Megalosaurus

Megalosaurus is a tetanuran theropod dinosaur genus of the the Bathonian stage of the Middle Jurassic, approximately 166-168 million years ago, from Southern England. The genus was first described by William Buckland in 1824. Based on the fragmentary fossil remains, he described the Megalosaurus as a large tetrapod which resembled a huge lizard and classified among the Lacerta lizards. Because there were no other known dinosaurs at that time, especially no other theropod dinosaurs, Buckland based his size estimate on Lacerta lizard body proportions. He estimated the length of Megalosaurus for 12 meters or 40 feet. According to another specimen's femur, the length of the Megalosaurus was even greater, 18 to 21 meters or 60 to 70 feet long[1]. However, even before Megalosaurus were validly named, the fossils of the genus were already known from science, but some of them had been misidentified for centuries. In the 17th century, the lower part of a femur was discovered from the Taynton Limestone Formation, in Oxfordshire in the United Kingdom. It was described by Robert Plot, who recognized there is not any known extant species in England what can have such a huge femur. Therefore, mistakenly, he concluded that it was the bone of a Roman war elephant, later that of a giant human and the bone got the name 'Scrotum humanum'[2]. Later, Edward Lhuyd considered a tooth fossil as a fish tooth and included in his illustration of 'lchthyodontes Cuspidati', in 1699[3]. Buckland did not give a specific name, only the name of the genus in his description. The name Megalosaurus conybeari given by Ferdinand von Ritgen in 1826 is considered a nomen oblitum, and since 1827, the 'Megalosaurus bucklandii' is the name of the type species of the genus.

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Known occurrences of Megalosaurus fossils.

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Early depiction of Megalosaurus from 1859. By Samuel Griswold Goodrich - Samuel Griswold Goodrich: Illustrated Natural History of the Animal Kingdom, vol. 2, S. 394.From [1], Public Domain, https://commons.wikimedia.org/w/index.php?curid=559957

The presumption about the appearance of the Megalosaurus completely changed during the decades after its first conception by Buckland. It was not an 18-21 meter long, quadrupedal, swamp-dwelling lizard. It was much smaller. Although, Richard Owen still thought that Megalosaurus was a quadrupedal creature, he stated that the Megalosaurus was standing on upright legs unlike a lizard, and its size was not more than 9 meters. Furthermore, Megalosaurus, besides Iguanodon and Hylaeosaurus, is one of the first three dinosaur genera that Owen based a new, separated taxonomic group, called Dinosauria[6].

Description and anatomy

Megalosaurus was a large bipedal carnivorous dinosaur, 6 meters long and weighing about 700 kilograms[7]. But the size of the thighbone of two individuals, the specimen BMNH 31806 and specimen OUM J13561, indicates that Megalosaurus could grow even larger, weighting 943 kilograms and likely reaching nearly 8 meters in length. The highly ossified bones indicate a stout and muscular built. The forelimbs were relatively short but robust and probably three fingered. The head was uncommonly large, with 13-14 large sharp teeth in each maxilla, but the fragmentary remains make it hard to describe how it looked as a whole. The short maxilla indicates that the snout was likely stubby, which is in line with the robust body-built[8]. No skin impression has yet been discovered from Megalosaurus, but feather-like filaments known of a juvenile specimen of another megalosauroid, the Sciurumimus albersdoerferi. That's why it can be assumed that Megalosaurus had feathers at least early in his life, if not further[9].

Paleobiology and paleoecology

Certain Megalosaurus fossils are known from a small area in South England. Bones and teeth have been found in the Taynton Limestone Formation, the Sharp's Hill Formation of Sarsgrove and the Chipping Norton Limestone Formation. However, possible Megalosaurus footprints in Burniston Bay prove that this apex predator might have a much wider distribution than we can assume from fossil records[10][11].

