Stegotherium

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Stegotherium
Temporal range: Early Miocene (Colhuehuapian-Santacrucian)
~21.0–16.3  Ma
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Stegotherium.jpg
Skeleton of Stegotherium tauberi (without carapace)
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Cingulata
Family: Dasypodidae
Subfamily: Dasypodinae
Genus:† Stegotherium
Ameghino, 1887
Type species
†Stegotherium tessellatum
Ameghino, 1887
Species
  • S. caroloameghinoiFernicola & Vizcaíno, 2008
  • S. notohippidensisGonzález & Scillato-Yané, 2009
  • S. pascualiFernicola & Vizcaíno, 2008
  • S. simplex? Ameghino, 1887
  • S. tauberiGonzález & Scillato-Yané, 2008 [1]
  • S. tessellatumAmeghino, 1887 (type species)
  • S. variegatumAmeghino, 1902
Synonyms
  • Scotaeops simplexAmeghino, 1887
  • Stegotheriopsis gaimanensisBordas, 1939

Stegotherium is an extinct genus of long-nosed armadillo, belonging to the Dasypodidae family alongside the nine-banded armadillo. It is currently the only genus recognized as a member of the tribe Stegotheriini. It lived during the Early Miocene of Patagonia and was found in Colhuehuapian rocks from the Sarmiento Formation, Santacrucian rocks from the Santa Cruz Formation, [2] and potentially also in Colloncuran rocks from the Middle Miocene Collón Curá Formation. [3] Its strange, almost toothless and elongated skull indicates a specialization for myrmecophagy, the eating of ants, unique among the order Cingulata, which includes pampatheres, glyptodonts and all the extant species of armadillos. [4]

Contents

History

Stegotherium tessellatum was described originally in 1887 by Florentino Ameghino based on the remains of a carapace collected by his brother Carlos in the Santa Cruz Province of Argentina. The same paper also described another genus and species of armadillo, Scaetops simplex, known from a fragmentary mandible. [5] In 1894, Stegotherium, at that time only known from osteoderms, was temporarily considered by Lydekker as a synonym of Peltephilus . This status was contested and proven wrong a year later by Ameghino.[ citation needed ]

In 1902, after a skull of Scaetops simplex was found in association with Stegotherium tessellatum osteoderms, Ameghino considered the two species synonymous, and proposed a new species Stegotherium variegatum based on osteoderms found in Chubut Province. [6] In 1904, after the discovery of additional remains of S. variegatum, William Berryman Scott re-evaluated Scaetops simplex as a species of Stegotherium different from S. tessellatum. [7]

In 2008, two important studies on the genus were published. The first, led by Fernicola and Vizcaíno, reviewed the material and species assigned to the genus. They proposed two new species, S. caroloameghinoi, with MACN-A 10443a, an osteoderm from the dorsal carapace, as holotype, and S. pascuali using MACN A-12680d, an osteoderm from the dorsal carapace, as holotype. This review also kept, not without some doubt, S. simplex as a valid taxon. [8] The second study from 2008, led by González Ruiz and Scillato-Yané, proposed ‘’Stegotherium tauberi’’ as a species, based on YPM PU 15565, a fairly complete specimen including a fragmentary dorsal carapace, a complete skull, several vertebra and a right foot, previously assigned to S. tessellatum. [1]

In 2009, another species was named by González Ruiz and Scillato-Yané, S. notohippidensis, with the holotype being MLP 84-III-5-10, a collection of 130 osteoderms from Argentina. [4]

Description

Skull of S. tauberi, showing the reduced teeth. Stegotherium skull.jpg
Skull of S. tauberi, showing the reduced teeth.

