Parareptilia

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Parareptiles
Temporal range: Moscovian - Rhaetian, 306–201.3  Ma
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Survive if neodiapsids descend from them [1]
Parareptile collage.png
A collage of five parareptile fossils. Clockwise from top, Mesosaurus tenuidens (a mesosaur), Delorhynchus cifellii (a probable acleistorhinid), Scutosaurus karpinskii (a pareiasaur), Nyctiphruretus acudens (a nyctiphruretid), Hypsognathus fenneri (a procolophonid)
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade:† Parareptilia
Olson, 1947
Orders

Parareptilia ("near-reptiles") is a subclass or clade of basal sauropsids/reptiles, typically considered the sister taxon to Eureptilia (the group that likely contains all living reptiles and birds). Parareptiles first arose near the end of the Carboniferous period and achieved their highest diversity during the Permian period. Several ecological innovations were first accomplished by parareptiles among reptiles. These include the first reptiles to return to marine ecosystems (mesosaurs), the first bipedal reptiles (bolosaurids such as Eudibamus ), the first reptiles with advanced hearing systems (nycteroleterids and others), and the first large herbivorous reptiles (the pareiasaurs). The only parareptiles to survive into the Triassic period were the procolophonoids, a group of small generalists, omnivores, and herbivores. The largest family of procolophonoids, the procolophonids, rediversified in the Triassic, but subsequently declined and became extinct by the end of the period. [2] [3]

Contents

Compared to most eureptiles, parareptiles retained fairly "primitive" characteristics such as robust, low-slung bodies and large supratemporal bones at the back of the skull. While all but the earliest eureptiles were diapsids, with two openings at the back of the skull, parareptiles were generally more conservative in the extent of temporal fenestration. In its modern usage, Parareptilia was first utilized as a cladistically correct alternative to Anapsida, a term which historically referred to reptiles with solid skulls lacking holes behind the eyes. [4] Nevertheless, not all parareptiles have 'anapsid' skulls, and some do have large holes in the back of the skull. They also had several unique adaptations, such as a large pit on the maxilla, a broad prefrontal-palatine contact, and the absence of a supraglenoid foramen of the scapula. [4] [5]

Like many other so-called 'anapsids', parareptiles were historically understudied. Interest in their relationships were reinvigorated in the 1990s, when several studies argued that Testudines (turtles and their kin) were members of Parareptilia. [4] Although this would suggest that Parareptilia was not extinct after all, the origin of turtles is still heavily debated. Many other morphological or genetic analyses find more support for turtles among diapsid eureptiles such as sauropterygians or archosauromorphs, rather than parareptiles. [6] [7] [8] [3]

Description

Skull

A skull diagram of Colobomycter pholeter, a probable acleistorhinid from the Early Permian. Unlike most parareptiles, this species lacks tabular bones and has a heterodont dentition with large caniform teeth. Colobomycter skull diagram.png
A skull diagram of Colobomycter pholeter , a probable acleistorhinid from the Early Permian. Unlike most parareptiles, this species lacks tabular bones and has a heterodont dentition with large caniform teeth.

Parareptilian skulls were diverse, from mesosaurs with elongated snouts filled with hundreds of thin teeth, to the snub-nosed, knob-encrusted skulls of pareiasaurs. Parareptile teeth were quite variable in shape and function between different species. However, they were relatively homogenous on the same skull. While most synapsids and many early eureptiles had a caniform region of enlarged fang-like teeth in the front half of the skull, very few parareptiles possessed caniform teeth. [5]

Many amniotes have a row of small pits running along bones at the edge of the mouth, but parareptiles have only a few pits, with one especially large pit near the front of the maxilla. [4] [9] [7] The rest of the skull was often strongly-textured by pits, ridges, and rugosities in most parareptile groups, occasionally culminating in complex bosses or spines. The maxilla is usually low, while the prefrontal and lacrimal bones in front of the eye are both fairly large. In all parareptiles except mesosaurs, the prefrontal has a plate-like inner branch which forms a broad contact with the palatine bone of the palate. [4] [7] [5] A prominent hole, the foramen orbitonasale, is present at the intersection of the prefrontal, palatine, and lacrimal. Parareptilian palates also have toothless and reduced ectopterygoid bones, a condition taken to extremes in mesosaurs, which have lost the ectopterygoid entirely. [4] [5]

