Animantarx
Encyclopedia
Animantarx is a genus
of nodosaurid ankylosauria
n dinosaur
from the Upper Cretaceous
of western North America
. Like other nodosaurs, it would have been a slow-moving quadruped
al herbivore
covered in heavy armor
scute
s, but without a tail club
. The skull
measures approximately 10 inches (25 cm) in length, suggesting the animal as a whole was no more than 10 feet (3 meters) long.
The generic name is composed of the Latin
words animatus ("living" or "animated") and arx ("fortress" or "citadel"), referring to its armored nature. In particular, the name is a reference to a comment made by paleontologist R. S. Lull
about ankylosaurs, that as "an animated citadel, these animals must have been practically unassailable..." The type species
is the only one known so far, and is called A. ramaljonesi after its discoverer, Ramal Jones. His wife, Carol Jones, also discovered the contemporaneous dinosaur Eolambia
nearby.
and quadratojugal
bones of the skull, and a mandible
which is only armoured
on half of its length.
These fossil
remains were discovered in the Mussentuchit Member of the Cedar Mountain Formation
in the eastern portion of the U.S. state of Utah
. This section of the formation
is believed to represent the late Albian
through early Cenomanian
stages of the Late Cretaceous
Period, or about 106 to 97 million years ago. At least 80 other vertebrate
species are known from the Mussentuchit, including fish
, frog
s, lizard
s, snake
s, crocodilia
ns, dinosaur
s, bird
s, and mammal
s, although not all are complete enough to name. Many dinosaur groups are represented by fossils from this member
, including carnivorous
theropods as well as several different herbivorous types, including the iguanodont
Eolambia. The presence of aquatic animals like fish and frogs, as well as the mudstone
in which their fossils are found, suggests that this was a floodplain
environment.
Earlier layers within the Cedar Mountain Formation contain different nodosaur species. The oldest layer, known as the Yellow Cat Member, contains Gastonia
, while the intermediate Poison Strip and Ruby Ranch Members contain remains which may belong to Sauropelta
. The Mussentuchit, which is the youngest member of the Cedar Mountain, contains only Animantarx. While there is still a lot of exploration left to be done, this division of nodosaur species corresponds with that of other dinosaur groups and provides support for the hypothesis
of three separate fauna
s in the Cedar Mountain Formation. The Mussentuchit fauna includes many taxa which may be of Asia
n origin and suggests a dispersal event
may have occurred from Asia into North America around this time.
Fossils in this region are often slightly radioactive, and remains of Animantarx were actually discovered following a radiological survey of the area performed by Ramal Jones, which located a higher level of radioactivity at a certain location. Subsequent excavation at this site turned up the fossil skeleton of Animantarx; no bones had been exposed on the surface.
because of its rounded supraorbital
protrusions and a "knoblike" acromion on the scapula
. Two separate studies have found Animantarx to be the sister taxon of Edmontonia
within Nodosauridae.
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 nodosaurid ankylosauria
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...
n 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 Upper 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 western 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...
. Like other nodosaurs, it would have been a slow-moving quadruped
Quadruped
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...
covered in heavy 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...
scute
Scute
A scute or scutum is a bony external plate or scale, as on the shell of a turtle, the skin of crocodilians, the feet of some birds or the anterior portion of the mesonotum in insects.-Properties:...
s, but without a tail club
Ankylosauridae
An ankylosaurid is a member of the Ankylosauridae family of armored dinosaurs that evolved 125 million years ago and became extinct 65 million years ago during the Cretaceous-Tertiary extinction event...
. The skull
Skull
The skull is a bony structure in the head of many animals that supports the structures of the face and forms a cavity for the brain.The skull is composed of two parts: the cranium and the mandible. A skull without a mandible is only a cranium. Animals that have skulls are called craniates...
measures approximately 10 inches (25 cm) in length, suggesting the animal as a whole was no more than 10 feet (3 meters) long.
