Sauropodomorpha
Encyclopedia
Sauropodomorpha is an extinct clade
of long-necked, herbivorous, saurischian dinosaur
s which includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had long necks and tails, were quadruped
al, and became the largest animals to ever walk the Earth. The "prosauropods" preceded the sauropods. They were smaller and were often able to walk on two legs. The sauropodomorphs were the dominant terrestrial herbivores throughout much of the Mesozoic Era, from their origins in the mid-Triassic
until their decline and extinction at the end of the Cretaceous
.
foliage. This feeding strategy is supported by many of their defining characteristics, such as: a light, tiny skull
on the end of a long neck
(with ten or more elongated cervical vertebrae) and a counterbalancing long tail
(with one to three extra sacral vertebrae).
Their teeth were weak, and shaped like leaves or spoons (lanceolate or spatulate). Instead of grinding teeth, they had stomach stones (gastrolith
s), similar to the gizzard
stones of modern bird
s and crocodile
s, to help digest tough plant fibers. The front of the upper mouth bends down in what may be a beak
.
One of the earliest known sauropodomorphs, Saturnalia
, was small and slender (1.5 metres, or 5 feet long), but by the end of the Triassic they were the largest dinosaurs of their time, and in the Jurassic/Cretaceous they kept on growing. Ultimately the largest sauropods like the Supersaurus
, Diplodocus hallorum
, and Argentinosaurus
reached 30–40 metres (100–130 ft) in length, and 60,000–100,000 kilograms (65–110 US short ton
s) or more in mass.
Initially biped
al, as their size increased they evolved to become graviportal quadruped
s (like elephant
s). The early sauropodomorphs were most likely omnivore
s as their shared common ancestor with the other saurischia
n lineage (the theropods) was a carnivore
. Therefore their evolution to herbivory went hand in hand with their increasing size and neck length.
They also had large nostril
s (nares), and retained a thumb
(pollex) with a big claw
which may have been used for defense — though their primary defensive adaptation was their extreme size.
Comparisons between the scleral ring
s of several sauropodmorph genera (Diplodocus
, Lufengosaurus
, Nemegtosaurus
, Plateosaurus
, and Riojasaurus
) and modern birds and reptiles suggest that they may have been cathemeral
, active throughout the day at short intervals.
Period, about 230 million years ago (Mya), they became the dominant herbivores by half way through the late Triassic (during the Norian
stage). Their perceived decline in the early Cretaceous
is most likely a bias in fossil sampling, as most fossils are known from Europe and North America. Sauropods were still the dominant herbivores in the Gondwana
landmasses, however. The spread of flowering plant
s (angiosperms) and "advanced" ornithischia
ns, another major group of herbivorous dinosaurs (noted for their highly developed chewing mechanisms) are most likely not a major factor in sauropod decline in the northern continents. Like all non-avian
dinosaurs, the sauropodomorphs became extinct 65 Mya, during the Cretaceous-Tertiary extinction event
.
The earliest and most basal
sauropodomorphs known are Chromogisaurus novasi and Panphagia protos, both from the Ischigualasto Formation, dated to 231.4 million years ago (late Ladinian
age of the Middle Triassic according to the ICS
; alternately called the early Carnian
age of the Late Triassic
in the system used by the Geological Society of America
). Some studies have found Eoraptor lunensis (also from the Ischigualasto Formation), traditionally considered a theropod, to be an early member of the sauropodomorph lineage, which would make it the most basal sauropodomorph known. Additional fragmentary remains from Madagascar
may represent an even earlier sauropodomorph from the middle Triassic.
Sauropodomorpha is one of the two major clade
s within the order
Saurischia
. The sauropodomorphs' sister group, the Theropoda
, includes bipedal carnivores like Velociraptor
and Tyrannosaurus
; as well as bird
s. However, sauropodomorphs also share a number of characteristics with the Ornithischia
, so a small minority of palaeontologists like Bakker have historically placed both sets of herbivores within a group called "Phytodinosauria" or "Ornithischiformes."