Most parareptiles had large orbits (eye sockets), significantly longer (from front-to-back) than the region of the skull behind the eyes. [5] The jugal bone, which forms the lower and rear edge of the orbit, has a very thin suborbital process (front branch), usually no subtemporal process (lower rear branch), and a thick dorsal process (upper rear branch). The squamosal and quadratojugal bones, which lie behind the jugal, are quite large and are embayed from behind to accommodate the internal ears. [4] [5] Parareptiles were traditionally considered to have an ‘anapsid’-type skull, with the jugal, squamosal, and quadratojugal firmly sutured together without any gaps or slits between them. This principle still holds true for some subgroups, such as pareiasaurs. However, a growing number of parareptile taxa are now known to have had an infratemporal fenestra, a large hole or emargination lying among the bones behind the eye. In some taxa, the margins of such openings may include additional bones such as the maxilla or postorbital. [10] [11] When seen from above, the rear edge of the skull is straight or has a broad median embayment. [5] From inside to outside, the rear edge of the skull is formed by three pairs of bones: the postparietals, tabulars, and supratemporals. Parareptiles have particularly large supratemporals, which often extend further backwards than the tabulars. [12]

Apart from the long, slender jaws of mesosaurs, most parareptile jaws were short and thick. The jaw joint is formed by the articular (in the lower jaw) and the quadrate (in the upper jaw). In many parareptiles, the jaw joint is shifted forwards on the skull past the rear part of the braincase. [4] [7] Jaw muscles attach to the coronoid process, a triangular spur in the rear half of the jaw. Both the tooth-bearing dentary bone and the posterior foramen intermandibularis (a hole on the inner surface of the jaw) reach as far back as the coronoid process. [4] [5] The surangular bone, which forms the upper rear part of the jaw, is narrow and plate-like. [13]

Postcranial skeleton

Skeleton of Kapes bentoni, a procolophonid from the Middle Triassic of England Kapes full skeleton.jpg
Skeleton of Kapes bentoni , a procolophonid from the Middle Triassic of England

There was some variation in the body shape of parareptiles, with early members of the group having an overall lizard-like appearance, with thin limbs and long tails. The most successful and diverse groups of parareptiles, the pareiasaurs and procolophonids, had massively-built bodies with reduced tails and stout limbs with short digits. This general body shape is shared with other ‘cotylosaurs’ such as captorhinids, diadectomorphs, and seymouriamorphs. [3] Another general ‘cotylosaurian’ feature in parareptiles is the ‘swollen’ appearance of their vertebrae, which have wide and convex upper surfaces. [12]

Parareptiles lacked a supraglenoid foramen on the scapula, a hole which is also absent in varanopids and neodiapsids. [5] [11] Most had a fairly short and thick humerus which was expanded near the elbow. Unlike early eureptiles, the outer part of the lower humerus possessed both a small supinator process and an ectepicondylar foramen and groove. [4] The ulna generally has a poorly developed olecranon process, another trait in contrast with the earliest eureptiles. [4] [5]

Most parareptiles had an ilium which was fan-shaped and vertically (rather than horizontally) oriented, an unusual trait among early amniotes. [4] [9] [7] The sacral ribs, which connect the spine to the ilium, were usually slender or fan-shaped, with large gaps between them. [4] The hindlimbs were typically not much longer than the forelimbs, and had thick reptilian ankle bones and short toes. There are some exceptions, such as Eudibamus , an early Permian bolosaurid with very elongated hindlimbs. [14]

History of classification

The name Parareptilia was coined by Olson in 1947 to refer to an extinct group of Paleozoic reptiles, as opposed to the rest of the reptiles or Eureptilia ("true reptiles"). [15] Olsen's term was generally ignored, and various taxa now known as parareptiles were generally not placed into exclusive groups with each other. Many were classified as 'cotylosaurs' (a wastebasket taxon of stout-bodied 'primitive' reptiles or reptile-like tetrapods) or 'anapsids' (reptiles without temporal fenestrae, such as modern turtles).

