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Mahakala (dinosaur)
Encyclopedia
Mahakala is a genus
of basal
dromaeosaurid
dinosaur
from the Campanian
-age (about 80 million years ago) Upper Cretaceous Djadokhta Formation of Ömnögov
, Mongolia
. It is based on a partial skeleton found in the Gobi Desert
. Mahakala was a small dromaeosaurid (approximately 70 centimeters long (28 in)), and its skeleton shows features that are also found in early troodontids
and avialans
. Despite its late appearance, it is among the most basal dromaeosaurids. Its small size, and the small size of other basal deinonychosauria
ns, suggests that small size appeared before flight capability in bird
s.
Mahakala is based on IGM 100/1033, a partial skeleton including skull bones, vertebrae, limb bones, and portions of the pelvis
and shoulder girdle. Although this individual was small, comparable in size to Archaeopteryx
, Caudipteryx
, and Mei
, it was close to adulthood. This genus can be distinguished from other paravians
(dromaeosaurids, troodontids, and birds) by details of the ulna
, thighbone
, ilium
, and tail vertebrae. Like Archaeopteryx and derived dromaeosaurids, but unlike basal troodontids and other dromaeosaurids, the middle (third) metatarsal
was not compressed, suggesting that the uncompressed version was the basal version. It had a typical dromaeosaurid form of the second toe, with an expanded claw. Mahakala also had very short forelimbs compared to other Dromaeosaurids.
performed by Turner and colleagues, who described the specimen, found Mahakala to be the most basal known dromaeosaurid. Their results, along with the small size of other theropods found at the base of paravian
lineages, suggest that small size was not an innovation of early birds, but a common trait of early paravians; small size would have preceded flight and would not have been a special avian autapomorphy
as the result of a size squeeze. Like birds, troodontids and dromaeosaurids did not retain small size throughout their evolutionary history, and had several separate size increases among different lineages. Mahakala also shows a combination of characteristics found among basal troodontids and birds, and is missing some that are present in more derived dromaeosaurids.
and alluvial
settings. The semiarid steppe
landscape was drained by intermittent streams and was sometimes affected by dust and sandstorms
, and moisture was seasonal. Animals present included terrestrial turtle
s and crocodilia
ns, lizard
s, mammal
s, and a variety of dinosaurs; aquatic animal
s like fish
were not present. The majority of the fauna
was small to medium-sized. Small coelurosauria
ns are the most diverse dinosaurs, including fellow dromaeosaurid Velociraptor
, troodontids Byronosaurus
and Saurornithoides
, oviraptorids
Citipati
, Khaan
, and Oviraptor
, and alvarezsaurs
Mononykus
and Shuvuuia
; other dinosaurs present included ceratopsia
n Protoceratops
and ankylosaurid
Pinacosaurus
. Like other dromaeosaurids, Mahakala would have been a small active predaceous carnivore
.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of basal
Basal (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:...
dromaeosaurid
Dromaeosauridae
Dromaeosauridae is a family of bird-like theropod dinosaurs. They were small- to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Greek dromeus meaning 'runner' and sauros meaning 'lizard'...
dinosaur
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 Campanian
Campanian
The Campanian is, in the ICS' geologic timescale, the fifth of six ages of the Late Cretaceous epoch . The Campanian spans the time from 83.5 ± 0.7 Ma to 70.6 ± 0.6 Ma ...
-age (about 80 million years ago) Upper Cretaceous Djadokhta Formation of Ömnögov
Ömnögovi Province
Ömnögovi is an aimag of Mongolia, located in the south of the country, in the Gobi Desert. Ömnögovi is Mongolia's largest aimag. The capital is Dalanzadgad....
, Mongolia
Mongolia
Mongolia is a landlocked country in East and Central Asia. It is bordered by Russia to the north and China to the south, east and west. Although Mongolia does not share a border with Kazakhstan, its western-most point is only from Kazakhstan's eastern tip. Ulan Bator, the capital and largest...
. It is based on a partial skeleton found in the Gobi Desert
Gobi Desert
The Gobi is a large desert region in Asia. It covers parts of northern and northwestern China, and of southern Mongolia. The desert basins of the Gobi are bounded by the Altai Mountains and the grasslands and steppes of Mongolia on the north, by the Hexi Corridor and Tibetan Plateau to the...
. Mahakala was a small dromaeosaurid (approximately 70 centimeters long (28 in)), and its skeleton shows features that are also found in early troodontids
Troodontidae
Troodontidae is a family of bird-like theropod dinosaurs. During most of the 20th century, troodontid fossils were few and scrappy and they have therefore been allied, at various times, with many dinosaurian lineages...
and avialans
Avialae
Avialae is a clade of dinosaurs containing their only living representatives, birds , and the most immediate extinct relatives of birds.-Competing definitions:...
. Despite its late appearance, it is among the most basal dromaeosaurids. Its small size, and the small size of other basal deinonychosauria
Deinonychosauria
The Deinonychosauria were a clade of coelurosaurian theropod dinosaurs from the Late Jurassic and Cretaceous periods. These omnivores and carnivores are known for their switchblade-like second toe claws and for displaying numerous bird-like characteristics. The clade has been divided into two...
ns, suggests that small size appeared before flight capability in bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s.
