# Massospondylus

Massospondylus (/ˌmæsoʊˈspɒndɪləs/ MASS-oh-spon-di-lus) is a genus of sauropodomorph dinosaur from the Early Jurassic (Hettangian to Pliensbachian ages, ca. 200–183 million years ago). It was described by Sir Richard Owen in 1854 from remains discovered in South Africa, and is thus one of the first dinosaurs to have been named. Fossils have since been found at other locations in South Africa, Lesotho, and Zimbabwe. Material from Arizona's Kayenta Formation, India, and Argentina has been assigned to the genus at various times, but the Arizonan and Argentinian material are now assigned to other genera.
The type species is M. carinatus; seven other species have been named during the past 150 years, but only M. kaalae is still considered valid. Early sauropodomorph systematics have undergone numerous revisions during the last several years, and many scientists disagree where exactly Massospondylus lies on the dinosaur evolutionary tree. The family name Massospondylidae was once coined for the genus, but because knowledge of an early sauropod relationship is in a state of flux, it is unclear which other dinosaurs—if any—belong in a natural grouping of massospondylids; several 2007 papers support the family's validity.
Although Massospondylus was long depicted as quadrupedal, a 2007 study found it to be bipedal. It was probably a plant eater (herbivore), although it is speculated that the early sauropodomorphs may have been omnivorous. The genus was 4–6 metres (13–20 ft) long, and had a long neck and tail and a small head and slender body. On each of its forefeet, it bore a sharp thumb claw that was used in defense or feeding. Recent studies indicate that Massospondylus grew steadily throughout its lifespan, possessed air sacs similar to those of birds, and may have cared for its young.

## History of discovery
### Owen's 1854 description and loss of the type material

The first fossils of Massospondylus were described by paleontologist Sir 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, and was donated to the Hunterian Museum at the Royal College of Surgeons in London, of which Owen was curator. Owen erected 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".$^{:97}$ 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'.$^{:97–100}$ Among the bones in Orpen's collection were vertebrae from the neck, back, hip, and tail; bones of the pelvis; the humerus; and parts of the hindlimb including the femur, tibia, 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 in their original anatomical compound), 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, seemingly "somewhat arbitrarily". In the decades after Owen's publication, the three species were neglected by other scholars, which has been speculated to be due to Owen's "rather perfunctory descriptions", which lacked illustrations.$^{:102}$
In 1888, Richard Lydekker studied the material and found Leptospondylus to be a likely synonym of Massospondylus, though he did not mention Pachyspondylus. He also mentioned very similar fossils he had previously described from the "Maleri beds" of India, which he assigned to Massospondylus. Lydekker furthermore proposed that Owen's description was invalid and that his own publication should instead be considered the source of the name Massospondylus carinatus, and selected a neck vertebra and a toe bone as types (representative specimens on which a taxon is based on). This proposal was mostly ignored by later authors, and Owen's description is valid according to the International Code of Zoological Nomenclature (ICZN). In 1895, Harry Seeley revised Massospondylus and illustrated many of the fossils for the first time.$^{:117}$ Seeley argued that the putative tail vertebrae of Massospondylus were actually neck vertebrae , and that the tail vertebrae of Pachyspondylus orpenii were probably those of Massospondylus. Therefore, he concluded that most of the fossils probably belonged to a single species and assigned them to Massospondylus, but noted that they represent at least three individuals. Another redescription of the Orpen specimens was published by Friedrich von Huene in 1906, who assigned all material to Massospondylus. At the beginning of World War II, the basements of the Hunterian Museum were strengthened to protect specimens from German bombing raids, and several collections were moved to remote locations. The museum was damaged during several nearby bombings before it was directly hit by a bomb in the night between the 10th and 11th of May, 1941, causing debris to fall into the dungeons and the building being flooded due to heavy rain. Only 23 of 550 specimens of the museums' comparative anatomy collection survived. The losses included many specimens that have been pivotal in the history of science, as well as Massospondylus, Pachyspondylus, and Leptospondylus, of which only illustrations and plaster casts remain.

