Psittacosaurus
Encyclopedia
Psittacosaurus is a genus
of psittacosaurid ceratopsia
n 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. Nine to eleven species are recognized from fossil
s found in different regions of modern-day China
, Mongolia
and Russia
, with a possible additional species from Thailand
.
All species of Psittacosaurus were gazelle
-sized biped
al herbivore
s characterized by a high, powerful beak
on the upper jaw. At least one species had long, quill-like structures on its tail and lower back, possibly serving a display function. Psittacosaurs were extremely early ceratopsians and, while they developed many novel adaptations of their own, they also shared many anatomical features with later ceratopsians, such as Protoceratops
and the elephant
-sized Triceratops
.
Psittacosaurus is not as familiar to the general public as its distant relative Triceratops but it is one of the most completely known dinosaur genera. Fossils of over 400 individuals have been collected so far, including many complete skeletons. Most different age classes are represented, from hatchling
through to adult, which has allowed several detailed studies of Psittacosaurus growth rates and reproductive biology
. The abundance of this dinosaur in the fossil record has led to its use as an index fossil
for Early Cretaceous sediments of central Asia
.
Different species of Psittacosaurus varied in size and specific features of the skull
and skeleton, but shared the same overall body shape. The best-known species, P. mongoliensis, reached 2 meters (6.5 ft) in length. The maximum adult body weight was most likely over 20 kilogram
s (44 lb) in P. mongoliensis. Several species approached P. mongoliensis in size (P. major, P. neimongoliensis, P. xinjiangensis), while others were somewhat smaller (P. sinensis, P. meileyingensis). P. ordosensis was the smallest known species, 30% smaller than P. mongoliensis. The largest were P. lujiatunensis and P. sibiricus, although neither was significantly larger than P. mongoliensis.
The skull of Psittacosaurus was highly modified compared to other ornithischia
n dinosaurs of its time. The skull was extremely tall in height and short in length, with an almost round profile
in some species. The portion in front of the orbit
(eye socket) was only 40% of total skull length, shorter than any other known ornithischian. The lower jaws of psittacosaurs are characterized by a bulbous vertical ridge down the center of each tooth. Both upper and lower jaws sported a pronounced beak, formed from the rostral and predentary bones, respectively. The bony core of the beak may have been sheathed in keratin
to provide a sharp cutting surface for cropping plant
material. As the generic name suggests, the short skull and beak superficially resembled those of modern parrots. Psittacosaurus skulls shared several adaptations with more derived
ceratopsians, such as the unique rostral bone at the tip of the upper jaw, and the flared jugal
(cheek) bones. However, there was still no sign of the bony neck frill or prominent facial horns which would develop in later ceratopsians. Bony horns did protrude from the skull of P. sibiricus, but these are thought to be an example of convergent evolution
.
Psittacosaurus postcranial skeletons were more typical of a 'generic' bipedal ornithischian. In P. mongoliensis, similarly to other species, the forelimbs were only 58% as long as the hindlimbs and their range of motion indicates that the hands could neither be pronated nor used to generate propulsive force, suggesting that these animals were totally bipedal in life. There were only four digits on the manus
('hand'), as opposed to the five found in most other ornithischians (including all other ceratopsians). Overall, the four-toed hindfoot was very similar to many other small ornithischians.
, paleontologist and president of the American Museum of Natural History
(AMNH) in a paper published on October 19. The generic name is composed of the Greek
words ψιττακος/psittakos ('parrot') and σαυρος/sauros ('lizard'), suggested by the superficially parrot-like beak of these animals and their reptilian
nature.
s). In contrast, most other dinosaur genera are monospecific, containing only a single known species. The difference is most likely due to quirks of the fossil record. While Psittacosaurus is known from hundreds of fossil specimens, most other dinosaur species are known from far fewer, and many are represented by only a single specimen. With a very high sample size, the diversity of Psittacosaurus can be analyzed more completely than that of most dinosaur genera, resulting in the recognition of more species. Most extant animal genera are represented by multiple species, suggesting that this may have been the case for extinct dinosaur genera as well, although most of these species may not have been preserved. In addition, most dinosaurs are known solely from bone
s and can only be evaluated from a morphological
standpoint, whereas extant species often have very similar skeletal morphology but differ in other ways which would not normally be preserved in the fossil record, such as behavior, or coloration. Therefore actual species diversity may be much higher than currently recognized in this and other dinosaur genera.
Psittacosaurus is the type genus
of the family Psittacosauridae, which was also named by Osborn in 1923. Only one other genus, Hongshanosaurus
, is currently classified in this family alongside Psittacosaurus. Psittacosaurids were basal
to almost all known ceratopsians except Yinlong
and perhaps Chaoyangsauridae
. While Psittacosauridae was an early branch of the ceratopsian family tree, Psittacosaurus itself was probably not directly ancestral to any other groups of ceratopsians. All other ceratopsians retained the fifth digit of the hand, a plesiomorphy or primitive trait, whereas all species of Psittacosaurus had only four digits on the hand. In addition, the antorbital fenestra, an opening in the skull between the eye socket and nostril
, was lost during the evolution
of Psittacosauridae, but is still found in most other ceratopsians and in fact most other archosaur
s. It is considered highly unlikely that the fifth digit or antorbital fenestra would evolve
a second time.