Parareptilia's usage was revived by cladistic studies, to refer to those traditional 'anapsids' that were thought to be unrelated to turtles. Gauthier et al. (1988) provided the first phylogenetic definitions for the names of many amniote taxa and argued that captorhinids and turtles were sister groups, constituting the clade Anapsida (in a much more limited context than typically applied). A name had to be found for a clade of various early-diversing Permian and Triassic reptiles no longer included in the anapsids. Olsen's term "parareptiles" was chosen to refer to this clade, although its instability within their analysis meant that Gauthier et al. (1988) were not confident enough to erect Parareptilia as a formal taxon. Their cladogram is as follows: [16]

Amniota  

Laurin & Reisz (1995) found a slightly different topology, in which Reptilia is divided into Parareptilia and Eureptilia. They argued that Testudines (turtles) were members of Parareptilia; in fact, they explicitly defined Parareptilia as "Testudines and all amniotes more closely related to them than to diapsids". Captorhinidae was transferred to Eureptilia, while Parareptilia included turtles alongside many of the taxa named as such by Gauthier et al. (1988). There was one major exception: mesosaurs were placed outside both groups, as the sister taxon to the crown group Reptilia. Mesosaurs were still considered sauropsids, as they were closer to reptiles than to synapsids. The traditional group 'Anapsida' was rejected as a paraphyletic assemblage. The cladogram of Laurin & Reisz (1995) is provided below: [4]

Amniota  

In contrast, several studies in the mid-to-late 1990s by Olivier Rieppel and Michael deBraga argued that turtles were actually lepidosauromorph diapsids related to the sauropterygians. [17] [18] [9] [6] [7] The diapsid affinities of turtles have been supported by molecular phylogenies. [19] [20] [21] [22] The first genome-wide phylogenetic analysis was completed by Wang et al. (2013). Using the draft genomes of Chelonia mydas and Pelodiscus sinensis, the team used the largest turtle data set to date in their analysis and concluded that turtles are likely a sister group of crocodilians and birds (Archosauria). [8] This placement within the diapsids suggests that the turtle lineage lost diapsid skull characteristics, since turtles possess an anapsid skull. This would make Parareptilia a totally extinct group with skull features that resemble those of turtles through convergent evolution. With turtles positioned outside of parareptiles, Tsuji and Müller (2009) redefined Parareptilia as "the most inclusive clade containing Milleretta rubidgei and Procolophon trigoniceps , but not Captorhinus aguti ." [3]

The cladogram below follows an analysis by M.S. Lee, in 2013. [23]

Amniota  

The cladogram below follows the analysis of Li et al. (2018). [24]

†Parareptilia Scutosaurus BW flipped.jpg

Eureptilia

A 2020 study by David P. Ford and Roger B. J. Benson found that Parareptilia was nested within Diapsida as the sister group to Neodiapsida, with the clade containing Neodiapsida and Parareptilia dubbed Neoreptilia, which suggests that parareptiles were ancestrally diapsid. This excluded mesosaurs, which were again found to be basal among the sauropsids. [11] Some studies have found Parareptilia to be paraphyletic, with some parareptiles more closely related to diapsids that to other parareptiles, with Simões et al. (2022) using Neoreptilia for the clade containing Procolophonomorpha+Neodiapsida. [25]

