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The first [[skeleton]] of ''Massospondylus'' was described by [[paleontology|paleontologist]] Sir [[Richard Owen]] in 1854,<ref>Owen, R. (1854). "Descriptive catalogue of the Fossil organic remains of Reptilia and Pisces contained in the Museum of the Royal College of Surgeons of England." London p. 1–184</ref> the name derived from the [[Ancient Greek|Greek]] terms ''masson'' 'longer'<ref name="Creisler">{{cite web| last =Creisler| first =Ben| authorlink =| title =Dinosauria Translation and Pronunciation Guide| work =| publisher =Dinosauria.com| date =2003| url =http://www.dinosauria.com/dml/names/dinom.htm| format =| doi =| accessdate =2007-11-23}}</ref> and ''sphondylos''/σφονδυλος 'vertebra'.<ref name="Liddell 1980">{{cite book | author = [[Henry Liddell|Liddell, Henry George]] and [[Robert Scott (philologist)|Robert Scott]] | year = 1980 | title = [[A Greek-English Lexicon]] (Abridged Edition) | publisher = [[Oxford University Press]] | location = United Kingdom | id = ISBN 0-19-910207-4}}</ref> The original [[holotype]] material was part of the [[Royal College of Surgeons of England|Royal College of Surgeons]] collection and was destroyed in [[World War II]]; only casts remain.<ref name=DFG97>{{cite book|chapter=Massospondylus |last=Glut |first=Donald F. |authorlink=Donald F. Glut |title=Dinosaurs: The Encyclopedia |year=1997 |publisher=McFarland & Co |location=Jefferson, North Carolina |pages=581–586 |isbn=0-89950-917-7}}</ref> Possible ''Massospondylus'' remains have been found in the [[Upper Elliot Formation]], the [[Clarens Formation]], and the [[Bushveld Sandstone]] of [[South Africa]] and [[Lesotho]]; the [[Forest Sandstone]] and the [[Upper Karroo Sandstone]] of [[Zimbabwe]]; the Cañon del Colorado Formation or [[El Tranquilo Formation]] of [[Argentina]];<!--Dino II says Cañon del Colorado, Aragosaurus.com says El Tranquilo, both using Martinez as the base ref; go figure--> and the [[Kayenta Formation]] of [[Arizona]]. These remains consist of at least 80 partial skeletons and four skulls, representing both juveniles and adults.<ref name="Dinosauria"/>
The first [[skeleton]] of ''Massospondylus'' was described by [[paleontology|paleontologist]] Sir [[Richard Owen]] in 1854,<ref>Owen, R. (1854). "Descriptive catalogue of the Fossil organic remains of Reptilia and Pisces contained in the Museum of the Royal College of Surgeons of England." London p. 1–184</ref> the name derived from the [[Ancient Greek|Greek]] terms ''masson'' 'longer'<ref name="Creisler">{{cite web| last =Creisler| first =Ben| authorlink =| title =Dinosauria Translation and Pronunciation Guide| work =| publisher =Dinosauria.com| date =2003| url =http://www.dinosauria.com/dml/names/dinom.htm| format =| doi =| accessdate =2007-11-23}}</ref> and ''sphondylos''/σφονδυλος 'vertebra'.<ref name="Liddell 1980">{{cite book | author = [[Henry Liddell|Liddell, Henry George]] and [[Robert Scott (philologist)|Robert Scott]] | year = 1980 | title = [[A Greek-English Lexicon]] (Abridged Edition) | publisher = [[Oxford University Press]] | location = United Kingdom | id = ISBN 0-19-910207-4}}</ref> The original [[holotype]] material was part of the [[Royal College of Surgeons of England|Royal College of Surgeons]] collection and was destroyed in [[World War II]]; only casts remain.<ref name=DFG97>{{cite book|chapter=Massospondylus |last=Glut |first=Donald F. |authorlink=Donald F. Glut |title=Dinosaurs: The Encyclopedia |year=1997 |publisher=McFarland & Co |location=Jefferson, North Carolina |pages=581–586 |isbn=0-89950-917-7}}</ref> Possible ''Massospondylus'' remains have been found in the [[Upper Elliot Formation]], the [[Clarens Formation]], and the [[Bushveld Sandstone]] of [[South Africa]] and [[Lesotho]]; the [[Forest Sandstone]] and the [[Upper Karroo Sandstone]] of [[Zimbabwe]]; the Cañon del Colorado Formation or [[El Tranquilo Formation]] of [[Argentina]];<!--Dino II says Cañon del Colorado, Aragosaurus.com says El Tranquilo, both using Martinez as the base ref; go figure--> and the [[Kayenta Formation]] of [[Arizona]]. These remains consist of at least 80 partial skeletons and four skulls, representing both juveniles and adults.<ref name="Dinosauria"/>


