Dilophosaurus, a dinosaur recognized by the distinctive twin crests on its skull, has captivated public imagination, though its portrayal in popular culture often misrepresents its true size and abilities. This article clarifies the geological period when this predator roamed Earth, detailing its world and how its age is determined. While often depicted as small and venomous, Dilophosaurus was a substantial early theropod, approximately 23 feet long and weighing around 880 pounds. It was a significant predator of its time, though it lacked the venom-spitting ability or neck frill seen in fiction.
Its Place in Geological Time
Dilophosaurus lived during the Early Jurassic period, following the Triassic-Jurassic extinction event. Specifically, its existence spans the Sinemurian and Pliensbachian stages of this epoch. This period occurred approximately 193 to 184 million years ago.
The Early Jurassic marked a recovery and diversification of life after a major extinction event. Dilophosaurus was one of the earliest large predatory dinosaurs of the Jurassic, emerging as an apex predator in North America. Its appearance signaled the rise of larger carnivores that would come to dominate terrestrial ecosystems throughout the Jurassic.
The World It Inhabited
The Early Jurassic had a warm, humid climate. The supercontinent Pangea had begun to rift apart, leading to changes in continental configurations and oceanographic patterns. This geological activity contributed to a more humid environment, with vast areas covered by forests.
The flora of this period was dominated by gymnosperms, including conifers, cycads, and ginkgos. True flowering plants had not yet evolved. Alongside Dilophosaurus, the terrestrial fauna included early sauropods, other theropods, and early mammals, which were generally small and shrew-like. Pterosaurs, the flying reptiles, also diversified during this time.
How Its Age Is Determined
Dilophosaurus’s age is determined by studying its fossils within geological formations. The primary source of Dilophosaurus fossils is the Kayenta Formation, located in northern Arizona. This formation is a sequence of sedimentary rocks, and paleontologists use stratigraphy, the study of rock layers, to establish the relative age of the fossils found within them.
To pinpoint a more precise age, scientists employ radiometric dating, particularly of volcanic ash layers found near the fossil-bearing strata. Radioactive elements in these ash layers decay at a predictable rate, acting as a geological clock. By measuring the ratio of parent to daughter isotopes, researchers can determine when these layers formed, thus bracketing the age of the Dilophosaurus fossils. Recent studies utilizing uranium-lead (U-Pb) analyses of detrital zircons from the Kayenta Formation have helped refine its age to the Pliensbachian-Toarcian stages.