Nyasasaurus
| Nyasasaurus Temporal range: Middle Triassic,
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| Approximation of animal based on partial skeleton shown in black (first specimen, six vertebrae and a humerus) and blue (second specimen, three cervical vertebrae). | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Genus: | †Nyasasaurus |
| Species: | †N. parringtoni
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| Binomial name | |
| †Nyasasaurus parringtoni Nesbitt et al., in press
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| Synonyms | |
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Nyasasaurus (meaning "Lake Nyasa lizard") is an extinct genus of dinosauriform reptile from the Middle Triassic Manda Beds of Tanzania that may be the earliest known dinosaur. The type species N. parringtoni was first described in 1956 in the doctoral dissertation of English paleontologist Alan J. Charig, but it was not formally described until 2012. Previously, the oldest record of dinosaurs was from Argentina and dated back to the late Carnian stage, about 230 million years ago (Ma). Nyasasaurus comes from a deposit that dates back to the Anisian Stage, meaning that it predates other early dinosaurs by about 15 million years.
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 and six vertebrae. A second specimen, SAM-PK-K10654 consisting of five 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. Because these characteristics are not unique to the two specimens (in other words, they are not autapomorphies), they do not by themselves provide sufficient evidence for grouping NHMUK R6856 and SAM-PK-K10654 under the same species. The authors of the 2012 description of Nysasaurus used a second line of evidence, the similar positions of the two specimens on evolutionary trees, to justify their placement in the same species.[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 Megapnosaurus than it does of dinosaur ancestors, suggesting that Nyasasaurus was closer to the ancestry of dinosaurs than were other archosaurs at the time.[1]
History of study
In the 1930s, fossils of Nyasasaurus were recovered from the Lifua Member of the Manda beds 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 dissertation and referred to as "Specimen 50b".[2] In 1967 Charig published the name Nyasasaurus parringtoni, in a review of the Archosauria,[3] but without description so that it was commonly considered a nomen nudum; the dissertation also was never published. The generic name referred to Lake Nyasa and the specific name honouring Parrington. In 2012 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 parringtoni.[1] The generic name is occasionally misspelled as "Nyasaurus", as by Theodore Elmer White in 1973.[4]
Relationships
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, and within Dinosauriformes, the group that includes birds, non-avian dinosaurs, and several non-dinosaurian groups from the Triassic.[1]
Nyasasaurus was suggested to have been a primitive prosauropod dinosaur in 1986,[5] but this hypothesis was disputed. The 2012 analysis suggests that Nyasasaurus may be the earliest known dinosaur, dating to the late Anisian Stage, about 243 million years ago, 10 to 15 million years older than any previously described dinosaur, such as Herrerasaurus.[1][6] Dinosaur affinities are supported by the long deltopectoral crest on the humerus, with a deflected top; the elongated neck vertebrae with hollowed-out sides; and, perhaps, the possession of three sacral vertebrae instead of two.[citation needed]
Nyasasaurus is likely either a basal dinosaur or close to Dinosauria. Other phylogenetic analyses have indicated that the sister taxon or most closely related group to Dinosauria is a family of herbivorous dinosauriforms called Silesauridae. The fossil record of silesaurids dates back to the late Anisian (the silesaurid Asilisaurus kongwe is also known from the Manda Beds), suggesting that the first dinosaurs also appeared around this time. Before Nyasasaurus was recognized as a possible dinosaur, a long ghost lineage existed between the earliest dinosaurs and silesaurids.[citation needed]
The 2012 study of Nyasasaurus 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.[citation needed] The following cladogram depicts these possibilities:
| Archosauria |
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References
- ^ a b c d e f Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1098/rsbl.2012.0949, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with
|doi=10.1098/rsbl.2012.0949instead. - ^ Charig, A.J., 1956, New Triassic archosaurs from Tanganyika, including Mandasuchus and Teleocrater. Dissertation, Cambridge University
- ^ Charig, A. J. (1967). "Archosauria," in The Fossil Record: A Symposium with Documentation, Geological Society of London pp 708–718
- ^ White T.E., 1973, "Catalogue of the genera of dinosaurs", Annals of the Carnegie Museum 44: 117–155
- ^ 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
- ^ "New contender for oldest dinosaur". 4 December 2012. Retrieved 4 December 2012.
- Lambert, David (1994). The Encyclopedia of Dinosaurs. Bloomsbury Books p 80.
External links
- Oldest Dinosaur Found from Discovery.com
- Discussion of "Nyasasaurus" from the Dinosaur Mailing List
- The oldest dinosaur: working from scraps - The Economist