Ammosaurus
Encyclopedia
Ammosaurus is a genus
of sauropodomorph dinosaur
from the Early and Middle Jurassic
Period of North America
. At 4 meters (13 feet) in length, it was small compared to some other members of its suborder, which included the largest animals
ever to walk the Earth
. It was a versatile animal, able to move both biped
ally and quadruped
ally, and may have been omnivorous
.
words ammos ("sandy ground") and sauros ("lizard"), referring to the sandstone
in which it was found and its reptilian nature. There is one currently valid species (A. major), which is so named because it is larger than Anchisaurus, of which it was originally considered a second species. Famous American
paleontologist Othniel Charles Marsh
created this specific name in 1889. In 1891, Marsh created the new genus Ammosaurus for this species and he subsequently named another species (Ammosaurus solus) in 1892, although scientists now consider it synonymous with A. major.
and is most closely related to Anchisaurus, with which it may actually be synonymous. Different paleontologists consider Anchisaurus to be either a basal
prosauropod (Galton & Upchurch, 2004), a basal sauropod (Yates & Kitching, 2003; Yates, 2004), or a sauropodomorph more derived than prosauropods but outside of Sauropoda.
Marsh originally described Ammosaurus major as Anchisaurus major, although he removed it to its own new genus only 2 years later. However, some recent studies have suggested that Ammosaurus and Anchisaurus are the same animal after all (Sereno, 1999; Yates, 2004). Other scientists prefer to keep the two genera separate due to anatomical differences in the pelvis
and hind foot, although the two animals are still considered sister taxa (Galton & Upchurch, 2004).
s of Ammosaurus were originally discovered in the Portland Formation
of the Newark Supergroup in the U.S. state of Connecticut
. This formation
preserves an arid environment with strong wet and dry seasons, from the Pliensbachian
through to Toarcian
stages of the Early Jurassic Period, roughly 190 to 176 million years ago. The original specimens were recovered from a sandstone quarry
, which was used in the construction of the South Manchester Bridge in Connecticut. In fact, the holotype
specimen was discovered by quarry workers. Unfortunately, it consists of only the rear half of the skeleton, as the block containing the front half had already been installed in the bridge. In 1969, the bridge was demolished
, and some Ammosaurus remains were recovered. Three other incomplete skeletons of different ages are also known from Connecticut, but there is no known skull
(Weishampel & Young, 1996). Ammosaurus is still found in Bajocian
stage deposits of North America, making it one of the few "prosauropod" genera to survive into the Middle Jurassic
(Weishampel et al., 2004).
The Navajo Sandstone
of Arizona
is the same age as the Portland Formation, and has produced prosauropod remains that have been referred to as Ammosaurus (Galton, 1971). However, it is possible that these actually belong to the genus Massospondylus
, otherwise known only from South Africa
(Galton & Upchurch, 2004).
In the Canadian
province of Nova Scotia
, scientists have unearthed prosauropods from the McCoy Brook Formation
, which is about 200 to 197 million years old, from the Early Jurassic Hettangian
stage. The Nova Scotia material provides clues about the diet of these animals. A large number of gastrolith
s, stones swallowed to grind up plant material in the gut, were found in the abdomen
, as well as bone from the skull of a small sphenodont
, Clevosaurus
. This indicates that these dinosaurs were omnivorous, with a diet mainly consisting of plants but with an occasional supplement of meat (Shubin et al., 1994). However, these remains have never been fully described or illustrated and are only tentatively referred to Ammosaurus. Further study may either confirm or falsify this hypothesis
.
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 sauropodomorph 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 and Middle Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
Period of North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
. At 4 meters (13 feet) in length, it was small compared to some other members of its suborder, which included the largest animals
Largest organisms
The largest organism found on Earth can be measured using a variety of methods. It could be defined as the largest by volume, mass, height or length. Some organisms group together to form a superorganism, though this cannot truly be classed as one large organism...
ever to walk the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
. It was a versatile animal, able to move both 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"...
ally and 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"...
ally, and may have been omnivorous
Omnivore
Omnivores are species that eat both plants and animals as their primary food source...
