| Massospondylus Temporal range:Early Jurassic,Hettangian–Pliensbachian | |
|---|---|
 | |
| Neotype skeleton shown from the left (above) and right side | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | †Sauropodomorpha |
| Clade: | †Bagualosauria |
| Clade: | †Plateosauria |
| Clade: | †Massopoda |
| Family: | †Massospondylidae |
| Genus: | †Massospondylus Owen,1854 |
| Species | |
Massospondylus (/ˌmæsoʊˈspɒndɪləs/MASS-oh-spon-di-lus[1]) is agenus ofsauropodomorph dinosaur from theEarly Jurassic ofsouthern Africa. It was described byRichard Owen in 1854 from remains discovered in South Africa, and is thus one of the first dinosaurs to have been named. The nameMassospondylus 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 inLondon during a bombing raid inWorld War II, 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 theHettangian,Sinemurian, andPliensbachian ages, which lasted from ca. 201 to 184 million years ago. Most fossils come from the upperElliot andClarens formations of South Africa and Lesotho, but the genus is also found in theForest Sandstone and theMpandi 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 andAdeopapposaurus). Because of their great abundance,Massospondylus fossils have been used todate rocks, and abiozone, theMassospondylus Range Zone, is named after the genus.
Two species are considered valid: thetype speciesM. carinatus, as well asM. 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 astheropods, but are now classified asbasal ("early diverging") members of Sauropodomorpha. This group also includessauropods. Within sauropodomorphs,Massospondylus is often classified in the familyMassospondylidae. 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. AlthoughMassospondylus was long depicted asquadrupedal (four-legged), it is now considered to have beenbipedal (two-legged).
It was probably aherbivore (plant-eater), although some have speculated that basal sauropodomorphs may have beenomnivorous. 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 with eggs have been found, some of which containedembryos; these are among the oldest eggs and embryos of anamniote in thefossil 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 thatMassospondylus 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.
The first fossils ofMassospondylus were described byRichard Owen in 1854.[2] The material, a collection of 56 bones or bone fragments, was found in 1853 or 1854 by the government surveyorJoseph Millard Orpen and his brothers on a farm in theDrakensberg mountains nearHarrismith, South Africa. Their father then donated the fossils to theHunterian Museum in London, of which Owen was curator.[3] Owen named three new species from this material based on differences in their supposed tail vertebrae:Massospondylus carinatus,Pachyspondylus orpenii, andLeptospondylus capensis. The nameMassospondylus (meaning'longer vertebra') is derived from theGreekμάσσων (massōn)'longer' andσπόνδυλος (spondylos)'vertebra'; Owen stated that he chose this name "because the vertebrae are proportionally longer than those of the extinct Crocodile calledMacrospondylus".[2]: 97 [4] The specific namecarinatus probably hints at the pronounced keel (carina) at the underside of the vertebrae.Leptospondylus means'slender vertebra',[a] whilePachyspondylus means'thick vertebra'.[b][2][3]: 97–100 Among the bones in Orpen's collection were vertebrae from the neck, back, hip, and tail; bones of the pelvis; thehumerus (upper arm bone); and parts of the hindlimb including thefemur (thigh bone),tibia (shin bone), and some foot bones. Orpen believed that more fossils would be found if the site were excavated.[5] All these bones were probably founddisarticulated (not connected to each other), making it difficult to determine whether or not they belonged to the same species.[4] Yet, Owen assigned most of the bones to eitherMassospondylus,Pachyspondylus, orLeptospondylus, whichHans-Dieter Sues found to be somewhat arbitrary in 2004.[6]: 240 In the decades after Owen's publication, the three species were neglected by other scholars, whichPaul Barrett and Kimberley Chapelle speculated was due to Owen's "rather perfunctory descriptions", which lacked illustrations.[3]: 102
In 1888,Richard Lydekker studied the material and foundLeptospondylus was likely asynonym ofMassospondylus, though he did not mentionPachyspondylus. Lydekker furthermore proposed that Owen's description was too incomplete for the nameMassospondylus carinatus to be consideredvalid, and that his own publication should instead be recognised as the source of the name. Consequently, he selected a neck vertebra and a toe bone astype specimens (representative specimens on which a taxon is based). This proposal was mostly ignored by later authors, and Owen's description is valid according to theInternational Code of Zoological Nomenclature (ICZN).[7][3] In 1895,Harry Seeley revisedMassospondylus and illustrated many of the fossils for the first time.[5][8]: 117 Seeley argued that the putative tail vertebrae ofMassospondylus were actually neck vertebrae, and that the tail vertebrae ofPachyspondylus orpenii were probably those ofMassospondylus. Therefore, he concluded that most of the fossils probably belonged to a single species and assigned them toMassospondylus, but noted that they represent at least three individuals.[5][8] Another redescription of the Orpen specimens was published byFriedrich von Huene in 1906, who assigned all material toMassospondylus.[9][8] 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 on the night between May 10 and 11, 1941, causing debris to fall into the dungeons and the building to be flooded due to heavy rain. Only 23 of 550 specimens in the museum's comparative anatomy collection survived. Many specimens that have been pivotal in the history of science were lost, as well as the entire Orpen collection, includingMassospondylus,Pachyspondylus, andLeptospondylus, of which only illustrations andplaster casts remain.[3]
