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Anaschisma

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Anaschisma
Temporal range:Late Triassic,227–208Ma
Skeleton ofAnaschismaat theAMNH
Scientific classificationEdit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Order: †Temnospondyli
Suborder: †Stereospondyli
Family: †Metoposauridae
Genus: †Anaschisma
Branson,1905
Type species
†Anaschisma browni
Branson, 1905
Synonyms
Genus synonymy
  • BorborophagusBranson & Mehl, 1929
  • BuettneriaCase 1922 (preoccupied)
  • KoskinonodonBranson & Mehl, 1929
Species synonymy
  • Anaschisma brachygnathaBranson, 1905
  • Borborophagus wyomingensisBranson & Mehl, 1929
  • Buettneria perfectaCase, 1922
  • Koskinonodon perfectus(Case, 1922)

Anaschisma( "ripped up" ) is an extinct genus of largetemnospondyls.These animals were part of the family calledMetoposauridae,which filled the crocodile-like predatorynichesin the late Triassic.[1]It had a large skull about 62 centimetres (24 in) long,[2]and possibly reached 3 metres (9.8 ft) long.[3]It was an ambush hunter, snapping up anything small enough to fit in its huge jaws.[3]It was very common during the LateTriassic(Norianage) in what is now the American Southwest.[4]

History of discovery

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Anaschismawas erected by Branson (1905) from two metoposaurid skulls from thePopo Agie Formationof Wyoming. The generic nameAnaschisma( "ripped up" ) was not explained but would derive fromAncient Greekἀνασχίζω [anaskhizo] "rip up, rend", likely alluding to the fragmented state of the original fossils noted by Branson: "The skulls were incased 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.[5]Moodie (1908) consideredA. brachygnathaa junior synonym ofA. browni,although Branson and Mehl (1929) retained the two species as distinct.[6][7]Colbert and Imbrie (1956) synonymizedAnaschismawith the Newark Supergroup genusEupelorbut retained it as a validEupelorspecies endemic to the Popo Aggie Formation.[8]Chowdhury (1965) synonymizedAnaschismawithMetoposaurusand sunk all North American metoposaurids from the Chinle and Dockum intobrowni.[9]

Hunt (1989) recoveredAnaschismaas an advanced or highly derived form.[4]Some specimens attributed toAnaschismafrom the Redonda Formation were renamedApachesaurusby Hunt (1993).[10][11]

Koskinonodon

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Koskinonodon perfectusskull, now thought to belong toAnaschisma

The genusKoskinonodonwas formerly namedBuettneriaby Case in 1922, but in 2007, B.D. Mueller realized that the nameBuettneriahad already been given to a bush cricket from the Republic of Congo by Karsch (1889), so he made the genusKoskinonodonthe earliest available unpreoccupied name for the temnospondyl.[12]Lucaset 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.[13]However, ICZN Opinion 2255 issued in 2010 rejected the petition.[14]

KnownKoskinonodonfossils have been found in theUnited States,especially theChinle Formationof Petrified Forest National Park and thePlaceriasQuarry in Arizona, theGarita Creek Formationof central New Mexico (the quarry at Lamy), thePetrified Forest Memberof northern New Mexico, theBluewater Creek Formationof western New Mexico, theNew Oxford Formationof Pennsylvania, theTecovas Formationof western Texas, and thePopo Agie Formationof the Chugwater Group of Wyoming.[15][7]

Synonymy ofKoskinonodonwithAnaschismastarted when Romer (1947) proposed thatAnaschismawas a senior synonym ofBuettneria,Koskinonodon,andBorborophagus.[15]This was followed by Geeet al.(2019), where they redescribed the holotypes of the two nominalAnaschismaspecies, and then synonymizedKoskinonodon,BuettneriaandBorborophaguswithAnaschisma.[16]The speciesB. bakeriwhich has long been assigned to the various synonyms ofAnaschisma,was moved to its own genus,Buettnererpeton,in 2022.[17]

Description

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Size ofAnaschisma(large) andApachesaurus(small) compared to a human

The skull ofAnaschismadiffers from the skulls of other closely related organisms in a few key ways. It is wider overall and features eye sockets that are veryanteriorand forward oriented, more so than its contemporaries.[6]Also, the skull has prominent slime canals, which are used for transporting mucus, as well as large external nares.[18]In addition, the upper jaw is relatively weak and thin, used only for holding teeth.[18]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.[18]The sheer size of the skull is one of the most defining traits for the genusAnaschisma.[18]

