Callovosaurus

Callovosaurus
Original illustration of the holotype from Lydekker's first description
Temporal occurrence
Upper Jurassic ( Oxfordium )
163.5 to 157.3 million years
Locations
Oxford Clay Formation ( England )
Systematics
Dinosaur (dinosauria) Pelvic dinosaur (Ornithischia) Ornithopoda Iguanodontia Dryosauridae Callovosaurus
Scientific name
Callovosaurus
Galton , 1980
species
Callovosaurus leedsi ( Lydekker , 1889)

Callovosaurus is an extinct genus of Iguanodontia from the ornithopod group. Fossils were found in the Oxford Clay Formation near Peterborough in England and are dated to the early Upper Jurassic .

The first and only find ( holotype ) consists of a femur (thigh bone), which is almost completely, but broken into three parts. The only species, Callovosaurus leedsi , was first described by Richard Lydekker in 1889 as Camptosaurus leedsi . In 1980 it was then placed under the new genus Callovosaurus by Peter Galton .

The original description of the Callovosaurus femur was short. Even though the femur was never described in detail, a length of 28 cm could be measured, so that it is assumed that the entire animal was about 2.5 m long (Galton, 1980a). Since Callovosaurus is only known from one femur, unique features ( autapomorphies ) can only be recognized by this . The lesser trochanter (small hillock ) is, for example, separated from the greater trochanter (large hillock) by a wide and deep cleft and its proximal end is below the tip of the greater trochanter .

The systematic classification was long considered controversial:

Initially, Callovosaurus was considered part of the Hypsilophodontidae . Later they asked this genus as relatives of Camptosaurus in the Camptosauridae .

However, many of the features of the femur of Callovosaurus speak for a classification in the Dryosauridae , whereby the above-mentioned gap between the trochanter minor and the trochanter major is also present in the genera Dryosaurus and Valdosaurus , which count as safe members of the Dryosauridae. So callovosaurus related probably closer to these two genres as for example with Hypsilophodon or Camptosaurus , which callovosaurus is the oldest dryosauridae that has ever been found. The following cladogram according to Barret et al. (2011) shows the relationships of Callovosaurus within the Dryosauridae:

Dryosauridae	Callovosaurus      Kangnasaurus      Dryosaurus      Dysalotosaurus      Valdosaurus      Elrhazosaurus

Individual evidence

1. ^ ^{A b} R. Lydekker: On the Remains and Affinities of five Genera of Mesozoic Reptiles. In: Quarterly Journal of the Geological Society. Vol. 45, 1889, pp. 41-59, ( digitized version ) .
2. ↑ ^{a b c d} José Ignacio Ruiz-Omeñaca, Xabier Pereda Suberbiola, Peter M. Galton : Callovosaurus leedsi, the earliest dryosaurid dinosaur (Ornithischia: Euornithopoda) from the Middle Jurassic of England. In: Kenneth Carpenter (Ed.): Horns and Beaks. Ceratopsian and Ornithopod Dinosaurs. Indiana University Press, Bloomington IN 2007, ISBN 978-0-253-34817-3 , pp. 3-16.
3. ↑ Peter M. Galton: English hypsilophodontid dinosaurs (Reptilia: Ornithischia). In: Palaeontology. Vol. 18, No. 4, 1975, ISSN  0031-0239 , pp. 741-752, digitized version (PDF; 1.39 MB) .
4. ↑ Peter M. Galton: European Jurassic ornithopod dinosaurs of the families Hypsilophodontidae and Camptosauridae. In: New Yearbook for Geology and Paleontology. Treatises. Vol. 160, No. 1, 1980, ISSN  0077-7749 , pp. 73-95.
5. ^ Paul M. Barrett , Richard J. Butler, Richard J. Twitchett, Stephen Hutt: New material of Valdosaurus canaliculatus (Ornithischia: Ornithopoda) from the Lower Cretaceous of southern England. In: Special Papers in Palaeontology. Vol. 86, 2011, ISSN  0038-6804 , pp. 131-163.