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Astrodon Rediscovered: America’s First Sauropod

Peter M. Kranz Dinosaur Fund
300 50th St. SE #103
Washington, D.C. 20019
Email: dinosaurfund@juno.com


Joseph Leidy, formally described and named Astrodon johnstoni, America's first sauropod in 1865. The fossils were said to have been found in "an iron mine near Bladensburg, in 1859. Recent research by Kranz has shown that the discovery was actually made at Muirkirk, Maryland, by Philip T. Tyson, "State Geologist," in late November 1858. The specimens were found on the property of J.D. Latchford and turned over to Dr. C. Johnston for study.

In December 1995, the Maryland-National Capitol Park and Planning Commission unknowingly acquired Latchford's property for the development of a dinosaur park because it was adjacent to an active dinosaur fossil site. The discovery of remains of Latchford's house in late 1996 confirmed this as the actual type locality.

O.C. Marsh in 1888 proposed the name Pleurocoelus (Astrodon), for a very small sauropod from the same area measuring under 5 meters in length., which he believed to be the smallest known adult Psauropod. He based his conclusions on presumably juvenile material excavated from nearby Swampoodle. However, in 1991, large teeth and an Astrodon femur (estimated at an original length near 2 meters) were discovered at a site adjoining and contiguous with Latchford's property. This confirms Astrodon as a large sauropod measuring at least 25 meters in the adult form.

Astrodon johnstoni became the official State Dinosaur of Maryland 1 October 1998.

Astrodon Rediscovered: America's First Sauropod

While engaged in field work to produce the first state geologic map of Maryland, Philip Thomas Tyson, the official State Agricultural Chemist (geologist) was given two unusual large teeth from an open pit iron mine on the property of John D. Latchford of Muirkirk, Maryland (Tyson, 1860). This happened in late November of 1858. He brought the teeth with him to the next meeting of the Maryland Academy of Sciences. They were turned over to Dr. Christopher Johnston, a professor at the Baltimore Dental College and a collaborator with Dr. Joseph Leidy of the University of Pennsylvania.

Dr. Johnston sectioned a tooth and finding a star burst pattern in the cross section proposed the generic name Astrodontaurus for saurian owner of the teeth. The name was later shortened to Astrodon (star-tooth) when Johnston published his findings in the American Journal of Dental Science in 1859.

This is how the first sauropod remains, to be identified from North America, came to light. And starting at that point also began much of their murky subsequent history. Johnston (1859) refers to the fossil teeth as coming from an iron mine near Bladensburg. Whether he was merely trying to obscure the locality of the find is unknown. Whatever the case, for everyone except the original participants, the actual type locality was unknown for almost the next 140 years. Even Joseph Leidy (1865) does not give the exact locality in his paper formally describing and naming Astrodon johnstoni (in honor of Dr. Christopher Johnston).

In 1888, O.C. Marsh making a study of the teeth appears to have asked Dr. Johnston for the loan of them. Philip R. Uhler of the Maryland Academy of Sciences acted as Johnston's agent in his absence.

Uhler (1888) copied Tyson's original notebook record of the discovery and sent it to him. [Note: Although I discovered Tyson's notebooks in the Maryland Academy of Sciences Archives during the summer of 1996, Notebook "C" for October to December, 1858 was missing. Whether it is elsewhere or destroyed is unknown at this writing.]

Marsh (1888) makes no mention of Astrodon johnstoni in his paper describing the Potomac Group dinosaurs. Although the letter from Uhler is dated about a month after Marsh submitted his paper for publication, I question whether a scientist of Marsh's caliber could have been unaware of Leidy's (1865) publication. Moreover, Marsh (1896) still fails to mention Astrodon johnstoni when writing in 1895, long after he certainly knew of its discovery; and that it came from virtually the same location as his own fossil specimens. One can only speculate on his motivations for ignoring this information, but it seems to me that it was deliberate (Appendix III shows that the teeth were actually in his possession by early May, 1888).

The name Astrodon was resurrected by Lull (1911) in the Lower Cretaceous volume of the Maryland Geological Survey along side Pleurocoelus. However, Marsh and his works being better known nationally and internationally became the standard for the last 110 years. Pleurocoelus has been "identified" in Western North America, Britain, Europe, Africa and possibly elsewhere (Glut, 1997).

