Masiakasaurus
Encyclopedia
Masiakasaurus was a small predatory theropod dinosaur
from the Late Cretaceous
of Madagascar
. It was named in 2001 by Scott D. Sampson
, Matthew Carrano, and Catherine A. Forster. Unlike most theropods, the front teeth of Masiakasaurus projected forward instead of straight down. This unique dentition suggests that Masiakasaurus had a specialized diet, perhaps including fish and other small prey. Other bones of the skeleton indicate that Masiakasaurus was bipedal, with much shorter forelimbs than hindlimbs. Masiakasaurus had an estimated adult body length of around 2 meters (about 6–7 feet).
Masiakasaurus lived around 70 million years ago, along with animals such as Majungasaurus
, Rapetosaurus
, and Rahonavis
. Masiakasaurus was closely related to the noasaurs, small predatory dinosaurs found in South America
.
In Malagasy
, masiaka means "vicious"; thus, the genus name means "vicious lizard". The type species
, Masiakasaurus knopfleri, was named after the musician Mark Knopfler
, "whose music inspired expedition crews".
Masiakasaurus was a small-bodied ceratosaur that grew up to around 1.8 to 2 m (5.9 to 6.6 ft) in length. The most distinctive characteristic of Masiakasaurus is its forward-projecting, or procumbent, front teeth. The teeth are heterodont
, meaning that they have different shapes along the jaw. The first four dentary teeth of the lower jaw project forward, with the first tooth angled only 10° from horizontal. These teeth are long and spoon-shaped with hooked edges. They have carinae, or sharp edges, that are weakly serrated. Serrations are more evident in the posterior teeth, which are also recurved and laterally compressed. The margin of the dentary curves downward so that the tooth sockets of the front teeth are directed forward. The front teeth of the upper jaw are also procumbent, and the margin of the premaxilla
curves slightly upward to direct them outward.
Unlike the skulls of abelisaurids, which are very deep, the skull of Masiakasaurus is long and low. The lacrimal
and postorbital bones around the eye are textured with bumpy projections. Not including the highly modified jaws and teeth, the skull of Masiakasaurus possesses many general ceratosaurian characteristics. Overall, its morphology is intermediate between abelisaurids and more basal ceratosaurs.
The neck is relatively narrow in comparison to abelisaurids. While many theropods have s-shaped necks, the back of the neck of Masiakasaurus is positioned almost horizontally, giving it 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.
The scapulocoracoid
, a bone that makes up the pectoral girdle, is large and broad. While abelisaurids have arms that are extremely reduced in size, Masiakasaurus and other noasaurids had longer forelimbs. The humerus is slender and the bones of the hand are relatively short. The related genus Noasaurus has a raptorial ungual
which was originally interpreted as a sickle-like claw on the foot, but has more recently been considered a claw of the hand. The penultimate phalanx, a 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.
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, pubis, hind limbs, and several vertebrae were also collected.
In 2011, additional specimens of Masiakasaurus were described. The braincase, premaxilla, facial bones, ribcage, portions of the hands and pectoral girdle, 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, but did not allow for a detailed study of its evolutionary relationships among ceratosaurs
. With the new material, around 65% of the skeleton is currently known.
abelisauroid related to Laevisuchus
and Noasaurus, two poorly-known genera named in 1933 and 1980, respectively. 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 their study showing the phylogenetic placement of Masiakasaurus:
e, 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.
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. The holes may also have been the result of an infection.
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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.
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. It may also have been piscivorous, catching fish with the ends of its jaws and cutting and tearing them with its back teeth.
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
from the Late Cretaceous
Late Cretaceous
The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...
of Madagascar
Madagascar
The Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...
. It was named in 2001 by Scott D. Sampson
Scott D. Sampson
Scott D. Sampson is a paleontologist and chief curator of the Utah Museum of Natural History. Sampson is notable for his work on the carnivorous theropod dinosaurs Majungasaurus and Masiakasaurus and his extensive research into the Late Cretaceous Period, particularly in...
, Matthew Carrano, and Catherine A. Forster. Unlike most theropods, the front teeth of Masiakasaurus projected forward instead of straight down. This unique dentition suggests that Masiakasaurus had a specialized diet, perhaps including fish and other small prey. Other bones of the skeleton indicate that Masiakasaurus was bipedal, with much shorter forelimbs than hindlimbs. Masiakasaurus had an estimated adult body length of around 2 meters (about 6–7 feet).
Masiakasaurus lived around 70 million years ago, along with animals such as Majungasaurus
Majungasaurus
Majungasaurus is a genus of abelisaurid theropod dinosaur that lived in Madagascar from 70 to 65.5 million years ago, at the end of the Cretaceous Period. Only one species has been identified...
, Rapetosaurus
Rapetosaurus
Rapetosaurus is a genus of sauropod dinosaur that lived in Madagascar from 70 to 65 million years ago, at the end of the Cretaceous Period. Only one species Rapetosaurus is a genus of sauropod dinosaur that lived in Madagascar from 70 to 65 million years ago, at the end of the Cretaceous Period....
, and Rahonavis
Rahonavis
Rahonavis is a genus of bird-like dinosaur from the Late Cretaceous of what is now northwestern Madagascar. It is known from a partial skeleton found in Maevarano Formation rocks at a quarry near Berivotra, Mahajanga Province...
. Masiakasaurus was closely related to the noasaurs, small predatory dinosaurs found in South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
.
In Malagasy
Malagasy language
Malagasy is the national language of Madagascar, a member of the Austronesian family of languages. Most people in Madagascar speak it as a first language as do some people of Malagasy descent elsewhere.-History:...
