Sauropodomorpha

Sauropodomorpha (/ˌsɔːrəˌpɒdəˈmɔːrfə/[1] SOR-ə-POD-ə-MOR-fə; from Greek, meaning "lizard-footed forms") is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had long necks and tails, were quadrupedal, and became the largest animals to ever walk the Earth. The "prosauropods", which preceded the sauropods, were smaller and were often able to walk on two legs. The sauropodomorphs were the dominant terrestrial herbivores throughout much of the Mesozoic Era, from their origins in the mid-Triassic (approximately 230 Ma) until their decline and extinction at the end of the Cretaceous (approximately 66 Ma).

Sauropodomorphs
Temporal range: Late TriassicLate Cretaceous, 231.4–66 Ma
Plateosaurus Skelett 2
Mounted skeleton of Plateosaurus engelhardti at Eberhard-Karls-University
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Saurischia
Suborder: Sauropodomorpha
Huene, 1932
Subgroups

Description

Nigersaurus taqueti skull
Skull of Nigersaurus taqueti and head posture in sauropodomorphs

Sauropodomorphs were adapted to browsing higher than any other contemporary herbivore, giving them access to high tree foliage. This feeding strategy is supported by many of their defining characteristics, such as: a light, tiny skull on the end of a long neck (with ten or more elongated cervical vertebrae) and a counterbalancing long tail (with one to three extra sacral vertebrae).

Their teeth were weak, and shaped like leaves or spoons (lanceolate or spatulate). Instead of grinding teeth, they had stomach stones (gastroliths), similar to the gizzard stones of modern birds and crocodiles, to help digest tough plant fibers. The front of the upper mouth bends down in what may be a beak.

One of the earliest known sauropodomorphs, Saturnalia, was small and slender (1.5 metres, or 5 feet long); but, by the end of the Triassic, they were the largest dinosaurs of their time, and throughout the Jurassic and Cretaceous they kept on growing. Ultimately the largest sauropods, like Supersaurus, Diplodocus hallorum, Patagotitan, and Argentinosaurus, reached 30–40 metres (98–131 ft) in length, and 60,000–100,000 kilograms (65–110 US short tons) or more in mass.

Initially bipedal, as their size increased they evolved a four-legged graviportal gait adapted only to walking slowly on land, like elephants. The early sauropodomorphs were most likely omnivores as their shared common ancestor with the other saurischian lineage (the theropods) was a carnivore. Therefore, their evolution to herbivory went hand in hand with their increasing size and neck length.

They also had large nostrils (nares), and retained a thumb (pollex) with a big claw, which may have been used for defense — though their primary defensive adaptation was their extreme size.

Distinguishing anatomical features

Sauropodomorphs can be distinguished as a group on the basis of some of the following synapomorphies:[2]

  • The presence of large nares.
  • The distal part of the tibia is covered by an ascending process of the astragalus.
  • Their hind limbs are short when compared to their torso length.
  • The presence of three or more sacral vertebrae.
  • The teeth are thin, flat and are spatula-like, with bladed and serrated crowns.
  • The presence of a minimum of 10 cervical vertebrae that are typically elongated
  • The presence of 25 presacral vertebrae
  • The manus had a large digit I

Evolutionary history

Among the very first dinosaurs to evolve in the Late Triassic Period,[3] about 230 million years ago (Mya), they became the dominant herbivores by halfway through the late Triassic (during the Norian stage). Their perceived decline in the early Cretaceous is most likely a bias in fossil sampling, as most fossils are known from Europe and North America. Sauropods were still the dominant herbivores in the Gondwanan landmasses, however. The spread of flowering plants (angiosperms) and "advanced" ornithischians, another major group of herbivorous dinosaurs (noted for their highly developed chewing mechanisms), are most likely not a major factor in sauropod decline in the northern continents. Like all non-avian dinosaurs, the sauropodomorphs became extinct 66 Mya, during the Cretaceous–Paleogene extinction event.

