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FIGURE 9.6 Tetanurans as represented by allosaurids. (A) Giganotosaurus, a carcharodontosaurine of the Early Cretaceous of Argentina. (B) Yangchuanosaurus, a sinraptorid of the Late Jurassic of China. The former is on permanent display at the Fernbank Museum of Natural History, Atlanta, Georgia; the latter is currently on display in the atrium of Hartsfield-Jackson International Airport, Atlanta.

FIGURE 9.6 Tetanurans as represented by allosaurids. (A) Giganotosaurus, a carcharodontosaurine of the Early Cretaceous of Argentina. (B) Yangchuanosaurus, a sinraptorid of the Late Jurassic of China. The former is on permanent display at the Fernbank Museum of Natural History, Atlanta, Georgia; the latter is currently on display in the atrium of Hartsfield-Jackson International Airport, Atlanta.

Cretaceous. These theropods may have weighed as much as 8 metric tons, which probably exceeded the mass of the most famous large theropod, Tyrannosaurus.

One of the mixed blessings of intensive scientific study of tetanurans is that what used to be simple becomes more complex. With dinosaurs, no group is more complicated in its classification than Tetanurae, and accordingly it has the highest number of taxa assigned to any clade within the Dinosauria (compare Table 9.2 with Table 9.1). Tetanurae in its simplest form is defined as all birds and theropods more evolutionarily related to birds than ceratosaurs, which makes it a stem-based clade. The most basal tetanuran known is Torvosaurus of the Late Jurassic, followed by the few members of the Megalosauridae, which includes the Middle Jurassic Megalosaurus, originally described by William Buckland in 1824 (Chapter 3). Megalosauridae is defined as an outgroup, in that it is outside of the other groups under study within Tetanurae, such as all those under the node-based clade, Avetheropoda. As mentioned in Chapter 5, node-based clades are those that have all of the descendants of the most recent common ancestor for two groups, where the common ancestor forms the node. Megalosauridae is also the most tenuous assignment for any clade within Tetanurae, because of its small number of members and their fragmentary fossil record.

The vast majority of tetanurans are avetheropods, and are classified on the basis of some of the following synapomorphies:

■ Increased anterior extension of the pubis into a pubic foot.

■ Pronounced cnemial process on the side of the tibia.

■ Loss of a foramen on the obturator, associated with the notch on the ischium.

■ Premaxillary teeth are asymmetrical.

Genus

Age

Geographic Location

Acrocanthosaurus

Early Cretaceous

Western and central USA

Afrovenator

Early Cretaceous

Niger

Albertosaurus

Late Cretaceous

Alberta, Canada

Alectrosaurus

Late Cretaceous

China; Mongolia

Allosaurus

Late Jurassic

Western and central USA

Alxasaurus

Early Cretaceous

Mongolia

Avimumus

Late Cretaceous

Mongolia, China

Bambiraptor

Late Cretaceous

Western USA

Baryonyx

Early Cretaceous

England

Beipiaosaurus

Early Cretaceous

China

Caracharodontosaurus

Early Cretaceous

Northern Africa

Caudipteryx

Early Cretaceous

China

Chirostenotes

Late Cretaceous

Alberta, Canada

Compsognathus

Late Jurassic

France; Germany

Crylophosaurus

Early Jurassic

Antarctica

Cryptovolans

Early Cretaceous

China

Daspletosaurus

Late Cretaceous

Western USA; Alberta, Canada

Deinocheirus

Late Cretaceous

Mongolia

Deinonychus

Early Cretaceous

Western and central USA

Deltadromeus

Late Cretaceous

Niger

Dromaeosaurus

Late Cretaceous

Western USA

Dryptosaurus

Late Cretaceous

Eastern USA

Erlikosaurus

Late Cretaceous

Mongolia

Gallimimus

Late Cretaceous

Mongolia

Gigagantosaurus

Late Cretaceous

Argentina

Gorgosaurus

Late Cretaceous

Western USA; Alberta, Canada

Ingenia

Late Cretaceous

Mongolia

Khaan

Late Cretaceous

Mongolia

Megalosaurus

Middle Jurassic

Western Europe

Microraptor

Early Cretaceous

China

Monolophosaurus

Late Jurassic

China

Neovenator

Early Cretaceous

Madagascar

Ornitholestes

Late Jurassic

Western USA

Ornithomimus

Late Cretaceous

Western USA

Oviraptor

Late Cretaceous

Mongolia

Pelecanimimus

Early Cretaceous

Spain

Piatnitzkysaurus

Late Jurassic

Argentina

Protarchaeopteryx

Early Cretaceous

China

Saurornithoides

Late Cretaceous

Mongolia

Saurornitholestes

Late Cretaceous

Alberta, Canada

Scipionxy

Early Cretaceous

Italy

Segnosaurus

Late Cretaceous

Mongolia

Shenzhousaurus

Early Cretaceous

China

Sinornithomimus

Early Cretaceous

China

Sinornithosaurus

Early Cretaceous

China

Sinosauropteryx

Early Cretaceous

China

Sinovenator

Early Cretaceous

China

Spinosaurus

Early Cretaceous

Northern Africa

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