Antetonitrus

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Antetonitrus
Temporal range: Early Jurassic,
Hettangian
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Antetonitrus ingenipes.jpg
Holotype
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Sauropodomorpha
Clade: Sauropoda
Clade: Lessemsauridae
Genus: Antetonitrus
Species:
A. ingenipes
Binomial name
Antetonitrus ingenipes
Yates & Kitching, 2003

Antetonitrus is a genus of sauropodiform dinosaur found in the Early Jurassic Elliot Formation of South Africa. The only species is Antetonitrus ingenipes. Sometimes considered a basal sauropod, it is crucial for the understanding of the origin and early evolution of this group. It was a quadrupedal herbivore, like its later relatives, but shows primitive adaptations to use the forelimbs for grasping, instead of purely for weight support. [1]

Contents

Discovery and naming

The Elliot Formation, where remains of Antetonitrus were discovered Elliot Formation Caves in 'Matalane Valley, Leribe, Lesotho - panoramio.jpg
The Elliot Formation, where remains of Antetonitrus were discovered

Adam Yates, an Australian expert on early sauropodomorphs, [2] named Antetonitrus in a 2003 report co-authored by South African James Kitching. The name is derived from the Latin ante- ("before") and tonitrus ("thunder"), which refers to its existence, before other known sauropods, specifically Brontosaurus ("thunder lizard"). The one known species of Antetonitrus is called A. ingenipes, from the Latin ingens ("massive") and pes ("foot"), because it shows the beginning of the development of feet designed solely to support weight. [1]

The fossils now known as Antetonitrus were discovered by Kitching in 1981 in the Free State of South Africa, [2] and were stored in the Bernard Price Institute where they were labeled as Euskelosaurus . Yates recognized them as a separate taxon and published a description several years later. [1] The holotype, or original specimen, consists of several vertebrae and numerous bones from both forelimb and hind limb, all presumed to be from one individual. Five more limb bones from another smaller individual were also referred to the genus. [1]

Description

Size of Antetonitrus compared to a human Antetonitrus size.jpg
Size of Antetonitrus compared to a human

The holotype specimen may have measured 8–10 metres (26–33 ft) in length, 1.5–2 metres (4.9–6.6 ft) in hip height and 5.6 metric tons (6.2 short tons) in body mass. [1] [3] However, the neural arches of the vertebrae were not fused with the centra, indicating that this individual perhaps was not fully grown. [1]

Antetonitrus shows several features which appear to be similar to those of later sauropods, but still retains some primitive features. Unlike most of its smaller and more lightly built ancestors, Antetonitrus was primarily quadrupedal. [1] Like sauropods, its forelimbs were much longer relative to its hind legs than earlier animals, while the metatarsus was shortened. [1] However, the first digit of the hand, also called the "thumb" or pollex, was still twisted and flexible, capable of grasping against the hand. In more derived sauropods, the wrist bones are large and thick, arranged in such a way as to lock the hand into a permanently pronated position for full-time weight support, and the hand is incapable of grasping. [1]

Antetonitrus already shows adaptations for an increasing body size as seen in all later sauropods: The wrist bones were broader and thicker to support more weight, whereas the femur was elliptical in cross section. [1] The vertebrae bear high neural spines and well developed hyposphene-hypantrum articulations which add rigidity to the trunk. [1] The first toe of the hind foot already bears a large claw longer than the first metatarsal; however, this claw was not sickle shaped as seen in later sauropods. [1] The femur was slightly sigmoidal (S-curved) in lateral view rather than straight as in other sauropods. [1]

Despite being a true sauropod, the long bone development of Antetonitrus was more characteristic of basal sauropodomorphs, with subadults possessing, as derived sauropods do, highly vascularised fibrolamellar bone throughout their cortices, but with intermittent growth lines as seen in more basal sauropodomorphs instead of the absence of growth lines or presence of growth lines exclusively in the outer circumferential layer. [4]

Classification

Skeletal reconstruction of Lessemsaurus, a closely related genus of basal sauropod Lessemsaurus Senckenberg.jpg
Skeletal reconstruction of Lessemsaurus , a closely related genus of basal sauropod
Restoration of Antetonitrus Antetonitrus reconstruction.jpg
Restoration of Antetonitrus