The earliest and most basal sauropodomorphs known are Chromogisaurus novasi and Panphagia protos, both from the Ischigualasto Formation, dated to 231.4 million years ago (late Ladinian age of the Middle Triassic according to the ICS;[4] alternately called the early Carnian age of the Late Triassic in the system used by the Geological Society of America).[5][6] Some studies have found Eoraptor lunensis (also from the Ischigualasto Formation), traditionally considered a theropod, to be an early member of the sauropodomorph lineage, which would make it the most basal sauropodomorph known.[7]

Classification

Panphagia NT
Restoration of Panphagia, one of the most basal sauropodomorphs known.
Sellosaurus
Plateosaurus is a well-known prosauropod.

Sauropodomorpha is one of the two major clades within the order Saurischia. The sauropodomorphs' sister group, the Theropoda, includes bipedal carnivores like Velociraptor and Tyrannosaurus; as well as birds. However, sauropodomorphs also share a number of characteristics with the Ornithischia, so a small minority of palaeontologists, like Bakker, have historically placed both sets of herbivores within a group called "Phytodinosauria" or "Ornithischiformes".

In Linnaean taxonomy, Sauropodomorpha (which means "lizard feet forms") is either a suborder or is left unranked. It was originally established by Friedrich von Huene in 1932, who broke it into two groups: the basal forms within Prosauropoda, and their descendants, the giant Sauropoda.

Phylogenetic analyses by Adam Yates (2004, 2006) and others firmly placed Sauropoda within a paraphyletic "Prosauropoda". Recent cladistic analyses suggest that the clade Prosauropoda, which was named by Huene in 1920 and was defined by Sereno, in 1998, as all animals more closely related to Plateosaurus engelhardti than to Saltasaurus loricatus,[8] is a junior synonym of Plateosauridae as both contain the same taxa.[9][10]

Most modern classification schemes break the prosauropods into a half-dozen groups that evolved separately from one common lineage. While they have a number of shared characteristics, the evolutionary requirements for giraffe-like browsing high in the trees may have caused convergent evolution, where similar traits evolve separately because they faced the same evolutionary pressure, instead of (homologous) traits derived from a shared ancestor.[11]

Phylogeny

Sauropodomorpha skull comparison
Skull comparison of several sauropodomorphs

Cladogram after Novas et al., 2011:[10]

Sauropodomorpha
Guaibasauridae

Unnamed form. Fossil ISI R277

Panphagia

Guaibasaurus

Saturnaliinae

Chromogisaurus

Saturnalia

Pantydraco

Thecodontosaurus

Nambalia

Efraasia

Plateosauravus

Ruehleia

Plateosauria

Plateosauridae

Massopoda

Riojasauridae

Anchisauria

Massospondylidae

Below is a cladogram of basal sauropodomorpha after Otero et al., 2015.[12]

Saurischia
Herrerasauridae

Herrerasaurus

Staurikosaurus

Eoraptor

Eusaurischia

Agnosphitys

Theropoda

Guaibasaurus

Chindesaurus

Neotheropoda

Sauropodomorpha
Saturnaliinae

Saturnalia

Chromogisaurus

Pantydraco

Thecodontosaurus

Efraasia

Plateosauravus

Plateosauria

Ruehleia

Plateosauridae

Unaysaurus

Plateosaurus

Massopoda
Riojasauridae

Eucnemesaurus

Riojasaurus

Sarahsaurus

Massospondylidae

Lufengosaurus

Glacialisaurus

Coloradisaurus

Massospondylus

Adeopapposaurus

Leyesaurus

Jingshanosaurus

Yunnanosaurus

Seitaad

Anchisauria

Anchisaurus

Sauropodiformes

Mussaurus

Aardonyx

Leonerasaurus

Sefapanosaurus

Melanorosaurus

Sauropoda

A large phylogenetic analysis of early dinosaurs published by Matthew Baron, David Norman and Paul Barrett (2017) in the journal Nature redefined Sauropodomorpha and Saurischia and recovered Herrerasauridae as the sister group to Sauropodomorpha within Saurischia. This resulted from the proposed removal of Theropoda from Saurischia and the formation of Ornithoscelida, a clade containing Theropoda and Ornithischia.[13]