Astrodon has over the recent years been relegated to the status of "nomen dubium" in part at least because it was based on only two teeth (YPM 798), the lack of information about the location of the type locality, and the preeminence of O.C. Marsh. Taxonomists, however, hold as one of their first and most important principles - priority. If nothing else, it is clear the name, Astrodon, has priority by more than twenty and possibly as much as thirty years.

Marsh (1888) named two species of Pleurocoelus to which Lull (1911) appended Astrodon johnstoni as a third. Is there, in fact, more than one species in Maryland? If so, then Pleurocoelus may be a valid genus separate from Astrodon or not. But, if there is only one definable species, then Astrodon johnstoni clearly has priority. Marsh (1888) argued that the bones which he had studied showed a small sauropod (Pleurocoelus nanus) under 5 meters in length as an adult and a large sauropod (Pleurocoelus altus) of at least 9 meters as an adult. The teeth which he associated with his sauropods were noted to be similar to those of Astrodon johnstoni (Hatcher 1903, Lucas 1904). Recent study of Marsh's Pleurocoelus nanus bones (Glut, 1997) has suggested that they are from a juvenile sauropod. Hatcher (1903) also recognized this fact.

If Pleurocoelus nanus is merely a juvenile Pleurocoelus, then Marsh's two species collapse to one. Moreover, if there is only one species whose associated teeth are similar to those on which Astrodon johnstoni was founded, why not use that name which clearly has priority?

In the past, the arguments against such a view held more weight. First, there were only two teeth associated with the name Astrodon johnstoni; and the locality from which they came was unknown. Second, if Pleurocoelus nanus was very small in its adult form clearly it could not be Astrodon johnstoni whose teeth belonged to a very large animal. As shown previously, these two objections are no longer applicable.

Current Work

As I have stated, I have discovered documents specifying the conditions of discovery and the location from which the Astrodon johnstoni teeth came. [Maryland Academy of Sciences minutes of meetings, November - December, 1858; Uhler, 1888]. The teeth came from an open pit iron mine on the property, also known as "White Oak Bottom", of John D. Latchford of Muirkirk, Maryland.

A search of Prince George's County, Maryland land records provides the precise boundaries of Latchford's property (Liber CSM#2 f404). This property is now adjacent to a brick clay quarry (Cherokee Sanford Corp.) from which I and others have recovered hundreds of dinosaur bones and teeth since 1989 (Kranz, 1996).

In late 1995, a portion of Latchford's property, presumably the part containing the mine in question (i.e. the type locality for Astrodon johnstoni) was inadvertently acquired by the Maryland National Capital Park and Planning Commission (MNCPPC) for a dinosaur park because of its close proximity to the active dinosaur fossil site and its availability.

When in the summer of 1996, I discovered that the property was Latchford's, I set about finding his house site to confirm that this was indeed his property. With the help of Bob Renn and Ivar Cooper, I located the site of the now destroyed house in late 1996. I, as a result, have no doubt that type locality for the Astrodon johnstoni teeth has been rediscovered (see Map 1).

localities of dinosaur discoveries
Map 1
Section of northern Prince George's County, Maryland, United States of America. Bold letters indicate localities of dinosaur discoveries (see Kranz, 1996, for more details). Large "L" indicates approximate location of John D. Latchford's property. Dinosaur park includes much of the northern portion of Latchford's property.

Knowing that the type locality is adjacent to and continuous with the deposits in the Cherokee Sanford brick clay pit (also known as Maryland Clay Products), I wish to propose the sauropod remains from that site, as well as those which will be recovered in the future from the park site, be considered potential lectotypes for Astrodon johnstoni, thereby providing a much firmer basis for the genus and species (Appendix IV indicates that bones and teeth of the original discovery are probably still on the park property).

Many teeth and post cranial elements of sauropod individuals have been recovered from that site since 1989. Most noteworthy is a femur which may have been about two meters long at its original length (Meyer, 1991; Kranz, 1996) [see Figure 1]. With luck, future discoveries at this site may yield skulls and articulated bones.

Astrodon johnstoni became the official State Dinosaur of Maryland 1 October 1998.

Astrodon johnstoni
Figure 1
Astrodon johnstoni - Astrodon femur, currently the largest dinosaur bone known from the East Coast of the United States: (a) femur being cast in plaster for removal from Muirkirk clay pit by Dan Chaney (left) and Peter Kroehler (right) of the National Museum of Natural History in May, 1991; (b) in the laboratory at the National Museum of Natural History, March, 1996; shown at approximately 1/10 size; note hammer for scale; (c) sketch of an Astrodon family.