Other more minor skull traits characterizeAnaschismaas well: elongation of thelachrymal,shortening of theprefrontal,reduction of theinterclavicle,and the most characteristic is the center lachrymal entering margin of theorbit.[3]While the shortened prefrontal is a characteristic of the family Metoposauridae, it is shorted even more inAnaschisma.[1]The interclavicle is reduced in the way that it has many hexagonal pits as well as grooves and ridges.[1]The skull ofAnaschismais also covered in this reticulate ornamentation.[19]Some researchers believe thatAnaschismahas 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.[1]Anaschismaalso has ossified opisthotics, the more posterior of the bones surrounding the inner ear.[19]

Anaschismahad sharp, pointy teeth for catching and killing prey. They had marginal teeth as well as larger teeth on the palate, specificallypalatineand ectopterygoid teeth.[1]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.[20]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.[20]These dental adaptations enhanced the ability ofAnaschismato 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.[20]

Anaschismahad a wide, wedge-shaped, powerful tail to assist it with swimming, hunting and likely defense.[3]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.[3]The legs ofAnaschismadisplay a sprawling stance and short legs with 4-digits on the front and 5 on the back limbs.[3]Anaschismalikely spent a lot of time motionless, waiting for prey, which these short legs were likely an adaptation to.[5]

Paleobiology

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Life restoration ofAnaschismachasing a fish

The hunting style ofAnaschismainvolved lying at the bottom of a shallow swamp, waiting for a fish,crustacean,smaller amphibian, or even a young phytosaur to wander by.[3]When it spotted prey, it used its huge jaws to engulf and consume them.[3]A few particular adaptations suggestKoskinonodonhad this aquatic lifestyle. First, they hadlateral linesformed 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.[18]

Paleoecology

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They lived mostly in the late Triassic; by the time theJurassicbegan, most temnospondyls,Anaschismaincluded, were gone.[21]It is likely that they went extinct during theTriassic-Jurassic extinction event,along with the majority of other large amphibians, the class ofConodontsand 34% of all marine genera. It is unknown what caused thismass extinction;hypotheses include huge volcanic eruptions (theCentral Atlantic magmatic provinceis a prime example), climate change,oceanic acidification,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.[22]It lived alongside many other smaller amphibians, and its fossils are also commonly found withphytosaurfossils.[18][23]It was named in 1931 by Case. The best conditions forfossilizationoccur in river valleys or floodplains where deposition is occurring, and this animal likely lived in similar shallow, swampy habitats. As it follows,Anaschismais famous for having extremely well preserved fossils, and they are often found in groups.[18]

