Altirhinus
Encyclopedia
Altirhinus is a genus
of iguanodontian ornithopod
dinosaur
from the Early Cretaceous
Period of Mongolia
.
estimated the length at 6.5 metres (21 ft), the weight at 1.1 tonnes. The skull alone is about 30 inches (760 mm) long, with a wide mouth and a distinctive tall arch on top of its snout, from which this dinosaur derives its name.
of Mongolia . The Khukhtek was formed in the Aptian
to Albian
stages of the Early Cretaceous Period, which lasted from between 125 and 100 million years ago. Psittacosaurus
and the primitive ankylosaurid
Shamosaurus
have also been found in these rocks.
Several fossil
specimens of different ages and sizes are known. The holotype
, PIN 3386/8, is a skull
which is well preserved on the left side, as well as some postcranial material consisting of pieces of the hands, feet, shoulder and pelvic
girdles. A more fragmentary skull was also recovered, associated with some ribs, fragmentary vertebrae, and a complete forelimb. A third specimen preserves many limb bones and a series of 34 tail vertebrae from a smaller individual. Two even smaller fragmentary skeletons, presumably of young individuals, were uncovered nearby.
The remains of this animal were originally referred to the species Iguanodon
orientalis, which was first described in 1952. However, I. orientalis has since been shown to be fragmentary, nondiagnostic, and virtually indistinguishable from the Europe
an I. bernissartensis (Norman, 1996). As no features of I. orientalis are shared exclusively with the 1981 specimens, which are clearly distinguishable from Iguanodon, a new name for those specimens was required. British
paleontologist David B. Norman
named them Altirhinus kurzanovi in 1998.
The name was created from a Latin
word, altus ("high") and a Greek
word, ῥίς, rhis, genitive rhinos ("nose" or "snout"). There is one known species
(A. kurzanovi), which honors Sergei Kurzanov
, the influential Russia
n paleontologist who originally found the specimens in 1981.
to the family Hadrosauridae, but there is little agreement on the arrangement of genera and species in this area of the ornithopod family tree.
In the original description, it was included with Iguanodon
and Ouranosaurus
in a family Iguanodontidae (Horman, 1998). More recent analyses all find Altirhinus more derived
than either of those two genera, but less than Protohadros
, Probactrosaurus
, and hadrosaurids (Head, 2001; Kobayashi & Azuma, 2003; Norman, 2004). The former two studies also place Eolambia
between Altirhinus and hadrosaurids, while Norman's analysis finds that the two genera share a clade
.
Fukuisaurus
is just basal to Altirhinus according to the only analysis in which the former has been included (Kobayashi & Azuma, 2003).
, the outside fingers (digits I & V) were modified in different ways. The first digit was a simple sharp spike, as seen in Iguanodon
. Aside from defense, the thumb spike could possibly have also been used for breaking the shells of seeds or fruit. The fifth digit was somewhat opposable to the rest of the hand and may have been useful for grasping food.
There is a large diastema, or gap, between the keratin
ous beak on the front of the mouth and the main chewing teeth in the side of the mouth, which would allow the two sections to work independently, so Altirhinus could crop with its beak while simultaneously chewing with its teeth. Many herbivorous mammal
s show a similar adaptation and can crop with their incisor
s without disturbing their chewing molar
s.
Altirhinus was one of a number of advanced iguanodontians with snouts expanded outwards towards the end. This is quite possibly an example of convergent evolution
with hadrosaurids, famous for their wide "duckbill" snouts. These adaptations are also paralleled in many living mammalian herbivores of different lineages. Modern cows, horse
s, and white rhinoceros
all exhibit wide muzzles and all are grazing
animals. Grazing most often occurs at ground level, and if the expanded muzzles of Altirhinus and other related species were an adaptation to grazing, this may also explain corresponding weight-bearing adaptations of the forelimbs in derived iguanodontians, in order to get the head closer to the ground.
s, and a similar structure is seen on the snout of the Australia
n Muttaburrasaurus
. Many different functions have been proposed for the nasal arch. It may have housed tissues to cool the blood, conserve water, or enhance the sense of smell. Alternatively, it may have facilitated communication
through vocalization or visual display. As only two skulls have been located, it is entirely possible that the arched snout is only found in one gender, in which case it may have been used for sexual display, like in modern-day elephant seal
s.
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 iguanodontian 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...
from the Early Cretaceous
Early Cretaceous
The Early Cretaceous or the Lower Cretaceous , is the earlier or lower of the two major divisions of the Cretaceous...
Period of Mongolia
Mongolia
Mongolia is a landlocked country in East and Central Asia. It is bordered by Russia to the north and China to the south, east and west. Although Mongolia does not share a border with Kazakhstan, its western-most point is only from Kazakhstan's eastern tip. Ulan Bator, the capital and largest...
.
