Dromaeosaurus
Encyclopedia
Dromaeosaurus was a genus
of theropod dinosaur
which lived during the Late Cretaceous
period (middle late Campanian
), sometime between 76.5 and 74.8 million years ago, in the western United States and Alberta
, Canada
. The name means 'running lizard'.
, about 2 m (6.5 ft) in length and 15 kg (33 lb) in weight. Its mouth was full of sharp teeth, and it had a sharp "sickle claw" on each foot. It lived during the Campanian
stage of the Late Cretaceous
, however, some fragmentary remains such as teeth which may belong to this genus have been found from the late Maastrichtian
age Lance
and Hell Creek Formation
s, dating to 65.5 million years ago.
Dromaeosaurus had a relatively robust skull with a deep snout. Its teeth were rather large and it had only nine of them in the maxilla
.
In Dromaeosaurus albertensis, a vein
at the back of the head, the vena capitis dorsalis, drains the front neck muscles through two long canals running to the posterior surface of the brain.
Despite receiving widespread attention in popular books on dinosaurs, and the usage of a complete mounted skeleton cast in museums throughout the world, Dromaeosaurus is surprisingly poorly known from actual fossils. The preparation of the popular cast by the Tyrrell Museum was only made possible by knowledge gained from other dromaeosaurids that have been discovered more recently.
The first known Dromaeosaurus remains were discovered by paleontologist Barnum Brown
during a 1914 expedition to Red Deer River
on behalf of the American Museum of Natural History. The area where these bones were collected is now part of Dinosaur Provincial Park
in Alberta, Canada. The find, holotype
AMNH 5356, consisted of a partial skull 24 cm (9.4 in) in length, a mandible
, two hyoids, a first metacarpal and some foot bones. The skull lacked most of the top of the snout. Several other skull fragments, and about thirty isolated teeth, are known from subsequent discoveries in Alberta and Montana
.
In 1922 William Diller Matthew
and Brown named and described the type species
of Dromaeosaurus: Dromaeosaurus albertenis. The generic name is derived from the Greek δρομεύς (dromeus) meaning 'runner' and σαύρος (sauros) meaning 'lizard'. The specific name, "albertenis", refers to Alberta
.
Another seven species of Dromaeosaurus were named: Dromaeosaurus laevifrons (Cope 1876) Matthew & Brown 1922; Dromaeosaurus cristatus (Cope 1876) Matthew & Brown 1922 (Troodon
); Dromaeosaurus? gracilis (Marsh 1888) Matthew & Brown 1922; Dromaeosaurus explanatus (Cope 1876) Kuhn 1939; Dromaeosaurus minutus (Marsh 1892) Russell 1972 (an alvarezsaurid); Dromaeosaurus falculus (Cope 1876) Olshevsky 1979 and Dromaeosaurus mongoliensis (Barsbold 1983) Paul 1988 (Velociraptor
). Most of them were based on fragmentary material, some belonging to other genera, and far less complete than that of Dromaeosaurus albertensis, and those that haven't been reclassified are considered nomina dubia
today. Nevertheless, it has grown apparent that Dromaeosaurus albertensis is even rarer in its habitat
than other small theropods, although it was the first dromaeosaurid of which reasonably good cranial material was described.
Dromaeosaurus differs from most of its relatives in having a short, massive skull, a deep mandible, and robust teeth. The teeth tend to be more heavily worn than those of its relative Saurornitholestes, suggesting that its jaws were used for crushing and tearing rather than simply slicing through flesh. Therrien et al. (2005) estimated that Dromaeosaurus had a bite nearly three times as powerful as that of Velociraptor and suggested it relied more on his jaws than on the sickle claw to kill its prey.
, within the "Deinodontidae" (now known as Tyrannosauridae
) based on some similarities in the general proportions of the skull. In 1969, John H. Ostrom
recognized that Dromaeosaurus shared many features with Velociraptor and the newly-discovered Deinonychus, and assigned these forms to a new family: Dromaeosauridae
. Since then, many new relatives of Dromaeosaurus have been found.