Stegotherium was an unusual armadillo, whose most striking feature was the elongated skull, often compared to the skull of an anteater. The posterior area of the jaws, the only one to bear teeth, was compressed compared to Dasypus , while the nasal area and the anterior parts of both jaws, completely toothless, were long and slender. The teeth were cylindricals and greatly reduced, both in number and in size, and were all contained in the posterior area of the lower and upper jaws. [7] While S. tauberi had six teeth in its lower mandible, the dubious S. simplex only had two. [8]

The body of Stegotherium was roughly the size of the modern species of Dasypus, [5] [8] and its carapace was composed of at least 23 mobile bands of osteoderms. [1] The osteoderms of Stegotherium, 3 to 7.5 mm thick [8] and 20 mm long, [6] were characterized by the presence of a number of piliferous foramina around their posterior and lateral margins, a granular appearance, and a compact bone structure. [9]

Species

The genus Stegotherium is unambiguously known from six species, S. tessellatum, S. variegatum, S. caroloameghinoi, S. pascuali, S. tauberi and S. notohippidensis. A seventh species, S. simplex, is generally considered too fragmentary, but has generally been considered valid with reservations by most recent scholars. As osteoderms are the most abundant fossils of Stegotherium known, they are commonly used as the main determinate of which species a given fossil belongs too.[ citation needed ]

Stegotherium tessellatum

S. tessellatum is the type species of Stegotherium. [5] Fossils of it have been recovered in the Santacrucian of the Santa Cruz Formation. It had quadrangular osteoderms, with a single large foramen in the exterior margin, devoid of longitudinal ridge of any kind in the central region. While non-osteoderm remains have been historically referred to this species in literature, they are now assigned to S. tauberi. [8]

Stegotherium simplex

S. simplex [5] is only known from its holotype, a fragmentary mandible with two alveoli, found in the Santa Cruz Formation and dated from the Santacrucian period. It is the only species in the genus whose osteoderms, usually considered diagnostic for armadillo fossils, are unknown. Its only diagnosis characteristic could be the presence of two molariform teeth on the mandible, while S. tessellatum had six; [10] the validity of the species has been debated since 1902, [8] [1] [4] and the holotype is probably lost. [10]

Stegotherium variegatum

S. variegatum is known from the Colhuehuapian Sarmiento Formation. The species is mainly known from fossilized quadrangular osteoderms, whose exposed surface showed several piliferous pits around a single granulated central figure, and a longitudinal ridge surrounded, in all of its length, by depressions. [8]

Stegotherium caroloameghinoi

S. caroloameghinoi is known from the Sarmiento Formation of Argentina, in rocks dating from the Colhuehuapian period. It is only known from osteoderms. Those were rectangular, with a granular textured dorsal surface. Piliferous pits are placed around a central figure, crossed by a median longitudinal ridge, and one to three smaller anterior figures.[ This paragraph needs citation(s) ]

The specific name, caroloameghinoi, is meant to honour Carlos Ameghino, who discovered the holotype of Stegotherium and was a prominent figure in the history of paleontology in Patagonia. [8]

Stegotherium pascuali

S. pascuali is known from the Colhuehuapian period in the Sarmiento Formation. It is known by fossilized osteoderms, whose various shapes all shared the same grainy-textured central figure surrounded by piliferous pits, without anterior figures. Two foramina, absent in S. variegatum and S. caroloameghinoi, and a ridge absent in S. tessellatum, were present on the osteoderms, completing the diagnostic characteristics. [8]

It was named to honour the Argentinian paleontologist Rosendo Pascual. [8]

Stegotherium tauberi

Shell of Stegotherium, now associated with S. tauberi. Stegotherium shell.jpg
Shell of Stegotherium, now associated with S. tauberi.

S. tauberi is known from the Santa Cruz Formation, in rocks dated from the Santacrucian period. It is distinguished from other species of Stegotherium by osteoderms more rugged and with a sharper ridge than S. variegatum. Those osteoderms had a large foramen in the anterior-central region, along with several smaller foramina assembled in a transversal row in the anterior region. The presence of a longitudinal ridge on the osteoderms also distinguishes them. Some of the non-osteoderm material used by González Ruiz and Scillato-Yané to describe S. tauberi was assigned by Fernicola and Vizcaíno to S. tessellatum; both species are, however, considered valid by the current consensus.[ This paragraph needs citation(s) ]

Its species name, tauberi, honours Adán Alejo Tauber, an Argentinian paleontologist who worked on the Santa Cruz Formation. [1]

