ANCESTRY of the DINOSAURIA


AMNIOTA [Fig. 8.5]


an abbreviated AMNIOTE TAXONOMY

Amniota
        Synapsida (includes Mammalia)
        Reptilia
             Testudines (turtles may be diapsids)
             Diapsida
                  Archosauromorpha [Crocodylia, Dinosaurs including Aves]
                  Lepidosauromorpha [lizards and snakes]

Paul Olsen's web page has an excellent discussion of the origin of the amniotes and the early diversification of the archosaurs

TEMPORAL OPENINGS and AMNIOTE CLASSIFICATION [fig. 15.1]

Anapsids
dermal skull roof completely covered with bone;  this is primitive for the amniotes.  Turtles have traditionally been considered anapsids, but they are now conidered modified diapsids.
Synapsids
single opening low on the cheek, bordered by the jugal, squamosal, and postorbital; condition found in mammals
Diapsids
two pairs of temporal openings; one pair ventral to the postorbital and squamosal (as in the synapsids); the second pair dorsal to the postorbital and squamosal and lateral to the parietal
Euryapsids
derived from the diapsid condition by loss of the lower temporal opening; evolved independently in plesiosaurs (lower temporal bar lost) and ichthyosaurs (opening closed by enlargement of bones of the cheek region

CLASSIFICATION OF THE REPTILES


REPTILIA
     Testudines (turtles and tortoises) 
     Diapsida [see cladogram, Fig. 15.3]
           Lepidosauria (lizards and snakes)
           Archosauromorpha 
                Eupakaria [Fig. 15.6]
                Archosauria 
                     Crocodilia (alligators and crocodiles)
                     Ornithodira 
                          Pterosauria
                          Dinosauromorpha
                              Lagosuchus, etc.
                              DINOSAURIA
                                   Ornithischia
                                        Stegosauria and Ankylosauria
                                        Ornithopoda and Ceratopsia
                                   Saurischia
                                        Sauropoda
                                        Theropoda
                                             Aves (birds)

Infraclass ARCHOSAUROMORPHA

Superorder ARCHOSAURIFORMES

Order Thecodontia

Proterosuchidae (early Triassic) Erythrosuchidae (early Triassic) Euparkeria (Lower Triassic)

ARCHOSAURIA [Cladogram Fig. 15.8]

CRUROTARSI

ORNITHOSUCHIDAE

PARASUCHIA

Family Phytosauridae (Upper Triassic)

SUCHIA

Family Stagonolepididae (Upper Triassic)

Family Rauisuchidae (middle and upper Triassic)

Superorder Crocodylimorpha

Order Crocodylia (early Jurassic - Recent)

ORNITHODIRA

Order Pterosauria

Ramphorhynchoidea (U. Trias. - U. Jur.)

Pterodactyloidea (U. Jur. - U. Cret.)

 

DINOSAURIA

Previous classifications usually considered dinosaurs a polyphyletic group with independent origins from thecodont ancestors. Dinosauria are now considered monophyletic because of numerous autapomorphies including elongate vomers, three or more sacral vertebrae, scapulacoracoidal glenoid facing fully backwards, low deltopectoral crest running 1/3 to 1/2 way down humerus, three or fewer phalanges on fourth digit of manus, largely to fully open acetabulum, fully offset proximal head of femur with a distinct neck and ball, greatly reduced fibula, well-developed ascending process of astragalus; upright posture, digitigrade stance. See Peczkis, J, 1994, JVP 14:520-533 for estimates of body mass of dinosaurs.

 


THE DINOSAUROMORPHA


DINOSAUROMORPHA

Included taxa

Characteristics

Middle Triassic Dinosauromorphs: Lagosuchidae

Characteristics

Included taxa

Reference


DINOSAURIA

Included Taxa




dino1A.gif (5188 bytes)

Discussion


CLASSIFICATION OF THE DINOSAURS

 

An overview of dinosaur classification from M. Alan Kazlev's Dinosaur Pages.

Everything you need to know about dinosaur classification in just 11 pages:  Paul C. Sereno.  1999.  The Evolution of Dinosaurs.  Science, 284:2137-2147.   This article is reprinted courtesy of Bill Tietjen, Bellarmine College


Dinosauria
      Herrerasauridae
      SAURISCHIA
            THEROPODA
                  Ceratosauria
                  Tetanurae
                        Carnosauria
                              Allosauridae
                        Coelurosauria
                              Tyrannosauridae
                              Ornithomimosauridae
                              Maniraptora
                                    Dromaeosauridae
                                    Aviale
                                          Archaeopterix
                                          Ornithurae
                                                Enantiornithes
                                                Aves
           Sauropodomorpha 
                  Prosauropoda
                  SAUROPODA
                        Vulcanodon, etc.
                         Neosauropoda
                              Diplodocidae
                              Macronaria
                                    Camarasaurus
                                    Titanosauriformes
                                           Brachiosauridae
                                           Titanosauridae

      ORNITHISCHIA
            Fabrosauridae [Lesothosaurus] 
            Genasauria
                  Thyreophora
                        unnamed group [Scelidosaurus, Scutellosaurus]
                        unnamed group
                              Ankylosauria
                                    Ankylosauridae
                                    Nodosauridae
                              Stegosauria
                                    Kentrosauridae
                                    Stegosauridae
                  Cerapoda
                        Marginocephalia
                              Pachycephalosauria
                              Ceratopsia
                                     Psittacosauridae
                                     Neoceratopsia
                                           Protoceratopsidae
                                           Ceratopsidae 
                        Ornithopoda
                              Heterodontosaurus
                              no name
                                    Hypsilophodontidae
                                    no name
                                          Iguanodontidae
                                          Hadrosauridae 

See Peczkis, J, 1994, JVP 14:520-533 for estimates of body mass of dinosaurs.


The oldest dinosaurs are Herrarasaurus and Eoraptor


HERRERASAURIDAE (upper Triassic)

Characteristics

Included taxa

Some references


SAURISCHIA

Characters


ORNITHISCHIA

Characters


spelvis.jpg (16173 bytes)copelvis.jpg (17222 bytes)

The Saurischian (on the left) and the Ornithischian (on the right) pelves.  Anterior is to the left.  Note the open acetabulum in both.  In the triradiate (primitive) saurischian pelvis, the pubis extends anteriorly.  In the tetraradiate ornithischian pelvis, note the anterior (to the left) extension of the ilium, and the backward (to the right) extension of the pubis below and adjacent to the ischium.  Illustrations from O. C. Marsh.  1896.  The dinosaurs of North America.  16th Annual Report, U.S. Geological Survey, pp. 133-244, 84 plates.

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