A cladistic analysis by Yates and Kitching recognizes Antetonitrus as a basal sauropod, occupying a position between more derived animals such as Isanosaurus or Vulcanodon , and more basal sauropods like Melanorosaurus . [1] The back vertebrae are extremely similar to Lessemsaurus from South America, while the limb bones are similar to Blikanasaurus , another stocky early sauropod from South Africa. However, these animals were not included in a cladistic analysis with Antetonitrus because they are poorly known. [1] Apaldetti et al. (2018) erected Lessemsauridae, a clade containing Antetonitrus, Lessemsaurus and Ingentia . Their cladogram is reproduced below: [5]

Sauropodiformes

The following cladogram shows the position of Antetonitrus within Massopoda, according to Oliver W. M. Rauhut and colleagues, 2020: [6]

Massopoda

Paleogeography

While Antetonitrus is not the earliest sauropod from a phylogenetic standpoint, it is currently one of the oldest known sauropod chronologically, or rather tied for that distinction with other early sauropods from the same formation, like Melanorosaurus and Blikanasaurus. Fossils of these animals were recovered from the Elliot Formation. Initially it was thought to have been recovered from the Lower Elliot Formation which dates to the Norian stage of the Late Triassic, or approximately 221 to 210 million years ago. Later studies indicate that it was actually recovered from the Early Jurassic Upper Elliot Formation. [7] [8] Before Antetonitrus and the other animals recovered from the Elliot Formation were recognized as sauropods, the oldest known sauropod had been Isanosaurus from the Rhaetian stage of Thailand. [9]

Early sauropods and their sauropodomorph relatives were found around the world as all of the continents were at the time united into the single supercontinent, Pangaea, which made dispersal across the entire terrestrial world possible.

Related Research Articles

<span class="mw-page-title-main">Sauropodomorpha</span> Extinct clade of dinosaurs

Sauropodomorpha is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had long necks and tails, were quadrupedal, and became the largest animals to ever walk the Earth. The prosauropods, which preceded the sauropods, were smaller and were often able to walk on two legs. The sauropodomorphs were the dominant terrestrial herbivores throughout much of the Mesozoic Era, from their origins in the Late Triassic until their decline and extinction at the end of the Cretaceous.

<i>Melanorosaurus</i> Sauropodomorph dinosaur genus from the Late Triassic period

Melanorosaurus is a genus of basal sauropodomorph dinosaur that lived during the Late Triassic period. An omnivore from South Africa, it had a large body and sturdy limbs, suggesting it moved quadrupedally. Its limb bones were massive and heavy like the limb bones of true sauropods.

<i>Riojasaurus</i> Extinct genus of dinosaurs

Riojasaurus was a herbivorous sauropodomorph dinosaur named after La Rioja Province in Argentina where it was found in the Los Colorados Formation in the Ischigualasto-Villa Unión Basin by José Bonaparte. It lived during the Late Triassic and grew to about 6.6 metres (22 ft) long. Riojasaurus is the only known riojasaurid to live in South America.

<i>Vulcanodon</i> Extinct genus of dinosaurs

Vulcanodon is an extinct genus of sauropod dinosaur from the Early Jurassic Uppermost Forest Sandstone of southern Africa. The only known species is V. karibaensis. Discovered in 1969 in Zimbabwe, it was regarded as the earliest-known sauropod for decades, and is still one of the most primitive sauropods that has been discovered. As a quadrupedal, ground-dwelling herbivore, Vulcanodon already showed the typical sauropod body plan with column-like legs and a long neck and tail. It was smaller than most other sauropods, measuring approximately eleven metres (36 ft) in length. Vulcanodon is known from a fragmentary skeleton including much of the pelvic girdle, hindlimbs, forearms, and tail, but lacking the trunk and neck vertebrae as well as the skull.

<i>Massospondylus</i> Sauropodomorph dinosaur genus from Early Jurassic South Africa and Botswana

Massospondylus was a genus of sauropodomorph dinosaur from the Early Jurassic. It was described by Sir Richard Owen in 1854 from remains discovered in South Africa, and is thus one of the first dinosaurs to have been named. Fossils have since been found at other locations in South Africa, Lesotho, and Zimbabwe. Material from Arizona's Kayenta Formation, India, and Argentina has been assigned to the genus at various times, but the Arizonan and Argentinian material are now assigned to other genera.