In Linnaean taxonomy
, Sauropodomorpha (which means "lizard
feet forms") is either a suborder or is left unranked. It was originally established by Friedrich von Huene
in 1932, who broke it into two groups: the basal forms within Prosauropoda, and their descendants, the giant Sauropoda
.
Recent phylogenetic analyses by Adam Yates (2004, 2006) and others firmly places Sauropoda within a paraphyletic "Prosauropoda". Also, finds of late Triassic sauropods demonstrate that there is no gap between the "prosauropod" and sauropod lineages. Recent cladistic
analyses suggest that the clade Prosauropoda, which was named by Huene in 1920 and was defined by Sereno, 1998 as all animals more closely related to Plateosaurus engelhardti than to Saltasaurus loricatus, is a junior synonym of Plateosauridae
as both contain the same taxa.
Evidence against sauropod ancestry within Prosauropoda comes from the fact that prosauropods had a smaller outer toe
on their hind feet than the sauropods. Many maintain that it is easier for digit
s to be reduced or lost during evolution
than the reverse, however there is no evidence for this. The lengthening, or gaining of extra digits is common in marine reptiles, and within the theropods digit lengthening occurred at least once. Therefore using this as evidence against ancestral prosauropods is questionable.
Most modern classification schemes break the prosauropods into a half-dozen groups that evolved separately from one common lineage. While they have a number of shared characteristics, the evolution
ary requirements for giraffe
-like browsing high in the trees may have caused convergent evolution
, where similar traits evolve separately because they faced the same evolutionary pressure, instead of (homologous
) traits derived from a shared ancestor.
simplified after an analysis presented by Apaldetti and colleagues in November 2011.
Cladogram after Novas et al., 2011:
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...
of long-necked, herbivorous, saurischian 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 which includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had long necks and tails, were 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, and became the largest animals to ever walk the Earth. The "prosauropods" preceded the sauropods. They were smaller and were often able to walk on two legs. The sauropodomorphs were the dominant terrestrial herbivores throughout much of the Mesozoic Era, from their origins in the mid-Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
until their decline and extinction at the end of the 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...
.
Description
Sauropodomorphs were adapted to browsing higher than any other contemporary herbivore, giving them access to high treeTree
A tree is a perennial woody plant. It is most often defined as a woody plant that has many secondary branches supported clear of the ground on a single main stem or trunk with clear apical dominance. A minimum height specification at maturity is cited by some authors, varying from 3 m to...
foliage. This feeding strategy is supported by many of their defining characteristics, such as: a light, tiny 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...
on the end of a long neck
Neck
The neck is the part of the body, on many terrestrial or secondarily aquatic vertebrates, that distinguishes the head from the torso or trunk. The adjective signifying "of the neck" is cervical .-Boner anatomy: The cervical spine:The cervical portion of the human spine comprises seven boney...
(with ten or more elongated cervical vertebrae) and a counterbalancing long tail
Tail
The tail is the section at the rear end of an animal's body; in general, the term refers to a distinct, flexible appendage to the torso. It is the part of the body that corresponds roughly to the sacrum and coccyx in mammals, reptiles, and birds...
(with one to three extra sacral vertebrae).
Their teeth were weak, and shaped like leaves or spoons (lanceolate or spatulate). Instead of grinding teeth, they had stomach stones (gastrolith
Gastrolith
A gastrolith, also called a stomach stone or gizzard stones, is a rock held inside a gastrointestinal tract. Gastroliths are retained in the muscular gizzard and used to grind food in animals lacking suitable grinding teeth. The grain size depends upon the size of the animal and the gastrolith's...
s), similar to the gizzard
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...
stones of 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 crocodile
Crocodile
A crocodile is any species belonging to the family Crocodylidae . The term can also be used more loosely to include all extant members of the order Crocodilia: i.e...
s, to help digest tough plant fibers. The front of the upper mouth bends down in what may be a 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...
.
