Trimerorhachis

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Trimerorhachis
Temporal range: Early Permian, 290.1–272.5  Ma
Trimerorhachis AMNH.jpg
A large skull of Trimerorhachis insignis (AMNH 7116) in the American Museum of Natural History
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Order: Temnospondyli
Suborder: Dvinosauria
Family: Trimerorhachidae
Genus: Trimerorhachis
Cope, 1878
Species
  • T. insignisCope, 1878 (type)
  • T. mesopsCope, 1896
  • T. rogersiOlson, 1955
  • T. sandovalensisBerman and Reisz, 1980
  • T. greggiMilner and Schoch, 2013

Trimerorhachis is an extinct genus of dvinosaurian temnospondyl within the family Trimerorhachidae. It is known from the Early Permian of the southwestern United States, with most fossil specimens having been found in the Texas Red Beds. The type species of Trimerorhachis, T. insignis, was named by American paleontologist Edward Drinker Cope in 1878. Cope named a second species from Texas, T. mesops, in 1896. The species T. rogersi (named in 1955) and T. greggi (named in 2013) are also from Texas, and the species T. sandovalensis (named in 1980) is from New Mexico.

Contents

Description

A dorsal view of a skull of Trimerorhachis insignis, part of a slab containing a large death assemblage of Trimerorhachis individuals (AMNH 4569) Trimerorhachis insignis AMNH 4569 assemblage 1.jpg
A dorsal view of a skull of Trimerorhachis insignis, part of a slab containing a large death assemblage of Trimerorhachis individuals (AMNH 4569)
A ventral view of several skeletons of Trimerorhachis insignis, also part of the death assemblage Trimerorhachis insignis AMNH 4569 assemblage 2.jpg
A ventral view of several skeletons of Trimerorhachis insignis, also part of the death assemblage

Largest specimens of Trimerorhachis reached a length of about 1.5 meters (5 ft), although most have been no more than 1.2 meters (4 ft) in length. [1] Trimerorhachis has a large triangular head with upward-facing eyes positioned near the front of the skull. The trunk is long and the limbs are relatively short. The presence of a branchial apparatus indicates that Trimerorhachis had external gills in life, much like the modern axolotl. [2] The body of Trimerorhachis is also completely covered by small and very thin osteoderms, which overlap and can be up to 20 layers thick. These osteoderms act as an armor-like covering, especially around the tail. Their weight may have helped Trimerorhachis sink to the bottom of lakes and rivers where it would feed. [3]

History

Edward Drinker Cope's illustration of fossils of Trimerorhachis insignis. Trimerorhachis Cope.jpg
Edward Drinker Cope's illustration of fossils of Trimerorhachis insignis.

Trimerorhachis was first described by Edward Drinker Cope in 1878. [4] Specimens are often preserved as masses of bones that are mixed together and densely packed in slabs of rock. [5] Fossils are rarely found in articulation, although a slab of rock has been found with sixteen skulls and their associated vertebrae in an intact position. [2] Most of these fossils preserve skulls and dorsal vertebrae, but rarely any other bones. Paleontologist S.W. Williston of the University of Chicago commented in 1915 that "it will only be by the fortunate discovery of a connected skeleton that the tail, ribs, and feet will be made known." [5] A nearly complete specimen was discovered the following year near Seymour, Texas, and Williston was able to describe the entire postcranial skeleton of Trimerorhachis. [6]

In 1955, paleontologist Edwin Harris Colbert described the scales of Trimerorhachis. He noted that they were oval-shaped and overlapping and that each had a base layer of longitudinal striations covered by another layer ring-like ridges, the growth rings of the scales. The scales were more similar to fish scales than they were to reptile scales. [7] In 1979, paleontologist Everett C. Olson claimed that there were no such scales in Trimerorhachis, and that Colbert was incorrect in his interpretation of the body covering of Trimerorhachis. [3]

A second species called T. sandovalensis was named from New Mexico in 1980. A nearly complete skeleton from the Abo Formation near Jemez Springs has been designated the holotype, but other fossils of the species are found throughout the state, giving it a wide distribution. [8]

Paleobiology

Trimerorhachis insignis life restoration Trimerorhachis insignis life restoration.jpg
Trimerorhachis insignis life restoration

Environment

Trimerorhachis was probably a fully aquatic temnospondyl. Like most dvinosaurs, it had external gills. The interclavicle and clavicle of the pectoral girdle are both very large, a feature that is shared with other aquatic temnospondyls. Many bones are poorly ossified, indicating that Trimerorhachis was poorly suited for movement on land. [9] Trimerorhachis was probably an aquatic predator that fed on fish and small vertebrates. [3] Microanatomical data also suggest a fairly aquatic lifestyle, as shown by the obvious osteosclerosis of its femur. [10]

During the Early Permian, the area of New Mexico and Texas was a broad coastal plain that stretched from an ocean in the south to highlands in the north. Other common animals that lived alongside Trimerorhachis included lungfish and crossopterygians, the lepospondyl Diplocaulus , and the large sail-backed synapsid Dimetrodon . [8]

Brooding

Trimerorhachis insignis AMNH 4570.jpg
Trimerorhachis insignis AMNH 4591.jpg
Trimerorhachis insignis AMNH 4595.jpg
Trimerorhachis insignis AMNH 4557.jpg
Trimerorhachis insignis AMNH 7116.jpg
Growth stages in Trimerorhachis insignis (not to scale). From left to right, specimens AMNH 4570, AMNH 4591, AMNH 4595, AMNH 4557, and AMNH 7116.