By 1976,Massospondylus was the most widespreadsauropodomorph known from southern Africa thanks to continued discoveries in South Africa, Lesotho, and Zimbabwe.[3] In that year, James Kitching discovered clutches with eggs in a roadcut inGolden Gate Highlands National Park, a locality known as Rooidraai ('Red Bend').[10][11][12] Already in 1961, a British-South African palaeontological expedition discovered the skeleton of a hatchling (SAM-PK-K413) atMafeteng, Lesotho, although this specimen was first misidentified as thevaranopidHeleosaurus.[12] In 1981, Michael Cooper published a comprehensivemonograph on the ZimbabweanMassospondylus material, describing the entire skeleton apart from the skull, of which no material was available.[13] He also discussed thepalaeobiology of the genus in detail for the first time. Cooper concluded that none of the othergracile (slender-built) sauropodomorph species from South Africa differed substantially fromM. carinatus, and consequently synonymised them all with the latter. A large number of specimens were assigned toM. carinatus as a result. Over the next two decades, new specimens of gracile sauropodomorphs from southern Africa were often assigned toM. carinatus by default and without much scrutiny because it was the only recognised species.[3] The skull ofMassospondylus was first described in detail in 1990 by Chris Gow and colleagues based on four well-preserved skulls housed at theEvolutionary Studies Institute[c] inJohannesburg.[14] In 2004,Hans-Dieter Sues and colleagues provided a more comprehensive description of the same four skulls, and proposed the first diagnosis ofM. carinatus (the set of distinguishing features).[3][6]
The five neck vertebrae on whichM. carinatus was originally based (thesyntype series) do not show distinguishing features and cannot serve as a basis for comparison. Consequently, Yates and Barrett, in 2010, proposed to designate a different specimen,BP/1/4934, as theneotype specimen (the new representative specimen).[4] This specimen consists of an almost complete skeleton with skull housed at the Evolutionary Studies Institute. The skull was described in detail in 2018 by Chapelle and Jonah Choiniere, while Barrett and colleagues described the remainder of the skeleton in 2019.[15][8] The specimen, nicknamed "Big Momma" although its sex is unknown, was found in March 1980 on a farm nearClocolan, South Africa, by Lucas Huma andJames Kitching. Other fossils were found on the same farm, including theholotype of theturtleAustralochelys africanus and thecynodontPachygenelus. "Big Momma" includes a nearly complete skull and large parts of an articulated skeleton. As of 2019, it is the largest and most completeMassospondylus specimen and probably the most completebasal (early diverging) sauropodomorph specimen discovered in Africa. Since 1990, it has been on public exhibit in the Evolutionary Studies Institute. To maintain the original positions of the bones as they had been found, the specimen wasprepared from above and below, but with most bones still partly encased in the originalrock matrix. However, the specimen has been divided into seven individual blocks, the heaviest of which is about 35 kg (77 lb) in weight.[16][8]: 117–119 In the 2000s, the specimen was extensively restored 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.[16]
Besides thetype speciesMassospondylus carinatus, one additional species,Massospondylus kaalae, is currently recognised.M. kaalae is known from a single partial skull (SAM-PK-K1325) from the Upper Elliot Formation nearHerschel, South Africa. This skull was collected in 1966 by Gow and others, but since then has remained undescribed in theIziko South African Museum in Cape Town. In 2004, Barrett noted that this skull belonged to a new species, which he namedM. kaalae in 2009. The species is named in honor of the museum's collections manager for theKaroo vertebrate fossils, Sheena Kaal, for her assistance to numerous scientists who have studied specimens at the museum.[8][17]
In 1895, Seeley named the speciesM. browni, although its assignment toMassospondylus was only tentative. 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 theWitteberg by Alfred Brown.[5][8]: 174 In 1906, von Huene concluded that the vertebrae and femora ofM. browni belonged to two separate species. He therefore restrictedM. browni to just the femora, and moved the species into the genusThecodontosaurus, asT. browni. He assigned the vertebrae as well as additional fossils stored in Vienna to another species,Hortalotarsus skirtopodus, which he also moved intoThecodontosaurus, asT. skirtopodus.[9]: 145 In 1920,Egbert Cornelis Nicolaas van Hoepen assigned a partial skeleton toM. browni, which was later assigned toM. harriesi and is now listed as a specimen ofM. carinatus.[3]: 103 M. browni was considered an indeterminate sauropodomorph in a 2004 review byPeter Galton and Paul Upchurch.[18]
