Dromomeron
Encyclopedia
Dromomeron is a genus
of lagerpetonid
dinosauromorph
archosaur from Late Triassic
-age rocks of the Southwestern United States
. It is known from partial remains, largely from the hindlimbs,, which indicate an animal with an overall length of less than 1.0 meters (3.3 ft). It is described as most closely related to the earlier Lagerpeton
of Argentina
, but was found among remains of true dinosaurs like Chindesaurus
, indicating that the first dinosaurs did not immediately replace related groups.
D. romeri is based on
GR 218, a complete left thigh bone
from the Hayden Quarry at Ghost Ranch
, New Mexico
. The rocks there are in the lower portion of the Petrified Forest Member of the Chinle Formation
, and are Norian
in age. Additional hindlimb bones, some probably from the same individual, are also known, and a partial skeleton has been recovered from Hayden Quarry, but has not yet been fully prepared. A few other specimens have been recovered from nearby localities, including the Snyder Quarry. The bones of Dromomeron are most similar to those of the older dinosauromorph Lagerpeton, and the two animals have been classified together in a clade
Lagerpetonidae
. The species name romeri honors influential 20th century vertebrate paleontologist Alfred Sherwood Romer.
Also found at the Hayden Quarry are the remains of phytosaur
s, aetosaur
s, rauisuchia
ns, and several types of dinosaurs and dinosaur relatives, including a Silesaurus
-like animal, the herrerasaurid Chindesaurus
, and an unnamed coelophysoid
theropod. Finding the remains of four types of dinosaurs and dinosaur relatives (including Dromomeron itself) is noteworthy because it shows that dinosaurs did not immediately replace related groups; that some of these groups, like the lagerpetonids, persisted for longer than previously known and diversified; and that dinosaurian replacement may have occurred at different times in different areas.
Other specimens from the Chinle Formation of Arizona
and a roughly contemporaneous part of the Dockum Group
of Texas
also have been assigned to this genus. These have been assigned to second species D. gregorii, named in 2009.
D. gregorii, named for Joseph T. Gregory
, is based on TMM
31100–1306, a right femur (thigh bone) from the Otis Chalk Quarry, Colorado City Formation, (Dockum Group), near Otis Chalk, Texas. Several other limb bones from the quarry, and a partial femur (thigh bone) from the Placerias
Quarry of eastern Arizona
have been assigned to this species. The rocks D. gregorii is known from are older than those D. romeri has been found in. As with D. romeri, the Otis Chalk Quarry also has at least one specimen of the early dinosaur Chindesaurus.
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 lagerpetonid
Lagerpetonidae
The Lagerpetonidae is a family of basal dinosauromorphs. Members of the family are known from the Late Triassic of Argentina, Arizona, New Mexico, and Texas.-Description:...
dinosauromorph
Dinosauromorpha
Dinosauromorpha is the name of a clade of archosaurs that includes the closest relatives of dinosaurs, and the order Dinosauria itself. Basal forms include Saltopus, Marasuchus, the perhaps identical Lagosuchus, the lagerpetonids Lagerpeton from the Ladinian of Argentina and Dromomeron from the...
archosaur from Late Triassic
Late Triassic
The Late Triassic is in the geologic timescale the third and final of three epochs of the Triassic period. The corresponding series is known as the Upper Triassic. In the past it was sometimes called the Keuper, after a German lithostratigraphic group that has a roughly corresponding age...
-age rocks of the Southwestern United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
. It is known from partial remains, largely from the hindlimbs,, which indicate an animal with an overall length of less than 1.0 meters (3.3 ft). It is described as most closely related to the earlier Lagerpeton
Lagerpeton
Lagerpeton is a genus of basal dinosauromorph from the Ladinian . Lagerpeton is known from several specimens of hindlimbs, hips, vertebrae, and feet. It was about 0.7 metres long and was found in the Chañares Formation of Argentina. It has unique feet, with an unusually long fourth toe...
of Argentina
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...
, but was found among remains of true dinosaurs like Chindesaurus
Chindesaurus
Chindesaurus is a genus of saurischian dinosaur named after Chinde Point , near where the genoholotype specimen was discovered in the Chinle Formation of Petrified Forest National Park, Arizona, by Bryan Small in 1985...
, indicating that the first dinosaurs did not immediately replace related groups.
Discovery and history
Dromomeron and type speciesType 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...
D. romeri is based on
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...
GR 218, a complete left thigh bone
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...
from the Hayden Quarry at Ghost Ranch
Ghost Ranch
Ghost Ranch is a retreat and education center located close to the village of Abiquiu in Rio Arriba County in north central New Mexico. The conference center and lodgings at Ghost Ranch are run by the Presbyterian Church but open to the general public.-History:Ghost Ranch is part of Piedra...
, New Mexico
New Mexico
New Mexico is a state located in the southwest and western regions of the United States. New Mexico is also usually considered one of the Mountain States. With a population density of 16 per square mile, New Mexico is the sixth-most sparsely inhabited U.S...
. The rocks there are in the lower portion of the Petrified Forest Member of the Chinle Formation
Chinle Formation
The Chinle is a geologic formation that is spread across the U.S. states of northern Arizona, Nevada, Utah, western New Mexico, and western Colorado. The Chinle is controversially considered to be synonymous to the Dockum Group in eastern Colorado, eastern New Mexico, southwestern Kansas, the...
