Stegomastodon

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Stegomastodon
Temporal range: Pliocene-Early Pleistocene
~4–1.2  Ma
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Stegomastodon mirificus - Smithsonian.JPG
S. mirificus fossil at the Smithsonian Natural History Museum
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Proboscidea
Family: Gomphotheriidae
Genus: Stegomastodon
Pohlig, 1912
Species
  • S. aftoniae
  • S. mirificus
  • S. nebrascensis
  • S. primitivus
Synonyms
  • Morrillia

Stegomastodon ('roof breast tooth') is an extinct genus of gomphotheres. It ranged throughout North America from the Pliocene (early Blancan ~4 Ma), to the Early Pleistocene (early Irvingtonian, ~1.2 Ma). The former South American species have been synonymized with Notiomastodon platensis .

Contents

Description

Skeleton of Stegomastodon compared with a human Stegomastodon skeletal.png
Skeleton of Stegomastodon compared with a human

Stegomastodon mirificus is known from NMNH 10707, a roughly 30-year-old male, of which most of the skeleton has been found. Alive, it stood about 2.6 m (8.5 ft) tall, with a weight around 4.7 tonnes (4.6 long tons; 5.2 short tons). [1] Unlike more primitive gomphotheres like Gomphotherium , it lacked lower tusks and had a shortened lower jaw. The upper tusks curved upward and were about 3.5 m (11.5 ft) long, and lacked enamel bands. The tall head and robust lower jaw suggest a strong vertical bite. Stegomastodon's third molars molars had at least 5 lophs (ridge-like structures), greater than previous gomphotheres. The strong bite and increased tooth complexity are suggested to be adaptations to a grazing diet. [2]

Origin and evolution

Stegomastodon is suggested to have ultimately originated from New World populations of Gomphotherium, possibly via the intermediate genus Rhynchotherium . [3] The earliest species of the genus appeared during the Pliocene (Blancan) around 3-4 million years ago. During the early Irvingtonian, around 1.2 million years ago, Stegomastodon became extinct, which is suggested to be due to competition with the recently arrived mammoths, which were more efficient grazers. [3] Originally, some specimens from Jalisco, Mexico were estimated to date to 28,000 years Before Present, [4] but this age was rejected in 2011 by Spencer G. Lucas et. al, who stated that the date was far too young to be viable and that it actually dates to the Blancan. [2]

Restoration of a S. mirificus herd Stegomastodon.jpg
Restoration of a S. mirificus herd

Taxonomy

Restoration of S. mirificus Stegomastodon arizonae.jpg
Restoration of S. mirificus

The number of species within the genus has varied between S. mirificus being the only valid species, to Osborn's seven species of “ascending mutations” (S. primitivus, S. successor, S. mirificus, S. chapmani, S. texanus, S. arizonae and S. aftoniae) Lucas et al., 2013 accepted 3 overlapping chronospecies S. primitivus, S. mirificus S. aftoniae. [5] The South American Stegomastodon fossils have been reassigned to Notiomastodon by the majority of recent authors. [6] [7] [3] Stegomastodon and Notiomastodon differ in numerous characters, including of the skull and limbs. [3] Revised taxonomy of Stegomastodon and other trilophodont gomphotheres according to Mothé et al., 2017: [8]

Gomphotheriidae (Gomphotheres)

Gomphotherium

Gnathabelodon

Eubelodon

Brevirostrine clade

Stegomastodon

Related Research Articles

<span class="mw-page-title-main">Proboscidea</span> Order of elephant-like mammals

Proboscidea is a taxonomic order of afrotherian mammals containing one living family (Elephantidae) and several extinct families. First described by J. Illiger in 1811, it encompasses the elephants and their close relatives. Proboscideans include some of the largest known land mammals. The largest land mammal of all time may have been a proboscidean; the elephant Palaeoloxodon namadicus has been estimated to be up to 5.2 m (17.1 ft) at the shoulder and may have weighed up to 22 t, surpassing the paraceratheres, the otherwise largest known land mammals, though this estimate was made based on a single fragmentary femur and is speculative. The largest extant proboscidean is the African bush elephant, with a record of size of 4 m (13.1 ft) at the shoulder and 10.4 t. In addition to their enormous size, later proboscideans are distinguished by tusks and long, muscular trunks, which were less developed or absent in early proboscideans.

<span class="mw-page-title-main">Mastodon</span> Extinct genus of proboscideans

A mastodon is a member of the genus Mammut, which strictly defined, was endemic to North America and lived from the late Miocene to the early Holocene. Mastodons belong to the order Proboscidea, the same order as elephants and mammoths. Mammut is the type genus of the extinct family Mammutidae, which diverged from the ancestors of modern elephants at least 25 million years ago, during the Oligocene.

