Saurischia

Introduction

Saurischian dinosaurs are among the oldest ever found and date back more than 220 million years. Though early Saurischia species were restricted to southern areas of Pangaea, the giant supercontinent at the time, by the Late Triassic saurischian dinosaurs such as the prosauropods and coelophysoids had dispersed across the entire terrestrial landscape. Dinosaurs are divided into one of two basic groups based on hip orientation, the Ornithischia (or “bird-hipped” dinosaurs) and the Saurischia (or “lizard-hipped” dinosaurs). Saurischia is currently defined as “birds and all dinosaurs that are closer to birds than they are to Ornithischia.” The Saurischia order is further comprised of two major groups: large herbivorous Sauropodomorpha, noted for their extremely long necks, and the predominantly carnivorous Theropoda.

Fast Facts

Pronunciation: Saurischia (pronounced saw-RIS-kee-a) means “lizard-hipped,” coined by paleontologist Harry Seeley in 1888

Time Period: Late Triassic (235 million years ago) to Current

Size: 6.2 cm to 60 m (2.5 in–200 ft) in length

Weight: 1.6 g to 120 metric tons (0.06 oz–264,555 lbs)

Diet: Carnivorous, Omnivorous, Insectivorous and/or Herbivorous

Location: Worldwide

Lifespan: 100 years or more

Homologous Traits

Many hundreds of saurischian species have lived, evolved, thrived, and finally gone extinct. Despite their great diversity, from the largest species such as Spinosaurus and Argentinosaurus, to the very smallest such as the bee hummingbird, certain homologous characteristics are shared by all saurischian dinosaurs.

Saurischian dinosaurs possess all the characteristics of the archosaurs—four limbs, oviparous (egg) reproduction, backbones, and upper and lower temporal skull openings, as well as the traits common in all dinosaur species, specifically upright posture, modified fourth and fifth digits on the hands, three-toed feet, specialized crests on the humerus and tibia bones, three or more sacral vertebrae, and a femur with a ball-like head at one end.

More specifically, however, saurischians are further defined by their hip orientation, in which the downward and forward positioning of their hips differs obviously from the backward pointing pubis of the ornithischians. Less obvious but still indicative are the large, distinct openings (antorbital fenestrae) between the eye socket and nostrils on saurischian skulls. Although these are also present in ornithischians, they are smaller and less pronounced.

Evolutionary Divergences

Saurischia are one of the two orders of Dinosauria, predominately classified by the arrangement of their hips. The saurischian dinosaurs are further classified as either large herbivorous Sauropodomorpha or predominately carnivorous Theropoda.

Sauropods are the infraorder of Sauropodomorpha, a term originally used to incorporate the sauropods and the more primitive prosauropods. The first true sauropods appeared as early as the Late Triassic, more than 210 million years ago and are believed to have evolved from basal (early) sauropodomorphs. The earliest sauropods are thought to resemble the earlier and smaller prosauropods, such as Anchisaurus and Massospondylus. Sauropods are generally defined by their herbivory, quadrupedalism, small heads, and extraordinarily long necks. Uniquely among dinosaur lineages, sauropods developed their extraordinary size within a relatively short geological time frame, and by the Middle Jurassic (166 million years ago), sauropods had diversified into a wide array of taxa. Theropoda are among the oldest and most successful dinosaurs to have ever lived, also appearing very early in the fossil record (about 230 million years ago) and surviving until the end of the Late Cretaceous (66 million years ago). Paleontologists believe theropods descended from much more primitive three-toed bipedal dinosaurs. Two of the earliest theropods are thought to be one of two Argentinean carnivores, Herrerasaurus or Eodromaeus. Nonavian theropods are generally defined by their carnivorous diet (although evidence has suggested this is not absolute), powerful clawed hands, sharp teeth, strong jaws, and bipedal locomotion. Theropoda is comprised of several clades, including the early ceratosaurs, which included Ceratosaurus and the abelisaurids; the tetanurans, which include the allosauroids, such as Allosaurus, and the Coelurosauria, such as the oviraptors and tyrannosaurids; and the Herrerasauridae, considered among the oldest known dinosaurs. Theropods are, in fact, an extant dinosaur lineage represented by all living bird species.

Creatures in This Group

Although debate continues regarding the classification of many dinosaur species, ongoing fossil discoveries, revision of taxa, and cladistic analysis have helped clarify many issues. Cladistics is considered the most reliable classification method for extinct species, such as nonavian dinosaurs, as it can analyze evolutionary relationships while compensating for the poor fossil record that paleontologists must use.