Description
Altirhinus was herbivorous and bipedal when walking or running, but probably became quadrupedal when feeding from the ground. According to the original description, the entire body probably extended 26 feet (8 m) from snout to tail tip. In 2010 Gregory S. PaulGregory S. Paul
Gregory Scott Paul is a freelance researcher, author and illustrator who works in paleontology, and more recently has examined sociology and theology. He is best known for his work and research on theropod dinosaurs and his detailed illustrations, both live and skeletal...
estimated the length at 6.5 metres (21 ft), the weight at 1.1 tonnes. The skull alone is about 30 inches (760 mm) long, with a wide mouth and a distinctive tall arch on top of its snout, from which this dinosaur derives its name.
History of Discovery
All known specimens of Altirhinus were recovered in 1981 during collaborative expeditions organized by Soviet and Mongolian scientists, from the Khukhtek Formation in the Dornogovi ProvinceDornogovi Province
Dornogovi is one of the 21 Aimags of Mongolia. It is located in the southeast of the country.-Administrative Subdivision:* - tosgon .** - The aimag capital Sainshand-References:...
of Mongolia . The Khukhtek was formed in the Aptian
Aptian
The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous epoch or series and encompasses the time from 125.0 ± 1.0 Ma to 112.0 ± 1.0 Ma , approximately...
to 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...
stages of the Early Cretaceous Period, which lasted from between 125 and 100 million years ago. Psittacosaurus
Psittacosaurus
Psittacosaurus is a genus of psittacosaurid ceratopsian dinosaur from the Early Cretaceous Period of what is now Asia, about 130 to 100 million years ago. It is notable for being the most species-rich dinosaur genus...
and the primitive ankylosaurid
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...
Shamosaurus
Shamosaurus
Shamosaurus is an extinct genus of basal ankylosaurid ankylosaur from Early Cretaceous deposits of Höövör, Mongolia. Shamosaurus is known from the holotype PIN N 3779/2 complete skull and jaw and the paratypes include partial skeleton remains and an armor. It was collected from the...
have also been found in these rocks.
Several fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
specimens of different ages and sizes are known. 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...
, PIN 3386/8, is a 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...
which is well preserved on the left side, as well as some postcranial material consisting of pieces of the hands, feet, shoulder and pelvic
Pelvis
In human anatomy, the pelvis is the lower part of the trunk, between the abdomen and the lower limbs .The pelvis includes several structures:...
girdles. A more fragmentary skull was also recovered, associated with some ribs, fragmentary vertebrae, and a complete forelimb. A third specimen preserves many limb bones and a series of 34 tail vertebrae from a smaller individual. Two even smaller fragmentary skeletons, presumably of young individuals, were uncovered nearby.
The remains of this animal were originally referred to the species Iguanodon
Iguanodon
Iguanodon is a genus of ornithopod dinosaur that lived roughly halfway between the first of the swift bipedal hypsilophodontids and the ornithopods' culmination in the duck-billed dinosaurs...
orientalis, which was first described in 1952. However, I. orientalis has since been shown to be fragmentary, nondiagnostic, and virtually indistinguishable from the Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
an I. bernissartensis (Norman, 1996). As no features of I. orientalis are shared exclusively with the 1981 specimens, which are clearly distinguishable from Iguanodon, a new name for those specimens was required. British
British people
The British are citizens of the United Kingdom, of the Isle of Man, any of the Channel Islands, or of any of the British overseas territories, and their descendants...
paleontologist David B. Norman
David B. Norman
David Bruce Norman is a British paleontologist, currently Director of the Sedgwick Museum, Cambridge University. He is a fellow at Christ's College, Cambridge where he teaches geology in the Natural Sciences tripos. He is a member of the Palaeontological Association. He has studied Iguanodon...
named them Altirhinus kurzanovi in 1998.
The name was created from a 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...
word, altus ("high") and a Greek
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...
word, ῥίς, rhis, genitive rhinos ("nose" or "snout"). There is one known species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
(A. kurzanovi), which honors Sergei Kurzanov
Sergei Kurzanov
Sergei Kurzanov is a Russian paleontologist at the Paleontological Institute of the Russian Academy of Sciences. He is known mainly for his work in Mongolia and the ex-Soviet republics in Central Asia. In 1998, a species of iguanodont dinosaur from Mongolia was named Altirhinus kurzanovi in his...
, the influential Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
n paleontologist who originally found the specimens in 1981.
Taxonomy
Altirhinus is definitely an advanced iguanodontian, just basalBasal (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:...
to the family Hadrosauridae, but there is little agreement on the arrangement of genera and species in this area of the ornithopod family tree.
In the original description, it was included with Iguanodon
Iguanodon
Iguanodon is a genus of ornithopod dinosaur that lived roughly halfway between the first of the swift bipedal hypsilophodontids and the ornithopods' culmination in the duck-billed dinosaurs...
and Ouranosaurus
Ouranosaurus
Ouranosaurus is an unusual genus of herbivorous iguanodont dinosaur that lived during the early Cretaceous about 110 million years ago in what is now Africa. Ouranosaurus measured about seven to eight meters long...
in a family Iguanodontidae (Horman, 1998). More recent analyses all find Altirhinus more 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...
than either of those two genera, but less than Protohadros
Protohadros
Protohadros is a genus of herbivorous ornithischian dinosaur from the Late Cretaceous , 95 million years ago....