### Later discoveries and the neotype specimen

By 1976, Massospondylus was the most widespread sauropodomorph known from southern Africa thanks to continued discoveries in South Africa, Lesotho, and Zimbabwe. In 1981, Michael Cooper published a comprehensive monograph on the Zimbabwean material, describing the entire skeleton apart from the skull, of which no material was available. He also discussed the paleobiology of the genus in detail for the first time. Cooper concluded that none of the other gracile (slender-built) sauropodomorph species from South Africa differed substantially from M. carinatus, and consequently synonymized them all with the latter. A large number of specimens was assigned M. carinatus as a result. Over the next two decades, new specimens of gracile sauropodomorphs from southern Africa were often assigned to M. carinatus by default and without much scrutiny because it was the only recognised species. The skull of Massospondylus was first described in detail in 1990 by Chris Gow and colleagues based on four well-preserved skulls housed at the Evolutionary Studies Institute in Johannesburg. In 2004, Hans-Dieter Sues and colleagues provided a more comprehensive description of the same four skulls, and proposed the first diagnosis of Massospondylus carinatus (the set of distinguishing traits).
The five neck vertebrae on which Massospondylus carinatus was originally based on (the syntype series) do not show diagnostic features and cannot serve as a basis for comparison. Consequently, Yates and Paul Barrett, in 2010, proposed to designate a different specimen, BP/1/4934, as the neotype specimen (representative specimen). The skull and postcranium (the skeleton apart from the skull) of this specimen has been described in detail in 2018 and 2019, respectively. The specimen, nicknamed "Big Momma" although its sex is unknown, was found in March 1980 on a farm near Clocolan, South Africa, by Lucas Huma and James Kitching. Other fossils were found on the same farm, including the holotype of the turtle Australochelys africanus and the cynodont Pachygenelus. "Big Momma" includes a nearly complete skull and large parts of an articulated skeleton. As of 2019, it is the largest and most complete Massospondylus specimen and probably the most complete basal sauropodomorph specimen discovered in Africa. Since 1990, it is on public exhibit in the Evolutionary Studies Institute in Johannesburg. In order to maintain the original positions of the bones as they had been found, the specimen was prepared from above and below, but with most bones still partly encased in the original rock matrix. However, the specimen has been divided into seven individual blocks, the heaviest of which is about 35 kg in weight.$^{:117–119}$ In the 2000s, the specimen was extensively renovated after it became apparent that the fossils were deteriorating due to repeated handling. These conservation efforts included the filling of gaps and cracks in the bones, the application of a resin for hardening, and new support jackets to support the blocks.

### Misidentified specimens

During the 21th century, two additional massospondylid genera were identified in southern Africa, raising the question of whether all of the previous identifications of Massospondylus specimens were correct. The first of these genera, Ignavusaurus, was described in 2010 from a young specimen. In 2011, Yates and colleagues considered it to be a probable synonym of Massospondylus, but cladistic analyses led by Kimberley Chapelle in 2018 and 2019 recovered it as a distinct taxon of massospondylid. The second genus, Ngwevu, was described in 2019 by Chapelle and colleagues based on a complete skull with a fragmentary skeleton that had been discovered in 1978 and was previously assigned to Massospondylus carinatus.
Massospondylus has been previously recognised from outside of Africa, namely from the Upper Maleri Formation of India, the Kayenta Formation of the US, and the Cañón del Colorado Formation of Argentina. Cooper, in his 1981 study, even suggested that the Chinese genera Yunnanosaurus and Lufengosaurus were synonyms of Massospondylus, which would have expanded its range to China. All of these specimens are no longer assigned to Massospondylus, and Cooper's suggestion of synonymy was not followed by subsequent authors. Material from India was first assigned to Massospondylus by Lydekker in 1888 and 1890. Other Massospondylus fossils were mentioned in 1987 by T.S. Kutty and colleagues but have instead been assigned to the family Guaibasauridae in 2011. The Argentinian material, consisting of several partial skeletons described in 1999, has been assigned to the new and closely related genus Adeopapposaurus in 2009, while the material from the US, which consists of a nearly complete skull with skeleton described in 1985, was assigned to the new and closely related genus Sarahsaurus in 2010–2011.