Two more species were described in the first half of the twentieth century:M. harriesi andM. schwarzi.M. harriesi was named byRobert 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 besidesM. carinatus which can possibly be assigned to hisM. harriesi.[19] Several additional specimens were assigned toM. harriesi in 1911 and 1924,[3]: 103 and in 1976, Galton and Michael Albert Cluver synonymised several other sauropodomorph species with it.[20]M. schwarzi was named bySydney H. Haughton in 1924 based on an incomplete foot found nearTlokoeng by Professor Schwarz.[21] Both species were considered as indeterminate sauropodomorphs in the 2004 review.[18]
Several other species from South Africa have originally been assigned to different genera, were later regarded as synonyms ofMassospondylus, and are currently regarded asindeterminate (too incomplete to be classified). These include the above-mentionedLeptospondylus capensis andPachyspondylus orpenii, as well asHortalotarsus skirtopodus,Aetonyx palustris,Gryponyx africanus,Gyposaurus capensis,Gryponyx transvaalensis,Thecodontosaurus minor,Aristosaurus erectus,Dromicosaurus gracilis,Thecodontosaurus dubius, andGryponyx taylori.[13][22][18][8]: 173–174
Hortalotarsus skirtopodus was named by Seeley in 1894, based on a specimen found in the Clarens Formation nearBarkly 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.[23][8]: 173–174 Aetonyx palustris,Gryponyx africanus andGyposaurus capensis were all named by Broom in 1911.Aetonyx palustris andGryponyx africanus are each based on a fragmentary skeleton without skull found in the upper Elliot Formation nearFouriesburg, whileGyposaurus capensis is based on a fragmentary skeleton without skull discovered in the Clarens Formation nearLadybrand.[19][8]: 173–174 One year later, in 1912, Broom namedGryponyx transvaalensis from two foot bones (an ungual and a metatarsal) discovered in theBushveld Sandstone Formation inLimpopo Province.[19][8]: 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 nearMaclear.[24][8]: 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 nearRosendal.[25][8]: 173–174 In another paper from the same year, van Hoepen also namedDromicosaurus gracilis from a fragmentary skeleton he had discovered nearBethlehem, South Africa.[26] In 1924, Haughton erected another species ofThecodontosaurus,T. dubius, as well asGryponyx 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.[21][20][13][8]: 173–174
Galton and Cluver, in 1976, assignedAetonyx palustris,Gryponyx africanus,Gryponyx taylori,Dromicosaurus gracilis, andThecodontosaurus dubius toM. harriesi.[20] Cooper, in 1981, instead considered all taxa as synonyms ofM. carinatus. Galton, in a 1990 review, only listedAetonyx palustris,Gryponyx africanus,Gyposaurus capensis, andGryponyx taylori as synonyms ofM. carinatus, while the 2004 review considers all species to be indeterminate sauropodomorphs rather than synonyms ofMassospondylus.[13][22][18][8]: 173–174
During the 21st century, two additional massospondylid genera were identified in southern Africa, raising the question of whether all of the previous identifications ofMassospondylus specimens were correct.[8] The first of these genera,Ignavusaurus, was described in 2010 from a juvenile specimen. In 2011, Yates and colleagues considered it to be a probable synonym ofMassospondylus,[27] butcladistic analyses led by Chapelle in 2018 and 2019 recovered it as a distinct taxon of massospondylid.[15][28] 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 toM. carinatus.[28] In 2023, Chapelle and colleagues concluded that a humerus from the upper Elliot Formation, which also had been provisionally assigned toMassospondylus, belonged to a new sauropodomorph genus that was unusually small. This potential genus remains unnamed.[29]
Massospondylus has been previously recognised from outside of Africa, namely from theLower Maleri andTakli formations of India, theKayenta Formation of the US, and theCañón del Colorado Formation of Argentina. In 1890, Lydekker described the speciesM. hislopi andM. rawesi from fossils found in India.M. hislopi was based on a single fragmentary vertebra from the Lower Maleri Formation inAndhra Pradesh, whileM. rawesi was based on a single tooth found by Mr. Rawes in theUpper Cretaceous Takli Formation inMaharashtra.[30][31][32][8]: 173 In 1906, von Huene believed that both species were not dinosaurs.[9]M. hislopi was listed as an indeterminate sauropodomorph in a 2004 review by Galton and Upchurch[18] butM. rawesi is an indeterminatetheropod.[32] OtherMassospondylus fossils from India were mentioned in 1987 by T.S. Kutty and colleagues but have instead been assigned to the familyGuaibasauridae in 2011.[33][34][3] 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 genusSarahsaurus in 2010–2011.[35] In 2009, the Argentinian material, which consists of several partial skeletons described in 1999, has likewise been recognised as a new genus,Adeopapposaurus.[36]
Cooper, in his 1981 study, suggested that the Chinese generaYunnanosaurus andLufengosaurus were synonyms ofMassospondylus, which would have expanded its range to China. He classifiedLufengosaurus as a separate species ofMassospondylus,M. huenei. This suggestion was not followed by subsequent authors.[13][3]