Although many species of Psittacosaurus have been named, their relationships to each other have not yet been fully explored and no scientific consensus exists on the subject. Several phylogenetic
analyses have been published, with the most detailed being those by Alexander Averianov and colleagues in 2006, Hai-Lu You and colleagues in 2008, and Paul Sereno
in 2010.
Averianov et al. (2006):
You et al. (2008):
Sereno (2010):
It has been suggested that P. lujiatunensis is basal to all other species. This would be consistent with its earlier appearance in the fossil record.
sediments in Asia, from southern Siberia
to northern China, or possibly as far south as Thailand. The most common age of geologic formation
s bearing Psittacosaurus fossils is from the late Barremian
through Albian
stages of the Early Cretaceous, or approximately 125 to 100 Ma (million years ago). Nearly all terrestrial sedimentary formations of this age in Mongolia and northern China have produced fossils of Psittacosaurus, leading its use as an index fossil for this time period in the region, along with the very common pterosaur
Dsungaripterus
.
The earliest known species is P. lujiatunensis, found in the lowest beds of the Yixian Formation
. Over 200 specimens attributed to this genus have been recovered from these and other beds of the Yixian, the age of which is the subject of much debate. Although many early studies using radiometric dating
put the Yixian in the Jurassic Period, tens of millions of years outside of the expected temporal range of Psittacosaurus, most recent work dates it to the Early Cretaceous. Using argon-argon dating
, a team of Chinese scientists dated the lowest beds
in the formation to about 128 Ma, and the highest to approximately 122 Ma. A more recent Chinese study, using uranium-lead dating
, suggests that the lower beds are younger, approximately 125 Ma, while agreeing with an age of 122 Ma for the upper beds. This work indicates that the Yixian is early Aptian in age, or possibly late Barremian
to early Aptian.
s of Psittacosaurus and modern birds and reptiles suggest that it may have been cathemeral
, active throughout the day at short intervals.
Psittacosaurs had self-sharpening teeth that would have been useful for cropping and slicing tough plant material. However, unlike later ceratopsians, they did not have teeth suitable for grinding or chewing their food. Instead, they used gastroliths, stones swallowed to wear down food as it passed through the digestive system. Gastroliths, sometimes numbering more than fifty, are occasionally found in the abdominal cavities of psittacosaurs, and may have been stored in a gizzard
, as in modern birds.
Unlike many other dinosaurs, psittacosaurs had akinetic skulls: the upper and lower jaws behaved as single units without internal joints. The only joint was the jaw joint itself, and psittacosaurs could slide their lower jaws forward and backward on the joint, permitting a shearing action. Unlike most ceratopsians, their beaks did not form curved tips, but were instead rounded and flattened. If the jaws were aligned, the beaks could be used to crop objects, but if the lower jaw was retracted so that the lower beak was inside the upper beak, the jaws may have served a nutcracking function. A nut- or seed-rich diet would also match well with the gastroliths often seen in well-preserved psittacosaur skeletons.
A histological
examination of P. mongoliensis has determined the growth rate of these animals. The smallest specimens in the study were estimated at three years old and less than 1 kilogram (2.2 lb), while the largest were nine years old and weighed almost 20 kilograms (44 lb). This indicates relatively rapid growth compared to most reptiles and marsupial
mammals, but slower than modern bird
s and placental mammals. An age determination
study performed on the fossil
ized remains of Psittacosaurus mongoliensis by using growth ring counts suggest that the longevity of the basal
ceratopsian was between 10 or 11 years.
museum
and arrangements are being made to return the specimen to China.
Most of the body was covered in scales
. Larger scales were arranged in irregular patterns, with numerous smaller scales occupying the spaces between them, similarly to skin impressions known from other ceratopsians, such as Chasmosaurus
. However, a series of what appear to be hollow, tubular bristles, approximately 16 centimeters (6.4 in) long, were also preserved, arranged in a row down the dorsal
(upper) surface of the tail. However, according to some scientists "[a]t present, there is no convincing evidence which shows these structures to be homologous
to the structurally different[ feather
s and protofeathers] of theropod dinosaurs." As the structures are only found in a single row on the tail, it is unlikely that they were used for thermoregulation
, but they may have been useful for communication
through some sort of display.
. The young Psittacosaurus, all approximately the same age, are intertwined in a group underneath the adult, although all 34 skulls are positioned above the mass of bodies, as they would have been in life. This suggests that the animals were alive at the time of burial, which must have been extremely rapid, perhaps due to the collapse of a burrow
.