### Species

Two species are currently recognized: the type species M. carinatus, described by Owen in 1854, and M. kaalae. M. kaalae is known from a single partial skull (SAM-PK-K1325) from the Upper Elliot Formation near Herschel, South Africa. This skull had been collected in 1966 by Gow and others but since then remained undescribed in the Iziko South African Museum in Cape Town. In 2004, Barrett noted that this skull belonged to a new species, which he named M. kaalae in 2009. The species is named in honor of the museum's collections manager for the Karoo vertebrate fossils, Sheena Kaal, for her assistance to numerous scientists who have studied specimens at the museum.
Multiple other species have been named but were considered as indeterminate by recent reviews. In 1890, Lydekker described the species M. hislopi and M. rawesi from fossils found in India. M. hislopi was based on a single fragmentary vertebra from the Lower Maleri Formation in Andhra Pradesh, while M. rawesi was based on a single tooth found by Mr Rawes in the Upper Cretaceous Takli Formation in Maharashtra.$^{:173}$ In 1906, von Huene believed that both species were not dinosaurs. M. hislopi was listed as an indeterminate sauropodomorph in the latest review, but M. rawesi is an indeterminate theropod. In 1895, Seeley named another species, M. browni, and tentatively assigned it to Massospondylus. This species was based on two neck, two back, and three tail vertebrae as well as femora and toe bones that were discovered north of the Witteberg by Mr. Alfred Brown.$^{:174}$ In 1906, von Huene concluded that the vertebrae and femora of M. browni belonged to two separate species. He therefore restricted M. browni to just the femora, and moved the species into the genus Thecodontosaurus, as T. browni. He assigned the vertebrae as well as additional fossils stored in Vienna to another species, Hortalotarsus skirtopodus, which he also moved into Thecodontosaurus, as T. skirtopodus.$^{:145}$ In 1920, Egbert Cornelis Nicolaas van Hoepen assigned a partial skeleton to M. browni, which was later assigned to M. harriesi and is now listed as a specimen of M. carinatus.$^{:103}$ M. browni was considered an indeterminate sauropodomorph in the most recent review.
Two more species were described in the first half of the twentieth century: M. harriesi and M. schwarzi. M. harriesi was named by Robert Broom in 1911 based on parts of a forelimb and hind limb discovered near Fouriesburg. Broom suggested that the original material described by Owen included a second species besides M. carinatus which can possibly be assigned to his M. harriesi. Several additional specimens were assigned to M. harriesi in 1911 and 1924,$^{:103}$ and in 1976, Galton and Michael Albert Cluver synonymized a number of other sauropodomorph species with it. M. schwarzi was named by Sydney H. Haughton in 1924 based on an incomplete foot found near Tlokoeng by Professor Schwarz. Both species were considered as indeterminate sauropodomorphs in the most recent review. In 1981, Cooper used the name M. huenei, a combination derived for Lufengosaurus huenei, as he considered Lufengosaurus and Massospondylus to be synonyms. This synonymy has not been accepted by subsequent authors.

### Previously synonymized species

Several other species from South Africa have been previously synonymized with Massospondylus. These include the above-mentioned Leptospondylus capensis and Pachyspondylus orpenii, as well as Hortalotarsus skirtopodus, Aetonyx palustris, Gryponyx africanus, Gyposaurus capensis, Gryponyx transvaalensis, Thecodontosaurus minor, Aristosaurus erectus, Dromicosaurus gracilis, Thecodontosaurus dubius, and Gryponyx taylori.
Hortalotarsus skirtopodus was erected by Seeley in 1894, based on a specimen found in the Clarens Formation near Barkly East. Most of the original skeleton was destroyed in an attempt to remove it from the rock matrix, and only a fragmentary hind limb remains.$^{:173–174}$ Aetonyx palustris, Gryponyx africanus and Gyposaurus capensis were all erected by Broom in 1911. Aetonyx palustris and Gryponyx africanus are each based on a fragmentary skeleton without skull found in the upper Elliot Formation near Fouriesburg, while Gyposaurus capensis is based on a fragmentary skeleton without skull discovered in the Clarens Formation near Ladybrand.$^{:173–174}$ One year later, in 1912, Broom erected Gryponyx transvaalensis from two foot bones (an ungual and a metatarsal) discovered in the Bushveld Sandstone Formation in Limpopo Province.$^{:173–174}$ Thecodontosaurus minor was named by Haughton in 1918 based on a neck vertebra, a tibia, and an ilium found in the Elliot Formation near Maclear. Haughton originally erected the taxon as a species of Thecodontosaurus.$^{:173–174}$ Aristosaurus erectus was named by van Hoepen in 1920 based on a nearly complete skeleton of a small and potentially juvenile individual found by quarry workers in the Clarens Formation near Rosendal.$^{:173–174}$ In another paper from the same year, van Hoepen also named Dromicosaurus gracilis from a fragmentary skeleton he had discovered near Bethlehem. In 1924, Haughton erected another species of Thecodontosaurus, T. dubius, as well as Gryponyx taylori. Thecodontosaurus dubius is based on a specimen comprising much of the skeleton from the Clarens Formation near Ladybrand, South Africa. Gryponyx taylori is based on a fragmentary pelvis from the Upper Elliot Formation near Fouriesburg.$^{:173–174}$
Galton and Cluver, in 1976, assigned Aetonyx palustris, Gryponyx africanus, Gryponyx taylori, Dromicosaurus gracilis, and Thecodontosaurus dubius to Massospondylus harriesi. Cooper, in 1981, instead considered all taxa as synonyms of Massospondylus carinatus. Galton, in a 1990 review, only listed Aetonyx palustris, Gryponyx africanus, Gyposaurus capensis, and Gryponyx taylori as synonyms of M. carinatus, while the latest review, by Galton and Paul Upchurch in 2004, considers all species to be indeterminate sauropodomorphs rather than synonyms of Massospondylus.$^{:173–174}$