The reports of ''Massospondylus'' from Argentina include several partial skeletons, including at least one skull, from the [[Early Jurassic|Lower Jurassic]] Cañon del Colorado Formation of [[San Juan, Argentina|San Juan]], Argentina.<ref name="Dinosauria"/> The report of ''Massospondylus'' from Arizona's Kayenta Formation is based on a skull described in 1985. The skull of the Kayenta specimen from Arizona is 25% larger than the largest skull from any African specimen. The Kayenta specimen possesses four teeth in the [[premaxilla]] and sixteen in the [[maxilla]]. Uniquely among dinosaurs, it also had tiny 1 [[millimetre]]-long palatal teeth.<ref name="Attridgeetal85">{{cite journal| last =Attridge| first =J.| authorlink =| coauthors =Crompton, A.W.; and Jenkins, Farish A. Jr. | title =The southern Liassic prosauropod ''Massospondylus'' discovered in North America| journal =Journal of Vertebrate Paleontology| volume =5| issue =2| pages =128–132| publisher =| location =| date =1985| url =| doi =| id =| accessdate = }}</ref> Recent restudy of African ''Massospondylus'' skulls, however, indicates that the Kayenta specimen does not pertain to ''Massospondylus''.<ref name=SRHR04>{{cite journal |last=Sues |first=H.-D. |coauthors=Reisz, R.R.; Hinic, S.; and Raath, M.A. |year=2004 |title=On the skull of ''Massospondylus carinatus'' Owen, 1854 (Dinosauria: Sauropodomorpha) from the Elliot and Clarens formations (Lower Jurassic) of South Africa |journal=Annals of Carnegie Museum |volume=73 |issue=4 |pages=239–257}}</ref>
The reports of ''Massospondylus'' from Argentina include several partial skeletons, including at least one skull, from the [[Early Jurassic|Lower Jurassic]] Cañon del Colorado Formation of [[San Juan, Argentina|San Juan]], Argentina.<ref name="Dinosauria"/> The report of ''Massospondylus'' from Arizona's Kayenta Formation is based on a skull described in 1985. The skull of the Kayenta specimen from Arizona is 25% larger than the largest skull from any African specimen. The Kayenta specimen possesses four teeth in the [[premaxilla]] and sixteen in the [[maxilla]]. Uniquely among dinosaurs, it also had tiny one–[[millimetre]]-long palatal teeth.<ref name="Attridgeetal85">{{cite journal| last =Attridge| first =J.| authorlink =| coauthors =Crompton, A.W.; and Jenkins, Farish A. Jr. | title =The southern Liassic prosauropod ''Massospondylus'' discovered in North America| journal =Journal of Vertebrate Paleontology| volume =5| issue =2| pages =128–132| publisher =| location =| date =1985| url =| doi =| id =| accessdate = }}</ref> Recent restudy of African ''Massospondylus'' skulls, however, indicates that the Kayenta specimen does not pertain to ''Massospondylus''.<ref name=SRHR04>{{cite journal |last=Sues |first=H.-D. |coauthors=Reisz, R.R.; Hinic, S.; and Raath, M.A. |year=2004 |title=On the skull of ''Massospondylus carinatus'' Owen, 1854 (Dinosauria: Sauropodomorpha) from the Elliot and Clarens formations (Lower Jurassic) of South Africa |journal=Annals of Carnegie Museum |volume=73 |issue=4 |pages=239–257}}</ref>