One of the earliest known sauropodomorphs, Saturnalia
Saturnalia (dinosaur)
Saturnalia is an extinct genus of basal sauropodomorph dinosaur known from the Triassic of Rio Grande do Sul, southern Brazil.-Discovery:Saturnalia was originally named on the basis of three partial skeletons...
, was small and slender (1.5 metres, or 5 feet long), but by the end of the Triassic they were the largest dinosaurs of their time, and in the Jurassic/Cretaceous they kept on growing. Ultimately the largest sauropods like the Supersaurus
Supersaurus
Supersaurus is a genus of diplodocid sauropod dinosaur discovered by Vivian Jones of Delta, Colorado, in the Upper Jurassic Morrison Formation of Colorado in 1972. The fossil remains came from the Brushy Basin Member of the formation, dating to about 153 million years ago...
, Diplodocus hallorum
Diplodocus
Diplodocus , or )is a genus of diplodocid sauropod dinosaur whose fossils were first discovered in 1877 by S. W. Williston. The generic name, coined by Othniel Charles Marsh in 1878, is a Neo-Latin term derived from Greek "double" and "beam", in reference to its double-beamed chevron bones...
, and Argentinosaurus
Argentinosaurus
Argentinosaurus is a genus of titanosaur sauropod dinosaur first discovered by Guillermo Heredia in Argentina. The generic name refers to the country in which it was discovered...
reached 30–40 metres (100–130 ft) in length, and 60,000–100,000 kilograms (65–110 US short ton
Short ton
The short ton is a unit of mass equal to . In the United States it is often called simply ton without distinguishing it from the metric ton or the long ton ; rather, the other two are specifically noted. There are, however, some U.S...
s) or more in mass.
Initially 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, as their size increased they evolved to become graviportal 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"...
s (like elephant
Elephant
Elephants are large land mammals in two extant genera of the family Elephantidae: Elephas and Loxodonta, with the third genus Mammuthus extinct...
s). The early sauropodomorphs were most likely omnivore
Omnivore
Omnivores are species that eat both plants and animals as their primary food source...
s as their shared common ancestor with the other saurischia
Saurischia
Saurischia meaning 'lizard' and ischion meaning 'hip joint') is one of the two orders, or basic divisions, of dinosaurs. In 1888, Harry Seeley classified dinosaurs into two orders, based on their hip structure...
n lineage (the theropods) was a carnivore
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...
. Therefore their evolution to herbivory went hand in hand with their increasing size and neck length.
They also had large 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...
s (nares), and retained a thumb
Thumb
The thumb is the first digit of the hand. When a person is standing in the medical anatomical position , the thumb is the lateral-most digit...
(pollex) with a big claw
Claw
A claw is a curved, pointed appendage, found at the end of a toe or finger in most mammals, birds, and some reptiles. However, the word "claw" is also often used in reference to an invertebrate. Somewhat similar fine hooked structures are found in arthropods such as beetles and spiders, at the end...
which may have been used for defense — though their primary defensive adaptation was their extreme size.
Comparisons between the scleral ring
Sclerotic 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 several sauropodmorph genera (Diplodocus
Diplodocus
Diplodocus , or )is a genus of diplodocid sauropod dinosaur whose fossils were first discovered in 1877 by S. W. Williston. The generic name, coined by Othniel Charles Marsh in 1878, is a Neo-Latin term derived from Greek "double" and "beam", in reference to its double-beamed chevron bones...
, Lufengosaurus
Lufengosaurus
Lufengosaurus is a genus of prosauropod dinosaur which lived during the Early Jurassic period in what is now southwestern China.-Discovery and species:...
, Nemegtosaurus
Nemegtosaurus
Nemegtosaurus was a sauropod dinosaur from Late Cretaceous Period of what is now Mongolia. It was named after the Nemegt Basin in the Gobi Desert, where the remains — a single skull — were found...
, Plateosaurus
Plateosaurus
Plateosaurus is a genus of plateosaurid dinosaur that lived during the Late Triassic period, around 216 to 199 million years ago, in what is now Central and Northern Europe. Plateosaurus is a basal sauropodomorph dinosaur, a so-called "prosauropod"...
