Dinosaurs: Their Rise & Fall

[Melody Stacker]

Most dinosaur fossils have been found in the Norian-Sinemurian, Kimmeridgian-Tithonian, and Campanian-Maastrichtian periods. Continuity of lineages across the intervening gaps shows that those gaps are artifacts of preservation rather than any reduction in diversity or abundance.

In many instances, cladistic analysis shows that ancestral lineages of varying durations fall in those gaps. The length of missing ancestral lineages in 1997[3] range from 25 Ma (Lesothosaurus, Genasauria, Hadrosauroidea, Sauropoda, Neoceratopsia, Coelurosauria) to 85 Ma (Carcharodontosauridae). Because the dinosaurian radiation began at small body size, the unrecorded early history may be due to less reliable fossilization of smaller species. However, some missing lineages, notably of Carcharodontosauridae and Abelisauridae, require alternative explanations because the missing range extends across stages rich in fossil material.

[Melody Stacker]

Evolutionary trends

Body size

Body size is important because of its correlation with metabolism, diet, life history, geographic range and extinction rate.[3] The modal body mass of dinosaurs lies between 1 and 10 tons throughout the Mesozoic and across all major continental regions. That said, there was a trend towards increasing body size within many dinosaur clades, including the Thyreophora, Ornithopoda, Pachycephalosauria, Ceratopsia, Sauropomorpha, and basal Theropoda. Marked decreases in body size have also occurred in some lineages, but are more sporadic. The best known example is the decrease in body size leading up to the first birds; Archaeopteryx was below 10 kg in weight, and later aves Confuciusornis and Sinornis are starling- to pigeon-sized.

[Melody Stacker]

Mobility

The ancestral dinosaur was a biped. The evolution of a quadrupedal posture occurred four times, among the ancestors of Euornithopoda, Thyreophora, Ceratopsia and Sauropodomorpha.[3] In all four cases this was associated with an increase in body size, and in all four cases the trend is unidirectional without reversal.

Dinosaurs exhibit a pattern of the reduction and loss of fingers on the lateral side of the hand (digits III, IV and V). The primitive function of the dinosaur hand is grasping with a partially opposable thumb, rather than weight-bearing.

[Melody Stacker]

Effect of food sources

The ancestral dinosaur was a carnivore. Herbivory among dinosaurs arose three times, at the origin of the ornithischian, sauropodomorph, and therizinosaurid clades. Individual therizinosaurids are herbivorous or omnivorous. Herbivory among the ornithischians and sauropodomorphs was never reversed.[3]

The potential co-evolution of plants and herbivorous dinosaurs has been subject to extensive speculation. The appearance of prosauropods in the late Triassic has been tentatively linked either to the demise or diversification of types of flora at that time. The rise of ceratopsids and iguanodont and hadrosaurid ornithopods in the Cretaceous has been tentatively linked to the angiosperm radiation. Unfortunately, there are still no hard data on dietary preferences of herbivorous dinosaurs, apart from data on chewing technique and gastroliths.

[Melody Stacker]

Biogeography

Dinosaurian faunas, which were relatively uniform in character when Pangaea began to break up, became markedly differentiated by the close of the Cretaceous. Biogeography is based on the splitting of an ancestral species by the emplacement of a geographic barrier. Interpretation is limited by a lack of fossil evidence for eastern North America, Madagascar, India, Antarctica and Australia. No unequivocal proof of the biogeographical action on Dinosaur species has been obtained,[3] but some authors have outlined centres of origin for many dinosaur groups, multiple dispersal routes, and intervals of geographic isolation.

[Melody Stacker]

Dinosaurs that have been given as evidence of biogeography include abelisaurid theropods from South America and possibly else where on Gondwana.

Relationships between dinosaurs show abundant evidence of dispersal from one region of the globe to another. Tetanuran theropods travelled widely through western North America, Asia, South America, Africa and Antarctica. Pachycephalosaurs and ceratopsians show clear evidence of multiple bidirectional dispersion events across Beringa.

[Melody Stacker]

Extinction

The Cretaceous–Tertiary extinction event, which occurred 65.5 million years ago at the end of the Cretaceous period, caused the extinction of all dinosaurs except for the line that had already given rise to the first birds.