<i>Isanosaurus</i> Genus of dinosaurs

Isanosaurus is an extinct genus of sauropod dinosaur from Thailand. It was originally dated to approximately 210 million years ago during the Late Triassic, which would make it one of the oldest known sauropods. Its age was later considered uncertain, and may be Early Jurassic or even as young as Late Jurassic. The only species is Isanosaurus attavipachi. Though important for the understanding of sauropod origin and early evolution, Isanosaurus is poorly known. Exact relationships to other early sauropods remain unresolved.

<i>Lessemsaurus</i> Sauropodomorph dinosaur genus from Late Triassic Argentina

Lessemsaurus is an extinct genus of sauropodiform dinosaur belonging to Lessemsauridae.

<i>Blikanasaurus</i> Extinct genus of dinosaur from the late Triassic of South Africa

Blikanasaurus is a genus of sauropodomorph dinosaur from the late Triassic of South Africa. The generic name Blikanasaurus is derived from Greek, meaning "lizard from Blikana". The species name cromptoni is taken from the surname of A.W. "Fuzz" Crompton, an American paleontologist who led numerous field expeditions in Elliot Formation outcrop localities in South Africa. Blikanasaurus is only known from partial hindlimb bones that were recovered from the lower Elliot Formation (LEF) in the Eastern Cape.

Gongxianosaurus is a genus of basal sauropod dinosaur from the early Jurassic Period. The only species is Gongxianosaurus shibeiensis. Based on four fragmentary to complete specimens found in China, it is one of the most completely known early sauropods. The skeleton is known in large part, missing both the hand and the majority of the skull. Gongxianosaurus was firstly named and described in a short note published in 1998; however, a comprehensive description has yet to be published. Gongxianosaurus shibeiensis was named for the place it was found, near the village Shibei in Gong County.

<span class="mw-page-title-main">Massopoda</span> Extinct clade of dinosaurs

Massopoda is a clade of sauropodomorph dinosaurs which lived during the Late Triassic to Late Cretaceous epochs. It was named by paleontologist Adam M. Yates of the University of the Witwatersrand in 2007. Massopoda is a stem-based taxon, defined as all animals more closely related to Saltasaurus loricatus than to Plateosaurus engelhardti.

<span class="mw-page-title-main">Elliot Formation</span> Lithostratigraphic layer of the Stormberg Group in South Africa

The Elliot Formation is a geological formation and forms part of the Stormberg Group, the uppermost geological group that comprises the greater Karoo Supergroup. Outcrops of the Elliot Formation have been found in the northern Eastern Cape, southern Free State, and in the eastern KwaZulu-Natal provinces of South Africa. Outcrops and exposures are also found in several localities in Lesotho such as Qacha's Neck, Hill Top, Quthing, and near the capital, Maseru. The Elliot Formation is further divided into the lower (LEF) and upper (UEF) Elliot formations to differentiate significant sedimentological differences between these layers. The LEF is dominantly Late Triassic (Norian-Hettangian) in age while the UEF is mainly Early Jurassic (Sinemurian-Pliensbachian) and is tentatively regarded to preserve a continental record of the Triassic-Jurassic boundary in southern Africa. This geological formation is named after the town of Elliot in the Eastern Cape, and its stratotype locality is located on the Barkly Pass, 9 km north of the town.

<i>Aardonyx</i> Extinct genus of dinosaur of the Jurassic from South Africa

Aardonyx is a genus of basal sauropodomorph dinosaur. It is known from the type species Aardonyx celestae found from the Early Jurassic Elliot Formation of South Africa. A. celestae was named after Celeste Yates, who prepared much of the first known fossil material of the species. It has arm features that are intermediate between basal sauropodomorphs and more derived sauropods.