The generic name is composed of the Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
words animatus ("living" or "animated") and arx ("fortress" or "citadel"), referring to its armored nature. In particular, the name is a reference to a comment made by paleontologist R. S. Lull
R. S. Lull
Richard Swann Lull was an American paleontologist from the early 20th century, active at Yale University, who is largely remembered now for championing a Pre-Neo-Darwinian Synthesis view of evolution, whereby mutation could unlock mysterious genetic drives that, over time, would lead populations...
about ankylosaurs, that as "an animated citadel, these animals must have been practically unassailable..." 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...
is the only one known so far, and is called A. ramaljonesi after its discoverer, Ramal Jones. His wife, Carol Jones, also discovered the contemporaneous dinosaur Eolambia
Eolambia
Eolambia is a genus of herbivorous iguanodontian dinosaur from the mid-Cretaceous Period of the USA.In 1992 Carole Jones and her husband Ramal Jones near Castle Dale in Emery County, Utah, on the San Rafael Swell Anticline discovered a fossil site which would be named the Carol Quarry in her honour...
nearby.
Discovery and species
Only one specimen of Animantarx has so far been recovered. The remains include the lower jaw and back half of the skull, along with neck and back vertebrae, and various limb elements. Animantarx is characterized by a unique combination of features, including a highly domed skull back, small horns on the postorbitalPostorbital
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...
and quadratojugal
Quadratojugal
The quadratojugal is a small jaw bone that is present in most amphibians, reptiles, and birds, but has been lost in mammals. It is connected to the jugal as well as other bones, though these may vary with species....
bones of the skull, and a mandible
Mandible
The mandible pronunciation or inferior maxillary bone forms the lower jaw and holds the lower teeth in place...
which is only armoured
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...
on half of its length.
These fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
remains were discovered in the Mussentuchit Member of the Cedar Mountain Formation
Cedar Mountain Formation
The Cedar Mountain Formation is the name given to distinctive sedimentary rocks in eastern Utah that occur between the underlying Morrison Formation and overlying Naturita Formation . It is composed of non-marine sediments, that is, sediments deposited in rivers, lakes and on flood plains...
in the eastern portion of the U.S. state of Utah
Utah
Utah is a state in the Western United States. It was the 45th state to join the Union, on January 4, 1896. Approximately 80% of Utah's 2,763,885 people live along the Wasatch Front, centering on Salt Lake City. This leaves vast expanses of the state nearly uninhabited, making the population the...
. This section of the formation
Geologic formation
A formation or geological formation is the fundamental unit of lithostratigraphy. A formation consists of a certain number of rock strata that have a comparable lithology, facies or other similar properties...
is believed to represent the late Albian
Albian
The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous epoch/series. Its approximate time range is 112.0 ± 1.0 Ma to 99.6 ± 0.9 Ma...
through early 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...
stages of the Late Cretaceous
Late Cretaceous
The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...
Period, or about 106 to 97 million years ago. At least 80 other vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
species are known from the Mussentuchit, including fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
, frog
Frog
Frogs are amphibians in the order Anura , formerly referred to as Salientia . Most frogs are characterized by a short body, webbed digits , protruding eyes and the absence of a tail...
s, lizard
Lizard
Lizards are a widespread group of squamate reptiles, with nearly 3800 species, ranging across all continents except Antarctica as well as most oceanic island chains...
s, snake
Snake
Snakes are elongate, legless, carnivorous reptiles of the suborder Serpentes that can be distinguished from legless lizards by their lack of eyelids and external ears. Like all squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales...
s, crocodilia
Crocodilia
Crocodilia is an order of large reptiles that appeared about 84 million years ago in the late Cretaceous Period . They are the closest living relatives of birds, as the two groups are the only known survivors of the Archosauria...
ns, 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...
s, bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s, and mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s, although not all are complete enough to name. Many dinosaur groups are represented by fossils from this member
Geologic unit
A geological unit is a volume of rock or ice of identifiable origin and age range that is defined by the distinctive and dominant, easily mapped and recognizable petrographic, lithologic or paleontologic features that characterize it....
