Anaschisma
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''Anaschisma'' ("ripped up") is an extinct genus of large
temnospondyl Temnospondyli (from Greek language, Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') or temnospondyls is a diverse ancient order (biology), order of small to giant tetrapods—often considered Labyrinth ...
s. These animals were part of the family called
Metoposauridae Metoposauridae is an extinct family of trematosaurian temnospondyls. The family is known from the Triassic period. Most members are large, approximately long and could reach 3 m long.Brusatte, S. L., Butler R. J., Mateus O., & Steyer S. J. (20 ...
, which filled the crocodile-like predatory
niche Niche may refer to: Science *Developmental niche, a concept for understanding the cultural context of child development and growth *Ecological niche, a term describing the relational position of an organism's species *Niche differentiation, in ec ...
s in the late Triassic. It had a large skull about long, and possibly reached long. It was an ambush hunter, snapping up anything small enough to fit in its huge jaws. It was very common during the Late
Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...
(
Carnian The Carnian (less commonly, Karnian) is the lowermost stage (stratigraphy), stage of the Upper Triassic series (stratigraphy), Series (or earliest age (geology), age of the Late Triassic Epoch (reference date), Epoch). It lasted from 237 to 227.3 ...
-
Norian The Norian is a division of the Triassic geological period, Period. It has the rank of an age (geology), age (geochronology) or stage (stratigraphy), stage (chronostratigraphy). It lasted from ~227.3 to Mya (unit), million years ago. It was prec ...
age) in what is now the American Southwest.


History of discovery

''Anaschisma'' was erected by Branson (1905) from two metoposaurid skulls from the
Popo Agie Formation The Popo Agie Formation ( )Locally "po-PO-zha" according to Don Pitcher, 2006, ''Moon Handbooks Wyoming,'' p. 26/ref>More ambiguous transcription of "po-po-zsha" at is a Triassic geologic Formation (geology), formation that outcrop, crops out in ...
(
Carnian The Carnian (less commonly, Karnian) is the lowermost stage (stratigraphy), stage of the Upper Triassic series (stratigraphy), Series (or earliest age (geology), age of the Late Triassic Epoch (reference date), Epoch). It lasted from 237 to 227.3 ...
) of Wyoming. The generic name ''Anaschisma'' ("ripped up") was not explained but would derive from
Ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...
ἀνασχίζω naskhizo"rip up, rend", likely alluding to the fragmented state of the original fossils noted by Branson: "The skulls were in a hard matrix of arenaceous shale, and had been broken in many pieces." The type species, ''A. browni'', was coined for the skull UC 447, while a second nominal species, ''A. brachygnatha'', was erected for the skull UC 448. Moodie (1908) considered ''A. brachygnatha'' a junior synonym of ''A. browni'', although Branson and Mehl (1929) retained the two species as distinct.Branson, E. B. & Mehl, M. G. 1929. Triassic amphibians from the Rocky Mountain region. The University of Missouri Studies, 4, 154–253. Colbert and Imbrie (1956) synonymized ''Anaschisma'' with the Newark Supergroup genus ''
Eupelor ''Eupelor'' is a dubious genus of prehistoric amphibian belonging to the temnospondyl family Metoposauridae. Fossils have been found in present-day Pennsylvania, within the Newark Supergroup, dating to the Late Triassic (Norian). Taxonomy Th ...
'' but retained it as a valid ''Eupelor'' species endemic to the Popo Aggie Formation. Chowdhury (1965) synonymized ''Anaschisma'' with ''Metoposaurus'' and sunk all North American metoposaurids from the Chinle and Dockum into ''browni''. Hunt (1989) recovered ''Anaschisma'' as an advanced or highly derived form. Some specimens attributed to ''Anaschisma'' from the Redonda Formation were renamed ''
Apachesaurus ''Apachesaurus'' is an extinct genus of metoposaurid temnospondyls from western North America. Description and taxonomy ''Apachesaurus'' was described from the Late Triassic (late Norian-Rhaetian The Rhaetian is the latest age (geology), ...
'' by Hunt (1993).


''Koskinonodon''