, and are Norian
Norian
The Norian is a division of the Triassic geological period. It has the rank of an age or stage . The Norian lasted from 216.5 ± 2.0 to 203.6 ± 1.5 million years ago. It was preceded by the Carnian and succeeded by the Rhaetian.-Stratigraphic definitions:The Norian was named after the Noric Alps in...
in age. Additional hindlimb bones, some probably from the same individual, are also known, and a partial skeleton has been recovered from Hayden Quarry, but has not yet been fully prepared. A few other specimens have been recovered from nearby localities, including the Snyder Quarry. The bones of Dromomeron are most similar to those of the older dinosauromorph Lagerpeton, and the two animals have been classified together in a 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...
Lagerpetonidae
Lagerpetonidae
The Lagerpetonidae is a family of basal dinosauromorphs. Members of the family are known from the Late Triassic of Argentina, Arizona, New Mexico, and Texas.-Description:...
. The species name romeri honors influential 20th century vertebrate paleontologist Alfred Sherwood Romer.
Also found at the Hayden Quarry are the remains of phytosaur
Phytosaur
Phytosaurs are an extinct group of large semi-aquatic Late Triassic archosaurs. Phytosaurs belong to the family Phytosauridae and the order Phytosauria. They were long-snouted and heavily armoured, bearing a remarkable resemblance to modern crocodiles in size, appearance, and lifestyle, an example...
s, aetosaur
Aetosaur
Aetosaurs are an extinct order of heavily armoured, medium- to large-sized Late Triassic herbivorous archosaurs. They have small heads, upturned snouts, erect limbs, and a body covered by plate-like scutes. All aetosaurs belong to the family Stagonolepididae...
s, rauisuchia
Rauisuchia
Rauisuchia is a group of predatory and mostly large Triassic archosaurs. As a clade, Rauisuchia includes these Triassic forms and all crocodylomorphs, which are descendants of Triassic rauisuchians. The group in its traditional sense is paraphyletic, because it does not include crocodylomorph...
ns, and several types of dinosaurs and dinosaur relatives, including a Silesaurus
Silesaurus
Silesaurus is a genus of dinosauriform from the Late Triassic, approximately 230 million years ago in the Carnian faunal stage of what is now Poland....
-like animal, the herrerasaurid Chindesaurus
Chindesaurus
Chindesaurus is a genus of saurischian dinosaur named after Chinde Point , near where the genoholotype specimen was discovered in the Chinle Formation of Petrified Forest National Park, Arizona, by Bryan Small in 1985...
, and an unnamed coelophysoid
Coelophysoidea
Coelophysoids were common dinosaurs of the Late Triassic and Early Jurassic periods. They were widespread geographically, probably living on all continents. Coelophysoids were all slender, carnivorous forms with a superficial similarity to the coelurosaurs, with which they were formerly...
theropod. Finding the remains of four types of dinosaurs and dinosaur relatives (including Dromomeron itself) is noteworthy because it shows that dinosaurs did not immediately replace related groups; that some of these groups, like the lagerpetonids, persisted for longer than previously known and diversified; and that dinosaurian replacement may have occurred at different times in different areas.
Other specimens from the Chinle Formation of Arizona
Arizona
Arizona ; is a state located in the southwestern region of the United States. It is also part of the western United States and the mountain west. The capital and largest city is Phoenix...
and a roughly contemporaneous part of the Dockum Group
Dockum Group
The Dockum is a Late Triassic geologic group found primarily on the Llano Estacado of western Texas and eastern New Mexico with minor exposures in southwestern Kansas, eastern Colorado, and Oklahoma panhandle. The Dockum reaches a maximum thickness of slightly over 650 m but is usually much...
of Texas
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...
also have been assigned to this genus. These have been assigned to second species D. gregorii, named in 2009.
D. gregorii, named for Joseph T. Gregory
Joseph T. Gregory
Dr. Joseph Tracy Gregory was an American paleontologist and professor.Joseph Tracy Gregory was born in Eureka, California, the only child of Frank Gregory, a civil engineer, and Edith Tracy, a high school teacher...
, is based on TMM
Texas Memorial Museum
The Texas Memorial Museum is the main exhibit hall of the Texas Natural Science Center at the University of Texas at Austin in Austin, Texas, USA....
31100–1306, a right femur (thigh bone) from the Otis Chalk Quarry, Colorado City Formation, (Dockum Group), near Otis Chalk, Texas. Several other limb bones from the quarry, and a partial femur (thigh bone) from the Placerias
Placerias
Placerias was a dicynodont that lived during the late Carnian age of the Triassic Period...
Quarry of eastern Arizona
Arizona
Arizona ; is a state located in the southwestern region of the United States. It is also part of the western United States and the mountain west. The capital and largest city is Phoenix...
have been assigned to this species. The rocks D. gregorii is known from are older than those D. romeri has been found in. As with D. romeri, the Otis Chalk Quarry also has at least one specimen of the early dinosaur Chindesaurus.
External links
- Online supplementary material for the Irmis et al.. article (PDF).
- A fact sheet for the Irmis et al.. article.