Massospondylus was a mid-sized sauropodomorph. In 2019, Barrett and colleagues estimated the particularly large neotype specimen at around 5 m (16 ft) in length.[8]Gregory S. Paul, in a popular book published in 2024, estimatedMassospondylus to be 4.3 m (14 ft) in length.[37] The body weight was estimated at 136.7 kg (301 lb) by Frank Seebacher in 2001, assuming a body length of 4 m (13 ft). Paul instead gave a body weight of 195 kg (430 lb).[37][38] It was a typical basal sauropodomorph, with a slender body, a long neck, and a proportionally very small head. It had a slighter build thanPlateosaurus, an otherwise similar but larger dinosaur.[18] Basal sauropodomorphs probably hadair sacs and possibly a bird-like flow-through lung.[39] In theropods andsauropods, these air sacs invaded bones, in particular the vertebrae (postcranial skeletal pneumaticity). Although some basal sauropodomorphs such asPlateosaurus show incipient pneumaticity in their vertebrae, those ofMassospondylus are apneumatic (lack any signs of pneumaticity).[40]
The skull ofMassospondylus was small and approximately half the length of thefemur (thigh bone). Several openings in the skull, calledfenestrae, reduced its weight and provided space for muscle attachment and sensory organs. At the front of the skull was the largeexternal naris (nostril), which was roughly half the size of theorbit (eye socket).[18] Theposterior (rear) margin of the external naris was semicircular, while the anterior (front) part of the opening was triangular. The orbit was circular and proportionally larger than that ofPlateosaurus. Theantorbital fenestra, situated between the orbit and the external naris, was triangular and smaller than that ofPlateosaurus.[8]: 169–171 [15]: 8 At the rear of the skull were the twotemporal fenestrae: thelateral temporal fenestrae immediately behind the orbit that was shaped like an inverted "T",[6] and the supratemporal fenestra on the top of the skull. In side view, the temporal region (the region behind the orbits) was shorter than inPlateosaurus.[41] A small fenestra, themandibular fenestra, also perforated themandible.[18] Traditionally, the skull was thought to be wider and shorter than that ofPlateosaurus, but these proportions may be the result of deformation during fossilisation.[18] Some features of the skull are variable between individuals; for example, the thickness of the upper border of the orbits and the height of theposterior (rear) portion of themaxilla, the main tooth-bearing bone of the upper jaw. These differences may be due tosexual dimorphism[14] or individual variation.[42] A singledistinguishing feature is found in the skull: thebasipterygoid processes, a pair of bony extensions that braces thebraincase against thepalate, form an angle of ca. 35°, whereas this angle is much larger in all other basal sauropodomorphs in which it can be measured.[15]: 55 [8]: 171 The speciesM. kaalae differs fromM. carinatus in themorphology 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 thelacrimal bone.[43]
Tooth count was variable between individuals and increased with skull size.[14] Thepremaxilla, 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 on each side of the lower jaw in the largest known skull.[6][14] The upper halves of thetooth crowns had serrated edges, with three to eightserrations on each side.[6][14][15]: 70 Their height decreased from front to back in the upper jaw, but remained almost constant in the lower jaw.[14] The rear edges of the teeth partially overlapped the front edges of the teeth behind them, forming a continuous cutting edge.[14][15]: 70 The teeth werereplaced throughout life, as in other dinosaurs. This resulted in neighbouring teeth being of different heights, giving the tooth row a profile similar to a saw.[14] The lack of pronouncedtooth wear suggests that tooth replacement was rapid;[14] a 2013 study estimated that a tooth remained in use for only 17 to 30 days.[44] The teeth varied in shape in different regions of the jaw; thisheterodonty was more pronounced than that present inPlateosaurus.[14] Teeth closer to the front of the snout had pointed tips and were slightly curved, unlike the posterior teeth that werespatulate (with a broad, flat tip) and more symmetrical.[18] The teeth were proportionally longer and slenderer than those ofPlateosaurus.[6]
Thevertebral column was composed of nine cervical (neck) vertebrae, 13 dorsal (back) vertebrae, three sacral (hip) vertebrae, and at least 40 tail vertebrae.[18] The neck was proportionally long, and thecentra (vertebral bodies) of theanterior cervicals were more than seven times as long as they were tall, more elongated than in any other basal sauropodomorph and therefore a distinguishing feature. 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 distinguishing feature.[8]: 119, 124
The shoulder blade had an expanded upper end. This expansion was more symmetrical than in related genera, in which thedorsal (front) expansion was much larger than theventral (rear) expansion, and is a distinguishing feature.[8]: 119, 147 In the hip, thepubis faced forward, as with mostsaurischians.[18] The 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 a distinguishing feature.[8]: 119, 165 The forelimbs were only half the length of the hind limbs[45] but quite powerful, as indicated by a broad flange on the upper portion of thehumerus called thedeltopectoral crest, which provided attachment areas for a large arm musculature.[46] This crest was longer than in related genera, extending for ca. 60% of the length of the bone, which is a distinguishing feature. The lower arm was proportionally short, with theulna measuring around 60% of the length of the humerus, which is another distinguishing feature.[8]: 119, 152 LikePlateosaurus, it had fivedigits 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.[46][13] 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.[8]: 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.[13]: 787
