Haplocanthosaurus
Encyclopedia
Haplocanthosaurus is a genus
of sauropod dinosaur
. Two species, H. delfsi and H. priscus, are known from incomplete fossil
skeletons. It lived during the late Jurassic
period (Kimmeridgian
stage), 155 to 152 million years ago. The type species is H. priscus, and the referred species H. delfsi was discovered by a young college student named Edwin Delfs in Colorado
. Haplocanthosaurus specimens have been found in the very lowest layer of the Morrison Formation
, along with Hesperosaurus
, Eobrontosaurus
, and Allosaurus jimmadensi
.
Haplocanthosaurus was one of the smallest sauropods of the Morrison. While some Morrison sauropods could reach lengths of over 20 meters (or over 70 feet), Haplocanthosaurus wasn't nearly as large, and reached a total length of 14.8 meters (49 feet) and an estimated weight of 12.8 metric tons.
, albeit with a completely speculative replica skull, as the actual skull was not recovered. Present in stratigraphic zones 1, 2, and 4.
in 1903. Soon after his original description, Hatcher came to believe the name Haplocanthus had already been used for a genus of acanthodian fish
(Haplacanthus, named by Louis Agassiz
in 1845), and was thus preoccupied. Hatcher re-classified his sauropod later in 1903, giving it the new name Haplocanthosaurus. However, the name was not technically preoccupied at all, since there was a variation in spelling: the fish was named Haplacanthus, not Haplocanthus. While Haplocanthus technically remained the valid name for this dinosaur, Hatcher's mistake was not noticed until many years after the name Haplocanthosaurus had become fixed in scientific literature. When the mistake was finally discovered, a petition was sent to the ICZN
(the body which governs scientific names in zoology), which officially discarded the name Haplocanthus and declared Haplocanthosaurus the official name (ICZN Opinion #1633).
Originally described as a "cetiosaurid", José Bonaparte
decided in 1999 that Haplocanthosaurus differed enough from other sauropods to warrant its own family
, the Haplocanthosauridae.
Phylogenetic studies have failed to clarify the exact relationships of Haplocanthosaurus with any certainty. Studies have variously found it to be more primitive than the neosauropods
, a primitive macronaria
n (related to the ancestor of more advanced forms such as Camarasaurus
and the brachiosaurids
), or a very primitive diplodocoid
, more closely related to Diplodocus
than to titanosaur
s, but more primitive than rebachisaurids
.
In 2005, Darren Naish
and Mike Taylor reviewed the various proposed positions of Haplocanthosaurus in their study of diplodocoid phylogeny. These positions are represented in the cladogram
below.
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 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...
. Two species, H. delfsi and H. priscus, are known from incomplete fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
skeletons. It lived during the late 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 (Kimmeridgian
Kimmeridgian
In the geologic timescale, the Kimmeridgian is an age or stage in the Late or Upper Jurassic epoch or series. It spans the time between 155.7 ± 4 Ma and 150.8 ± 4 Ma . The Kimmeridgian follows the Oxfordian and precedes the Tithonian....
stage), 155 to 152 million years ago. The type species is H. priscus, and the referred species H. delfsi was discovered by a young college student named Edwin Delfs in Colorado
Colorado
Colorado is a U.S. state that encompasses much of the Rocky Mountains as well as the northeastern portion of the Colorado Plateau and the western edge of the Great Plains...
. Haplocanthosaurus specimens have been found in the very lowest layer of the Morrison Formation
Morrison Formation
The Morrison Formation is a distinctive sequence of Late Jurassic sedimentary rock that is found in the western United States, which has been the most fertile source of dinosaur fossils in North America. It is composed of mudstone, sandstone, siltstone and limestone and is light grey, greenish...
, along with Hesperosaurus
Hesperosaurus
Hesperosaurus was a herbivorous dinosaur from the Kimmeridgian to Tithonian epochs of the Jurassic period , whose fossils are found in the state of Wyoming in the United States of America...
, Eobrontosaurus
Eobrontosaurus
Eobrontosaurus is the name given to a genus of dinosaur from the Late Jurassic of North America. It was a sauropod probably closely related to Apatosaurus. It is known from a single site from the lower Morrison Formation, dating to about 154 million years ago. It grew up to long.The type species, E...
, and Allosaurus jimmadensi
Allosaurus
Allosaurus is a genus of large theropod dinosaur that lived 155 to 150 million years ago during the late Jurassic period . The name Allosaurus means "different lizard". It is derived from the Greek /allos and /sauros...
.
Description
Specimens
There are four known specimens of Haplocanthosaurus, one of H. delfsi, and three of H. priscus. Of these, the type of H. delfsi is the only adult, and the only one complete enough to mount. The mounted specimen of H. delfsi now stands in the Cleveland Museum of Natural HistoryCleveland Museum of Natural History
The Cleveland Museum of Natural History is a natural history museum located approximately five miles east of downtown Cleveland, Ohio in University Circle, a 550-acre concentration of educational, cultural and medical institutions...