Paleobiology

Comparisons between the scleral rings of several sauropodmorph genera (Diplodocus, Lufengosaurus, Nemegtosaurus, Plateosaurus, and Riojasaurus) and modern birds and reptiles suggest that they may have been cathemeral, active throughout the day at short intervals.[14]

Sauropodomorphs reached the age of sexual maturity well before they were fully-grown adults.[15][16] A study by Griebeler et al. (2013) concluded that the maximum growth rates of sauropodomorphs were comparable to those of precocial birds and the black rhinoceros but lower than the growth rates of average mammals.[16]

A long-standing hypothesis has been that early sauropodomorphs were carnivorous, as expected for most early dinosaurs. This hypothesis is supported by the current basalmost sauropodomorph, Buriolestes, and its plesiomorphic, theropod-like teeth.[17] The teeth of more derived sauropodomorphs such as Eoraptor, Panphagia, and Pampadromaeus are better-suited for herbivorous (or possibly omnivorous) diets.[18] Regardless of the phylogenetic position of herrerasaurids or Eoraptor (which are in flux),[19][20][18] ancestral state reconstructions recover carnivory as being ancestral to sauropodomorphs.[17]

References

  1. ^ Cf. "sauropodomorph - definition of sauropodomorph in English from the Oxford dictionary". OxfordDictionaries.com. Retrieved 2016-01-20.
  2. ^ Martin, A.J. (2006). Introduction to the Study of Dinosaurs. Second Edition. Oxford, Blackwell Publishing. pg. 299-300. ISBN 1-4051-3413-5.
  3. ^ Müller, Rodrigo T.; Garcia, Maurício S. (2019-03-08). "Rise of an empire: analysing the high diversity of the earliest sauropodomorph dinosaurs through distinct hypotheses". Historical Biology: 1–6. doi:10.1080/08912963.2019.1587754. ISSN 0891-2963.
  4. ^ Gradstein, F.M., Ogg, J.G. and Smith, A.G. (2004). A Geologic Time Scale 2004, Cambridge University Press.
  5. ^ Luciano A. Leal, Sergio A. K. Azevodo, Alexander W. A. Kellner, and Átila A. S. da Rosa (October 18, 2004). "A new early dinosaur (Sauropodomorpha) from the Caturrita Formation (Late Triassic), Paraná Basin, Brazil" (PDF). Zootaxa. 690: 1–24.CS1 maint: Multiple names: authors list (link) (Warning: abstract is 12 kb PDF)
  6. ^ Martínez, Ricardo N.; Alcober, Oscar A. (2009). Sereno, Paul (ed.). "A basal sauropodomorph (Dinosauria: Saurischia) from the Ischigualasto Formation (Triassic, Carnian) and the early evolution of Sauropodomorpha" (pdf). PLoS ONE. 4 (2): 1–12. doi:10.1371/journal.pone.0004397. PMC 2635939. PMID 19209223.
  7. ^ Ricardo N. Martinez, Paul C. Sereno, Oscar A. Alcober, Carina E. Colombi, Paul R. Renne, Isabel P. Montañez and Brian S. Currie (2011). "A Basal Dinosaur from the Dawn of the Dinosaur Era in Southwestern Pangaea". Science. 331 (6014): 206–210. doi:10.1126/science.1198467. PMID 21233386.CS1 maint: Multiple names: authors list (link)
  8. ^ Sereno, P.C. (1998). "A rationale for phylogenetic definitions, with applications to the higher-level taxonomy of Dinosauria". Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen. 210: 41–83. doi:10.1127/njgpa/210/1998/41.
