Plagiosauridae

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Plagiosauridae
Temporal range: Early Triassic - Late Triassic
Gerrothorax pustuloglomeratus.JPG
Fossil of Gerrothorax pustuloglomeratus
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Order: Temnospondyli
Suborder: Stereospondyli
Superfamily: Plagiosauroidea
Family: Plagiosauridae
Abel, 1919
Genera

Plagiosauridae is a clade of temnospondyls of the Middle to Late Triassic. Deposits of the group are most commonly found in non-marine aquatic depositional environments from central Europe and Greenland, but other remains have been found in Russia, Scandinavia, and possibly Thailand.

Contents

Material

The majority of plagiosaurid remains are of the genus Gerrothorax, which have been recovered from the Fleming Fjord Formation of Jameson Land, East Greenland, [1] and from many localities in southern Germany. [2] [3] [4] All of this material is currently assigned to a single species, pulcherrimus. [1] Plagiosuchus material is also very abundant, though poorly preserved and has been found only from Germany. [5] Additional material, including the material of all other plagiosaurids, is significantly more fragmentary and less abundant than that of Gerrothorax. These additional materials are predominantly from Germany and Russia [2] with some potential material also reported from Thailand [6] and Brazil. [7]

Description

Plagiosaurids are predominantly characterized by the unique structure of their skulls and the armor that lines their trunk. The heads of these animals are short and wide with an overall semi-circular layout [1] and extremely large orbital fenestrae. [1] [8] The skull and trunk of these organisms are generally vertically compressed to varying degrees within members of the clade to form an overall flattened body plan. Some articulated, three-dimensional preservation of plagiosaurids indicates that this flattening was a feature of the animals in life and is not a preservation artifact. The amount of vertical compression in plagiosaurids varies somewhat with the most basal member, Plagiosuchus, being only somewhat compressed while more derived members such as Gerrothorax and Megalopthalma being much significantly more compressed. [1] [8] [5] Their skull, also vertically compressed, has dorsally oriented large orbital fenestrae and contained a battery of small teeth the curve inward. [5] The trunks of these animals have shortened limbs relative their body size and the backs were generally covered in bony armor which is denser in the more derived members of the clade. [1]

Ecology

Plagiosaurids are believed to have lived an almost entirely aquatic lifestyle. Much of this interpretation stems from analysis of the remains of Gerrothorax because specimens of this group are so much more abundant and well preserved than other plagiosaurid remains. [1] Aside from their remains being found dominantly within aquatic settings, evidence for an aquatic lifestyle comes primarily from evidence that the clade possessed internal gills, given by the presence of branchial arches that were lined with arteries. [3] Additionally, the limbs of plagiosaurids are short relative to their body size and the size of their pectoral girdle. Coupled with their vertically compressed body plan, a popular interpretation for these organisms has been that they lived on the floor of freshwater systems and were obligatorily aquatic. [1] [8] To facilitate a bottom dwelling lifestyle these organisms possess a special jaw joint, the atlanto-occipital joint, which facilitates the lifting of the cranium to open the mouth rather than lowering the jaw as would be expected in other organisms. [1] [5] Consequently, it is presumed that the animal would lay flat on river or lake beds waiting in ambush to catch prey, such as fish. [1] [8] [5] It has been proposed that they may have captured prey via suction by rapidly opening their mouth and then clamping down with their curved teeth. [1] [5] This is somewhat supported by the lateral elongation of the skull in later plagiosaurids like Gerrothorax and Plagiosternum compared to earlier members such as Plagiosuchus . [7] The elongation of the skull is interpreted to have facilitated muscle attachment to the back of the skull and increasing the ability and force directed toward lifting the head.

The large orbits of plagiosaurids have only been extensively analyzed in a single study which put forth two plausible eye structures. [8] According to this study, because of their incredibly flat and vertically compressed skulls, it is unlikely that the eyes actually filled the space of the groups large orbits because the eyes would permanently protrude into at least part of the palate. Thus, it is most plausible that, like many modern amphibians, the eyes of these animals were actually significantly smaller than the orbit and positioned toward the front of the skull, though there is not enough data to make conclusive judgment about their exact position. Schoch et al. (2014) [8] also put forward the hypothesis that the group had large, flat, lensless eyes similar to a family of abyss dwelling teleost fish, the Ipnopidae. These lensless eyes would allow plagiosaurids to detect when something is moving directly above them by causing a shadow in the light detected by the retina. While not observed among modern amphibians today, this hypothesis does align with the interpreted life habit of plagiosaurids and helps to explain the abnormal space afforded to the orbits of these animals.

Plagiosaurids also represent an interesting case of extreme evolutionary and morphological stasis. The features of these animals change very little through their evolutionary history despite changes. Schoch and Witzmann [9] analyzed the collections of Gerrothorax material and noted that, despite being recovered from multiple environments that encompass approximately 40 million years of time, the general body plan of Gerrothorax was relatively static. This was interpreted to support a relatively high degree of biological flexibility in these animals despite their somewhat unique ecology.