[Melody Stacker]

References

   1. ^ a b c d e f g Weishampel, Dodson & Osmolska, 2004, The Dinosauria
   2. ^ a b Senter, P. (2007). "A new look at the phylogeny of Coelurosauria (Dinosauria: Theropoda)." Journal of Systematic Palaeontology, (doi:10.1017/S1477201907002143)
   3. ^ a b c d e f g h i j PC Sereno (1997) "The origin and evolution of dinosaurs" Annu. Rev. Earth Planet. Sci. 25:435-489

Paul C. Sereno (1999) The evolution of dinosaurs, Science, Vol 284, pp. 2137-2146 http://www.sciencemag.org/cgi/content/abstract/284/5423/2137

[Melody Stacker]

Mounted skeletons of Tyrannosaurus (left) and Apatosaurus (right) at the AMNH.

[Melody Stacker]

List of dinosaurs

This list of dinosaurs is a comprehensive listing of all genera that have ever been included in the superorder Dinosauria, excluding class Aves (birds, both living and those known only from fossils) and purely vernacular terms. The list includes all commonly accepted genera, but also genera that are now considered invalid, doubtful (nomen dubium), or were not formally published (nomen nudum), as well as junior synonyms of more established names, and genera that are no longer considered dinosaurs. Many listed dinosaurs have since been reclassified as everything from birds to crocodilians to petrified wood. The list contains 1249 names, of which approximately 860 are considered either valid dinosaur genera or nomina dubia.

[Melody Stacker]

Scope and terminology

There is no official, canonical list of dinosaur genera. The closest is the Dinosaur Genera List, compiled by biological nomenclature expert George Olshevsky, which was first published online in 1995 and is regularly updated. The most authoritative general source in the field is the second (2004) edition of The Dinosauria. The vast majority of citations are based on Olshevsky's list, and all subjective determinations (such as junior synonymy or non-dinosaurian status) are based on The Dinosauria, except where they conflict with primary literature. These exceptions are noted.

[Melody Stacker]

Naming conventions and terminology follow the International Code of Zoological Nomenclature. Technical terms used include:

    * Junior synonym: A name which describes the same taxon as a previously published name. If two or more genera are formally designated and the type specimens are later assigned to the same genus, the first to be published (in chronological order) is the senior synonym, and all other instances are junior synonyms. Senior synonyms are generally used, except by special decision of the ICZN (see Tyrannosaurus), but junior synonyms cannot be used again, even if deprecated. Junior synonymy is often subjective, unless the genera described were both based on the same type specimen.
    * Nomen nudum (Latin for "naked name"): A name that has appeared in print but has not yet been formally published by the standards of the ICZN. Nomina nuda (the plural form) are invalid, and are therefore not italicized as a proper generic name would be. If the name is later formally published, that name is no longer a nomen nudum and will be italicized on this list. Often, the formally published name will differ from any nomina nuda that describe the same specimen.
    * Nomen oblitum (Latin for "forgotten name"): A name that has not been used in the scientific community for more than fifty years after its original proposal.
    * Preoccupied name: A name that is formally published, but which has already been used for another taxon. This second use is invalid (as are all subsequent uses) and the name must be replaced. Preoccupied names are not valid generic names.
    * Nomen dubium (Latin for "dubious name"): A name describing a fossil with no unique diagnostic features. As this can be an extremely subjective and controversial designation (see Hadrosaurus), this term is not used on this list.
http://en.wikipedia.org/wiki/List_of_dinosaurs

[Melody Stacker]