  9. ^ Yates, Adam M. (2007). "The first complete skull of the Triassic dinosaur Melanorosaurus Haughton (Sauropodomorpha: Anchisauria)". In Barrett & Batten (eds.), Evolution and Palaeobiology: 9–55.
  10. ^ a b Fernando E. Novas, Martin D. Ezcurra, Sankar Chatterjee and T. S. Kutty (2011). "New dinosaur species from the Upper Triassic Upper Maleri and Lower Dharmaram formations of central India". Earth and Environmental Science Transactions of the Royal Society of Edinburgh. 101 (3–4): 333–349. doi:10.1017/S1755691011020093.CS1 maint: Multiple names: authors list (link)
  11. ^ Pol D., Garrido A., Cerda I.A. (2011). Farke, Andrew Allen (ed.). "A New Sauropodomorph Dinosaur from the Early Jurassic of Patagonia and the Origin and Evolution of the Sauropod-type Sacrum". PLoS ONE. 6 (1): e14572. doi:10.1371/journal.pone.0014572. PMC 3027623. PMID 21298087.CS1 maint: Multiple names: authors list (link)
  12. ^ Otero, Alejandro; Krupandan, Emil; Pol, Diego; Chinsamy, Anusuya; Choiniere, Jonah (2015). "A new basal sauropodiform from South Africa and the phylogenetic relationships of basal sauropodomorphs". Zoological Journal of the Linnean Society. 174 (3): 589. doi:10.1111/zoj.12247.
  13. ^ Baron, M.G., Norman, D.B., and Barrett, P.M. (2017). A new hypothesis of dinosaur relationships and early dinosaur evolution. Nature, 543: 501–506. doi:10.1038/nature21700
  14. ^ Schmitz, L.; Motani, R. (2011). "Nocturnality in Dinosaurs Inferred from Scleral Ring and Orbit Morphology". Science (6030): 705–8. doi:10.1126/science.1200043. PMID 21493820. Text "V→→→§332 " ignored (help)
  15. ^ Sander PM (2000) Long bone histology of the Tendaguru sauropods: implications for growth and biology. Paleobiology 26: 466–488.
  16. ^ a b Griebeler EM, Klein N, Sander PM (2013) Aging, Maturation and Growth of Sauropodomorph Dinosaurs as Deduced from Growth Curves Using Long Bone Histological Data: An Assessment of Methodological Constraints and Solutions. PLoS ONE 8(6): e67012. doi:10.1371/journal.pone.0067012
  17. ^ a b Cabreira, S.F.; Kellner, A.W.A.; Dias-da-Silva, S.; da Silva, L.R.; Bronzati, M.; de Almeida Marsala, J.C.; Müller, R.T.; de Souza Bittencourt, J.; Batista, B.J.; Raugust, T.; Carrilho, R.; Brodt, A.; Langer, M.C. (2016). "A Unique Late Triassic Dinosauromorph Assemblage Reveals Dinosaur Ancestral Anatomy and Diet". Current Biology. 26 (22): 3090–3095. doi:10.1016/j.cub.2016.09.040. PMID 27839975.
  18. ^ a b Paul C. Sereno, Ricardo N. Martínez & Oscar A. Alcober (2013) Osteology of Eoraptor lunensis (Dinosauria, Sauropodomorph a). Basal sauropodomorphs and the vertebrate fossil record of the Ischigualasto Formation (Late Triassic: Carnian-Norian) of Argentina. Journal of Vertebrate Paleontology Memoir 12: 83-179 DOI:10.1080/02724634.2013.820113
  19. ^ Hans-Dieter Sues, Sterling J. Nesbitt, David S. Berman and Amy C. Henrici (2011). "A late-surviving basal theropod dinosaur from the latest Triassic of North America". Proceedings of the Royal Society B 278 (1723): 3459–3464
  20. ^ Hendrickx, C.; Hartman, S.A.; Mateus, O. (2015). "An Overview of Non- Avian Theropod Discoveries and Classification". PalArch's Journal of Vertebrate Palaeontology. 12 (1): 1–73.