.
Naming
The generic name Ammosaurus is derived from the GreekAncient 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 ammos ("sandy ground") and sauros ("lizard"), referring to the sandstone
Sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
in which it was found and its reptilian nature. There is one currently valid species (A. major), which is so named because it is larger than Anchisaurus, of which it was originally considered a second species. Famous American
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
paleontologist Othniel Charles Marsh
Othniel Charles Marsh
Othniel Charles Marsh was an American paleontologist. Marsh was one of the preeminent scientists in the field; the discovery or description of dozens of news species and theories on the origins of birds are among his legacies.Born into a modest family, Marsh was able to afford higher education...
created this specific name in 1889. In 1891, Marsh created the new genus Ammosaurus for this species and he subsequently named another species (Ammosaurus solus) in 1892, although scientists now consider it synonymous with A. major.
Synonym with Anchisaurus?
The relationships of Ammosaurus with other dinosaurs are highly uncertain at this time. It is an early member of the suborder SauropodomorphaSauropodomorpha
Sauropodomorpha is an extinct clade of long-necked, herbivorous, saurischian dinosaurs which includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had long necks and tails, were quadrupedal, and became the largest animals to ever walk the Earth. The...
and is most closely related to Anchisaurus, with which it may actually be synonymous. Different paleontologists consider Anchisaurus to be either a 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:...
prosauropod (Galton & Upchurch, 2004), a basal sauropod (Yates & Kitching, 2003; Yates, 2004), or a sauropodomorph more derived than prosauropods but outside of Sauropoda.
Marsh originally described Ammosaurus major as Anchisaurus major, although he removed it to its own new genus only 2 years later. However, some recent studies have suggested that Ammosaurus and Anchisaurus are the same animal after all (Sereno, 1999; Yates, 2004). Other scientists prefer to keep the two genera separate due to anatomical differences in the pelvis
Pelvis
In human anatomy, the pelvis is the lower part of the trunk, between the abdomen and the lower limbs .The pelvis includes several structures:...
and hind foot, although the two animals are still considered sister taxa (Galton & Upchurch, 2004).
Fossil discoveries
FossilFossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s of Ammosaurus were originally discovered in the Portland Formation
Portland Formation
The Portland Formation is a geological formation in the northeastern United States. It dates back to the Early Jurassic.-Vertebrate fauna:Dinosaur coprolites located in Massachusetts, USA. Ornithischian tracks located in Massachusetts and Connecticut, USA. Theropod tracks located in Massachusetts...
of the Newark Supergroup in the U.S. state of Connecticut
Connecticut
Connecticut is a state in the New England region of the northeastern United States. It is bordered by Rhode Island to the east, Massachusetts to the north, and the state of New York to the west and the south .Connecticut is named for the Connecticut River, the major U.S. river that approximately...
. This 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...
preserves an arid environment with strong wet and dry seasons, from the Pliensbachian
Pliensbachian
The Pliensbachian is an age of the geologic timescale or stage in the stratigraphic column. It is part of the Early or Lower Jurassic epoch or series and spans the time between 189.6 ± 1.5 Ma and 183 ± 1.5 Ma . The Pliensbachian is preceded by the Sinemurian and followed by the Toarcian.The...
through to Toarcian
Toarcian
The Toarcian is, in the ICS' geologic timescale, an age or stage in the Early or Lower Jurassic. It spans the time between 183.0 Ma and 175.6 Ma...
stages of the Early Jurassic Period, roughly 190 to 176 million years ago. The original specimens were recovered from a sandstone quarry
Quarry
A quarry is a type of open-pit mine from which rock or minerals are extracted. Quarries are generally used for extracting building materials, such as dimension stone, construction aggregate, riprap, sand, and gravel. They are often collocated with concrete and asphalt plants due to the requirement...
, which was used in the construction of the South Manchester Bridge in Connecticut. In fact, the holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
specimen was discovered by quarry workers. Unfortunately, it consists of only the rear half of the skeleton, as the block containing the front half had already been installed in the bridge. In 1969, the bridge was demolished
Demolition
Demolition is the tearing-down of buildings and other structures, the opposite of construction. Demolition contrasts with deconstruction, which involves taking a building apart while carefully preserving valuable elements for re-use....
