''Haplocanthosaurus'' (meaning "simple spined lizard") is a
genus
Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
of
diplodocoid sauropod
Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their b ...
dinosaur
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...
. Two species, ''H. delfsi'' and ''H. priscus'', are known from incomplete
fossil
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...
skeletons
A skeleton is the structural frame that supports the body of most animals. There are several types of skeletons, including the exoskeleton, which is a rigid outer shell that holds up an organism's shape; the endoskeleton, a rigid internal fram ...
. They lived during the Late
Jurassic
The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...
(
Kimmeridgian
In the geologic timescale, the Kimmeridgian is an age in the Late Jurassic Epoch and a stage in the Upper Jurassic Series. It spans the time between 154.8 ±0.8 Ma and 149.2 ±0.7 Ma (million years ago). The Kimmeridgian follows the Oxfordian ...
stage), 155 to 152 million years ago in North America.
[Turner, C.E. and Peterson, F., (1999). "Biostratigraphy of dinosaurs in the Upper Jurassic Morrison Formation of the Western Interior, U.S.A." Pp. 77–114 in Gillette, D.D. (ed.), ''Vertebrate Paleontology in Utah''. Utah Geological Survey Miscellaneous Publication 99-1.] The type species is ''H. priscus,'' named in 1903
John Bell Hatcher '','' and the referred species ''H. delfsi'' was discovered by a young college student named Edwin Delfs in
Colorado
Colorado is a U.S. state, state in the Western United States. It is one of the Mountain states, sharing the Four Corners region with Arizona, New Mexico, and Utah. It is also bordered by Wyoming to the north, Nebraska to the northeast, Kansas ...
, United States and described by
Jack McIntosh and Michael Williams in 1988. ''Haplocanthosaurus'' specimens have been found in the very lowest layer of the
Morrison Formation
The Morrison Formation is a distinctive sequence of Upper Jurassic sedimentary rock 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, siltston ...
, along with ''
Hesperosaurus mjosi'', ''
Brontosaurus yahnahpin'', and ''
Allosaurus jimmadseni''.
[Foster, J. (2007). ''Jurassic West: The Dinosaurs of the Morrison Formation and Their World''. Indiana University Press. 389pp.]
Discovery

There are four known specimens of ''Haplocanthosaurus'': one of ''H. delfsi'', and three of ''H. priscus''. Of these, the
type
Type may refer to:
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* TYPE (DOS command), a command to display contents of a file.
* ...
of ''H. delfsi'' is the only one complete enough to mount. The mounted specimen of ''H. delfsi'' now stands in the
Cleveland Museum of Natural History
The Cleveland Museum of Natural History is a natural history museum in University Circle, a district of educational, cultural and medical institutions approximately five miles (8 km) east of Downtown Cleveland, Ohio, United States. The ...
, albeit with a completely speculative replica skull, as the actual skull was not recovered. Present in stratigraphic zones 1, 2, and 4.
[Foster, J. (2007). "Appendix." ''Jurassic West: The Dinosaurs of the Morrison Formation and Their World''. Indiana University Press. pp. 327-329.] Recently described specimens from a different region of the Morrison Formation were assigned to ''Haplocanthosaurus'' in 2014. The study describing them noted that ''Haplocanthosaurus'' is known for certain from at least four specimens, assigned to ''H. priscus'' (CM 572), ''H. utterbacki'' (=''H. priscus''; CM 879), ''H. delfsi'' (CMNH 10380), and ''H.'' sp. (MWC 8028). Up to seven additional specimens have been assigned to ''Haplocanthosaurus''? or Haplocanthosauridae indet.
One potential specimen has been nicknamed "Big Monty," for its discovery in Montana. It has been claimed to measure an incredible long. However, much controversy surrounds the specimen and, as such, little is truly known about it.
Description

''Haplocanthosaurus'' was one of the smallest
sauropods
Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their b ...
of the Morrison.
While some Morrison sauropods could reach lengths of over 20 meters (or over 66 feet), ''Haplocanthosaurus'' was smaller, reaching a total length of 14.8 meters (49 feet) and an estimated weight of .
''Haplocanthosaurus'' is known from many elements, mostly of vertebra. In the middle and cervical caudals of ''
Apatosaurus
''Apatosaurus'' (; meaning "deceptive lizard") is a genus of herbivorous sauropod dinosaur that lived in North America during the Late Jurassic period. Othniel Charles Marsh described and named the first-known species, ''A. ajax'', in 1877, a ...
'', ''
Camarasaurus
''Camarasaurus'' ( ) is a genus of sauropod dinosaur that lived in North America during the Late Jurassic period. Its fossil remains have been found in the Morrison Formation, dating to the Kimmeridgian and Tithonian ages of the Jurassic, betwe ...
'', ''
Cetiosaurus
''Cetiosaurus'' ( meaning 'whale lizard', from the Greek '/ meaning 'sea monster' (later, 'whale') and '/ meaning 'lizard'), is a genus of herbivorous sauropod dinosaur from the Middle Jurassic Period, living about 171 to 165 million years ago ...
'' and ''Haplocanthosaurus'', the intraprezygapophyseal lamina is separate from the root of the neural canal by a vertical midline lamina. In the last few caudals and the most cranial dorsals, the lateral edge of the prezygapophyseal lamina becomes widened and roughened. Hatcher (1901) interpreted this as forming the attachment area for the muscles from which the scapular blade was suspended.
[Weishample, D.B.; Dodson, P.; Osmolska, H. (2004). "The Dinosauria: Second Edition". ''Berkeley, University of California Press''. 2: 266, 281-286, 288, 296-299, 302-302.]
