Oryctodromeus
Encyclopedia
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. A member of the small, presumably fast-running herbivorous
family
Hypsilophodontidae, Oryctodromeus is the first dinosaur published that shows evidence of burrowing behavior.
specimens from the Blackleaf Formation: MOR 1636a
, a partial skeleton of an adult individual including: the premaxilla
e (upper beak
); part of the braincase; three neck
, six back, seven hip
, and twenty-three tail
vertebrae; ribs; the shoulder girdle; an arm (minus the hand); both tibia
e and an incomplete fibula; and a metatarsal
. Two additional individuals, both juveniles
about 55 to 65% the size of MOR 1636a, are represented by MOR 1636b. Numerous additional partial skeletons are known from the Wayan Formation
. Oryctodromeus was originally described as lacking ossified tendons in the tail. However, specimens from the Wayan Formation
demonstrate the presence of a thick tendon lattice in the dorsal, sacral, and caudal columns of some specimens; perhaps indicating more flexibility in ossified tendons than has previously been supposed.
Adaptations in the jaws, forelimbs, and pelvis were described in the Blackleaf specimens that could have helped move and manipulate soil.
The authors pointed out that Oryctodromeus had only modest forelimb modifications in comparison to dedicated burrowing animals, like moles
, echidna
s, and wombat
s. Instead, it was comparable to, but somewhat more specialized for digging than animals that both run and burrow today, like aardwolves
, cavies
, hyena
s, and rabbit
s. Because it was a biped, it could have a more modified forelimb without affecting its ability to run.
Under a cladistic
analysis, Oryctodromeus was found to be basal within Euornithopoda and a close relative of the hypsilophodonts Orodromeus
and Zephyrosaurus
, which are also known from the Cretaceous of Montana. These two animals share adaptations with Oryctodromeus that may have been used for burrowing, such as a broad snout. Additionally, Orodromeus specimens have been found preserved in a similar way, suggesting that they too were in burrows. This would not be the first time that a hypsilophodont has been suggested as a burrower; Robert Bakker has informally claimed since the 1990s that Drinker
, from the late Jurassic
of Wyoming
, lived in burrows, but this has yet to be published.
or burrow
, measuring about 2 meters long (6.5 feet) and 70 centimeters wide (2.3 ft). The skeletons were densely packed and disarticulated, indicating that the animals died and decayed within the burrow. The burrow is similar to those made by hyena
s and puffin
s today. It was filled with sand
, and the resulting sandstone
stands out against the surrounding mudstone
and claystone
.
There are two turns in the preserved burrow section, and smaller secondary sandstone cylinders of various sizes (a few centimeters or inches in cross-section at most) that were probably made by smaller animals sharing the burrow (commensal
). The burrow closely fits the probable proportions of the adult dinosaur, another indication that it was the digger.
. This aspect, coupled with where it was discovered, gives it its name: Oryctodromeus cubicularis translates as "digging runner of the lair", in reference to its presumed lifestyle. The adult Oryctodromeus itself measured 2.1 m long (6.8 ft) and would have weighed about 22-32 kilogram
s (50-70 pounds
), and the juveniles would have been about 1.3 m long (4.3 ft). The presence of juveniles with the adult suggests parental care, and that at least one motivation for burrowing was to rear the juveniles. The size of the juveniles suggests an extended period of parental care.
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 small 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...
. Fossils are known from the middle 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...
Blackleaf Formation of southwestern 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,...
and the Wayan Formation
Wayan Formation
The Wayan Formation is a geological formation in Idaho whose strata date back to the earliest Late Cretaceous. Dinosaur remains are among the fossils that have been recovered from the formation.-Geology and Age:...
of southeastern Idaho, both of the Cenomanian
Cenomanian
The Cenomanian is, in the ICS' geological timescale the oldest or earliest age of the Late Cretaceous epoch or the lowest stage of the Upper Cretaceous series. An age is a unit of geochronology: it is a unit of time; the stage is a unit in the stratigraphic column deposited during the corresponding...
stage, roughly 95 million years ago. A member of the small, presumably fast-running herbivorous
Herbivore
Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...
family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Hypsilophodontidae, Oryctodromeus is the first dinosaur published that shows evidence of burrowing behavior.
Description
Oryctodromeus is based onHolotype
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...
specimens from the Blackleaf Formation: MOR 1636a
Museum of the Rockies
The Museum of the Rockies, is located in Bozeman, Montana. The museum, originally affiliated with Montana State University in Bozeman, and now, also the Smithsonian Institution, is known for its paleontological collections, although these are not its sole focus...