The juvenile bones are very small but are well-ossified
. This has been taken as evidence of extensive parental care, as the young must have been in the nest long enough for their bones to become ossified. A separate find of a herd of six Psittacosaurus individuals killed by a volcanic mudflow indicates the presence of at least two age groups from two distinct clutches. This find has been taken as evidence for group fidelity and gregariousness extending beyond the nest; the earliest such evidence for any ceratopsian. Even very young psittacosaur teeth appear worn, indicating they chewed their own food and may have been precocial
, although this does not rule out continued parental care.
(and with the bristles on the tail interpreted as possibly skin-covered, forming a fin), providing a propulsive surface; and the presence of gastroliths, interpreted as ballast. They further suggested that some species of Psittacosaurus were more terrestrial than others.
, a large triconodont mammal, is preserved with the remains of a juvenile Psittacosaurus in its abdominal cavity. Several of the juvenile's bones are still articulated, indicating that the carnivorous
mammal swallowed its prey in large chunks. This specimen is notable in that it is the first known example of Mesozoic
mammals preying on live dinosaurs. Heavy predation on juvenile Psittacosaurus may have resulted in R-selection
, the production of more numerous offspring to counteract this loss.
. The specimen in question, consisting of a complete adult skeleton and tentatively assigned to P. mongoliensis, was found in the lower beds of the Yixian Formation of China. There is no sign of a bone fracture
, but very clear signs of an infection
can be seen near the midpoint of the right fibula. The bone exhibits a large round pit, evidence of necrosis
due to a lack of blood
supply to the region. The pit is surrounded by a massive amount of swelling along the lower third of the bone. This large amount of bone deposited around the injury indicates that the animal survived for quite a while despite the injury and subsequent infection. As psittacosaurids were bipedal animals, a similar injury to a weight bearing
bone in the leg would likely have been fatal. However, unlike the femur
and tibia
, the fibula is not a weight-bearing bone, so this animal would still have been able to walk to some extent. The source of the injury remains unknown.
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 psittacosaurid ceratopsia
Ceratopsia
Ceratopsia or Ceratopia is a group of herbivorous, beaked dinosaurs which thrived in what are now North America, Europe, and Asia, during the Cretaceous Period, although ancestral forms lived earlier, in the Jurassic. The earliest known ceratopsian, Yinlong downsi, lived between 161.2 and 155.7...
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 Early 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...
Period of what is now 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...
, about 130 to 100 million years ago. It is notable for being the most 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...
-rich dinosaur genus. Nine to eleven species are recognized from fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s found in different regions of modern-day China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
, 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...
and 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...
, with a possible additional species from Thailand
Thailand
Thailand , officially the Kingdom of Thailand , formerly known as Siam , is a country located at the centre of the Indochina peninsula and Southeast Asia. It is bordered to the north by Burma and Laos, to the east by Laos and Cambodia, to the south by the Gulf of Thailand and Malaysia, and to the...
.
All species of Psittacosaurus were gazelle
Gazelle
A gazelle is any of many antelope species in the genus Gazella, or formerly considered to belong to it. Six species are included in two genera, Eudorcas and Nanger, which were formerly considered subgenera...
-sized biped
Biped
Bipedalism is a form of terrestrial locomotion where an organism moves by means of its two rear limbs, or legs. An animal or machine that usually moves in a bipedal manner is known as a biped , meaning "two 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...
s characterized by a high, powerful beak
Beak
The beak, bill or rostrum is an external anatomical structure of birds which is used for eating and for grooming, manipulating objects, killing prey, fighting, probing for food, courtship and feeding young...
on the upper jaw. At least one species had long, quill-like structures on its tail and lower back, possibly serving a display function. Psittacosaurs were extremely early ceratopsians and, while they developed many novel adaptations of their own, they also shared many anatomical features with later ceratopsians, such as Protoceratops
Protoceratops
Protoceratops is a genus of sheep-sized herbivorous ceratopsian dinosaur, from the Upper Cretaceous Period of what is now Mongolia. It was a member of the Protoceratopsidae, a group of early horned dinosaurs...
and the elephant
Elephant
Elephants are large land mammals in two extant genera of the family Elephantidae: Elephas and Loxodonta, with the third genus Mammuthus extinct...
-sized Triceratops
Triceratops
Triceratops is a genus of herbivorous ceratopsid dinosaur which lived during the late Maastrichtian stage of the Late Cretaceous Period, around 68 to 65 million years ago in what is now North America. It was one of the last dinosaur genera to appear before the great Cretaceous–Paleogene...
.
Psittacosaurus is not as familiar to the general public as its distant relative Triceratops but it is one of the most completely known dinosaur genera. Fossils of over 400 individuals have been collected so far, including many complete skeletons. Most different age classes are represented, from hatchling
Hatchling
In oviparous biology, a hatchling is the newborn of animals that develop and emerge from within hard-shell eggs. The offspring of birds are often hatched naked and with their eyes closed. The hatchling relies totally on its parents for feeding and warmth. Hatchlings precede nestlings in the chick's...
through to adult, which has allowed several detailed studies of Psittacosaurus growth rates and reproductive biology
Biology
Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...