## Description

Massospondylus was a mid-sized sauropodomorph. In a 2024 popular book, Gregory S. Paul estimated Massospondylus to be 4.3 m (14 ft) in length, while Barrett and colleagues estimated the particularly large neotype specimen at around 5 m (16 ft) in length, in 2019. Paul gave a body weight of 195 kg (430 lb), while Frank Seebacher, in 2001, gave an estimate of 136.7 kg (301 lb) while assuming a body length of 4 m (13 ft). It was a typical early sauropodomorph, with a slender body, a long neck, and a proportionally very small head. It had a slighter build than Plateosaurus, an otherwise similar but larger dinosaur.

### Skull

The small skull of Massospondylus was approximately half the length of the femur (upper thigh bone). Several openings, or fenestrae, in the skull reduced its weight and provided space for muscle attachment and sensory organs. At the front of the skull was the large external naris (nostril), which was roughly half the size of the orbit (eye socket). The posterior margin of the external naris was semicircular, while the anterior part of the opening was triangular. The orbit was circular and proportionally larger than that of Plateosaurus. The antorbital fenestra, situated between the orbit and the external naris, was triangular and smaller than that of Plateosaurus.$^{:169–171}$$^{:8}$ At the rear of the skull were the two temporal fenestrae: the lateral temporal fenestrae immediately behind the orbit that was shaped like an inverted "T", and the supratemporal fenestra on the top of the skull. A small fenestra also penetrated the mandible. Traditionally, the skull was thought to be wider and shorter than that of Plateosaurus, but these proportions may be the result of deformation during fossilisation. Some features of the skull are variable between individuals; for example, the thickness of the upper border of the orbits and the height of the posterior (rear) portion of the maxilla, the main tooth-bearing bone of the upper jaw. These differences may be due to sexual dimorphism or individual variation. A single autapomorphy (distinguishing feature) is found in the skull: the basipterygoid processes, a pair of bony extensions that braces the braincase against the palate, form an angle of ca. 35°, whereas this angle is much larger in all other basal sauropodomorphs in which it can be measured.$^{:55}$$^{:171}$
Tooth count was variable between individuals and increased with skull size. The premaxilla, the front bone of the upper jaw, showed the constant number of four teeth per side in all known skulls. In the maxilla, the tooth count varied from 14 to 22. There were 26 teeth in each side of the lower jaw in the largest known skull. The upper halves of the tooth crowns had serrated edges, with three to eight serrations on each side.$^{:70}$ The teeth were proportionally longer and slenderer than those of Plateosaurus. Their height decreased from front to back in the upper jaw, but was more or less constant in the lower jaw. The rear edges of the teeth did partially overlap the front edges of the teeth behind them, forming a continuous cutting edge.$^{:70}$ The teeth were replaced throughout life, as in other dinosaurs. This resulted in neighbouring teeth being of different heights, giving the tooth row the profile of a saw. The lack of pronounced tooth wear suggests that tooth replacement was rapid. The teeth varied in shape in different regions of the jaw. This heterodonty was more pronounced than that present in Plateosaurus, although not as pronounced as the specialization of teeth in Heterodontosaurus. Teeth closer to the front of the snout had round cross-sections and pointed tips, unlike the posterior teeth that were spatulate with oval cross-sections.
As with other early sauropodomorphs, it has been proposed that Massospondylus had fleshy cheeks, as there were few but large holes for blood vessels on the surfaces of the jaw bones, unlike the numerous small holes present on the jaws of cheekless reptiles. The cheeks would have prevented food from spilling out when Massospondylus ate. In 1986, Crompton and Attridge described skulls of Massospondylus as possessing pronounced overbites and suggested the presence of a horny beak on the tip of the lower jaw to make up the difference in length. However, the difference in length may be a misinterpretation and caused by crushing of the skull in a top–bottom plane, and more recent studies consider the possession of a beak as unlikely. The species M. kaalae differs from M. carinatus in the morphology of the braincase; the proportionally longer premaxillary tooth row that accounted for more than 30% of the upper tooth row; and a better developed ridge on the upper edge of the lacrimal bone.