, and Riojasaurus
Riojasaurus
Riojasaurus was a herbivorous prosauropod dinosaur named after La Rioja Province in Argentina where it was found by José Bonaparte. It lived during the Late Triassic and grew to about long. Riojasaurus is the only known riojasaurid to live in South America.-Description:Riojasaurus had a heavy...
) and modern birds and reptiles suggest that they 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.
Time range
Among the very first dinosaurs to evolve in the middle TriassicTriassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
Period, about 230 million years ago (Mya), they became the dominant herbivores by half way through the late Triassic (during the Norian
Norian
The Norian is a division of the Triassic geological period. It has the rank of an age or stage . The Norian lasted from 216.5 ± 2.0 to 203.6 ± 1.5 million years ago. It was preceded by the Carnian and succeeded by the Rhaetian.-Stratigraphic definitions:The Norian was named after the Noric Alps in...
stage). Their perceived decline in 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...
is most likely a bias in fossil sampling, as most fossils are known from Europe and North America. Sauropods were still the dominant herbivores in the Gondwana
Gondwana
In paleogeography, Gondwana , originally Gondwanaland, was the southernmost of two supercontinents that later became parts of the Pangaea supercontinent. It existed from approximately 510 to 180 million years ago . Gondwana is believed to have sutured between ca. 570 and 510 Mya,...
landmasses, however. The spread of flowering plant
Flowering plant
The flowering plants , also known as Angiospermae or Magnoliophyta, are the most diverse group of land plants. Angiosperms are seed-producing plants like the gymnosperms and can be distinguished from the gymnosperms by a series of synapomorphies...
s (angiosperms) and "advanced" 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'...
ns, another major group of herbivorous dinosaurs (noted for their highly developed chewing mechanisms) are most likely not a major factor in sauropod decline in the northern continents. Like all non-avian
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...
dinosaurs, the sauropodomorphs became extinct 65 Mya, during the Cretaceous-Tertiary extinction event
Cretaceous-Tertiary extinction event
The Cretaceous–Paleogene extinction event, formerly named and still commonly referred to as the Cretaceous-Tertiary extinction event, occurred approximately 65.5 million years ago at the end of the Maastrichtian age of the Cretaceous period. It was a large-scale mass extinction of animal and plant...
.
The earliest and most basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
sauropodomorphs known are Chromogisaurus novasi and Panphagia protos, both from the Ischigualasto Formation, dated to 231.4 million years ago (late Ladinian
Ladinian
The Ladinian is a stage and age in the Middle Triassic series or epoch. It spans the time between 237 ± 2 Ma and 228 ± 2 Ma...
age of the Middle Triassic according to the ICS
International Commission on Stratigraphy
The International Commission on Stratigraphy , sometimes referred to by the unofficial "International Stratigraphic Commission" is a daughter or major subcommittee grade scientific daughter organization that concerns itself with stratigraphy, geological, and geochronological matters on a global...
; alternately called the early Carnian
Carnian
The Carnian is the lowermost stage of the Upper Triassic series . It lasted from about 228.7 till 216.5 million years ago . The Carnian is preceded by the Ladinian and is followed by the Norian...
age of the Late Triassic
Late Triassic
The Late Triassic is in the geologic timescale the third and final of three epochs of the Triassic period. The corresponding series is known as the Upper Triassic. In the past it was sometimes called the Keuper, after a German lithostratigraphic group that has a roughly corresponding age...
in the system used by the Geological Society of America
Geological Society of America
The Geological Society of America is a nonprofit organization dedicated to the advancement of the geosciences. The society was founded in New York in 1888 by Alexander Winchell, John J. Stevenson, Charles H. Hitchcock, John R. Proctor and Edward Orton and has been headquartered at 3300 Penrose...
). Some studies have found Eoraptor lunensis (also from the Ischigualasto Formation), traditionally considered a theropod, to be an early member of the sauropodomorph lineage, which would make it the most basal sauropodomorph known. Additional fragmentary remains from Madagascar
Madagascar
The Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...
may represent an even earlier sauropodomorph from the middle Triassic.
