Nyasasaurus

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Nyasasaurus
Temporal range: ?Anisian
 ?243  Ma
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Nyasasaurus NT.png
Life restoration of N. parringtoni
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Archosauria
Clade: Avemetatarsalia
Clade: Ornithodira
Clade: Dinosauromorpha (?)
Genus:† Nyasasaurus
Nesbitt et al., 2013
Type species
†Nyasasaurus parringtoni
Nesbitt et al., 2013
Synonyms

Nyasasaurus (meaning "Lake Nyasa lizard") is an extinct genus of avemetatarsalian archosaur from the putatively Middle Triassic Manda Formation of Tanzania that may be the earliest known dinosaur. The type species Nyasasaurus parringtoni was first described in 1956 in the doctoral thesis of English paleontologist Alan J. Charig, but it was not formally described until 2013.

Contents

Previously, the oldest record of dinosaurs was from Brazil and Argentina and dated back to the mid-late Carnian stage, about 233.23 to 231.4 million years ago. Nyasasaurus comes from a deposit formerly considered Anisian in age, meaning that it would predate other early dinosaurs by about 12 million years. [1] However, more recent studies cast doubt to this age, [2] pointing out that the deposits would actually be Carnian in age, [3] [4] which would considerably reduce this temporal gap.

History of study

Approximation of animal based on partial skeleton shown in black (first specimen, six vertebrae and a humerus) and blue (second specimen, three cervical vertebrae). Nyasasaurus.jpg
Approximation of animal based on partial skeleton shown in black (first specimen, six vertebrae and a humerus) and blue (second specimen, three cervical vertebrae).

In the 1930s, the holotype of Nyasasaurus was collected in Parrington's locality B36 from the Lifua Member of the Manda Formation, Ruhuhu Basin near Lake Nyasa in southern Tanzania by Francis Rex Parrington. Other fossils from the same locality included those of cynodonts, dicynodonts, and rhynchosaurs. Most, including those of Nyasasaurus, consist only of fragments of bone. The remains were first described in English paleontologist Alan J. Charig's 1956 doctoral thesis and referred to as "Specimen 50b". [5] In 1967 Charig used the name "Nyasasaurus cromptoni", in a review of Archosauria, but without any description, so it was commonly considered a nomen nudum; the dissertation was also never published. [6] The generic name referred to Lake Nyasa and the specific name honouring Alfred Crompton. In 2013 a new description was published by Sterling Nesbitt, Paul Barrett, Sarah Werning and Christian Sidor, including the late Charig as posthumous co-author, ensuring the validity of the name Nyasasaurus, though the specific name was changed to parringtoni, in honour of Parrington. [1] The generic name is occasionally misspelled as "Nyasaurus", [1] as by Theodore Elmer White in 1973. [7]

The referred specimen of Nyasasaurus, SAM-PK-K10654, was collected by G. M. Stockley in the early 1930s in the western portion of the Manda Formation at Stockley's locality B27. [8] This locality is listed as a locality from the "Upper Bone Bed" of the Manda Formation (currently understood to be from the Lifua Member) by Haughton (1932). The specimen was collected under a single field number, S507, presumably from a small area. The specimen was probably associated as evidenced by the bone quality, color and surrounding matrix (dark gray to black carbonate). The consistent sizes of the remains indicate that they probably represent a single individual.

