Post by Infinity Blade on Aug 12, 2020 20:58:43 GMT 5
Stegotetrabelodon spp.
Life reconstruction of S. orbus. © @ Mauricion Antón->
Temporal range: Neogene; Late Miocene to Early Pliocene[1]
Scientific classification:
Life
Domain: Eukaryota
(unranked): Unikonta
(unranked): Opisthokonta
(unranked): Holozoa
(unranked): Filozoa
Kingdom: Animalia
Subkingdom: Eumetazoa
(unranked): Bilateria
Superphylum: Deuterostomia
Phylum: Chordata
Infraphylum: Gnathostomata
Clade: Eugnathostomata
Clade: Teleostomi
Clade: Tetrapoda
Clade: Reptiliomorpha
Clade: Amniota
Clade: Synapsida
Clade: Eupelycosauria
Clade: Sphenacodontia
Clade: Sphenacodontoidea
Order: Therapsida
Clade: Cynodontia
Clade: Prozostrodontia
Clade: Mammaliaformes
Class: Mammalia
Legion: Cladotheria
Sublegion: Zatheria
Infralegion: Tribosphenida
Subclass: Theria
Clade: Eutheria
Infraclass: Placentalia
Subcohort: Exafroplacentalia
Magnorder: Atlantogenata
Superorder: Afrotheria
Clade: Paenungulata
Order: Proboscidea
Suborder: Elephantiformes
Clade: Elephantimorpha
Clade: Elephantida
Superfamily: Elephantoidea
Family: Elephantidae
Genus: †Stegotetrabelodon
Species: †S. syrticus, †S. orbus
Stegotetrabelodon is an extinct early genus of the Elephantidae. It lived in northern and eastern Africa[1], as well as southern Italy[2] during the Late Miocene to Early Pliocene.[1]
Taxonomy:
Two species are recognized: S. syrticus and S. orbus. However, incorporation of S. orbus into S. syrticus has been proposed and merits considerations, as morphological considerations are only slight and tusk differences could simply be ontogenetic.[1]
Description, evolution, and paleobiology:
Stegotetrabelodon was a member of the Elephantidae, and therefore a true elephant, but its most distinguishing feature is its possession of four tusks instead of two. These tusks were very long (reaching >2,000 mm for both upper and lower tusks in S. syrticus[1]), straight, and are described as being relatively slender and very thin.[1][3] The lower tusks were closely appressed, and set in an elongate and downturned mandibular symphysis[3] (in S. orbus, the alveolar bone was surprisingly thin for support of such elongated teeth[1]). While the upper tusks were circular in cross section, the lower ones were ovoid, being higher than wide[1] (for example, S. orbus tusks are 1,000 mm long, but only 70 mm tall and 58 mm wide[1]).
Fig. 17C shows a reconstruction of the skull of S. syrticus. Note the elongated mandibular symphysis and slender tusks. From [4].
Although S. orbus has no recovered cranium[1], stegotetrabelodonts were in the middle of a trend for elephants to develop shorter skulls, mandibles, and lower tusks. Starting with Stegotetrabelodon and co., elephants had begun to specialize for fore-and-aft power-shearing with their jaws, allowing them to chew more efficiently. The molars of Stegotetrabelodon also differed from those of gomphotheres. While the latter had molars with three blunt cusps that had thick enamel and a thin cap of cementum, stegotetrabelodonts turned the cusps into low, parallel ridges, containing deep V-shaped valleys and little cementum.[1][5] Although the molars were still low crowned, the stegotetrabelodonts were still grazers. This dietary preference seems to have evolved in response to increased seasonality and aridity during the late Miocene, allowing for the spread of C4 plant ecosystems.[1] S. syrticus had less compressed molar crowns than did S. orbus, which had thinner enamel and deeper valleys.[3]
Evolution of proboscidean molars, shown in cross section. A shows gomphothere molars, B shows stegotetrabelodont molars, and C shows the molars of Primelephas. Screen capture from [5].
Evolution of skull shape in proboscideans. Screen capture from [5].