Many species have been named, although most are no longer considered valid. ''M. carinatus'', named by Richard Owen, is the [[type species]].<ref name="PaleobiologyDB">{{cite web| last =| first =| authorlink =| coauthors =| title =Massospondylus| work =| publisher =The Paleobiology Database| date =2007| url =http://paleodb.org/cgi-bin/bridge.pl?action=checkTaxonInfo&taxon_no=38642&is_real_user=1| format =| doi =| accessdate =2007-11-03}}</ref> Other named species include: ''M. browni'' ([[Harry Seeley|Seeley]], 1895),<ref name="Seeley1895">{{cite journal| last =Seeley| first =H.G.| authorlink =| coauthors =| title =On the type of the genus ''Massospondylus'' and on some Vertebrae and limb-bone of ''M. (?) browni''| journal =Annals and Magazine of Natural History| volume =15| issue =| pages =102–125| publisher =| location =| date =1895| url =| doi =| id =| accessdate = }}</ref> ''M. harriesi'' ([[Robert Broom|Broom]] 1911),<ref name="Broom11">{{cite journal| last =Broom| first =Robert| authorlink =| coauthors =| title =On the dinosaurs of the Stormberg, South Africa| journal =Annals of the South African Museum| volume =7| issue =4| pages =291–308| publisher =| location =| date =1911| url =| doi =| id =| accessdate = }}</ref> ''M. hislopi'' ([[Richard Lydekker|Lydekker]], 1890),<ref name="Lydekker">{{cite journal| last =Lydekker| first =Richard| authorlink =| coauthors =| title =Note on certain vertebrate remains from the Nagpur district| journal =Records of the Geological Survey of India| volume =23| issue =1| pages =21–24| publisher =| location =| date =1890| url =| doi =| id =| accessdate = }}</ref> ''M. huenei'' (Cooper, 1981),<ref name="Cooper">{{cite journal| last =Cooper| first =M.R.| authorlink =| coauthors =| title =The prosauropod dinosaur ''Massospondylus carinatus'' Owen from Zimbabwe: its biology, mode of life and phylogenetic significance| journal =Occasional Papers of the National Museums and Monuments of Rhodesia, Series B, Natural Sciences| volume =6| issue =10| pages =689–840| publisher =| location =| date =1981| url =| doi =| id =| accessdate = }}</ref> ''M. rawesi'' (Lydekker, 1890),<ref name="Lydekker"/> and ''M. schwarzi'' ([[Sydney H. Haughton|Haughton]], 1924).<ref name="Haughton1924">{{cite journal| last =Haughton| first =Sydney H.| authorlink =| coauthors =| title =The fauna and stratigraphy of the Stormberg Series| journal =Annals of the South African Museum| volume =12| issue =| pages =323–497| publisher =| location =| date =1924| url =| doi =| id =| accessdate = }}</ref>
Many species have been named, although most are no longer considered valid. ''M. carinatus'', named by Richard Owen, is the [[type species]].<ref name="PaleobiologyDB">{{cite web| last =| first =| authorlink =| coauthors =| title =Massospondylus| work =| publisher =The Paleobiology Database| date =2007| url =http://paleodb.org/cgi-bin/bridge.pl?action=checkTaxonInfo&taxon_no=38642&is_real_user=1| format =| doi =| accessdate =2007-11-03}}</ref> Other named species include: ''M. browni'' ([[Harry Seeley|Seeley]], 1895),<ref name="Seeley1895">{{cite journal| last =Seeley| first =H.G.| authorlink =| coauthors =| title =On the type of the genus ''Massospondylus'' and on some Vertebrae and limb-bone of ''M. (?) browni''| journal =Annals and Magazine of Natural History| volume =15| issue =| pages =102–125| publisher =| location =| date =1895| url =| doi =| id =| accessdate = }}</ref> ''M. harriesi'' ([[Robert Broom|Broom]] 1911),<ref name="Broom11">{{cite journal| last =Broom| first =Robert| authorlink =| coauthors =| title =On the dinosaurs of the Stormberg, South Africa| journal =Annals of the South African Museum| volume =7| issue =4| pages =291–308| publisher =| location =| date =1911| url =| doi =| id =| accessdate = }}</ref> ''M. hislopi'' ([[Richard Lydekker|Lydekker]], 1890),<ref name="Lydekker">{{cite journal| last =Lydekker| first =Richard| authorlink =| coauthors =| title =Note on certain vertebrate remains from the Nagpur district| journal =Records of the Geological Survey of India| volume =23| issue =1| pages =21–24| publisher =| location =| date =1890| url =| doi =| id =| accessdate = }}</ref> ''M. huenei'' (Cooper, 1981),<ref name="Cooper">{{cite journal| last =Cooper| first =M.R.| authorlink =| coauthors =| title =The prosauropod dinosaur ''Massospondylus carinatus'' Owen from Zimbabwe: its biology, mode of life and phylogenetic significance| journal =Occasional Papers of the National Museums and Monuments of Rhodesia, Series B, Natural Sciences| volume =6| issue =10| pages =689–840| publisher =| location =| date =1981| url =| doi =| id =| accessdate = }}</ref> ''M. rawesi'' (Lydekker, 1890),<ref name="Lydekker"/> and ''M. schwarzi'' ([[Sydney H. Haughton|Haughton]], 1924).<ref name="Haughton1924">{{cite journal| last =Haughton| first =Sydney H.| authorlink =| coauthors =| title =The fauna and stratigraphy of the Stormberg Series| journal =Annals of the South African Museum| volume =12| issue =| pages =323–497| publisher =| location =| date =1924| url =| doi =| id =| accessdate = }}</ref>

