Dinosauria

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(check the following menu and phylogeny - the taxon in bold refers to the topic on this page)


DINOSAUROMORPHA
Taxonomy Phylogeny - note that many of these early forms are scrappy and their relationships poorly known 
o Ornithodira
|--Pterosauria
`--o DINOSAUROMORPHA
   |--Lagerpeton
   `--o Dinosauriformes
      |--Lagosuchus (Lagosuchidae)
      `--+?-Pseudolagosuchus (Lewisuchidae)
         `--+?-Teyuwasu
            |?-Silesaurus
            `--+?-Herrerasauria (or Saurischia/Theropoda)
               `--+?-Agnostiphitys
                  `--o Dinosauria
                     |--Ornithischia
                     `--Saurischia


Dinosauria



The South Gondwanan (Antarctic) Early Jurassic theropod dinosaur, Cryolophosaurus ellioti (Saurischia, Theropoda,Tetanurae,Carnosauria,). Many dinosaurs developed strange crests, which in life wree doubtless brightly couloured. Their purpose would have been most likely to attract mate or intimidate rivals. Artwork by John Conway
The South Gondwanan (Antarctic) Early Jurassic theropod dinosaur, Cryolophosaurus ellioti (Saurischia, Theropoda,Tetanurae,Carnosauria,). Many dinosaurs developed strange crests, which in life wree doubtless brightly couloured. Their purpose would have been most likely to attract mate or intimidate rivals. Artwork by John Conway

Contents

[edit] Introduction

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Probably no creatures that have lived upon this Earth have excited the imagination more than the Dinosauria. For some 150 million years they dominated over the medium to large to gigantic terrestrial vertebrate ecological niche, evolving into a wide range of forms and populating every continent. Our infatuation is perhaps because they often had such bizarre forms, perhaps because they sometimes grew to such huge size, perhaps because after ruling this earth for so long they suddenly vanished, seemingly without a trace; all things add to the appeal of the Dinosauria in the popular -- and scientific! -- imagination.

While dinosaurs have gripped people's imaginations like no other creature of the past, and as wonderful as the dinosaurs were, they should be considered in the context of many other fascinating and wonderful creatures, both extinct and extant. True, many dinosaurs did have rather strange forms, but were they any stranger in appearance than, say, a giraffe or an elephant? True, many dinosaurs grew to be quite large and even enormous, but no dinosaur ever rivalled the size of a smaller baleen whale. It would, in fact, be physiologically impossible for a land animal of more than 100 tonnes to exist, since structural support would require it's legs to be so massive they would touch, leaving no space for the body between! So much for Godzilla and the dinosaurs of One Million Years B.C. (a cult film better known for a much smaller, but equally impressive, 60 kg and 180 cm Rachel Welch in a fur bikini) - such creatures belong to the realm of Hollywood fantasy. The majority of dinosaurs were actually medium-sized creatures, equivalent to modern, medium to large mammals in size. Finally, as for dying out without a trace, this is also incorrect. One lineage of small insectivorous and carnivorous dinosaurs did survive the great Mesozoic terminal extinction and are still with us today -- they are called birds.

Eoentantiornis buhleri, a Cretaceous bird from Liaoning Province of China
Eoentantiornis buhleri, a Cretaceous bird from Liaoning Province of China

Some ecological niches the dinosaurs didn't invade. They never established themselves in the small terrestrial vertebrate niche (this was already taken over by mammals and lizards), nor (contrary to popular belief) did any of them ever adopt a marine or aquatic mode of life. They did, however, take to the air with style; and so successfully that their descendents are still the most numerous and diverse of the tetrapod (land-living vertebrates) even today. While their is no evidence in the fossil record that the pre-avian dinosaurs could fly, there were many flying, non-avian reptiles that lived during the time of the dinosaurs. Notably, the pterosaurs including Pteranodon, Pterodactylus, Dimorphodon, and numerous others, hunted and eluded hunters via flight.(MAK 010930)


(The following menu and phylogeny refers to subtopics of this page)


DINOSAURIA (The Dinosaurs)
Taxonomy Phylogeny (some taxa are of uncertain relationship and hence mentioned twice) 
o Dinosauromorpha
`--o DINOSAURIA
   |--Ornithischia
   `--o Saurischia
      |?-Eoraptor
      |?-Guaibasaurus
      |?-Herrerasauria
      `--+--Sauropodomorpha
         `--o Theropoda
            |?-Eoraptor
            `--+?-Herrerasauria
               `--+?-Guaibasaurus 
                  `--Neotheropoda / Avepoda (= Theropoda?)



