ABSTRACT Outcrops of Late Cretaceous Gulf Series strata (Woodbine, Eagle Ford, and Austin) in the Dallas area expose middle Cenomanian to the early Campanian (96 to ˜ 83 Ma) rocks, which are well known in the subsurface of the oil-rich East Texas Basin. Together with the underlying Comanche Series and overlying younger Gulf Series, this set of strata provides a record of the last 50 million years of the Cretaceous. Although both marine and terrestrial vertebrates are known in this interval, the Late Cretaceous record is primarily marine. On this field trip, sites are visited that have yielded sharks, bony fish, turtles, dinosaurs, crocodiles, pterosaurs, mammals, long- and short-necked plesiosaurs, and a classic record of mosasaur evolution.

A new Early Cretaceous dinosaur locality in the Twin Mountains Formation at Proctor Lake, Texas, reveals information concerning hypsilophodontid social behavior. Both adults and congregations of juvenile hypsilophodontids occur at the site. Recent excavation of one mass of juveniles shows that it occurs in a shallow depression on a paleosol surface. The distribution of skeletal elements and age structure of individuals within congregations may indicate nesting and parental care of the young after hatching. Hypsilophodontids occupied the site over a long period of time, indicating attraction to the area for some reason. The region was a semi-arid flood plain within a lowland valley. Attractive features of the site may have included abundant vegetation and water or protection from predators. The accumulations of juvenile bones may represent attritional mortality of individuals from a single clutch or a succession of clutches in the nest area.