Masiakasaurus

Masiakasaurus
	Skull of Masiakasaurus
Temporal occurrence
	Upper Cretaceous ( Campanium )
	83.6 to 72 million years
Locations
	Mahajanga , Madagascar ( Maevarano Formation );
Systematics
	Lizard dinosaur (Saurischia)
	Theropoda
	Ceratosauria
	Abelisauroidea
	Noasauridae
	Masiakasaurus
Scientific name
	Masiakasaurus
	Sampson et al., 2001
Art
	Masiakasaurus knopfleri;

Masiakasaurus is a genus of small theropod dinosaur from the Upper Cretaceous Madagascar . It is the best known member of the Noasauridae , a very little known group within the Ceratosauria . The teeth were characteristic of this two-legged dinosaur - the foremost teeth were directed forward. This unique feature suggests a specialized diet; so the foremost teeth could possibly have been used to pack fish or insects. The only species is Masiakasaurus knopfleri .

Find, research history and naming

Masiakasaurus is known for fossils from 30 different sites, which are located near the village of Berivotra in northwestern Madagascar. The fossils recovered in 2001, 2003, 2005 and 2007 from expeditions of the Mahajanga Basin Project . The numerous individual finds cover a total of around 65% of the skeleton; important parts of the skeleton still missing include some skull bones, various bones of the hand and the forearm.

All fossils come from the Upper Cretaceous ( Campanium ) of the Maevarano Formation - this formation is known for its rich fossil fauna and contained, among other things, the fossils of the Abelisaurid Majungasaurus , the Dromaeosaurid Rahonavis , the Titanosaur Rapetosaurus as well as various genera of Crocodylomorpha and fossil birds.

Masiakasaurus was scientifically described in 2001 by three paleontologists from the University of Utah - Scott Sampson , Matthew Carrano and Catherine Forster - in the journal Nature . A more detailed description followed in 2002. In 2011, a description of other fossils discovered since 2002 appeared.

The name Masiakasaurus means something like "malignant lizard" ( Malagasy masiaka - "malignant", Greek sauros - "lizard"). The second part of the species name, knopfleri , is named after the British singer and songwriter Mark Knopfler , " whose music inspired expedition crews ".

features

Live graphic representation of Masiakasaurus

Masiakasaurus was a small, two-legged running dinosaur that reached a body length of about 2 m. The eye sockets were large while the muzzle was long, which gave the skull a long and low profile. In plan view, the snout tapers to the front. These features follow the blueprint typical of most primitive (basal) theropods. The front edge of the frontal bone (frontal) marks the widest point of the skull, behind this point the sides of the skull run roughly parallel. The lower jaw, especially the connection points between the front, tooth-bearing part of the lower jaw (dental) and the rear jawbone, resembles those of the Abelisauridae : For example, the mandibular window enclosed by this jawbone was very large.

Masiakasaurus differed from all other known theropods by the dentition: The tooth-bearing edges of the upper and lower jaw were not parallel to each other, but were curved upwards and downwards in the front section of the snout, which resulted in the foremost teeth in the lower - and the upper jaw were directed forward. In addition, the teeth were distinctly heterodontic , that is, the shape of the teeth varied along the row of teeth. In the paired lower jaw, the first four teeth were directed forward, with the first tooth having an angle of only 10 ° relative to the horizontal. The forward-facing teeth of the lower jaw were long and weakly spoon-shaped, with their tips sloping backwards like a hook. The cutting edges were weakly serrated. The rear teeth were laterally flattened, with the cutting edges more serrated.

The neck was long compared to representatives of the Abelisauridae, but about as long as that of many other smaller theropods such as Elaphrosaurus . Almost all theropods have an S-shaped neck. In Masiakasaurus, however, the spine was straight in the shoulder area, which is indicated by the only slight variation in the vertebral bodies in this section of the spine. This unusual feature suggests that the front half of the neck was curved while the back half joined the shoulder and front back areas in a horizontal line. Only in the area of the posterior vertebrae and the sacrum did the back tilt slightly upwards.

While representatives of the Abelisauridae had strongly receded and presumably functionless arms, the arms of Masiakasaurus were not regressed and resembled those of typical basal (original) theropods. The upper arm bone (humerus) was long and slender. The number of hand rays cannot be determined from the fossils found; However, related genera had four rays, which is why this number is also assumed for Masiakasaurus (principle of phylogenetic clasps).

The fragmentary find of the related genus Noasaurus includes an enlarged, strongly curved claw that resembles the "sickle claws" of the Deinonychosauria . In fact, this claw has been described as a foot claw, although recent studies show that it was actually a hand claw. Whether Masiakasaurus had a similar claw is unknown - although the phalanx of Masiakasaurus , which was steered with the claws, had a similar morphology to the phalanx of Noasaurus , which was steered with the enlarged claw.