. The abundance of this dinosaur in the fossil record has led to its use as an index fossil
Index fossil
Index fossils are fossils used to define and identify geologic periods . They work on the premise that, although different sediments may look different depending on the conditions under which they were laid down, they may include the remains of the same species of fossil...
for Early Cretaceous sediments of central Asia
Central Asia
Central Asia is a core region of the Asian continent from the Caspian Sea in the west, China in the east, Afghanistan in the south, and Russia in the north...
.
Description
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...
and skeleton, but shared the same overall body shape. The best-known species, P. mongoliensis, reached 2 meters (6.5 ft) in length. The maximum adult body weight was most likely over 20 kilogram
Kilogram
The kilogram or kilogramme , also known as the kilo, is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype Kilogram , which is almost exactly equal to the mass of one liter of water...
s (44 lb) in P. mongoliensis. Several species approached P. mongoliensis in size (P. major, P. neimongoliensis, P. xinjiangensis), while others were somewhat smaller (P. sinensis, P. meileyingensis). P. ordosensis was the smallest known species, 30% smaller than P. mongoliensis. The largest were P. lujiatunensis and P. sibiricus, although neither was significantly larger than P. mongoliensis.
The skull of Psittacosaurus was highly modified compared to other ornithischia
Ornithischia
Ornithischia or Predentata is an extinct order of beaked, herbivorous dinosaurs. The name ornithischia is derived from the Greek ornitheos meaning 'of a bird' and ischion meaning 'hip joint'...
n dinosaurs of its time. The skull was extremely tall in height and short in length, with an almost round profile
Profile
- Computing and technology :* Profile , a concept in Unified Modeling Language* Apple ProFile, a hard drive* User profile refers to the computer representation of user information...
in some species. The portion in front of the orbit
Orbit (anatomy)
In anatomy, the orbit is the cavity or socket of the skull in which the eye and its appendages are situated. "Orbit" can refer to the bony socket, or it can also be used to imply the contents...
(eye socket) was only 40% of total skull length, shorter than any other known ornithischian. The lower jaws of psittacosaurs are characterized by a bulbous vertical ridge down the center of each tooth. Both upper and lower jaws sported a pronounced beak, formed from the rostral and predentary bones, respectively. The bony core of the beak may have been sheathed in 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...
to provide a sharp cutting surface for cropping plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
material. As the generic name suggests, the short skull and beak superficially resembled those of modern parrots. Psittacosaurus skulls shared several adaptations with 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...
ceratopsians, such as the unique rostral bone at the tip of the upper jaw, and the flared jugal
Jugal
The jugal is a skull bone found in most reptiles, amphibians, and birds. In mammals, the jugal is often called the malar or Zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by species....
(cheek) bones. However, there was still no sign of the bony neck frill or prominent facial horns which would develop in later ceratopsians. Bony horns did protrude from the skull of P. sibiricus, but these are thought to be 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...
.
Psittacosaurus postcranial skeletons were more typical of a 'generic' bipedal ornithischian. In P. mongoliensis, similarly to other species, the forelimbs were only 58% as long as the hindlimbs and their range of motion indicates that the hands could neither be pronated nor used to generate propulsive force, suggesting that these animals were totally bipedal in life. There were only four digits on the manus
Manus (zoology)
The manus is the zoological term for the distal portion of the fore limb of an animal. In tetrapods, it is the part of the pentadactyl limb that includes the metacarpals and digits . During evolution, it has taken many forms and served a variety of functions...
('hand'), as opposed to the five found in most other ornithischians (including all other ceratopsians). Overall, the four-toed hindfoot was very similar to many other small ornithischians.
Taxonomy
Psittacosaurus was named in 1923 by Henry Fairfield OsbornHenry Fairfield Osborn
Henry Fairfield Osborn, Sr. ForMemRS was an American geologist, paleontologist, and eugenicist.-Early life and career:...
, paleontologist and president of the American Museum of Natural History
American Museum of Natural History
The American Museum of Natural History , located on the Upper West Side of Manhattan in New York City, United States, is one of the largest and most celebrated museums in the world...
(AMNH) in a paper published on October 19. The generic name is composed of the 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...
words ψιττακος/psittakos ('parrot') and σαυρος/sauros ('lizard'), suggested by the superficially parrot-like beak of these animals and their reptilian
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
nature.
Species of Psittacosaurus
Seventeen species have been referred to the genus Psittacosaurus, although only nine to eleven are considered valid today. This is the highest number of valid species currently assigned to any single dinosaur genus (not including birdBird
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). In contrast, most other dinosaur genera are monospecific, containing only a single known species. The difference is most likely due to quirks of the fossil record. While Psittacosaurus is known from hundreds of fossil specimens, most other dinosaur species are known from far fewer, and many are represented by only a single specimen. With a very high sample size, the diversity of Psittacosaurus can be analyzed more completely than that of most dinosaur genera, resulting in the recognition of more species. Most extant animal genera are represented by multiple species, suggesting that this may have been the case for extinct dinosaur genera as well, although most of these species may not have been preserved. In addition, most dinosaurs are known solely from bone
Bone
Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...
s and can only be evaluated from a morphological
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
standpoint, whereas extant species often have very similar skeletal morphology but differ in other ways which would not normally be preserved in the fossil record, such as behavior, or coloration. Therefore actual species diversity may be much higher than currently recognized in this and other dinosaur genera.