Revision as of 16:42, 2 December 2007

Massospondylus
Temporal range: Early Jurassic
A mounted Massospondylus skeleton at the Natural History Museum, London, showing outdated pre-2007 pose.
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Class:
Sauropsida
Superorder:
Dinosauria
Order:
Saurischia
Suborder:
Sauropodomorpha
Infraorder:
Prosauropoda
Family:
Massospondylidae
Genus:
Massospondylus

Owen, 1854
Species

M. carinatus Owen, 1854 (type)

Synonyms
  • ?Aristosaurus Hoepen, 1920
  • ?Dromicosaurus Hoepen, 1920
  • ?Gryponyx Broom, 1912
  • ?Hortalotarsus Seeley, 1894
  • ?Leptospondylus Owen, 1895
  • ?Pachyspondylus Owen, 1854

Massospondylus (from Greek, meaning "elongated vertebra"), is a genus of prosauropod dinosaur from the early Jurassic Period (Hettangian to Pliensbachian ages, around 200 to 183 million years ago). It was described by Sir Richard Owen in 1854 from remains found in South Africa, and is thus one of the first dinosaurs to have been named. Fossils have since been found in Lesotho, Zimbabwe, and other parts of South Africa. Further material from Arizona's Kayenta Formation, India, and Argentina has been ascribed to this genus, but may not belong to Massospondylus. The type, and only universally recognized species, is M. carinatus, although six other species have been named during the past 150 years. The family name Massospondylidae was once erected for the genus, but because knowledge of prosauropod relationships is in a state of flux, it is unclear which other dinosaurs, if any, belong in a natural grouping of massospondylids.

Long depicted as quadrupedal, a recent study indicates Massospondylus was a biped. It was probably a plant eater (herbivore), although it is speculated that the prosauropods may have been omnivorous. This four meter long animal had a long neck and tail with a small head and slender body. It bore a sharp thumb claw on each of its forefeet, used in defense or feeding. Recent studies indicate Massospondylus grew steadily, possessed air sacs similar to those of birds, and may have cared for its young.

Description

This artist's impression of Massospondylus depicts the animal as bipedal. Recent studies indicate Massospondylus and its sister taxon Plateosaurus could not move about quadrupedally.