The genus ''Koskinonodon'' was formerly named ''Buettneria'' by Case in 1922, but in 2007, B.D. Mueller realized that the name '' Buettneria'' had already been given to a bush cricket from the Republic of Congo by Karsch (1889), so he made the genus ''Koskinonodon'' the earliest available unpreoccupied name for the temnospondyl. Lucas ''et al.'' (2007), however, petitioned the ICZN to suppress Karsch's name in favor of Case's name, citing evidence that the amphibian name is much more well known and widely used (the authors cited 75 uses of the name in scientific literature and books over the last 85 years), and that the bush cricket name had been seldom used in technical literature. However, ICZN Opinion 2255 issued in 2010 rejected the petition. Known ''Koskinonodon'' fossils have been found in the
United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
, especially the
Chinle Formation The Chinle Formation is an Upper Triassic continental geological formation of fluvial, lacustrine, and palustrine to eolian deposits spread across the U.S. states of Nevada, Utah, northern Arizona, western New Mexico, and western Colorado. In ...
of Petrified Forest National Park and the ''Placerias'' Quarry in Arizona, the
Garita Creek Formation The Garita Creek Formation is a geologic formation in New Mexico that contains vertebrate fossils characteristic of the Carnian Age of the late Triassic .Lucas and Hunt 1989 The formation may be synonymous with the Tecovas Formation in Texas. ...
of central New Mexico (the quarry at Lamy), the
Petrified Forest Member The Petrified Forest Member is a stratigraphic unit of the Chinle Formation in Arizona, Colorado, New Mexico, Nevada, and Utah. It preserves fossils dating back to the Triassic period. Subunits Beds (are in alphabetical order, asterisks (*) ind ...
of northern New Mexico, the
Bluewater Creek Formation The Bluewater Creek Formation is a geologic formation in west-central New Mexico. It preserves fossils dating back to the late Triassic period. Description The formation consists of red sandstones and mudstones and has a total thickness in exce ...
of western New Mexico, the
New Oxford Formation The New Oxford Formation is a mapped bedrock unit consisting primarily of sandstones, conglomerates, and shales. The New Oxford Formation was first described in Adams County, Pennsylvania in 1929, and over the following decade was mapped in adjace ...
of Pennsylvania, the
Tecovas Formation The Tecovas Formation is a geological Formation (geology), formation in the Texas panhandle and eastern New Mexico. It is one of several formations encompassed by the Late Triassic Dockum Group.Weishampel, David B; et al. (2004). "Dinosaur distri ...
of western Texas, and the
Popo Agie Formation The Popo Agie Formation ( )Locally "po-PO-zha" according to Don Pitcher, 2006, ''Moon Handbooks Wyoming,'' p. 26/ref>More ambiguous transcription of "po-po-zsha" at is a Triassic geologic Formation (geology), formation that outcrop, crops out in ...
of the Chugwater Group of Wyoming. Synonymy of ''Koskinonodon'' with ''Anaschisma'' started when Romer (1947) proposed that ''Anaschisma'' was a senior synonym of ''Buettneria'', ''Koskinonodon'', and ''Borborophagus''. This was followed by Gee ''et al.'' (2019), where they redescribed the holotypes of the two nominal ''Anaschisma'' species, and then synonymized ''Koskinonodon'', ''Buettneria'' and ''Borborophagus'' with ''Anaschisma''. The species ''B. bakeri'' which has long been assigned to the various synonyms of ''Anaschisma'', was moved to its own genus, ''
Buettnererpeton ''Buettnererpeton'' is an extinct genus of large temnospondyls known from the Late Triassic Dockum Group in Texas. The type species, ''B. bakeri'', was long classified as part of other genera, such as '' Metoposaurus'' and ''Koskinonodon ' ...
'', in 2022.


Description

The skull of ''Anaschisma'' differs from the skulls of other closely related organisms in a few key ways. It is wider overall and features eye sockets that are very
anterior Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...
and forward oriented, more so than its contemporaries. Also, the skull has prominent slime canals, which are used for transporting mucus, as well as large external nares. In addition, the upper jaw is relatively weak and thin, used only for holding teeth. Their large jaws could have held many teeth at once, maybe even over 100 on each side of the upper and lower jaws, but the actual number varies constantly over the animal's lifetime due to natural causes such as fighting, eating, disease, etc. The sheer size of the skull is one of the most defining traits for the genus ''Anaschisma''. Other more minor skull traits characterize ''Anaschisma'' as well: elongation of the lacrimal, shortening of the
prefrontal Prefrontal may refer to: *Prefrontal bone, a skull bone in some tetrapods *Prefrontal cortex, a region of the brain of a mammal *Prefrontal scales The prefrontal scales on snakes and other reptiles are the scales adjacent and anterior to the fr ...
, reduction of the
interclavicle An interclavicle is a bone which, in most tetrapods, is located between the clavicles. Therian mammals ( marsupials and placentals) are the only tetrapods which never have an interclavicle, although some members of other groups also lack one. In ...
, and the most characteristic is the center lachrymal entering margin of the
orbit In celestial mechanics, an orbit (also known as orbital revolution) is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an ...
. While the shortened prefrontal is a characteristic of the family Metoposauridae, it is shorted even more in ''Anaschisma''. The interclavicle is reduced in the way that it has many hexagonal pits as well as grooves and ridges. The skull of ''Anaschisma'' is also covered in this reticulate ornamentation. Some researchers believe that ''Anaschisma'' has a shorter posterior process of the interclavicle, which may discriminate it from other closely related species, while others believe that there is not enough information to make that distinction. ''Anaschisma'' also has ossified opisthotics, the more posterior of the bones surrounding the inner ear. ''Anaschisma'' had sharp, pointy teeth for catching and killing prey. They had marginal teeth as well as larger teeth on the palate, specifically
palatine A palatine or palatinus (Latin; : ''palatini''; cf. derivative spellings below) is a high-level official attached to imperial or royal courts in Europe since Roman Empire, Roman times.
and ectopterygoid teeth. They had two basic types: large with shallow grooves and small with deeper grooves. These grooves run lengthwise down the teeth and aided the animals in catching prey. The teeth are elongated labio-lingually at their base and opposite, mesiodistally, at their tip. In the middle, they are not elongated either way but instead circular. These dental adaptations enhanced the ability of ''Anaschisma'' to capture prey; the teeth are optimized for piercing prey and not allowing it to escape, resisting the bending force applied by the struggling organism, and propagating cracks in the hard parts of the object, such as bone, allowing for easier eating and digestion. ''Anaschisma'' had a wide, wedge-shaped, powerful tail to assist it with swimming, hunting and likely defense. It was not long like the crocodiles of today, but more likely short and strong to enable it to quickly spring up from hiding and capture prey before it escapes. The legs of ''Anaschisma'' display a sprawling stance and short legs with 4-digits on the front and 5 on the back limbs. ''Anaschisma'' likely spent a lot of time motionless, waiting for prey, which these short legs were likely an adaptation to.


