships is likely due to the adaptive radiation of stereospondylomorphs that took place during the late Permian and early Triassic. [8] Terrestrial temnospondyls were devastated during this period, caused by selective pressures for semi-aquatic or fully aquatic temnospondyls to acquire many new niches in a relatively short time period. [8]

Description and paleobiology

Rhineceps was a medium-sized, semi-aquatic, carnivorous, basal stereospondyl of the Lopingian of Malawi. [1] They lived in fresh water bodies, including rivers lakes and lagoons, where they had diets mainly of fish. [2] [3] [4] Stereospondyls were historically compared with contemporary crocodilians and giant salamanders due to their similar position as freshwater predators. [2] However, they likely existed in a niche that is unique and independent from crocodilians and giant salamanders. [2] These niche differences are inferred from cranial stress and structural patterns along with labyrinthodont dentition (labyrinthodonty refers to infolding of enamel and dentine within a tooth). [2] The morphology of Rhineceps thus likely restricts its ability to hunt in specific ways that crocodilians and giant salamanders such as sweeping sideways bites. Rhineceps also used its unique morphology in service of catching prey, including its strong powerful bite and its palatal tooth row to grasp and hold fish in its jaw. [2] Many temnospondyls including Rhineceps likely shared certain physiological characteristics with modern amphibians that cannot be directly observed in the fossil record. Rhineceps likely possessed heightened phenotypic plasticity among juvenile individuals like seen in modern amphibians. [3] This plasticity allowed physiological changes during an organism's lifetime to alter its morphology during development to specific and different environmental factors experienced. [3] Plasticity was a means for stereospondyls to adaptively radiate to many different species and niches. [3] Rhineceps like other temnospondyls were ecological indicator species like modern amphibians, and thus likely were sensitive to chemical changes, UV radiation and other mutagens within its ecosystem. [8]

Fossils of the only known individual of Rhineceps nyasaensis. Rhineceps nyasaensis fossil.jpg
Fossils of the only known individual of Rhineceps nyasaensis.

Rhineceps like modern amphibians had obligatory aquatic young. [4] Rhineceps like other stereospondyls was the result of evolutionary gigantism which resulted in stunted metamorphosis with few morphological differences between adults and larvae. [4] Metamorphosis was likely lost in stereospondyls because extreme phenotypic plasticity allowed environmental acclimation through changes in morphology without needing a binary developmental life history with larval and adult stages. [3] This eventually led to neoteny whereby the larval stage is morphologically very similar to the adult stage. [3] Stereospondyls including Rhineceps only had gradual changes between juvenile and adult stages, and their fossils do not suggest the presence of any type of metamorphosis, major or minor. [9] Greater ambiguity is created because stereospondyls including Rhineceps have traits traditionally associated with metamorphosis, including amphibious dermal pitting. [9]

The presence of the types of gills in temnospondyls has largely been difficult to determine because conflicting interpretation of osteological evidence. Phylogenetic information has also created uncertainty of where external gills evolved and internal gills were lost. [10] The evolutionary explanation for this contradiction known as Bystrow's Paradox is that temnospondyls had both internal gills and external gills, with external gills only present in larvae and internal gills that are homologous with Osteichthyes (bony fish) gills that later become modern amphibian gills. [10] Thus, Rhineceps larvae likely had external gills and adult Rhineceps had internal gills, although this is difficult to confirm given the lack of evidence for metamorphosis in stereospondyls including Rhineceps.

Rhineceps as a temnospondyl, possesses diagnostic temnospondyl traits including wide vomers, large and round interpterygoid vacuities, otic notches, contact between post-pareital and exoccipital skull bones, and a stapes that articulates with the parasphenoid. [11] Rhineceps fossils are differentiated from other rhinesuchids by the following traits “presence of a vomerine depression immediately anterior to cultriform process of the parasphenoid; ectopterygoids with enlarged tusks at their anterior end; transverse vomerine tooth row anteriorly convex; quadrate condyles projected behind the tip of the tabular horns; vomers with a continuous raised field of denticles; parasphenoid plate wider than long; well-developed transversely wide ‘pockets’; internarial vacuity between nasals and premaxillae; mandible with two anterior meckelian foraminae; chordatympanic foramen located on the suture between the articular and the prearticular.”. [1]