The exact relationships of Dromaeosaurus are unclear. Although its rugged build gives it a primitive appearance, it was actually a very specialized animal. In analyses of the present clade
Dromaeosaurinae species as Utahraptor
, Achillobator
and Adasaurus
are often recovered.
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 theropod 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...
which lived during 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...
period (middle late 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 ...
), sometime between 76.5 and 74.8 million years ago, in the western United States and Alberta
Alberta
Alberta is a province of Canada. It had an estimated population of 3.7 million in 2010 making it the most populous of Canada's three prairie provinces...
, Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
. The name means 'running lizard'.
Description
Dromaeosaurus was a small carnivoreCarnivore
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...
, about 2 m (6.5 ft) in length and 15 kg (33 lb) in weight. Its mouth was full of sharp teeth, and it had a sharp "sickle claw" on each foot. It lived during 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 ...
stage of 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...
, however, some fragmentary remains such as teeth which may belong to this genus have been found from the late Maastrichtian
Maastrichtian
The Maastrichtian is, in the ICS' geologic timescale, the latest age or upper stage of the Late Cretaceous epoch or Upper Cretaceous series, the Cretaceous period or system, and of the Mesozoic era or erathem. It spanned from 70.6 ± 0.6 Ma to 65.5 ± 0.3 Ma...
age Lance
Lance Formation
The Lance Formation is a division of Late Cretaceous rocks in the western United States. Named after Lance Creek, Wyoming, the microvertebrate fossils and dinosaurs represent important components of the latest Mesozoic vertebrate faunas...
and Hell Creek Formation
Hell Creek Formation
The Hell Creek Formation is an intensely-studied division of Upper Cretaceous to lower Paleocene rocks in North America, named for exposures studied along Hell Creek, near Jordan, Montana...
s, dating to 65.5 million years ago.
Dromaeosaurus had a relatively robust skull with a deep snout. Its teeth were rather large and it had only nine of them in the maxilla
Maxilla
The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...
.
In Dromaeosaurus albertensis, a vein
Vein
In the circulatory system, veins are blood vessels that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated blood to the heart...
at the back of the head, the vena capitis dorsalis, drains the front neck muscles through two long canals running to the posterior surface of the brain.
Discovery and later findings
The first known Dromaeosaurus remains were discovered by paleontologist Barnum Brown
Barnum Brown
Barnum Brown , a paleontologist born in Carbondale, Kansas, and named after the circus showman P.T. Barnum, discovered the second fossil of Tyrannosaurus rex during a career that made him one of the most famous fossil hunters working from the late Victorian era into the early 20th century.Sponsored...
during a 1914 expedition to Red Deer River
Red Deer River
The Red Deer River is a river in Alberta, Canada. It is a major tributary of the South Saskatchewan River.Red Deer River has a total length of and a drainage area of...
on behalf of the American Museum of Natural History. The area where these bones were collected is now part of Dinosaur Provincial Park
Dinosaur Provincial Park
Dinosaur Provincial Park is a UNESCO World Heritage Site located about two and a half hours drive southeast of Calgary, Alberta, Canada or , about a half hour drive, northeast of Brooks....
in Alberta, Canada. The find, holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
AMNH 5356, consisted of a partial skull 24 cm (9.4 in) in length, a mandible
Mandible
The mandible pronunciation or inferior maxillary bone forms the lower jaw and holds the lower teeth in place...
, two hyoids, a first metacarpal and some foot bones. The skull lacked most of the top of the snout. Several other skull fragments, and about thirty isolated teeth, are known from subsequent discoveries in Alberta and Montana
Montana
Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...
.