[edit] The main Dinosaur groups

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Traditionally, the dinosaurs were divided into two orders, depending on the structure of the hip bones. Those that had a reptilian-like pelvic bone were put in the Order Saurischia or "lizard-hips"; while the ones with a bird-like pelvic bone made up the Order Ornithischia or "bird-hips". (Paradoxically, it was from "lizard-hipped" and not the "bird-hipped" forms that birds evolved). This classification is still adhered to in some (especially older) popular and academic books, but has pretty much been rejected in favour of the cladistic interpretation.

The earliest proto-dinosaurs [1] (basal Ornithodira) were a group of small early dinosaur-like archosaurs, known only from a few scrappy Argentinian fossils of Mid-Triassic age. These are neither saurischian nor ornithischian. These creatures, previously considered ornithosuchid thecodonts, are not even formally considered dinosaurs (although they are dinosauromorphs, which means dinosaurs and a few related forms more closely related to dinosaurs then to pterosaurs.). They are the stem forms from among which which the dinosaurs evolved. It has also for some years been felt that they are closely related to the Pterosaurs (flying reptiles). There is however a rival theory which derives the pterosaurs from prolacertiform "lizards," or perhaps even more distantly related stock.

See Ornithodira and Dinosauriformes for more.

The Saurischia or "lizard hipped" dinosaurs are those more closely related to birds than to Triceratops. Conventionally, they are divided in turn into two groups, one largely carnivorous, the other herbivorous. The first of these are the Theropoda, the bipedal carnivorous dinosaurs, with their bird-like legs and necks. Theropoda means "beast-feet", a rather inappropriate name; "bird(-like) feet" would have been better. Included in this huge and diverse group are both small forms (including the birds themselves) and large predators such as Allosaurus and Tyrannosaurus.

The other group of Saurischia, the Sauropodomorpha, were herbivores. There are two main subgroups, the Sauropoda (the inappropriately named "lizard-feet"), and their ancestors or uncles, the Prosauropoda ("before the sauropods"). Although the prosauropods were relatively small, the more advanced types, and all of the sauropods, were elephantine giants with tiny heads, very long necks and tails, massive bodies, and pillar-like legs. This group includes the famous "Brontosaurus" (or Apatosaurus) and its relatives. Like modern-day elephants, they relied on their great size as a defense against carnivores.

See Saurischia for more.

The Ornithischia ("bird hipped" dinosaurs), or Predentata (so called beacuse they posses a unique extra predentary bone in front of the jaw, which served as a sort of beak) were a more diverse group of herbivores. Being much smaller than the sauropods, they survived because they evolved various other means to avoid becoming fast food for their meat-eating theropod contemporaries. The ornithopods, for example, depended on fleetness of foot and acute sight and hearing. The Ceratopsian dinosaurs (Triceratops, etc) were the rhinoceroses of the dinosaur world, their formidable horns at least appear to be ample protection against even the largest and fiercest carnivores. There is a substantial body of opinion that these horns were more decorative than functional -- although we have probably not heard the end of this issue. The Stegosaurs and Ankylosaurs evolved armour plates, spikes, and tail-clubs as defensive and offensive weapons.

The Ornithischia -- unlike saurischian dinosaurs, reptiles and birds -- possessed mammal-like cheek muscles and cheek pouches to aid in chewing. In this respect they paralleled the mammalian form. Certainly, many Ornithischia filled ecological roles similar to those of the mammalian ungulates.

See Ornithischia for more.

So we see among the dinosaurs the tendency towards both an avimorphisation or bird-form-tendency in the Theropods, and a theromorphisation or mammal-form-tendency) in the Ornithischia. The dinosaurs of the Mesozoic era in a sense presaged the birds and mammals of the Cenozoic era.

A word now about birds. Most palaeontologists and dino-enthusiasts today also consider the Birds to be a subgroup of dinosaurs. Cladistically (phylogenetically) speaking this is correct: birds evolved from dinosaurs, so if dinosaurs are to retain their monophyletic status they must include birds. MAK010930. Revised ATW050609.

[1] The discussion here assumes a more or less conventional view of archosaur evolution. We are aware of unpublished work which might drastically alter this view. For both scientific and historical reasons, the data sets used to produce the present consensus tree of the archosaurs are weak. Some of those factors are discussed elsewhere. A complete restructuring of archosaur evolution, based on new data, is not at all out of the question.