- Valid Psittacosaurus species
- Psittacosaurus mongoliensis — Mongolia, northern China
- Psittacosaurus sinensis — northeastern China
- Psittacosaurus meileyingensis — north-central China
- Psittacosaurus xinjiangensis — northwestern China
- Psittacosaurus neimongoliensis — north-central China
- Psittacosaurus ordosensis — north-central China
- Psittacosaurus mazongshanensis — northwestern China
- Psittacosaurus sibiricus — Russia (southern SiberiaSiberiaSiberia is an extensive region constituting almost all of Northern Asia. Comprising the central and eastern portion of the Russian Federation, it was part of the Soviet Union from its beginning, as its predecessor states, the Tsardom of Russia and the Russian Empire, conquered it during the 16th...
) - Psittacosaurus lujiatunensis — northeastern China
- Psittacosaurus major — northeastern China
- Psittacosaurus gobiensis — Inner Mongolia
- Possible Psittacosaurus species
- ?Psittacosaurus sattayaraki — Thailand
Classification
Type genus
In biological classification, a type genus is a representative genus, as with regard to a biological family. The term and concept is used much more often and much more formally in zoology than it is in botany, and the definition is dependent on the nomenclatural Code that applies:* In zoological...
of the family Psittacosauridae, which was also named by Osborn in 1923. Only one other genus, Hongshanosaurus
Hongshanosaurus
Hongshanosaurus is a genus of psittacosaurid ceratopsian dinosaur from the Early Cretaceous Period of eastern Asia. Although two skulls are the only fossil material described, comparisons with close relatives suggest it was a small, bipedal herbivore with a bony beak on the end of both upper and...
, is currently classified in this family alongside Psittacosaurus. Psittacosaurids were 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:...
to almost all known ceratopsians except Yinlong
Yinlong
Yinlong is a genus of basal ceratopsian dinosaur from the Late Jurassic Period of central Asia. It was a small, primarily bipedal herbivore, approximately 1.2 meters long...
and perhaps Chaoyangsauridae
Chaoyangsauridae
Chaoyangsauridae is a family of dinosaurs. They were the first marginocephalian dinosaurs to appear on the planet, about 148 million years ago, in the Late Jurassic period. Members of this group had sharp beaks for snipping off leaves to eat, and a very small frill...
. While Psittacosauridae was an early branch of the ceratopsian family tree, Psittacosaurus itself was probably not directly ancestral to any other groups of ceratopsians. All other ceratopsians retained the fifth digit of the hand, a plesiomorphy or primitive trait, whereas all species of Psittacosaurus had only four digits on the hand. In addition, the antorbital fenestra, an opening in the skull between the eye socket and nostril
Nostril
A nostril is one of the two channels of the nose, from the point where they bifurcate to the external opening. In birds and mammals, they contain branched bones or cartilages called turbinates, whose function is to warm air on inhalation and remove moisture on exhalation...
, was lost during the evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
of Psittacosauridae, but is still found in most other ceratopsians and in fact most other archosaur
Archosaur
Archosaurs are a group of diapsid amniotes whose living representatives consist of modern birds and crocodilians. This group also includes all extinct non-avian dinosaurs, many extinct crocodilian relatives, and pterosaurs. Archosauria, the archosaur clade, is a crown group that includes the most...
s. It is considered highly unlikely that the fifth digit or antorbital fenestra would evolve
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
a second time.
Although many species of Psittacosaurus have been named, their relationships to each other have not yet been fully explored and no scientific consensus exists on the subject. Several phylogenetic
Phylogenetics
In biology, phylogenetics is the study of evolutionary relatedness among groups of organisms , which is discovered through molecular sequencing data and morphological data matrices...
analyses have been published, with the most detailed being those by Alexander Averianov and colleagues in 2006, Hai-Lu You and colleagues in 2008, and Paul Sereno
Paul Sereno
Paul Callistus Sereno is an American paleontologist from the University of Chicago who discovered several new dinosaur species on several continents. He has conducted excavations at sites as varied as Inner Mongolia, Argentina, Morocco, and Niger...
in 2010.
Averianov et al. (2006):
You et al. (2008):
Sereno (2010):
It has been suggested that P. lujiatunensis is basal to all other species. This would be consistent with its earlier appearance in the fossil record.