Stegotetrabelodon syrticus might have had a shoulder height of ~400 cm and weighed ~11-12 tonnes. This is based upon a very long femur ~1,470 mm in length, as well as two very long tibiae measuring 840 mm and 950 mm, respectively. Stegotetrabelodon is noted to have had considerably more slender humeri than contemporary Sahabi (Lybia) proboscideans Amebelodon and Anancus[6] (both of these genera are in completely different proboscidean families from Stegotetrabelodon).
The true elephants evolved in Africa from a gomphotheriid ancestor.[7] If crown elephantid (Loxodonta, Elephas, Mammuthus) evolved from the stegotetrabelodont subfamily, this would require a reversal to the dental morphology of gomphotheres, which have features not present in stegotetrabelodonts (gomphotheres had free anterior and posterior accessory conules associated with their lophids). Despite this, Stegotetrabelodon and its kin seem to be sufficiently adequate models of the ancestral elephant.[1]
References:
[1] Werdelin, L., & Sanders, W. J. (2010). Cenozoic mammals of Africa. Univ of California Press.
[2] Ferretti, M. P., Rook, L., Carone, G., & Marra, A. C. (2017). New findings of Stegotetrabelodon syrticus from the Late Miocene of Cessaniti, southern Italy. Boll. Soc. Paleontol. It, 56, 89-92.
[3] Kingdon, J. (1988). East African mammals: an atlas of evolution in Africa, volume 3, Part B: Large Mammals (Vol. 3). University of Chicago Press.
[4] Sanders, W. J. G. E., Gheerbrant, E., Harris, J., Saegusa, H., & Delmer, C. (2010). Proboscidea. Cenozoic Mammals of Africa, eds Werdelin L, Sanders WJ.
[5] Prothero, D. R., & Schoch, R. M. (2002). Horns, tusks, and flippers: the evolution of hoofed mammals. JHU Press.
[6] Larramendi, A. (2015). Shoulder height, body mass, and shape of proboscideans. Acta Palaeontologica Polonica, 61(3), 537-574.
[7] Maglio, V. J. (1973). Origin and evolution of the Elephantidae. Transactions of the American Philosophical Society, 63(3), 1-149.
Life reconstruction of S. orbus. © @ Mauricion Antón->
Temporal range: Neogene; Late Miocene to Early Pliocene[1]
Scientific classification:
Life
Domain: Eukaryota
(unranked): Unikonta
(unranked): Opisthokonta
(unranked): Holozoa
(unranked): Filozoa
Kingdom: Animalia
Subkingdom: Eumetazoa
(unranked): Bilateria
Superphylum: Deuterostomia
Phylum: Chordata
Infraphylum: Gnathostomata
Clade: Eugnathostomata
Clade: Teleostomi
Clade: Tetrapoda
Clade: Reptiliomorpha
Clade: Amniota
Clade: Synapsida
Clade: Eupelycosauria
Clade: Sphenacodontia
Clade: Sphenacodontoidea
Order: Therapsida
Clade: Cynodontia
Clade: Prozostrodontia
Clade: Mammaliaformes
Class: Mammalia
Legion: Cladotheria
Sublegion: Zatheria
Infralegion: Tribosphenida
Subclass: Theria
Clade: Eutheria
Infraclass: Placentalia
Subcohort: Exafroplacentalia
Magnorder: Atlantogenata
Superorder: Afrotheria
Clade: Paenungulata
Order: Proboscidea
Suborder: Elephantiformes
Clade: Elephantimorpha
Clade: Elephantida
Superfamily: Elephantoidea
Family: Elephantidae
Genus: †Stegotetrabelodon
Species: †S. syrticus, †S. orbus
Stegotetrabelodon is an extinct early genus of the Elephantidae. It lived in northern and eastern Africa[1], as well as southern Italy[2] during the Late Miocene to Early Pliocene.[1]
Taxonomy:
Two species are recognized: S. syrticus and S. orbus. However, incorporation of S. orbus into S. syrticus has been proposed and merits considerations, as morphological considerations are only slight and tusk differences could simply be ontogenetic.[1]
Description, evolution, and paleobiology:
Stegotetrabelodon was a member of the Elephantidae, and therefore a true elephant, but its most distinguishing feature is its possession of four tusks instead of two. These tusks were very long (reaching >2,000 mm for both upper and lower tusks in S. syrticus[1]), straight, and are described as being relatively slender and very thin.[1][3] The lower tusks were closely appressed, and set in an elongate and downturned mandibular symphysis[3] (in S. orbus, the alveolar bone was surprisingly thin for support of such elongated teeth[1]). While the upper tusks were circular in cross section, the lower ones were ovoid, being higher than wide[1] (for example, S. orbus tusks are 1,000 mm long, but only 70 mm tall and 58 mm wide[1]).