In 1922 William Diller Matthew
William Diller Matthew
William Diller Matthew FRS was a vertebrate paleontologist who worked primarily on mammal fossils....
and Brown named and described 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...
of Dromaeosaurus: Dromaeosaurus albertenis. The generic name is derived from the Greek δρομεύς (dromeus) meaning 'runner' and σαύρος (sauros) meaning 'lizard'. The specific name, "albertenis", refers to Alberta
Alberta
Alberta is a province of Canada. It had an estimated population of 3.7 million in 2010 making it the most populous of Canada's three prairie provinces...
.
Another seven species of Dromaeosaurus were named: Dromaeosaurus laevifrons (Cope 1876) Matthew & Brown 1922; Dromaeosaurus cristatus (Cope 1876) Matthew & Brown 1922 (Troodon
Troodon
Troodon is a genus of relatively small, bird-like dinosaur from the Late Cretaceous period . Discovered in 1855, it was among the first dinosaurs found in North America...
); Dromaeosaurus? gracilis (Marsh 1888) Matthew & Brown 1922; Dromaeosaurus explanatus (Cope 1876) Kuhn 1939; Dromaeosaurus minutus (Marsh 1892) Russell 1972 (an alvarezsaurid); Dromaeosaurus falculus (Cope 1876) Olshevsky 1979 and Dromaeosaurus mongoliensis (Barsbold 1983) Paul 1988 (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...
). Most of them were based on fragmentary material, some belonging to other genera, and far less complete than that of Dromaeosaurus albertensis, and those that haven't been reclassified are considered nomina dubia
Nomen dubium
In zoological nomenclature, a nomen dubium is a scientific name that is of unknown or doubtful application...
today. Nevertheless, it has grown apparent that Dromaeosaurus albertensis is even rarer in its habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
than other small theropods, although it was the first dromaeosaurid of which reasonably good cranial material was described.
Paleobiology and diet
Phylogeny
Matthew and Brown originally placed Dromaeosaurus to its own subfamily, the DromaeosaurinaeDromaeosaurinae
Dromaeosaurinae is a subfamily of Dromaeosauridae. Most dromaeosaurines lived in what is now the USA and Canada, , as well as Mongolia, , and possibly Denmark, , as well. Isolated teeth that may belong to African dromaeosaurines have also been discovered in Ethiopia...
, within the "Deinodontidae" (now known as Tyrannosauridae
Tyrannosauridae
Tyrannosauridae is a family of coelurosaurian theropod dinosaurs which comprises two subfamilies containing up to six genera, including the eponymous Tyrannosaurus. The exact number of genera is controversial, with some experts recognizing as few as three...
) based on some similarities in the general proportions of the skull. In 1969, John H. Ostrom
John Ostrom
John H. Ostrom was an American paleontologist who revolutionized modern understanding of dinosaurs in the 1960s, when he demonstrated that dinosaurs are more like big non-flying birds than they are like lizards , an idea first proposed by Thomas Henry Huxley in the 1860s, but which had garnered...
recognized that Dromaeosaurus shared many features with Velociraptor and the newly-discovered Deinonychus, and assigned these forms to a new family: Dromaeosauridae
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'...
. Since then, many new relatives of Dromaeosaurus have been found.
The exact relationships of Dromaeosaurus are unclear. Although its rugged build gives it a primitive appearance, it was actually a very specialized animal. In analyses of the present clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
Dromaeosaurinae species as Utahraptor
Utahraptor
Utahraptor is a genus of theropod dinosaurs, including the largest known members of the family Dromaeosauridae. Fossil specimens date to the upper Barremian stage of the early Cretaceous period...
, Achillobator
Achillobator
Achillobator is a genus of dromaeosaurid theropod dinosaur from the late Cretaceous Period of what is now Mongolia, about 90 million years ago. It was probably an active bipedal predator, hunting with the large sickle-shaped claw on the second toe of each hind foot...
and Adasaurus
Adasaurus
Adasaurus is a genus of dromaeosaurid theropod dinosaur from the Late Cretaceous Period of what is now Central Asia. It was a small bipedal carnivore with a sickle-shaped claw on the second toe of each hind foot. An adult was perhaps about long....
are often recovered.