Massospondylus was a mid-sized prosauropod at around 4 meters (13 ft) long and weighed around 135 kilograms (300 lb),[1] possibly reaching a length of 6 meters (20 ft).[2] Although long assumed to have been quadrupedal, a recent anatomical study of the forelimbs has questioned this, arguing that their range of motion precludes effective habitual quadrupedal gait. The study also ruled out the possibility of "knuckle-walking" and other forms of locomotion that would avoid the issue of the limited ability of Massospondylus to pronate its hands. Although its mass suggests a quadrupedal nature, it would have been restricted to its hind legs for locomotion.[3]

Massospondylus was a typical prosauropod in most other respects. It possessed a slender body and long neck, with around nine long cervical (neck) vertebrae, 13 dorsal (back) vertebrae, three sacral (hip) vertebrae, and at least 40 caudal (tail) vertebrae. The pubis faced forward, as with most saurischians. It had a slighter build than that of Plateosaurus, an otherwise similar prosauropod dinosaur.[4] A recent discovery shows that Massospondylus possessed well-developed clavicles, joined in a furcula-like arrangement, suggesting both that it had immobile shoulder blades, and that clavicles were not rudimentary and nonfunctional in those dinosaurs that did not have true furculae. This discovery also indicates that the furcula of birds is derived from clavicles.[5]

Like Plateosaurus, it had five digits on each foot, with a large thumb claw used for feeding or defense against predators. The fourth and fifth digits of the forepaws were tiny, giving the forepaws a lopsided look. The 2007 study indicated that Massospondylus held its manus (hands) in a semi-supinated ("prayer-like") orientation, with the palmar surfaces facing one another; the wrist was never found rotated in articulated (still-connected) fossil specimens.[3]

The small head of Massospondylus was approximately half the length of the femur. The skull bore two pairs of temporal fenestrae, two almost circular eye sockets, and large elliptical nares. The orbit was proportionally larger in Massospondylus than in related genera such as Plateosaurus. A pair of antorbital fenestrae were between the eyes and the nose, which were smaller than those seen in Plateosaurus. Behind the eyes was a fourth pair of holes called the infratemporal fenestrae. These holes reduced the weight of the skull, and were filled with nonbony tissue in the living animal.[4] The shape of the skull is traditionally restored as wider and shorter than that of Plateosaurus, but this appearance may just be due to differential crushing experienced by the various specimens.[4] Some features of the skull are variable between individuals, for example the thickness of the upper border of the orbit and the height of the posterior maxilla. These differences may be due to sexual dimorphism[6] or individual variation.[7]

As with other prosauropods, it has been proposed that Massospondylus had cheeks. This is based on there being 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.[4] Crompton and Attridge (1986) 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 and account for tooth wear on the teeth at the tip of the snout.[8] However, this was later shown to be a misinterpretation based on crushing in a top-bottom plane. Skulls not crushed in this orientation do not show an overbite.[6] There also seems to be some variation of tooth morphology, based on the position of teeth in the jaw, although this is not as pronounced as the specialization of teeth in Heterodontosaurus. Teeth occupying a position closer to the front of the snout had round cross-sections and tapered to points, unlike the back teeth, which were spatulate and had oval cross-sections.[4]

Discovery and species

The first skeleton of Massospondylus was described by paleontologist Sir Richard Owen in 1854,[9] the name derived from the Greek terms masson 'longer'[10] and sphondylos/σφονδυλος 'vertebra'.[11] The original holotype material was part of the Royal College of Surgeons collection and was destroyed in World War II; only casts remain.[12] Possible Massospondylus remains have been found in the Upper Elliot Formation, the Clarens Formation, and the Bushveld Sandstone of South Africa and Lesotho; the Forest Sandstone and the Upper Karroo Sandstone of Zimbabwe; the Cañon del Colorado Formation or El Tranquilo Formation of Argentina; and the Kayenta Formation of Arizona. These remains consist of at least 80 partial skeletons and four skulls, representing both juveniles and adults.[4]

The reports of Massospondylus from Argentina include several partial skeletons, including at least one skull, from the Lower Jurassic Cañon del Colorado Formation of San Juan, Argentina.[4] The report of Massospondylus from Arizona's Kayenta Formation is based on a skull described in 1985. The skull of the Kayenta specimen from Arizona is 25% larger than the largest skull from any African specimen. The Kayenta specimen possesses four teeth in the premaxilla and sixteen in the maxilla. Uniquely among dinosaurs, it also had tiny one–millimetre-long palatal teeth.[13] Recent restudy of African Massospondylus skulls, however, indicates that the Kayenta specimen does not pertain to Massospondylus.[14]