Description
Pelvis
In human anatomy, the pelvis is the lower part of the trunk, between the abdomen and the lower limbs .The pelvis includes several structures:...
and shoulder girdle. Although this individual was small, comparable in size to Archaeopteryx
Archaeopteryx
Archaeopteryx , sometimes referred to by its German name Urvogel , is a genus of theropod dinosaur that is closely related to birds. The name derives from the Ancient Greek meaning "ancient", and , meaning "feather" or "wing"...
, Caudipteryx
Caudipteryx
Caudipteryx is a genus of peacock-sized theropod dinosaurs that lived in the Aptian age of the early Cretaceous Period . They were feathered and remarkably birdlike in their overall appearance....
, and Mei
Mei (dinosaur)
Mei is a genus of duck-sized troodontid dinosaur first unearthed by paleontologists in Liaoning, China in 2004. Mei lived during the Early Cretaceous Period. Its binomial name, Mei long means sleeping dragon...
, it was close to adulthood. This genus can be distinguished from other paravians
Paraves
Paraves is a branch-based clade containing birds and other closely related dinosaurs. The paravians include the Avialae, including Archaeopteryx and modern birds, and the Deinonychosauria, which includes the dromaeosaurids and troodontids....
(dromaeosaurids, troodontids, and birds) by details of the ulna
Ulna
The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form and runs parallel to the radius, which is shorter and smaller. In anatomical position The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form...
, thighbone
Femur
The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...
, ilium
Ilium (bone)
The ilium is the uppermost and largest bone of the pelvis, and appears in most vertebrates including mammals and birds, but not bony fish. All reptiles have an ilium except snakes, although some snake species have a tiny bone which is considered to be an ilium.The name comes from the Latin ,...
, and tail vertebrae. Like Archaeopteryx and derived dromaeosaurids, but unlike basal troodontids and other dromaeosaurids, the middle (third) metatarsal
Metatarsus
The metatarsus or metatarsal bones are a group of five long bones in the foot located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the medial side : the first, second, third, fourth, and fifth...
was not compressed, suggesting that the uncompressed version was the basal version. It had a typical dromaeosaurid form of the second toe, with an expanded claw. Mahakala also had very short forelimbs compared to other Dromaeosaurids.
Classification
A phylogenetic analysisCladistics
Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...
performed by Turner and colleagues, who described the specimen, found Mahakala to be the most basal known dromaeosaurid. Their results, along with the small size of other theropods found at the base of paravian
Paraves
Paraves is a branch-based clade containing birds and other closely related dinosaurs. The paravians include the Avialae, including Archaeopteryx and modern birds, and the Deinonychosauria, which includes the dromaeosaurids and troodontids....
lineages, suggest that small size was not an innovation of early birds, but a common trait of early paravians; small size would have preceded flight and would not have been a special avian autapomorphy
Autapomorphy
In cladistics, an autapomorphy is a distinctive anatomical feature, known as a derived trait, that is unique to a given terminal group. That is, it is found only in one member of a clade, but not found in any others or outgroup taxa, not even those most closely related to the group...
as the result of a size squeeze. Like birds, troodontids and dromaeosaurids did not retain small size throughout their evolutionary history, and had several separate size increases among different lineages. Mahakala also shows a combination of characteristics found among basal troodontids and birds, and is missing some that are present in more derived dromaeosaurids.
Paleoecology and paleobiology
The paleoenvironment of the Djadokhta Formation is interpreted as having a semiarid climate, with sand duneDune
In physical geography, a dune is a hill of sand built by wind. Dunes occur in different forms and sizes, formed by interaction with the wind. Most kinds of dunes are longer on the windward side where the sand is pushed up the dune and have a shorter "slip face" in the lee of the wind...
and alluvial
Alluvium
Alluvium is loose, unconsolidated soil or sediments, eroded, deposited, and reshaped by water in some form in a non-marine setting. Alluvium is typically made up of a variety of materials, including fine particles of silt and clay and larger particles of sand and gravel...
settings. The semiarid steppe
Steppe
In physical geography, steppe is an ecoregion, in the montane grasslands and shrublands and temperate grasslands, savannas, and shrublands biomes, characterized by grassland plains without trees apart from those near rivers and lakes...
landscape was drained by intermittent streams and was sometimes affected by dust and sandstorms
Dust storm
A dust / sand storm is a meteorological phenomenon common in arid and semi-arid regions. Dust storms arise when a gust front or other strong wind blows loose sand and dirt from a dry surface. Particles are transported by saltation and suspension, causing soil to move from one place and deposition...