Small bones that likely belong to immature Trimerorhachis individuals have been found in the pharyngeal pouches of larger Trimerorhachis specimens. At first these bones were thought to be part of the branchial arches which surround the pouch, or remains of prey that had just been eaten before the animal died. If Trimerorhachis was a mouth brooder, the closest living analogue would be Darwin's Frog, which broods its young in its vocal sac. The bones in Trimerorhachis belong to juveniles that were much larger than those of Darwin's Frog, however. The young of the Gastric-brooding frogs of Australia were comparable in size to those of Trimerorhachis but were brooded in the stomach rather than the throat. The number of brooded young in Darwin's Frog and the Gastric-brooding frogs is also much higher than that of Trimerorhachis, as only a few individuals can be distinguished in the collection of bones. The only living amphibian that raises similarly sized young is the Golden coquí, although it does so through ovovivipary rather than brooding. [3]

Another possible explanation for the small bones is that they were originally located in the throat and were pushed into the pharyngeal pouch during fossilization. If this was the case, Trimerorhachis may have eaten its young instead of brooding them. This type of cannibalism is widespread in living amphibians, and most likely occurred among some prehistoric amphibians as well. [3]

See also

Related Research Articles

<i>Eryops</i> Species of amphibian

Eryops is a genus of extinct, amphibious temnospondyls. It contains the single species Eryops megacephalus, the fossils of which are found mainly in early Permian rocks of the Texas Red Beds, located in Archer County, Texas. Fossils have also been found in late Carboniferous period rocks from New Mexico. Several complete skeletons of Eryops have been found in lower Permian rocks, but skull bones and teeth are its most common fossils.

<i>Dimetrodon</i> Genus of carnivorous synapsids from the Permian

Dimetrodon is an extinct genus of non-mammalian synapsid belonging to the family Sphenacodontidae that lived during the Cisuralian age of the Early Permian period, around 295–272 million years ago. With most species measuring 1.7–4.6 m (5.6–15.1 ft) long and weighing 28–250 kg (62–551 lb), the most prominent feature of Dimetrodon is the large neural spine sail on its back formed by elongated spines extending from the vertebrae. It was an obligate quadruped and had a tall, curved skull with large teeth of different sizes set along the jaws. Most fossils have been found in the Southwestern United States, the majority of these coming from a geological deposit called the Red Beds of Texas and Oklahoma. More recently, its fossils have also been found in Germany and over a dozen species have been named since the genus was first erected in 1878.

<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.

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

Cacops, is a genus of dissorophid temnospondyls from the Kungurian stage of the early Permian of the United States. Cacops is one of the few olsoniforms whose ontogeny is known. Cacops fossils were almost exclusively known from the Cacops Bone Bed of the Lower Permian Arroyo Formation of Texas for much of the 20th century. New material collected from the Dolese Brothers Quarry, near Richards Spur, Oklahoma in the past few decades has been recovered, painting a clearer picture of what the animal looked and acted like.

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

Dissorophidae is an extinct family of medium-sized temnospondyls that flourished during the late Carboniferous and early Permian periods. The clade is known almost exclusively from North America.

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

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

Platyhystrix is an extinct temnospondyl amphibian with a distinctive sail along its back, similar to the unrelated synapsids, Dimetrodon and Edaphosaurus. It lived during the boundary between the latest Carboniferous and earliest Permian periods throughout what is now known as the Four Corners, Texas, and Kansas about 300 million years ago.

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

Diplocaulus is an extinct genus of lepospondyl amphibians which lived from the Late Carboniferous to the Late Permian of North America and Africa. Diplocaulus is by far the largest and best-known of the lepospondyls, characterized by a distinctive boomerang-shaped skull. Remains attributed to Diplocaulus have been found from the Late Permian of Morocco and represent the youngest-known occurrence of a lepospondyl.

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

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

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

Dvinosaurus is an extinct genus of amphibious temnospondyls localized to regions of western and central Russia during the middle and late Permian, approximately 265-254 million years ago. Its discovery was first noted in 1921 by Russian paleontologist Vladimir Prokhorovich Amalitskii in a posthumously published paper that documents the findings of a site in Russia's Arkhangelsk District. Its name is derived from the proximity of this site to the Northern Dvina River.

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

Trimerorhachidae is a family of dvinosaurian temnospondyls, including Lafonius, Trimerorhachis, Procuhy and Neldasaurus.

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

Trematopidae is a family of dissorophoid temnospondyls spanning the late Carboniferous to the early Permian. Together with Dissorophidae, the family forms Olsoniformes, a clade comprising the medium-large terrestrial dissorophoids. Trematopids are known from numerous localities in North America, primarily in New Mexico, Oklahoma, and Texas, and from the Bromacker quarry in Germany.