Stegotherium notohippidensis

S. notohippidensis is found in sediments from the "Notohippidian" period (traditionally considered as the lower part of the Santacrucian period) of the Santa Cruz Formation. Its osteoderms had several foramina in their anterior region, larger than S. variegatum and S. tauberi. In addition, the longitudinal ridge present in the osteoderms of other species of Stegotherium was absent in S. notohippidensis.[ This paragraph needs citation(s) ]

The species name, "notohippidensis" means, in Neo-Latin, "from the Notohippidian", which was itself named after the large herbivore Notohippus , considered to be characteristic of this period. [4]

Paleoecology

Painting by Charles R. Knight (1913), showing a group of Stegotherium tesselatum interacting with a couple of Protypotherium australe, a gracile Notoungulate, in a dry environment. Protypotherium australe.jpg
Painting by Charles R. Knight (1913), showing a group of Stegotherium tesselatum interacting with a couple of Protypotherium australe , a gracile Notoungulate, in a dry environment.

The morphology of the jaws of Stegotherium shows that most of the mastication muscles were specialized for a horizontal and propalinal movement; the teeth were reduced but could still be used for masticating relatively soft food. Those important specializations pushed most scholars to consider Stegotherium as a specialized myrmecophage, similar ecologically to anteaters and to the less specialized giant armadillo. [7]

The area where Stegotherium lived was, during the Early Miocene, a forested savannah with a mild climate. [7] It lived alongside a diversity of related cingulates, such as the Euphractine Prozaedyus , the basal Chlamyphorid Proeutatus , the Dasypodid Stenotatus , the horned armadillo Peltephilus and several genera of glyptodonts, such as Asterostemma , Propalaehoplophorus , Cochlops and Eucinepeltus . [11]

The specialisation of Stegotherium may have caused the extinction of the genus during the Santacrucian, as it may have suffered from the large-scale environmental and climatic changes occurring in Patagonia during this period, the result of the rise of the Andes, causing an aridization that may have caused the rarefaction of ant and termite colonies it fed upon, and cooling making it harder for the animal to regulate its own body temperature. [7] After the Santacrucian, the genus is only known by one Colloncuran fossilized osteoderm, MLP 91-IV-1-66 from the Collón Curá Formation, tentatively assigned to Stegotherium sp. and different from all currently known species of Stegotherium, although other Colloncuran osteoderms of indeterminate Stegotheriini have also been recovered in the Chubut Province. [3]

Related Research Articles

<span class="mw-page-title-main">Cingulata</span> Order of armored mammals from the Americas

Cingulata, part of the superorder Xenarthra, is an order of armored New World placental mammals. Dasypodids and chlamyphorids, the armadillos, are the only surviving families in the order. Two groups of cingulates much larger than extant armadillos existed until recently: pampatheriids, which reached weights of up to 200 kg (440 lb) and chlamyphorid glyptodonts, which attained masses of 2,000 kg (4,400 lb) or more.

<i>Peltephilus</i> An extinct genus of mammals belonging to the armadillo order of xenarthrans

Peltephilus, the horned armadillo, is an extinct genus of armadillo xenarthran mammals that first inhabited Argentina during the Oligocene epoch, and became extinct in the Miocene epoch. Notably, the scutes on its head were so developed that they formed horns. Aside from the horned gophers of North America, it is the only known fossorial horned mammal. P. ferox had skull about 11.7 centimetres (4.6 in), and estimated body mass is around 11.07 kilograms (24.4 lb).

The Magallanes Basin or Austral Basin is a major sedimentary basin in southern Patagonia. The basin covers a surface of about 170,000 to 200,000 square kilometres and has a NNW-SSE oriented shape. The basin is bounded to the west by the Andes mountains and is separated from the Malvinas Basin to the east by the Río Chico-Dungeness High. The basin evolved from being an extensional back-arc basin in the Mesozoic to being a compressional foreland basin in the Cenozoic. Rocks within the basin are Jurassic in age and include the Cerro Toro Formation. Three ages of the SALMA classification are defined in the basin; the Early Miocene Santacrucian from the Santa Cruz Formation and Friasian from the Río Frías Formation and the Pleistocene Ensenadan from the La Ensenada Formation.

