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Patranomodon (from Greek πατρ- patr- “father”, thus “father of anomodonts”) is an extinct genus belonging to the group of anomodontia.[1] Rubidge and Hopson named this anomodont in 1990 after discovering its skull.[2] Anomodontia is a group of terrestrial organisms that roamed the land on four limbs. Other genera belonging to the same group of anomodontia include Suminia, which is the most complete basal anomodont, although Patranomodon is the most primitive.[3][4] Patranomodon is the sister taxon to Dicynodon, which belongs to the group of Dicynodontia.[2] Dicynodontia are known to be carnivorous, unlike Patranomodon, which fed on plant material. It is also a sister taxon to Galechirus, Galeops, and Galepus.[5] Patranomodon is known to have ranged in the Karoo of Southern Africa, though it has been proposed that anomodonts ranged from present-day Europe to southern Africa as well as China and India.[2] This is because the continents known today as Europe, Asia, and Africa were connected in the single large land mass of Pangaea, which was walkable for many terrestrial organisms. Patranomodon roamed this planet during the middle and late Permian era, about 268 to 265 million years ago.[2] These land-dwelling creatures belong to a group of Synapsida called Therapsida.[5]

Description and paleobiology

Known from only one nearly complete skull, Patranomodon nyaphulii is the most primitive genus of anomodontia based on its morphological features compared to its sister taxon, Dicynodontia.[6] Patranomodon have a short exposure of their palatine and premaxilla, which creates a shorter face compared to other anomodontons.[6] This gives Patranomodon a shorter facial structure, shorter in length as well as small in size. They also have a reduced tabular, a slit-like interpterygoid vacuity, three sacral vertebrae, and a screw-shape jaw.[6] Patranomodon has many features indicating its herbivorous behavior: the division of the external adductor muscles in the jaw into two separate components, the medial and lateral side, as well as using a propalinal jaw movement while feeding on plant material.[7] This feature is important for the diet of the anomodont because being able to grind down tough plant matter is necessary for survival. The teeth formation of Patranomodon allows crushing and grinding to occur as the jaws connect and move. Other aspects include widening of the palatal areas for breaking down plant matter in feeding, widening of the external adductors, the higher raised jaw hinge, reduction in the number and size of teeth, and acquiring a horn that extends to the jaw.[7] A key feature of the anomodontia is its raised zygomatic arch. This feature allows for jaw muscles to connect and form as powerful jaws began to develop further. The teeth of Patranomodon fit perfectly together when the upper and lower jaw came together and the mouth is closed. They also possessed a complete set of teeth. The transition from its carnivorous ancestor to the herbivorous Patranomodon occurred rapidly compared to the longevity of the species of anomodonts.[7] Sister taxa to Patranomodon and the anomodonts are believed to be carnivorous. The relative size of these terrestrial organisms is about the size of your average mongoose,[8] which, at about 38 centimetres (15 in) long, is relatively small compared to the average human.[9] This estimate is based on the small skull of Patranomodon that was found.

Geology and paleoenvironment

Cast of Anomodont

The environment during the late Permian era, when Patranomodon roamed the earth, was typically aquatic-based, with plentiful precipitation concentrated in the mountains and plateaux of terrestrial habitats.[10] Rainfall was very frequent during this era. There were times of warm humid greenhouse-like climate with soil erosion and stagnation in the wetlands, which may have led to the mass extinctions in the middle to late Permian era.[11] These environmental conditions created harsh living conditions for terrestrial creatures, some of which died off. The mass extinction affected most of the terrestrial and aquatic species; however, the terrestrial species evolved greatly after the mass extinction. Patranomodon was one of the early terrestrial species that evolved from the fully aquatic environments. Flash floods were the main reason why there were sediment deposits, along with overflowing rivers from melting ice caps.[12] Fossilization requires specific factors that allow preservation of hard tissues such as bone. In southern Africa, where Patranomodon lived during the late Permian era, there was probably migration due to the progressive climatic drying and the shrinking of the basin. This migration occurred in a northward direction to warmer environments.[13] Evidence for migration is also found in the distribution of fossils of certain anomodonts northward from the southern cape of Africa. The Beaufort Group, where Patranomodon was found in the fossil record, dominated most of the basin with fluvial sedimentation.[13] During the Permian era, Europe, Africa, Asia, America, and Antarctica were joined in one large supercontinent called Pangea. Scattered fossils of Anomodonts provide evidence for this huge land mass as well as for migration from one end of the land mass to the other. Fluvial sedimentation refers to the sediment carried by streams and rivers that deposit into landforms, thus preserving the fossil skull of Patranomodon. These streams and rivers were most likely formed by ice masses such as glaciers.