Related Research Articles

<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">Zatracheidae</span> Extinct family of temnospondyls

Zatracheidae is a family of Late Carboniferous and Early Permian temnospondyls known from North America and Europe. Zatracheidids are distinguished by lateral (sideways) bony protuberances of the quadratojugal bone of the skull, and a large opening in the snout called the internarial fontanelle that is bordered by enlarged premaxillae. The skull is flattened, with small orbits or eye sockets set far back. The opening in the snout may have housed a gland for producing a sticky substance so that prey would adhere to the tongue. If so, this indicates that these animals spent a large part of their time on land.

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

Gerrothorax is an extinct genus of temnospondyl amphibian from the Triassic period of Greenland, Germany, Poland, Sweden, and possibly Thailand. It is known from a single species, G. pulcherrimus, although several other species such as G. pustuloglomeratus have been named in the past.

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

Mastodonsaurus is an extinct genus of temnospondyl from the Middle Triassic of Europe. It belongs to a Triassic group of temnospondyls called Capitosauria, characterized by their large body size and presumably aquatic lifestyles. Mastodonsaurus remains one of the largest amphibians known, and may have exceeded 6 meters in length.

<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>Cochleosaurus</i> Extinct genus of amphibians

Cochleosaurus (“spoon lizard”, from the Latin cochlear "spoon" and Greek sauros “lizard”_ were medium-sized edopoid temnospondyls that lived in Euramerica during the Muscovian period. Two species, C. bohemicus and C. florensis, have been identified from the fossil record.

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

Cyclotosaurus is an extinct genus of temnospondyl within the family Mastodonsauridae. It was of great size for an amphibian, had an elongated skull up to 56 cm (22 in).

Micromelerpetontidae is an extinct family of dissorophoid temnospondyls that lived from the Late Carboniferous to the Early Permian in what is now Europe, with one Carboniferous species also known from North Africa. They were biologically similar to the related branchiosaurids, but proportionally akin to the unrelated microsaurs.

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

Eocyclotosaurus is an extinct genus of mastodonsauroid temnospondyl from the Middle Triassic (Anisian). The name Eocyclotosaurus means "dawn round-eared lizard". It is characterized as a capitosauroid with a long and slender snout, closed otic fenestra, and small orbits. It measured over one metre and had a 22 cm skull.

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

Actinodon is an extinct genus of eryopoidean temnospondyl within the family Eryopidae.

Hyperokynodon is an extinct genus of trematosaurian temnospondyl within the family Trematosauridae. Fossils have been found in Germany. While most trematosaurids existed during the Early Triassic, Hyperokynodon has been found in Late Triassic deposits, making it the youngest known trematosaurid. Hyperokynodon was known since 1852, but it was not identified as a trematosaurid until 1987. The type and only species is H. keuperinus.

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

Rhineceps is an extinct genus of temnospondyl amphibian in the family Rhinesuchidae. Rhineceps was found in Northern Malawi in Southern Africa known only from its type species R. nyasaensis. Rhineceps was a late Permian semi-aquatic carnivore that lived in streams, rivers, lakes or lagoons. 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.

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

Plagiosuchus is an extinct genus of plagiosaurid temnospondyl. It is known from several collections from the Middle Triassic of Germany.

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

Stanocephalosaurus is an extinct genus of large-sized temnospondyls living through the early to mid Triassic. The etymology of its name most likely came from its long narrow skull when compared to other temnospondyls. Stanocephalosaurus lived an aquatic lifestyle, with some species even living in salt lakes. There are currently three recognized species and another that needs further material to establish its legitimacy. The three known species are Stanocephalosaurus pronus from the Middle Triassic in Tanzania, Stanocephalosaurus amenasensis from the Lower Triassic in Algeria, and Stanocephalosaurus birdi, from the middle Triassic in Arizona. Stanocephalosaurus rajareddyi from the Middle Triassic in central India needs further evidence in order to establish its relationship among other Stanocephalosaurs. Like other temnospondyls, Stanocephalosaurus was an aquatic carnivore. Evidence of multiple species discovered in a wide range of localities proves that Stanocephalosaurus were present all across Pangea throughout the early to mid Triassic.

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

Acanthostomatops is an extinct genus of zatracheidid temnospondyl from the Lower Permian Döhlen Basin of Saxony.

<span class="mw-page-title-main">Erfurt Formation</span>

The Erfurt Formation, also known as the Lower Keuper, is a stratigraphic formation of the Keuper group and the Germanic Trias supergroup. It was deposited during the Ladinian stage of the Triassic period. It lies above the Upper Muschelkalk and below the Middle Keuper.