, a partial skeleton of an adult individual including: 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....
e (upper beak
Beak
The beak, bill or rostrum is an external anatomical structure of birds which is used for eating and for grooming, manipulating objects, killing prey, fighting, probing for food, courtship and feeding young...
); part of the braincase; three neck
Neck
The neck is the part of the body, on many terrestrial or secondarily aquatic vertebrates, that distinguishes the head from the torso or trunk. The adjective signifying "of the neck" is cervical .-Boner anatomy: The cervical spine:The cervical portion of the human spine comprises seven boney...
, six back, seven hip
Sacrum
In vertebrate anatomy the sacrum is a large, triangular bone at the base of the spine and at the upper and back part of the pelvic cavity, where it is inserted like a wedge between the two hip bones. Its upper part connects with the last lumbar vertebra, and bottom part with the coccyx...
, and twenty-three tail
Tail
The tail is the section at the rear end of an animal's body; in general, the term refers to a distinct, flexible appendage to the torso. It is the part of the body that corresponds roughly to the sacrum and coccyx in mammals, reptiles, and birds...
vertebrae; ribs; the shoulder girdle; an arm (minus the hand); both tibia
Tibia
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 and an incomplete fibula; and a 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...
. Two additional individuals, both juveniles
Juvenile (organism)
A juvenile is an individual organism that has not yet reached its adult form, sexual maturity or size. Juveniles sometimes look very different from the adult form, particularly in terms of their colour...
about 55 to 65% the size of MOR 1636a, are represented by MOR 1636b. Numerous additional partial skeletons are known from the Wayan Formation
Wayan Formation
The Wayan Formation is a geological formation in Idaho whose strata date back to the earliest Late Cretaceous. Dinosaur remains are among the fossils that have been recovered from the formation.-Geology and Age:...
. Oryctodromeus was originally described as lacking ossified tendons in the tail. However, specimens from the Wayan Formation
Wayan Formation
The Wayan Formation is a geological formation in Idaho whose strata date back to the earliest Late Cretaceous. Dinosaur remains are among the fossils that have been recovered from the formation.-Geology and Age:...
demonstrate the presence of a thick tendon lattice in the dorsal, sacral, and caudal columns of some specimens; perhaps indicating more flexibility in ossified tendons than has previously been supposed.
Adaptations in the jaws, forelimbs, and pelvis were described in the Blackleaf specimens that could have helped move and manipulate soil.
The authors pointed out that Oryctodromeus had only modest forelimb modifications in comparison to dedicated burrowing animals, like moles
Mole (animal)
Moles are small cylindrical mammals adapted to a subterranean lifestyle. They have velvety fur; tiny or invisible ears and eyes; and short, powerful limbs with large paws oriented for digging. The term is especially and most properly used for the true moles, those of the Talpidae family in the...
, echidna
Echidna
Echidnas , also known as spiny anteaters, belong to the family Tachyglossidae in the monotreme order of egg-laying mammals. There are four extant species, which, together with the platypus, are the only surviving members of that order and are the only extant mammals that lay eggs...
s, and wombat
Wombat
Wombats are Australian marsupials; they are short-legged, muscular quadrupeds, approximately in length with a short, stubby tail. They are adaptable in their habitat tolerances, and are found in forested, mountainous, and heathland areas of south-eastern Australia, including Tasmania, as well as...
s. Instead, it was comparable to, but somewhat more specialized for digging than animals that both run and burrow today, like aardwolves
Aardwolf
The aardwolf is a small, insectivorous mammal, native to Eastern and Southern Africa. The name means "earth wolf" in Afrikaans/Dutch. It is also called "maanhaar jackal". It is related to hyenas, but unlike its relatives, it does not hunt large prey. This unusual animal preys on insects...
, cavies
Guinea pig
The guinea pig , also called the cavy, is a species of rodent belonging to the family Caviidae and the genus Cavia. Despite their common name, these animals are not in the pig family, nor are they from Guinea...
, hyena
Hyena
Hyenas or Hyaenas are the animals of the family Hyaenidae of suborder feliforms of the Carnivora. It is the fourth smallest biological family in the Carnivora , and one of the smallest in the mammalia...
s, and rabbit
Rabbit
Rabbits are small mammals in the family Leporidae of the order Lagomorpha, found in several parts of the world...
s. Because it was a biped, it could have a more modified forelimb without affecting its ability to run.
Under a cladistic
Cladistics
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...
analysis, Oryctodromeus was found to be basal within Euornithopoda and a close relative of the hypsilophodonts Orodromeus
Orodromeus
Orodromeus is a genus of herbivorous ornithopod dinosaur from the Late Cretaceous of North America.-Discovery and naming:...
and Zephyrosaurus
Zephyrosaurus
Zephyrosaurus is a genus of hypsilophodont ornithopod dinosaur. It is based on a partial skull and postcranial fragments discovered in the Aptian-Albian-age Lower Cretaceous Cloverly Formation of Carbon County, Montana...
