Orodromeus
Encyclopedia
Orodromeus is a genus
of herbivorous ornithopod
dinosaur
from the Late Cretaceous
of North America
.
, Montana
, of the Egg Mountain brooding colony of a much larger relative, Maiasaura
. The type species
, Orodromeus makelai, was named and shortly described by Jack Horner
and David B. Weishampel in 1988
. The generic name is derived from Greek ὄρος, oros, "mountain", in reference to the Egg Mountain site, and δρομεύς, dromeus, "runner", referring to the cursorial habits of the animal. The specific name honoured the late Makela.
The holotype
specimen, MOR 294, was found in a layer of the Two Medicine Formation
, dating from the Campanian
stage, about 75 million years ago. It consists of a partial skeleton with skull. The paratype
s are MOR 249, a clutch of nineteen eggs, some with embryo
; PP 22412, a set of hindlimbs; MOR 331, a partial skeleton; MOR 248, a skeleton with skull; and MOR 403, a braincase. A full description is still lacking.
and Einiosaurus
. Its length was estimated by Horner & Weishampel at 2.5 metres.
Orodromeus is distinguished by a palpebral that is at its back attached to the postorbital
; a boss on the jugal
; a non-fused wrist; and triangular maxillary
and dentary teeth with a vertical occlusion
.
Because of the advanced development of the bones and teeth of the embryos, Horner concluded that the young of Orodromeus were precocial
, in contrast to those of Maiasaura that would have been altricial
.
It has been speculated that this animal may have burrowed much like its relative Oryctodromeus
, based upon the packing of their bones in situations where they typically would have been scattered.
TV series Dinosaur Planet
where it is shown to live in herds and is hunted by a pack of Troodon
.
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 herbivorous ornithopod
Ornithopod
Ornithopods or members of the clade Ornithopoda are a group of ornithischian dinosaurs that started out as small, bipedal running grazers, and grew in size and numbers until they became one of the most successful groups of herbivores in the Cretaceous world, and dominated the North American...
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 Late Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
of North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
.
Discovery and naming
The remains of Orodromeus were discovered by Robert Makela during the excavation in Teton CountyTeton County
Teton County is the name of several counties in the United States:* Teton County, Idaho* Teton County, Montana* Teton County, Wyoming...
, 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,...
, of the Egg Mountain brooding colony of a much larger relative, Maiasaura
Maiasaura
Maiasaura is a large duck-billed dinosaur genus that lived in the area currently covered by the state of Montana in the Upper Cretaceous Period , about 74 million years ago....
. 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...
, Orodromeus makelai, was named and shortly described by Jack Horner
Jack Horner (paleontologist)
John "Jack" R. Horner is an American paleontologist who discovered and named Maiasaura, providing the first clear evidence that some dinosaurs cared for their young. He is one of the best-known paleontologists in the United States...
and David B. Weishampel in 1988
1988 in paleontology
-Newly named dinosaurs:Data courtesy of George Olshevsky's dinosaur genera list and Dr. Jeremy Montague's dinosaur genus database.* The dubious family, Ornitholestidae is named by Gregory Scott Paul.-New taxa:-Non-mammalian:...
. The generic name is derived from Greek ὄρος, oros, "mountain", in reference to the Egg Mountain site, and δρομεύς, dromeus, "runner", referring to the cursorial habits of the animal. The specific name honoured the late Makela.
The 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...
specimen, MOR 294, was found in a layer of the Two Medicine Formation
Two Medicine Formation
The Two Medicine Formation is a geologic formation, or rock body, that was deposited between 83.5 ± 0.7 Ma to 70.6 ± 0.6 Ma , during Campanian time, and is located in northwestern Montana...
, dating 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 ...
stage, about 75 million years ago. It consists of a partial skeleton with skull. The paratype
Paratype
Paratype is a technical term used in the scientific naming of species and other taxa of organisms. The exact meaning of the term paratype when it is used in zoology is not the same as the meaning when it is used in botany...
s are MOR 249, a clutch of nineteen eggs, some with embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
; PP 22412, a set of hindlimbs; MOR 331, a partial skeleton; MOR 248, a skeleton with skull; and MOR 403, a braincase. A full description is still lacking.
Description
Orodromeus was a small fast bipedal herbivore that probably coexisted with dinosaurs such as DaspletosaurusDaspletosaurus
Daspletosaurus is a genus of tyrannosaurid theropod dinosaur that lived in western North America between 77 and 74 million years ago, during the Late Cretaceous Period. Fossils of the only named species were found in Alberta, although other possible species from Alberta and Montana await...
and Einiosaurus
Einiosaurus
Einiosaurus is a medium-sized centrosaurine ceratopsian from the Upper Cretaceous of northwestern Montana. The name means 'buffalo lizard', in a combination of Blackfeet Indian and Latinized Ancient Greek; the specific name Einiosaurus is a medium-sized centrosaurine (“short-frilled”)...
. Its length was estimated by Horner & Weishampel at 2.5 metres.
Orodromeus is distinguished by a palpebral that is at its back attached to the postorbital
Postorbital
The postorbital is one of the bones in vertebrate skulls which forms a portion of the dermal skull roof and, sometimes, a ring about the orbit. Generally, it is located behind the postfrontal and posteriorly to the orbital fenestra. In some vertebrates, the postorbital is fused with the postfrontal...
; a boss on the jugal
Jugal
The jugal is a skull bone found in most reptiles, amphibians, and birds. In mammals, the jugal is often called the malar or Zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by species....
; a non-fused wrist; and triangular maxillary
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...
and dentary teeth with a vertical occlusion
Occlusion
Occlusion may refer to:* Occlusion , the manner in which the upper and lower teeth come together when the mouth is closed* Occlusion effect, an audio phenomenon that occurs when one closes the opening into the ear canal and the loudness of low pitched sounds increases* Occlusion miliaria, a skin...
.
Because of the advanced development of the bones and teeth of the embryos, Horner concluded that the young of Orodromeus were precocial
Precocial
In biology, the term precocial refers to species in which the young are relatively mature and mobile from the moment of birth or hatching. The opposite developmental strategy is called "altricial," where the young are born or hatched helpless. Extremely precocial species may be called...
, in contrast to those of Maiasaura that would have been altricial
Altricial
Altricial, meaning "requiring nourishment", refers to a pattern of growth and development in organisms which are incapable of moving around on their own soon after hatching or being born...
.
It has been speculated that this animal may have burrowed much like its relative Oryctodromeus
Oryctodromeus
Oryctodromeus was a genus of small ornithopod dinosaur. Fossils are known from the middle Cretaceous Blackleaf Formation of southwestern Montana and the Wayan Formation of southeastern Idaho, both of the Cenomanian stage, roughly 95 million years ago...
, based upon the packing of their bones in situations where they typically would have been scattered.
Phylogeny
Orodromeus was by Horner & Weishampel assigned to the Hypsilophodontidae, as the youngest known member. Today these are seen as an unnatural, paraphyletic, group, and Orodromeus is simply considered to be a basal member of the Euornithopoda.In popular culture
Orodromeus is featured in the third episode of the Discovery ChannelDiscovery Channel
Discovery Channel is an American satellite and cable specialty channel , founded by John Hendricks and distributed by Discovery Communications. It is a publicly traded company run by CEO David Zaslav...
TV series Dinosaur Planet
Dinosaur Planet (television series)
Dinosaur Planet is a four-part American nature documentary first aired on Discovery Channel in 2003. It was hosted by Scott Sampson and narrated by Christian Slater....
where it is shown to live in herds and is hunted by a pack of 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...
.