Massospondylus ( MASS-oh-SPON-di-lus) is a genus of sauropodomorph dinosaur from the Early Jurassic of southern Africa. It was described by Richard Owen in 1854 from remains discovered in South Africa, and is thus one of the first dinosaurs to have been named. The name Massospondylus means 'longer vertebra', alluding to what Owen identified as tail vertebrae; these vertebrae are now known to be from the neck. Although the original fossils were destroyed in London during The Blitz, a plethora of specimens have since been assigned to the genus, making it one of the best-known sauropodomorphs from the Early Jurassic. The genus lived during the Hettangian, Sinemurian, and Pliensbachian ages, which lasted from ca. 201 to 184 million years ago. Most fossils come from the upper Elliot and Clarens formations of South Africa and Lesotho, but the genus is also found in the Forest Sandstone and the Mpandi Formation of Zimbabwe. Material from the US, India, and Argentina was previously assigned to the genus, but the US and Argentinian specimens are now assigned to their own genera (Sarahsaurus and Adeopapposaurus). Because of their great abundance, Massospondylus fossils have been used to date rocks, and a biozone, the Massospondylus Range Zone, is named after the genus. Two species are considered valid: the type species M. carinatus, as well as M. kaalae, which was named in 2009 and is known from a single skull. Six other species have been named during the past 150 years but are no longer recognised. Originally, Massospondylus and similar dinosaurs have been regarded as theropods, but are now classified as basal ("early diverging") members of Sauropodomorpha. This group also includes sauropods. Within sauropodomorphs, Massospondylus is often classified in the family Massospondylidae. The genus was 4–6 metres (13–20 ft) long, with a long neck and tail, a small head, and a slender body. It is distinguished from related genera by the very elongated vertebrae of the front portion of the neck, amongst other features. Although Massospondylus was long depicted as quadrupedal (four-legged), it is now considered to have been bipedal (two-legged). This dinosaur was probably a herbivore (plant-eater), although some have speculated that basal sauropodomorphs may have been omnivorous. On each of its hands, it bore a sharp thumb claw that was probably used in feeding, possibly to uproot vegetation or to pull down branches while rearing up. Clutches of eggs have been found, some of which contained embryos; these are among the oldest eggs and embryos of an amniote in the fossil record. The eggshell was extremely thin, less than 0.1 mm (0.0039 in), unlike the much thicker eggshells in later dinosaurs. The embryos had proportionally longer arms than adults and a very large head, leading researchers to suggest that they were quadrupedal and shifted to a bipedal posture later during growth. Newer research instead suggested that Massospondylus was bipedal at all ages. Individuals accelerated or slowed down their growth depending on environmental factors such as food availability. The oldest known specimen was around 20 years of age.
History of discovery
Owen's 1854 description and loss of the type material The first fossils of Massospondylus were described by Richard Owen in 1854. The material, a collection of 56 bones or bone fragments, was found in 1853 or 1854 by the government surveyor Joseph Millard Orpen and his brothers on a farm in the Drakensberg mountains near Harrismith, South Africa. Their father then donated the fossils to the Hunterian Museum in London, of which Owen was curator. Owen named three new species from this material based on differences in their supposed tail vertebrae: Massospondylus carinatus, Pachyspondylus orpenii, and Leptospondylus capensis. The name Massospondylus (meaning 'longer vertebra') is derived from the Greek μάσσων (massōn) 'longer' and σπόνδυλος (spondylos) 'vertebra'; Owen stated that he chose this name "because the vertebrae are proportionally longer than those of the extinct crocodile called Macrospondylus". The specific name carinatus probably hints at the pronounced keel (carina) at the underside of the vertebrae. Leptospondylus means 'slender vertebra', while Pachyspondylus means 'thick vertebra'. Among the bones in Orpen's collection were vertebrae from the neck, back, hip, and tail; bones of the pelvis; the humerus (upper arm bone); and parts of the hindlimb including the femur (thigh bone), tibia (shin bone), and some foot bones. Orpen believed that more fossils would be found if the site were excavated. All these bones were probably found disarticulated (not connected to each other), making it difficult to determine whether or not they belonged to the same species. Yet, Owen assigned most of the bones to either Massospondylus, Pachyspondylus, or Leptospondylus, which Hans-Dieter Sues found to be somewhat arbitrary in 2004. In the decades after Owen's publication, the three species were neglected by other scholars, which Paul Barrett and Kimberley Chapelle speculated was due to Owen's "rather perfunctory descriptions", which lacked illustrations.
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