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Sauropodomorpha

Sauropodomorpha(/ˌsɔːrəˌpɒdəˈmɔːrfə/[2]SOR-ə-POD-ə-MOR-fə;from Greek, meaning "lizard-footed forms" ) is an extinctcladeof long-necked,herbivorous,saurischiandinosaurs that includes thesauropodsand their ancestral relatives. Sauropods generally grew to very large sizes, had long necks and tails, werequadrupedal,and became the largest animals to ever walk the Earth. Theprosauropods,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 theMesozoic Era,from their origins in theLate Triassic(approximately 230Ma) until their decline and extinction at the end of theCretaceous.

Sauropodomorphs
Temporal range:233.23–66Ma[1]
Six sauropodomorphs (top left to bottom right):Plateosaurus,Brontosaurus,Massospondylus,Eoraptor,Thecodontosaurus,Cetiosaurus
Scientific classificationEdit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Eusaurischia
Clade: †Sauropodomorpha
Huene,1932
Subgroups

Description

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Skull ofNigersaurus taquetiand 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 cervicalvertebrae) and a counterbalancing long tail (with one to three extra sacral vertebrae).[citation needed]

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

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 theJurassicandCretaceousthey kept on growing. Ultimately the largest sauropods, likeSupersaurus,Diplodocus hallorum,Patagotitan,andArgentinosaurus,reached 30–40 metres (98–131 ft) in length, and 60,000–100,000kilograms(65–110 USshort tons) or more in mass.[citation needed]

Initiallybipedal,as their size increased they evolved afour-leggedgraviportalgait adapted only to walking slowly on land, like elephants. The early sauropodomorphs were most likelyomnivoresas their shared common ancestor with the othersaurischianlineage (thetheropods) was acarnivore.Therefore, their evolution to herbivory went hand in hand with their increasing size and neck length.[citation needed]

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.[citation needed]

Distinguishing anatomical features

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Sauropodomorphs can be distinguished as a group on the basis of some of the followingsynapomorphies:[3]

  • The presence of large nares.
  • The distal part of thetibiais covered by an ascending process of theastragalus.
  • 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
  • Themanushad a large digit I.

Evolutionary history

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Among the first dinosaurs to evolve in the Late Triassic period,[4]about 230 million years ago (Mya), they became the dominant herbivores by halfway through the late Triassic (during theNorianstage). 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, but sauropods were still the dominant herbivores in theGondwananlandmasses. The spread offlowering 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[citation needed].Like all non-avian dinosaurs (birds), the sauropodomorphs became extinct 66 Mya, during theCretaceous–Paleogene extinction event.

The earliest and mostbasalsauropodomorphs known areChromogisaurus novasiandPanphagia protos,both from theIschigualasto Formation,dated to 231.4 million years ago (lateCarnianage of the Late Triassic according to theICS[5][6]). Some studies have foundEoraptor 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

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Restoration ofPanphagia,one of the most basal sauropodomorphs known.
Plateosaurusis a well-known prosauropod.

Sauropodomorpha is one of the two major clades within the orderSaurischia.The sauropodomorphs' sister group, theTheropoda,includes bipedal carnivores likeVelociraptorandTyrannosaurus;as well as birds. However, sauropodomorphs also share a number of characteristics with theOrnithischia,so a small minority ofpalaeontologists,likeBakker,have historically placed both sets of herbivores within a group called "Phytodinosauria" or "Ornithischiformes".[citation needed]

InLinnaean taxonomy,Sauropodomorpha (which means "lizard feet forms" ) is either asuborderor is left unranked. It was originally established byFriedrich von Huenein 1932, who broke it into two groups: the basal forms withinProsauropoda,and their descendants, the giantSauropoda.[citation needed]

Phylogeneticanalyses by Adam Yates (2004, 2006) and others firmly placed Sauropoda within aparaphyletic"Prosauropoda". Recent cladistic analyses suggest that the cladeProsauropoda,which was named by Huene in 1920 and was defined by Sereno, in 1998, as all animals more closely related toPlateosaurus engelhardtithan toSaltasaurus loricatus,[8]is a junior synonym ofPlateosauridaeas 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 causedconvergent evolution,where similar traits evolve separately because they faced the same evolutionary pressure, instead of (homologous) traits derived from a shared ancestor.[11]