### Vertebrae, girdles, and limbs

The vertebral column was composed of nine cervical (neck) vertebrae, 13 dorsal (back) vertebrae, three sacral (hip) vertebrae, and at least 40 tail vertebrae. The neck was proportionally long, and the centra (vertebral bodies) of the anterior (front) cervicals were more than seven times as long as they were tall, more elongated than in any other basal sauropodomorph and therefore an autapomorphy. In the anterior cervicals, the neural spine, the bony keel that formed the top of each vertebra, was elongated, and its anterior end had a hook-like protuberance that constitutes another autapomorphy.$^{:119,124}$
The shoulder blade had an expanded distal (upper) end. This expansion was more symmetrical than in related genera, in which the dorsal (front) expansion was much larger than the ventral (rear) expansion, and is an autapomorphy.$^{:119,147}$ In the hip, the pubis faced forward, as with most saurischians. The distal (front) end of the pubis was expanded in side view, but this expansion affected only its posterior margin, while the bone was flat anteriorly, which is an autapomorphy.$^{:119,165}$ The forelimbs were only half the length of the hind limbs but quite powerful, as indicated by a broad flange on the upper portion of the humerus called the deltopectoral crest, which provided attachment areas for a large arm musculature. This crest was longer than in related genera, extending for ca. 60% of the length of the bone, which is an autapomorphy. The lower arm was proportionally short, with the ulna measuring around 60% of the length of the humerus, which is another autapomorphy.$^{:119,152}$ Like Plateosaurus, it had five digits on each hand and foot. The hand was short and wide, with a large sickle shaped thumb claw used for feeding or defence against predators. The thumb was the longest finger in the hand, while the fourth and fifth digits were tiny, giving the hands a lopsided look. The phalangeal formula of the hand, which states the number of finger bones from the thumb to the fifth digit, was 2-3-4-3-2.$^{:153}$ The foot also had a large claw on the first digit, which was curved and flattened laterally (side-to-side). The claws on the middle three digits instead were smaller, less curved, and flattened dorsoventrally (top to bottom). The fifth toe only had a single toe bone and no claw. The phalangeal formula of the foot was 2-3-4-5-1.$^{:787}$

