Masiakasaurus
Masiakasaurus | |
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Reconstructed skeleton, Royal Ontario Museum, Toronto, Canada | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Clade: | Dinosauria |
Clade: | Saurischia |
Clade: | Theropoda |
Clade: | † Abelisauria
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Family: | †Noasauridae |
Subfamily: | † Noasaurinae
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Genus: | †Masiakasaurus Sampson et al., 2001 |
Species: | †M. knopfleri
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Binomial name | |
†Masiakasaurus knopfleri Sampson et al., 2001
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Masiakasaurus is a
Masiakasaurus lived around 70 million years ago, along with animals such as Majungasaurus, Rapetosaurus, and Rahonavis. Masiakasaurus was a member of the group Noasauridae, small predatory ceratosaurs found primarily in South America.
History
Remains of Masiakasaurus have been found in the Late Cretaceous Maevarano Formation in northwestern Madagascar and were first described in the journal Nature in 2001. Fragmentary bones comprising around 40% of the skeleton were collected near the village of Berivotra. Several parts of the skull, including the distinctive teeth, were found. The humerus (upper arm bone), pubis, hindlimbs, and several vertebrae were also collected.[1]
In 2011, additional specimens of Masiakasaurus were described. The braincase, premaxilla, facial bones, ribcage, portions of the hands and pectoral girdle (coracoid), and much of the cervical and dorsal vertebral column were described for the first time. The discovery of this new material clarified many aspects of noasaurid anatomy and made the genus among the best known dinosaurs.[4] The new finds did however not allow for a detailed study of its evolutionary relationships among ceratosaurs. With the new material, around 65% of the skeleton is currently known.[5]
Description
Skull
The most distinctive characteristic of Masiakasaurus is the forward-projecting, or procumbent, front teeth. The teeth are
Vertebrae
The neck is relatively narrow in comparison to abelisaurids and bear stout neck ribs. While many theropods have s-shaped necks, the ribs would make the neck rather stiff in Masiakasaurus, and the back of the neck is positioned almost horizontally, giving it only a slighter curve. Like those of other abelisauroids, the vertebrae are heavily pneumaticized, or hollowed, and have relatively short neural spines. Pneumaticity is limited to the neck and foremost back vertebrae, however. Pneumatic cavities are also present in the braincase.[5]
Forelimbs
As in other ceratosaurs, the shoulder blade (scapula) and shoulder girdle fuse into a single bone, the scapulocoracoid. This bone is very large and broad, even compared to the condition in other ceratosaurs. The scapula portion (above the glenoid, or arm socket) tapers towards the back while the coracoid portion (below the glenoid) is expanded into a curved blade-like structure. While abelisaurids have arms that are extremely reduced in size, Masiakasaurus and other noasaurids had longer forelimbs. The humerus is slender and known bones of the hand are relatively short. The related genus Noasaurus has a large and curved raptorial ungual (claw) which was originally interpreted as a sickle-like foot claw as in dromaeosaurids such as Velociraptor. More recently, this has been re-evaluated as a claw of the hand. The penultimate phalanx, the finger bone that immediately precedes the raptorial ungual in Noasaurus, is also known in Masiakasaurus and has a similar appearance. The enlarged ungual, however, is unknown in Masiakasaurus.[5] It is assumed that members of this genus had four fingers, with the middle two fingers being the longest as in other ceratosaurians.
Classification
In its initial 2001 description, Masiakasaurus was classified as a basal abelisauroid related to Laevisuchus and Noasaurus, two poorly known genera named in 1933 and 1980, respectively.[1] In the following year, Carrano et al. (2002) placed Masiakasaurus along with Laevisuchus and Noasaurus in the family Noasauridae. They conducted a phylogenetic analysis of abelisauroids using characteristics from Masiakasaurus. Below is a cladogram from an updated version of their analysis showing the phylogenetic placement of Masiakasaurus.[7]
Abelisauroidea |
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Paleobiology
Carrano et al. (2002) distinguished two forms of Masiakasaurus, a robust form and a gracile form. The robust morph includes specimens with thicker bones and more pronounced projections for the attachment of ligaments and muscles. The gracile form includes specimens that are more slender and have less pronounced muscle attachments. It also has unfused tibiae, unlike the fused tibiae of the robust form. These two varieties may be an indication of sexual dimorphism in Masiakasaurus, but they may also represent two distinct populations.[6]
One specimen of Masiakasaurus, a right scapulocoracoid, bears holes that may be puncture marks from predation or scavenging. Majungasaurus, a large abelisaurid from the Maevarano Formation, may have preyed upon Masiakasaurus.[8] The holes may also have been the result of an infection.[5]
Diet
The procument front teeth of Masiakasaurus were likely an adaptation for grasping small prey. They would have been unsuitable for tearing larger food apart. In the front of the jaws, carinae are restricted to the base of the teeth and would not have been used to tear prey. The back teeth, however, share the same general characteristics as those of most other theropods, suggesting that they served a similar function in Masiakasaurus such as cutting and slicing.[6]
Several feeding behaviors have been proposed for Masiakasaurus on the basis of its unusual dentition. Because the front teeth would have been well suited for grasping, Masiakasaurus may have consumed small vertebrates, invertebrates, and possibly even fruits.[6]
Growth
In 2013, Lee and O'Connor observed that Masiakasaurus would be a good subject for an analysis of theropod growth, considering that there is an abundance of fossil material to examine from a broad range of
See also
References
- ^ S2CID 205013285.
- .
- ISBN 9780691137209.
- ^ Switek, Brian. "Masiakasaurus Gets a Few Touch-Ups". Smithsonian.com. Smithsonian. Retrieved 21 July 2014.
- ^
- ^ S2CID 85655323.
- S2CID 4389583.
- ^ Andrew H. Lee & Patrick M. O’Connor (2013) Bone histology confirms determinate growth and small body size in the noasaurid theropod Masiakasaurus knopfleri. Journal of Vertebrate Paleontology 33(4): 865-876.[2]
External links
- The Geological Society of London (25 January 2001). "Palaeontologists in dire straits name dinosaur for the Sultan of Swing". Retrieved 7 October 2005.