I thank Roger Cuffy of Penn State, James Reger of the Maryland Geological Survey, and John Latchford Beck of Ellicott City, Maryland for their reading and comments on the manuscript. In addition, I thank John Latchford Beck, great-grandson of John D. Latchford, and June A. Ventura for their help in preparing the manuscript.


Glut, D., 1997, Dinosaurs, The Encyclopedia, McFarland & Co., Jefferson, North Carolina, pp. 713-1

Hatcher, J. B., 1903, June "Discovery of Remains of Atlantodon (Pleurocoelus) in the Atlantosaurus Beds of Wyoming", Ann. Carnegie Museum, Vol. II, #1, pp. 9-14.

Johnston, C., 1859, "Note on odontography," Amer. Journal Dental Sci. 9:337-343.

, 1888, "Letter to O. C. Marsh of Yale University, May 11, 1888", Collections Division of Div. of Vert. Paleo., Peabody Museum, Yale University.

Kranz, P.M. 1996, "Notes on the Sedimentary Iron Ores of Maryland and their Dinosaurian Fauna", in Maryland Geological Survey Special Publication No. 3, pp. 87-115.

Leidy, J 1865, Memoir on the extinct reptiles of the Cretaceous formations of the United States. Smithson. Contrib. Knowl. XIV: atr. VI: 1-135.

Lucas, F.A. 1904, "Paleontological notes," Science (n.s.) XIX (480): 436-437.

Lull, R.S. 1911, "The Reptillian Fauna of the Arundel Formation" and "Systematic Paleontology of the Lower Cretaceous Deposits of Maryland -Dinosauria", Lower Cretaceous : Maryland Geological Survey Systematic Reports, pp. 173-178, 183-211.

Marsh, O.C. 1888, "Notice of a New Genus of Sauropoda and Other New Dinosaurs from the Potomac Group," American Journal of Science, 3rd Series, Vol. XXXV, pp. 89-94.

Marsh, O.C., 1896, "Dinosaurs of North America," Ann. Rept. USGS XIV [1]: 133-244.

Maryland Academy of Sciences, 1858, Minutes of Meetings November-December, 1858.

Meyer, E. L., 1991, "Early 'suburbanite' shows a lot of leg", Washington Post, May 25, pp. A1, A15

Tyson, P. T., 1858, "Letter to James Hall, State Geologist of New York, Dec. 25, 1858", Copy, 2 pages, Silliman (Benjamin) 1779-1864 Collection (1816-1871), MS.30, Johns Hopkins University Special Collections.

, 1859, "Fossil Remains", Daily National Intelligencer, Washington, D.C., Jan. 8,1859, Page 3.

, 1859, Notebook "E", Field Notes of P. T. Tyson, State Agricultural Chemist of Maryland,

Page 7, Maryland Academy of Sciences/Maryland Science Center Archives, Box 11.

, 1860, "1st Report of the State Agricultural Chemist," Maryland State Legislature, p.42

Uhler, P. R., 1888, Othniel Charles Marsh Papers, Manuscript #343, Sterling Library, Yale

University,New Haven, Connecticut.

Wieland, G. R., 1906, American Fossil Cycads, Vol. 1, Carnegie Institution of Washington, 296 pages.

, 1916, American Fossil Cycads, Vol. II, Carnegie Institution of Washington, 277 pages.

Appendix I

Text of Uhler (1888)

Baltimore, Jan. 23, 1888

Prof. O.C. Marsh,

Dear Sir,

Doctor Christopher Johnston sends his compliments and expresses regret that he was not at home to receive you last week. He has placed in my charge, and I have sent to you per Adams Express, the tooth of Astrodon Johnstonii which was the type employed by Dr. Leidy in describing the genus. It surprises me to see that the specimen is breaking apart and disintegrating into small grains.

In looking again at Mr. Tyson's Journal, I find that the tooth came from Latchford's iron-ore beds near Contee, and that they, together with the rib of a whale?, were dug out of the lead colored clay between the upper bed of iron-ore and the lower or more stratified bed of ore.

I do not know where the other piece of tooth now is. Perhaps Dr. Leidy has it; as I now remember, it was only a small fragment of a tooth. The specimens were said to have been found at a depth of only "seven feet below the surface" of the ground.

Dr. Johnston asks me if the tooth can be returned within a few weeks. ..