Stockley's locality B27 is located near the village of Gingama and it was probably the only specimen found at this locality, although a nearby locality B26, also listed as Gingama, produced cynodonts, lungfish, amphibians, and a shark. Dicynodonts, cynodonts and archosaurs such as Asilisaurus were also found nearby in the Lifua Member. [1]

The name Thecodontosaurus alophos was coined for this specimen by Haughton (1932). [9] Its holotype consists of three cervical vertebrae and two middle to posterior dorsal vertebrae that are poorly preserved as they are highly fractured and parts of the bone and bone surfaces are eroded. Originally, a comparison of Thecodontosaurus alophos was made only with Coelophysis longicollis . Since then, the species has been largely ignored by all subsequent vertebrate workers and no formal diagnosis of the specimen was ever provided. Nesbitt et al. (2013) found the specimen to not be diagnostic because it does not have any autapomorphic features or a unique combination of characteristics. Therefore, they suggested to abandon the name Thecodontosaurus alophos and to refer its specimen to Nyasasaurusparringtoni. [1]

Description

The type specimen, NHMUK R6856, is a partial skeleton belonging to an individual estimated to have been two to three metres in length. It consists of a right humerus, three partial sacral vertebrae and three presacral vertebrae. A second specimen, SAM-PK-K10654 consisting of three cervical vertebrae and two posterior presacral vertebrae, is also known. It was attributed to the same species as NHMUK R6856 because the dorsal or back vertebrae of the two specimens are nearly identical. However, the vertebral features that link NHMUK R6856 and SAM-PK-K10654, including a connection between two bony projections called the hyposphene and hypantrum, are also found in other Triassic archosaurs. Since these characteristics are not unique to the two species they do not by themselves provide sufficient evidence for grouping NHMUK R6856 and SAM-PK-K10654 under the same species. The 2013 description of Nyasasaurus by Sterling Nesbitt, Paul Barrett, Sarah Werning and Christian Sidor used a second line of evidence, the similar positions of the two specimens on the evolutionary tree, to justify their placement as the same species. [1]

The study also mentioned the similarity between the presacral vertebrae of both specimens of Nyasasaurus parringtoni and those of the enigmatic avemetatarsalian archosaur, Teleocrater rhadinus . Additionally, the anterior cervical vertebra attributed to NHMUK PV R6795 is extremely elongated relative to that of the middle dorsal vertebrae with a low centrum to neural arch ratio and a significant displacement between the two sides of the articular facet of the centrum. However, it is probable that the limb bones and other elements included in NHMUK PV R6795 do not belong to the same individual. Therefore, it is possible that the vertebrae of Teleocrater rhadinus are also referable to Nyasasaurus parringtoni. [1]

An analysis of the interior structure of the humerus indicates that bone growth was rapid, with interwoven bone fibers, many channels for blood vessels that radiate in all directions, and few lines of arrested growth. This structure more closely matches that of the early dinosaur Coelophysis than it does of dinosaur ancestors, suggesting that Nyasasaurus was closer to the ancestry of dinosaurs than other archosaurs at the time. [1]

Classification

Because it is based on incomplete remains, Nyasasaurus has been difficult to classify. It can be placed confidently within Archosauria, the group of reptiles represented today by crocodilians and birds, Dinosauria, the group of dinosaurs; and possibly within Dinosauriformes, the group that includes birds, dinosaurs, and several non-dinosaurian groups from the Triassic. [1] [10]

Nyasasaurus was suggested to have been a primitive prosauropod dinosaur in 1986, [11] but this hypothesis was disputed. The 2013 study suggests that Nyasasaurus may be the earliest known dinosaur, dating to the late Anisian stage, about 243 million years ago, [12] 10 to 15 million years older than any previously described dinosaur, such as Herrerasaurus . [1] [13] However, this age is being questioned in recent papers. [2] [3] [4]

Dinosaur affinities of the holotype are supported by the long deltopectoral crest on the humerus, an unambiguously dinosaur top, another feature present only in dinosaurs. The humerus does not share any synapomorphies exclusively with any other Triassic archosaur clade. The supposed possession of three sacral vertebrae instead of two could represent a dinosaur plesiomorphy, but has a complex distribution among dinosauriforms. The elongated neck vertebrae with hollowed-out sides of the referred specimen provides two characters that are exclusive to the derived silesaurid Silesaurus (but absent in the earlier and more basal silesaurid Asilisaurus ), and to early theropod dinosaurs. These characters can be interpreted as possibly homologous with features that represent unambiguously skeletal pneumaticity in theropods. [1]