Sources

External links

Adeopapposaurus

Adeopapposaurus (meaning "far eating lizard", in reference to its long neck) is a genus of prosauropod dinosaur from the Early Jurassic Cañón del Colorado Formation of San Juan, Argentina. It was similar to Massospondylus. Four partial skeletons with two partial skulls are known.The type specimen, PVSJ568, includes a skull and most of a skeleton to just past the hips. The form of the bones at the tips of the upper and lower jaws suggests it had keratinous beaks. The fossils now named Adeopapposaurus were first thought to represent South American examples of Massospondylus; while this is no longer the case, Adeopapposaurus is classified as a massospondylid. Adeopapposaurus was described in 2009 by Ricardo N. Martínez. The type species is A. mognai, referring to the Mogna locality where it was found.

Anchisauria

The Anchisauria were a clade of sauropodomorph dinosaurs that lived during the Late Triassic and Early Jurassic. The name Anchisauria was first used by Galton and Upchurch in the second edition of The Dinosauria. Galton and Upchurch assigned two families of dinosaurs to the Anchisauria: the Anchisauridae and the Melanorosauridae. The more common prosauropods Plateosaurus and Massospondylus were placed in the sister clade Plateosauria.

However, recent research indicates that Anchisaurus is closer to sauropods than traditional prosauropods; thus, Anchisauria would also include Sauropoda.The following cladogram simplified after an analysis presented by Blair McPhee and colleagues in 2014.

Coloradisaurus

Coloradisaurus (meaning "Colorados [from Los Colorados Formation] lizard") is a genus of massospondylid sauropodomorph dinosaur. It lived during the Late Triassic period (Norian to Rhaetian stages) in what is now La Rioja Province, Argentina. It is known from the holotype PVL 5904, nearly complete skull. It was discovered and collected from the upper section of the Los Colorados Formation of the Ischigualasto-Villa Unión Basin.

Euskelosaurus

Euskelosaurus browni ("good leg lizard") is a semi-bipedal plateosaurid sauropodomorph dinosaur from the early Triassic of South Africa and Lesotho. Fossils have only been recovered from the lower Elliot Formation in South Africa and Lesotho, and in one locality in Zimbabwe.

Guaibasauridae

Guaibasauridae is a family of basal saurischian dinosaurs, known from fossil remains of late Triassic period formations in Brazil and Argentina.

Jingshanosaurus

Jingshanosaurus (meaning "Jingshan lizard") is a genus of sauropodomorph dinosaurs from the early Jurassic period.

Melanorosauridae

The Melanorosauridae were a family of sauropodomorph dinosaurs which lived during the Late Triassic and Early Jurassic. The name Melanorosauridae was first coined by Friedrich von Huene in 1929. Huene assigned several families of dinosaurs to the infraorder "Prosauropoda": the Anchisauridae, the Plateosauridae, the Thecodontosauridae, and the Melanorosauridae. Since then, these families have undergone numerous revisions. Galton and Upchurch (2004) considered Camelotia, Lessemsaurus, and Melanorosaurus members of the family Melanorosauridae. A more recent study by Yates (2007) indicates that the melanorosaurids were instead early sauropods.

Mussaurus

Mussaurus (meaning "mouse lizard") is a genus of herbivorous sauropodomorph dinosaur that lived in southern Argentina during the Late Triassic, about 215 million years ago. It receives its name from the small size of the skeletons of juvenile and infant individuals, which were once the only known specimens of the genus. However, since Mussaurus is now known from adult specimens, the name is something of a misnomer; adults possibly reached 6 metres (20 ft) in length and weighed more than 1,000 kilograms (2,200 lb). Mussaurus possesses anatomical features suggesting a close, possibly transitional evolutionary relationship with true sauropods.

Ngwevu

Ngwevu intloko (pronounced 'Ng-g'where-voo; directly from Xhosa 'ngwevu' and 'intloko' meaning "grey skull") is a genus of massospondylid sauropodomorph dinosaur from the Lower Jurassic Elliot Formation of South Africa. The type and only known specimen, BP/1/4779, was discovered in 1978 by James William Kitching. It had in 1990 and 2004 been regarded as an unusual specimen of the related Massospondylus, with a horizontally and vertically compressed skull, but in 2019 the specimen was after restudy concluded to belong to a new distinct genus. The genus is primarily distinguished by its skull being more robust than that of Massospondylus.