Described in 1854,Massospondylus was one of the first named dinosaurs from theSouthern Hemisphere.[8]: 114 Although Owen himself had named the group Dinosauria twelve years earlier, in 1842, he did not recogniseMassospondylus as a dinosaur. Instead, he attributed it to "large extinctcarnivorous Reptiles" of uncertain classification, noting similarities withcrocodilians, lizards, and dinosaurs.[2]: 97 [5] In an 1860 book, Owen classifiedMassospondylus as a crocodilian but did not explain this decision.[47][3] In 1888, Lydekker demonstrated thatMassospondylus is a genus of dinosaur, and classified it in the familyAnchisauridae, withinTheropoda.[7][3] Seeley, in his 1895 revision, also foundMassospondylus to be a theropod (a "megalosaurian saurischian").[5][3] Huene, in his 1906 redescription of the Orpen fossils, classifiedMassospondylus as a member ofThecodontosauridae, together withThecodontosaurus andAnchisaurus.[9] In 1914, von Huene instead named a new family,Massospondylidae, to accommodateM. carinatus,M. harriesi, andAetonyx palustris, but in 1932 returned to his former classification ofMassospondylus within Thecodontosauridae.[48][49][3]
In 1920, von Huene named the new group Prosauropoda to unite the early long-necked dinosaurs includingMassospondylus. In 1932, he also named the new group Sauropodomorpha, which contained his Prosauropoda as well as Sauropoda, abandoning the traditional classification ofMassospondylus and related genera within Theropoda.[46] Yet, the relationships between Theropoda and Prosauropoda remained contested until 1965, when Alan J. Charig argued that Prosauropoda was more closely related to Sauropoda. Charig divided Prosauropoda into three families, following earlier studies: the small-sized Thecodontosauridae, which still includedMassospondylus; the medium-sizedPlateosauridae; and the large-sizedMelanorosauridae.[50][46] This division of Prosauropoda into three families was generally upheld during the following decades, although several studies classifiedMassospondylus within the Plateosauridae or within another family, the Anchisauridae.[51][46] In the 1990 edition of the encyclopediaThe Dinosauria, Galton recognised additional prosauropod families including a resurrected Massospondylidae that containedMassospondylus as its only member.[22] Massospondylidae has since been recognised by a majority of studies.[51] The name "Prosauropoda" meanwhile fell into disuse as some prosauropods were closer to sauropods than to other prosauropods. Massospondylidae is instead classified within the groupPlateosauria, which also includes the Plateosauridae, theRiojasauridae, and, depending on the study, may or may not include sauropods.[46] Adam Yates, in 2007, named the groupMassopoda as a sub-group of Plateosauria that includes Massospondylidae and sauropods but not Plateosauridae.[52]
BesidesMassospondylus itself, Massospondylidae typically includesAdeopapposaurus,Coloradisaurus,Leyesaurus, andLufengosaurus.[3]: 105 Glacialisaurus has also been consistently recovered as a member of Massospondylidae,[53][54] andPradhania,[55]Ignavusaurus,[56] andNgwevu[28] might also be members. The following cladogram shows the position ofMassospondylus according to Oliver Rauhut and colleagues, 2020:[57]
Basal sauropodomorphs such asMassospondylus may have beenherbivorous oromnivorous. As recently as the 1980s, palaeontologists debated the possibility ofcarnivory in basal sauropodomorphs.[13][58] However, the hypothesis of carnivorous sauropodomorphs has been discredited, and all recent studies favour a herbivorous or omnivorous lifestyle for these animals. In 2004, Galton and Upchurch 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 toothcrown is similar to those of modern herbivorous or omnivorousiguanas. 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.[18] In 2000, Barrett proposed that basal sauropodomorphs supplemented their herbivorous diets with small prey orcarrion.[59]
Like other basal sauropodomorphs,Massospondylus was an orthal feeder (its jaws made simple up-and-down movements).[41] In their 1986 study,Alfred Crompton and John Attridge suggested thatMassospondylus andPlateosaurus had weak bites because their skulls were lightly constructed and had long tooth rows.[d][60] However, the jaw joint was lowered with respect to the tooth row, which increased muscle leverage and therefore led to a stronger bite.[41] In 2019, Ali Nabavizadeh suggested thatMassospondylus andAnchisaurus had a stronger bite than other basal sauropodomorphs because of the more anterior position of the jaw joint, resulting in a more vertical action of the palatal muscles (Musculus pterygoideus).[41]