Respectfully yours,

P.R. Uhler

Appendix II

Text of Maryland Academy of Sciences, Minutes of Meetings Nov-Dec, 1858

Baltimore - November 22, 1858

Regular meeting of the Committee. Present, Dr. C. Johnston (Author's note: P.T. Tyson not present)

Baltimore - November 29, 1858

Regular meeting of the Committee. Present Dr. C. Johnston, P.T. Tyson, P.R. Uhler

A specimen of Lignite from Washington R.R. was presented by Mr. Tyson. Dr. C. Johnston exhibited a fossil - found by Mr. P.T. Tyson, 16 miles from Washington, mile s. of B. & W. R. Road, on the place of Mr. J.B. {sic}Latchford. The specimen found was 2 feet long & 7 inches thick, and that, exhibited to the committee, was 7 inches long by 3 thick - being a portion of the original specimen. Dr. J. exhibited a section under the microscope & proved the fact of its being a cetacean from its anatomical structure.

Mr. Tyson exhibited a fossil tooth, which had been discovered on Mr. Latchford's farm, which seems to belong to no species as yet described. Dr. Johnston considered it as nearly resembling the iguanodon's tooth, but still sufficiently different to justify the idea of its being the tooth of an undescribed animal.

Baltimore - December 6, 1858

Regular meeting of the Committee: Present Dr. C. Johnston Mr. P.T. Tyson

Specimen of fossil wood, discovered by our State Geologist, Mt. Tyson, were referred to Dr. C. Johnston at a previous meeting, who now reported that they were not palms but coniferas: The Dr. came to this result by comparing his finely executed sections with those which were well determined. Dr. J. then exhibited the different sections to the Committee.

Dr. Johnston then communicated verbally his observations on some rare fossil teeth of a new and very extraordinary herbivorous reptile which will soon be described by Dr. Leidy. Dr. J., to illustrate his remarks, placed under the microscope his beautiful sections for the examination of the Committee.

Baltimore - December 13, 1858

Regular meeting of the Committee: Present Mr. R.T. Tyson, P.R. Uhler, Dr. C. Johnston

Dr. Johnston then read an abstract of his remarks made at the meeting of the 29th ult., & the 6th inst.

Dr. C. Johnston exhibited microscopic sections of a fossil tooth of a new Thecodont Reptile. The tooth was found by Mr. Tyson - the State Geologist, on the place of Mr. Latchford.

No existing reptile exhibits the mode of implications indicated by the tooth in question, which must have been received into a distinct socket or Theca , whence the name - Thecodont. The common actual dental attachments of Saurians are exemplified by the Iguanas and the Monitors in the former, the teeth are anchylosed to the outer and more elevated maxillary or premandibular parapet, all inner support being wanting - and in the latter, these organs are anchylosed by the whole of their base to the jaw. The first are known as pleurodonts, the last as Acrodonts. It is interesting to observe that while the fossil remains of extinct Lacertians of the Pleurodont and Acrodonts varieties are yielded by various strata of the Earth, most of the Thecodont Saurians belong to the Triassic or permian Beds.

The tooth may be described as sub-cylindrical, not distinctly expanded in the crown, which is compressed, pointed, obliquely recurved, presenting one very convex side, one straight non-serrated edge, and one more convex edge somewhat worn from the point downwards for about an inch. It is solid, excepting a linear pulp-cavity extending almost to the point of the cusp; is composed of a body of dentine, invested by a thin coronal layer of enamel over which the cement of the fang is produced in a delicate stratum.

The transverse section is oval except in the crown where the margins destroy that figure. The dentinal tubes radiate from the pulp-cavity at nearly right angles, and are associated in bundles, giving to the section a peculiar asteroid appearance. The whole tooth measures 1 inches in length by inch in breath. It is proposed to assign to this great Saurian the provisional name of Astrodontaurus.

Dr. Johnston exhibited microscopic sections, prepared by him for Prof. Leidy of Philadelphia. One was a very rare tooth of an extraordinary extinct carnivorous reptile. It was scutiform and the tooth was bayonet shaped.

Appendix III

Letter of Christopher Johnston (1822-1891) to O. C. Marsh of Yale University

May 11, 1888.

This letter indicates that Johnston made a gift of the Astrodon teeth recovered by Tyson in November, 1858 to O. C. Marsh. They were received and subsequently given the number YPM798. The teeth are still in the possession of the Peabody Museum of Yale University.