, albeit with a completely speculative replica skull, as the actual skull was not recovered. Present in stratigraphic zones 1, 2, and 4.
Classification
Haplocanthosaurus priscus was originally named Haplocanthus priscus by John Bell HatcherJohn Bell Hatcher
John Bell Hatcher was an American paleontologist and fossil hunter best known for discovering Torosaurus.-Biography:...
in 1903. Soon after his original description, Hatcher came to believe the name Haplocanthus had already been used for a genus of acanthodian fish
Acanthodii
Acanthodii is a class of extinct fishes, sharing features with both bony fish and cartilaginous fish. In form they resembled sharks, but their epidermis was covered with tiny rhomboid platelets like the scales of holosteans...
(Haplacanthus, named by Louis Agassiz
Louis Agassiz
Jean Louis Rodolphe Agassiz was a Swiss paleontologist, glaciologist, geologist and a prominent innovator in the study of the Earth's natural history. He grew up in Switzerland and became a professor of natural history at University of Neuchâtel...
in 1845), and was thus preoccupied. Hatcher re-classified his sauropod later in 1903, giving it the new name Haplocanthosaurus. However, the name was not technically preoccupied at all, since there was a variation in spelling: the fish was named Haplacanthus, not Haplocanthus. While Haplocanthus technically remained the valid name for this dinosaur, Hatcher's mistake was not noticed until many years after the name Haplocanthosaurus had become fixed in scientific literature. When the mistake was finally discovered, a petition was sent to the ICZN
International Commission on Zoological Nomenclature
The International Commission on Zoological Nomenclature is an organization dedicated to "achieving stability and sense in the scientific naming of animals". Founded in 1895, it currently comprises 28 members from 20 countries, mainly practicing zoological taxonomists...
(the body which governs scientific names in zoology), which officially discarded the name Haplocanthus and declared Haplocanthosaurus the official name (ICZN Opinion #1633).
Originally described as a "cetiosaurid", 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...
decided in 1999 that Haplocanthosaurus differed enough from other sauropods to warrant its own family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
, the Haplocanthosauridae.
Phylogenetic studies have failed to clarify the exact relationships of Haplocanthosaurus with any certainty. Studies have variously found it to be more primitive than the neosauropods
Neosauropoda
Neosauropoda is a division-level clade of sauropods within Dinosauria, and consists of the group leading to Diplodocoidea and Macronaria. Haplocanthosaurus was a typical basal neosauropod from around 150 million years ago, in the Late Jurassic...
, a primitive macronaria
Macronaria
Macronaria is a clade of sauropod dinosaurs from the Middle Jurassic to Late Cretaceous Periods of what are now North America, South America, Europe, Asia and Africa. The name means 'large nostrils' , in reference to the large nasal openings high on the head that probably supported fleshy...
n (related to the ancestor of more advanced forms such as Camarasaurus
Camarasaurus
Camarasaurus meaning 'chambered lizard', referring to the hollow chambers in its vertebrae was a genus of quadrupedal, herbivorous dinosaurs. It was the most common of the giant sauropods to be found in North America...
and the brachiosaurids
Brachiosauridae
Brachiosauridae are a family of dinosaurs, whose members are known as brachiosaurids. They were herbivorous quadrupeds with longer forelegs than hind legs - the name derives from the Greek for arm lizard - and long necks...
), or a very primitive diplodocoid
Diplodocoidea
Diplodocoidea was a superfamily of sauropod dinosaurs, which included some of the longest animals of all time, including slender giants like Supersaurus, Diplodocus, Apatosaurus, and Amphicoelias...
, more closely related to 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...
than to titanosaur
Titanosaur
Titanosaurs were a diverse group of sauropod dinosaurs, which included Saltasaurus and Isisaurus. It includes some of the heaviest creatures ever to walk the earth, such as Argentinosaurus and Paralititan — which some believe have weighed up to 100 tonnes...
s, but more primitive than rebachisaurids
Rebbachisauridae
Rebbachisauridae is a family of sauropod dinosaurs known from fragmentary fossil remains from the Cretaceous of South America, Africa, and Europe.-Taxonomy:...
.
In 2005, Darren Naish
Darren Naish
Darren Naish is a vertebrate palaeontologist and science writer. He obtained a geology degree at the University of Southampton and later studied vertebrate palaeontology under British palaeontologist David Martill at the University of Portsmouth, where he obtained both an M. Phil...
and Mike Taylor reviewed the various proposed positions of Haplocanthosaurus in their study of diplodocoid phylogeny. These positions are represented in the cladogram
Cladogram
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...
below.