## Classification

Massospondylus was one of the first named dinosaurs from the southern hemisphere,$^{:114}$ a group that Owen himself had named twelve years earlier, in 1842. Owen, however, did not recognize the finds as dinosaurian, and instead attributed them to "large extinct carnivorous Reptiles" of uncertain classification, noting similarities with crocodilians, lizards, and dinosaurs.$^{:97}$ In an 1860 book, Owen classified Massospondylus as a crocodilian without explanation. In 1888, Lydekker demonstrated that Massospondylus is a genus of dinosaur, and classified in the family Anchisauridae, within Theropoda – anchisaurids and other taxa today classified as basal sauropodomorphs have historically been classified as theropods until the mid-twentieth century. Seeley, in his 1895 revision, also found Massospondylus to be a theropod (a "megalosaurian saurischian"). Huene, in his 1906 redescription of the Orpen fossils, classified Massospondylus as a member of Thecodontosauridae, together with Thecodontosaurus and Anchisaurus. In 1914, von Huene instead erected a new family, Massospondylidae, to accommodate M. carinatus, M. harriesi, and Aetonyx palustris, but in 1932 returned to his former classification of Massospondylus within Thecodontosauridae.
Basal sauropodomorph systematics continue to undergo revision, and many genera once considered classic "prosauropods" have recently been removed from the group in phylogenetic nomenclature, on the grounds that their inclusion would not constitute a clade (a natural grouping containing all descendants of a single common ancestor). Yates and Kitching (2003) published a clade consisting of Riojasaurus, Plateosaurus, Coloradisaurus, Massospondylus, and Lufengosaurus. Galton and Upchurch (2004) included Ammosaurus, Anchisaurus, Azendohsaurus, Camelotia, Coloradisaurus, Euskelosaurus, Jingshanosaurus, Lessemsaurus, Lufengosaurus, Massospondylus, Melanorosaurus, Mussaurus, Plateosaurus, Riojasaurus, Ruehleia, Saturnalia, Sellosaurus, Thecodontosaurus, Yimenosaurus and Yunnanosaurus in a monophyletic Prosauropoda. Wilson (2005) considered Massospondylus, Jingshanosaurus, Plateosaurus, and Lufengosaurus a natural group, with Blikanasaurus and Antetonitrus possible sauropods. Bonnan and Yates (2007) considered Camelotia, Blikanasaurus and Melanorosaurus possible sauropods. Yates (2007) placed Antetonitrus, Melanorosaurus, and Blikanasaurus as basal sauropods and declined to use the term Prosauropoda, as he considered it synonymous with Plateosauridae. However, he did not rule out the possibility that a small group of prosauropods consisting of Plateosaurus, Riojasaurus, Massospondylus and their closest kin were monophyletic.
Massospondylus is the type genus of the proposed family Massospondylidae, to which it gives its name. The Massospondylidae may also include Yunnanosaurus, although Lu et al. (2007) placed Yunnanosaurus in its own family. Yates (2007) considered Massospondylus, Coloradisaurus, and Lufengosaurus massospondylids, with Yunnanosaurus in Anchisauria. Smith and Pol (2007) also found a Massospondylidae in their phylogenetic analysis, including Massospondylus, Coloradisaurus, and Lufengosaurus, as well as their new genus, Glacialisaurus. Adeopapposaurus, based on the fossils once thought to belong to a South American form of Massospondylus, was also classified as a massospondylid, as was Leyesaurus, another South American genus that was named in 2011. Pradhania was originally regarded as a more basal sauropodomorph but new cladistic analysis performed by Novas et al., 2011 suggests that Pradhania is a massospondylid. Pradhania presents two shared traits of the Massospondylidae recovered in their phylogenetic analysis, and the fossils of Pradhania were discovered from the same region and basin in India as M. hislopi.
The following cladogram shows the position of Massospondylus within Massospondylidae, according to Fernando E. Novas and colleagues, 2011:
The following cladogram shows the position of Massospondylus within Massopoda, according to Oliver W. M. Rauhut and colleagues, 2020:

## Paleobiology

As with all dinosaurs, much of the biology of Massospondylus, including its behavior, coloration, and physiology, remains unknown. However, recent studies have allowed for informed speculation on subjects such as growth patterns, diet, posture, reproduction, and respiration.
A 2007 study suggested that Massospondylus may have used its short arms for defense against predators ("defensive swats"), in intraspecies combat, or in feeding, although its arms were too short to reach its mouth. Scientists speculate that Massospondylus could have used its large pollex (thumb) claw in combat, to strip plant material from trees, digging, or for grooming.

### Growth

A 2005 study indicated that Massospondylus' sister taxon, Plateosaurus, exhibited growth patterns affected by environmental factors. The study indicated that, when food was plentiful or when the climate was favorable, Plateosaurus exhibited accelerated growth. This pattern of growth is called "developmental plasticity". It is unseen in other dinosaurs, including Massospondylus, despite the close relationship between the two. The study indicated that Massospondylus grew along a specific growth trajectory, with little variation in the growth rate and ultimate size of an individual. Another study of age determination indicated that Massospondylus grew at a maximum rate of 34.6 kg (76.3 lb) per year and was still growing at around 15 years of age.

