Magnosaurus

Magnosaurus (meaning 'large lizard') was a genus of basal tetanuran theropod dinosaur from the Middle Jurassic of England. It is based on fragmentary remains and has often been confused with or included in Megalosaurus.

Magnosaurus Temporal range: Middle Jurassic, 173–169 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Skeletal diagram of the holotype specimen
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	Saurischia
Clade:	Theropoda
Family:	†Megalosauridae
Subfamily:	†Afrovenatorinae
Genus:	†Magnosaurus Huene, 1932
Type species
†Megalosaurus nethercombensis Huene, 1923
Species
†M. nethercombensis (Huene, 1923 [originally Megalosaurus]) †M. lydekkeri (Huene, 1932 [originally Megalosaurus]) †M. woodwardi Huene, 1932

History and taxonomy

Life restoration

In 1923, Friedrich von Huene named Megalosaurus nethercombensis from a partial skeleton (OUM J12143) from the Aalenian-Bajocian-age Middle Jurassic Inferior Oolite, found in the nineteenth century by W. Parker near Nethercomb, north of Sherborne, in Dorset, England. The material included partial dentaries, dorsal and caudal vertebrae, a partial ilium, a partial right pubis, internal casts of the femora, and tibiae, from a possible juvenile individual. Huene interpreted it as a more primitive species of Megalosaurus.[1]

In 1926, he named the tooth species Megalosaurus lydekkeri for a specimen, BMNH 41352, from the Lower Lias (Lower Jurassic) of England that Richard Lydekker had first described in 1888.[2][3] Finally, in 1932, he created the genus Magnosaurus for M. nethercombensis, referred M. lydekkeri to it, and created a third species, M. woodwardi, for the genus. M. woodwardi was based on a tibia (BMNH R.3542) from the Lower Lias, which he simultaneously and accidentally also named Sarcosaurus andrewsi;[4] in 1956 the latter name was given priority by von Huene. Even more confusing, in the same 1932 publication von Huene renamed Sarcosaurus woodi into Magnosaurus woodi.

Until the 1990s, the genus had been ignored as a species of Megalosaurus.[5] However, with growing concern over what exactly is constituted by Megalosaurus, Magnosaurus has been generally separated as its own genus.[6][7][8] Also, there are morphological differences: for example, possible Megalosaurus tibiae are compressed at the far end, unlike those of Magnosaurus.[8] Rauhut (2003) considered it and Eustreptospondylus to be the same genus, because the two share a similarly expanded front tip of the dentary and enlarged third dentary tooth. He therefore renamed Eustreptospondylus oxoniensis a Magnosaurus oxoniensis but this has not been generally followed.[7] Reviews have found it to most likely be a basal tetanuran, probably a megalosaurid.[8][9][10] A detailed redescription by Roger Benson in 2010 concluded Magnosaurus was valid taxon, a megalosaurid megalosauroid, and at about 175 million years old the oldest certain known member of the Tetanurae.[11]

Species

Magnosaurus is known from many species, most of were originally named as a different genus.[12]

• Magnosaurus nethercombensis (Huene, 1923) Huene, 1932 = Megalosaurus nethercombensis Huene, 1923
• Magnosaurus lydekkeri (Huene, 1926) Huene, 1932 (nomen dubium) = Megalosaurus lydekkeri Huene, 1926[8]
• Magnosaurus woodwardi Huene, 1932 (nomen dubium) = Sarcosaurus andrewsi Huene, 1932 = Megalosaurus woodwardi (Huene, 1932)[13]

The type species of Eustreptospondylus, Megalosaurus and Sarcosaurus are also sometimes assigned to Magnosaurus. In such cases the combinations are:

• Magnosaurus woodi (Andrews, 1921) = Sarcosaurus woodi Andrews, 1921
• Magnosaurus oxoniensis (Walker, 1964) Rahut, 2003 = Eustreptospondylus oxoniensis Walker, 1964
• Magnosaurus bucklandi (Meyer, 1832) Weishampel et al., 2004 = lapsus calami, Megalosaurus bucklandi Meyer, 1832 = Megalosaurus bucklandii Mantell, 1827[12]

Description

Size of Magnosaurus (in green) compared to two other afrovenatorines

Because the remains are sparse and fragmentary, most details about its anatomical features are unknown. It would have been a bipedal carnivore of moderate size for a dinosaur. The most similar animals to it would probably be Eustreptospondylus, Dubreuillosaurus, and Afrovenator.[8] Paul (1988) roughly estimated the mass of the type individual as around 175 kg (386 lb), which would correspond to a length of roughly four metres (13.1 ft), judging by his estimates for the sizes of other theropods.[9] Benson however, in 2010 gave a higher estimation of about half a tonne; the animal would have stood at over a metre at the hip.