As with other basal sauropodomorphs, it has been proposed thatMassospondylus 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 whenMassospondylus ate.[18] However, in the early 2020s, Nabavizadeh argued that cheeks in dinosaurs are speculative and unlikely.[61] In 1986, Crompton and Attridge described skulls ofMassospondylus as possessing pronouncedoverbites and suggested the presence of ahorny beak on the tip of the lower jaw to make up the difference in length.[60] 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.[6][62][63] Gow, in 1990, suggested that the articulation between the premaxilla and the maxilla allowed for some degree ofcranial kinesis (movement between skull bones), and that the same was true for the articulation between thequadrate and thequadratojugal, a condition known asstreptostyly.[14] However, a later study found these articulations to be relatively rigid.[63]Gastroliths (gizzard stones) have been found in association with threeMassospondylus fossils from the Forest Sandstone in Zimbabwe.[64] In one of these specimens, the preserved gastroliths made up ca. 1% of the body mass.[46] Until recently, scientists believed that these stones functioned as a gastric mill to aid ingestion of plant material, compensating for their inability to chew, as is the case in many modern birds. However, Oliver Wings and Martin Sander showed in 2007 that the polished nature and the abundance of those stones precluded their use as an effective gastric mill in most non-theropod dinosaurs, includingMassospondylus.[46][65]
Although long assumed to have beenquadrupedal (four-legged), Matthew Bonnan and Phil Senter questioned this in 2007, arguing that the animal was restricted tobipedal (two-legged) gaits. Neither could the forelimb swing forward and behind in a fashion similar to the hindlimbs, nor could the hand bepronated (rotated so that the fingers face forwards when the forelimb is vertical). This inability to pronate the hand is also supported by findings ofarticulated (still-connected) arms that always show palmar surfaces facing each other. The study also ruled out the possibility ofknuckle-walking that would make effective locomotion possible without the need to pronate the hand. Bonnan and Senter suggested that some bipedaltrackways of theichnogenusOtozoum might have been produced byMassospondylus or similar bipedal sauropodomorphs.[45]
It was often assumed that the large thumb claw ofMassospondylus and other basal sauropodomorphs was used in defence against predators. In their 2007 study, Bonnan and Senter questioned this because thehumerus could not swing forwards past the vertical. However, using the thumb claw for defence would have been possible if the animal reared up by using the tail as a third "leg". Although the hand could not reach the mouth, the thumb claw was probably used for feeding, such as for disrooting vegetation or, when rearing up, for pulling down branches.[45] In 2025, Mooney and colleagues observed that the thumb claw is sickle-shaped in adult individuals but only slightly curved in the hatchling SAM-PK-K413 and relatively straight in one of the embryos. In the embryo, the thumb was already ossified while most other parts of the hands and feet were unossified, which might suggest that it had important functions already at early developmental stages.[12]
Since the discovery of rudimentary and nonfunctionalclavicles inceratopsians, it was assumed that these shoulder bones were reduced in all dinosaurs that did not have truefurculae.[67] In 1987,Robert Bakker suggested that this would have allowed theshoulder blades to swing with the forelimbs in quadrupedal dinosaurs, increasing their functional forelimb length.[68] This would have reduced the discrepancy of length between fore- and hindlimbs in a quadrupedalMassospondylus. However, theMassospondylus specimen BP-1-5241 preserves well-developed clavicles that are joined in a furcula-like arrangement, showing that they acted as a clasp between the right and left shoulder blades, prohibiting any rotation of these bones. According to a 2005 study by Yates and Cecilio Vasconcelos, the specimen indicates that clavicle reduction is limited to the evolutionary line leading to the ceratopsians. It also indicates that the furcula of birds is derived from clavicles.[67]
In 1981, Michael Cooper argued that thezygapophyses (projections that form joints between vertebrae) of the neck were inclined, impeding horizontal neck movements and forcing the animal to move its entire body instead.[13] This was contradicted by Barrett and Upchurch in 2007, who noted that only the hindmost cervicals showed inclined zygapophyses, allowing sufficient horizontal movement of the neck as a whole.[63]
Growth in dinosaurs can be reconstructed usingthin sections of bones that reveal growth rings, similar to thegrowth rings in trees. The first such study forMassospondylus was conducted byAnusuya Chinsamy-Turan in 1993, who, based on femora of different sizes, found that growth was cyclic, with one growth ring formed each year. Because an external fundamental system (tightly packed growth rings that indicate that growth had stopped) was absent, she suggested thatMassospondylus had indeterminate growth (growth throughout life). This suggests that thephysiology ofMassospondylus was intermediate betweenectothermy ("cold-bloodedness") andendothermy ("warm-bloodedness").[69] In a 2001 study,Gregory M. Erickson and colleagues indicated thatMassospondylus grew at a maximum rate of 34.6 kg per year and were still growing at around 15years of age.[70]