[edit] Information

Dinosauria: Eoraptor. LCA birds & Triceratops.

Range: from Late Triassic (Carnian). (Although non-avian dinosaurs are no longer with us, birds are technically a subgroup of the dinosauria according to cladistic taxonomy)

Phylogeny: Dinosauriformes: Lagosuchidae + Dinosauria: Ornithischia + Saurischia.

[edit] Characters

  • Ectopterygoid lateral to transverse flange of pterygoid.
  • $ Postfrontal absent.
  • $ Temporal muscles extend anteriorly onto skull roof.
  • Quadrate head laterally exposed;
  • S-shaped neck.
  • Dorsal vertebrae shorter;
  • $ At least 3 fully incorporated sacral vertebrae (with 3rd incorporated from dorsal vertebrae).
  • Forelimb <50% length of rear (reversals in several groups).
  • Deltopectoral crest extends further down humerus.
  • $ Humerus with elongate deltopectoral crest.
  • Manus 4 with <4 phalanges.
  • Claws on manual digits 1-3 only.
  • Semi-perforate (usually fully perforated) acetabulum with buttress.
  • Brevis shelf on ilium.
  • Ischium with obturator process restricted to anterior 1/3rd.
  • $ Femur with ball-like head.
  • medial tuberosity of femur reduced.
  • Shaft of femur straight or bowed anteriorly.
  • Femur vertical.
  • Femur has greater, lesser & 4th trochanters.
  • $ Tibia with cnemial crest.
  • $ Well-developed ascending process of astragalus on anterior face of tibia.
  • $ Calcaneum with concave surface for articulation of fibula.
  • Metatarsals elongate and function as part of pes.

[edit] Discussion

The limiting factor is that muscles contract only about 30% of their length. Increasing muscle length therefore increases motion of the bone.

The tetrapod model of the pelvic girdle consists of a simple, tri-radiate structure. Pubis, ilium and ischium meet at Y-shaped junction. The acetabulum is located at the junction, and head of femur extends outward at 90° along its long axis. Protraction: Pubis extends antero-ventrally. Muscles insert on femur (pubofemoral) and protract (forward) it. Retraction: Tail (and/or ischium?) extends posteriorly and retract femur (caudofemoral). Abduction: Ilium extends posteriorly and muscles inserting on femur abduct it towards mid-line. Basic Tetrapod pelvis is plate-like. Extensions of pelvic bones are relatively small, and ilium articulates with only 1-2 vertebrae in sacrum. Muscles to pubis and ischium extend ventrally, countered to some extend by iliofemoral muscles.

The problem is that as the femur rotated downwards to become more vertical, the length of the muscle running from the pubis and ischium shortened relative to the length of the femur.

The solution common to all dinosaurs is an open acetabulum with bracing dorsally. Saurischians compounded on this with an extended pubis an ischium and rotated pubis antero-dorsally. Early ornithischians retroverted pubis, having it parallel to the ischium, and protracted the femur by attachment to anterior extension of ileum (see image). Later ornithischians secondarily developed an anterior projection of the pubis, as well as retaining the retroverted shaft.

[edit] Phylogeny

<==Dinosauria [Eudinosauria]
   |  i. s.: Palaeopteryx thomsoni
   |--Saurischia
   |    |  i. s.: Ornithodesmus Seeley 1887
   |    |           `--*O. cluniculus Seeley 1887
   |    |--Eoraptor lunensis
   |    `--+--Herrerasauridae
   |       |    |--Herrerasaurus [incl. Frenguellisaurus]
   |       |    |    `--H. ischigualastensis Reig 1963
   |       |    |--Ischisaurus
   |       |    `--Staurikosaurus
   |       `--+--Sauropodomorpha
   |          `--Theropoda
   `--Ornithischia
        |  i. s.: Fabrosaurus australis
        |         Nanosaurus
        |         Alocodon
        |         Trimucrodon
        |         Gongbusaurus
        |         Lusitanosaurus
        |         Jeholosaurus shangyuanensis
        |--+--Emausaurus
        |  `--+--Scelidosaurus Owen 1859
        |     `--Thyreophora
        |          |--Stegosauria
        |          `--Ankylosauria
        `--+--Cerapoda
           |    |--Ornithopoda
           |    `--Marginocephalia
           |         |--Pachycephalosauria
           |         `--Ceratopsia
           `--+--Lesothosaurus
              |    |--L. australis
              |    `--L. diagnosticus
              `--+--Scutellosaurus
                 `--Echinodon becklesii

