Hoplitosaurus
Encyclopedia
Hoplitosaurus was a genus
of armored dinosaur
related to Polacanthus
. It was named from a partial skeleton found in the ?Barremian
-age Lower Cretaceous Lakota Formation
of Custer County
, South Dakota
. It is an obscure genus which has been subject to some misinterpretation of its damaged remains. Although there was a push to synonymize it with Polacanthus in the late 1980s-early 1990s, Hoplitosaurus has been accepted as a valid albeit poorly-known genus in more recent reviews.
specimen, USNM 4752, was discovered in 1898 by Nelson Horatio Darton
, near Buffalo Gap Station, and consisted of rib
s, caudal vertebrae, part of a right scapulocoracoid
, parts of both humeri
, a right femur
, and a variety of armor
(including tall spines). Frederic Augustus Lucas
described it briefly in 1901 as a new species of Stegosaurus
, but soon gave the material its own genus. Charles W. Gilmore
fully described the material in 1914.
William T. Blows and Javier Pereda-Suberbiola both considered the genus to be the same as Polacanthus
, creating the new combination Polacanthus marshii, but this has since been rejected. Ken Carpenter
and James Kirkland noted that many of the resemblances between the two were more widely distributed among ankylosaurs than previously thought, or were based on damage to the bones, such as some femoral characters.
However, its similarity to Polacanthus has been noted since Lucas first published on it in 1901, the two being most similar in armor, although Hoplitosaurus lacks the sacral
shield of armor found in Polacanthus. Today, both are considered to be polacanthine or polacanthid ankylosaurs
, depending on classification preference (see for example), or ankylosaurians of uncertain relationships.
One point of similarity that was found to be spurious was the possession of a tail club
. In Polacanthus, this turned out to be a misinterpretation of caudal vertebrae, ossified tendon
s, and armor. (It is not clear what the report in Hoplitosaurus was based on).
al herbivore
, eating low to the ground; armor was its main defense.
Blows (2001) reconsidered the armor in light of new data on polacanthine dinosaurs, and found it to fall into the following categories:
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 armored 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...
related to Polacanthus
Polacanthus
Polacanthus, deriving its name from the Ancient Greek poly-/πολυ- "many" and acantha/ακανθα "thorn" or "prickle", was an early armored, spiked, plant-eating ankylosaur from the early Cretaceous period. Early depictions often gave it a very vague head as it was only known from the rear half of the...
. It was named from a partial skeleton found in the ?Barremian
Barremian
The Barremian is an age in the geologic timescale between 130.0 ± 1.5 Ma and 125.0 ± 1.0 Ma). It is a subdivision of the Early Cretaceous epoch...
-age Lower Cretaceous Lakota Formation
Lakota Formation
The Lakota Formation is a sequence of rocks from the Barremian epoch from Western North America. Located in South Dakota, the name is derived from the Lakota Native American tribe....
of Custer County
Custer County, South Dakota
As of the census of 2000, there were 7,275 people, 2,970 households, and 2,067 families residing in the county. The population density was 5 people per square mile . There were 3,624 housing units at an average density of 2 per square mile...
, South Dakota
South Dakota
South Dakota is a state located in the Midwestern region of the United States. It is named after the Lakota and Dakota Sioux American Indian tribes. Once a part of Dakota Territory, South Dakota became a state on November 2, 1889. The state has an area of and an estimated population of just over...
. It is an obscure genus which has been subject to some misinterpretation of its damaged remains. Although there was a push to synonymize it with Polacanthus in the late 1980s-early 1990s, Hoplitosaurus has been accepted as a valid albeit poorly-known genus in more recent reviews.
History and Taxonomy
The holotypeHolotype
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, USNM 4752, was discovered in 1898 by Nelson Horatio Darton
Nelson Horatio Darton
Nelson Horatio Darton was a geologist who worked for the United States Geological Survey. He was born in Brooklyn, New York, and started working in his uncle's drug business at the age of 13, also becoming a practicing chemist. His interest in geology started as a sideline, and he was hired by...
, near Buffalo Gap Station, and consisted of rib
Rib
In vertebrate anatomy, ribs are the long curved bones which form the rib cage. In most vertebrates, ribs surround the chest, enabling the lungs to expand and thus facilitate breathing by expanding the chest cavity. They serve to protect the lungs, heart, and other internal organs of the thorax...
s, caudal vertebrae, part of a right scapulocoracoid
Scapulocoracoid
The Scapulocoracoid is the unit of the pectoral girdle that contains the coracoid and scapula.The coracoid itself is a beak-shaped bone that is commonly found in most vertebrates with a few exceptions.The scapula is commonly known as the shoulder blade...