The dorsoventrally elongate oval outlines are characteristic of ''Haplocanthosaurus'' with only ''Camarasaurus'' also possessing them. The parapophyses remaining as oval facets on the craniolateral margin, and the sacral spines 1-3 fused are also found in both ''Haplocanthosaurus'' and ''Camarasaurus''.
[
The ''Cetiosaurus'' specimen OUMNH J13695 has a low horizontal ridge on each of its lateral surfaces, creating a slightly subhexagonal transverse cross-section, a feature also seen on '']Cetiosauriscus
''Cetiosauriscus'' ( ) is a genus of sauropod dinosaur that lived between 166 and 164 million years ago during the Callovian (Middle Jurassic Period (geology), Period) in what is now England. A herbivore, ''Cetiosauriscus'' had – by saur ...
'', the anterior caudals of ''Haplocanthosaurus'', and caudals 15-30 of ''Omeisaurus
''Omeisaurus'' (meaning "Omei lizard") is a genus of sauropod dinosaur from the Middle to Late Jurassic Period (Bathonian- Oxfordian stage) of what is now China. Its name comes from Mount Emei, where it was discovered in the lower Shaximiao ...
''. Also, the area around the periphery of each articular face is flattened, creating a ‘bevelled’ appearance, and also occurs in ''Haplocanthosaurus'' and ''Cetiosauriscus''.
Distinguishing characteristics
''Haplocanthosaurus'' is distinguished by dorsal vertebra lacking cranial centrodiapophyseal laminae. Also, it is distinguished by elongate intrapostzygapophyseal laminae, dorsoventrally directed dorsal transverse processes that approach the height of the neural spines, and the distal end of the scapular blade being dorsally and ventrally expanded.[
]
Classification
''Haplocanthosaurus priscus'' was originally named ''Haplocanthus priscus'' by John Bell Hatcher 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
Jean Louis Rodolphe Agassiz ( ; ) FRS (For) FRSE (May 28, 1807 – December 14, 1873) was a Swiss-born American biologist and geologist who is recognized as a scholar of Earth's natural history.
Spending his early life in Switzerland, he recei ...
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 International Code of Zoological Nomenclature (ICZN) is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals. It is also informally known as the ICZN Code, for its formal author, t ...
(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 Fernando Bonaparte (14 June 1928–18 February 2020) was an Argentine paleontologist who discovered a plethora of South American dinosaurs and mentored a new generation of Argentine paleontologists. He has been described by paleontologist ...
decided in 1999 that ''Haplocanthosaurus'' differed enough from other sauropods to warrant its own family
Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...
, the Haplocanthosauridae.[Bonaparte, J. F. (1999). "An armoured sauropod from the Aptian of northern Patagonia, Argentina." In Tomida, Y., Rich, T. H. & Vickers-Rich, P. (eds.), 1999.'' Proceedings of the Second Gondwanan Dinosaur Symposium'', National Science Museum Monographs #15, Tokyo: 1-12.]
Phylogenetic
In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...
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
Macronaria is a clade of sauropod dinosaurs. Macronarians are named after the large diameter of the nasal opening of their skull, known as the external naris, which exceeded the size of the orbit, the skull opening where the eye is located (hence ...
n (related to the ancestor of more advanced forms such as ''Camarasaurus
''Camarasaurus'' ( ) is a genus of sauropod dinosaur that lived in North America during the Late Jurassic period. Its fossil remains have been found in the Morrison Formation, dating to the Kimmeridgian and Tithonian ages of the Jurassic, betwe ...
'' and the brachiosaurids
The Brachiosauridae ("arm lizards", from Greek ''brachion'' (βραχίων) = "arm" and ''sauros'' = "lizard") are a family or clade of herbivorous, quadrupedal sauropod dinosaurs. Brachiosaurids had long necks that enabled them to access the le ...
), or a very primitive diplodocoid, more closely related to ''Diplodocus
''Diplodocus'' (, , or ) is an extinct genus of diplodocid sauropod dinosaurs known from the Late Jurassic of North America. The first fossils of ''Diplodocus'' were discovered in 1877 by S. W. Williston. The generic name, coined by Othnie ...
'' than to titanosaur
Titanosaurs (or titanosaurians; members of the group Titanosauria) were a diverse group of sauropod dinosaurs, including genera from all seven continents. The titanosaurs were the last surviving group of long-necked sauropods, with taxa still thr ...
s, but more primitive than rebbachisaurids.
In 2005, Darren Naish
Darren William Naish (born 26 September 1975) is a British vertebrate palaeontologist, author and science communicator.
As a researcher, he is best known for his work describing and reevaluating dinosaurs and other Mesozoic reptiles, including ...
and Mike Taylor reviewed the various proposed positions of ''Haplocanthosaurus'' in their study of diplodocoid phylogeny. They found it could be a non-neosauropod eusauropod, a basal macronarian, or a basal diplodocoid. In 2011, an analysis by Whitlock recovered Haplocanthosaurus as the basalmost member of the Diplodocoidea, the third potentiality of Taylor & Naish. In 2015, a specimen-level phylogenetic analysis was published, finding ''Haplocanthosaurus'' to be a confirmed diplodocoid, either very basal, or more derived than rebbachisaurids. Their implied weighting cladogram is shown below.
References
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Diplodocoidea
Dinosaur genera
Kimmeridgian dinosaurs
Morrison Formation
Taxa named by John Bell Hatcher
Fossil taxa described in 1903
Dinosaurs of the United States