Museum Of Natural History Troodon

Museum The Rockies Dinosaurs
FIGURE 9.8 Troodon, a relatively small tetanuran with a relatively large brain for a dinosaur. Temporary display on loan from the Museum of the Rockies, at the Fernbank Museum of Natural History, Atlanta, Georgia.
FIGURE 9.9 Deinonychus, a Late Cretaceous dromaeosaur of the western USA. (A) Skeletal reconstruction of Deinonychus. (B) Close-up view of the upraised digit I of left pes. North Carolina Museum of Natural History.

that apparently departed considerably from expectations for theropods. Included within Maniraptoriformes is the stem-based Maniraptora, the lineage that led to birds. This clade diverged into two other stem-based clades, Deinonychosauria, which include the dromaeosaurids, such as Deinonychus, Velociraptor, and Utahraptor, and Aviale (Fig. 9.9). The latter is composed of Archaeopteryx, all fossil ancestors of modern birds, and modern birds. For the sake of simplicity, Aviale will be discussed in detail in Chapter 15.

The body fossil record for tetanurans is not only diverse, especially in comparison to herrerasaurids and ceratosaurs, but is becoming better understood through

FIGURE 9.10 Acrocanthosaurus, an Early Cretaceous allosaurid from Texas. (A) Skeletal reconstruction: North Carolina Museum of Natural History. (B) Large theropod track affiliated with Acrocanthosaurus, preserved in limestone but slightly submerged in Paluxy River, eastern Texas. Human footprint in river mud (right) for scale.

FIGURE 9.10 Acrocanthosaurus, an Early Cretaceous allosaurid from Texas. (A) Skeletal reconstruction: North Carolina Museum of Natural History. (B) Large theropod track affiliated with Acrocanthosaurus, preserved in limestone but slightly submerged in Paluxy River, eastern Texas. Human footprint in river mud (right) for scale.

an ever-increasing database of trace fossil evidence. In some cases, these trace fossils can be directly linked to tracemakers within a specific clade or species within Tetanurae. For example, large theropod tracks in the Lower Cretaceous of east Texas, discovered by Roland Bird in the 1940s (Chapters 3 and 14), have been tentatively correlated with the similarly-sized and shaped feet of Acrocanthosaurus, an allosaurid within same-age strata of the same region (Fig. 9.10). Thin-toed footprints found in Lower Cretaceous strata of Colorado, which are the right size and shape for these ostrich-like dinosaurs, represent probable ornithomimid tracks. Perhaps the best fit between a track and a tetanuran tracemaker of the same age is a little-doubted tyrannosaurid track from the Late Cretaceous of New Mexico. This track is so large (85 cm long) that it could be assigned only to Tyrannosaurus (Fig. 9.11). Besides tracks, other tetanuran trace fossils include the following:

FIGURE 9.11 "Before" and "after" depictions of Tyrannosaurus foot anatomy. (A) "Before" of a large, fleshy foot represented by a probable Tyrannosaurus track (left foot) from the Upper Cretaceous Raton Formation, New Mexico. Cast at University of Colorado, Denver. (B) "After" ventral (sole) view of Tyrannosaurus foot (left again) without the flesh from the viewpoint of being stepped on. Specimen part of skeletal mount in Denver Museum of Science and Nature. Note the corresponding position of the hallux in both track and foot.

FIGURE 9.11 "Before" and "after" depictions of Tyrannosaurus foot anatomy. (A) "Before" of a large, fleshy foot represented by a probable Tyrannosaurus track (left foot) from the Upper Cretaceous Raton Formation, New Mexico. Cast at University of Colorado, Denver. (B) "After" ventral (sole) view of Tyrannosaurus foot (left again) without the flesh from the viewpoint of being stepped on. Specimen part of skeletal mount in Denver Museum of Science and Nature. Note the corresponding position of the hallux in both track and foot.

1 Troodon nests from the Late Cretaceous of Montana;

2 probable tyrannosaurid coprolites from the Late Cretaceous of Alberta, Canada;

3 gastroliths within the body cavity of the Early Cretaceous coelurosaur Caudipteryx of China; and

4 toothmarks attributed to Allosaurus, Troodon, and tyrannosaurids, among others (Chapter 14).

A wealth of other theropod trace fossils from the Jurassic and Cretaceous ensure that more links between tetanurans and the artifacts of their behavior will be made in the future.

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