No. 201 W. Franklin Street
May 11, 1888
Prof. O. C. Marsh
New Haven, Connt.

Dear Sir,

As my tooth of Astrodon is a unique specimen - according to Prof. Uhler - I take great pleasure in presenting it to you that it may fill a gap in your series of reptilian dentitions in discoveries which you have been so fortunate in our state.

I beg also to and for acceptance of a section of another tooth of this same creature, which shows the structure very well.

Congratulating you upon this great success attending your researches.

I remain

Most Truly Yours,

Christopher Johnston

Appendix IV

Writings of Philip Thomas Tyson (1799-1877) on the discovery of Astrodon johnstoni

The texts of the letters and other writings which are here appended bring to light several new details about the original discovery of Astrodon johnstoni:

  1. The two original teeth were part of a much larger assemblage of fossils from a probable single individual, including as many as four additional teeth and several vertebrae.
  2. The discoveries were not made by Tyson himself but by miners working in John D. Latchford's iron mine on his property at "White Oak Bottom" at Muirkirk, Maryland, who subsequently discarded the additional fossil material.
  3. Tyson only learned of the discovery in late November, 1858 by which time all he was able to recover was the two teeth which are now specimen YPM 798.
  4. The other fossils are presumably still buried on the Latchford property which is now the Dinosaur Park of Prince George's County Maryland and may yet be recovered during park development.
  5. A photograph was taken within a month of the discovery and perhaps others. The photograph was sent to Prof. James Hall, New York State Geologist. Additional copies were sent to other scientists including O. C. Marsh in 1867 (Wieland, VOL. I). A reproduction of the photograph appears on page 28, Wieland, VOL. II. In the photograph the central object is said to be a "whale" rib, in all likelihood it is an Astrodon rib (whereabouts unknown).
  6. Tyson made arrangements with Latchford to save future fossil discoveries and on May 5, 1859 he apparently received several bone "fragments" (whereabouts unknown).


Letter from Philip T. Tyson to Prof. Jas. Hall Balto 25 Dec. 1858

Prof. Jas. Hall


Dear Sir

When I had the pleasure of your company with another gentlemen in May last there was one subject of conversation to which I desire to call your attention. I allude to the characters and age of the heavy beds of grey and lead cold clays which extend from near Newark in Delaware; south westward to Washington. It constitutes a belt of very variable width nowhere exceeding 10 miles.

There are in those clays at least two layers of carbonate or iron, which have been worked more or less for 150 years.

The Messes. Rogers think the deposit peculiar to Maryland; as they have seen nothing of the same formation in other parts of the country.

Until recently no other fossils than cetaceans and lignites (coniferous) have been met with.

I have at length got hold of some that begin to throw some light upon the subject.

At one point there were found several teeth and bones a few feet below the upper layer of ore, but unfortunately before I knew of the discovery the bones were covered by the rubbish, by ore diggers and of five or six teeth I secured but two. These are undoubtedly Saurian, and the microscopic investigations by my friend Dr. C. Johnson (sic) and the mode of insertion into the socket indicate a saurian of an older secondary period perhaps Oolitic or Trias.

A close examination of the owner of the mine satisfies me that the lost vertebrae were those of a saurian, but I have strong hopes that I shall yet get bones sufficient to make out the monster. Dr. Johnson (sic) says that the structure (as shown in the cross section) differs from any hitherto discovered.

About 200 yards from where the teeth and bones occurred, there was found a silicified trunk of a tree 26 in by 6 ft: above the ore. At another point in the vicinity also a fragment of a large cetacean rib.

About one mile off I secured a fossil cycas but we are without books in this city to determine whether it (has) been described or not. Neither could I make it out at the Academy of Sciences in Philada. There is nothing of its tribe in their collection. Is it described?

The enclosed photograph will give you some idea of it, but it was done in my absence and is too much foreshortened, owing to having been too much inclined. The 2 ft. rule partially obscures by its shadow the whale's rib. The bottom and left hand objects show the coniferous wood.

I shall probably have another photograph taken of the cycas placed erect. Besides the other side is most perfect. The line down the front shows that it was cracked before silicification and the fissure has been filled with sand cemented by oxide of iron.

I have so arranged matters as to prevent the loss of specimens that may be hereafter exhumed and shall personally explore the region early in the spring.

