DINOSAUR HISTORY

Since the early part of the twentieth century, when local iron mining ceased, very few dinosaur bones have been recovered from Maryland and its environs. This is, for the most part, due to a lack of knowledge about local bones by the general public. In addition, modern excavation methods using large machines have removed workers from close contact with the ground. Two noteworthy but isolated discoveries took place in Washington, D.C. In 1898, some men digging a sewer at First and F Streets, S.E., found the remains of a carnosaur ("Dryptosaurus," or a related species). Workers found a very large legbone from Astrodon, a brachiosaurid, while building the McMillan Water Filtration Plant at First and Channing Streets, N.W. in 1942. There have been other finds at other locations, but much needs to be done. The bones are still here, but few people are looking for them!

The position of dinosaurs in geologic time is illustrated in Figure 2. In this chart you may have noticed many unfamiliar words and names. They are, however, not as confusing as they may at first appear. Geologists and paleontologists have very simple rules for assigning names. In general, one tries to give a name that is descriptive of the animal, plant or rock. Frequently, a rock layer will be named for the place where it was first described or most commonly found.
Thus, we see that dinosaurs lived during the era known as Mesozoic (meaning "middle life"), which consists of three periods: Triassic (three-part rock system) 245-208 mya (million years ago); Jurassic (Jura Mountains) 208-144 mya; and Cretaceous (chalk) 144-66.4 mya. In Maryland, dinosaur fossils are found in rock units known as the Newark Group, the Potomac Group, and the Severn Formation (named for Newark, New Jersey, the Potomac River, and the Severn River, respectively). The fact that these units cover much but not all of the Mesozoic, or "dinosaur time," should not be taken to mean that there were no dinosaurs living here during the missing time periods, but only that rock units from those time periods were buried, removed by erosion, or never deposited. Furthermore, outcrops of rocks containing dinosaur fossils are not restricted by state boundaries; thus, a dinosaur from rock units in a neighboring state or the District of Columbia may occasionally be mentioned.
Thus, we see that dinosaurs lived during the era known as Mesozoic (meaning "middle life"), which consists of three periods: Triassic (three-part rock system) 245-208 mya (million years ago); Jurassic (Jura Mountains) 208-144 mya; and Cretaceous (chalk) 144-66.4 mya. In Maryland, dinosaur fossils are found in rock units known as the Newark Group, the Potomac Group, and the Severn Formation (named for Newark, New Jersey, the Potomac River, and the Severn River, respectively). The fact that these units cover much but not all of the Mesozoic, or "dinosaur time," should not be taken to mean that there were no dinosaurs living here during the missing time periods, but only that rock units from those time periods were buried, removed by erosion, or never deposited. Furthermore, outcrops of rocks containing dinosaur fossils are not restricted by state boundaries; thus, a dinosaur from rock units in a neighboring state or the District of Columbia may occasionally be mentioned.

A list of dinosaurs and the rock units in which they were found in Maryland is presented in Table 1.

Scientific Name	Common Name	Rock Unit
Archeornithomimus affinis Astrodon altus Astrodon johnstoni Astrodon nanus "Coelophysis" "Coelurus gracilis" "Dryptosaurus medius" "Dryptosaurus potens" "Hadrosaurus foulkii"	Ostrich dinosaur Brachiosaur Brachiosaur Brachiosaur Small carnivore Small carnivore Large carnosaur Large carnosaur Duckbill dinosaur	Arundel (LK) Arundel (LK) Arundel (LK) Arundel (LK) Gettysburg (UTr) Arundel (LK) Arundel (LK) Arundel (LK) Severn (UK)
"Quotes" around names indicate uncertain identification in Maryland. UK: Upper Cretaceous. LK: Lower Cretaceous. UTr: Upper Triassic.