Evolutionary history

The oldest known parareptiles are the bolosaur Erpetonyx and the acleistorhinid Carbonodraco from the Late Carboniferous (Moscovian-Gzhelian) of North America, which represents the only currently known Carboniferous parareptiles, indicating that the initial diversification of the group took place in the Late Carboniferous. [1] Numerous parareptile lineages appeared during the early Permian and the group reached a cosmopolitan distribution. Parareptile diversity declined towards the end of the Permian and procolophonoids, which first appeared during the Late Permian, were the only group of parareptiles to survive the Permian–Triassic extinction event. Procolophonid diversity sharply declined beginning in the Middle Triassic, with the group becoming extinct by the end of the Triassic. [26]

Related Research Articles

<span class="mw-page-title-main">Anapsid</span> Subclass of reptiles

An anapsid is an amniote whose skull lacks one or more skull openings near the temples. Traditionally, the Anapsida are the most primitive subclass of amniotes, the ancestral stock from which Synapsida and Diapsida evolved, making anapsids paraphyletic. It is however doubtful that all anapsids lack temporal fenestra as a primitive trait, and that all the groups traditionally seen as anapsids truly lacked fenestra.

<span class="mw-page-title-main">Sauria</span> Clade of reptiles

Sauria is the clade containing the most recent common ancestor of Archosauria and Lepidosauria, and all its descendants. Since most molecular phylogenies recover turtles as more closely related to archosaurs than to lepidosaurs as part of Archelosauria, Sauria can be considered the crown group of diapsids, or reptiles in general. Depending on the systematics, Sauria includes all modern reptiles or most of them as well as various extinct groups.

<span class="mw-page-title-main">Diapsid</span> Clade of amniote tetrapods with two holes in each side of their skulls

Diapsids are a clade of sauropsids, distinguished from more primitive eureptiles by the presence of two holes, known as temporal fenestrae, in each side of their skulls. The group first appeared about three hundred million years ago during the late Carboniferous period. All diapsids other than the most primitive ones in the clade Araeoscelidia are sometimes placed into the clade Neodiapsida. The diapsids are extremely diverse, and include birds and all modern reptile groups, including turtles, which were historically thought to lie outside the group. Although some diapsids have lost either one hole (lizards), or both holes, or have a heavily restructured skull, they are still classified as diapsids based on their ancestry. At least 17,084 species of diapsid animals are extant: 9,159 birds, and 7,925 snakes, lizards, tuatara, turtles, and crocodiles.

<span class="mw-page-title-main">Sauropsida</span> Taxonomic clade

Sauropsida is a clade of amniotes, broadly equivalent to the class Reptilia, though typically used in a broader sense to include both extinct stem-group relatives of modern reptiles, as well as birds. The most popular definition states that Sauropsida is the sibling taxon to Synapsida, the other clade of amniotes which includes mammals as its only modern representatives. Although early synapsids have historically been referred to as "mammal-like reptiles", all synapsids are more closely related to mammals than to any modern reptile. Sauropsids, on the other hand, include all amniotes more closely related to modern reptiles than to mammals. This includes Aves (birds), which are now recognized as a subgroup of archosaurian reptiles despite originally being named as a separate class in Linnaean taxonomy.

<span class="mw-page-title-main">Mesosaur</span> Extinct family of reptiles

Mesosaurs were a group of small aquatic reptiles that lived during the early Permian period (Cisuralian), roughly 299 to 270 million years ago. Mesosaurs were the first known aquatic reptiles, having apparently returned to an aquatic lifestyle from more terrestrial ancestors. It is uncertain which and how many terrestrial traits these ancestors displayed; recent research cannot establish with confidence if the first amniotes were fully terrestrial, or only amphibious. Most authors consider mesosaurs to have been aquatic, although adult animals may have been amphibious, rather than completely aquatic, as indicated by their moderate skeletal adaptations to a semiaquatic lifestyle. Similarly, their affinities are uncertain; they may have been among the most basal sauropsids or among the most basal parareptiles.

<span class="mw-page-title-main">Eureptilia</span> Taxon of tetrapods

Eureptilia is one of the two major subgroups of the clade Sauropsida, the other one being Parareptilia. Eureptilia includes Diapsida, as well as a number of primitive Permo-Carboniferous forms previously classified under Anapsida, in the old order "Cotylosauria".