### Diet

Early sauropodomorphs such as Massospondylus may have been herbivorous or omnivorous. As recently as the 1980s, paleontologists debated the possibility of carnivory in the "prosauropods". However, the hypothesis of carnivorous "prosauropods" has been discredited, and all recent studies favor a herbivorous or omnivorous lifestyle for these animals. Galton and Upchurch (2004) found that cranial characteristics (such as jaw articulation) of most basal sauropodomorphs are closer to those of herbivorous reptiles than those of carnivorous ones, and the shape of the tooth crown is similar to those of modern herbivorous or omnivorous iguanas. The maximum width of the crown was greater than that of the root, resulting in a cutting edge similar to those of extant herbivorous or omnivorous reptiles. Barrett (2000) proposed that basal sauropodomorphs supplemented their herbivorous diets with small prey or carrion. Gastroliths (gizzard stones) have been found in association with three Massospondylus fossils from the Forest-Sandstone in Zimbabwe, and with a Massospondylus-like animal from the Late Triassic of Virginia. Until recently, scientists believed that these stones functioned as a gastric mill to aid ingestion of plant material, compensating for its inability to chew, as it is the case in many modern birds. However, Wings and Sander (2007) showed that the polished nature and the abundance of those stones precluded a use as an effective gastric mill in most non-theropod dinosaurs, including Massospondylus.

### Gait and range of motion

Although long assumed to have been quadrupedal, a 2007 anatomical study of the forelimbs has questioned this, arguing that their limited range of motion precluded effective habitual quadrupedal gait. Neither could the forelimbs swing fore and behind in a fashion similar to the hindlimbs, nor could the hand be rotated with the palmar surfaces facing downwards. This inability to pronate the hand is also supported by in-situ finds of articulated (still-connected) arms that always show unrotated hands with palmar faces facing each other. The study also ruled out the possibility of "knuckle-walking" and other forms of locomotion that would make an effective locomotion possible without the need to pronate the hand. Although its mass suggests a quadrupedal nature, Massospondylus would have been restricted to its hind legs for locomotion.
Since the discovery of rudimentary and nonfunctional clavicles in ceratopsians, it was assumed that these shoulder bones were reduced in all dinosaurs that did not have true furculae. Robert Bakker (1987) suggested that this would have allowed the shoulder blades to swing with the forelimbs in quadrupedal dinosaurs, increasing their functional forelimb length. This would have reduced the discrepancy of length between fore- and hindlimbs in a quadrupedal Massospondylus. However, a recent discovery shows that Massospondylus possessed well-developed clavicles that were joined in a furcula-like arrangement, acting like a clasp between the right and left shoulder blades and prohibiting any rotation of these bones. This discovery indicates that the clavicle reduction is limited to the evolutionary line leading to the ceratopsians. It also indicates that the furcula of birds is derived from clavicles.
Michael Cooper (1981) noted that the zygapophyses of the neck vertebrae were inclined, prohibiting significant horizontal movement of the neck, so that "consequently any significant movement in this direction must have been accomplished by a change in the position of the entire body". This was contradicted in a recent study, noting that only the basalmost cervicals show inclined zygapophyses, allowing sufficient horizontal movement of the neck as a whole.

### Reproduction

In 1976, a clutch of seven 190-million-year-old Massospondylus eggs was found in Golden Gate Highlands National Park in South Africa by James Kitching, who identified them as most likely belonging to Massospondylus. It was nearly 30 years before extraction was started on the fossils of the 15-centimetre- (6 in-) long embryos. They remain the oldest dinosaur embryos ever found. By early 2012, at least 10 egg clutches from at least four fossiliferous horizons had been found, with up to 34 eggs per clutch. This indicates that this nesting site may have been used repeatedly (site fidelity), by groups of animals (colonial nesting); in both cases, these represent the oldest evidence of this behaviour. Sedimentary structures indicate that the nesting area was in the vicinity of a lake. The eggshells were very thin (about 0.1 mm), allowing gas exchange even in a low oxygen and carbon dioxide rich environment, which indicates that the eggs were at least partly buried in the substrate. There are no hints that Massospondylus constructed nests; however, the arrangement of the eggs in tight rows indicates that the eggs were pushed in this position by the adults.
The embryos probably represented near-hatchlings. While the skeletal features were similar to those of the adults, the body proportions were very dissimilar. The head was big with a short snout and very large orbits, whose diameter amounts 39% of the entire skull length. The neck was short, contrasting to the very long neck in the adults. Girdle bones and tail vertebrae were relatively tiny. The forelimbs were of equal length to the hindlimbs, indicating that newly hatched Massospondylus were quadrupedal, unlike the bipedal adults. However, the reliability of these results has been questioned. The discovery of hatching footprints with manus impressions confirmed their quadrupedality. These impressions show that the hand was not pronated, with palm faces facing each other and the thumb facing forwards. The unpronated manus and the big head indicate that an effective locomotion was not possible for newly hatched Massospondylus. Notably, the near-hatchings had no teeth, suggesting they had no way of feeding themselves. Based on the lack of teeth and the ineffective locomotion, scientists speculate that postnatal care might have been necessary. This is further supported by evidence that the hatchings remained at the nest sites until they had doubled in size.
Newly hatched juveniles are known from a second sauropodomorph, Mussaurus; these remains resemble those of the embryonic Massospondylus, suggesting that quadrupedality was present in newly hatched Mussaurus and presumably other basal sauropodomorphs as well. The quadrupedality of the hatchings suggests that the quadrupedal posture of later sauropods may have evolved from retention of juvenile characteristics in adult animals, an evolutionary phenomenon known as paedomorphosis. This discovery therefore "sheds some light in the evolutionary pathways through which the peculiar adaptations of giant dinosaurs were attained", stated French paleontologist Eric Buffetaut. However, a recent study, which evaluated locomotion in extinct taxa based on limb robusticity, found that previous conclusions that Massospondylus transitioned from quadrupedality to bipedality through ontogeny were based on unreliable allometric comparisons between limb lengths, but a model based on the circumferences of the humerus and femur supported bipedality throughout ontogeny.