Many species have been named, although most are no longer considered valid. M. carinatus, named by Richard Owen, is the type species.[15] Other named species include: M. browni (Seeley, 1895),[16] M. harriesi (Broom 1911),[17] M. hislopi (Lydekker, 1890),[18] M. huenei (Cooper, 1981),[19] M. rawesi (Lydekker, 1890),[18] and M. schwarzi (Haughton, 1924).[20]

M. browni, M. harriesi, and M. schwarzi were all found in the Upper Elliot Formation of Cape Province, South Africa. All three are based on scrappy material, and were regarded as indeterminate in the most recent review.[4] M. browni is based on two cervical, two back, and three caudal vertebrae and miscellaneous hindlimb elements.[16] M. harriesi is known from a forelimb.[17] M. schwarzi is known from an incomplete hindlimb and sacrum.[20] M. hislopi and M. rawesi were named from fossils found in India.[18] M. hislopi is based on vertebrae from the Upper Triassic Maleri Formation of Andhra Pradesh, whereas M. rawesi is based on a tooth from the Upper Cretaceous Takli Formation of Maharashtra.[21] M. hislopi was tentatively retained as an indeterminate sauropodomorph in the latest review,[4] but M. rawesi may be a theropod[22] or nondinosaur.[12] M. huenei is a combination derived by Cooper for Lufengosaurus huenei, as he considered Lufengosaurus and Massospondylus to be synonyms.[19] This synonymy is no longer accepted.[4]

Several dinosaurs are often considered synonymous with Massospondylus. These include Aristosaurus, Dromicosaurus, Gryponyx, Hortalotarsus, Leptospondylus, and Pachyspondylus, which are dubious names of little scientific value.[19] Under the rules of zoological nomenclature, these names are junior synonyms. They were named after Massospondylus was described in a scientific paper; thus the name Massospondylus takes priority.

Classification

Massospondylus is a prosauropod, a grouping of early saurischian dinosaurs that lived during the Triassic and Jurassic, but which had died out by the end of the Jurassic. Other members of the group include Plateosaurus,[4] Yunnanosaurus,[4] and Riojasaurus.[23] 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). Exactly which animals constitute a monophyletic (natural grouping) of prosauropods is unclear. Yates and Kitching (2003) published a clade consisting of Riojasaurus, Plateosaurus, Coloradisaurus, Massospondylus, and Lufengosaurus.[24] 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.[4] Wilson (2005) considered Massospondylus, Jingshanosaurus, Plateosaurus, and Lufengosaurus a natural group, with Blikanasaurus and Antetonitrus possible sauropods.[25] Bonnan and Yates (2007) considered Camelotia, Blikanasaurus and Melanorosaurus possible sauropods.[26] 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.[27]

Massospondylus is the type genus of the proposed family Massospondylidae, to which it gives its name. The Massospondylidae family may also include Yunnanosaurus[28] although Lu et al. (2007) placed Yunnanosaurus in its own family.[29] Yates (2007) considered Massospondylus, Coloradisaurus, and Lufengosaurus massospondylids, with Yunnanosaurus in Anchisauria.[27]

Paleoecology

The faunas and floras of the Early Jurassic were similar worldwide, with conifers adapted for hot weather becoming the common plants,[30] and prosauropods and basal theropods the main constituents of a worldwide dinosaur fauna.[31] African Massospondylus was a contemporary of early crocodylomorphs, tritylodontid and trithelodontid therapsids, morganucodontid mammals,[4] and dinosaurs including the small theropod Megapnosaurus rhodesiensis, a species of Melanorosaurus (M. thabanensis) and several genera of early ornithischians, such as Lesothosaurus and the heterodontosaurids Abrictosaurus, Heterodontosaurus, and Lycorhinus.[32]

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,[33] diet,[34] posture,[3] reproduction,[35] and respiration.[36]

A 2007 study suggested that Massospondylus may have used its short arms in defense from 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 or to strip plant material from trees.[3]