, and some Ammosaurus remains were recovered. Three other incomplete skeletons of different ages are also known from Connecticut, but there is no known 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...
(Weishampel & Young, 1996). Ammosaurus is still found in Bajocian
Bajocian
In the geologic timescale, the Bajocian is an age or stage in the Middle Jurassic. It lasted from approximately 171.6 Ma to around 167.7 Ma . The Bajocian age succeeds the Aalenian age and precedes the Bathonian age....
stage deposits of North America, making it one of the few "prosauropod" genera to survive into the Middle Jurassic
Middle Jurassic
The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from 176-161 million years ago. In European lithostratigraphy, rocks of this Middle Jurassic age are called the Dogger....
(Weishampel et al., 2004).
Ammosaurus outside Connecticut
Ammosaurus remains have been reported from other parts of North America, but may not represent the species A. major, if they represent the genus at all.The Navajo Sandstone
Navajo Sandstone
Navajo Sandstone is a geologic formation in the Glen Canyon Group that is spread across the U.S. states of northern Arizona, northwest Colorado, and Utah; as part of the Colorado Plateau province of the United States...
of Arizona
Arizona
Arizona ; is a state located in the southwestern region of the United States. It is also part of the western United States and the mountain west. The capital and largest city is Phoenix...
is the same age as the Portland Formation, and has produced prosauropod remains that have been referred to as Ammosaurus (Galton, 1971). However, it is possible that these actually belong to the genus Massospondylus
Massospondylus
Massospondylus and ) is a genus of prosauropod dinosaur from the early Jurassic Period . It was described by Sir Richard Owen in 1854 from remains found in South Africa, and is thus one of the first dinosaurs to have been named...
, otherwise known only from South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
(Galton & Upchurch, 2004).
In the Canadian
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
province of Nova Scotia
Nova Scotia
Nova Scotia is one of Canada's three Maritime provinces and is the most populous province in Atlantic Canada. The name of the province is Latin for "New Scotland," but "Nova Scotia" is the recognized, English-language name of the province. The provincial capital is Halifax. Nova Scotia is the...
, scientists have unearthed prosauropods from the McCoy Brook Formation
McCoy Brook Formation
The McCoy Brook Formation is a Mesozoic geologic formation on Nova Scotia. Dinosaur remains diagnostic to the genus level are among the fossils that have been recovered from the formation.-Synapsids:-Ornitodires:-Dinosaurs:-See also:...
, which is about 200 to 197 million years old, from the Early Jurassic Hettangian
Hettangian
The Hettangian is the earliest age or lowest stage of the Jurassic period of the geologic timescale. It spans the time between 199.6 ± 0.6 Ma and 196.5 ± 1 Ma . The Hettangian follows the Rhaetian and is followed by the Sinemurian.In Europe stratigraphy the Hettangian is a part of the time span in...
stage. The Nova Scotia material provides clues about the diet of these animals. A large number of 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, stones swallowed to grind up plant material in the gut, were found in the abdomen
Abdomen
In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...
, as well as bone from the skull of a small sphenodont
Sphenodontia
Sphenodontia is an order of lizard-like reptiles that includes only one living genus, the tuatara , and only two living species...
, Clevosaurus
Clevosaurus
Clevosaurus is an extinct genus of sphenodontian reptile from the Triassic and the Jurassic periods of Nova Scotia, Great Britain, and Yunnan...
. This indicates that these dinosaurs were omnivorous, with a diet mainly consisting of plants but with an occasional supplement of meat (Shubin et al., 1994). However, these remains have never been fully described or illustrated and are only tentatively referred to Ammosaurus. Further study may either confirm or falsify this hypothesis
Hypothesis
A hypothesis is a proposed explanation for a phenomenon. The term derives from the Greek, ὑποτιθέναι – hypotithenai meaning "to put under" or "to suppose". For a hypothesis to be put forward as a scientific hypothesis, the scientific method requires that one can test it...
.