Paleobiology

The hunting style of ''Anaschisma'' involved lying at the bottom of a shallow swamp, waiting for a fish,
crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...
, smaller amphibian, or even a young phytosaur to wander by. When it spotted prey, it used its huge jaws to engulf and consume them. A few particular adaptations suggest ''Koskinonodon'' had this aquatic lifestyle. First, they had
lateral line The lateral line, also called the lateral line organ (LLO), is a system of sensory organs found in fish, used to detect movement, vibration, and pressure gradients in the surrounding water. The sensory ability is achieved via modified epithelia ...
s formed by the sensory sulci. These are useful for detecting changes in water pressure made by the swimming motions of nearby organisms. Their sprawling limbs were also adapted for water. They would not move quickly or efficiently on land, although they may have done it to find another water pool with more food or other resource. Mass graves have been found, thought to be a result of a group of these animals gathering together in a withering water pool during a drought and all perishing because the water was never replenished.


Paleoecology

They lived mostly in the late Triassic; by the time the
Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...
began, most temnospondyls, ''Anaschisma'' included, were gone. It is likely that they went extinct during the Triassic-Jurassic extinction event, along with the majority of other large amphibians, the class of
Conodonts Conodonts, are an extinct group of marine jawless vertebrates belonging to the Class (biology), class Conodonta (from Ancient Greek κῶνος (''kōnos''), meaning "cone", and ὀδούς (''odoús''), meaning "tooth"). They are primarily known ...
and 34% of all marine genera. It is unknown what caused this
mass extinction An extinction event (also known as a mass extinction or biotic crisis) is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a sharp fall in the diversity and abundance of multicellular organisms. It occ ...
; hypotheses include huge volcanic eruptions (the
Central Atlantic magmatic province The Central Atlantic magmatic province (CAMP) is the Earth's largest continental large igneous province, covering an area of roughly 11 million km2. It is composed mainly of basalt that formed before Pangaea broke up in the Mesozoic Era, near the ...
is a prime example), climate change,
oceanic acidification Ocean acidification is the ongoing decrease in the pH of the Earth's ocean. Between 1950 and 2020, the average pH of the ocean surface fell from approximately 8.15 to 8.05. Carbon dioxide emissions from human activities are the primary cause of ...
, or an asteroid impact. It is known, however, that over half of the species living on Earth at that time went extinct from this event. It lived alongside many other smaller amphibians, and its fossils are also commonly found with
phytosaur Phytosaurs (Φυτόσαυροι in Greek, meaning 'plant lizard') are an extinct group of large, mostly semiaquatic Late Triassic archosauriform or basal archosaurian reptiles. Phytosaurs belong to the order Phytosauria and are sometimes ref ...
fossils. It was named in 1931 by Case. The best conditions for
fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...
ization occur in river valleys or floodplains where deposition is occurring, and this animal likely lived in similar shallow, swampy habitats. As it follows, ''Anaschisma'' is famous for having extremely well preserved fossils, and they are often found in groups.


See also

*
Prehistoric amphibian This list of prehistoric amphibians is an attempt to create a comprehensive listing of all genera from the fossil record that have ever been considered to be amphibians, excluding purely vernacular terms. The list includes all commonly accepted gen ...
*
List of prehistoric amphibians This list of prehistoric amphibians is an attempt to create a comprehensive listing of all genera from the fossil record that have ever been considered to be amphibians, excluding purely vernacular terms. The list includes all commonly accepted gen ...


References

{{Taxonbar, from=Q4751797 Metoposauridae Norian genera Triassic temnospondyls of North America Fossil taxa described in 1905 Taxa named by Edwin Branson