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

Megalophthalma is an extinct genus of temnospondyl amphibian belonging to the family Plagiosauridae. It is represented by the single type species Megalophthalma ockerti from the Middle Triassic Erfurt Formation in southern Germany, which is itself based on a single partial skull and a fragment of the lower jaw. Megalophthalma is distinguished from other temnospondyls by its very large orbits or eye sockets, which occupy most of the skull and are bordered by thin struts of bone. Like those of most plagiosaurids, the skull flat, wide, and roughly triangular. The orbits are pentagon-shaped. The bones at the back of the skull are highly modified and show similarities with those of the plagiosaurid Plagiosternum. Both Megalophthalma and Plagiosternum lack prefrontal and postfrontal bones. In fact, Megalophthalma and Plagiosternum are thought to form their own clade or evolutionary grouping within Plagiosauridae called Plagiosterninae. In overall form Megalophthalma and Plagiosternum are intermediate between the basal plagiosaurid Plagiosuchus and the derived Gerrothorax.

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.

This list of fossil amphibians described in 2018 is a list of new taxa of fossil amphibians that were described during the year 2018, as well as other significant discoveries and events related to amphibian paleontology that occurred in 2018.

References

  1. 1 2 3 4 5 6 7 8 9 10 11 Jenkins, Farish A.; Shubin, Neil H.; Gatesy, Stephen M.; Warren, Anne (2008-12-01). "Gerrothorax pulcherrimus from the Upper Triassic Fleming Fjord Formation of East Greenland and a Reassessment of Head Lifting in Temnospondyl Feeding". Journal of Vertebrate Paleontology. 28 (4): 935–950. doi:10.1671/0272-4634-28.4.935. ISSN   0272-4634. S2CID   86523094.
  2. 1 2 Hellrung, Hanna (2003). Gerrothorax pustuloglomeratus, ein Temnospondyle (Amphibia) mit knöcherner Branchialkammer aus dem Unteren Keuper von Kupferzell (Süddeutschland): Gerrothorax pustuloglomeratus, a temnospondyle (Amphibia) with a bony branchial chamber from the Lower Keuper of Kupferzell (South Germany). Staatliches Museum für Naturkunde.
  3. 1 2 Schoch, Rainer R.; Witzmann, Florian (2010-06-18). "Bystrow's Paradox - gills, fossils, and the fish-to-tetrapod transition". Acta Zoologica. 92 (3): 251–265. doi:10.1111/j.1463-6395.2010.00456.x. ISSN   0001-7272.
  4. WITZMANN, FLORIAN; SCHOCH, RAINER R.; HILGER, ANDRÉ; KARDJILOV, NIKOLAY (2011-11-25). "Braincase, palatoquadrate and ear region of the plagiosaurid Gerrothorax pulcherrimus from the Middle Triassic of Germany". Palaeontology. 55 (1): 31–50. doi: 10.1111/j.1475-4983.2011.01116.x . ISSN   0031-0239.
  5. 1 2 3 4 5 6 Damiani, Ross; Schoch, Rainer R.; Hellrung, Hanna; Werneburg, Ralf; Gastou, Stéphanie (2009-02-01). "The plagiosaurid temnospondyl Plagiosuchus pustuliferus (Amphibia: Temnospondyli) from the Middle Triassic of Germany: anatomy and functional morphology of the skull". Zoological Journal of the Linnean Society. 155 (2): 348–373. doi: 10.1111/j.1096-3642.2008.00444.x . ISSN   0024-4082.
  6. Suteethorn, Varavudh; Janvier, Philippe; Morales, Michael (January 1988). "Evidence for a plagiosauroid amphibian in the upper triassic Huai Hin Lat formation of Thailand". Journal of Southeast Asian Earth Sciences. 2 (3–4): 185–187. doi:10.1016/0743-9547(88)90029-3. ISSN   0743-9547.
  7. 1 2 Dias-Da-Silva, Sérgio; Milner, Andrew R. (September 2010). "The Pustulated Temnospondyl Revisited—a Plagiosternine Plagiosaurid from the Lower Triassic of Brazil". Acta Palaeontologica Polonica. 55 (3): 561–563. doi: 10.4202/app.2009.0131 . ISSN   0567-7920.
  8. 1 2 3 4 5 6 Schoch, Rainer R.; Milner, Andrew R.; Witzmann, Florian (2014-02-26). "Skull morphology and phylogenetic relationships of a new Middle Triassic plagiosaurid temnospondyl from Germany, and the evolution of plagiosaurid eyes". Palaeontology. 57 (5): 1045–1058. doi: 10.1111/pala.12101 . ISSN   0031-0239.
  9. SCHOCH, RAINER R.; WITZMANN, FLORIAN (2011-10-13). "Cranial morphology of the plagiosaurid Gerrothorax pulcherrimus as an extreme example of evolutionary stasis". Lethaia. 45 (3): 371–385. doi:10.1111/j.1502-3931.2011.00290.x. ISSN   0024-1164.