Nesbitt et al. (2013) incorporated both specimens, NHMUK R6856 and SAM-PK-K10654, into a phylogenetic analysis. This analysis was based on data from a 2011 analysis by Sterling Nesbitt that included many Triassic archosaurs. [1] When NHMUK R6856 was added to the data set, several possible relationships were found. Various possible evolutionary trees place it as the sister taxon of Dinosauria, the most basal member of Ornithischia (the group that includes most herbivorous Mesozoic dinosaurs), or a member of Theropoda (the group that includes most carnivorous dinosaurs as well as birds). When SAM-PK-K10654 was added to the analysis, it was found to be a theropod. SAM-PK-K10654 possesses several theropod features, including deep pits or fossae in its neck vertebrae, which are not found in NHMUK R6856 because of the limited overlap between the specimens. [1] The following cladogram depicts these possibilities:

Archosauria  

A large phylogenetic analysis of early dinosaurs and dinosauromorphs by Matthew Baron, David B. Norman and Paul Barrett (2017) found that Nyasasaurus may represent a derived member of Sauropodomorpha most closely related to massospondylids like Massospondylus and Lufengosaurus . [14] In his 2018 thesis on dinosaur interrelationships, Matthew Baron cast doubt on the referral of "Thecodontosaurus" alophos to Nyasasaurus, arguing that SAM-PK-K10654 instead represents a neotheropod due to the lack of skeletal pneumaticity seen in massospondylids. [15]

In 2021, Fernando Novas and colleagues used the aforementioned characteristics shared by Nyasasaurus and Teleocrater—and not by dinosauriforms such as Asilisaurus and Silesaurus—to suggest that a position for Nyasasaurus in the Dinosauriformes is uncertain. However, they elected not to comment further on Nyasasaurus' affinities given the fragmentary nature of the fossils. [10]

See also

Contemporaries

Related Research Articles

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Spondylosoma is a genus of avemetatarsalian archosaur belonging to the clade Aphanosauria from the late Ladinian-age Middle Triassic Lower Santa Maria Formation in Paleorrota Geopark, Brazil.

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

Teleocrater is a genus of avemetatarsalian archosaur from the Middle Triassic Manda Formation of Tanzania. The name was coined by English paleontologist Alan Charig in his 1956 doctoral dissertation, but was only formally published in 2017 by Sterling Nesbitt and colleagues. The genus contains the type and only species T. rhadinus. Uncertainty over the affinities of Teleocrater have persisted since Charig's initial publication; they were not resolved until Nesbitt et al. performed a phylogenetic analysis. They found that Teleocrater is most closely related to the similarly enigmatic Yarasuchus, Dongusuchus, and Spondylosoma in a group that was named the Aphanosauria. Aphanosauria was found to be the sister group of the Ornithodira, the group containing dinosaurs and pterosaurs.

<span class="mw-page-title-main">Dinosauromorpha</span> Clade of reptiles

Dinosauromorpha is a clade of avemetatarsalians that includes the Dinosauria (dinosaurs) and some of their close relatives. It was originally defined to include dinosauriforms and lagerpetids, with later formulations specifically excluding pterosaurs from the group. Birds are the only dinosauromorphs which survive to the present day.

<span class="mw-page-title-main">Avemetatarsalia</span> Clade of archosaur reptiles

Avemetatarsalia is a clade of diapsid reptiles containing all archosaurs more closely related to birds than to crocodilians. The two most successful groups of avemetatarsalians were the dinosaurs and pterosaurs. Dinosaurs were the largest terrestrial animals for much of the Mesozoic Era, and one group of small feathered dinosaurs has survived up to the present day. Pterosaurs were the first flying vertebrates and persisted through the Mesozoic before dying out at the Cretaceous-Paleogene (K-Pg) extinction event. Both dinosaurs and pterosaurs appeared in the Triassic Period, shortly after avemetatarsalians as a whole. The name Avemetatarsalia was first established by British palaeontologist Michael Benton in 1999. An alternate name is Pan-Aves, or "all birds", in reference to its definition containing all animals, living or extinct, which are more closely related to birds than to crocodilians.

