Pelanomodon (lat.) - a genus of extinct terapsids from the group of dicynodonts , which lived during the late Permian period . Most of the fossils were found in the Karoo basin in South Africa , in the Daptocephalus Assembly Zone ( Daptocephalus Assemblage Zone) [1] . The absence of fossils in later sediments indicates that the genus did not survive the Permian-Triassic extinction .
| † Pelanomodon | |||||||||||||||||||||||||||||||||||||||||
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Pelanomodon Broom , 1938 | |||||||||||||||||||||||||||||||||||||||||
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| Geochronology 259—252 Ma
◄ Nowadays◄ Cretaceous-Paleogene extinction◄ Triassic extinction◄ Mass Permian Extinction◄ Devonian extinction◄ Ordovician-Silurian extinction◄ Cambrian explosion | |||||||||||||||||||||||||||||||||||||||||
The generic name consists of three parts: Pel - “ dirt ”, anomo - “without” and don - “ tooth ”. Thus, the full name can be translated as “dirty anomodont ” [2] .
During the existence of the genus, the Karu basin was a vast floodplain area [3] .
Pelanomodon is in the family Geikiidae along with Aulacephalodon and Geikia . Aulacephalodon most likely lived next to the Pelanomodon in the Karoo Basin, while Geikia fossils were discovered in Scotland and Tanzania . A distinctive feature of Pelanomodon that separates it from Aulacocephalodon is the absence of tusks [1] . A number of features of the anatomy of the skulls of different individuals caused the separation of two separate species of Pelanomodon : P. moschops ( typical ) and P. rubidgei . However, a recent analysis indicates their likely synonymy [1] .
Content
Description
Skull
Pelanomodon is known mainly for full and partial skulls . It is for this reason that skull morphology is used to distinguish Pelanomodon from other genera in the Geikiidae family. The absence of fangs is an important feature that is used to separate Pelanomodon from Aulacephalodon (in addition to ridges over the nostrils and orbits and bends on the zygomatic bone ) [1] . Pelanomodon differs from Geikia in more elongated temporal orifice and muzzle , less developed pharyngeal crest and pineal orifice [1] .
In addition to these differences, the skull of Pelanomodon has many other characteristic features. The most obvious feature is that the skull is larger in width than in height, because of which the head has a triangular shape when viewed from above, since the corners of the temporal windows are strongly protruding to the sides [1] . Relative to other dicynodonts, the external nostrils are located rather high and somewhat elongated [1] . The orbits are also located higher than that of other representatives of the infraorder [1] . Like other anomodonts, Pelanomodon has cheek teeth, but there are no molars [2] . In addition, as with other therapsides, premaxilla expands posteriorly to form a secondary palate [1] .
Detection and Views
The first Pelanomodon specimen was discovered by Robert Brum in 1913 in the Karu basin. It consisted of an almost complete skull without a lower jaw [4] . Initially, the fossil was described as a species of the Dicynodon genus, D. moschops , however, in a 1969 analysis by Keyser AW, Pelanomodon moschops was identified as a separate genus and species [5] . The second species, Pelanomodon rubidgei , was described by Broome in 1938 on the basis of a full skull found in the same region by Samuel Rubidge [6] .
Between 1913 and 1950, Broome described another 5 species based on differences in the anatomy of a number of full and fragmented skulls [4] [6] [7] [8] , but later studies have shown that differences in morphology are insufficient to isolate individual taxa [5 ] [9] .
A new analysis conducted in 2015 showed that the morphological features that separate Pelanomodon moschops and Pelanomodon rubidgei are probably the result of intraspecific sexual dimorphism [1] . In the same analysis, the assumption is made that another dicinodont from the Karu basin, described by Broome in 1913 [4] - Propelanomodon - is actually a juvenile form of Pelanomodon [1] . The authors of the analysis place all reclassified species in the type species Pelanomodon moschops [1] .
Paleobiology
Sexual Dimorphism
In the past, differences in the morphology of various skulls were interpreted as autapomorphies for individual species [5] , but in the 2015 review they were revised as examples of sexual dimorphism within a single taxon [1] . Previously, two species were distinguished: P. moschops (the skull has a length of about 18 cm, ridges above the orbits and nostrils are weakly expressed) and P. rubidgei (skull length is about 18 cm, the ridges above the orbits and nostrils are more powerful and larger than P. moschops ) [1] . According to a number of paleontologists, these differences are a consequence of sexual dimorphism [1] .