Systematics

Initially Masiakasaurus was classified as a basal representative of the Abelisauroidea , which was related to Laevisuchus and Noasaurus . In 2002, Carrano and colleagues assigned these three genera to the Noasauridae , a group within the Abelisauroidea that is compared to the Abelisauridae as a sister group . The relationships within the Noasauridae have not yet been resolved; In phylogenetic analyzes, the representatives of this group thus always form a polytomy .

Paleobiology

On the basis of the limb bones found, two different morphs can be distinguished - a “robust” and a “graceful” mophe. The robust Morph differs from the graceful Morph in that it has enlarged attachment points for muscles and ligaments ; In addition, the shinbone (tibia) was fused with the tarsal bones (tarsalia) in the robust morph. Carrano and colleagues (2002) suspect that this variation could possibly be gender dimorphism . The possibility that this variation is due to different populations cannot be ruled out, but it seems unlikely, since most of the fossils come from the same site.

The forward-facing front teeth were believed to be useful as a precision tool for packing small pieces of booty, but were not suitable for tearing or cutting, as indicated by their orientation, rounded tips, and weak sawing. The rear teeth, on the other hand, followed the blueprint typical of theropods and were flattened, curved and sawn on both sides, which indicates a function as a cutting tool. Carrano and colleagues (2002) note that this combination of traits could potentially identify Masiakasaurus as an insect eater or a fish eater.

One of the found Rabe legs (coracoid) has a series of small openings. These could be unhealed bite marks, either inflicted by a predator or a scavenger. However, these openings may also be the result of an infection, as indicated by the raised edge of one of the openings.

supporting documents

literature

Scott D. Sampson, Matthew T. Carrano, Catherine A. Forster: A bizarre predatory dinosaur from the Late Cretaceous of Madagascar. In: Nature . Vol. 409, No. 6819, 2001, pp. 504-506, doi : 10.1038 / 35054046 .
Matthew T. Carrano, Scott D. Sampson, Catherine A. Forster: The Osteology of Masiakasaurus knopfleri, a small Abelisauroid (Dinosauria: Theropoda) from the Late Cretaceous of Madagascar. In: Journal of Vertebrate Paleontology. Vol. 22, No. 3, 2002, ISSN 0272-4634 , pp. 510-534, doi : 10.1671 / 0272-4634 (2002) 022 [0510: TOOMKA] 2.0.CO; 2 .
Matthew T. Carrano, Mark A. Loewen, Joseph JW Sertich: New materials of Masiakasaurus knopfleri Sampson, Carrano, and Forster, 2001, and implications for the morphology of the Noasauridae (Theropoda: Ceratosauria) (= Smithsonian Contributions to Paleobiology. No. 95, ISSN 0081-0266 ). Smithsonian Institution Scholarly Press, Washington DC 2011, online .

Individual evidence

^ Gregory S. Paul : The Princeton Field Guide To Dinosaurs. Princeton University Press, Princeton NJ et al. 2010, ISBN 978-0-691-13720-9 , p. 82, online .
↑ ^a ^b Carrano et al. 2011 , pp. 1–3
↑ ^a ^b ^c Sampson et al. 2001
↑ Carrano et al. 2002
↑ Carrano et al. 2011
↑ Carrano et al. 2002 , p. 512
↑ Carrano et al. 2011 , pp. 3–12
↑ ^a ^b Carrano et al. 2002 , pp. 510-511
↑ ^a ^b Carrano et al. 2011 , p. 35
↑ Carrano et al. 2011 , p. 28
↑ Carrano et al. 2002 , p. 527
↑ ^a ^b Carrano et al. 2002 , pp. 127-129
↑ Carrano et al. 2011 , p. 24

[paul_10-1] Gregory S. Paul : The Princeton Field Guide To Dinosaurs. Princeton University Press, Princeton NJ et al. 2010, ISBN 978-0-691-13720-9 , p. 82, online .

[carrano_11_1-3-2] Carrano et al. 2011 , pp. 1–3

[sampson_01-3] Sampson et al. 2001

[carrano_02-4] Carrano et al. 2002

[carrano_11-5] Carrano et al. 2011

[carrano_02_512-6] Carrano et al. 2002 , p. 512

[carrano_11_3-12-7] Carrano et al. 2011 , pp. 3–12

[carrano_02_510-511-8] Carrano et al. 2002 , pp. 510-511

[carrano_11_35-9] Carrano et al. 2011 , p. 35

[carrano_11_28-10] Carrano et al. 2011 , p. 28

[carrano_02_527-11] Carrano et al. 2002 , p. 527

[carrano_02_127-129-12] Carrano et al. 2002 , pp. 127-129

[carrano_11_24-13] Carrano et al. 2011 , p. 24