See also

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References

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  1. ^abcdeBrusatte, Stephen L (2015). "A new species ofMetoposaurusfrom the Late Triassic of Portugal and comments on the systematics and biogeography of metoposaurid temnospondyls ".Journal of Vertebrate Paleontology.35(3): e912988.doi:10.1080/02724634.2014.912988.S2CID84007744.
  2. ^Hunt, Adrian P.; Lucas, Spencer G. (1993)."Taxonomy and stratigraphic distribution of Late Triassic metoposaurid amphibians from Petrified Forest National Park, Arizona".Journal of the Arizona-Nevada Academy of Science.27(1): 89–96.JSTOR40023709.
  3. ^abcdefgh"Palaeos Vertebrates Temnospondyli: Trematosauria: Metaposaurs".palaeos.
  4. ^abHunt, A.P. (1989)."Comments on the taxonomy of North American metoposaurids and a preliminary phylogenetic analysis of the family Metoposauridae"(PDF).In Lucas, SG; Hunt, AP (eds.).Dawn of the age of dinosaurs in the American Southwest.Albuquerque: New Mexico Museum of Natural History. pp. 292–300.
  5. ^abBranson, E. B. (1905)."Structure and Relationships of American Labyrinthodontidæ".The Journal of Geology.13(7): 568–610.Bibcode:1905JG.....13..568B.doi:10.1086/621258.hdl:2027/njp.32101055916710.
  6. ^abMoodie, Roy L. (1908)."The lateral line system in extinct amphibia".Journal of Morphology.19(2): 511–540.doi:10.1002/jmor.1050190206.S2CID83822416.
  7. ^abBranson, E. B. & Mehl, M. G. 1929. Triassic amphibians from the Rocky Mountain region. The University of Missouri Studies, 4, 154–253.
  8. ^Colbert, Edwin; Imbrie, John (1956)."Triassic metoposaurid amphibians".Bulletin of the American Museum of Natural History.110:399–452.hdl:2246/431.
  9. ^Chowdhury, T. Roy (1965). "A new metoposaurid amphibian from the upper Triassic Maleri formation of Central India".Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences.250(761): 1–52.Bibcode:1965RSPTB.250....1C.doi:10.1098/rstb.1965.0019.S2CID86592771.
  10. ^Sulej, T. (2002)."Species discrimination of the Late Triassic temnospondyl amphibianMetoposaurus diagnosticus"(PDF).Acta Palaeontologica Polonica.47(3): 535–546.
  11. ^Hunt, A.P. 1993. Revision of the Metoposauridae (Amphibia: Temnospondyli) and description of a new genus from Western North America. In: M. Morales (eds.), Aspects of Mesozoic Geology and Paleontology of the Colorado Plateau. Museum of Northern Arizona Bulletin 59: 67–97.
  12. ^Mueller, B.D. (2007). "KoskinonodonBranson and Mehl, 1929, a replacement name for the preoccupied temnospondylBuettneriaCase, 1922 ".Journal of Vertebrate Paleontology.27(1): 225.doi:10.1671/0272-4634(2007)27[225:KBAMAR]2.0.CO;2.S2CID85763026.
  13. ^Lucas, SG; Rinehart, LF; Spielmann, JA (2008)."Comments on the proposed conservation ofBuettneriaCase, 1922 (Amphibia) 2 (Case 3420) ".Bulletin of Zoological Nomenclature.65(3): 218–219.
  14. ^"OPINION 2255 (Case 3420) Buettneria Case, 1922 (Amphibia): Generic name not conserved | International Commission on Zoological Nomenclature".Archived fromthe originalon 2018-10-04.Retrieved2019-06-09.
  15. ^abRomer, A.S. (1947)."Review of the Labyrinthodontia".Bulletin of the Museum of Comparative Zoology.99(1): 1–368.
  16. ^Gee, Bryan M.; Parker, William G.; Marsh, Adam D. (2020)."Redescription ofAnaschisma(Temnospondyli: Metoposauridae) from the Late Triassic of Wyoming and the phylogeny of the Metoposauridae ".Journal of Systematic Palaeontology.18(3): 233–258.doi:10.1080/14772019.2019.1602855.S2CID190896742.
  17. ^Gee, Bryan M.; Kufner, Aaron M. (2022)."Revision of the Late Triassic metoposaurid"Metoposaurus" bakeri(Amphibia: Temnospondyli) from Texas, USA and a phylogenetic analysis of the Metoposauridae ".PeerJ.10:e14065.doi:10.7717/peerj.14065.
  18. ^abcdefgPeredo, Carlos."Koskinonodon perfectus".Encyclopedia of Life.
  19. ^abRinehart, Larry F; Lucas, Spencer G (2013). "The functional morphology of dermal bone ornamentation in temnospondyl amphibians". In Tanner, Lawrence H.; Justin A. Spielmann; Spencer G. Lucas (eds.).The Triassic System: New Developments in Stratigraphy and Paleontology.Bulletin of the New Mexico Museum of Natural History and Science. Vol. 61. pp. 524–532.
  20. ^abcTanner, Lawrence H.; Justin A. Spielmann; Spencer G. Lucas, eds. (2013).The Triassic System: New Developments in Stratigraphy and Paleontology.Bulletin of the New Mexico Museum of Natural History and Science. Vol. 61.
  21. ^McHugh, Julia Beth (2012).Temnospondyl ontogeny and phylogeny, a window into terrestrial ecosystems during the Permian-Triassic mass extinction(PhD thesis). Graduate College of the University of Iowa.
  22. ^"End-Triassic extinction".Encyclopedia Britannica.
  23. ^Parker, W.G.; Martz, J.W. (2010). "The Late Triassic (Norian) Adamanian–Revueltian tetrapod faunal transition in the Chinle Formation of Petrified Forest National Park, Arizona".Earth and Environmental Science Transactions of the Royal Society of Edinburgh.101(3–4): 231–260.doi:10.1017/S1755691011020020.S2CID140536630.
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