Yarasuchus is an extinct genus of avemetatarsalian archosaur that lived during the Anisian stage of the Middle Triassic of India. The genus was named and described in 2005 from a collection of disarticulated but fairly complete fossil material found from the Middle Triassic Yerrapalli Formation. The material is thought to be from two individuals, possibly three, with one being much more complete and articulated than the other. The type and only species is Y. deccanensis. Yarasuchus was a quadruped roughly 2–2.5 metres (6.6–8.2 ft) long, with an elongated neck and tall spines on its vertebrae. Unlike other quadrupedal Triassic reptiles, the limbs and shoulders of Yarasuchus were slender, and more like those of ornithodirans.

Sterling Nesbitt is an American paleontologist best known for his work on the origin and early evolutionary patterns of archosaurs. He is currently an associate professor at Virginia Tech in the Department of Geosciences.

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

Mandasuchus is an extinct genus of loricatan pseudosuchian from the Manda Formation of Tanzania, which dates back to the Anisian stage of the Middle Triassic. Although this genus was first mentioned by Alan Charig in 1956, a formal description was not published until 2018.

<i>Asilisaurus</i> Genus of reptiles (fossil)

Asilisaurus ; from Swahili, asili, and Greek, σαυρος is an extinct genus of silesaurid archosaur. The type species is Asilisaurus kongwe.Asilisaurus fossils were uncovered in the Manda Beds of Tanzania and date back to the early Carnian, making it one of the oldest known members of the Avemetatarsalia. It was the first non-dinosaurian dinosauriform recovered from Africa. The discovery of Asilisaurus has provided evidence for a rapid diversification of avemetatarsalians during the Middle Triassic, with the diversification of archosaurs during this time previously only documented in pseudosuchians.

<span class="mw-page-title-main">Lagerpetidae</span> Extinct family of reptiles

Lagerpetidae is a family of basal avemetatarsalians. Though traditionally considered the earliest-diverging dinosauromorphs, fossils described in 2020 suggest that lagerpetids may instead be pterosauromorphs. Lagerpetid fossils are known from theTriassic of Argentina, Arizona, Brazil, Madagascar, New Mexico, and Texas. They were typically small, although some lagerpetids, like Dromomeron gigas and a specimen from the Santa Rosa Formation attributed to Dromomeron sp., were able to get quite large. Lagerpetid fossils are rare; the most common finds are bones of the hindlimbs, which possessed a number of unique features.

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

Stenaulorhynchus is an extinct genus of hyperodapedontid rhynchosaur known from the Middle Triassic deposits of Tanganyika Territory, Tanzania. It was found in the Lifua Member of the Manda Formation in the Karoo Supergroup. It was named and first described by Sidney Henry Haughton in 1932. The type species is Stenaulorhynchus stockleyi, a beaked herbivore measuring 1–6 meters in length.

<i>Diodorus scytobrachion</i> Extinct species of reptile

Diodorus is a genus of silesaurid dinosauromorph that lived during the Late Triassic in what is now Morocco. Fossils were discovered in the Timezgadiouine Formation of the Argana Basin, and were used to name the new genus and species Diodorus scytobrachion. The genus name honors the mythological king Diodorus and the ancient historian Diodorus Siculus; the specific name is ancient Greek for 'leathery arm' and also honors the mythographer Dionysius Scytobrachion. The holotype specimen is a partial dentary bone (front of the lower jaw), and assigned specimens include isolated teeth, two humeri (upper arm bones), a metatarsal (foot bone), and femur (thigh bone).