Classification

The phylogenetic position of Magnosaurus according to Carrano et al. (2012) is shown by this cladogram:[14]

Megalosauroidea	Piatnitzkysauridae   Megalosauria   Streptospondylus     Spinosauridae   Megalosauridae Eustreptospondylinae   Eustreptospondylus       Megalosaurinae   Duriavenator       Megalosaurus     Torvosaurus       Afrovenatorinae   Afrovenator       Dubreuillosaurus     Magnosaurus         Leshansaurus     Piveteausaurus

References

1. von Huene, F. (1923). Carnivorous Saurischia in Europe since the Triassic. Bulletin of the Geological Society of America 34:449-458.
2. von Huene, F. (1926). The carnivorous Saurischia in the Jura and Cretaceous formations, principally in Europe. Revista del Museo de La Plata 29:35-167.
3. Lydekker, R. (1888). Catalogue of the Fossil Reptilia and Amphibia in the British Museum (Natural History). Part I. Containing the Orders Ornithosauria, Crocodilia, Dinosauria, Squamata, Rhynchocephalia, and Proterosauria. British Museum (Natural History):London, 309 p.
4. von Huene, F. (1932). Die fossile Reptil-Ordnung Saurischia, ihre Entwicklung und Geschichte. Monographien zur Geologie und Palaeontologie 1(4) [German]
5. Waldman, M. (1974). "Megalosaurids from the Bajocian (Middle Jurassic) of Dorset". Palaeontology 17(2):325-339.
6. Molnar, R.E., Kurzanov, S.M., and Dong, Z. (1990). "Carnosauria". In: Weishampel, D.B., Dodson, P., and Osmólska, H. (eds.), The Dinosauria. University of California Press:Berkeley and Los Angeles, p. 169-209. ISBN 0-520-06727-4
7. Rauhut, O.W.M. (2003). "The Interrelationships and Evolution of Basal Theropod Dinosaurs." Special Papers in Palaeontology 69. The Palaeontological Association:London, 213 p.
8. Holtz Jr., T.R., Molnar, R.E., and Currie, P.J. (2004). "Basal Tetanurae". In: Weishampel, D.B., Dodson, P., and Osmólska, H. (eds.), The Dinosauria (second edition). Berkeley: University of California Press:Berkeley, p. 71-110. ISBN 0-520-24209-2
9. Paul, G.S. (1988). Predatory Dinosaurs of the World. Simon & Schuster:New York, 464 p. ISBN 0-671-61946-2
10. Benson, R.B.J. (2010). "A description of Megalosaurus bucklandii (Dinosauria: Theropoda) from the Bathonian of the UK and the relationships of Middle Jurassic theropods". Zoological Journal of the Linnean Society. 158 (4): 882–935. doi:10.1111/j.1096-3642.2009.00569.x.
11. Benson, Roger B. J., 2010, "The osteology of Magnosaurus nethercombensis (Dinosauria, Theropoda) from the Bajocian (Middle Jurassic) of the United Kingdom and a re-examination of the oldest records of tetanurans", Journal of Systematic Palaeontology, 8(1): 131-146
12. Weishampel, D.B.; Dodson, P.; Osmolska, H. (eds.). "The Dinosauria: Second Edition". Berkeley: University of California Press, p 99. ISBN 0-520-24209-2.
13. Carrano, M.T., and Sampson, S.D. (2004). A review of coelophysoids (Dinosauria: Theropoda) from the Early Jurassic of Europe, with comments on the late history of the Coelophysoidea. Neues Jahrbuch für Geologie und Paläontologie - Monatshefte 2004(9):537-558.
14. M.T. Carrano, R.B.J. Benson, and S.D. Sampson, 2012, "The phylogeny of Tetanurae (Dinosauria: Theropoda)", Journal of Systematic Palaeontology 10(2): 211-300