THE DINOSAURS OF MARYLAND
|As indicated in the preceding section, dinosaur remains are distributed in three different rock units in Maryland. Dinosaurs of the very earliest and latest types are found here. In fact, Maryland has dinosaur forms represented throughout much of their approximately 160 million-year history. The reader is cautioned, however, that this is not to suggest that dinosaurs in Maryland were anywhere nearly as abundant or diverse as they were in other parts of the U.S. or the world. They were not.
THE DINOSAURS OF THE NEWARK GROUP
Dinosaur bones and teeth have been reported from beds of this age outside of Maryland. To date, however, neither has been found in Maryland. Bones of fish and other vertebrates have been found in our State, and there is no reason that dinosaur bones should not eventually be found. The dinosaurs of Maryland in this time period are known solely from their tracks (Fig. 4).
It is very difficult to identify an unknown creature from its tracks alone. Therefore, the tracks, or ichnofaunas, have been assigned their own species names. It may be possible to make some good guesses about the dinosaurs that lived here from the bones and teeth found in nearby states, as well as track morphology. We are necessarily less certain about these dinosaurs than some of the later ones.
In 1895, James A. Mitchell, a graduate student at Johns Hopkins University, reported upon and drew pictures of dinosaur footprints from a quarry north of Emmitsburg. The current location of the original fossil footprints from which he drew the pictures is unknown. The quarry, however, still exists, although it is overgrown. Most of the tracks are reported to be of a three-toed type, about 3 inches in length, with about a one-foot stride. Such a dinosaur would be about 4 feet long and 20 pounds in weight. A good candidate might look something like Coelophysis (Fig. 5).
There have been two other rare tracks reported, also three-toed; one is about 1 inch long, the other a webbed foot. What these are is difficult to say without studying the actual specimen.
From nearby locations in Virginia, larger three-toed prints, some greater than 12 inches long, have come to light. Such creatures presumably lived in Maryland. They may have been similar to the carnosaur in Figure 5.
If one goes yet farther afield to the Connecticut Valley, dozens of track varieties have been recorded. Here, too, there are very few bones to associate with the tracks. All that one can say with certainty is that there were a variety of dinosaurs living in the eastern United States, including Maryland, during the Late Triassic and Early Jurassic periods, 230-187 mya. Perhaps the greater interest currently being shown in these rocks may lead to a better understanding of the dinosaur fauna.
THE DINOSAURS OF THE POTOMAC GROUP
The record of Jurassic and very early Cretaceous time, if it exists at all in Maryland, is apparently buried. The dinosaur story resumes in the middle of Early Cretaceous times. It is from the clays of the Potomac Group that most of the dinosaur bones have come. It is of interest that many of these bones were found 100 years ago in 1887-1888 by John Bell Hatcher. They were recovered from sedimentary iron mines. In 1894-1896, Arthur Bagnold Bibbins also made a significant collection while a graduate student at the Johns Hopkins University. Since that time, there have been only isolated finds. This case of limited discovery is in large degree due to the cessation of iron mining, but also to the fact that few people are aware that the bones are there. Recently, bones have been recovered from the Potomac Group because people have been encouraged to look for them.
Dr. Johnston described this tooth in the American Journal of Dental Science in 1859 and named it Astrodon, or "star tooth" (Fig. 7 and Frontispiece). In 1865, the famous pioneer of American paleontology, Dr. Joseph Leidy, formally named and described the fossil as Astrodon johnstoni, making it the first sauropod dinosaur described from North America. This dinosaur was discovered almost simultaneously with Leidy's most famous find, Hadrosaurus foulkii, dug up in New Jersey and considered to be the first dinosaur found in North America.
Although herbivorous dinosaur remains dominate the Arundel (Potomac) fauna, making up more than five times as much material as all other forms, several carnivorous dinosaurs are also represented. "Dryptosaurus" (Fig. 7) is the largest and most impressive of them. It was a carnosaur about 20 feet long, and may have been a close relative of the tyrannosaurs. Marsh had previously identified these bones as Allosaurus, believing the Potomac Group to be of Jurassic age. Later, R.S. Lull called them Creosaurus. "Dryptosaurus" had once been called Laelaps, the leaping hunting dog of mythology. Indeed, it is pictured leaping in Charles Knight's illustration (Fig. 8).
Archeornithomimus affinis, an ostrich dinosaur (Fig. 7), has a curious history in that it was not originally recognized by Marsh as part of the Potomac Group fauna. In 1911, Lull assigned its bones to Dryosaurus grandis, a herbivore. Only in 1920 did Charles Gilmore of the U.S. National Museum recognize them as bones from an ornithomimid. Ornithomimids were the fastest of the dinosaurs, perhaps able to run faster than modern-day horses. They were about 11 feet long.
THE DINOSAURS OF THE SEVERN AND RELATED FORMATIONS
Dinosaur remains in the Severn Formation and other Upper Cretaceous units are scarce indeed. This is mostly attributable to the fact that these formations are marine. Despite their marine origin, however, these beds have yielded some dinosaur bones among which is the first and perhaps most famous dinosaur find in Eastern North America. The New Jersey Hadrosaurus was found in one of these marine deposits. The reason that dinosaurs, which were terrestrial animals, ended up in the marine deposits of the Late Cretaceous is that these deposits were laid down quite near the shore where dinosaur carcasses and bones could be carried into the sea by rivers in flood. Such bones have been found in these deposits largely because they are so frequently hunted for the abundant marine fossils they contain.
Little is known about the land in these times because so few terrestrial deposits of the Upper Cretaceous have been identified in Maryland. We can presume it was a warm, forested lowland, based on some of the vegetation which has also been found in these deposits. To date, only one dinosaur has been given a formal name: Ornithomimus antiquus, although remains of others have been found (Fig. 9).
On the basis of the sparse material___a few broken leg bones___Ornithomimus antiquus cannot be said to be significantly different from the one described earlier from the Potomac Group. It was probably about 11 feet long.
Hadrosaur remains include some broken leg bones and a recently discovered tooth. They may perhaps best be compared with the New Jersey specimen, Hadrosaurus foulkii. This creature was what is commonly called a duck-bill dinosaur. Hadrosaurs frequently walked or ran on their much larger hind legs (Fig. 9). They had a mouth full of grinding teeth and lived mostly by browsing on conifers and other vegetation. Hadrosaurs are currently believed to have been completely terrestrial, and not aquatic as often pictured. Adults may have been 26-32 feet long, and weighed more than a ton.