Provenance
Psittacosaurus is known from over 400 individual specimens, of which over 75 have been assigned to the type species, P. mongoliensis. All Psittacosaurus fossils discovered so far have been found in Early CretaceousEarly Cretaceous
The Early Cretaceous or the Lower Cretaceous , is the earlier or lower of the two major divisions of the Cretaceous...
sediments in Asia, from southern Siberia
Siberia
Siberia is an extensive region constituting almost all of Northern Asia. Comprising the central and eastern portion of the Russian Federation, it was part of the Soviet Union from its beginning, as its predecessor states, the Tsardom of Russia and the Russian Empire, conquered it during the 16th...
to northern China, or possibly as far south as Thailand. The most common age of geologic 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...
s bearing Psittacosaurus fossils is from the late 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...
through 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, or approximately 125 to 100 Ma (million years ago). Nearly all terrestrial sedimentary formations of this age in Mongolia and northern China have produced fossils of Psittacosaurus, leading its use as an index fossil for this time period in the region, along with the very common pterosaur
Pterosaur
Pterosaurs were flying reptiles of the clade or order Pterosauria. They existed from the late Triassic to the end of the Cretaceous Period . Pterosaurs are the earliest vertebrates known to have evolved powered flight...
Dsungaripterus
Dsungaripterus
Dsungaripterus was a genus of pterosaur, with an average wingspan of . It lived during the Early Cretaceous, in China, where the first fossil was found in the Junggar Basin.-Discovery and species:...
.
The earliest known species is P. lujiatunensis, found in the lowest beds of the Yixian Formation
Yixian Formation
The Yixian Formation is a geological formation in Jinzhou, Liaoning, People's Republic of China, that spans 11 million years during the early Cretaceous period...
. Over 200 specimens attributed to this genus have been recovered from these and other beds of the Yixian, the age of which is the subject of much debate. Although many early studies using radiometric dating
Radiometric dating
Radiometric dating is a technique used to date materials such as rocks, usually based on a comparison between the observed abundance of a naturally occurring radioactive isotope and its decay products, using known decay rates...
put the Yixian in the Jurassic Period, tens of millions of years outside of the expected temporal range of Psittacosaurus, most recent work dates it to the Early Cretaceous. Using argon-argon dating
Argon-argon dating
Argon-argon dating is a radiometric dating method invented to supersede potassium-argon dating in accuracy. The older method required two samples for dating while the newer method requires only one...
, a team of Chinese scientists dated the lowest beds
Stratum
In geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...
in the formation to about 128 Ma, and the highest to approximately 122 Ma. A more recent Chinese study, using uranium-lead dating
Uranium-lead dating
Uranium-lead is one of the oldest and most refined of the radiometric dating schemes, with a routine age range of about 1 million years to over 4.5 billion years, and with routine precisions in the 0.1-1 percent range...
, suggests that the lower beds are younger, approximately 125 Ma, while agreeing with an age of 122 Ma for the upper beds. This work indicates that the Yixian is early Aptian in age, or possibly late 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...
to early Aptian.
Daily activity patterns
Comparisons between the scleral ringSclerotic ring
Sclerotic rings are rings of bone found in the eyes of several groups of vertebrate animals, except for mammals and crocodilians. They can be made up of single bones or small bones together. They are believed to have a role in supporting the eye, especially in animals whose eyes are not spherical,...
s of Psittacosaurus and modern birds and reptiles suggest that it may have been cathemeral
Cathemeral
A cathemeral organism is one that has sporadic and random intervals of activity during the day or night in which food is acquired, socializing with other organisms occurs, and any other activities necessary for livelihood are performed...
, active throughout the day at short intervals.
Diet
Gizzard
The gizzard, also referred to as the ventriculus, gastric mill, and gigerium, is an organ found in the digestive tract of some animals, including birds, reptiles, earthworms and some fish. This specialized stomach constructed of thick, muscular walls is used for grinding up food; often rocks are...
, as in modern birds.
Unlike many other dinosaurs, psittacosaurs had akinetic skulls: the upper and lower jaws behaved as single units without internal joints. The only joint was the jaw joint itself, and psittacosaurs could slide their lower jaws forward and backward on the joint, permitting a shearing action. Unlike most ceratopsians, their beaks did not form curved tips, but were instead rounded and flattened. If the jaws were aligned, the beaks could be used to crop objects, but if the lower jaw was retracted so that the lower beak was inside the upper beak, the jaws may have served a nutcracking function. A nut- or seed-rich diet would also match well with the gastroliths often seen in well-preserved psittacosaur skeletons.