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 Plateosaurus and Massospondylus. The study indicated that Massospondylus grew along a specific growth trajectory with little variation in the growth rate and ultimate size of an individual.[33] Another study indicated that Massospondylus grew at a maximum rate of 34.6 kg year–1 and was still growing at around 15 years of age.[37]

Diet

Prosauropods such as Massospondylus may have been either herbivorous or possibly omnivorous. As recently as the 1980s, there was debate amongst paleontologists concerning possible carnivory in prosauropods.[19][13] However, the hypothesis of carnivorous prosauropods has been discredited, and all recent studies favor a herbivorous or omnivorous lifestyle for these animals.[4] Gastroliths (gizzard stones) have been found in association with Massospondylus fossils,[34] indicating Massospondylus swallowed stones to aid in digestion.

Reproduction

An artist's depiction of a juvenile Massospondylus, shown here as a quadruped

In the 1970s, seven 190-million year old Massospondylus eggs were found in Golden Gate Highlands National Park in South Africa by James Kitching, who identified them as most likely belonging to Massospondylus. It took nearly 30 years before extraction was started on the fossils of the 15 centimeter (6 in) long embryos. They remain the oldest dinosaur embryos ever found. Notably, the near-hatchlings had no teeth, suggesting they had no way of feeding themselves. Scientists speculate that after-birth care might have been necessary based on the body proportions and the lack of teeth. The four legs of the near-hatchlings were of equal length, indicating that newly hatched Massospondylus were quadrupedal. The skull and eye were proportionately over-sized, as in other very young vertebrates. The quadrupedality of the hatchlings suggest that the quadrupedal posture of later sauropods may have evolved from retention of juvenile characteristics in adult animals, an evolutionary phenomenon known as pedomorphosis.[35]

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 avians, 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. This complex method of respiration is very efficient.[38] Prosauropods were unusual as the only major group of saurischians that lacked an extensive system of pneumatic foramina. Although possible pneumatic indentations have been found in Plateosaurus and Thecodontosaurus, these hollows were very small. One study in 2007 concluded that it was likely that prosauropods like Massospondylus had abdominal and cervical air sacs because of the good evidence for them in sister taxa (theropods and sauropods). The study concluded that it was impossible to determine whether prosauropods had a bird-like flow-through lung, but that the air sacs were almost certainly present.[36]

See also

References

  1. ^ Seebacher, Frank (2001). "A new method to calculate allometric length-mass relationships of dinosaurs". Journal of Vertebrate Paleontology. 21 (1): 51–60. {{cite journal}}: |access-date= requires |url= (help); Cite has empty unknown parameter: |coauthors= (help)
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Further reading

  • Chinsamy, A. (1992). "Ontogenetic growth of the dinosaurs Massospondylus carinatus and Syntarsus rhodesiensis". In: Abstracts of papers. Society of Vertebrate Paleontology, fifty-second annual meeting. Royal Ontario Museum Toronto, Ontario, Journal of Vertebrate Paleontology, 12, 3, 23A.
  • Gow, C. E. (1990). "Morphology and growth of the Massospondylus braincase (Dinosauria, Prosauropoda)". Palaeontologia Africana, 27, 59–75.
  • Gow, C.E., Kitching, J.W. & Raath, M.A. (1990). "Skulls of the prosauropod dinosaur Massospondylus carinatus Owen in the collections of the Bernard Price Institute for Palaeontological Research". Palaeontologia Africana, 27, 45–58.
  • Hinic, S. (2002). "The cranial anatomy of Massospondylus carinatus Owen, 1854 and its implications for prosauropod phylogeny". Journal of Vertebrate Paleontology. Abstracts of papers. Society of Vertebrate Paleontology, 22, Supplement to number 3, 65A.
  • Martínez, R. (1999). "The first South American record of Massospondylus (Dinosauria: Sauropodomorpha)". Journal of Vertebrate Paleontology, Abstracts of papers. Society of Vertebrate Paleontology, 20–23 October, 19, Suppl. 3, 61A.
  • Martínez, R.N. (1999). "Massospondylus (Dinosauria sauropodomorpha) in northwestern Argentina". Abstracts VII International Symposium on Mesozoic Terrestrial Ecosystems, Buenos Aires, 40.

External links

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