, Probactrosaurus
Probactrosaurus
Probactrosaurus is an early herbivorous hadrosauroid iguanodont dinosaur. It lived in China during the Early Cretaceous period....
, and hadrosaurids (Head, 2001; Kobayashi & Azuma, 2003; Norman, 2004). The former two studies also place 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...
between Altirhinus and hadrosaurids, while Norman's analysis finds that the two genera share 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...
.
Fukuisaurus
Fukuisaurus
Fukuisaurus is a genus of herbivorous dinosaur from the Early Cretaceous. It was an ornithopod which lived in what is now Japan....
is just basal to Altirhinus according to the only analysis in which the former has been included (Kobayashi & Azuma, 2003).
Locomotion
As its forelimbs were roughly half the length of its hindlimbs, Altirhinus appears to have been primarily bipedal. However, its carpals (wrist bones) were thick and blocky, and the three middle fingers of its hand were wide, hyperextendable, and ended in hoof-like bones. This indicates that the forelimbs were also capable of supporting weight. Like many ornithopods, Altirhinus may have spent a significant amount of time in a quadrupedal position, perhaps while feeding.Feeding
While the three middle digits of each forelimb (digits II, III, & IV) were very thick and probably weight bearingWeight bearing
In orthopedics, weight-bearing is the amount of weight a patient puts on the leg on which surgery has been performed. In general, it is described as a percentage of the body weight, because each leg of a healthy person carries the full body weight when walking, in an alternating fashion.After...
, the outside fingers (digits I & V) were modified in different ways. The first digit was a simple sharp spike, as seen in Iguanodon
Iguanodon
Iguanodon is a genus of ornithopod dinosaur that lived roughly halfway between the first of the swift bipedal hypsilophodontids and the ornithopods' culmination in the duck-billed dinosaurs...
. Aside from defense, the thumb spike could possibly have also been used for breaking the shells of seeds or fruit. The fifth digit was somewhat opposable to the rest of the hand and may have been useful for grasping food.
There is a large diastema, or gap, between the keratin
Keratin
Keratin refers to a family of fibrous structural proteins. Keratin is the key of structural material making up the outer layer of human skin. It is also the key structural component of hair and nails...
ous beak on the front of the mouth and the main chewing teeth in the side of the mouth, which would allow the two sections to work independently, so Altirhinus could crop with its beak while simultaneously chewing with its teeth. Many herbivorous 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 show a similar adaptation and can crop with their incisor
Incisor
Incisors are the first kind of tooth in heterodont mammals. They are located in the premaxilla above and mandible below.-Function:...
s without disturbing their chewing molar
Molar (tooth)
Molars are the rearmost and most complicated kind of tooth in most mammals. In many mammals they grind food; hence the Latin name mola, "millstone"....
s.
Altirhinus was one of a number of advanced iguanodontians with snouts expanded outwards towards the end. This is quite possibly an example of convergent evolution
Convergent evolution
Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...
with hadrosaurids, famous for their wide "duckbill" snouts. These adaptations are also paralleled in many living mammalian herbivores of different lineages. Modern cows, horse
Horse
The horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...
s, and white rhinoceros
White Rhinoceros
The White Rhinoceros or Square-lipped rhinoceros is one of the five species of rhinoceros that still exist. It has a wide mouth used for grazing and is the most social of all rhino species...
all exhibit wide muzzles and all are grazing
Grazing
Grazing generally describes a type of feeding, in which a herbivore feeds on plants , and also on other multicellular autotrophs...
animals. Grazing most often occurs at ground level, and if the expanded muzzles of Altirhinus and other related species were an adaptation to grazing, this may also explain corresponding weight-bearing adaptations of the forelimbs in derived iguanodontians, in order to get the head closer to the ground.
Nasal Arch
The characteristic arched snout of Altirhinus was formed primarily by the nasal boneNasal bone
The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face, and form, by their junction, "the bridge" of the nose.Each has two surfaces and four borders....
s, and a similar structure is seen on the snout of the Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
n Muttaburrasaurus
Muttaburrasaurus
Muttaburrasaurus is a genus of herbivorous ornithopod dinosaur, living in what is now northeastern Australia between 100 and 98 million years ago during the early Cretaceous Period. It has been recovered in some analyses as a member of the iguanodontian family Rhabdodontidae...
. Many different functions have been proposed for the nasal arch. It may have housed tissues to cool the blood, conserve water, or enhance the sense of smell. Alternatively, it may have facilitated communication
Animal communication
Animal communication is any behavior on the part of one animal that has an effect on the current or future behaviour of another animal. The study of animal communication, is sometimes called Zoosemiotics has played an important part in the...
through vocalization or visual display. As only two skulls have been located, it is entirely possible that the arched snout is only found in one gender, in which case it may have been used for sexual display, like in modern-day elephant seal
Elephant seal
Elephant seals are large, oceangoing seals in the genus Mirounga. There are two species: the northern elephant seal and the southern elephant seal . Both were hunted to the brink of extinction by the end of the 19th century, but numbers have since recovered...
s.