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seen from the left and right side. Scale bar = 2.5 inches (6 cm). From Chure and oth- ers 2010.

portions of the postcranial skeleton of Abydosaurus are known, so it is not yet clear if this early Creta- ceous sauropod had a giraffelike posture like its bra- chiosaurid relatives and exactly how long the entire body might have been. The four individuals whose remains are preserved in the Mussentuchit Member may be part of an Abydosaurus herd that perished about 105 million years ago while crossing a stream bed. Future excavations at the site may reveal many more details about this new species of early Creta- ceous sauropod.

In addition, the upper members of the Cedar Mountain Formation have yielded the remains of many other kinds of dinosaur herbivores. Most notable are the fossils that document the pres- ence of several taxa belonging to the large family of armored quadrupedal herbivores known as ankylo- saurs. In particular the nodosaurids (a subset of the ankylosaurs that lack the famous tail club) are well represented. Collectively the ankylosaurs from the upper portions of the Cedar Mountain Formation constitute one of the richest assemblages of armored dinosaurs in the world (Carpenter and others 2008) and include at least three different genera, proba- bly more. One of the larger of these ankylosaurs is Peloroplites cedarimontanus (Carpenter and oth- ers 2008), whose species name is a reflection of the formation that preserves its fossils. Peloroplites was

15–18 feet (5–6 meters) long but was built rather low to the ground, with massive limbs to support the weight of an armored body. Its head, nearly 2 feet (0.6 meter) long, was broad and relatively flat, was tipped with a squarish toothless beak, and included powerful jaws that bore teeth designed to pro- cess tough vegetation. Little of the bony armor that probably covered much of the body was preserved with the skeletal remains, so no one can be sure just how well protected from predators Peloroplites was. It is clear, however, that Peloroplites was a mas- sive, slow-moving herbivore that probably fed on tough, low-growing vegetation. In the presence of the predators of early Cretaceous Utah such a crea- ture would most likely have carried substantial der- mal armor.

In addition to Peloroplites, two other species of nodosaurid ankylosaurs are known from the upper Cedar Mountain Formation: Animantarx (Car- penter and others 1999) and Cedarpelta (Carpen- ter, Miles, and Cloward 2001). Animantarx was a relatively small animal, reaching an average length of some 10 feet (3.3 meters), with a skull (fig. 6.21) barely a foot long. It was well armored, with rows of keel-shaped bony knobs covering its back and prominent spikes protecting its neck and flanks (fig. 6.22). Cedarpelta appears to have been a some- what larger nodosaurid, attaining a typical adult body length of 25 feet (8 meters) or more. The skull of Cedarpelta was about 2 feet (0.6 meter) long and, as in most other nodosaurids, was armored with numerous plates and small knobs. In addition to Peloroplites, Animantarx, and Cedarpelta, other fos- sils collected from the upper Cedar Mountain For- mation appear to belong to one or perhaps several other species of armored dinosaurs such as Sau- ropelta (fig. 6.23). The skeletal anatomy of Sauro- pelta is well known from the abundant remains of this nodosaurid found in early Cretaceous strata in Wyoming and Montana. Sauropelta is a good model for the general appearance of the armored dinosaurs in the Cedar Mountain Formation, though the fos- sil evidence clearly indicates several variations on 6.20. Reconstruction of the skull and neck vertebrae of

Abydosaurus. Based on reconstruction by Chure and

this morphological theme. The armored dinosaurs known from the Mussentuchit and Ruby Ranch Members thus suggest a much more diverse assem- blage of these creatures than was present in preced- ing Yellow Cat fauna.

In addition to the armored dinosaur herbivores from the upper Cedar Mountain members, at least one type of relatively advanced ornithopod foraged with them in the forests of the early Cretaceous. In 1992 the remains of a bipedal herbivore were discov- ered from the same strata near Castle Dale that pro- duced fossils of Animantarx. On the basis of these fossils, James Kirkland later described Eolambia car- oljonesa as an advanced ornithopod, possibly related to the hadrosaurs or “duck-billed dinosaurs” of the later Cretaceous (Kirkland 1998a). Additional Eol- ambia fossils, including the remains of several juve- niles, have been identified from quarries in the Mussentuchit Member in the southern San Rafael Swell (Garrison and others 2007). Eolambia was a large ornithopod that reached adult lengths of per- haps 20–30 feet (7–10 meters) though none of the juvenile specimens would have been that long (fig. 6.24). This ornithopod had a broad snout, though it was not as well developed as the shovel-snouts of the hadrosaurs that lived in Utah later in the Cre- taceous period. Other skeletal details suggest that Eolambia was somewhat more advanced and spe- cialized than the iguanodontid ornithopods of the lower Cedar Mountain Formation. Though it was for a time considered the earliest hadrosaur or “duckbill,” the most recent analyses of the skeletal features of Eolambia suggest that it was a specialized iguanodontid, a descendant of the more primitive members of this group known from the Yellow Cat Member and Poison Strip Sandstone (Head 2001). Nonetheless, Eolambia was a large herbivore and 6.21. Reconstructed skull of Animantarx displayed at

the College of Eastern Utah Prehistoric Museum. Total length of the skull is slightly less than 1 foot. Photo by Frank DeCourten.