Saurischia includes Sauropodomorpha, large herbivores, and Theropoda, two-footed carnivores. According to cladistic analysis, Sauropodomorpha are characterized by such shared features as skulls that are less than half the length of the femur, commonalities related to dentition, 10 cervical vertebrae, and a funnel- or paddle-shaped fifth (V) metatarsal. Sauropodomorpha include the nodes Eusauropoda, Neoseuropoda, Camarasauromorpha, Titanosauriformes, Lithostrotia, and Saltasauridae. Differentiation among these nodes often has to do with skull shape and size, length of neck, placement of nares (nostrils or nasal passages), teeth formation, armor, and other, more complex anatomical differences. As new discoveries are made, placement of creatures may move between nodes, or uncertainties may arise about specific relationships.

Sauropodomorpha is comprised of a number of families, including the diplodocids, such as Diplodocus and Apatosaurus, the brachiosaurids, such as Brachiosaurus, the camarasaurids, such as Camarasaurus, the euhelopodids, the titanosaurids such as Titanosaurus, and the cetiosaurids, such as Cetiosaurus.

Theropoda is a sister taxon to Sauropodomorpha and is divided into two nodes, Ceratosauria and Tetanurae, and theropods range in size from Microraptor, a four-winged dinosaur that is about the same size as a crow, and Tyrannosaurus, which had a jaw measuring 1.2 meters (4 ft), was 12 meters long (40 ft), and weighed 5 to 7 metric tons (11,000 to 15,432 lbs). Theropoda are all bipedal, have serrated and flattened teeth, have pneumatic skulls, share long and narrow metatarsal features, and have forearms that are about two-thirds the size of the hind limbs. Ceratosauria are considered relatively primitive theropods and include Ceratosaurus and the abelisaurids, such as Abelisaurus. Tetanurae are more advanced theropods such as the Megalosauroidea and Avetheropoda.

Ecology

Macroevolutionary relationships can be seen in the fossils of dinosaurs and other ancient vertebrate animals. Though researchers can hypothesize on possible associations, it is from new and existing fossils that these ideas can be examined. Fossils have the ability to solidify a hypothesis or change current thinking in new and unexpected directions. Determining past behavior and ecology is difficult given the incomplete record, but fossils can help define dinosaur body plans and anatomical features, which can, in turn, help determine possible behavior exhibited and ecological niches filled by dinosaurs.

From the gigantic plant-eating sauropods to the fast carnivorous theropods, nonavian saurischian dinosaurs were diverse and widely distributed across the entire terrestrial landscape. They exhibited a range of different social behaviors: herding to solitary hunting; reproductive care such as egg-brooding to egg-burial; breeding behavior that included male ornamental display and fighting for mates; carnivorous and herbivorous feeding behavior; and significant size ranges. Such diversity was instrumental in their success and longevity and explains how such large animals, with high energy requirements, were able to coexist in a resource-limited environment.

Paleontology News

Saurischia, meaning “lizard-hipped,” was first introduced by paleontologist Harry Seeley in 1888. Although Seeley's ideas related to the paraphyletic Dinosauria have largely been disproven, his classification of dinosaurs based on hip orientation, which is the fundamental basis for the division of Saurischia and Ornithischia, remains to this day.

In the years since saurischian dinosaurs have been formally classified, a significant amount of research has been conducted on their classification and forms. Initial research into sauropod and theropod species focused on descriptions of exceedingly rare and isolated skeletal remains; newer, almost complete fossil finds progressed understanding of body forms and probable habitat and behavior. Despite their often ruthless rivalry, the “Bones Wars” between paleontologists Edward Drinker Cope and Othniel Charles Marsh in the late 1800s were instrumental in advancing scientific insight into dinosaurs.

The evolution of the dinosaur story will continue as long as new fossils are found, and researchers develop ever more sophisticated technology. To date, paleontologists have, for example, thought that the significant diversification of dinosaurs occurred during the Late Triassic. Evidence from a saurischian species located in Argentina has suggested that dinosaurs appeared on the fossil record as an already diverse group. This is significant if proven, as it suggests that dinosaur diversity and dominance over other terrestrial animals may have occurred earlier than previously thought.

Bibliography

Books

Fastovsky, David E., and David B. Weishampel. Dinosaurs: A Concise Natural History. New York: Cambridge University Press, 2009.

  • Aimed at nonspecialists and those with little understanding or background in dinosaurs, this work focuses on many aspects of the natural sciences and how they relate to dinosaur biology, evolution, life history, and classification.

—. Evolution and Extinction of the Dinosaurs. New York: Cambridge University Press, 2005.

