   #copyright

Sauropodomorpha

2007 Schools Wikipedia Selection. Related subjects: Dinosaurs

     iSauropodomorphs

                     Fossil range: Triassic - Cretaceous

   Statue of Diplodocus carnegiei outside the Carnegie Museum
   Statue of Diplodocus carnegiei outside the Carnegie Museum

                             Conservation status

   Extinct (fossil)
                   Scientific classification

   Kingdom:    Animalia
   Phylum:     Chordata
   Class:      Sauropsida
   Superorder: Dinosauria
   Order:      Saurischia
   Suborder:   Sauropodomorpha
               von Huene, 1932

                                 Infraorders

     * Prosauropoda
     * Sauropoda

   The Sauropodomorpha were a group of long-necked, herbivorous dinosaurs
   that eventually dropped down on all fours and became the largest
   animals that ever walked the earth.

Description

   Sauropodomorphs were adapted to higher browsing than any other
   contempary herbivore, giving them access high tree foilage]]. 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.

   The first known sauropodomorph, 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 in the Jurassic/Cretaceous they
   kept on growing. Ultimately the largest sauropods like the Supersaurus,
   Seismosaurus, and Argentinosaurus reached 30–40 metres (100–130 ft) in
   length, and 60,000–100,000  kilograms (65–110 US short tons) or more in
   mass.

   Initially bipedal, though as their size increased they evolved to
   become graviportal quadrupeds (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 (pollux)
   with a big claw which may have been used for defense — though their
   primary defensive adaptation was their extreme size.

Range

   Among the very first dinosaurs to evolve in the late Triassic Period,
   about 230 million years ago (Mya). They became the dominant herbivores
   by half way through the late Triassic - Norian age. Their percieved
   decline in the early Cretaceous is most likely a bias in fossil
   sampling, as most fossils are known from Europe and North America.
   Sauropods however, in the Gondwana landmasses where still the dominant
   herbivores. 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 65 Mya, during
   the Cretaceous-Tertiary extinction event.

   The most basal sauropodomorph, Saturnalia, was discovered in 1999, and
   is dated to the Carnian stage of the late Triassic. However,
   fragmentary remains from Madagascar may represent an even earlier
   sauropodomorph from the middle Triassic.

Classification

   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. However,
   Sauropodomorpha also share a number of characteristics with the
   Ornithischia, so a small minority of palaeontologists like Bakker place
   both sets of herbivores within 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.

   Recent phylogenetic analyses by Adam Yates (2004, 2006) firmly places
   Sauropoda within a paraphyletic Prosauropoda. Also, finds of late
   Triassic sauropods demonstrate that there is no gap between the
   "prosauropod" and sauropod lineages.

   Evidence against sauropod ancestry within Prosauropoda comes from the
   the fact that prosauropods had a smaller outer toe on their hind feet
   than the sauropods. Many maintain that it is easier for digits to be
   reduced or lost during evolution than the reverse, however there is no
   evidence for this. The lengthening, or gaining of extra digits is
   common in marine reptiles, and within the theropods digit lengthening
   occured at least once. Therefore using this as evidence against
   ancestral prosauropods is questionable.

   While the sauropodomorphs are still grouped into prosauropods and
   sauropods for convenience, most modern classification schemes break the
   prosauropods into a half-dozen groups that evolved separately from one
   or more common ancestors. 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.

   Since the modern preference is for groups that are composed of all
   descendants of the same common ancestor ( clades), instead of groups
   that exclude certain descendants of that ancestor ( paraphyletic taxa),
   Prosauropoda is unpopular except as an informal collection of primitive
   ( basal) sauropodomorphs. However, some like Michael Benton, consider
   the prosauropods and sauropods to be a distinct lineage descended from
   a common saurischian ancestor. While this is a minority view, supported
   by weak evidence, there is considerable support for a small,
   monophyletic Prosauropoda clade containing only smaller percentage of
   its previous members ( taxa).

   Saturnalia has the teeth, backbone, pelvis, and legs of traditional
   prosauropods, while lacking all of the unique sauropod characteristics.
   This lends some support to the prosauropod paraphyly theory, as it is
   the most basal sauropodomorph. However, it also lacks some of
   characteristics traditionally associated with Sauropodomorpha.
   Although, again being the most basal species this is not too
   surprising. The suggestion that the lack of some derived sauropodomorph
   characters in Saturnalia can be taken as evidence that Sauropodomorpha
   eis polyphyletic (evolved separately from different saurischian
   ancestors) has not been demonstrated by any cladistic analysis of
   sauropodomorphs.

Taxonomy

   The following is based on several sources, including Wilson 2002
     * SUBORDER SAUROPODOMORPHA
          + Saturnalia
          + Thecodontosaurus
          + Efraasia
          + Prosauropoda
               o Family Plateosauridae
          + Sauropoda
               o Family Vulcanodontidae
               o Eusauropoda
                    # Family Cetiosauridae (paraphyletic?)
                    # Family Omeisauridae
                    # Neosauropoda
                         @ Haplocanthosaurus
                         @ Diplodocoidea
                              - Family Rebbachisauridae
                                   = Flagellicaudata
                                   * Family Dicraeosauridae
                                   * Family Diplodocidae
                         @ Macronaria
                              - Family Camarasauridae
                              - Titanosauriformes
                                   = Family Brachiosauridae
                                   * Somphospondyli
                                   + Family Euhelopodidae
                                   + Titanosauria

   Retrieved from " http://en.wikipedia.org/wiki/Sauropodomorpha"
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   with only minor checks and changes (see www.wikipedia.org for details
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