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

Broiliellus is an extinct genus of dissorophoid temnospondyl within the family Dissorophidae. Broiliellus is most closely related to the genus Dissorophus, and both have been placed in the subfamily Dissorophinae. Broiliellus is known from five species from the Early Permian: the type species is Broiliellus texensis, and the other species are Broiliellus brevis,Broiliellus olsoni, Broiliellus arroyoensis, and Broiliellus reiszi. An additional species, Broiliellus novomexicanus, which was originally named Aspidosaurus novomexicanus, is now thought to fall outside the genus as a member of the subfamily Eucacopinae.

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

Dissorophus (DI-soh-ROH-fus) is an extinct genus of temnospondyl amphibian that lived during the Early Permian Period about 273 million years ago. Its fossils have been found in Texas and in Oklahoma in North America. Its heavy armor and robust build indicate Dissorophus was active on land, similar to other members of the clade Dissorophidae that are known from the Late Carboniferous to the Early Permian periods. Dissorphus is distinguished by its small body size, disproportionately large head and short trunk.

<i>Lydekkerina</i> Extinct genus of temnospondyls from the Early Triassic

Lydekkerina is an extinct genus of stereospondyl temnospondyl. It is the type genus of the family Lydekkerinidae. Fossils have been collected from Early Triassic deposits in South Africa and Australia. The type species is L. huxleyi, first described in 1889. While most other stereospondyls were semiaquatic, Lydekkerina was exclusively terrestrial.

Slaugenhopia is an extinct genus of dvinosaurian temnospondyl within the family Tupilakosauridae. Fossils have been found from the Early Permian San Angelo Formation in Texas. The type and only species, S. texensis, was named in 1962. It may be closely related to the dvinosaur Kourerpeton. Slaugenhopia was once classified as a trimerorhachid but is now classified as a tupilakosaurid.

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

Adamanterpeton is a genus of Edopoid Temnospondyl within the family Cochleosauridae. The type species A. ohioensis was named in 1998 and is currently the only known species within this genus. Adamanterpeton is rare in the Linton vertebrate assemblage, with other amphibians like Sauropleura, Ophiderpeton, and Colosteus being more common. Unlike other Linton vertebrates, Adamanterpeton may have been adapted to a terrestrial lifestyle.

Parioxys is an extinct genus of temnospondyl amphibian from the Early Permian of Texas.

<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.

<span class="mw-page-title-main">Red Beds of Texas and Oklahoma</span> Geologic strata in the southwestern United States

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References

  1. Andrew R. Milner; Rainer R. Schoch (2013). "Trimerorhachis (Amphibia: Temnospondyli) from the Lower Permian of Texas and New Mexico: cranial osteology, taxonomy and biostratigraphy". Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen. 270 (1): 91–128. doi:10.1127/0077-7749/2013/0360.
  2. 1 2 Case, E.C. (1935). "Description of a collection of associated skeletons of Trimerorhachis". University of Michigan Contributions from the Museum of Paleontology. 4 (13): 227–274. hdl:2027.42/48206.
  3. 1 2 3 4 5 Olson, E.C. (1979). "Aspects of the biology of Trimerorhachis (Amphibia: Temnospondyli)". Journal of Paleontology. 53 (1): 1–17. JSTOR   1304028.
  4. Cope, E.D. (1878). "Descriptions of extinct Batrachia and Reptilia from the Permian formation of Texas". Proceedings of the American Philosophical Society. 17: 182–193.
  5. 1 2 Williston, S.W. (1915). "Trimerorhachis, a Permian temnospondyl amphibian". The Journal of Geology. 23 (3): 246–255. Bibcode:1915JG.....23..246W. doi: 10.1086/622229 . JSTOR   30066442.
  6. Williston, S.W. (1916). "The skeleton of Trimerorhachis". The Journal of Geology. 24 (3): 291–297. Bibcode:1916JG.....24..291W. doi:10.1086/622329. JSTOR   30079362. S2CID   128401645.
  7. Colbert, E.H. (1955). "Scales in the Permian amphibian Trimerorhachis" (PDF). American Museum Novitates (1740): 1–17.
  8. 1 2 Berman, D.S.; Reisz, R.R. (1980). "A new species of Trimerorhachis (Amphibia, Temnospondyli) from the Lower Permian Abo Formation of New Mexico, with discussion of Permian faunal distributions in that state". Annals of the Carnegie Museum. 49: 455–485.
  9. Pawley, K. (2007). "The postcranial skeleton of Trimerorhachis insignis Cope, 1878 (Temnospondyli: Trimerorhachidae): a plesiomorphic temnospondyl from the Lower Permian of North America". Journal of Paleontology. 81 (5): 873–894. doi:10.1666/pleo05-131.1. S2CID   59045725.
  10. Quémeneur, S.; de Buffrénil, V.; Laurin, M. (2013). "Microanatomy of the amniote femur and inference of lifestyle in limbed vertebrates". Biological Journal of the Linnean Society. 109 (3): 644–655. doi: 10.1111/bij.12066 .