    * Aachenosaurus — actually a piece of petrified wood
    * "Abdallahsaurus" — nomen nudum, probably Brachiosaurus or Giraffatitan
    * Abelisaurus
    * Abrictosaurus
    * Abrosaurus
    * Acanthopholis
    * Achelosaurus[1] — misspelling of Achelousaurus
    * Achelousaurus
    * Achillesaurus
    * Achillobator
    * "Acracanthus" — original invalid name of Acrocanthosaurus
    * Acrocanthosaurus
    * Actiosaurus — probably an ichthyosaur
    * Adamantisaurus
    * Adasaurus
    * Adeopapposaurus
    * Aegyptosaurus
    * Aeolosaurus
    * Aepisaurus
    * Aerosteon
    * Aetonyx — possible junior synonym of Massospondylus
    * Afrovenator
    * Agathaumas
    * Aggiosaurus — actually a metriorhynchid crocodilian
    * Agilisaurus
    * Agnosphitys
    * Agrosaurus — probably a junior synonym of Thecodontosaurus
    * Agujaceratops
    * Agustinia
    * "Airakoraptor" — nomen nudum
    * Alamosaurus
    * "Alashansaurus" — nomen nudum; Shaochilong
    * Alaskacephale
    * Albertaceratops
    * Albertonykus
    * Albertosaurus
    * Albisaurus — a non-dinosaurian reptile
    * Alectrosaurus
    * Aletopelta
    * Algoasaurus
    * Alioramus
    * Aliwalia — junior synonym of Eucnemesaurus

[Melody Stacker]

    * Allosaurus
    * Alocodon
    * Altirhinus
    * Altispinax
    * Alvarezsaurus
    * Alwalkeria
    * Alxasaurus
    * Amargasaurus
    * Amargatitanis
    * Amazonsaurus
    * Ammosaurus
    * Ampelosaurus
    * Amphicoelias
    * "Amphicoelicaudia" — nomen nudum; possibly Huabeisaurus
    * "Amphisaurus" — preoccupied name, now known as Anchisaurus
    * Amtosaurus — possibly Talarurus
    * Amurosaurus
    * Amygdalodon
    * Anabisetia
    * Anasazisaurus
    * Anatosaurus — junior synonym of Edmontosaurus
    * Anatotitan
    * Anchiceratops
    * Anchiornis
    * Anchisaurus
    * Andesaurus
    * Angaturama — probable junior synonym of Irritator
    * "Angloposeidon"[2][3] — nomen nudum
    * Angulomastacator
    * Aniksosaurus
    * Animantarx
    * Ankistrodon — actually a proterosuchid archosauriform
    * Ankylosaurus
    * Anodontosaurus — junior synonym of Euoplocephalus or Dyoplosaurus
    * Anoplosaurus
    * Anserimimus
    * Antarctopelta
    * Antarctosaurus

[Melody Stacker]

    * Antetonitrus
    * Anthodon — actually a pareiasaur
    * Antrodemus — possibly a junior synonym of Allosaurus
    * Apatodon — possibly a junior synonym of Allosaurus
    * Apatosaurus — popularly known as Brontosaurus
    * Appalachiosaurus
    * Aragosaurus
    * Aralosaurus
    * "Araucanoraptor" — nomen nudum; Neuquenraptor
    * Archaeoceratops
    * Archaeodontosaurus
    * Archaeopteryx — actually a bird (by definition)
    * "Archaeoraptor" — now known as the bird Yanornis and the dromaeosaur Microraptor
    * Archaeornis — junior synonym of the bird Archaeopteryx
    * Archaeornithoides
    * Archaeornithomimus
    * Archaeovolans — junior synonym of the bird Yanornis
    * Arctosaurus — actually some sort of non-dinosaurian reptile
    * Arenysaurus
    * Argentinosaurus
    * Argyrosaurus
    * Aristosaurus — junior synonym of Massospondylus
    * Aristosuchus
    * Arizonasaurus — actually a rauisuchian
    * "Arkanosaurus" — variant spelling of "Arkansaurus"
    * "Arkansaurus" — nomen nudum
    * Arrhinoceratops
    * Arstanosaurus
    * Asiaceratops
    * Asiamericana
    * Asiatosaurus
    * Astrodon
    * Astrodonius — junior synonym of Astrodon
    * Astrodontaurus — junior synonym of Astrodon
    * Asylosaurus
    * Atlantosaurus — possible junior synonym of Apatosaurus or Camarasaurus
    * Atlasaurus
    * Atlascopcosaurus
    * Atrociraptor
    * Aublysodon

Artist's restoration of a trio of Aucasaurus.

    * Aucasaurus