  • Covers complex scientific processes and dinosaur species in an informative and comprehensible way, with illustrations.

Lucas, Spencer George. Dinosaurs: The Textbook. New York: McGraw-Hill, 2004.

  • An overview of important aspects of dinosaur discovery, behavior, biology, and classification.

Martin, Anthony J. Introduction to the Study of Dinosaurs. Malden, MA: Blackwell, 2006.

  • A comprehensive and up-to-date introduction to dinosaurs, providing scientific-based chapters on the major dinosaur clades, as well as anatomical, physiological, and behavioral information.

Parker, Steve. Dinosaurus: The Complete Guide to Dinosaurs. Richmond hill, on: Firefly, 2009.

  • Information on more than 500 dinosaurs, such as discovery and location and characteristics, such as anatomy and diet.

Weishampel, David B., Peter Dodson, and Halszka Osmólska. Dinosauria. Berkeley: University of California Press, 2007.

  • An in-depth text providing resources and scientific papers on dinosaurs, especially looking at the Saurichia and Ornithisia orders in regards to their evolution, distribution, and ecology.

Journals

Brusatte, Stephen L., Roger B. J. Benson, and Xu Xing. “The Evolution of Large-bodied Theropod Dinosaurs During the Mesozoic in Asia.” Journal of Iberian Geology 36.2 (2010): 275–96.

  • A discussion of the origin of dinosaurs and how they spread into new habitats.

Langer, Max C., Martin D. Ezcurra, Jonathas S. Bittencourt, and Fernando E. Novas. “The Origin and Early Evolution of Dinosaurs.” Biological Review 85 (2010): 55–110.

  • Discusses how dinosaurs originated from fully bipedal ancestors and how their origins help to inform paleobiology.

Nesbitt, Sterling J. “The Early Evolution of Archosaurs: Relationships and the Origin of Major Clades.” Bulletin of the American Museum of Natural History 352 (2011): 1–292.

  • Discusses the origin and evolution of archosaurs, which includes crocodilians, pterosaurs (flying reptiles), and dinosaurs. Includes phylogenetic analysis of approximately 80 taxonomic groups.

Ősi, Attila, Sebastián Apesteguía, and Michał Kowalewski. “Non-avian Theropod Dinosaurs from the Early Late Cretaceous of Central Europe.” Cretaceous Research 31.3 (2010): 304–20.

  • Using teeth, digits, and leg bones discovered in Hungary, the authors identify Gondwanan and Euramerican therapods that inhabited central Europe during the Late Cretaceous. Includes supporting photographs, plots, and maps. http://www.sciencedirect.com/science/article/pii/S0195667110000029

Taylor, Michael. “Sauropod Dinosaur Research: A Historical Review.” Geological Society, London 343 (2010): 361–86.

  • Discusses three phases of sauropod dinosaur research, claiming that since the 1960s, the public appetite for dinosaur-related news is prompting new and more descriptive work.

Additional Works Used

Brusatte, Stephen L. et al. “The Origin and Early Radiation of Dinosaurs.” Earth-Science Reviews 101.1–2 (2010): 68–100.

—, et al. Macroevolutionary Patterns in the Evolutionary Radiation of Archosaurs (Tetrapoda: Diapsida). Earth and Environmental Science Transactions of the Royal Society of Edinburgh 101 (2011): 367–82.

Butler, Richard J., Paul Upchurch, and David B. Norman. “The Phylogeny of the Ornithischian Dinosaurs.”Journal of Systematic Palaeontology 6.1(2008): 1–40.

Dinodata. Web. June 2011. www.dinodata.org.“Dinosaurs.” Wikipedia. Web. June 2011. <http://en.wikipedia.org>.Ezcurra, M. D. A New Early Dinosaur (Saurischia: Sauropodomorpha) from the Late Triassic of Argentina: A Reassessment of Dinosaur Origin and Phylogeny. Journal of Systematic Palaeontology 8.3(2010): 371–425.

Jacobsen, Aase Roland. “Feeding Behaviour of Carnivorous Dinosaurs as Determined by Tooth Marks on Dinosaur Bones.” Historical Biology: An International Journal of Paleobiology 13.1 (1998): 17–26.

http://www.sciencedirect.com/science/article/pii/S0195667110000029Sereno, P. C. “Basal Archosaurs: Phylogenetic Relationships and Functional Implications.” Journal of Vertebrate Paleontology 11.S4 (1991): 1–53.

Varricchio, D. J. et al. “Mud-trapped Herd Captures Evidence of Distinctive Dinosaur Sociality.”. Acta Palaeontologica Polonica 53.4 (2008): 567–78.