Ornithodesmus
Encyclopedia
Ornithodesmus is a genus
of small, deinonychosauria
n dinosaur
from the Isle of Wight
in England
, dating to about 125 million years ago. The name was originally assigned to a bird-like sacrum
(a series of vertebrae fused to the hip bones), initially believed to come from a pterosaur
. More complete pterosaur remains were later assigned to Ornithodesmus, until recently a detailed analysis determined that the original specimen in fact came from a small theropod, specifically a dromaeosaur
. All pterosaurian material previously assigned to this genus has been re-named Istiodactylus
.
Based on its apparent identity as a dromaeosaur, it was probably carnivorous, and likely measured about 1.5 meters long in life. Dromaeosaur teeth probably belonging to a velociraptorine are known from the same formation, but are too large to have belonged to Ornithodesmus; rather, these must have come from a theropod closer in size to the giant Utahraptor
.
of Brook Bay
. Seeley thought the bones came from a primitive bird
, and gave it a name meaning "bird link", from Greek ὄρνις (ornis), "bird", en δεσμός (desmos), "link". The specific name cluniculus means "little buttock" in Latin
, a reference to the small thighs indicated by the size of the specimen.
Later that year, John Hulke
(in an anonymous paper) suggested the remains actually belonged to a pterosaur
. Seeley himself later changed his opinion when he described the complete skeleton (specimen number BMNH R176) of a new pterosaur species he believed was closely related to O. cluniculus. He named this new species Ornithodesmus latidens in 1901. Although he now considered it a pterosaur, Seeley at the time still considered Ornithodesmus close to the origin of birds, and suggested the (now defunct) theory that birds and pterosaurs shared a close common ancestry. For over a century following this, the pterosaur O. latidens was used as the standard example of Ornithodesmus, and the fragmentary type specimen was largely ignored. In 1913, Reginald Walter Hooley named a new family to distinguish Ornithodesmus from other large pterosaurs known at the time, Ornithodesmidae.
In 1993, Stafford C. Howse and Andrew Milner re-examined the type specimen of O. cluniculus and determined that Seeley had incorrectly referred the pterosaur species to this genus. They identified O. cluniculus as a theropod dinosaur. Specifically, they suggested it was a troodontid
, based on its similarity to the supposed troodontid specimen BMNH R4463. However, later study by Peter Makovicky and Mark Norell showed this specimen to be a dromaeosaurid
; because of this mis-identification, they suggested Ornithodesmus was likely a dromaeosaurid as well. Darren Naish
and colleagues in 2001 argued against a dromaeosaurid identity for Ornithodesmus, suggesting instead it was related to the ceratosaurs
or coelophysids
. However, those scientists later changed their opinions, publishing a paper in 2007 that agreed with previous studies and classifying Ornithodesmus as a dromaeosaurid.
The more complete pterosaur specimens that had long been associated with the name Ornithodesmus were given a new name in 2001, Istiodactylus
.
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 small, deinonychosauria
Deinonychosauria
The Deinonychosauria were a clade of coelurosaurian theropod dinosaurs from the Late Jurassic and Cretaceous periods. These omnivores and carnivores are known for their switchblade-like second toe claws and for displaying numerous bird-like characteristics. The clade has been divided into two...
n 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 Isle of Wight
Isle of Wight
The Isle of Wight is a county and the largest island of England, located in the English Channel, on average about 2–4 miles off the south coast of the county of Hampshire, separated from the mainland by a strait called the Solent...
in England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
, dating to about 125 million years ago. The name was originally assigned to a bird-like sacrum
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...
(a series of vertebrae fused to the hip bones), initially believed to come from a pterosaur
Pterosaur
Pterosaurs were flying reptiles of the clade or order Pterosauria. They existed from the late Triassic to the end of the Cretaceous Period . Pterosaurs are the earliest vertebrates known to have evolved powered flight...
. More complete pterosaur remains were later assigned to Ornithodesmus, until recently a detailed analysis determined that the original specimen in fact came from a small theropod, specifically a dromaeosaur
Dromaeosauridae
Dromaeosauridae is a family of bird-like theropod dinosaurs. They were small- to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Greek dromeus meaning 'runner' and sauros meaning 'lizard'...
. All pterosaurian material previously assigned to this genus has been re-named Istiodactylus
Istiodactylus
Istiodactylus was a medium sized pterosaur from the Early Cretaceous period.-History and species:In 1887 Harry Govier Seeley named the remains of a fossil pelvis discovered on the Isle of Wight, Ornithodesmus cluniculus, thinking it was a bird. In 1901 he considered that it might have been a...
.