* Type species of genus indicated

[edit] References

[edit] General references

this section from Wikipedia:
  • Kevin Padian, and Philip J. Currie. (1997). Encyclopedia of Dinosaurs. Academic Press. ISBN 0-12-226810-5. (Articles are written by experts in the field).
  • Paul, Gregory S. (2000). The Scientific American Book of Dinosaurs. St. Martin's Press. ISBN 0-312-26226-4.
  • Paul, Gregory S. (2002). Dinosaurs of the Air: The Evolution and Loss of flight in Dinosaurs and Birds. Baltimore: The Johns Hopkins University Press. ISBN 0-8018-6763-0.
  • Weishampel, David B. (2004). The Dinosauria. University of California Press; 2nd edition. ISBN 0-520-24209-2.

[edit] Technical References

Benton (1997); Hutchinson & Gatesy (2000); Novas (1996); White (2001). 010324.

[edit] Phylogeny References

Juul, L. 1994. The phylogeny of basal archosaurs. Palaeontologia Africana 31: 1-38.

Maryańska, T., H. Osmólska & M. Wolsan. 2002. Avialan status for Oviraptorosauria. Acta Palaeontologica Polonica 47 (1): 97-116.

Norman, D. 1985 (reprinted 2000). The Illustrated Encyclopedia of Dinosaurs. Salamander Books: London.

Prothero, D. R. 1998. Bringing Fossils to Life: An introduction to paleobiology. WCB McGraw-Hill: Boston.

Rauhut, O. W. M. 2005. Osteology and relationships of a new theropod dinosaur from the Middle Jurassic of Patagonia. Palaeontology 48 (1): 87-110.

Wellnhofer, P. 1991. The Illustrated Encyclopedia of Pterosaurs. Salamander Books: London (reprinted 2000, in The Illustrated Encyclopedia of Dinosaurs (D. Norman & P. Wellnhofer). Salamander Books).

Wilson, J. A., P. C. Sereno, S. Srivastava, D. K. Bhatt, A. Khosla & A. Sahni. 2003. A new abelisaurid (Dinosauria, Theropoda) from the Lameta Formation (Cretaceous, Maastrichtian) of India. Contributions from the Museum of Paleontology, The University of Michigan 31 (1): 1-42.

Xu, X., P. J. Makovicky, X.-L. Wang, M. A. Norell & H.-L. You. 2002. A ceratopsian dinosaur from China and the early evolution of Ceratopsia. Nature 416: 314-317.

Xu, X., M. A. Norell, X.-L. Wang, P. J. Makovicky & X.-C. Wu. 2002. A basal troodontid from the Early Cretaceous of China. Nature 415: 780-784.

Xu, X., X.-L. Wang & H.-L. You. 2001. A juvenile ankylosaur from China. Naturwissenschaften 88: 297-300.

Yates, A. M. 2003. A new species of the primitive dinosaur Thecodontosaurus (Saurischia: Sauropodomorpha) and its implications for the systematics of early dinosaurs. Journal of Systematic Palaeontology 1: 1-42.

Zhou, Z., P. M. Barrett & J. Hilton. 2003. An exceptionally preserved Lower Cretaceous ecosystem. Nature 421: 807-814.

[edit] Links

[edit] General Links

[edit] Graded Links

(from Wikipedia, and sorted roughly from least to most technical)
For children
Popular
Technical
Very technical
  • Dinobase A searchable dinosaur database, from the University of Bristol, with dinosaur lists, classification, pictures, and more.
  • DinoData Technical site, essays, classification, anatomy.
  • Dinosauria On-Line Technical site, essays, pronunciation, dictionary.
  • The Dinosauricon By T. Michael Keesey. Technical site, cladogram, illustrations and animations.
  • Thescelosaurus! By Justin Tweet. Includes a cladogram and small essays on each relevant genera and species.
  • Dinosauromorpha Cladogram From Palaeos. A detailed and wonderful amateur site about all things paleo.
  • Planet Dinosaur A very extensive site regarding dinosaur information.
Bird-dinosaur and dinosaur warm-bloodedness discussion

[edit] Credits

MAK 010930 and ATW Palaeos com ; This page MAK061024, MAK070109; phylogeny CKT071130

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