### Respiratory system

Many saurischian dinosaurs possessed vertebrae and ribs that contained hollowed-out cavities (pneumatic foramina), which reduced the weight of the bones and may have served as a basic 'flow-through ventilation' system similar to that of modern birds. In such a system, the neck vertebrae and ribs are hollowed out by the cervical air sac; the upper back vertebrae, by the lung; and the lower back and sacral (hip) vertebrae, by the abdominal air sac. These organs constitute a complex and very efficient method of respiration. "Prosauropods" are the only major group of saurischians without an extensive system of pneumatic foramina. Although possible pneumatic indentations have been found in Plateosaurus and Thecodontosaurus, the indentations were very small. One study in 2007 concluded that basal sauropodomorphs like Massospondylus likely had abdominal and cervical air sacs, based on the evidence for them in sister taxa (theropods and sauropods). The study concluded that it was impossible to determine whether basal sauropodomorphs had a bird-like flow-through lung, but that the air sacs were almost certainly present.

## Paleoecology
### Distribution and abundance

Most Massospondylus remains have been found in the Upper Elliot Formation and the Clarens Formation of South Africa and Lesotho, which are part of the Karoo Supergroup. The genus also been found in the Forest Sandstone and the Mpandi Formation of Zimbabwe. These formations were deposited during the very end of the Late Triassic and the very beginning of the Early Jurassic. The genus is known from numerous almost complete skeletons including at least 13 reasonably complete skulls, and thousands of isolated bones and fragments.$^{:114}$$^{:1}$ This wealth of material makes Massospondylus one of the best-known sauropodomorphs from the Early Jurassic. Because of its great abundance, it is used as the defining taxon of a biozone, the Massospondylus Assemblage Zone, and has been used to determine the relative ages of sedimentary rocks.

### Paleoenvironment and predators

The faunas and floras of the Early Jurassic were similar worldwide, with conifers adapted for hot weather becoming the common plants; basal sauropodomorphs and theropods were the main constituents of a worldwide dinosaur fauna. The environment of early Jurassic southern Africa has been described as a desert. African Massospondylus was a contemporary of temnospondyli; turtles; a sphenodont; rauisuchids; early crocodylomorphs; tritylodontid and trithelodontid therapsids; morganucodontid mammals; and dinosaurs including the small theropod Megapnosaurus and several genera of early ornithischians, such as Lesothosaurus and the heterodontosaurids Abrictosaurus, Heterodontosaurus, Lycorhinus and Pegomastax. Until recently, Massospondylus was regarded as the only known sauropodomorph from the Upper Elliot Formation. However, newer finds revealed a diverse contemporary sauropodomorph fauna with six additional species, including Ignavusaurus, Arcusaurus and two unnamed taxa as well as two unnamed sauropods.
It is not clear which carnivores may have preyed on Massospondylus. Most of the theropods that have been discovered in rocks of Early Jurassic age in southern Africa, such as Coelophysis, were smaller than mid-sized sauropodomorphs like Massospondylus. These smaller predators have been postulated as using fast slashing attacks to wear down sauropodomorphs, which could have defended themselves with their large hand and foot claws. The 6-metre-(20 ft-) long carnivorous theropod Dracovenator lived during the same period (Hettangian to Sinemurian stages) as Massospondylus and has also been found in the Elliot Formation of South Africa.