<span class="mw-page-title-main">Manda Formation</span>

The Manda Formation is a Middle Triassic (Anisian?) or possibly Late Triassic (Carnian?) geologic formation in Tanzania. It preserves fossils of many terrestrial vertebrates from the Triassic, including some of the earliest dinosauromorph archosaurs. The formation is often considered to be Anisian in age according to general tetrapod biochronology hypotheses and correlations to the Cynognathus Assemblage Zone of South Africa. However, some recent studies cast doubt to this age, suggesting that parts deposits may actually be younger (Carnian) in age.

<span class="mw-page-title-main">Epipophyses</span> Bony projections of neck vertebrae in certain reptiles

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

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

Asperoris is an extinct genus of archosauriform reptile known from the Middle Triassic Manda Beds of southwestern Tanzania. It is the first archosauriform known from the Manda Beds that is not an archosaur. However, its relationships with other non-archosaurian archosauriforms are uncertain. It was first named by Sterling J. Nesbitt, Richard J. Butler and David J. Gower in 2013 and the type species is Asperoris mnyama. Asperoris means "rough face" in Latin, referring to the distinctive rough texture of its skull bones.

<span class="mw-page-title-main">Usili Formation</span> Geologic formation in Tanzania

The Usili Formation is a Late Permian geologic formation in Tanzania. It preserves fossils of many terrestrial vertebrates from the Permian, including temnospondyls, pareiasaurs, therapsids and the archosauromorph Aenigmastropheus.

Nundasuchus is an extinct genus of crurotarsan, possibly a suchian archosaur related to Paracrocodylomorpha. Remains of this genus are known from the Middle Triassic Manda beds of southwestern Tanzania. It contains a single species, Nundasuchus songeaensis, known from a single partially complete skeleton, including vertebrae, limb elements, osteoderms, and skull fragments.

Aphanosauria is an extinct group of reptiles distantly related to dinosaurs. They are at the base of a group known as Avemetatarsalia, one of two main branches of archosaurs. The other main branch, Pseudosuchia, includes modern crocodilians. Aphanosaurs possessed features from both groups, indicating that they are the oldest and most primitive known clade of avemetatarsalians, at least in terms of their position on the archosaur family tree. Other avemetatarsalians include the flying pterosaurs, small bipedal lagerpetids, herbivorous silesaurids, and the incredibly diverse dinosaurs, which survive to the present day in the form of birds. Aphanosauria is formally defined as the most inclusive clade containing Teleocrater rhadinus and Yarasuchus deccanensis but not Passer domesticus or Crocodylus niloticus. This group was first recognized during the description of Teleocrater. Although only known by a few genera, Aphanosaurs had a widespread distribution across Pangaea in the Middle Triassic. They were fairly slow quadrupedal long-necked carnivores, a biology more similar to basal archosaurs than to advanced avemetatarsalians such as pterosaurs, lagerpetids, and early dinosaurs. In addition, they seemingly possess 'crocodile-normal' ankles, showing that 'advanced mesotarsal' ankles were not basal to the whole clade of Avemetatarsalia. Nevertheless, they possessed elevated growth rates compared to their contemporaries, indicating that they grew quickly, more like birds than other modern reptiles. Despite superficially resembling lizards, the closest modern relatives of aphanosaurs are birds.

