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 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

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.

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

    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  

   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.

Early Cretaceous, 130-95 mya

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.
   The dinosaurs of the Potomac Group are the best known, most abundant, and first ones found in the State. In 1859, only about 17 years after the name "dinosaur" had been coined, Philip Tyson, the State Agricultural Chemist, made available to Dr. Christopher Johnston, a local physician, a strange tooth that he had found in a mine "near Bladensburg"

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.
     Astrodon's history has not been a simple one. John Bell Hatcher is said to have commented that "no two bones or fragments of all that material collected from the Potomac beds in Maryland were found in such relation to one another as to demonstrate that they belonged to the same individual." Such fragmentary, disarticulated remains naturally led to confusion and controversy. There are hundreds, perhaps thousands, of Astrodon bones in the collections of the Smithsonian. Despite this fact, exactly what kind of dinosaur Astrodon was and what it looked like has been debated for many years. It is currently believed to be a brachiosaurid. In the past it was called a morosaur by O.C. Marsh, and a brontosaur by Gilmore on at least one occasion. Some of the published life-restoration pictures are different from either.
   It is not always easy to differentiate the skeleton of a juvenile reptile from an adult. This has led to confusion about the true size of Astrodon. If the known bones are truly those of an adult, then it is one of the smallest sauropods known, with some individuals only 10 feet long. On the other hand, a leg bone found in 1942 at the McMillan Reservoir in Washington, D.C., was from an animal of considerable size___certainly more than 40 feet long.
    The animal was definitely vegetarian, but as with all dinosaurs it is difficult to be specific about the exact diet. Astrodon probably browsed the conifers, cycads and low-growing plants. It probably was a forest dweller. Although its bones have been recovered from river deposits, if current ideas are correct, it did not spend its time in the water.
   Taxonomically, there is great confusion about Astrodon. It has been known in the past as Pleurocoelus and some paleontologists have even suggested that it is synonymous with Brachiosaurus. At present, it is thought that Astrodon and Pleurocoelus are synonymous, with AstrodonBrachiosaurus. Where else it is found and how many species exist are areas of greater uncertainty. It may be found in Texas in the Comanchean beds and in Montana in the Cloverly Formation. There are three species recognized in Maryland: Astrodon nanus, Astrodon altus, and Astrodon johnstoni. The latter two, however, are known from very limited material.
    As uncertain and limited as the Astrodon material is, it is far more abundant than that of any other dinosaur in the Potomac Group. The other plant-eating dinosaurs known from present collections consist of an ankylosaur, Priconodon crassus, known from six teeth (now seven because of an amateur's recent discovery of the largest and best preserved tooth) and presumed to be a nodosaur; and an iguanodontid, perhaps Tenontosaurus, known from a single tooth fragment (USNM 244564). Dryosaurus grandis, another herbivorous dinosaur, which was believed to have existed in the Potomac Group, has been shown by Gilmore to be the remains of Archeornithomimus affinis.
    Nodosaurs are armored dinosaurs that walked on all fours and are presumed to have been low browsers. These animals are known only from Cretaceous times, with one possible exception. Priconodon crassus is estimated to have been about 20 feet long (Fig. 7).
   The iguanodontid tooth fragment mentioned earlier may be that of Tenontosaurus (Fig. 7). There is also a caudal (tail) vertebra (USNM 8508) in the U.S. National Museum, which may belong to this same creature, but this is uncertain. If the animal can be shown to be Tenontosaurus or if future finds confirm its existence in the Potomac Group, then it would be known from the eastern U.S., as well as the West. Tenontosaurus was 21 feet long and weighed about one ton.
having precedence. Although it is probably a brachiosaurid, it is not


    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).
    One other story, which may be apocryphal, is that E.D. Cope, the paleontologist who proposed the name Laelaps, did so because he liked to think of his dinosaur attacking the slow-moving plant eaters described by his archrival, O.C. Marsh.
    Nothing resembling a complete skeleton of "Dryptosaurus" has ever been found, but it is represented by many bones and teeth. There are believed to be at least two species known from this area: the more common being "Dryptosaurus" medius, and a larger species, "Dryptosaurus" potens, known from a large vertebra and bone fragments found by workers digging a sewer on Capitol Hill in Washington, D.C., in 1898

Dinosaur Drawing

    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.
     Archeornithomimus affinis is known only from foot bones. Its diet may have included seeds, plants, fruit and eggs, as well as meat, but this is mostly speculation. Much of what is understood about this animal is by analogy with ostriches and their kin because they have a similar body form and are similarly toothless.
    Coelurus gracilis was a typical small meat-eating dinosaur, in some ways very similar to Coelophysis (Fig. 5). They were about 6 feet long, could run swiftly, and probably fed upon smaller creatures. Some scientists believe they may have been scavengers. Coelurosaurs are particularly interesting because they are thought to be close relatives of bird ancestors. The Coelurus from the Potomac Group is very poorly known, being based largely on a claw and a few broken bones.
    As mentioned previously, because the preservation of Potomac Group dinosaurs is so infrequent and so few people are looking for them, there is much yet to be learned about this interesting group of eastern North American dinosaurs. Several bone fragments were recovered from some of the historic localities near Muirkirk, Maryland, in 1973 by area resident Marion "Pete" Rath and recently by the author and his students. Though none of these finds has yet added significantly to our knowledge of the fauna, in early 1989 the author tentatively identified what may prove to be a new species. Perhaps renewed searches of the clays will bring new species to light.

Late Cretaceous, 86-70 mya

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 

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.


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