Discovery and history

Patranomodon holotype

The skull fossil of Patranomodon was found in the Eodicynodon Assemblage Zone of South Africa, belonging to the lowest biozone of the Beaufort Group.[6] The Beaufort Group time period extends from the middle of the Permian to the early Triassic era.[14] It is one of the three main subdivisions of the Karoo Supergroup in what today is southern Africa. Rubidge and Hopson were the first to discover the skull of Patranomodon. These paleobiologists also named Patranomodon and were the first to publish literature on it starting in 1990. The most abundant remains of Patranomodon were found on the Eastern Cape of South Africa; however, fossil parts were also found in Europe, China, as well as India, which indicated migration occurring among these terrestrial creatures.[15] The paleontologist Nyaphuli collected the fossil of this creature in South Africa and gave it the species name of "Patranomodon nyaphuli".[5] The length of the skull that was discovered was only 5 centimeters in length, predicting its body to be a total of only 30 centimetres (12 in).[2] Patranomodon is thus quite small when compared to an average adult human. The discovery of the Patranomodon nyaphuli was an important group because it led to the evolution of larger dominant herbivores by the end of the Permian and into the early Triassic era.[6] Patranomodon was one of the earliest terrestrial herbivores as well as the most primitive anomodont. Using the information that was gathered from the skull of Patranomodon as well as fossils from its sister taxa, the group of paleontologists' discoveries led to major advances in understanding the phylogenetic relationships among synapsids, even though much major taxonomic information is still missing.[16]

See also

References

  1. ^ “Patranomodon”. Online Etymology Dictionary. Retrieved Feb. 13, 2017.
  2. ^ a b c d e Rubidge, B. S., & Hopson, J. A. (1990). A new anomodont therapsid from South Africa and its bearing on the ancestry of Dicynodontia. South African Journal of Science, 86(1), 43-45.
  3. ^ Sidor, C. (2017, February 10). Lecture 10 - Synapsids 2. Lecture presented in University of Washington, Seattle.
  4. ^ Froebisch, J., & Reisz, R. R. (2011). The postcranial anatomy of Suminia getmanovi (Synapsida: Anomodontia), the earliest known arboreal tetrapod. Zoological Journal of the Linnean Society, 162(3), 661-698.
  5. ^ a b c "Fossil Works". Retrieved February 24, 2017. 
  6. ^ a b c d e RUBIDGE, B. S. And HOPSON, J. A. (1996), A primitive anomodont therapsid from the base of the Beaufort Group (Upper Permian) of South Africa. Zoological Journal of the Linnean Society, 117: 115–139. Doi:10.1111/j.1096-3642.1996.tb02152.x
  7. ^ a b c King, G. M. (1994). The early anomodont Venjukovia and the evolution of the anomodont skull. Journal of Zoology, 232(4), 651-673.
  8. ^ Mccarthy, T. & Rubidge, B. 2005. The story of Earth & Life. A southern African perspective on a 4.6-billion-year journey. Struik Publishers, Cape Town. 333pp.
  9. ^ "Mongoose". Wikipedia. 2017-02-24. 
  10. ^ Kutzbach, J. E., & Ziegler, A. M. (1993). Simulation of Late Permian climate and biomes with an atmosphere-ocean model: Comparisons with observations. Philosophical Transactions of the Royal Society of London B: Biological Sciences, 341(1297), 327-340.
  11. ^ Retallack, G. J., Metzger, C. A., Greaver, T., Jahren, A. H., Smith, R. M., & Sheldon, N. D. (2006). Middle-Late Permian mass extinction on land. Geological Society of America Bulletin, 118(11-12), 1398-1411.
  12. ^ Rubidge, B. S., Hancox, P. J., & Catuneanu, O. (2000). Sequence analysis of the Ecca—Beaufort contact in the southern Karoo of South Africa. South African Journal of Geology, 103(1), 81-96.
  13. ^ a b Smith, R. M. H. (1990). A review of stratigraphy and sedimentary environments of the Karoo Basin of South Africa. Journal of African Earth Sciences (and the Middle East), 10(1-2), 117-137.
  14. ^ "Beaufort Group". Wikipedia. 2016-03-08. 
  15. ^ Kurkin, A. A. (2011). Permian anomodonts: paleobiogeography and distribution of the group. Paleontological Journal, 45(4), 432.
  16. ^ Kammerer, C. F., & Angielczyk, K. D. (2009). A proposed higher taxonomy of anomodont therapsids. Zootaxa, 2018, 1-24.

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