| Sauropodomorphs | |
|---|---|
 | |
| Six sauropodomorphs (top left to bottom right):Plateosaurus,Brontosaurus,Massospondylus,Eoraptor,Thecodontosaurus,Cetiosaurus | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Eusaurischia |
| Clade: | †Sauropodomorpha Huene, 1932 |
| Subgroups | |
Sauropodomorpha (/ˌsɔːrəˌpɒdəˈmɔːrfə/[3]SOR-ə-POD-ə-MOR-fə; from Greek, meaning "lizard-footed forms") is an extinctclade of long-necked,herbivorous,saurischian dinosaurs that includes thesauropods and 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 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 thegizzard stones 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 theJurassic andCretaceous they kept on growing. Ultimately the largest sauropods, likeSupersaurus,Diplodocus hallorum,Patagotitan, andArgentinosaurus, reached 30–40 metres (98–131 ft) in length, and 60,000–100,000 kilograms (65–110 USshort tons) or more in mass.[citation needed]
Initiallybipedal, as their size increased they evolved afour-leggedgraviportal gait adapted only to walking slowly on land, like elephants. The early sauropodomorphs were most likelyomnivores as their shared common ancestor with the othersaurischian lineage (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]
Sauropodomorphs can be distinguished as a group on the basis of some of the followingsynapomorphies:[4]
Among the first dinosaurs to evolve in the Late Triassic period,[5] about 230 million years ago (Mya), they became the dominant herbivores by halfway through the late Triassic (during theNorian 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, but sauropods were still the dominant herbivores in theGondwanan landmasses. 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 mostbasal sauropodomorphs known areChromogisaurus novasi andPanphagia protos, both from theIschigualasto Formation, dated to 231.4 million years ago (lateCarnian age of the Late Triassic according to theICS[6][7]). 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.[8]
Sauropodomorpha is one of the two major clades within the orderSaurischia. The sauropodomorphs' sister group, theTheropoda, includes bipedal carnivores likeVelociraptor andTyrannosaurus; 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 asuborder or is left unranked. It was originally established byFriedrich von Huene in 1932, who broke it into two groups: the basal forms withinProsauropoda, and their descendants, the giantSauropoda.[citation needed]
Phylogenetic analyses 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 engelhardti than toSaltasaurus loricatus,[9] is a junior synonym ofPlateosauridae as both contain the same taxa.[10][11]
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.[12]
The phylogenetic analysis of Otero et al., 2015 found Sauropodomorpha to be in a polytomy withAgnosphitys andTheropoda withinEusaurischia, withHerrerasauridae andEoraptor external to it withinSaurischia.[13] A large phylogenetic analysis of early dinosaurs published by Matthew Baron,David Norman and Paul Barrett (2017) in the journalNature redefined Sauropodomorpha andSaurischia and recoveredHerrerasauridae as thesister group to Sauropodomorpha within Saurischia. This resulted from the proposed removal ofTheropoda from Saurischia and the formation ofOrnithoscelida, a clade containing Theropoda andOrnithischia.[14]
Within Sauropodomorpha, there is a large clade namedPlateosauria. The name Plateosauria was first coined byGustav Tornier in 1913.[15] The name afterwards fell out of use until the 1980s. Plateosauria is anode-based taxon. In 1998,Paul Sereno defined Plateosauria as thelast common ancestor ofPlateosaurus engelhardti andMassospondylus carinatus, and its descendants.[9]Peter Galton andPaul Upchurch in 2004 used a different definition: the last common ancestor ofPlateosaurus engelhardti andJingshanosaurus xinwaensis, and its descendants. In theircladistic analysis the Plateosauria belonged to the Prosauropoda, and included thePlateosauridae subgroup. In Galton's and Upchurch's study alsoColoradisaurus,Euskelosaurus,Jingshanosaurus,Massospondylus,Mussaurus,Sellosaurus, andYunnanosaurus proved to be plateosaurians.[16]
However, recentcladistic analyses suggest that the Prosauropoda as traditionally defined isparaphyletic tosauropods.[17][10][12][11][18] Prosauropoda, as currently defined, is asynonym ofPlateosauridae as both contain the same taxa by definition. The phylogenetic analysis of 2021 recoveredIssi andPlateosaurus as the basal-most plateosaurs.[19]
Cladogram afterNovas et al., 2011:[11]
| Sauropodomorpha | |
Below is a cladogram of basal sauropodomorpha after Müller, 2019.[20]
| Sauropodomorpha | |
Comparisons between thescleral rings of 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.[21]
Sauropodomorphs reached the age of sexual maturity well before they were fully-grown adults.[22][23] 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.[23]
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.[24] The teeth of more derived sauropodomorphs such asEoraptor,Panphagia, andPampadromaeus are better-suited for herbivorous (or possibly omnivorous) diets.[25] Regardless of the phylogenetic position of herrerasaurids orEoraptor (which are in flux),[25][26][27] ancestral state reconstructions recover carnivory as being ancestral to sauropodomorphs.[24]
Data related toSauropodomorpha at Wikispecies
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