, which are also known from the Cretaceous of Montana. These two animals share adaptations with Oryctodromeus that may have been used for burrowing, such as a broad snout. Additionally, Orodromeus specimens have been found preserved in a similar way, suggesting that they too were in burrows. This would not be the first time that a hypsilophodont has been suggested as a burrower; Robert Bakker has informally claimed since the 1990s that Drinker
Drinker
Drinker was a genus of hypsilophodont dinosaur from the late Jurassic period of North America. Although based on good remains, it remains obscure due to a lack of post-naming publications.-Description:...
, from the late Jurassic
Late Jurassic
The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 161.2 ± 4.0 to 145.5 ± 4.0 million years ago , which is preserved in Upper Jurassic strata. In European lithostratigraphy, the name "Malm" indicates rocks of Late Jurassic age...
of Wyoming
Wyoming
Wyoming is a state in the mountain region of the Western United States. The western two thirds of the state is covered mostly with the mountain ranges and rangelands in the foothills of the Eastern Rocky Mountains, while the eastern third of the state is high elevation prairie known as the High...
, lived in burrows, but this has yet to be published.
Burrow
The three Oryctodromeus individuals were found buried within the remains of an underground denLair
Lair may refer to:*An animal's lair or home; see :Category:Shelters built or used by animals*Lair , a 2007 video game*In Scots language, lair refers to a burial-plot in a graveyard...
or burrow
Burrow
A burrow is a hole or tunnel dug into the ground by an animal to create a space suitable for habitation, temporary refuge, or as a byproduct of locomotion. Burrows provide a form of shelter against predation and exposure to the elements, so the burrowing way of life is quite popular among the...
, measuring about 2 meters long (6.5 feet) and 70 centimeters wide (2.3 ft). The skeletons were densely packed and disarticulated, indicating that the animals died and decayed within the burrow. The burrow is similar to those made by hyena
Hyena
Hyenas or Hyaenas are the animals of the family Hyaenidae of suborder feliforms of the Carnivora. It is the fourth smallest biological family in the Carnivora , and one of the smallest in the mammalia...
s and puffin
Puffin
Puffins are any of three small species of auk in the bird genus Fratercula with a brightly coloured beak during the breeding season. These are pelagic seabirds that feed primarily by diving in the water. They breed in large colonies on coastal cliffs or offshore islands, nesting in crevices among...
s today. It was filled with sand
Sand
Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...
, and the resulting sandstone
Sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
stands out against the surrounding mudstone
Mudstone
Mudstone is a fine grained sedimentary rock whose original constituents were clays or muds. Grain size is up to 0.0625 mm with individual grains too small to be distinguished without a microscope. With increased pressure over time the platey clay minerals may become aligned, with the...
and claystone
Claystone
Claystone is a geological term used to describe a clastic sedimentary rock that is composed primarily of clay-sized particles ....
.
There are two turns in the preserved burrow section, and smaller secondary sandstone cylinders of various sizes (a few centimeters or inches in cross-section at most) that were probably made by smaller animals sharing the burrow (commensal
Commensalism
In ecology, commensalism is a class of relationship between two organisms where one organism benefits but the other is neutral...
). The burrow closely fits the probable proportions of the adult dinosaur, another indication that it was the digger.
Paleobiology
As a hypsilophodont, Oryctodromeus would have been a small, swift herbivoreHerbivore
Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...
. This aspect, coupled with where it was discovered, gives it its name: Oryctodromeus cubicularis translates as "digging runner of the lair", in reference to its presumed lifestyle. The adult Oryctodromeus itself measured 2.1 m long (6.8 ft) and would have weighed about 22-32 kilogram
Kilogram
The kilogram or kilogramme , also known as the kilo, is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype Kilogram , which is almost exactly equal to the mass of one liter of water...
s (50-70 pounds
Pound (mass)
The pound or pound-mass is a unit of mass used in the Imperial, United States customary and other systems of measurement...
), and the juveniles would have been about 1.3 m long (4.3 ft). The presence of juveniles with the adult suggests parental care, and that at least one motivation for burrowing was to rear the juveniles. The size of the juveniles suggests an extended period of parental care.
External links
- Dinosaur den diggers discovered - BBC Dinosauriweb about the Oryctodromeus
- Full abstract of description
- Article about burrowing dinosaurs from The Cambrian Explosion blog