Classification
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...
s within the order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
Saurischia
Saurischia
Saurischia meaning 'lizard' and ischion meaning 'hip joint') is one of the two orders, or basic divisions, of dinosaurs. In 1888, Harry Seeley classified dinosaurs into two orders, based on their hip structure...
. The sauropodomorphs' sister group, the Theropoda
Theropoda
Theropoda is both a suborder of bipedal saurischian dinosaurs, and a clade consisting of that suborder and its descendants . Dinosaurs belonging to the suborder theropoda were primarily carnivorous, although a number of theropod groups evolved herbivory, omnivory, and insectivory...
, includes bipedal carnivores like Velociraptor
Velociraptor
Velociraptor is a genus of dromaeosaurid theropod dinosaur that existed approximately 75 to 71 million years ago during the later part of the Cretaceous Period. Two species are currently recognized, although others have been assigned in the past. The type species is V. mongoliensis; fossils...
and Tyrannosaurus
Tyrannosaurus
Tyrannosaurus meaning "tyrant," and sauros meaning "lizard") is a genus of coelurosaurian theropod dinosaur. The species Tyrannosaurus rex , commonly abbreviated to T. rex, is a fixture in popular culture. It lived throughout what is now western North America, with a much wider range than other...
; as well as 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. However, sauropodomorphs also share a number of characteristics with the 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'...
, so a small minority of palaeontologists like Bakker have historically placed both sets of herbivores within a group called "Phytodinosauria" or "Ornithischiformes."
In Linnaean taxonomy
Linnaean taxonomy
Linnaean taxonomy can mean either of two related concepts:# the particular form of biological classification set up by Carl Linnaeus, as set forth in his Systema Naturæ and subsequent works...
, Sauropodomorpha (which means "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...
feet forms") is either a suborder or is left unranked. It was originally established by Friedrich von Huene
Friedrich von Huene
Friedrich von Huene was a German paleontologist who named more dinosaurs in the early 20th century than anyone else in Europe.-Biography:...
in 1932, who broke it into two groups: the basal forms within Prosauropoda, and their descendants, the giant Sauropoda
Sauropoda
Sauropoda , or the sauropods , are an infraorder of saurischian dinosaurs. They had long necks, long tails, small heads , and thick, pillar-like legs. They are notable for the enormous sizes attained by some species, and the group includes the largest animals to have ever lived on land...
.
Recent phylogenetic analyses by Adam Yates (2004, 2006) and others firmly places Sauropoda within a paraphyletic "Prosauropoda". Also, finds of late Triassic sauropods demonstrate that there is no gap between the "prosauropod" and sauropod lineages. Recent cladistic
Cladistics
Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...
analyses suggest that the clade Prosauropoda, which was named by Huene in 1920 and was defined by Sereno, 1998 as all animals more closely related to Plateosaurus engelhardti than to Saltasaurus loricatus, is a junior synonym of Plateosauridae
Plateosauridae
Plateosauridae is a family of plateosaurian sauropodomorphs. Plateosaurids were early sauropodomorph dinosaurs which existed in Asia, Europe and South America during the Late Triassic period. Although several dinosaurs have been classified as plateosaurids over the years, a 2007 study by Adam M....
as both contain the same taxa.
Evidence against sauropod ancestry within Prosauropoda comes from the fact that prosauropods had a smaller outer toe
Toe
Toes are the digits of the foot of a tetrapod. Animal species such as cats that walk on their toes are described as being digitigrade. Humans, and other animals that walk on the soles of their feet, are described as being plantigrade; unguligrade animals are those that walk on hooves at the tips of...
on their hind feet than the sauropods. Many maintain that it is easier for digit
Digit (anatomy)
A digit is one of several most distal parts of a limb, such as fingers or toes, present in many vertebrates.- Names:Some languages have different names for hand and foot digits ....
s to be reduced or lost during 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...
than the reverse, however there is no evidence for this. The lengthening, or gaining of extra digits is common in marine reptiles, and within the theropods digit lengthening occurred at least once. Therefore using this as evidence against ancestral prosauropods is questionable.