The Santacrucian age is a period of geologic time within the Early Miocene epoch of the Neogene, used more specifically with SALMA classification in South America. It follows the Colhuehuapian and precedes the Friasian age.

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

Neosclerocalyptus was an extinct genus of glyptodont that lived during the Pliocene, Pleistocene, and Holocene of Southern South America, mostly Argentina. It was small compared to many Glyptodonts at only around 2 meters long and 360 kilograms.

<i>Lomaphorus</i> Extinct genus of mammals belonging to the armadillo order of xenarthrans

Lomaphorus is a possibly dubious extinct genus of glyptodont that lived during the Pleistocene in eastern Argentina. Although many species have been referred, the genus itself is possibly dubious or synonymous with other glyptodonts like Neoslerocalyptus from the same region.

Utaetus is an extinct genus of mammal in the order Cingulata, related to the modern armadillos. The genus contains two species, Utaetus buccatus and U. magnum. It lived in the Late Paleocene to Late Eocene and its fossil remains were found in Argentina and Brazil in South America.

Epipeltephilus is an extinct genus of armadillo, belonging to the family Peltephilidae, the "horned armadillos", whose most famous relative was Peltephilus. Epipeltephilus is the last known member of its family, becoming extinct during the Chasicoan period. It was found in the Rio Mayo Formation and the Arroyo Chasicó Formation of Argentina, and in northern Chile.

Kraglievichia is an extinct genus of cingulate belonging to the family Pampatheriidae. It lived from the Late Miocene to the Early Pliocene, and its fossilized remains were discovered in South America.

<i>Stenotatus</i> An extinct genus of mammals belonging to the armadillo order of xenarthrans

Stenotatus is an extinct genus of cingulate, belonging to the family Dasypodidae. It lived from the Early to the Late Miocene in South America.

Neoglyptatelus is an extinct genus of xenarthran, belonging to the order Cingulata. It lived from the Middle to the Late Miocene, and its fossilized remains are found in South America.

Proeuphractus is an extinct genus of xenarthran, related to the modern armadillos. It lived from the Early to the Late Miocene, and its fossilized remains were discovered in South America.

<i>Prozaedyus</i> An extinct genus of mammals belonging to the armadillo order of xenarthrans

Prozaedyus is an extinct genus of chlamyphorid armadillo that lived during the Middle Oligocene and Middle Miocene in what is now South America.

Eucinepeltus is an extinct genus of Glyptodont. It lived during the Early Miocene, and its fossilized remains were discovered in South America.

Glyptatelus is an extinct genus of glyptodont. It lived from the Late Eocene to the Middle Oligocene in what is now Argentina and Bolivia.

<i>Cochlops</i> An extinct genus of mammals belonging to the armadillo order of xenarthrans

Cochlops is an extinct genus of glyptodont. It lived from the Early to Middle Miocene, and its fossilized remains have been found in South America.

Nanoastegotherium is an extinct genus of cingulate, belonging to the family Dasypodidae, which includes the modern nine-banded armadillos. The name of the genus means "small Astegotherium", referring to its small size, smaller than the modern southern long-nosed armadillo, and to its affinities with Astegotherium, with which it forms the tribe Astegotheriini, within the family Dasypodidae. Its type species is Nanoastegotherium prostatum, whose species translates to "earlier" due to its age compared to Astegotherium.

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<span class="mw-page-title-main">Santa Cruz Formation</span> Geological formation in Patagonia

The Santa Cruz Formation is a geological formation in the Magallanes/Austral Basin in southern Patagonia in Argentina and in adjacent areas of Chile. It dates to the late Early Miocene epoch, and is contemporaneous with eponymous Santacrucian SALMA. The formation extends from the Andes to the Atlantic coast. In its coastal section it is divided into two members, the lower, fossil rich Estancia La Costa Member, which has a lithology predominantly consisting of tuffaceous deposits and fine grained sedimentary claystone and mudstone, and the upper fossil-poor Estancia La Angelina Member, which consists of sedimentary rock, primarily claystone, mudstone, and sandstone. The environment of deposition is interpreted to have been mostly fluvial, with the lowermost part of the Estancia La Costa Member being transitional between fluvial and marine conditions. The environment of the Estancia La Costa Member is thought to have been relatively warm and humid, but likely became somewhat cooler and drier towards the end of the sequence. The Santa Cruz Formation is known for its abundance of South American native ungulates, as well as an abundance of rodents, xenarthrans, and metatherians.

