Amargasaurus
Encyclopedia
Amargasaurus is a genus
of dicraeosaurid
sauropod dinosaur
from the Early Cretaceous
Period (130-125 mya) of what is now South America
. It was small for a sauropod, reaching 10 meters (33 feet) length. It would have been a quadrupedal herbivore
with a long, low skull
on the end of a long neck, much like its relative Dicraeosaurus
. However, this dinosaur sported two parallel rows of tall spines down its neck and back, taller than in any other known sauropod. These spines have been reconstructed supporting skin sails, but the "skin sail" hypothesis was rejected by Gregory S. Paul
in 2000.
paleontologists Leonardo Salgado and José Bonaparte
, because its fossil
remains were found alongside the La Amarga Arroyo
in the Neuquén
province of Argentina. La Amarga is also the name of a nearby town, as well as the geologic formation
the remains were recovered from. The word amarga itself is Spanish
for "bitter," while sauros is Greek
for "lizard." The one named species
(A. cazaui) is named in honor of the man who discovered the site, Dr. Luis Cazau, a geologist
with the YPF oil
company, which at the time was state-owned.
This site is located in the lower (older) sections of the La Amarga Formation
, which dates to the Barremian
through early Aptian
stages of the Early Cretaceous Period, or around 130 to 120 million years ago.
Amargasaurus is known from a relatively complete skeleton from a single individual. This skeleton includes the back of the skull
, and all vertebrae of the neck, back, and hips, as well as a bit of the tail. The right side of the shoulder girdle is also known, as are the left forelimb and hind limb, and the left ilium
, a bone of the pelvis
.
The most obvious feature of Amargasaurus skeleton is the series of tall spines on the neck and back vertebrae. The spines are tallest on the neck, where they are paired in two parallel rows. These rows continue along the back, decreasing in height as they approach the hips. The lower back and sacral
(hip) vertebrae feature only single spines, which are long but much shorter than those of the neck, comparable to other sauropods. These spines may have supported a pair of tall skin sails. Similar sails are seen in the unrelated dinosaurs Spinosaurus
and Ouranosaurus
, as well as the pelycosaur
s Dimetrodon
and Edaphosaurus
. There are a variety of hypotheses
for the function of these such sails, including defense, communication
(for mating purposes or for simple species recognition
), or temperature regulation
.
Gregory Paul argued that parallel neck sails would have reduced neck flexion. Instead, he proposed that, with their circular rather than flat cross-sections, these spines were more likely covered with a horny sheath. He even suggests that they could have been clattered together for a sound display.
Similar spines are found on the presacral vertebrae of Dicraeosaurus from Africa
, although not nearly as tall.
in the family Dicraeosauridae. Dicraeosaurids and diplodocid
sauropods are included in a group called Flagellicaudata.
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 dicraeosaurid
Dicraeosauridae
Dicraeosauridae is a family of sauropod dinosaurs known from the Late Jurassic and Early Cretaceous of Africa and South America. Currently only three genera are recognised; the Jurassic South American genus Brachytrachelopan, the Jurassic African Dicraeosaurus and the South American Early...
sauropod dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
from the Early Cretaceous
Early Cretaceous
The Early Cretaceous or the Lower Cretaceous , is the earlier or lower of the two major divisions of the Cretaceous...
Period (130-125 mya) of what is now South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
. It was small for a sauropod, reaching 10 meters (33 feet) length. It would have been a quadrupedal 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...
with a long, low 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, much like its relative Dicraeosaurus
Dicraeosaurus
Dicraeosaurus is a genus of small diplodocoid sauropod dinosaur. It was named for the spines on the back of the neck. The first fossil was described by paleontologist Werner Janensch in 1914.Unlike most diplodocoids, Dicraeosaurus had a large head with a relatively short and wide neck...
. However, this dinosaur sported two parallel rows of tall spines down its neck and back, taller than in any other known sauropod. These spines have been reconstructed supporting skin sails, but the "skin sail" hypothesis was rejected by Gregory S. Paul
Gregory S. Paul
Gregory Scott Paul is a freelance researcher, author and illustrator who works in paleontology, and more recently has examined sociology and theology. He is best known for his work and research on theropod dinosaurs and his detailed illustrations, both live and skeletal...
in 2000.
Discovery and species
The name Amargasaurus was coined in 1991 by ArgentineArgentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...
paleontologists Leonardo Salgado and José Bonaparte
José Bonaparte
José Fernando Bonaparte, Ph.D. , is an Argentine paleontologist who discovered a plethora of South American dinosaurs and mentored a new generation of Argentine paleontologists like Rodolfo Coria...