Geological and paleoenvironmental information

Rhineceps was found in the South African Karoo Supergroup, a group of sedimentary rocks that span from the Carboniferous period to the Jurassic period. These sedimentary layers were created from sediment shed from lakes and rivers near the Gondwanide mountains on the continent of Gondwana. [12] Rhineceps was found in the “Upper Bone Beds” of the Chiweta beds in the North Waller Area in Northern Malawi, which is in South Central Africa. [6] The sedimentary rocks from the Chiweta beds originated from mostly river sediments which often contain fossil bones surrounded by pedogenic carbonates. [12] The lacustrine (lake derived) sediment does not contain bone, but instead contains pollen that were used to identify the age range of the Chiweta beds to be less than 263 Mya. [12] The overlap of stratigraphic ranges of specific therapsid taxa place the Cistecephalus Assemblage Zone in the Chiweta beds (the zone where Rhineceps was found) within 256-258 Mya. [12]

Rhineceps lived during the late Permian of northern Malawi 256-258 Mya. [12] The ecosystems of Southern Africa were mainly tropical and were dominated by many rivers and river systems. [12] Terrestrial ecosystems are dominated by Therapsids and river ecosystems are dominated by fishes and aquatic carnivorous temnospondyls. [8] [12] The late Permian is also characterized by reductions in biodiversity that limited the number of existing genera and species. [8] [13] Most groups of temnospondyls that existed terrestrially went extinct and consequently stereospondyls were the only temnospondyls to survive into the late Permian and early Triassic by adapting to a mostly or fully aquatic lifestyle. [8] The ecosystems that Rhineceps lived in experienced significant ecological change causing dwindling biodiversity before the traditional date for the Permian-Triassic mass extinction event (252 Mya), likely caused by global cooling and growing glaciers at the end of the Guadalupian (end of middle Permian). [13]

See also

Related Research Articles

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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 large armour-like bony plates (osteoderms) that generally distinguish them from the modern soft-bodied lissamphibians.

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

Rhinesuchus is a large temnospondyl. Remains of the genus are known from the Permian of the South African Karoo Basin's Tapinocephalus and Cistecephalus assemblage zones, both belonging to the Beaufort Group. The skull of Rhinesuchus had a flat triangular shape with blunt snout similar to some of the other large temnospondyls, and had a palate filled with small sharp teeth, suggesting that it hunted fish. Also, the small eyes were on top of the head suggesting that it approached its prey from below.

<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>Uranocentrodon</i> Extinct genus of temnospondyls

Uranocentrodon is an extinct genus of temnospondyls in the family Rhinesuchidae. Known from a 50 centimetres (20 in) skull, Uranocentrodon was a large predator with a length up to 3.75 metres (12.3 ft). Originally named Myriodon by van Hoepen in 1911, it was transferred to a new genus on account of the name being preoccupied in 1917. It has been synonymized with Rhinesuchus, but this has not been widely supported. It was also originally considered to be of Triassic age, but more recent analysis has placed its age as just below the Permian-Triassic boundary.

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

Intasuchus is an extinct genus of temnospondyl amphibian from the Middle Permian of Russia. It is known from a single species, Intasuchus silvicola, which was named in 1956. Intasuchus belongs to the family Intasuchidae and is probably its sole member, although other taxa such as Syndyodosuchus and Cheliderpeton have been assigned to the family in the past. Intasuchus most likely belongs to the group Archegosauroidea, Permian relatives of the large, mostly Mesozoic temnospondyl clade Stereospondyli.

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

Laidleria is an extinct genus of temnospondyl that likely lived between the Early to Middle Triassic, though its exact stratigraphic range is less certain. Laidleria has been found in the Karoo Basin in South Africa, in Cynognathus Zone A or B. The genus is represented by only one species, L. gracilis, though the family Laidleriidae does include other genera, such as Uruyiella, sister taxon to Laidleria, which was discovered and classified in 2007. 

<i>Konzhukovia</i> Genus of amphibians (fossil)

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

Australerpeton is an extinct genus of stereospondylomorph temnospondyl currently believed to belong to the family Rhinesuchidae. When first named in 1998, the genus was placed within the new family Australerpetontidae. However, studies published a few years later questioned the systematics used in the original description and included the genus within Archegosauridae. A study by Dias & Schultz (2003) reassigned Australerpeton to the family Rhinesuchidae within the suborder Stereospondyli based on an earlier evaluation of the family. In this study, the close similarities between Australerpeton and archegosaurids were attributed to convergent evolution as a result of similar semi-aquatic lifestyles. A redescription of the skeleton of this genus was published by Eltink & Langer in 2014, and the skull was redescribed in a follow-up study published by Eltink et al. in 2016. These studies, as well as a 2017 study focusing on rhinesuchids in general, confirmed that Australerpeton was a rhinesuchid rather than an archegosaurid. Fossils of the genus have been found in the Rio do Rasto Formation of Brazil.