Growth rate
Several juvenile Psittacosaurus have been found. The smallest is a P. mongoliensis hatchling in the AMNH collection, which is only 11 to 13 centimeters (4–5 inches) long, with a skull 2.8 centimeters (1 in) in length. Another hatchling skull at the AMNH is only 4.6 centimeters (1.8 inches) long. Both specimens are from Mongolia. Juveniles discovered in the Yixian Formation are approximately the same age as the larger AMNH specimen. Adult Psittacosaurus mongoliensis approached 2 meters (6.5 ft) in length.A histological
Histology
Histology is the study of the microscopic anatomy of cells and tissues of plants and animals. It is performed by examining cells and tissues commonly by sectioning and staining; followed by examination under a light microscope or electron microscope...
examination of P. mongoliensis has determined the growth rate of these animals. The smallest specimens in the study were estimated at three years old and less than 1 kilogram (2.2 lb), while the largest were nine years old and weighed almost 20 kilograms (44 lb). This indicates relatively rapid growth compared to most reptiles and marsupial
Marsupial
Marsupials are an infraclass of mammals, characterized by giving birth to relatively undeveloped young. Close to 70% of the 334 extant species occur in Australia, New Guinea, and nearby islands, with the remaining 100 found in the Americas, primarily in South America, but with thirteen in Central...
mammals, but slower than modern 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 placental mammals. An age determination
Age determination of dinosaurs
Age determination in dinosaurs is mainly used to determine the approximate age of a dinosaur when the animal died.-History:Early attempts to estimate the longevity of dinosaurs used allometric scaling principles. Ages were determined by dividing individual mass estimates by rates of growth for...
study performed on the fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
ized remains of Psittacosaurus mongoliensis by using growth ring counts suggest that the longevity of the 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:...
ceratopsian was between 10 or 11 years.
Integument
The integument, or body covering, of Psittacosaurus is known from a Chinese specimen, which most likely comes from the Yixian Formation of Liaoning. The specimen, which is not yet assigned to any particular species, was illegally exported from China, in violation of Chinese law, but was purchased by a GermanGermany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
museum
Museum
A museum is an institution that cares for a collection of artifacts and other objects of scientific, artistic, cultural, or historical importance and makes them available for public viewing through exhibits that may be permanent or temporary. Most large museums are located in major cities...
and arrangements are being made to return the specimen to China.
Most of the body was covered in scales
Scale (zoology)
In most biological nomenclature, a scale is a small rigid plate that grows out of an animal's skin to provide protection. In lepidopteran species, scales are plates on the surface of the insect wing, and provide coloration...
. Larger scales were arranged in irregular patterns, with numerous smaller scales occupying the spaces between them, similarly to skin impressions known from other ceratopsians, such as Chasmosaurus
Chasmosaurus
Chasmosaurus is a genus of ceratopsid dinosaur from the Upper Cretaceous Period of North America. Its name means 'opening lizard', referring to the large openings in its frill . With a length of and a weight of , Chasmosaurus was a ceratopsian of average size...
. However, a series of what appear to be hollow, tubular bristles, approximately 16 centimeters (6.4 in) long, were also preserved, arranged in a row down the dorsal
Dorsum (biology)
In anatomy, the dorsum is the upper side of animals that typically run, fly, or swim in a horizontal position, and the back side of animals that walk upright. In vertebrates the dorsum contains the backbone. The term dorsal refers to anatomical structures that are either situated toward or grow...
(upper) surface of the tail. However, according to some scientists "[a]t present, there is no convincing evidence which shows these structures to be homologous
Homology (biology)
Homology forms the basis of organization for comparative biology. In 1843, Richard Owen defined homology as "the same organ in different animals under every variety of form and function". Organs as different as a bat's wing, a seal's flipper, a cat's paw and a human hand have a common underlying...
to the structurally different
Feather
Feathers are one of the epidermal growths that form the distinctive outer covering, or plumage, on birds and some non-avian theropod dinosaurs. They are considered the most complex integumentary structures found in vertebrates, and indeed a premier example of a complex evolutionary novelty. They...
s and protofeathers] of theropod dinosaurs." As the structures are only found in a single row on the tail, it is unlikely that they were used for thermoregulation
Thermoregulation
Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different...
, but they may have been useful for 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 some sort of display.
Limb function
Studies by Phil Senter in 2007 conducted on Psittacosaurus neimongoliensis and Psittacosaurus mongoliensis concluded that the forelimbs of these taxa (and likely those of other Psittacosaurus species) were too short to reach the ground and could neither be pronated nor generate propulsive force for locomotion, suggesting that Psittacosaurus was entirely bipedal. The forelimbs were also too short to be used in digging or bringing food to the mouth, and Senter suggested that if Psittacosaurus needed to dig depressions in the ground it may have used its hindlimbs instead. The forelimbs could be used for two-handed grasping of objects or scratching the body, but due to their extremely limited flexibility and reach, they could have only been used to grasp objects very close to the belly or sides of the animal and could have scratched only the belly, flank and knees. Even though the hands couldn't reach the mouth, Psittacosaurus could have still used them to carry nesting material or food to a desired location.Parental care and gregariousness
An extremely well preserved specimen found in the Yixian Formation of Liaoning Province, China provides some of the best evidence for parental care in dinosaurs. This specimen consists of an adult Psittacosaurus (not assigned to any particular species), which is closely associated with 34 articulated juvenile skeletons, all preserved in three dimensionsDimension
In physics and mathematics, the dimension of a space or object is informally defined as the minimum number of coordinates needed to specify any point within it. Thus a line has a dimension of one because only one coordinate is needed to specify a point on it...