Fig. 17C shows a reconstruction of the skull of S. syrticus. Note the elongated mandibular symphysis and slender tusks. From [4].
Although S. orbus has no recovered cranium[1], stegotetrabelodonts were in the middle of a trend for elephants to develop shorter skulls, mandibles, and lower tusks. Starting with Stegotetrabelodon and co., elephants had begun to specialize for fore-and-aft power-shearing with their jaws, allowing them to chew more efficiently. The molars of Stegotetrabelodon also differed from those of gomphotheres. While the latter had molars with three blunt cusps that had thick enamel and a thin cap of cementum, stegotetrabelodonts turned the cusps into low, parallel ridges, containing deep V-shaped valleys and little cementum.[1][5] Although the molars were still low crowned, the stegotetrabelodonts were still grazers. This dietary preference seems to have evolved in response to increased seasonality and aridity during the late Miocene, allowing for the spread of C4 plant ecosystems.[1] S. syrticus had less compressed molar crowns than did S. orbus, which had thinner enamel and deeper valleys.[3]
Evolution of proboscidean molars, shown in cross section. A shows gomphothere molars, B shows stegotetrabelodont molars, and C shows the molars of Primelephas. Screen capture from [5].
Evolution of skull shape in proboscideans. Screen capture from [5].
Stegotetrabelodon syrticus might have had a shoulder height of ~400 cm and weighed ~11-12 tonnes. This is based upon a very long femur ~1,470 mm in length, as well as two very long tibiae measuring 840 mm and 950 mm, respectively. Stegotetrabelodon is noted to have had considerably more slender humeri than contemporary Sahabi (Lybia) proboscideans Amebelodon and Anancus[6] (both of these genera are in completely different proboscidean families from Stegotetrabelodon).
The true elephants evolved in Africa from a gomphotheriid ancestor.[7] If crown elephantid (Loxodonta, Elephas, Mammuthus) evolved from the stegotetrabelodont subfamily, this would require a reversal to the dental morphology of gomphotheres, which have features not present in stegotetrabelodonts (gomphotheres had free anterior and posterior accessory conules associated with their lophids). Despite this, Stegotetrabelodon and its kin seem to be sufficiently adequate models of the ancestral elephant.[1]
References:
[1] Werdelin, L., & Sanders, W. J. (2010). Cenozoic mammals of Africa. Univ of California Press.
[2] Ferretti, M. P., Rook, L., Carone, G., & Marra, A. C. (2017). New findings of Stegotetrabelodon syrticus from the Late Miocene of Cessaniti, southern Italy. Boll. Soc. Paleontol. It, 56, 89-92.
[3] Kingdon, J. (1988). East African mammals: an atlas of evolution in Africa, volume 3, Part B: Large Mammals (Vol. 3). University of Chicago Press.
[4] Sanders, W. J. G. E., Gheerbrant, E., Harris, J., Saegusa, H., & Delmer, C. (2010). Proboscidea. Cenozoic Mammals of Africa, eds Werdelin L, Sanders WJ.
[5] Prothero, D. R., & Schoch, R. M. (2002). Horns, tusks, and flippers: the evolution of hoofed mammals. JHU Press.
[6] Larramendi, A. (2015). Shoulder height, body mass, and shape of proboscideans. Acta Palaeontologica Polonica, 61(3), 537-574.
[7] Maglio, V. J. (1973). Origin and evolution of the Elephantidae. Transactions of the American Philosophical Society, 63(3), 1-149.