The phylogenetic analysis of Otero et al., 2015 found Sauropodomorpha to be in a polytomy withAgnosphitysandTheropodawithinEusaurischia,withHerrerasauridaeandEoraptorexternal to it withinSaurischia.[12]A large phylogenetic analysis of early dinosaurs published by Matthew Baron,David Normanand Paul Barrett (2017) in the journalNatureredefined Sauropodomorpha andSaurischiaand recoveredHerrerasauridaeas thesister groupto Sauropodomorpha within Saurischia. This resulted from the proposed removal ofTheropodafrom Saurischia and the formation ofOrnithoscelida,a clade containing Theropoda andOrnithischia.[13]

Phylogeny

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Skull comparison of several sauropodomorphs

Within Sauropodomorpha, there is a large clade namedPlateosauria.The name Plateosauria was first coined byGustav Tornierin 1913.[14]The name afterwards fell out of use until the 1980s. Plateosauria is anode-based taxon.In 1998,Paul Serenodefined Plateosauria as thelast common ancestorofPlateosaurus engelhardtiandMassospondylus carinatus,and its descendants.[8]Peter GaltonandPaul Upchurchin 2004 used a different definition: the last common ancestor ofPlateosaurus engelhardtiandJingshanosaurus xinwaensis,and its descendants. In theircladisticanalysis the Plateosauria belonged to the Prosauropoda, and included thePlateosauridaesubgroup. In Galton's and Upchurch's study alsoColoradisaurus,Euskelosaurus,Jingshanosaurus,Massospondylus,Mussaurus,Sellosaurus,andYunnanosaurusproved to be plateosaurians.[15]

However, recentcladisticanalyses suggest that the Prosauropoda as traditionally defined isparaphyletictosauropods.[16][9][11][10][17]Prosauropoda, as currently defined, is asynonymofPlateosauridaeas both contain the same taxa by definition. The phylogenetic analysis of 2021 recoveredIssiandPlateosaurusas the basal-most plateosaurs.[18]

Cladogram afterNovaset al., 2011:[10]

Sauropodomorpha

Below is a cladogram of basal sauropodomorpha after Müller, 2019.[19]

Sauropodomorpha

Paleobiology

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Comparisons between thescleral ringsof several sauropodomorph genera (Diplodocus,Lufengosaurus,Nemegtosaurus,Plateosaurus,andRiojasaurus) and modern birds and reptiles suggest that they may have beencathemeral,active throughout the day at short intervals.[20]

Sauropodomorphs reached the age of sexual maturity well before they were fully-grown adults.[21][22]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.[22]

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 itsplesiomorphic,theropod-like teeth.[23]The teeth of more derived sauropodomorphs such asEoraptor,Panphagia,andPampadromaeusare better-suited for herbivorous (or possibly omnivorous) diets.[24]Regardless of the phylogenetic position of herrerasaurids orEoraptor(which are in flux),[24][25][26]ancestral state reconstructions recover carnivory as being ancestral to sauropodomorphs.[23]