, and moisture was seasonal. Animals present included terrestrial turtle
Turtle
Turtles are reptiles of the order Testudines , characterised by a special bony or cartilaginous shell developed from their ribs that acts as a shield...
s and crocodilia
Crocodilia
Crocodilia is an order of large reptiles that appeared about 84 million years ago in the late Cretaceous Period . They are the closest living relatives of birds, as the two groups are the only known survivors of the Archosauria...
ns, lizard
Lizard
Lizards are a widespread group of squamate reptiles, with nearly 3800 species, ranging across all continents except Antarctica as well as most oceanic island chains...
s, mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s, and a variety of dinosaurs; aquatic animal
Aquatic animal
An aquatic animal is an animal, either vertebrate or invertebrate, which lives in water for most or all of its life. It may breathe air or extract its oxygen from that dissolved in water through specialised organs called gills, or directly through its skin. Natural environments and the animals that...
s like fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
were not present. The majority of the fauna
Fauna
Fauna or faunæ is all of the animal life of any particular region or time. The corresponding term for plants is flora.Zoologists and paleontologists use fauna to refer to a typical collection of animals found in a specific time or place, e.g. the "Sonoran Desert fauna" or the "Burgess shale fauna"...
was small to medium-sized. Small coelurosauria
Coelurosauria
Coelurosauria is the clade containing all theropod dinosaurs more closely related to birds than to carnosaurs. In the past, it was used to refer to all small theropods, although this classification has been abolished...
ns are the most diverse dinosaurs, including fellow dromaeosaurid Velociraptor
Velociraptor
Velociraptor is a genus of dromaeosaurid theropod dinosaur that existed approximately 75 to 71 million years ago during the later part of the Cretaceous Period. Two species are currently recognized, although others have been assigned in the past. The type species is V. mongoliensis; fossils...
, troodontids Byronosaurus
Byronosaurus
Byronosaurus is a genus of troodontid dinosaur which lived during the Late Cretaceous Period. It was named for Byron Jaffe, "in recognition of his family's support for the Mongolian Academy of Sciences-American Museum of Natural History Paleontological Expeditions." The first example of...
and Saurornithoides
Saurornithoides
Saurornithoides is a genus of troodontid maniraptoran dinosaur, living during the Late Cretaceous period. These creatures were predators, which could run fast on their hind legs and had excellent sight and hearing...
, oviraptorids
Oviraptoridae
Oviraptoridae is a group of bird-like, herbivorous and omnivorous maniraptoran dinosaurs. Oviraptorids are characterized by their toothless, parrot-like beaks and, in some cases, elaborate crests. They were generally small, measuring between one and two metres long in most cases, though some...
Citipati
Citipati
Citipati is a genus of oviraptorid theropod dinosaur from the Late Cretaceous Period of what is now Mongolia . It is one of the best-known oviraptorids, thanks to a number of well-preserved skeletons, including several specimens found in brooding positions atop nests of eggs...
, Khaan
Khaan
Khaan was an oviraptorid dinosaur that was found in the Djadochta Formation of Mongolia and lived in the Late Cretaceous Period , 75 million years ago....
, and Oviraptor
Oviraptor
Oviraptor is a genus of small Mongolian theropod dinosaur, first discovered by the paleontologist Roy Chapman Andrews, and first described by Henry Fairfield Osborn, in 1924...
, and alvarezsaurs
Alvarezsauridae
Alvarezsauridae is an enigmatic family of small, long-legged running dinosaurs. Although originally thought to represent the earliest known flightless birds, a consensus of recent work suggests that they are primitive members of the Maniraptora. Other work found them to be the sister group to the...
Mononykus
Mononykus
Mononykus was a theropod dinosaur from late Cretaceous Mongolia with long, skinny legs. It moved about on two legs, was very nimble, and could run at high speeds, something that would have been useful in the open desert plains where it lived...
and Shuvuuia
Shuvuuia
Shuvuuia is a genus of bird-like theropod dinosaur from the late Cretaceous period of Mongolia. It is a member of the family Alvarezsauridae, small coelurosaurian dinosaurs which are characterized by short but powerful forelimbs specialized for digging. The type species is Shuvuuia deserti, or...
; other dinosaurs present included ceratopsia
Ceratopsia
Ceratopsia or Ceratopia is a group of herbivorous, beaked dinosaurs which thrived in what are now North America, Europe, and Asia, during the Cretaceous Period, although ancestral forms lived earlier, in the Jurassic. The earliest known ceratopsian, Yinlong downsi, lived between 161.2 and 155.7...
n Protoceratops
Protoceratops
Protoceratops is a genus of sheep-sized herbivorous ceratopsian dinosaur, from the Upper Cretaceous Period of what is now Mongolia. It was a member of the Protoceratopsidae, a group of early horned dinosaurs...
and ankylosaurid
Ankylosauridae
An ankylosaurid is a member of the Ankylosauridae family of armored dinosaurs that evolved 125 million years ago and became extinct 65 million years ago during the Cretaceous-Tertiary extinction event...
Pinacosaurus
Pinacosaurus
Pinacosaurus is a genus of medium-sized ankylosaur dinosaurs that lived from the late Santonian to the late Campanian stages of the late Cretaceous Period , in Mongolia and China...
. Like other dromaeosaurids, Mahakala would have been a small active predaceous carnivore
Carnivore
A carnivore meaning 'meat eater' is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of animal tissue, whether through predation or scavenging...
.