Most modern classification schemes break the prosauropods into a half-dozen groups that evolved separately from one common lineage. While they have a number of shared characteristics, 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...
ary requirements for giraffe
Giraffe
The giraffe is an African even-toed ungulate mammal, the tallest of all extant land-living animal species, and the largest ruminant...
-like browsing high in the trees may have caused 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...
, where similar traits evolve separately because they faced the same evolutionary pressure, instead of (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...
) traits derived from a shared ancestor.
Taxonomy
The following taxonomy follows Apaldetti et al., 2011 unless otherwise noted.- Suborder Sauropodomorpha
- ArcusaurusArcusaurusArcusaurus is an extinct genus of sauropodomorph dinosaur from the Early Jurassic of South Africa.Arcusaurus was first named by Adam Yates, Matthew Bonnan and Johann Neveling in 2011 and the type species is Arcusaurus pereirabdalorum. The generic name is derived from Latin arcus, "rainbow", a...
- AsylosaurusAsylosaurusAsylosaurus is a genus of basal sauropodomorph dinosaur from the Late Triassic of England. It is based on partial remains, described in 1836 by Henry Riley and Samuel Stutchbury as pertaining to Thecodontosaurus, that Othniel Charles Marsh brought to Yale University between 1888 and 1890...
- EoraptorEoraptorEoraptor was one of the world's earliest dinosaurs. It was a two-legged saurischian, close to the ancestry of theropods and sauropodomorphs. It lived ca. 231.4 million years ago, in what is now the northwestern region of Argentina...
? - EfraasiaEfraasiaEfraasia is a genus of basal sauropodomorph dinosaur. It was a herbivore which lived during the middle Norian stage of the Late Triassic, around 210 million years ago, in what is now Germany...
- NambaliaNambaliaNambalia is a genus of basal sauropodomorph dinosaur. It lived during the Late Triassic period in what is now Andhra Pradesh, central India...
- PampadromaeusPampadromaeusPampadromaeus is an extinct genus of basal sauropodomorph dinosaurs known from the Triassic of Rio Grande do Sul, southern Brazil.-Discovery:...
- PantydracoPantydracoPantydraco was a genus of basal sauropodomorph dinosaur from the Late Triassic of United Kingdom...
- PlateosauravusPlateosauravusPlateosauravus is a basal sauropodomorph of uncertain affinities from the late Triassic of South Africa....
- RuehleiaRuehleiaRuehleia is a genus of prosauropod dinosaur from the Late Triassic period of Germany. The type species is R. bedheimensis, described by Galton in 2001, and is named for the German paleontologist Hugo Ruehle von Lilienstern...
- ThecodontosaurusThecodontosaurusThecodontosaurus is a genus of herbivorous basal sauropodomorph dinosaur which lived during the late Triassic period ....
- Family GuaibasauridaeGuaibasauridaeGuaibasauridae is a family of primitive saurischian dinosaurs, known from fossil remains of late Triassic period formations in Brazil and Argentina....
- Node PlateosauriaPlateosauriaPlateosauria is a clade of sauropodomorph dinosaurs which lived during the Late Triassic to the Late Cretaceous. The name Plateosauria was first coined by Gustav Tornier in 1913. The name afterwards fell out of use until the 1980s, when a new generation of paleontologists began using the name...
- Family PlateosauridaePlateosauridaePlateosauridae is a family of plateosaurian sauropodomorphs. Plateosaurids were early sauropodomorph dinosaurs which existed in Asia, Europe and South America during the Late Triassic period. Although several dinosaurs have been classified as plateosaurids over the years, a 2007 study by Adam M....
- Branch MassopodaMassopodaThe Massopoda is a clade of sauropodomorph dinosaurs which lived during the Late Triassic to the Late Cretaceous periods. Massopoda, which was first named by paleontologist Adam M...