A 2005 study by Martin Sander and Nicole Klein indicated that the relatedPlateosaurus adjusted its growth according to environmental conditions: when food was plentiful or when the climate was favourable,Plateosaurus exhibited accelerated growth. Consequently, body size is only weakly correlated with age. This pattern of growth is called "developmental plasticity" and is common in ectothermic animals but uncommon in endothermic animals. According to Sander and Klein, developmental plasticity is absent inMassospondylus, which they found to grow along a specific growth trajectory with little variation in the growth rate and ultimate size of an individual.[71] In 2022, Chapelle and colleagues analysed multiple different bones from 27Massospondylus specimens and instead found substantial growth variation as inPlateosaurus, suggesting that developmental plasticity was widespread in basal sauropodomorphs. These authors also argue thatMassospondylus had determinate growth, contradicting the 1993 study of Chinsamy that suggested that growth was indeterminate. Growth had stopped in the oldest analysed specimen, which was estimated at 20 years old.[72]
%2c_Golden_Gate_National_Park%2c_South_Africa%2c_Early_Jurassic_-_Royal_Ontario_Museum_-_DSC00145.JPG)
Although the Rooidraai nesting site was already discovered by Kitching in 1976, the embryos where not described before 2005.[73] After additional excavations at the site between 2005 and 2012, Reisz and colleagues reported that 10 egg clutches from at least four fossiliferous horizons had been found, with up to 34 eggs per clutch, and that more clutches are likely present at the site. According to these authors, this indicates that this breeding site wasused repeatedly bygroups of animals, representing the oldest evidence of these behaviours. Sedimentary structures indicate that the breeding area was in the vicinity of a lake and has been repeatedly flooded. The arrangement of the eggs in tight rows might indicates that the eggs were pushed into this position by the adults, butnest structures are not preserved.[74]
Massospondylus eggs are amongst the oldest knownamniote eggs from the fossil record, together with the roughly contemporaneous eggs ofLufengosaurus andMussaurus. The eggshell consisted of a thick membrane covered by a layer ofcalcite that was very thin, less than 0.1 mm (0.0039 in), and had a rugged surface with few, unevenly distributed pores.[75][74][12] Later dinosaurs had much thicker calcite layers, which must have evolvedindependently in the different groups. According to a 2019 study by Koen Stein and colleagues, the eggs were probably rigid rather than flexible despite their thin calcitic layers. This is because the calcite crystals interlocked with each other, and because the fossil eggshells retained their original shape.[75] In contrast, a 2020 study byMark Norell and colleagues argued that the eggshell of early dinosaurs such asMassospondylus was soft, as the eggshell microstructure resembles that of the soft eggs of modern turtles.[76] The thin shells allowed for gas exchange even in a low-oxygen andcarbon dioxide-rich environment, which indicates that the eggs were at least partly buried in the substrate.[74]
The embryos are amongst the oldest dinosaur embryos ever found.[73][e][11] The most complete embryonic skeleton is stillarticulated and belonged to an individual measuring about 8.1 cm (3.2 in) insnout-vent length (body length excluding the incompletely preserved tail).[73] In 2010, Reisz and colleagues stated that five of the seven eggs contained embryonic remains, but in 2020, Chapelle and colleagues determined that such remains are present in only three of the eggs. The empty eggs could have resulted from various factors such as lack offertilisation, death of the embryo before the skeletonossified, or loss during fossilisation.[78] While the skeletal features of the embryos 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 to 39% of the entire skull length. The neck was short, in contrast 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 and the head was proportionally very large.[73]
In their 2005 study, Reisz and colleages suggested that the embryos were close to hatching based on their size in relation to the size of the eggs and their advanced ossification. Because the embryos lacked well-developed teeth and probably could not move around efficiently due to their body proportions, these authors proposed that they had no way of feeding themselves after hatching and possibly requiredparental care.[45][73] In their 2020 study, Chapelle and colleagues found that theMassospondylus embryos only completed about 60% of theirincubation period, as modern animals show a comparable degree of ossification of various skull bones at this stage. These researchers also detected null-generation teeth – small and simple teeth without function that would be replaced by functional teeth before hatching – again suggesting an early developmental stage of the embryos.[78] In 2025, Ethan Mooney and colleagues described an additional clutch of embryo-containing eggs that had already been collected by Kitching but not yet beenprepared and analysed. These embryos are slightly larger and more developed than the other embryos from the site, but their eggs had thinner shells, suggesting that eggshell was gradually resorbed as the embryo grew, as is the case with modern birds.[12]