<i>Leonerasaurus</i> Genus of sauropodomorph dinosaur from the Early Jurassic period

Leonerasaurus is a basal genus of sauropodomorph dinosaur. Currently, there is only one species known, named L. taquetrensis by Diego Pol, Alberto Garrido and Ignacio A. Cerda in 2011. The fossil, an incomplete subadult individual, was found in the Las Leoneras Formation in Argentina. This formation is probably Early Jurassic in age. Leonerasaurus was a small non-sauropod sauropodomorph, showing an unusual combination of basal and derived characters. This indicates that the evolution of early sauropodomorphs witnessed a great degree of convergent evolution.

Sefapanosaurus was an early, herbivorous sauropodomorph dinosaur occurring in the southern regions of Gondwana some 200 million years ago in the Late Triassic or Early Jurassic. The sauropodomorphs were the dominant terrestrial herbivores throughout much of the Mesozoic Era, from their origins in the mid-Triassic until their decline and fall at the end of the Cretaceous. A distinctive feature of this dinosaur is the cross-shaped astragalus or talus bone in its ankle. The generic name is derived from the Sesotho word sefapano, meaning ‘cross’ and the Greek word saurus, meaning 'lizard'. The specific name refers to Zastron, the type locality, where the specimen was discovered.

<i>Pulanesaura</i> Extinct genus of dinosaurs from the early Jurassic of South Africa

Pulanesaura is an extinct genus of basal sauropodiform known from the Early Jurassic Upper Elliot Formation of the Free State, South Africa. It contains a single species, Pulanesaura eocollum, known from partial remains of at least two subadult to adult individuals.

<i>Meroktenos</i> Extinct genus of dinosaur from Triassic southern Africa

Meroktenos is a genus of basal sauropodomorph dinosaur that lived during the Late Triassic period of what is now Lesotho.

<i>Xingxiulong</i> Extinct genus of reptiles

Xingxiulong is a genus of bipedal sauropodiform from the Early Jurassic of China. It contains a single species, X. chengi, described by Wang et al. in 2017 from three specimens, two adults and an immature individual, that collectively constitute a mostly complete skeleton. Adults of the genus measured 4–5 metres (13–16 ft) long and 1–1.5 metres tall. Phylogenetic analysis suggests that Xingxiulong is most closely related to its contemporary Jingshanosaurus, although an alternative position outside of both the Sauropodiformes and Massospondylidae is also plausible.

Ingentia is a genus of early sauropodiform dinosaur, sometimes considered a basal sauropod, from the Late Triassic of Argentina. The type specimen of Ingentia, PVSJ 1086, was discovered in the Quebrada del Barro Formation of northwestern Argentina. It was described in 2018 by Cecilia Apaldetti, Ricardo Nestor Martínez, Ignacio Alejandro Cerda, Diego Pol and Oscar Alcober who named the type and only species Ingentia prima, meaning "first huge one", as the taxon was one of the first very large sauropodomorphs to evolve, along with its close relative Lessemsaurus. A second specimen, PVSJ 1087, was referred, containing five tail vertebrae, both ulnae and radii, a left calfbone and a right foot.

<span class="mw-page-title-main">Lessemsauridae</span> Extinct clade of dinosaurs

Lessemsauridae is a clade of early sauropodiform dinosaurs that lived in the Triassic and Jurassic of Argentina, South Africa and possibly Lesotho. A phylogenetic analysis performed by Apaldetti and colleagues in 2018 recovered a new clade of sauropodiforms uniting Lessemsaurus, Antetonitrus, and Ingentia which they named Lessemsauridae. It is a node-based taxon, defined as all descendants of the most recent common ancestor of Lessemsaurus sauropoides and Antetonitrus ingenipes. Depending on the definition of Sauropoda, Lessemsauridae is either one of the most basal sauropod taxa, or a sister taxon of Sauropoda. An additional member of the clade was named later in 2018, Ledumahadi. A 2021 study by Pol and colleagues also assigned the genera Kholumolumo and Meroktenos to the group.

<i>Ledumahadi</i> Sauropodomorph dinosaur genus from Early Jurassic South Africa

Ledumahadi is a genus of lessemsaurid sauropodomorph dinosaur from the Early Jurassic Elliot Formation in Free State Province, South Africa. The type and only species is L. mafube, known from a singular incomplete postcranial specimen. A quadruped, it was one of the first giant sauropodomorphs, reaching a weight of around 12 tonnes, despite not having evolved columnar limbs like its later huge relatives.

References

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