Description
As it is only known from isolated vertebrae, little is known about the appearance of Ornithodesmus. The neural spines of the vertebrae are fused and form a blade over the 9.6 centimetres long sacrum, which is slightly arched. The bases of the neural spines form a lateral platform, and the first two vertebrae of the sequence have deep hollow cavities, which formed space for air sacs.Based on its apparent identity as a dromaeosaur, it was probably carnivorous, and likely measured about 1.5 meters long in life. Dromaeosaur teeth probably belonging to a velociraptorine are known from the same formation, but are too large to have belonged to Ornithodesmus; rather, these must have come from a theropod closer in size to the giant Utahraptor
Utahraptor
Utahraptor is a genus of theropod dinosaurs, including the largest known members of the family Dromaeosauridae. Fossil specimens date to the upper Barremian stage of the early Cretaceous period...
.
History and classification
Ornithodesmus cluniculus was first described by Harry Govier Seeley in 1887, based on a set of six fused vertebrae from the hip (sacrum), specimen number BMNH R187, found by William D. Fox in the Wessex FormationWessex Formation
The Wessex Formation is an English fossil site and geological formation that dates to the Barremian stage of the Early Cretaceous. It is part of the Wealden Group and underlies the younger Vectis Formation.-Invertebrates:...
of Brook Bay
Brook Bay
Brook Bay is a bay on the south eastern coast of the Isle of Wight, England. It lies to the west of the village of Brook. It faces south west out into the English Channel. It stretches about 2km from Hanover Point in the east to Sudmoor Point to the west. Much of the surrounding land, including the...
. Seeley thought the bones came from a primitive 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...
, and gave it a name meaning "bird link", from Greek ὄρνις (ornis), "bird", en δεσμός (desmos), "link". The specific name cluniculus means "little buttock" in Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
, a reference to the small thighs indicated by the size of the specimen.
Later that year, John Hulke
John Hulke
John Whitaker Hulke FRCS FRS FGS was a British surgeon, geologist and fossil collector. He was the son of a physician in Deal, who became a Huxleyite despite being deeply religious....
(in an anonymous paper) suggested the remains actually belonged to a pterosaur
Pterosaur
Pterosaurs were flying reptiles of the clade or order Pterosauria. They existed from the late Triassic to the end of the Cretaceous Period . Pterosaurs are the earliest vertebrates known to have evolved powered flight...
. Seeley himself later changed his opinion when he described the complete skeleton (specimen number BMNH R176) of a new pterosaur species he believed was closely related to O. cluniculus. He named this new species Ornithodesmus latidens in 1901. Although he now considered it a pterosaur, Seeley at the time still considered Ornithodesmus close to the origin of birds, and suggested the (now defunct) theory that birds and pterosaurs shared a close common ancestry. For over a century following this, the pterosaur O. latidens was used as the standard example of Ornithodesmus, and the fragmentary type specimen was largely ignored. In 1913, Reginald Walter Hooley named a new family to distinguish Ornithodesmus from other large pterosaurs known at the time, Ornithodesmidae.
In 1993, Stafford C. Howse and Andrew Milner re-examined the type specimen of O. cluniculus and determined that Seeley had incorrectly referred the pterosaur species to this genus. They identified O. cluniculus as a theropod dinosaur. Specifically, they suggested it was a troodontid
Troodontidae
Troodontidae is a family of bird-like theropod dinosaurs. During most of the 20th century, troodontid fossils were few and scrappy and they have therefore been allied, at various times, with many dinosaurian lineages...
, based on its similarity to the supposed troodontid specimen BMNH R4463. However, later study by Peter Makovicky and Mark Norell showed this specimen to be a dromaeosaurid
Dromaeosauridae
Dromaeosauridae is a family of bird-like theropod dinosaurs. They were small- to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Greek dromeus meaning 'runner' and sauros meaning 'lizard'...
; because of this mis-identification, they suggested Ornithodesmus was likely a dromaeosaurid as well. 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 colleagues in 2001 argued against a dromaeosaurid identity for Ornithodesmus, suggesting instead it was related to the ceratosaurs
Ceratosauria
Ceratosaurs are members of a group of theropod dinosaurs defined as all theropods sharing a more recent common ancestry with Ceratosaurus than with birds. There is presently no universally agreed upon listing of species or diagnostic characters of Ceratosauria, though they were less derived...
or coelophysids
Coelophysidae
The Coelophysidae are a family of primitive carnivorous theropod dinosaurs. Most species were relatively small in size. The family flourished in the Late Triassic and Early Jurassic periods....
. However, those scientists later changed their opinions, publishing a paper in 2007 that agreed with previous studies and classifying Ornithodesmus as a dromaeosaurid.
The more complete pterosaur specimens that had long been associated with the name Ornithodesmus were given a new name in 2001, Istiodactylus
Istiodactylus
Istiodactylus was a medium sized pterosaur from the Early Cretaceous period.-History and species:In 1887 Harry Govier Seeley named the remains of a fossil pelvis discovered on the Isle of Wight, Ornithodesmus cluniculus, thinking it was a bird. In 1901 he considered that it might have been a...
.