Paleontology in Iowa
[1] During the early Paleozoic Iowa was covered by a shallow sea that would later be home to creatures like brachiopods, bryozoans, cephalopods, corals, fishes, and trilobites.
As this sea began to withdraw a new subtropical coastal plain environment which was home to duck-billed dinosaurs spread across the state.
The early Cenozoic is missing from the local rock record, but during the Ice Age evidence indicates that glaciers entered the state, which was home to mammoths and mastodons.
The bottom of this sea was home to creatures like brachiopods, bryozoans, cephalopods, corals, molluscs, and trilobites.
Further, dinosaur fossils have been found in neighboring states like Minnesota, Missouri, Nebraska, and South Dakota.
[6] No Jurassic dinosaur fossils are known from Iowa, although the Iowan Fort Dodge Formation is the same age as the dinosaur-bearing deposits of the western states.
[6] Between 95 and 100 million years ago, areas of Iowa were covered by a complex of rivers flowing toward the west through floodplains and coastal lowlands.
These deposited the sediments that are now called the Dakota Formation, the oldest Cretaceous rocks in the state.
[8] Gradually over time the rivers depositing the Dakota Formation sediments were submerged by the northward expansion of the Western Interior Seaway.
[11] During the mid-Campanian, about 75 million years ago, an asteroid roughly 1.5 miles in diameter struck the earth from the southeast near the east coast of the Western Interior Seaway.
At this time Iowa was home to mammoths and mastodons, whose remains were preserved in a wide variety of locations in the state.
[2] During the glaciations of the Ice Age over the past 2.5 million years the glaciers transported and deposited fossils eroded from Cretaceous sediments.
[15] Geographical features were likely regarded as nahurac sites because of the bones of strange extinct wildlife preserved in their sediments.
[20] In 1824, Dr. Richard T. Harlan would formally name the species that left the jaw Saurocephalus lanciformis, but mistook it for the remains of a marine reptile.
[21] In 1858 W. James Hall, the New York state geologist, made an early major discovery in the history of Iowa paleontology.
[1] Later in the 1930s, a Materials Inspector working for the Iowa Highway Commission named John Holdefer noticed a fossil bone on a conveyor in a Plymouth County gravel pit, not far from Akron.
On September 7, 2000, The Des Moines Register reported the discovery of the state's first identifiable dinosaur fossil.
The darkly colored, three inch long fossil originated among landscaping gravel from a nearby pit.
[23]In 2015, paleontologists discovered the remains of a giant Megalograptid eurypterid in the middle Ordovician Winneshiek lagerstätte near the town of Decorah.