References

  1. 1 2 3 4 5 6 7 8 9 10 11 12 13 Nesbitt, S. J.; Barrett, P. M.; Werning, S.; Sidor, C. A.; Charig, A. J. (2013). "The oldest dinosaur? A Middle Triassic dinosauriform from Tanzania". Biol. Lett. 9 (1): 20120949. doi:10.1098/rsbl.2012.0949. PMC   3565515 . PMID   23221875.
  2. 1 2 Nesbitt, S; Butler, R; Ezcurra, M; Charig, A; Barrett, P (2020-07-08). "The anatomy of Teleocrater Rhadinus, an early avemetatarsalian from the lower portion of the Lifua Member of the Manda Beds (Middle Triassic) (project)". MorphoBank datasets. doi:10.7934/p3173. S2CID   226195075.
  3. 1 2 Marsicano, Claudia A.; Irmis, Randall B.; Mancuso, Adriana C.; Mundil, Roland; Chemale, Farid (2015-12-07). "The precise temporal calibration of dinosaur origins". Proceedings of the National Academy of Sciences. 113 (3): 509–513. doi: 10.1073/pnas.1512541112 . ISSN   0027-8424. PMC   4725541 . PMID   26644579.
  4. 1 2 Ottone, Eduardo G.; Monti, Mariana; Marsicano, Claudia A.; de la Fuente, Marcelo S.; Naipauer, Maximiliano; Armstrong, Richard; Mancuso, Adriana C. (December 2014). "A new Late Triassic age for the Puesto Viejo Group (San Rafael depocenter, Argentina): SHRIMP U–Pb zircon dating and biostratigraphic correlations across southern Gondwana". Journal of South American Earth Sciences. 56: 186–199. Bibcode:2014JSAES..56..186O. doi:10.1016/j.jsames.2014.08.008. hdl: 11336/85022 . ISSN   0895-9811.
  5. ↑ Charig, A.J., 1956, New Triassic archosaurs from Tanganyika, including Mandasuchus and Teleocrater. Dissertation, Cambridge University
  6. ↑ Charig, A. J. (1967). "Archosauria," in The Fossil Record: A Symposium with Documentation, Geological Society of London pp 708–718
  7. ↑ White, T.E. (1973). "Catalogue of the genera of dinosaurs". Annals of the Carnegie Museum. 44: 117–155. doi: 10.5962/p.243870 . S2CID   91935861.
  8. ↑ Stockley, G.M. (1932). "The geology of the Ruhuhu coalfields, Tanganyika Territory". The Quarterly Journal of the Geological Society of London. 88 (1–4): 610–622. doi:10.1144/gsl.jgs.1932.088.01-04.20. S2CID   129371059.
  9. ↑ Haughton, S.H. (1932). "On a collection of Karroo vertebrates from Tanganyika Territory". The Quarterly Journal of the Geological Society of London. 88 (1–4): 634–671. doi:10.1144/gsl.jgs.1932.088.01-04.22. S2CID   128417120.
  10. 1 2 Novas, F.E.; Agnolin, F.L.; Ezcurra, M.D.; Temp Müller, R.; Martinelli, A.G.; Langer, M.C. (2021). "Review of the fossil record of early dinosaurs from South America, and its phylogenetic implications". Journal of South American Earth Sciences. 110: 103341. Bibcode:2021JSAES.11003341N. doi:10.1016/j.jsames.2021.103341.
  11. ↑ Ginsburg, L., 1986, "Régressions marines et extinction des Dinosaures", Les Dinosaures de la Chine à la France, Colloque International de Paléontologie, Toulouse, France, 2-6 Septembre 1985; Muséum d'Histoire Naturelle de Toulouse, Toulouse pp 141-149
  12. ↑ Sterling J. Nesbitt (2011). "The Early Evolution of Archosaurs: Relationships and the Origin of Major Clades". Bulletin of the American Museum of Natural History. 352: 1–292. doi: 10.1206/352.1 . hdl:2246/6112. S2CID   83493714.
  13. ↑ "New contender for oldest dinosaur". 4 December 2012. Retrieved 4 December 2012.
  14. ↑ Baron, M.G., Norman, D.B., and Barrett, P.M. (2017). A new hypothesis of dinosaur relationships and early dinosaur evolution. Nature, 543: 501–506. doi : 10.1038/nature21700
  15. ↑ Baron, Matthew (5 February 2018). The Origin and Early Evolution of the Dinosauria (PhD). Retrieved 7 April 2022.

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