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

Deltasaurus is an extinct genus of Carnian temnospondyl amphibian of the family Rhytidosteidae.

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

Rhinesuchidae is a family of tetrapods that lived primarily in the Permian period. They belonged to the broad group Temnospondyli, a successful and diverse collection of semiaquatic tetrapods which modern amphibians are probably descended from. Rhinesuchids can be differentiated from other temnospondyls by details of their skulls, most notably the interior structure of their otic notches at the back of the skull. They were among the earliest-diverging members of the Stereospondyli, a subgroup of temnospondyls with flat heads and aquatic habits. Although more advanced stereospondyls evolved to reach worldwide distribution in the Triassic period, rhinesuchids primarily lived in the high-latitude environments of Gondwana during the Guadalupian and Lopingian epochs of the Permian. The taxonomy of this family has been convoluted, with more than twenty species having been named in the past; a 2017 review recognized only eight of them to be valid. While several purported members of this group have been reported to have lived in the Triassic period, most are either dubious or do not belong to the group. However, at least one valid genus of rhinesuchid is known from the early Triassic, a small member known as Broomistega. The most recent formal definition of Rhinesuchidae, advocated by Mariscano et al. (2017) is that of a stem-based clade containing all taxa more closely related to Rhinesuchus whaitsi than to Lydekkerina huxleyi or Peltobatrachus pustulatus. A similar alternate definition is that Rhinesuchidae is a stem-based clade containing all taxa more closely related to Uranocentrodon senekalensis than to Lydekkerina huxleyi, Trematosaurus brauni, or Mastodonsaurus giganteus.

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

Lydekkerinidae is a family of stereospondyl temnospondyls that lived in the Early Triassic period. During this time period, lydekkerinids were widely distributed, with putative remains reported from Russia, Greenland, India, South Africa, Madagascar, Australia, and Antarctica. In contrast to most other stereospondyls, lydekkerinids were relatively small-bodied. The type genus is Lydekkerina, the namesake of the family and the best-known lydekkerinid.

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

Microposaurus is an extinct genus of trematosaurid temnospondyl. Fossils are known from the Cynognathus Assemblage Zone of the Beaufort Group in South Africa and the Rouse Hill Siltstone of Australia that date back to the Anisian stage of the Middle Triassic. These aquatic creatures were the short snouted lineage from Trematosaurinae.

<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>Indobrachyops</i> Extinct genus of amphibians

Indobrachyops is an extinct genus of temnospondyl amphibian from the Early Triassic of India. It is known from a nearly complete fossil skull that was first described by paleontologists Friedrich von Huene and M. R. Sahni in 1958 from the Panchet Formation in Raniganj Coalfield. Indobrachyops belongs to a group of mostly semi-aquatic temnospondyls called Stereospondyli, but its exact placement within the group has been uncertain since its first description.

<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.

<span class="mw-page-title-main">Derwentiinae</span> Extinct subfamily of amphibians

Derwentiinae is a subfamily of rhytidosteid temnospondyls from the Permian and Triassic periods of Australia and India. It includes the genera Arcadia, Deltasaurus, Derwentia, Indobrachyops, and Rewana. Derwentiinae was named in a 2011 study that analyzed the phylogenetic relationships of rhytidosteids. It was a replacement name for the family Derwentiidae, which was named in 2000.

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

Branchiosauridae is an extinct family of small amphibamiform temnospondyls with external gills and an overall juvenile appearance. The family has been characterized by hundreds of well-preserved specimens from the Permo-Carboniferous of Middle Europe. Specimens represent well defined ontogenetic stages and thus the taxon has been described to display paedomorphy (perennibranchiate). However, more recent work has revealed branchiosaurid taxa that display metamorphosing trajectories. The name Branchiosauridae refers to the retention of gills.

Latiscopus disjunctus is a small Late Triassic temnospondyl collected in 1940 by a Works Projects Administration crew working near Otis Chalk, Texas that was described by John Wilson in 1948.

Rastosuchus is an extinct genus of stereospondyl temnospondyl within the family Rhinesuchidae. It contains one species, Rastosuchus hammeri, found in the Permian Rio do Rasto Formation of Brazil.

References

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