<span class="mw-page-title-main">Mammutidae</span> Extinct family of mammals

Mammutidae is an extinct family of proboscideans belonging to Elephantimorpha. It is best known for the mastodons, which inhabited North America from the Late Miocene until their extinction at beginning of the Holocene, around 11,000 years ago. The earliest fossils of the group are known from the Late Oligocene of Africa, around 24 million years ago, and fossils of the group have also been found across Eurasia. The name "mastodon" derives from Greek, μαστός "nipple" and ὀδούς "tooth", referring to their characteristic teeth.

<span class="mw-page-title-main">Gomphothere</span> Extinct family of proboscidean mammals

Gomphotheres are an extinct group of proboscideans related to modern elephants. They were widespread across Afro-Eurasia and North America during the Miocene and Pliocene epochs and dispersed into South America during the Pleistocene as part of the Great American Interchange. Gomphotheres are a paraphyletic group that is ancestral to Elephantidae, which contains modern elephants, as well as Stegodontidae. While most famous forms such as Gomphotherium had long lower jaws with tusks, which is the ancestral condition for the group, some later members developed shortened (brevirostrine) lower jaws with either vestigial or no lower tusks, looking very similar to modern elephants, an example of parallel evolution, which outlasted the long-jawed gomphotheres. By the end of the Early Pleistocene, gomphotheres became extinct in Afro-Eurasia, with the last two genera, Cuvieronius ranging from southern North America to western South America, and Notiomastodon having a wide range over most of South America until the end of the Pleistocene around 12,000 years ago, when they became extinct following the arrival of humans.

<i>Gomphotherium</i> Extinct genus of elephant-like mammals

Gomphotherium is an extinct genus of gomphothere proboscidean from the Neogene of Eurasia, Africa and North America. The genus is probably paraphyletic.

<i>Anancus</i> Genus of proboscideans

Anancus is an extinct genus of "tetralophodont gomphothere" native to Afro-Eurasia, that lived from the Tortonian stage of the late Miocene until its extinction during the Early Pleistocene, roughly from 8.5–2 million years ago.

<i>Cuvieronius</i> Extinct genus of mammals

Cuvieronius is an extinct New World genus of gomphothere which ranged from southern North America to western South America during the Pleistocene epoch. Among the last gomphotheres, it became extinct at the end of the Pleistocene, approximately 12,000 years ago, following the arrival of humans to the Americas.

<i>Sinomastodon</i> Extinct genus of gomphothere proboscidean

Sinomastodon is an extinct gomphothere genus known from the Late Miocene to Early Pleistocene of Asia, including China, Japan, Thailand, Myanmar, Indonesia and probably Kashmir.

<i>Tetralophodon</i> Extinct genus of mammals

Tetralophodon is an extinct genus of "tetralophodont gomphothere" belonging to the superfamily Elephantoidea, known from the Miocene of Afro-Eurasia.

<i>Rhynchotherium</i> Extinct genus of proboscid

Rhynchotherium is an extinct genus of proboscidea endemic to North America and Central America during the Miocene through Pliocene from 13.650 to 3.6 Ma, living for approximately 10 million years.

Gnathabelodon is an extinct genus of gomphothere endemic to North America that includes species that lived during the Middle to Late Miocene.

<i>Eubelodon</i> Extinct genus of proboscid

Eubelodon is an extinct genus of gomphothere which lived in North America during the Miocene Epoch. It contains a single species: Eubelodon morrilli.

<i>Notiomastodon</i> Extinct genus of mammals

Notiomastodon is an extinct genus of gomphothere proboscidean, endemic to South America from the Pleistocene to the beginning of the Holocene. Notiomastodon specimens reached a size similar to that of the modern Asian elephant. Like other brevirostrine gomphotheres such as Cuvieronius and Stegomastodon, Notiomastodon had a shortened lower jaw and lacked lower tusks, unlike more primitive gomphotheres like Gomphotherium.

<i>Choerolophodon</i> Extinct genus of mammals

Choerolophodon is an extinct genus of proboscidean that lived during the Miocene of Eurasia and Africa. Fossils of Choerolophodon have been found in Africa, Southeast Europe, Turkey, Iraq, Iran, the Indian subcontinent, and China.

Surameryx is an extinct genus of herbivorous artiodactyls originally described as belonging to the extinct family Palaeomerycidae. A single species, S. acrensis, was described from the Late Miocene of the Madre de Dios Formation, South America. It was originally interpreted as one of the few northern mammals that entered South America before the Pliocene. However, both its identification as a member of the family Palaeomerycidae and claims about its Miocene age were subsequently challenged.

