During the Campanian age, a radiation among dinosaur species occurred. In North America, for example, the number of known dinosaur genera rises from 4 at the base of the Campanian to 48 in the upper part. This development is sometimes referred to as the "Campanian Explosion". However, it is not yet clear if the event is artificial, i.e. the low number of genera in the lower Campanian can be caused by a lower preservation chance for fossils in deposits of that age. The generally warm climates and large continental area covered in shallow sea during the Campanian probably favoured the dinosaurs. In the following Maastrichtian stage, the number of North American dinosaur genera found is 30% less than in the upper Campanian.
A stocky ankylosaur protected by armor plates embedded in the skin. Although a complete skeleton has not been found, the species is estimated to have reached a maximum length of 4 meters (13 ft). Displays characteristics of both ankylosaurids and nodosaurids.
A bulky nodosaurid at roughly 6.6 m (22 ft) long. It had small, ridged bony plates on its back and many sharp spikes along its body sides. The four largest spikes jutted out from the shoulders on each side, two of which were split into subspines in some specimens. Its skull had a pear-like shape when viewed from above.
Aralosaurus was about the size of an elephant. Although very little is known about Aralosaurus (only one near complete skull has been found); it was identified by a beak with nearly 1,000 small teeth in 30 rows. These teeth were used for breaking up plant matter by chewing, a feature common in herbivorous dinosaurs, but unusual for reptiles.The back of an Aralosaurus skull was wide, a feature suggestive of large jaw muscles used to power its chewing apparatus.
Corythosaurus weighed in at 4 tonnes and measured roughly 10 metres (33 ft) from nose to tail. Like other hadrosaurs it had a toothless beak, the back of the jaws contained a dental battery composed of hundreds of small, interlocking teeth. These were used to crush and grind plant matter and were continually replaced as they wore away.
Hypacrosaurus is most easily distinguished from other hollow-crested duckbills by its tall neural spines and the form of its crest. The neural spines, which project from the top of the vertebrae, are 5 to 7 times the height of the body of their respective vertebrae in the back, which would have given it a tall back in profile. The skull's hollow crest is like that of Corythosaurus, but is more pointed along its top, not as tall, wider side to side, and has a small bony point at the rear
Maiasaura was large, attaining an adult length of about 9 metres (30 ft) and had the typical hadrosaurid flat beak and a thick nose. It had a small, spiky crest in front of its eyes. The crest may have been used in headbutting contests between males during the breeding season.
Naashoibitosaurus, based as it is on a single partial skeleton, is not well known in terms of anatomy. Its skull, the most thoroughly described portion, has a low nasal crest that peaks in front of the eyes, but does not strongly arch as in Gryposaurus.
Prosaurolophus was a large-headed duckbill; the most complete described specimen has a skull around 0.9 meters long (2.9 ft) on a ~8.5 meter long skeleton (~28 ft). It had a small, stout, triangular crest in front of the eyes; the sides of this crest were concave, forming depressions. The upper arm was relatively short.
Saurolophus is known from material including nearly complete skeletons, giving researchers a clear picture of its bony anatomy. S. osborni, the rarer Albertan species, was around 9.8 meters long (32 feet), with its skull a meter long (3.3 feet). Its weight is estimated at 1.9 tonnes (2.1 tons). S. angustirostris, the Mongolian species, was larger; the type skeleton is roughly 12 meters long (39.4 ft), and larger remains are reported.
It is one of the longest and largest known hadrosaurids; the composite skeleton of a medium-sized individual mounted at the Geological Institute of China in Beijing measures 14.72 metres (48.3 ft) in length.
Varricchio, D. J. 2001. Late Cretaceous oviraptorosaur (Theropoda) dinosaurs from Montana. pp. 42–57 in D. H. Tanke and K. Carpenter (eds.), Mesozoic Vertebrate Life. Indiana University Press, Indianapolis, Indiana.
Weishampel, D.B.; Barrett, P.M.; Coria, R.A.; Le Loueff, J.; Xu, X.; Zhao, X.; Sahni, A.; Gomani, E.M.P. & Noto, C.N.; 2004: Dinosaur distribution, in: Weishampel, D.B.; Dodson, P. & Osmólska, H. (eds.): The Dinosauria, University of California Press, Berkeley (2nd ed.), ISBN 0-520-24209-2, pp 517–606.