- ChuxiongosaurusChuxiongosaurusChuxiongosaurus is a genus of basal sauropodomorph dinosaur which lived during the Early Jurassic Period. Fossils of this genus have been found in the Lower Lufeng Formation, Yunnan Province, southern China...
- IgnavusaurusIgnavusaurusIgnavusaurus is a genus of basal sauropodomorph dinosaur that lived during the Early Jurassic in what is now present-day Lesotho. Its fossils were found in the upper Elliot Formation which is probably Hettangian in age. It was described on the basis of a partial, well preserved articulated skeleton...
- JingshanosaurusJingshanosaurusJingshanosaurus is a genus of prosauropod dinosaurs from the Early Jurassic. Its fossils, a nearly complete skeleton including the skull, were found near the town of Jingshan , Lufeng County, Yunnan Province, China, from which the name derives. First described in 1995, the type species is J....
- MussaurusMussaurusMussaurus was a genus of herbivorous prosauropod dinosaur that lived in southern Argentina during the Late Triassic Period, about 215 million years ago...
- SarahsaurusSarahsaurusSarahsaurus is a genus of basal sauropodomorph dinosaur which lived during the lower Jurassic period in what is now northeastern Arizona, USA....
- SeitaadSeitaadSeitaad is a genus of sauropodomorph dinosaur which lived during the lower Jurassic period in what is now southern Utah, USA.Seitaad is known from an articulated partial postcranial holotype skeleton referred to as UMNH VP 18040. The skeleton is missing its head, neck and tail...
- XixiposaurusXixiposaurusXixiposaurus is a genus of prosauropod dinosaur which existed in what is now Lower Lufeng Formation, China during the lower Jurassic period. It was first named by Sekiya Toru in 2010 and the type species is Xixiposaurus suni....
- YunnanosaurusYunnanosaurusYunnanosaurus is a genus of prosauropod dinosaur from the Early to Middle Jurassic Period, a position in time that makes it one of the last prosauropods. It is closely related to Lufengosaurus...
- Family Gryponychidae
- Family MassospondylidaeMassospondylidaeMassospondylidae is a family of massopod sauropodomorphs. Massospondylids are early sauropodomorph dinosaurs which existed in Asia, Africa and South America during the Late Triassic to the Early Jurassic periods...
- Family RiojasauridaeRiojasauridaeRiojasauridae is a family of sauropod-like dinosaurs from the Upper Triassic. It is known primarily from the genera Riojasaurus and Eucnemesaurus...
- Node AnchisauriaAnchisauriaThe Anchisauria were a clade of sauropodomorph dinosaurs which lived during the Late Triassic and Early Jurassic. The name Anchisauria was first used by Galton and Upchurch in the second edition of The Dinosauria...
(including Infraorder SauropodaSauropodaSauropoda , or the sauropods , are an infraorder of saurischian dinosaurs. They had long necks, long tails, small heads , and thick, pillar-like legs. They are notable for the enormous sizes attained by some species, and the group includes the largest animals to have ever lived on land...
)
- Chuxiongosaurus
- Family Plateosauridae
- Arcusaurus
Phylogeny
The following cladogramCladogram
A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...
simplified after an analysis presented by Apaldetti and colleagues in November 2011.
Cladogram after Novas et al., 2011:
External links
- Sauropodomorpha: Overview, from Palæos.
- Sauropodmorpha, from When Dinosaurs Ruled Texas, by Jon A. Baskin.
- Geol 104 Dinosaurs: A natural history: Sauropodomorpha: Size matters, by Thomas R. Holtz Jr.Thomas R. Holtz Jr.Thomas Richard Holtz, Jr., Ph.D. is a vertebrate palaeontologist and senior lecturer at the University of Maryland's Department of Geology. He has published extensively on the phylogeny, morphology, ecomorphology, and locomotion of terrestrial predators, especially on tyrannosaurids and other...
, from the University of Maryland. - Sauropodomorpha: The prosauropods and the sauropods