Plateosauria

Plateosauria is a clade of sauropodomorph dinosaurs which lived during the Late Triassic to the Late Cretaceous. The name Plateosauria was first coined by Gustav Tornier in 1913. The name afterwards fell out of use until the 1980s.

Plateosauria is a node-based taxon. In 1998, Paul Sereno defined Plateosauria as the last common ancestor of Plateosaurus engelhardti and Massospondylus carinatus, and its descendants. Peter Galton and Paul Upchurch in 2004 used a different definition: the last common ancestor of Plateosaurus engelhardti and Jingshanosaurus xinwaensis, and its descendants. In their cladistic analysis the Plateosauria belonged to the Prosauropoda, and included the Plateosauridae subgroup. In Galton's and Upchurch's study also Coloradisaurus, Euskelosaurus, Jingshanosaurus, Massospondylus, Mussaurus, Sellosaurus, and Yunnanosaurus proved to be plateosaurians.However, recent cladistic analyses suggest that the Prosauropoda as traditionally defined is paraphyletic to sauropods. Prosauropoda, as currently defined, is a synonym of Plateosauridae as both contain the same taxa by definition.

The following cladogram simplified after an analysis presented by Apaldetti and colleagues in 2011.

The following cladogram simplified after an analysis presented by Blair McPhee and colleagues in 2014.

Plateosauridae

Plateosauridae is a family of plateosaurian sauropodomorphs from the Late Triassic of Europe. Although several dinosaurs have been classified as plateosaurids over the years, the family Plateosauridae is now restricted to Plateosaurus. In another study, Yates (2003) sunk Sellosaurus into Plateosaurus (as P. gracilis).

Pulanesaura

Pulanesaura is an extinct genus of basal sauropod known from the Early Jurassic (late Hettangian to Sinemurian) Upper Elliot Formation of the Free State, South Africa. It contains a single species, Pulanesaura eocollum, known from partial remains of at least two subadult to adult individuals.

Riojasauridae

Riojasauridae is a family of sauropod-like dinosaurs from the Upper Triassic. It is known primarily from the genera Riojasaurus and Eucnemesaurus. Sites containing Riojasauridae include the Lower Elliot Formation of Orange Free State, South Africa (where fossils of Eucnemesaurus have been found), and Ischigualasto, in La Rioja Province, Argentina ( where fossils of Riojasaurus have been recovered).

Ruehleia

Ruehleia is a genus of sauropodomorph dinosaur from the Late Triassic period of Germany. The type species is R. bedheimensis, described by Galton in 2001, and is named for the German paleontologist Hugo Ruehle von Lilienstern. The fossils consist of one nearly complete skeleton, consisting of cervical (neck), dorsal (back), and caudal (tail) vertebrae; a partial sacrum; a scapula-coracoid; pelvic bones; most of the limb bones; and partially complete manus (hands).

The fossils were found in central Germany and date to the Norian stage, around 216 to 203 million years ago.

Saturnaliinae

Saturnaliinae is a clade of sauropodomorph dinosaurs found in Brazil and Argentina.

In 2010, Martin Ezcurra defined the subfamily Saturnaliinae for the clade containing Saturnalia and Chromogisaurus, which were found to be close relatives in several studies. While they are sometimes found to be a subgroup within the Guaibasauridae, other studies have found the saturnaliines to form an independent lineage at the very base of the sauropodomorph family tree. Langer and colleagues (2019) recovered Pampadromaeus and Panphagia as relatives of Saturnalia and Chromogisaurus, elevating Saturnaliinae to family rank as Saturnaliidae. They recovered Guaibasaurus as a basal theropod.

Unaysauridae

Unaysauridae is a family of basal sauropodomorphs from the Late Triassic of India and Brazil.

Xixiposaurus

Xixiposaurus is a genus of prosauropod dinosaur which existed in what is now Lower Lufeng Formation, China during the lower Jurassic period. It was first named by Sekiya Toru in 2010 and the type species is Xixiposaurus suni.

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