, parts of both humeri
Humerus
The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....
, a right femur
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...
, and a variety of armor
Armour (zoology)
Armour in animals is external or superficial protection against attack by predators, formed as part of the body , usually through the hardening of body tissues, outgrowths or secretions. It has therefore mostly developed in 'prey' species...
(including tall spines). Frederic Augustus Lucas
Frederic Augustus Lucas
Frederic Augustus Lucas, Sc.D. was an American museum director.-Early years:Frederic A. Lucas was born March 25, 1852 at Plymouth, Massachusetts.-Career:...
described it briefly in 1901 as a new species of Stegosaurus
Stegosaurus
Stegosaurus is a genus of armored stegosaurid dinosaur. They lived during the Late Jurassic period , some 155 to 150 million years ago in what is now western North America. In 2006, a specimen of Stegosaurus was announced from Portugal, showing that they were present in Europe as well...
, but soon gave the material its own genus. Charles W. Gilmore
Charles W. Gilmore
Charles Whitney Gilmore was an American paleontologist, who named dinosaurs in North America and Mongolia, including the Cretaceous sauropod Alamosaurus, Alectrosaurus, Archaeornithomimus, Bactrosaurus, Brachyceratops, Chirostenotes, Mongolosaurus, Parrosaurus, Pinacosaurus, Styracosaurus and...
fully described the material in 1914.
William T. Blows and Javier Pereda-Suberbiola both considered the genus to be the same as Polacanthus
Polacanthus
Polacanthus, deriving its name from the Ancient Greek poly-/πολυ- "many" and acantha/ακανθα "thorn" or "prickle", was an early armored, spiked, plant-eating ankylosaur from the early Cretaceous period. Early depictions often gave it a very vague head as it was only known from the rear half of the...
, creating the new combination Polacanthus marshii, but this has since been rejected. Ken Carpenter
Kenneth Carpenter
Kenneth Carpenter is a paleontologist. He is the museum director of the USU Eastern Prehistoric Museum and author or co-author of a number of books on dinosaurs and Mesozoic life...
and James Kirkland noted that many of the resemblances between the two were more widely distributed among ankylosaurs than previously thought, or were based on damage to the bones, such as some femoral characters.
However, its similarity to Polacanthus has been noted since Lucas first published on it in 1901, the two being most similar in armor, although Hoplitosaurus lacks the sacral
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...
shield of armor found in Polacanthus. Today, both are considered to be polacanthine or polacanthid ankylosaurs
Ankylosauria
Ankylosauria is a group of herbivorous dinosaurs of the order Ornithischia. It includes the great majority of dinosaurs with armor in the form of bony osteoderms. Ankylosaurs were bulky quadrupeds, with short, powerful limbs. They are first known to have appeared in the early Jurassic Period of...
, depending on classification preference (see for example), or ankylosaurians of uncertain relationships.
One point of similarity that was found to be spurious was the possession of a tail club
Club (zoology)
In zoology, a club is a bony mass at the end of the tail of some dinosaurs and of some mammals, most notably the ankylosaurids and the glyptodonts...
. In Polacanthus, this turned out to be a misinterpretation of caudal vertebrae, ossified tendon
Tendon
A tendon is a tough band of fibrous connective tissue that usually connects muscle to bone and is capable of withstanding tension. Tendons are similar to ligaments and fasciae as they are all made of collagen except that ligaments join one bone to another bone, and fasciae connect muscles to other...
s, and armor. (It is not clear what the report in Hoplitosaurus was based on).
Paleobiology
Gilmore described the animal as being about 1.2 m (4 ft) tall at the hips. It would have been a quadrupedQuadruped
Quadrupedalism is a form of land animal locomotion using four limbs or legs. An animal or machine that usually moves in a quadrupedal manner is known as a quadruped, meaning "four feet"...
al herbivore
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...
, eating low to the ground; armor was its main defense.
Blows (2001) reconsidered the armor in light of new data on polacanthine dinosaurs, and found it to fall into the following categories:
- PectoralShoulderThe human shoulder is made up of three bones: the clavicle , the scapula , and the humerus as well as associated muscles, ligaments and tendons. The articulations between the bones of the shoulder make up the shoulder joints. The major joint of the shoulder is the glenohumeral joint, which...
spines - PresacralTorsoTrunk or torso is an anatomical term for the central part of the many animal bodies from which extend the neck and limbs. The trunk includes the thorax and abdomen.-Major organs:...
spines - Splates (spine+plate) from the sacral region
- Tall, asymmetric, hollow-based caudalTailThe 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...
plates - Small to large solid-based, ridged ossicles (filling spaces)