<span class="mw-page-title-main">Amebelodontidae</span> Extinct family of mammals

Amebelodontidae is an extinct family of large herbivorous proboscidean mammals related to elephants. They were formerly assigned to Gomphotheriidae, but recent authors consider them a distinct family. They are distinguished from other proboscideans by having flattened lower tusks and very elongate mandibular symphysis. The lower tusks could grow considerable size, with those of Konobelodon reaching 1.61 metres (5.3 ft) in length. Their molar teeth are typically trilophodont, and possessed posttrite conules. In the past, amebelodonts' shovel-like mandibular tusks led to them being portrayed scooping up water plants, however, dental microwear suggests that they were browsers and mixed feeders. The lower tusks have been proposed to have had a variety of functions depending on the species, including stripping bark, cutting through vegetation, as well as possibly digging. They first appeared in Africa during the Early Miocene, and subsequently dispersed into Eurasia and then North America. They became extinct by the beginning of the Pliocene. While some phylogenetic studies have recovered Amebelodontidae as a monophyletic group that forms the sister group to Gomphotheriidae proper, some authors have argued that Amebelodontidae may be polyphyletic, with it being suggested that the shovel-tusked condition arose several times independently within Gomphotheriidae, thus rendering the family invalid.

<i>Eozygodon</i>

Eozygodon is an extinct genus of proboscidean in the family Mammutidae that is based on a single species, E. morotoensis, named in 1983. It is known from the Early Miocene of Africa and well as possibly the Middle Miocene of China. It is considered a primitive member of the family, retaining a long lower jaw (longirostrine) with lower tusks. The upper tusks are small and are parallel to each other. The body mass is considerably smaller than the American mastodon. Dental mesowear from East African specimens suggests a browsing diet.

<span class="mw-page-title-main">Sabana Formation</span> Geological formation in the Colombian Andes

The Sabana Formation is a geological formation of the Bogotá savanna, Altiplano Cundiboyacense, Eastern Ranges of the Colombian Andes. The formation consists mainly of shales with at the edges of the Bogotá savanna lignites and sandstones. The Sabana Formation dates to the Quaternary period; Middle to Late Pleistocene epoch, and has a maximum thickness of 320 metres (1,050 ft), varying greatly across the savanna. It is the uppermost formation of the lacustrine and fluvio-glacial sediments of paleolake Humboldt, that existed at the edge of the Eastern Hills until the latest Pleistocene.

Stenobelodon is an extinct genus of amebelodont proboscidean from the Miocene of North America. The only known species was formerly considered to belong to the genus Amebelodon but was distinguished in 2023 based on the short and only partially flattened lower tusks and the closer resemblance of its cheek teeth to those of Gomphotherium than to its purported close relatives. Fossils are known from Florida and Kansas.

References

  1. Larramendi, A. (2016). "Shoulder height, body mass and shape of proboscideans" (PDF). Acta Palaeontologica Polonica. 61. doi:10.4202/app.00136.2014. S2CID   2092950.
  2. 1 2 Lucas, Spencer G.; Aguilar, Ricardo H.; Speilmann, Justin A. (2011). "Stegomastodon (Mammalia, Proboscidea) from the Pliocene of Jalisco, Mexico and the species-level taxonomy of Stegomastodon". New Mexico Museum of Natural History and Science Bulletin. 53: 517–553.
  3. 1 2 3 4 Spencer LG 2022. The last North American gomphotheres. N Mex Mus Nat Hist Sci. 88:45–58.
  4. Alberdi, María Teresa; Juárez-Woo, Javier; Polaco, Oscar J.; Arroyo-Cabrales, Joaquín (2009-02-01). "Description of the most complete skeleton of Stegomastodon (Mammalia, Gomphotheriidae) recorded for the Mexican Late Pleistocene". Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen. 251 (2): 239–255. doi:10.1127/0077-7749/2009/0251-0239.
  5. Lucas, Spencer G. Taxonomy and evolution of the Plio-Pleistocene proboscidean Stegomastodon in North America. OCLC   798103439.
  6. Mothé, Dimila; Ferretti, Marco P.; Avilla, Leonardo S. (June 2019). "Running Over the Same Old Ground: Stegomastodon Never Roamed South America". Journal of Mammalian Evolution. 26 (2): 165–177. doi:10.1007/s10914-017-9392-y. ISSN   1064-7554.
  7. Alberdi, María T.; Prado, José L. (2022-08-03). "Diversity of the fossil gomphotheres from South America". Historical Biology. 34 (8): 1685–1691. doi:10.1080/08912963.2022.2067754. ISSN   0891-2963.
  8. Mothé, Dimila; dos Santos Avilla, Leonardo; Asevedo, Lidiane; Borges-Silva, Leon; Rosas, Mariane; Labarca-Encina, Rafael; Souberlich, Ricardo; Soibelzon, Esteban; Roman-Carrion, José Luis; Ríos, Sergio D.; Rincon, Ascanio D.; de Oliveira, Gina Cardoso; Lopes, Renato Pereira (2 July 2017). "Sixty years after 'The mastodonts of Brazil': The state of the art of South American proboscideans (Proboscidea, Gomphotheriidae)". Quaternary International. 443: 52–64. Bibcode:2017QuInt.443...52M. doi:10.1016/j.quaint.2016.08.028.