Very truly yours,

(Signed) Philip T. Tyson

P. S. When will the 3d vol of your Paleontology of N. York be published?

FOSSIL REMAINS January 8, 1859

The geological researches of Mr. P. T. Tyson, State Agricultural Chemist of Maryland, have recently brought to light some very interesting fossil remains, which have been entombed during perhaps countless ages in the iron ore hills between this city and Baltimore.

The formation consists principally of thick beds of lead-colored clays with lignite. The iron ore is in the form of large nodules, and consists of the carbonate of iron. The fossils discovered are:

1. Fossil teeth, which have been fully investigated by Dr. Christopher Johnston, of Baltimore, and determined to be those of a Thecodont Saurian, not hitherto described.

We regret to learn that several vertebrae, which doubtless formed part of this huge animal, and which were thrown out by the ore diggers at Mr. Latchford's mine, were lost amongst the refuse before Mr. Tyson reached the place.

This Saurian has been named, provisionally by Dr. Johnston, "Astrodon", from the stellated appearance of cross sections of the teeth under the microscope.

2. At a short distance from where the Saurian remains had been buried was found a fragment of what must have been a rib of a large Cetacean.

3. Also, about six feet in length and more than two feet in diameter, the trunk of a tree completely silicified, or, in popular language, "turned into stone". Dr. Johnston's microscopic investigations prove this to have belonged to the coniferous or pine family.

All of the above were found about 220 feet above the level of tide water.

4. About one mile distant, on the farm of Dr. Theodore Jenkins, a vegetable fossil was found by

Dr. J. which belongs to the cycades, (a tribe of tropical plants,) resembling the existing sago palm often seen in our hothouses. It is shaped somewhat like the pine-apple, and is about eighteen inches high and fifteen inches in diameter, and is also silicified.

These discoveries prove that the clays and iron ore ranging from Washington, via Baltimore, to the vicinity of Elkton, constitute secondary strata probably older than the cretaceous green sand of New Jersey. In fact, the investigations of Dr. Johnston indicate that the Saurian teeth may have belonged to a much older period.

The continued inclement weather since these fossils were discovered has arrested further researches for the present, but we are informed that they will be resumed by Mr. Tyson early in the ensuing spring. It is his opinion that the cretaceous green sand, so largely and usefully applied as marl in New Jersey, may be expected to rest upon the southeastern edge of this iron ore formation, and be accessible within a few miles of the Washington and Baltimore railroad.

This must not be confounded with the eocene green sands or marls of Charles, Prince George's, Anne Arundel, Cecil, and Kent counties of Maryland, and which are more or less diluted with siliceous sand. The lower beds of the Jersey green sand or marl are nearly free from siliceous sand. It contains from eight or twelve per cent. Of potash, and is highly prized as a manure. It will prove to be a valuable resource if it shall be found in Maryland contiguous to a railroad or tide-water. This article is largely exported from New Jersey, and enters into the composition of some of the artificial fertilizers imported from New York or its vicinity.

What wonderful changes must have taken place in this part of the world since Whales and Saurians were entombed upon this (then) marshy coast! The remains of the Saurian and Cycas indicate that a tropical climate then prevailed in this latitude. At the same period also almost the only portion of what now constitutes the dry land of Maryland and Delaware was north and west of a curved line drawn from Wilmington , near Elkton and Baltimore, to Washington. All the remainder, comprising half of Maryland and nearly the whole of Delaware, was covered by the waters of the ancient ocean.

"Notebook E" 1859

May 5. To Latchford's iron mine and got fragments of Saurian bones just exhumed. They were found near a lignite, the remains of a large tree more than 60 ft long.

From thence to Dr. Jenkins and noted the locality of the Cycas to be at or near the base of the lead colored iron clays.

Retd to Wentenbuone (?) & thence for RR and reached Balto at 8pm.


Map 1: Site of Astrodon's original discovery.

Section of northern Prince George's County, Maryland, United States of America. Bold letters indicate localities of dinosaur discoveries (see Kranz, 1996, for more details). Large "L" indicates approximate location of John D. Latchford's property. Dinosaur park includes much of the northern portion of Latchford's property.

Figure 1: Astrodon johnstoni

Astrodon femur, currently the largest dinosaur bone known from the East Coast of the United States: (a) femur being cast in plaster for removal from Muirkirk clay pit by Dan Chaney (left) and Peter Kroehler (right) of the National Museum of Natural History in May, 1991; (b) in the laboratory at the National Museum of Natural History, March, 1996; shown at approximately 1/10 size; note hammer for scale; (c) sketch of an Astrodon family.