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Modern depiction of Megalosaurus. By LadyofHats Mariana Ruiz Altered by FunkMonk and Steveoc 86 - i did it myself based on the images i found [here:http://perso.orange.fr/thierry.rebours/dinowebard2/8.htm][1][2]and[3]The feathering shown here is speculative, skin remains are not currently known for Megalosaurus., Public Domain, https://commons.wikimedia.org/w/index.php?curid=1260055

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Megalosaurus. By Conty - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=7733587

The Megalosaurus is the largest known theropod from British Bathonian ecosystem of its time, and probably also the apex predator of its ecosystem[8]. In this era, South England had a subtropical, humid climate. The land was covered with open woodland and coastal vegetation, dominated by conifers and ginkgos[11][12].

Megalosaurus was probably not the only large theropod in southern England at the time. It probably shared the land with another large tetanuran, the Cruxicheiros newmanorum. However, due to the very limited fossil materials, there is not much certainty about this species and genus[13]. Other terropods have also roamed this area. An adult Megalosaurus had nothing to fear from a Proceratosaurus bradleyi, a 3-meters-long basal tyrannosaurid[14], but its chicks and juveniles mihgt were in threat from this small-sized theropod. Large sauropods, such as Cetiosaurus oxoniensis and Cardiodon rugulosus, roamed the forests and plains of South England, and probably were prey species of the Megalosaurus. Healthy adults were safe because of their size and strength when Megalosaurus might hunt sauropods. They might preferred to prey on young, old, or weak individuals. However, there is no direct evidence of predator-prey interaction of Megalosaurus and sauropods yet[15][16]. As much of Europe was made by archipelagos this time, probably the carcass of Ichthyosaurus and Plesiosaurus were also frequently washed off the coast of England, serving as a good source of food for scavengers. As well as the carcasses of large herbivore dinosaurus. Modern apex predators such as lions, hyenas, sharks, wolves and crocodiles seize the opportunity to eat for free from the carcass, and Megalosaurus could behave similarly[17][18][19].

Taxonomy

The classification of the genus Megalosaurus had many turnovers throughout the centuries. The genus was a wastebasket taxon. If the characteristics of the often very fragmentary fossils of a potentially new theropod species were not very distinctive, they have been described as a new Megalosaurus species[20]. Currently, only one species, Megalosaurus bucklandii belongs to the genus[8]. Others become nomina dubia and were sorted into other genera;some of them belongs to the family Megalosauridae, like the Magnosaurus nethercombensis which was originally described as Megalosaurus nethercombensis[21], while others not, like the allosauroid Poekilopleuron bucklandii which was originally named as Megalosaurus poikilopleuron[8][22] or the tyrannosaurid Proceratosaurus bradleyi which was called Megalosaurus bradleyi before[14]. In a 2010 study, Megalosaurus has been placed in the Megalosaurinae clade with the Torvosaurus as sister taxon[8]. However, the desciption of the Wiehenvenator changed the position of Megalosaurus, and now it is not the sister taxon of the Torvosaurus yet, but a branch of the Megalosaurinae clade after the separation of Duriavenator and before the separation of Wiehenvenator[20].

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Fossil Megalosaurus skeleton. By Reptonix free Creative Commons licensed photos - http://reptonix.awardspace.co.uk/photos/2012-02-19.htm, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=18665352

Author: Péter Imre Fábián, Biologist MSc student

Scientific references

[1] Buckland, W. (1824): XXI.-Notice on the Megalosaurus or great Fossil Lizard of Stonesfield. Transactions of the Geological Society of London, 2(2), 390-396. doi: 10.1144/transgslb.1.2.390.

[2] Plot, R. (1705): The Natural History of Oxford-shire: Being an Essay Towards the Natural History of England. Leon. Lichfield. , Oxford. 366 pp., 16.

[3] Delair, J. B., & Sarjeant, W. A. (2002): The earliest discoveries of dinosaurs: the records re-examined. Proceedings of the Geologists' Association, 113(3), 185-197. doi: 10.1016/S0016-7878(02)80022-0

[4] Ritgen, F. V. (1826): Versuchte Herstellung einiger Becken urweltlichter Thiere. Nova Acta Academiae Caesarea Leopoldino-Carolinae Germanicae Naturae Curiosorum, 13, 331-358.