In 2005, Reisz and colleagues suggested that newly hatchedMassospondylus must have been quadrupedal due to their long forelimbs and large heads, unlike the bipedal adults. The quadrupedality of the hatchings suggests that the quadrupedal posture of latersauropods may have evolved from retention of juvenile characteristics in adult animals, an evolutionary phenomenon known aspaedomorphosis.[73] Hatchlings are known from a second sauropodomorph,Mussaurus; these remains resemble those of the embryonicMassospondylus, suggesting that quadrupedality was present in newly hatchedMussaurus and presumably other basal sauropodomorphs as well.[45][11] In 2012, Reisz and colleagues suggested that tracks at the same site at which the embryos were discovered were produced by juvenileMassospondylus. These tracks include both pes (hindfoot) and manus (hand) tracks, with the manus tracks rotated outwards, suggesting a quadrupedal trackmaker with unpronated hands. Only the base of the thumb is impressed, suggesting that the enlarged thumb claw was held clear off the ground. The tracks vary in size but reach up to 15 mm (0.59 in) in length, larger than the estimated 7 mm (0.28 in) of a freshly hatched individual. Reisz and colleagues therefore speculated thatMassospondylus hatchlings remained at the nest sites at least until they had doubled in size.[74]
In 2019, James Neenan and colleagues tested the postural shift hypothesis by analysing thebony labyrinth of theinner ear based oncomputed microtomography scans of eight skulls covering the age spectrum from embryo to adult. The labyrinth houses thesense of balance, and one of its three canals (the lateral semicircular canal) is roughly horizontal when the head is in an alert posture in modern animals. Since Neenan and colleagues did not observe a change in orientation of this canal during growth, no support for a postural shift was found.[79] In a 2020 study, Chapelle and colleagues also presented evidence against the postural shift hypothesis. These researchers argued that limb length ratios cannot reliably predict posture, and instead proposed an alternative method based on the minimum circumferences of the humeri and femora. Although the posture of the analysedMassospondylus embryo was found to be ambiguous, the hatchling (SAM-PK-K413) was found to be bipedal. This hatchling would have been the size of a newly hatched individual, suggesting thatMassospondylus was bipedal at all ages.Mussaurus, in contrast, was confirmed to show a postural shift from juvenile to adult.[80] In their 2025 study, Mooney and colleagues argued that the humerus shaft of the hatchling is incompletely preserved, so that posture cannot be reliably estimated based on minimum shaft circumferences for this key individual. These authors estimated that the forelimb is 71% of the hindlimb length in a smaller embryo, 69% in their newly described larger embryo, 58% in the smallest hatchling, and 44% in the neotype specimen, the largest known individual. These estimates suggest that the forelimb shortened during growth, which supports the postural shift hypothesis.[12]
MostMassospondylus remains have been found in the upperElliot Formation and theClarens Formation of South Africa and Lesotho, which are part of theStormberg Group within theKaroo Supergroup. Theseformations were deposited during theHettangian,Sinemurian, andPliensbachian ages of theEarly Jurassic, ca. 201–184 million years ago.[81]Massospondylus has also been found in theForest Sandstone and theMpandi Formation of Zimbabwe, which are thought to be contemporaneous with the upper Elliot and Clarens formations.[8]: 114
Massospondylus is known from numerous almost complete skeletons, including at least 13 reasonably complete skulls and thousands of isolated bones and fragments.[8]: 114 [15]: 1 This wealth of material makesMassospondylus one of the best-known sauropodomorphs from the Early Jurassic. Because of its great abundance, it is used as the defining taxon of abiozone, theMassospondylus Range Zone, which is the uppermost such zone in the Karoo Supergroup. The presence of its fossils has been used todetermine the relative ages of sedimentary rocks.[8]: 114 [4]
During the deposition of the Stormberg Group, the climate became gradually drier. The oldest part of the group (theMolteno Formation) consists ofsandstones that weredeposited by rivers and show evidence of heavy rainfall. As the Elliot Formation was deposited, the climate becamesemi-arid and the environment was characterised by short-lived rivers and lakes that deposited sandstones andmudstones. During deposition of the upper Elliot Formation,aeolian (wind) erosion and sedimentation created depressions in whichplaya lakes formed. The overlying Clarens Formation consists mostly of aeolian sandstones deposited by dunes in a desert environment.[82]
Thefaunas andfloras of the Early Jurassic were similar worldwide, withconifers adapted for hot weather becoming the common plants;[83]basal sauropodomorphs and theropods were the main constituents of a worldwide dinosaur fauna.[84]Massospondylus was a contemporary oftemnospondyli; turtles; asphenodont; earlycrocodylomorphs;cynodonts; and earlymammaliforms.[85] Predatory dinosaurs included the small theropodMegapnosaurus as well as the 6-metre-long[86] theropodDracovenator, which might have preyed on the sauropodomorphs.[87] Several genera of earlyornithischians are known, such asLesothosaurus and theheterodontosauridsAbrictosaurus,Heterodontosaurus,Lycorhinus andPegomastax.[88][85][89] Until recently,M. carinatus was regarded as the only known sauropodomorph from the upper Elliot and Clarens formations.[8] However, newer finds revealed a diverse contemporary sauropodomorph fauna with at least seven additional species from the upper Elliot Formation, includingAardonyx celestae,Antetonitrus ingenipes,Ignavusaurus rachelis,Arcusaurus pereirabdalorum,Pulanesaura eocollum,Ngwevu intloko, as well as a second species ofMassospondylus,M. kaalae.[8]
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