, including carnivorous
Carnivore
A carnivore meaning 'meat eater' is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of animal tissue, whether through predation or scavenging...
theropods as well as several different herbivorous types, including the iguanodont
Iguanodont
Iguanodonts were herbivorous dinosaurs that lived from the mid-Jurassic to Late Cretaceous. Some members include Camptosaurus, Callovosaurus, Iguanodon, Ouranosaurus, and the hadrosaurids or "duck-billed dinosaurs". Iguanodonts were one of the first groups of dinosaurs to be found...
Eolambia. The presence of aquatic animals like fish and frogs, as well as the 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...
in which their fossils are found, suggests that this was a floodplain
Floodplain
A floodplain, or flood plain, is a flat or nearly flat land adjacent a stream or river that stretches from the banks of its channel to the base of the enclosing valley walls and experiences flooding during periods of high discharge...
environment.
Earlier layers within the Cedar Mountain Formation contain different nodosaur species. The oldest layer, known as the Yellow Cat Member, contains Gastonia
Gastonia (dinosaur)
Gastonia is a genus of nodosaurid dinosaur from the Early Cretaceous of North America, around 125 million years ago. Closely related to Polacanthus, it has a sacral shield and large shoulder spikes. It is also the first polacanthine dinosaur to have been mounted for display at the Denver Museum of...
, while the intermediate Poison Strip and Ruby Ranch Members contain remains which may belong to Sauropelta
Sauropelta
Sauropelta is a genus of nodosaurid dinosaur that existed in the Early Cretaceous Period of North America. One species has been named although others may have existed. Anatomically, Sauropelta is one of the most well-understood nodosaurids, with fossilized remains recovered in the U.S. states of...
. The Mussentuchit, which is the youngest member of the Cedar Mountain, contains only Animantarx. While there is still a lot of exploration left to be done, this division of nodosaur species corresponds with that of other dinosaur groups and provides support for the hypothesis
Hypothesis
A hypothesis is a proposed explanation for a phenomenon. The term derives from the Greek, ὑποτιθέναι – hypotithenai meaning "to put under" or "to suppose". For a hypothesis to be put forward as a scientific hypothesis, the scientific method requires that one can test it...
of three separate fauna
Fauna
Fauna or faunæ is all of the animal life of any particular region or time. The corresponding term for plants is flora.Zoologists and paleontologists use fauna to refer to a typical collection of animals found in a specific time or place, e.g. the "Sonoran Desert fauna" or the "Burgess shale fauna"...
s in the Cedar Mountain Formation. The Mussentuchit fauna includes many taxa which may be of 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...
n origin and suggests a dispersal event
Biological dispersal
Biological dispersal refers to species movement away from an existing population or away from the parent organism. Through simply moving from one habitat patch to another, the dispersal of an individual has consequences not only for individual fitness, but also for population dynamics, population...
may have occurred from Asia into North America around this time.
Fossils in this region are often slightly radioactive, and remains of Animantarx were actually discovered following a radiological survey of the area performed by Ramal Jones, which located a higher level of radioactivity at a certain location. Subsequent excavation at this site turned up the fossil skeleton of Animantarx; no bones had been exposed on the surface.
Classification
Animantarx is universally thought of as a nodosaurid ankylosaur, although its precise relationships within that family are uncertain. The most recent cladistic analysis of ankylosaur phylogeny does not include Animantarx, although the authors recognize the genus as Nodosauridae incertae sedisIncertae sedis
, is a term used to define a taxonomic group where its broader relationships are unknown or undefined. Uncertainty at specific taxonomic levels is attributed by , , and similar terms.-Examples:*The fossil plant Paradinandra suecica could not be assigned to any...
because of its rounded supraorbital
Supraorbital foramen
The supraorbital foramen is a bony elongated path located above the orbit and under the forehead. The supraorbital foramen lies directly under the eyebrow....
protrusions and a "knoblike" acromion on the scapula
Scapula
In anatomy, the scapula , omo, or shoulder blade, is the bone that connects the humerus with the clavicle ....
. Two separate studies have found Animantarx to be the sister taxon of Edmontonia
Edmontonia
Edmontonia was an armoured dinosaur, a part of the nodosaur family from the Late Cretaceous Period. It is named after the Edmonton Formation , the unit of rock it was found in.-Description:...
within Nodosauridae.