[5] Mantell, G. (1827): Illustrations of the geology of Sussex: a general view of the geological relations of the southeastern part of England, with figures and descriptions of the fossils of Tilgate Forest. London: Fellow of the Royal College of Surgeons. pp. 92.

[6] Owen, R. (1842):. Report on British fossil reptiles, part II. Report of the British Association for the Advancement of Science. 11: 32-37.

[7] Paul, G. S. (2010): The Princeton Field Guide to Dinosaurs. Princeton University Press. pp. 93.

[8] Benson, R. B. (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

[9] Foth, C., Haug, C., Haug, J. T., Tischlinger, H., & Rauhut, O. W. (2020): Two of a feather: a comparison of the preserved integument in the juvenile theropod dinosaurs Sciurumimus and Juravenator from the Kimmeridgian Torleite Formation of southern Germany. In The Evolution of Feathers, 79-101. doi: 10.1007/978-3-030-27223-4_6

[10] Paul, G. S. (2010): The Princeton field guide to dinosaurs. Princeton University Press. pp. 86.

[11] Slater, S. M., Wellman, C. H., Romano, M., and Vajda, V. (2018): Dinosaur-plant interactions within a Middle Jurassic ecosystem-palynology of the Burniston Bay dinosaur footprint locality, Yorkshire, UK. Palaeobiodiversity and Palaeoenvironments, 98(1), 139-151.

[12] van Konijnenburg-van Cittert, J. H. (2008): The Jurassic fossil plant record of the UK area. Proceedings of the Geologists' Association, 119(1), 59-72. doi: 10.1016/S0016-7878(08)80258-1

[13] Benson, R. B., Radley, J. D. (2009): A new large-bodied theropod dinosaur from the Middle Jurassic of Warwickshire, United Kingdom. Acta Palaeontologica Polonica, 55(1), 35-42. doi: 10.4202/app.2009.0083

[14] Rauhut, O. W., Milner, A. C., & Moore-Fay, S. (2010): Cranial osteology and phylogenetic position of the theropod dinosaur Proceratosaurus bradleyi (Woodward, 1910) from the Middle Jurassic of England. Zoological Journal of the Linnean Society, 158(1), 155-195. doi: 10.1111/j.1096-3642.2009.00591.x

[15] Weishampel, D.B.; Dodson, P.; Osmolska, H., eds. (2004): The Dinosauria (2nd ed.). University of California Press. pp. 265-784.

[16] Benton, M. J., Spencer, P. S. (2012): Fossil reptiles of great britain (Vol. 10). Springer Science & Business Media.

[17] Kane, A., Healy, K., Ruxton, G. D., & Jackson, A. L. (2016): Body size as a driver of scavenging in theropod dinosaurs. The American Naturalist, 187(6), 706-716. doi: 10.1086/686094

[18] Benbow, M. E., Tomberlin, J. K., & Tarone, A. M. (Eds.). (2015): Carrion ecology, evolution, and their applications. CRC press.

[19] Gallagher, A. J., Papastamatiou, Y. P., and Barnett, A. (2018): Apex predatory sharks and crocodiles simultaneously scavenge a whale carcass. Journal of Ethology, 36(2), 205-209. doi: 10.1007/s10164-018-0543-2

[21] von Huene, F. R. F. (1932): Die Fossile Reptil-ordnung Saurischia ihre Entwicklung und Geschichte. Monographien zur Geologie und Paleontologie. Liepzig, Verlaf von Gebrüder Borntraeger.

[20] Carrano, M. T., Benson, R. B. J., and Sampson, S. D. (2012). Erratum: The phylogeny of Tetanurae (Dinosauria: Theropoda)( Journal of Systematic Palaeontology (2012) 10: 2 (211-300)). Journal of Systematic Palaeontology, 10(3).

[22] von Huene, F. (1923): Carnivorous saurischia in Europe since the Triassic. Bulletin of the Geological Society of America, 34(3), 449-458. doi: 10.1130/GSAB-34-449