Protohadros
Encyclopedia
Protohadros is a genus
of herbivorous ornithischian dinosaur
from the Late Cretaceous
(Cenomanian
stage), 95 million years ago.
Gary Byrd, a part-time palaeontologist
, discovered some remains of this euornithopod (ribs and an ungual
) during early 1994 at Flower Mound
, Denton County, north-central Texas
. He informed professional palaeontologist Yuong-Nam Lee of the find, who arranged for the entire preserved fossil to be excavated. It was first reported upon in 1996 by Jason Head of the Dedman College of Humanities and Sciences
, Southern Methodist University
. The type species
Protohadros byrdi was described and named by Head in 1998. The genus name is derived from Greek πρῶτος, protos, "first", en ἁδρός, hadros, "thick", a reference to the fact that Head considered the species the oldest known hadrosaur. The specific name honours Byrd.
The holotype
, specimen SMU 74582, of Protohadros, was found in the Woodbine Formation
, which dates to the middle Cenomanian
. It consists of a partial skull, pieces of ribs, a hand ungual and a neural arch. In 1997 Yuong named possible tracks of Protohadros as the ichnospecies Caririchnium
protohadrosaurichnos.
Due to the paucity of the remains much of the reconstruction of this dinosaur is speculative. The skull is about seventy centimetres long. From this Head estimated the length of the type specimen of Protohadros at seven to eight metres. He pointed out that this specimen was that of a subadult and that fully-grown individuals could have been longer. Protohadros had a massive, very deep set of lower jaws, and the snout was strongly turned down at the front, which according to Head suggested a habit of grazing on low-growing plants, rather than browsing from bushes or overhanging branches. Its diet would then have consisted of the swamp plants which grew in the delta streams in its habitat, scooped up by the broad, down-turned mouth. In some respects Protohadros was intermediate in morphology to more derived hadrosaurids. Like these it did have pleurokinesis, a cranial joint system that produced the food-grinding action, but only partially in that the quadrate at the back of the skull was still relatively immobile.
Protohadros rear legs were probably longer than the front pair, and it could move on all fours or walk and run on its hind legs only.
Protohadros was first described as the most basal
member of the Hadrosauridae, hence its generic name. However, scientific opinion has since changed and it is now regarded as a non-hadrosaurid iguanodontian, a basal member of the Hadrosauroidea
, though one closely related to the Hadrosauridae. The dinosaur's discovery conflicted with the idea that hadrosaurid evolved in Asia
, but its reassessment as a less-derived
iguanodontian has rendered this discrepancy less problematic.
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 ornithischian 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...
(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), 95 million years ago.
Gary Byrd, a part-time palaeontologist
Paleontology
Paleontology "old, ancient", ὄν, ὀντ- "being, creature", and λόγος "speech, thought") is the study of prehistoric life. It includes the study of fossils to determine organisms' evolution and interactions with each other and their environments...
, discovered some remains of this euornithopod (ribs and an ungual
Ungual
An ungual is a highly modified distal toe bone which ends in a hoof, claw, or nail. Elephants and other ungulates have ungual phalanges, as did the sauropods and horned dinosaurs. A claw is a highly modified ungual phalange.As an adjective, ungual means related to nail, as in periungual .-External...
) during early 1994 at Flower Mound
Flower Mound, Texas
Flower Mound is a town in Denton and Tarrant counties in the U.S. state of Texas, and a suburb of Fort Worth and Dallas. Its population was 50,702 at the U.S. Census Bureau's 2000 census, and 64,669 at the 2010 Census. The town derives its name from the prominent mound located in the southern...
, Denton County, north-central 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...
. He informed professional palaeontologist Yuong-Nam Lee of the find, who arranged for the entire preserved fossil to be excavated. It was first reported upon in 1996 by Jason Head of the Dedman College of Humanities and Sciences
Dedman College of Humanities and Sciences
Dedman College of Southern Methodist University was named in 1981 in honor of its benefactors, Robert H. Dedman Sr. and his wife, Nancy McMillan Dedman, both of Dallas.- Areas of Study :...
, Southern Methodist University
Southern Methodist University
Southern Methodist University is a private university in Dallas, Texas, United States. Founded in 1911 by the Methodist Episcopal Church, South, SMU operates campuses in Dallas, Plano, and Taos, New Mexico. SMU is owned by the South Central Jurisdiction of the United Methodist Church...
. 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...
Protohadros byrdi was described and named by Head in 1998. The genus name is derived from Greek πρῶτος, protos, "first", en ἁδρός, hadros, "thick", a reference to the fact that Head considered the species the oldest known hadrosaur. The specific name honours Byrd.
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 SMU 74582, of Protohadros, was found in the Woodbine Formation
Woodbine Formation
The Woodbine Formation is a geological formation in east Texas whose strata date back to the Late Cretaceous. Dinosaur remains are among the fossils that have been recovered from the formation.-Vertebrate paleofauna:...
, which dates to the middle 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...
. It consists of a partial skull, pieces of ribs, a hand ungual and a neural arch. In 1997 Yuong named possible tracks of Protohadros as the ichnospecies Caririchnium
Caririchnium
Caririchnium is an ichnogenus of dinosaur footprint.-References:...
protohadrosaurichnos.
Due to the paucity of the remains much of the reconstruction of this dinosaur is speculative. The skull is about seventy centimetres long. From this Head estimated the length of the type specimen of Protohadros at seven to eight metres. He pointed out that this specimen was that of a subadult and that fully-grown individuals could have been longer. Protohadros had a massive, very deep set of lower jaws, and the snout was strongly turned down at the front, which according to Head suggested a habit of grazing on low-growing plants, rather than browsing from bushes or overhanging branches. Its diet would then have consisted of the swamp plants which grew in the delta streams in its habitat, scooped up by the broad, down-turned mouth. In some respects Protohadros was intermediate in morphology to more derived hadrosaurids. Like these it did have pleurokinesis, a cranial joint system that produced the food-grinding action, but only partially in that the quadrate at the back of the skull was still relatively immobile.
Protohadros rear legs were probably longer than the front pair, and it could move on all fours or walk and run on its hind legs only.
Protohadros was first described as the most 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:...
member of the Hadrosauridae, hence its generic name. However, scientific opinion has since changed and it is now regarded as a non-hadrosaurid iguanodontian, a basal member of the Hadrosauroidea
Hadrosauroidea
Hadrosauroidea is a clade or superfamily of ornithischian dinosaurs that includes the "duck-billed" dinosaurs, or hadrosaurids, and their close relatives. Many primitive hadrosauroids, such as the sail-backed Ouranosaurus, have traditionally been included in a paraphyletic "Iguanodontidae"...
, though one closely related to the Hadrosauridae. The dinosaur's discovery conflicted with the idea that hadrosaurid evolved in Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
, but its reassessment as a less-derived
Derived
In phylogenetics, a derived trait is a trait that is present in an organism, but was absent in the last common ancestor of the group being considered. This may also refer to structures that are not present in an organism, but were present in its ancestors, i.e. traits that have undergone secondary...
iguanodontian has rendered this discrepancy less problematic.