. The young Psittacosaurus, all approximately the same age, are intertwined in a group underneath the adult, although all 34 skulls are positioned above the mass of bodies, as they would have been in life. This suggests that the animals were alive at the time of burial, which must have been extremely rapid, perhaps due to the collapse of a burrow
Burrow
A burrow is a hole or tunnel dug into the ground by an animal to create a space suitable for habitation, temporary refuge, or as a byproduct of locomotion. Burrows provide a form of shelter against predation and exposure to the elements, so the burrowing way of life is quite popular among the...
.
The juvenile bones are very small but are well-ossified
Endochondral ossification
Endochondral ossification is one of the two essential processes during fetal development of the mammalian skeletal system by which bone tissue is created. Unlike intramembranous ossification, which is the other process by which bone tissue is created, cartilage is present during endochondral...
. This has been taken as evidence of extensive parental care, as the young must have been in the nest long enough for their bones to become ossified. A separate find of a herd of six Psittacosaurus individuals killed by a volcanic mudflow indicates the presence of at least two age groups from two distinct clutches. This find has been taken as evidence for group fidelity and gregariousness extending beyond the nest; the earliest such evidence for any ceratopsian. Even very young psittacosaur teeth appear worn, indicating they chewed their own food and may have been precocial
Precocial
In biology, the term precocial refers to species in which the young are relatively mature and mobile from the moment of birth or hatching. The opposite developmental strategy is called "altricial," where the young are born or hatched helpless. Extremely precocial species may be called...
, although this does not rule out continued parental care.
Possible aquatic behavior
Ford and Martin (2010) proposed that Psittacosaurus was semi-aquatic, swimming through the use of its tail similar to crocodiles, and through paddling and kicking. They based their interpretation on evidence including: the lacustrine (lake) depositional setting of many specimens; the position of the nostrils and eyes; interpretations of the motions of the arms and legs; tails with long chevronsChevron (anatomy)
A chevron is one of a series of bones on the ventral side of the tail in many reptiles, dinosaurs , and some mammals such as kangaroos and manatees....
(and with the bristles on the tail interpreted as possibly skin-covered, forming a fin), providing a propulsive surface; and the presence of gastroliths, interpreted as ballast. They further suggested that some species of Psittacosaurus were more terrestrial than others.
Predation
Another fossil from the Yixian Formation provides direct evidence of Psittacosaurus as a prey animal. One skeleton of Repenomamus robustusRepenomamus
Repenomamus is the largest mammal known from the Cretaceous period of Manchuria, and it is the mammal for which there is the best evidence that it fed on dinosaurs. It is not possible to determine if Repenomamus actively hunted live dinosaurs or scavenged dead dinosaurs.-Paleobiology:Repenomamus...
, a large triconodont mammal, is preserved with the remains of a juvenile Psittacosaurus in its abdominal cavity. Several of the juvenile's bones are still articulated, indicating that the 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...
mammal swallowed its prey in large chunks. This specimen is notable in that it is the first known example of Mesozoic
Mesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...
mammals preying on live dinosaurs. Heavy predation on juvenile Psittacosaurus may have resulted in R-selection
R/K selection theory
In ecology, r/K selection theory relates to the selection of combinations of traits in an organism that trade off between quantity or quality of offspring...
, the production of more numerous offspring to counteract this loss.
Pathology
Out of over 400 known Psittacosaurus specimens, only one has been published with any sort of pathologyPathology
Pathology is the precise study and diagnosis of disease. The word pathology is from Ancient Greek , pathos, "feeling, suffering"; and , -logia, "the study of". Pathologization, to pathologize, refers to the process of defining a condition or behavior as pathological, e.g. pathological gambling....
. The specimen in question, consisting of a complete adult skeleton and tentatively assigned to P. mongoliensis, was found in the lower beds of the Yixian Formation of China. There is no sign of a bone fracture
Bone fracture
A bone fracture is a medical condition in which there is a break in the continuity of the bone...
, but very clear signs of an infection
Infection
An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...
can be seen near the midpoint of the right fibula. The bone exhibits a large round pit, evidence of necrosis
Necrosis
Necrosis is the premature death of cells in living tissue. Necrosis is caused by factors external to the cell or tissue, such as infection, toxins, or trauma. This is in contrast to apoptosis, which is a naturally occurring cause of cellular death...
due to a lack of blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
supply to the region. The pit is surrounded by a massive amount of swelling along the lower third of the bone. This large amount of bone deposited around the injury indicates that the animal survived for quite a while despite the injury and subsequent infection. As psittacosaurids were bipedal animals, a similar injury to a weight bearing
Weight 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...
bone in the leg would likely have been fatal. However, unlike the 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 tibia
Tibia
The tibia , shinbone, or shankbone is the larger and stronger of the two bones in the leg below the knee in vertebrates , and connects the knee with the ankle bones....
, the fibula is not a weight-bearing bone, so this animal would still have been able to walk to some extent. The source of the injury remains unknown.
External links
- Summary of known ceratopsians on Justin S. Tweet's Thescelosaurus! website.