<span class="mw-page-title-main">Pareiasauria</span> Extinct clade of reptiles

Pareiasaurs are an extinct clade of large, herbivorous parareptiles. Members of the group were armoured with osteoderms which covered large areas of the body. They first appeared in southern Pangea during the Middle Permian, before becoming globally distributed during the Late Permian. Pareiasaurs were the largest reptiles of the Permian, reaching sizes equivalent to those of contemporary therapsids. Pareiasaurs became extinct in the Permian–Triassic extinction event.

<span class="mw-page-title-main">Protorothyrididae</span> Family of reptiles

Protorothyrididae is an extinct family of small, lizard-like reptiles belonging to Eureptilia. Their skulls did not have fenestrae, like the more derived diapsids. Protorothyridids lived from the Late Carboniferous to Early Permian periods, in what is now North America. Many genera of primitive reptiles were thought to be protorothyridids. Brouffia, Coelostegus, Paleothyris and Hylonomus, for example, were found to be more basal eureptiles in Muller and Reisz (2006), making the family as historically defined paraphyletic, though three genera, Protorothyris, Anthracodromeus, and Cephalerpeton, were recovered as a monophyletic group. Anthracodromeus, Paleothyris, and Protorothyris were recovered as a monophyletic group in Ford and Benson (2020), who recovered them as more derived than captorhinids and Hylonomus, but less so than araeoscelidians. Anthracodromeus is the earliest known reptile to display adaptations to climbing. The majority of phylogenetic studies recover protorothyridids as basal members of Eureptilia; however, Simões et al. (2022) recover them as stem-amniotes instead.

<span class="mw-page-title-main">Captorhinidae</span> Extinct family of tetrapods

Captorhinidae is an extinct family of tetrapods, typically considered primitive reptiles, known from the late Carboniferous to the Late Permian. They had a cosmopolitan distribution across Pangea.

<span class="mw-page-title-main">Procolophonia</span> Extinct suborder of reptiles

Procolophonia is an extinct suborder (clade) of herbivorous reptiles that lived from the Middle Permian till the end of the Triassic period. They were originally included as a suborder of the Cotylosauria but are now considered a clade of Parareptilia. They are closely related to other generally lizard-like Permian reptiles such as the Millerettidae, Bolosauridae, Acleistorhinidae, and Lanthanosuchidae, all of which are included under the Anapsida or "Parareptiles".

<span class="mw-page-title-main">Procolophonomorpha</span> Order of reptiles (fossil)

Procolophonomorpha is an order or clade containing most parareptiles. Many papers have applied various definitions to the name, though most of these definitions have since been considered synonymous with modern parareptile clades such as Ankyramorpha and Procolophonia. The current definition of Procolophonomorpha, as defined by Modesto, Scott, & Reisz (2009), is that of as a stem-based group containing Procolophon and all taxa more closely related to it than to Milleretta. It constitutes a diverse assemblage that includes a number of lizard-like forms, as well as more diverse types such as the pareiasaurs. Lee 1995, 1996, 1997 argues that turtles evolved from pareiasaurs, but this view is no longer considered likely. Rieppel and deBraga 1996 and deBraga and Rieppel, 1997 argue that turtles evolved from sauropterygians, and there is both molecular and fossil (Pappochelys) evidence for the origin of turtles among diapsid reptiles.

<i>Colobomycter</i> Extinct genus of reptiles

Colobomycter is an extinct genus of lanthanosuchoid parareptile known from the Early Permian of Oklahoma.

<i>Eunotosaurus</i> Extinct genus of reptiles

Eunotosaurus is an extinct genus of amniote, possibly a close relative of turtles. Eunotosaurus lived in the late Middle Permian and fossils can be found in the Karoo Supergroup of South Africa. Eunotosaurus resided in the swamps of southern Africa. Its ribs were wide and flat, forming broad plates similar to a primitive turtle shell, and the vertebrae were nearly identical to those of some turtles. Accordingly, it is often considered as a possible transitional fossil between turtles and their prehistoric ancestors. However, it is possible that these turtle-like features evolved independently of the same features in turtles, since other anatomical studies and phylogenetic analyses suggest that Eunotosaurus may instead have been a parareptile, an early-diverging neodiapsid unrelated to turtles, or a synapsid.