, because its fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
remains were found alongside the La Amarga Arroyo
Arroyo (creek)
An arroyo , a Spanish word translated as brook, and also called a wash is usually a dry creek or stream bed—gulch that temporarily or seasonally fills and flows after sufficient rain. Wadi is a similar term in Africa. In Spain, a rambla has a similar meaning to arroyo.-Types and processes:Arroyos...
in the Neuquén
Neuquén
Neuquén is the name of the following things:* Neuquén, Argentina* Neuquén Province* Neuquén River* Neuquén Group...
province of Argentina. La Amarga is also the name of a nearby town, as well as the 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...
the remains were recovered from. The word amarga itself is Spanish
Spanish language
Spanish , also known as Castilian , is a Romance language in the Ibero-Romance group that evolved from several languages and dialects in central-northern Iberia around the 9th century and gradually spread with the expansion of the Kingdom of Castile into central and southern Iberia during the...
for "bitter," while sauros is 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...
for "lizard." The one named species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
(A. cazaui) is named in honor of the man who discovered the site, Dr. Luis Cazau, a geologist
Geologist
A geologist is a scientist who studies the solid and liquid matter that constitutes the Earth as well as the processes and history that has shaped it. Geologists usually engage in studying geology. Geologists, studying more of an applied science than a theoretical one, must approach Geology using...
with the YPF oil
Oil
An oil is any substance that is liquid at ambient temperatures and does not mix with water but may mix with other oils and organic solvents. This general definition includes vegetable oils, volatile essential oils, petrochemical oils, and synthetic oils....
company, which at the time was state-owned.
This site is located in the lower (older) sections of the La Amarga Formation
La Amarga Formation
The La Amarga Formation is a geologic formation with outcrops in the Argentine provinces of Río Negro, Neuquén, and Mendoza. It is the oldest Cretaceous terrestrial formation in the Neuquén Basin....
, which dates to the 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 early Aptian
Aptian
The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous epoch or series and encompasses the time from 125.0 ± 1.0 Ma to 112.0 ± 1.0 Ma , approximately...
stages of the Early Cretaceous Period, or around 130 to 120 million years ago.
Paleobiology
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 all vertebrae of the neck, back, and hips, as well as a bit of the tail. The right side of the shoulder girdle is also known, as are the left forelimb and hind limb, and the left ilium
Ilium (bone)
The ilium is the uppermost and largest bone of the pelvis, and appears in most vertebrates including mammals and birds, but not bony fish. All reptiles have an ilium except snakes, although some snake species have a tiny bone which is considered to be an ilium.The name comes from the Latin ,...
, a bone of 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:...
.
Vertebral spines
Sacrum
In vertebrate anatomy the sacrum is a large, triangular bone at the base of the spine and at the upper and back part of the pelvic cavity, where it is inserted like a wedge between the two hip bones. Its upper part connects with the last lumbar vertebra, and bottom part with the coccyx...
(hip) vertebrae feature only single spines, which are long but much shorter than those of the neck, comparable to other sauropods. These spines may have supported a pair of tall skin sails. Similar sails are seen in the unrelated dinosaurs Spinosaurus
Spinosaurus
Spinosaurus is a genus of theropod dinosaur which lived in what is now North Africa, from the lower Albian to lower Cenomanian stages of the Cretaceous period, about 112 to 97 million years ago. This genus was first known from Egyptian remains discovered in 1912 and described by German...
and Ouranosaurus
Ouranosaurus
Ouranosaurus is an unusual genus of herbivorous iguanodont dinosaur that lived during the early Cretaceous about 110 million years ago in what is now Africa. Ouranosaurus measured about seven to eight meters long...
, as well as the pelycosaur
Pelycosaur
The pelycosaurs are an informal grouping composed of basal or primitive Late Paleozoic synapsid amniotes. Some species were quite large and could grow up to 3 meters or more, although most species were much smaller...
s Dimetrodon
Dimetrodon
Dimetrodon was a predatory synapsid genus that flourished during the Permian period, living between 280–265 million years ago ....
and Edaphosaurus
Edaphosaurus
Edaphosaurus is a genus of prehistoric synapsid which lived around 303 to 265 million years ago, during the late Carboniferous to early Permian periods. The name Edaphosaurus means "ground lizard" and is derived from the Greek edaphos/εδαφος and σαυρος/sauros...
. There are a variety of hypotheses
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...
for the function of these such sails, including defense, 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...
(for mating purposes or for simple species recognition
Intra-species recognition
Intra-species recognition is recognition by a member of a species of a conspecific . In many species, such recognition is necessary for procreation....
), or temperature regulation
Thermoregulation
Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different...
.
Gregory Paul argued that parallel neck sails would have reduced neck flexion. Instead, he proposed that, with their circular rather than flat cross-sections, these spines were more likely covered with a horny sheath. He even suggests that they could have been clattered together for a sound display.
Similar spines are found on the presacral vertebrae of Dicraeosaurus from Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
, although not nearly as tall.
Classification
Amargasaurus and Dicraeosaurus are united with the more recently discovered BrachytrachelopanBrachytrachelopan
Brachytrachelopan is an unusual short-necked sauropod dinosaur from the latest Jurassic Period of Argentina. The holotype and only known specimen was collected from an erosional exposure of fluvial sandstone within the Cañadón Cálcero Formation on a hill approximately 25 km north-northeast...
in the family Dicraeosauridae. Dicraeosaurids and diplodocid
Diplodocid
Diplodocids, or members of the family Diplodocidae , are a group of sauropod dinosaurs. The family includes some of the longest creatures ever to walk the earth, including Diplodocus and Supersaurus, which may have reached lengths of up to .-Description:While still massive, when compared to the...
sauropods are included in a group called Flagellicaudata.