Ontogenesis
Propelanomodon tylorhinus is a species of dicynodonts and the Karu basin, which is probably a young Pelanomodon [1] . He had a shorter (about 14 cm) skull with slightly pronounced crests and slightly different temporal windows (in Propelanomodon they form a straight line, while in Pelanomodon they are slightly inclined to the side, giving the head a triangular shape). Propelanomodon's nostrils are relatively small, and the orbits, on the contrary, are slightly enlarged [1] . Proponents of synonymy indicate that these differences are a consequence of the small age of the individual at the time of death [1] .
Nutrition
Like other dicynodonts, Pelanomodon was a herbivorous animal [2] . Keyser indicates the structural features of the skull, based on which chewing movements could be carried out only by the front end of the jaw [5] . This, as well as several other features, such as the high placement of eye sockets and nostrils, may indicate nutrition of aquatic and near-water vegetation from small reservoirs [5] .
Paleoecology
All currently known fossils were found only in the Karu basin [1] . Pelanomodon , as well as other dicynodonts from this region, are part of the Beaufort group (the third layer of the Karu basin sediments, consisting of Late Permian and Middle Triassic deposits). Analysis of the rocks indicates the presence of several large rivers in the region [3] . The climate was semi-arid and the precipitation was seasonal [10] . This type of climate, combined with large reservoirs periodically overlooking the coast, favored the abundant growth of various coastal vegetation, which in turn led to the appearance of a large number of herbivorous animals [10] . In fact, dicynodonts turned out to be the most common group in the area [11] .
Notes
- ↑ 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 Kammerer CF, KD Angielczyk and Jörg Fröbisch. Redescription of the geikiid Pelanomodon (Therapsida, Dicynodontia), with a reconsideration of 'Propelanomodon' (Eng.) // Journal of Vertebrate Paleontology. - 2015. - DOI : 10.1080 / 02724634.2015.1030408 .
- ↑ 1 2 3 Toerien MJ Convergent trends in anomodontia (English) // Evolution. - 1954. - Vol. 9 . - P. 152-156 . - DOI : 10.1111 / j.1558-5646.1955.tb01528.x. .
- ↑ 1 2 Smith Roger; Botha Jennifer. The recovery of terrestrial vertebrate diversity in South African Karoo Basin after the end-Permian extinction // Comptes Rendus Palevol. - P. 623-636 .
- ↑ 1 2 3 Broom Robert. On some new genera and species of dicynodont reptiles, with notes on a few others // Bulletin of the American Museum of Natural History. - Vol. 32 . - P. 441-457 .
- ↑ 1 2 3 4 5 Keyser AW Re-evaluation of the systematics and morphology of certain anomodont Therapsida (Eng.) // University of the Witwatersrand. - Johannesburg, 1969.
- ↑ 1 2 Broom Robert. On two new anomodont genera (Eng.) // Annals of the Transvaal Museum. - 1938. - Vol. 19 . - P. 247-250 .
- ↑ Broom Robert. On some new genera and species of fossil reptiles from the Karroo beds of Graaff-Reinet (Eng.) // Annals of the Transvaal Museum. - 1940. - Vol. 20 . - P. 157-192 .
- ↑ Broom Robert. Three new species of anomodonts from the Rubidge Collection (Eng.) // Annals of the Transvaal Museum. - 1950. - Vol. 21 . - P. 246-250 .
- ↑ CF Kammerer, KD Angielczyk, and J. Frobisch. A comprehensive taxonomic revision of Dicynodon (Therapsida, Anomodontia) and its implications for dicynodont phylogeny, biogeography, and biostratigraphy (Eng.) // Journal of Vertebrate Paleontology. - 2011 .-- Vol. 31 . - P. 1-158 .
- ↑ 1 2 Smith RMH; Botha, WJ A review of the stratigraphy and sedimentary environments of the Karoo-aged basins of Southern Africa (Eng.) // Journal of African Earth Sciences (and the Middle East). - 1993. - 1 January ( vol. 16 , iss. 1-2 ). - P. 143-169 . - ISSN 0899-5362 . - DOI : 10.1016 / 0899-5362 (93) 90164-L .
- ↑ Hancox, PJ; Rubidge, BS Breakthroughs in the biodiversity, biogeography, biostratigraphy, and basin analysis of the Beaufort group (Eng.) // Journal of African Earth Sciences. - 2001 .-- 1 January ( vol. 33 , iss. 3-4 ). - P. 563-577 . - ISSN 1464-343X . - DOI : 10.1016 / S0899-5362 (01) 00081-1 .