<i>Acleistorhinus</i> Extinct genus of reptiles

Acleistorhinus (ah-kles-toe-RYE-nuss) is an extinct genus of parareptile known from the Early Permian of Oklahoma. It is notable for being the earliest known anapsid reptile yet discovered. The morphology of the lower temporal fenestra of the skull of Acleistorhinus bears a superficial resemblance to that seen in early synapsids, a result of convergent evolution. Only a single species, A. pteroticus, is known, and it is classified in the Family Acleistorhinidae, along with Colobomycter.

<i>Owenetta</i> Extinct genus of reptiles

Owenetta is an extinct genus of owenettid procolophonian parareptile. Fossils have been found from the Beaufort Group in the Karoo Basin of South Africa. Although most procolophonians lived during the Triassic, Owenetta existed during the Wuchiapingian and Changhsingian stages of the Late Permian as well as the early Induan stage of the Early Triassic. It is the type genus of the family Owenettidae, and can be distinguished from other related taxa in that the posterior portion of the supratemporal bears a lateral notch and that the pineal foramen is surrounded by a depressed parietal surface on the skull table.

<i>Microleter</i> Extinct genus of reptiles

Microleter is an extinct genus of basal procolophonomorph parareptiles which lived in Oklahoma during the Early Permian period. The type and only known species is Microleter mckinzieorum. Microleter is one of several parareptile taxa described from the Richards Spur fissure fills, and can be characterized from its high tooth count, lacrimal/narial contact, short postfrontal, and slit-like temporal emargination edged by the postorbital, jugal, squamosal, and quadratojugal. Contrary to Australothyris, which had a similar phylogenetic position as a basal procolophonomorph, Microleter suggests that early parareptile evolution occurred in Laurasia and that multiple lineages developed openings or emarginations in the temporal region.

<span class="mw-page-title-main">Evolution of reptiles</span> Origin and diversification of reptiles through geologic time

Reptiles arose about 320 million years ago during the Carboniferous period. Reptiles, in the traditional sense of the term, are defined as animals that have scales or scutes, lay land-based hard-shelled eggs, and possess ectothermic metabolisms. So defined, the group is paraphyletic, excluding endothermic animals like birds that are descended from early traditionally-defined reptiles. A definition in accordance with phylogenetic nomenclature, which rejects paraphyletic groups, includes birds while excluding mammals and their synapsid ancestors. So defined, Reptilia is identical to Sauropsida.

<span class="mw-page-title-main">Ankyramorpha</span> Extinct clade of reptiles

Ankyramorpha is an extinct clade of procolophonomorph parareptiles which lived between the early Cisuralian epoch and the latest Triassic period of Africa, Antarctica, Asia, Australia, Europe, North America and South America.

<span class="mw-page-title-main">Pantestudines</span> Clade of reptiles

Pantestudines or Pan-Testudines is the group of all reptiles more closely related to turtles than to any other living animal. It includes both modern turtles and all of their extinct relatives. Pantestudines with a complete shell are placed in the clade Testudinata.

<i>Pappochelys</i> Extinct genus of reptiles

Pappochelys is an extinct genus of diapsid reptile possibly related to turtles. The genus contains only one species, Pappochelys rosinae, from the Middle Triassic of Germany, which was named by paleontologists Rainer Schoch and Hans-Dieter Sues in 2015. The discovery of Pappochelys provides strong support for the placement of turtles within Diapsida, a hypothesis that has long been suggested by molecular data, but never previously by the fossil record. It is morphologically intermediate between the definite stem-turtle Odontochelys from the Late Triassic of China and Eunotosaurus, a reptile from the Middle Permian of South Africa.

References

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