Megalosaurid
Encyclopedia
Megalosauridae was a family
of relatively primitive tetanuran
theropod dinosaurs, order Saurischia
. They were small-to-large carnivores with sharp teeth and three claws on each hand. Some members of this group were Megalosaurus
, Eustreptospondylus
, Streptospondylus
and Torvosaurus
. Megalosaurids first appeared in the mid Jurassic
and seemed to have been displaced and replaced by other theropods by the end of that period; their fossils are known from Europe, North America, South America and Africa. They are considered by most researchers (Sereno 2005, Olshevsky 1995, Holtz 2004, etc.) to be close relatives of the spinosaurs
.
itself, the family Megalosauridae, coined by Huxley in 1869, had traditionally been used as a 'wastebasket' group, which included a wide variety of unrelated species (such as Dryptosaurus
, Ceratosaurus
, Indosaurus
, and even Velociraptor
). Because of this traditionally polyphyletic use, some scientists, such as Paul Sereno
, reject the family name Megalosauridae in favor of Torvosauridae (coined by Jensen
in 1985), despite the fact that Megalosauridae has priority under the ICZN
rules governing family-level names in zoology. While a 2008 review of Megalosaurus by Benson and colleagues also found that the relationships of Megalosaurus to other theropods could not be determined, and that the assignment of basal spinosauroids to the family Megalosauridae should be discontinued, further work by Benson reversed this position, finding a well-supported Megalosauridae in phylogenetic analyses.
Megalosauridae was first given a phylogenetic definition by Allain in 2002. According to Allain's definition, a megalosaurid is any dinosaur that shares a common ancestor with Poekilopleuron valesdunensis (since reclassified as Dubreuillosaurus), Torvosaurus, and Afrovenator. In 2004, Holtz and colleagues proposed a new definition: all dinosaurs more closely related to Megalosaurus than to Spinosaurus, Allosaurus, or modern birds (represented by Passer domesticus). In 2005, Sereno rejected the use of Megalosauridae as a clade altogether, due to the fragmentary nature of Megalosaurus, and used the name Torvosauridae instead, using the same definition as Holtz but replacing Megalosaurus with Torvosaurus.
The cladogram
presented here follows Benson (2010) and Benson et al. (2010).
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...
of relatively primitive tetanuran
Tetanurae
Tetanurae, or "stiff tails", is a clade that includes most theropod dinosaurs, as well as birds. Tetanurans first appear during the early or middle Jurassic Period.-Definition:...
theropod dinosaurs, order Saurischia
Saurischia
Saurischia meaning 'lizard' and ischion meaning 'hip joint') is one of the two orders, or basic divisions, of dinosaurs. In 1888, Harry Seeley classified dinosaurs into two orders, based on their hip structure...
. They were small-to-large carnivores with sharp teeth and three claws on each hand. Some members of this group were Megalosaurus
Megalosaurus
Megalosaurus is a genus of large meat-eating theropod dinosaurs of the Middle Jurassic period of Europe...
, Eustreptospondylus
Eustreptospondylus
Eustreptospondylus is a genus of megalosaurid dinosaur, from the Callovian stage of the Middle Jurassic period in southern England, at a time when Europe was a series of scattered islands Eustreptospondylus ("well-curved vertebra", in reference to the arrangement of the spine in the original...
, Streptospondylus
Streptospondylus
Streptospondylus is a genus of tetanuran theropod dinosaur known from the Middle Jurassic period of France, 161 million years ago. It was a medium-sized predator.-Discovery and naming:...
and Torvosaurus
Torvosaurus
Torvosaurus is a genus of large theropod dinosaur that lived during the Late Jurassic period...
. Megalosaurids first appeared in the mid 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...
and seemed to have been displaced and replaced by other theropods by the end of that period; their fossils are known from Europe, North America, South America and Africa. They are considered by most researchers (Sereno 2005, Olshevsky 1995, Holtz 2004, etc.) to be close relatives of the spinosaurs
Spinosauridae
Spinosauridae is a family of specialised theropod dinosaurs. Members of this family were large, bipedal predators with elongated, crocodile-like skulls, sporting conical teeth with no or only very tiny serrations. The front dentary teeth fanned out, giving the animal a characteristic look...
.
Classification
Like MegalosaurusMegalosaurus
Megalosaurus is a genus of large meat-eating theropod dinosaurs of the Middle Jurassic period of Europe...
itself, the family Megalosauridae, coined by Huxley in 1869, had traditionally been used as a 'wastebasket' group, which included a wide variety of unrelated species (such as Dryptosaurus
Dryptosaurus
Dryptosaurus was a genus of primitive tyrannosaur that lived in Eastern North America during the middle Maastrichtian stage of the Late Cretaceous period. Although largely unknown now outside of academic circles, a famous painting of the genus by Charles R...
, Ceratosaurus
Ceratosaurus
Ceratosaurus meaning "horned lizard", in reference to the horn on its nose , was a large predatory theropod dinosaur from the Late Jurassic Period , found in the Morrison Formation of North America, in Tanzania and Portugal...
, Indosaurus
Indosaurus
Indosaurus is a genus of theropod dinosaur once living in what is now India. It lived approximately 69 million years ago, in the Maastrichtian division of the Late Cretaceous...
, and even Velociraptor
Velociraptor
Velociraptor is a genus of dromaeosaurid theropod dinosaur that existed approximately 75 to 71 million years ago during the later part of the Cretaceous Period. Two species are currently recognized, although others have been assigned in the past. The type species is V. mongoliensis; fossils...
). Because of this traditionally polyphyletic use, some scientists, such as Paul Sereno
Paul Sereno
Paul Callistus Sereno is an American paleontologist from the University of Chicago who discovered several new dinosaur species on several continents. He has conducted excavations at sites as varied as Inner Mongolia, Argentina, Morocco, and Niger...
, reject the family name Megalosauridae in favor of Torvosauridae (coined by Jensen
James A. Jensen
James A. Jensen , was an American paleontologist. His extensive collecting program at BYU in the Utah-Colorado region which spanned 23 years was comparable in terms of the number of specimens collected to that of Barnum Brown during the early 20th century. He was given the name "Dinosaur Jim"...
in 1985), despite the fact that Megalosauridae has priority under the ICZN
International Code of Zoological Nomenclature
The International Code of Zoological Nomenclature is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals...
rules governing family-level names in zoology. While a 2008 review of Megalosaurus by Benson and colleagues also found that the relationships of Megalosaurus to other theropods could not be determined, and that the assignment of basal spinosauroids to the family Megalosauridae should be discontinued, further work by Benson reversed this position, finding a well-supported Megalosauridae in phylogenetic analyses.
Phylogeny
The cladeClade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
Megalosauridae was first given a phylogenetic definition by Allain in 2002. According to Allain's definition, a megalosaurid is any dinosaur that shares a common ancestor with Poekilopleuron valesdunensis (since reclassified as Dubreuillosaurus), Torvosaurus, and Afrovenator. In 2004, Holtz and colleagues proposed a new definition: all dinosaurs more closely related to Megalosaurus than to Spinosaurus, Allosaurus, or modern birds (represented by Passer domesticus). In 2005, Sereno rejected the use of Megalosauridae as a clade altogether, due to the fragmentary nature of Megalosaurus, and used the name Torvosauridae instead, using the same definition as Holtz but replacing Megalosaurus with Torvosaurus.
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...
presented here follows Benson (2010) and Benson et al. (2010).