References

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  1. ^Langer, M.C.; Ramezani, J.; Da Rosa, Á.A.S. (2018). "U-Pb age constraints on dinosaur rise from south Brazil".Gondwana Research.X(18): 133–140.Bibcode:2018GondR..57..133L.doi:10.1016/j.gr.2018.01.005.
  2. ^Cf."sauropodomorph - definition of sauropodomorph in English from the Oxford dictionary".OxfordDictionaries.com.Archived fromthe originalon November 1, 2015.Retrieved2016-01-20.
  3. ^Martin, A.J. (2006). Introduction to the Study of Dinosaurs. Second Edition. Oxford, Blackwell Publishing. pg. 299-300.ISBN1-4051-3413-5.
  4. ^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.32(10): 1334–1339.doi:10.1080/08912963.2019.1587754.ISSN0891-2963.S2CID92177386.
  5. ^Luciano A. Leal; Sergio A. K. Azevodo; Alexander W. A. Kellner & 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.doi:10.11646/zootaxa.690.1.1.(Warning:abstract is 12 kbPDF)
  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".PLOS ONE.4(2): 1–12.Bibcode:2009PLoSO...4.4397M.doi:10.1371/journal.pone.0004397.PMC2635939.PMID19209223.
  7. ^Ricardo N. Martinez; Paul C. Sereno; Oscar A. Alcober; Carina E. Colombi; Paul R. Renne; Isabel P. Montañez & Brian S. Currie (2011)."A Basal Dinosaur from the Dawn of the Dinosaur Era in Southwestern Pangaea".Science.331(6014): 206–210.Bibcode:2011Sci...331..206M.doi:10.1126/science.1198467.hdl:11336/69202.PMID21233386.S2CID33506648.
  8. ^abSereno, 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. ^abYates, Adam M. (2007). Barrett, Paul M.; Batten, David J. (eds.). "The first complete skull of the Triassic dinosaurMelanorosaurusHaughton (Sauropodomorpha: Anchisauria) ".Evolution and Palaeobiology.77:9–55.ISBN978-1-4051-6933-2.
  10. ^abcFernando E. Novas; Martin D. Ezcurra; Sankar Chatterjee; 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.S2CID128620874.
  11. ^abPol 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.Bibcode:2011PLoSO...614572P.doi:10.1371/journal.pone.0014572.PMC3027623.PMID21298087.
  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.hdl:11336/38019.
  13. ^Baron, M.G.; Norman, D.B.; Barrett, P.M. (2017). "A new hypothesis of dinosaur relationships and early dinosaur evolution".Nature.543(7646): 501–506.Bibcode:2017Natur.543..501B.doi:10.1038/nature21700.PMID28332513.S2CID205254710.
  14. ^Tornier, G., 1913, "Reptilia (Paläontologie)" In:Handwörterbuch Naturwissenschaften8:337-376
  15. ^Galton, P.M & Upchurch, P. (2004). "Prosauropoda".In D. B. Weishampel, P. Dodson, & H. Osmólska (Eds.), the Dinosauria (Second edition). University of California Press, Berkeley:232–258.
  16. ^Yates, Adam M. (2003)."Species taxonomy of the sauropodomorph dinosaurs from the Löwenstein Formation (Norian, Late Triassic) of Germany".Palaeontology.46(2): 317–337.doi:10.1111/j.0031-0239.2003.00301.x.S2CID86801904.
  17. ^Cecilia Apaldetti; Ricardo N. Martinez; Oscar A. Alcober; Diego Pol (2011)."A New Basal Sauropodomorph (Dinosauria: Saurischia) from Quebrada del Barro Formation (Marayes-El Carrizal Basin), Northwestern Argentina".PLOS ONE.6(11): e26964.Bibcode:2011PLoSO...626964A.doi:10.1371/journal.pone.0026964.PMC3212523.PMID22096511.
  18. ^Beccari, Victor; Mateus, Octávio; Wings, Oliver; Milàn, Jesper; Clemmensen, Lars B. (November 2021)."Issi saaneq gen. et sp. nov.—A New Sauropodomorph Dinosaur from the Late Triassic (Norian) of Jameson Land, Central East Greenland".Diversity.13(11): 561.doi:10.3390/d13110561.hdl:10362/128951.
  19. ^Müller, Rodrigo Temp (2019). "Craniomandibular osteology ofMacrocollum itaquii(Dinosauria: Sauropodomorpha) from the Late Triassic of southern Brazil ".Journal of Systematic Palaeontology.18(10): 805–841.doi:10.1080/14772019.2019.1683902.S2CID209575985.
  20. ^Schmitz, L.; Motani, R. (2011). "Nocturnality in Dinosaurs Inferred from Scleral Ring and Orbit Morphology".Science.→→→§332 (6030): 705–8.Bibcode:2011Sci...332..705S.doi:10.1126/science.1200043.PMID21493820.S2CID33253407.
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  22. ^abGriebeler, 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.Bibcode:2013PLoSO...867012G.doi:10.1371/journal.pone.0067012.PMC3686781.PMID23840575.
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  25. ^Sues, Hans-Dieter; Nesbitt, Sterling J.; Berman, David S.; Henrici, Amy C. (2011)."A late-surviving basal theropod dinosaur from the latest Triassic of North America".Proceedings of the Royal Society B.278(1723): 3459–3464.doi:10.1098/rspb.2011.0410.PMC3177637.PMID21490016.
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Sources

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