Science, Tech, Math › Animals & Nature The Dinosaurs and Prehistoric Animals of Delaware Share Flipboard Email Print Animals & Nature Dinosaurs Basics Paleontologists Carnivores Dinosaurs & Birds Herbivores Marine Reptiles Prehistoric Mammals Amphibians Birds Habitat Profiles Mammals Reptiles Wildlife Conservation Insects Marine Life Forestry Evolution View More By Bob Strauss Science Writer B.S., Cornell University Bob Strauss is a science writer and the author of several books, including "The Big Book of What, How and Why" and "A Field Guide to the Dinosaurs of North America." our editorial process Bob Strauss Updated July 22, 2019 The fossil record of Delaware pretty much begins and ends in the Cretaceous period: before 140 million years ago, and after 65 million years ago, this state was mostly underwater, and even then geologic conditions did not lend themselves to the fossilization process. Fortunately, however, Delaware's sediments have yielded enough Cretaceous dinosaurs, prehistoric reptiles and invertebrates to make this state an active site of paleontological research, as you can learn by perusing the following slides. 01 of 05 Duck-Billed and Bird-Mimic Dinosaurs Alain Beneteau The dinosaur fossils discovered in Delaware mostly consist of teeth and toes, not enough evidence to assign them to a specific genus. However, paleontologists have broadly classified these itty-bitty fossils, excavated from the Delaware and Chesapeake Canals, as belonging to various hadrosaurs (duck-billed dinosaurs) and ornithomimids ("bird-mimic" dinosaurs), the carcasses of which washed out into the Delaware Basin sometime during the late Cretaceous period. 02 of 05 Various Marine Reptiles Wikimedia Commons Even during the Cretaceous period, when the sediments in what would become Delaware lent themselves to fossil preservation, much of this state was still underwater. That explains this state's profusion of mosasaurs, the fierce marine reptiles (including Mosasaurus, Tylosaurus, and Globidens) that dominated the later Cretaceous period, as well as prehistoric turtles. As with Delaware's dinosaurs, these remains are too incomplete to assign them to specific genera; mostly they just consist of teeth and bits of shells. 03 of 05 Deinosuchus Wikimedia Commons The closet thing Delaware has to a truly impressive prehistoric animal, Deinosuchus was a 33-foot-long, 10-ton crocodile of late Cretaceous North America, so fierce and relentless that two separate tyrannosaurs have been discovered bearing Deinosuchus bite marks. Unfortunately, the Deinosuchus remains dredged up from Delaware's canals are scattered and fragmentary, consisting of teeth, bits of jaws, and assorted scutes (the thick armor plating with which this prehistoric crocodile was covered). 04 of 05 Belemnitella Wikimedia Commons The state fossil of Delaware, Belemnitella was a type of animal known as a belemnite--a small, squidlike, shelled invertebrate that was eaten in bulk by the ravenous marine reptiles of the Mesozoic Era. Belemnites started to appear in the world's oceans about 300 million years ago, during the late Carboniferous and early Permian periods, but this particular Delaware genus dates from about 70 million years ago, shortly before the K/T Extinction Event. 05 of 05 Various Megafauna Mammals Wikimedia Commons Megafauna mammals (such as horses and deer) undoubtedly lived in Delaware during the Cenozoic Era; the trouble is that their fossils are as scarce and fragmentary as all the other animals discovered in this state. The closest thing Delaware possesses to a Cenozoic fossil assembly is the Pollack Farm Site, which has yielded scattered remains of prehistoric whales, porpoises, birds and terrestrial mammals dating to the early Miocene epoch, about 20 million years ago.