<span class="mw-page-title-main">Peltephilidae</span> Family of South American cingulates (armadillos)

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References

  1. 1 2 3 4 5 González Laureano Raúl, Scillato-Yané Gustavo Juan. Una nueva especie de Stegotherium Ameghino (Xenarthra, Dasypodidae, Stegotheriini) del Mioceno de la provincia de Santa Cruz (Argentina). Ameghiniana, 2008 Dic; 45(4): 641-648.
  2. ↑ Stegotherium at Fossilworks.org
  3. 1 2 Gonzalez-Ruiz, Laureano (October 2010). 1. Los Cingulata (Mammalia, Xenarthra) del Mioceno temprano y medio de Patagonia (edades Santacrucense y "Friasense"). Revisión sistemática y consideraciones bioestratigráficas (Doctor). Facultad de Ciencias Naturales y Museo Universidad Nacional de La Plata.
  4. 1 2 3 4 González Ruiz, L. R. L.; Scillato-Yané, G. J. (2009). "A new Stegotheriini (Mammalia, Xenarthra, Dasypodidae) from the "Notohippidian" (early Miocene) of Patagonia, Argentina". Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen. 252: 81–90. doi:10.1127/0077-7749/2009/0252-0081. hdl: 11336/95016 .
  5. 1 2 3 4 Ameghino, F. (1887). "Enumeracion sistematica de las especies de mamiferos fosiles coleccionados por Carlos Ameghino en los terrenos eocenos de la Patagonia austral y depositados en el Museo La Plata". Boletin del Museo la Plata. 1: 1–26.
  6. 1 2 Ameghino, F. (1902). "Première contribution a la connaissance de la faune mammalogique des couches a Colpodon". Boletin de la Academia Nacional de Ciencias en Córdoba, República Argentina. 17: 71–141.
  7. 1 2 3 4 5 Vizcaíno, S.F. (1994). "Mecánica masticatoria de Stegotherium tessellatum Ameghino (Mammalia, Xenarthra) del Mioceno temprano de Santa Cruz (Argentina). Algunos aspectos paleoecológicos relacionados". Ameghiniana. 231 (3): 283–290.
  8. 1 2 3 4 5 6 7 8 9 10 Fernicola, J.C.; Vizcaíno, S.F. (2008). "Revisión del género Stegotherium Ameghino, 1887 (Mammalia, Xenarthra, Dasypodidae)". Ameghiniana. 245 (2): 321–332.
  9. ↑ Ciancio, M.R.; Krmpotic, C.M.; Scarano, A.C.; Epele, M.B. (2019). "Internal Morphology of Osteoderms of Extinct Armadillos and Its Relationship with Environmental Conditions". Journal of Mammalian Evolution. 26 (1): 71–93. doi:10.1007/s10914-017-9404-y. S2CID   39630502.
  10. 1 2 Fernicola, J.C.; Vizcaíno, S.F. (2019). "Cingulates (Mammalia, Xenarthra) of the Santa Cruz Formation (Early-Middle Miocene) from the Rio Santa Cruz, Argentine Patagonia". Publicación Electrónica de la Asociación Paleontológica Argentina. 19 (2): 85–101.
  11. ↑ Vizcaíno, S. F.; Kay, R.F.; Bargo, M. S. (2012). "Paleobiology of Santacrucian glyptodonts and armadillos (Xenarthra, Cingulata)". In Vizcaíno, S. F.; Kay, R. F.; Bargo, M. S. (eds.). Early Miocene Paleobiology in Patagonia: high-latitude paleocommunities of the Santa Cruz Formation. Cambridge University Press. pp. 194–215. doi:10.1017/CBO9780511667381. ISBN   9780511667381.
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