, masiaka means "vicious"; thus, the genus name means "vicious lizard". The type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
, Masiakasaurus knopfleri, was named after the musician Mark Knopfler
Mark Knopfler
Mark Freuder Knopfler, OBE is a Scottish-born British guitarist, singer, songwriter, record producer and film score composer. He is best known as the lead guitarist, vocalist, and songwriter for the British rock band Dire Straits, which he co-founded in 1977...
, "whose music inspired expedition crews".
Description
Heterodont
The anatomical term heterodont refers to animals which possess more than a single tooth morphology. For example, members of the Synapsida generally possess incisors, canines , premolars, and molars. The presence of heterodont dentition is evidence of some degree of feeding/hunting specialization...
, meaning that they have different shapes along the jaw. The first four dentary teeth of the lower jaw project forward, with the first tooth angled only 10° from horizontal. These teeth are long and spoon-shaped with hooked edges. They have carinae, or sharp edges, that are weakly serrated. Serrations are more evident in the posterior teeth, which are also recurved and laterally compressed. The margin of the dentary curves downward so that the tooth sockets of the front teeth are directed forward. The front teeth of the upper jaw are also procumbent, and the margin of the premaxilla
Premaxilla
The incisive bone is the portion of the maxilla adjacent to the incisors. It is a pair of small cranial bones at the very tip of the jaws of many animals, usually bearing teeth, but not always. They are connected to the maxilla and the nasals....
curves slightly upward to direct them outward.
Unlike the skulls of abelisaurids, which are very deep, the skull of Masiakasaurus is long and low. The lacrimal
Lacrimal bone
The lacrimal bone, the smallest and most fragile bone of the face, is situated at the front part of the medial wall of the orbit. It has two surfaces and four borders.-Lateral or orbital surface:...
and postorbital bones around the eye are textured with bumpy projections. Not including the highly modified jaws and teeth, the skull of Masiakasaurus possesses many general ceratosaurian characteristics. Overall, its morphology is intermediate between abelisaurids and more basal ceratosaurs.
The neck is relatively narrow in comparison to abelisaurids. While many theropods have s-shaped necks, the back of the neck of Masiakasaurus is positioned almost horizontally, giving it 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.
The scapulocoracoid
Scapulocoracoid
The Scapulocoracoid is the unit of the pectoral girdle that contains the coracoid and scapula.The coracoid itself is a beak-shaped bone that is commonly found in most vertebrates with a few exceptions.The scapula is commonly known as the shoulder blade...
, a bone that makes up the pectoral girdle, is large and broad. While abelisaurids have arms that are extremely reduced in size, Masiakasaurus and other noasaurids had longer forelimbs. The humerus is slender and the bones of the hand are relatively short. The related genus Noasaurus has a raptorial ungual
Ungual
An ungual is a highly modified distal toe bone which ends in a hoof, claw, or nail. Elephants and other ungulates have ungual phalanges, as did the sauropods and horned dinosaurs. A claw is a highly modified ungual phalange.As an adjective, ungual means related to nail, as in periungual .-External...
which was originally interpreted as a sickle-like claw on the foot, but has more recently been considered a claw of the hand. The penultimate phalanx, a 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.
History
Remains of Masiakasaurus have been found in the Late Cretaceous Maevarano FormationMaevarano Formation
The Maevarano Formation is an Upper Cretaceous sedimentary rock formation found in the Mahajanga Province of northwestern Madagascar. It is most likely Maastrichtian in age, and records a seasonal, semiarid environment with rivers that had greatly varying discharges...
in northwestern Madagascar and were first described in the journal Nature
Nature (journal)
Nature, first published on 4 November 1869, is ranked the world's most cited interdisciplinary scientific journal by the Science Edition of the 2010 Journal Citation Reports...
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, pubis, hind limbs, and several vertebrae were also collected.
In 2011, additional specimens of Masiakasaurus were described. The braincase, premaxilla, facial bones, ribcage, portions of the hands and pectoral girdle, 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, but did not allow for a detailed study of its evolutionary relationships among ceratosaurs
Ceratosauria
Ceratosaurs are members of a group of theropod dinosaurs defined as all theropods sharing a more recent common ancestry with Ceratosaurus than with birds. There is presently no universally agreed upon listing of species or diagnostic characters of Ceratosauria, though they were less derived...
. With the new material, around 65% of the skeleton is currently known.
Classification
In its initial 2001 description, Masiakasaurus was classified as a basalBasal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
abelisauroid related to Laevisuchus
Laevisuchus
Laevisuchus is a genus of abelisauroid theropod dinosaur from the Late Cretaceous.Its remains were discovered by Charles Alfred Matley near Jabalpur in Maastrichtian deposits in the Lameta Formation in India, and named and described by paleontologists Friedrich von Huene and Matley in 1933. The...
and Noasaurus, two poorly-known genera named in 1933 and 1980, respectively. 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
Cladogram
A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...
from their study showing the phylogenetic placement of Masiakasaurus:
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 tibiaTibia
The tibia , shinbone, or shankbone is the larger and stronger of the two bones in the leg below the knee in vertebrates , and connects the knee with the ankle bones....
e, unlike the fused tibiae of the robust form. These two varieties may be an indication of sexual dimorphism
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
in Masiakasaurus, but they may also represent two distinct populations.
One specimen of Masiakasaurus, a right scapulocoracoid, bears holes that may be puncture marks from predation or scavenging. Majungasaurus
Majungasaurus
Majungasaurus is a genus of abelisaurid theropod dinosaur that lived in Madagascar from 70 to 65.5 million years ago, at the end of the Cretaceous Period. Only one species has been identified...
, a large abelisaurid from the Maevarano Formation, may have preyed upon Masiakasaurus. The holes may also have been the result of an infection.
Diet
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. It may also have been piscivorous, catching fish with the ends of its jaws and cutting and tearing them with its back teeth.