Requiem for ACM 41109, the first holotype of Anchisaurus

ACM 41109, also known as AM 41/109, was until recently the holotype or defining specimen of Megadactylus polyzelus, better known as Anchisaurus. ACM 41109 includes eleven back and tail vertebrae, a partial shoulder blade, most of the right hand, part of the right forearm, much of the left leg, and parts of both ischia. These are all that remain of a basal sauropodomorph that lived about 200 million years ago. Unlike the overwhelming majority of its brethren, the mortal remains of ACM 41109 were not only buried and fossilized, but through sheer inconceivable luck were buried in a place where, 200 million years later, they would be uncovered by earth-moving operations carried out by a species that was not even a hint of a glimmer of a twinkle in the eye of one of the therapsids that lived at the same time as the dinosaur. Its rebirth in 1855 was difficult: it suffered blasting and its bones were then dispersed by workmen who were preparing improvements to the great Springfield Armory, a timely effort given the Civil War to come a few years in the future. As much of the skeleton as could be salvaged was sent to pioneering paleontologist Edward Hitchcock of Amherst College, which is how the specimen came to be labeled "ACM"; the college's museum is today the Beneski Museum of Natural History. Although the first reports came out in the 1850s, a formal name would have to wait until 1865, when the task fell to Hitchcock's son, Edward Jr. At the time, it was one of the few dinosaur specimens of any completeness known, and was part of the first wave of North American dinosaur body fossils along with Hadrosaurus, "Laelaps", Leidy's Judith River scraps, and other bits and pieces. In one of those strange comedies that happen from time to time, it went through two genus names (Megadactylus and Amphisaurus) before finally coming upon one which wasn't already in use (Anchisaurus). ACM 41109 was sufficient to define Anchisaurus polyzelus for many years. Now this function has been passed to YPM 1883, previously known as Anchisaurus colurus or Yaleosaurus, both names which now must be considered rejected. YPM 1883 was somewhat more fortunate in terms of how it was preserved and discovered, but has no particularly colorful stories behind it. The quarry that produced it is now occupied by a shopping center, and by the time it was found dozens of good dinosaur specimens had already been recovered. Perhaps ACM 41109 will now be forgotten, a handful of bones in a drawer. Yet though it no longer suits the changing needs of taxonomy, it somehow reached out beyond 200 million years and briefly become the exemplar of untold forever-vanished animals.

Further reading:

International Commission on Zoological Nomenclature (ICZN). 2015. Opinion 2361 (Case 3561): Anchisaurus Marsh, 1885 (Dinosauria, Sauropodomorpha): usage conserved by designation of a neotype for its type species Megadactylus polyzelus Hitchcock, 1865. Bulletin of Zoological Nomenclature 72(2):176–177.

Tweet, J. S., and V. L. Santucci. 2011. Anchisaurus from Springfield Armory. Brigham Young University Geology Studies 49(A):75–82.

A tale of two packrat species

This is Neotoma cinerea, the bushy-tailed packrat:

From Oregon Caves via Wikimedia Commons.

The Decorah Shale

So we've gotten through the St. Peter, Glenwood, and Platteville. It's high time that the collection is completed with the one and only Decorah Shale. The Decorah is a bit of a shy bird in the Twin Cities because it's not the most resistant unit in the world and is pretty well covered otherwise. It's often more easily seen by what it erodes into: a gray-green clay with bits of buff-colored heavily fossiliferous limestone. In the metro, it is best known from western St. Paul and just south of the Mississippi River in the Mendota Heights/Lilydale area, but I suspect it is more widely distributed than it is usually mapped. Along the Minneapolis side of the gorge, I've encountered characteristic gray-green clay and buff fossiliferous limestone fragments near or at the top of the bluffs in a few places, perhaps representing erosional outliers.

The slope photo strikes again!

Crystal ball for 2016

Welcome to 2016! I trust you have arrived safely; this darn travel through time only goes one way. 2015 was all right, as years go. I crossed a couple of fossils off the "see in the wild" list (tabulate corals and conulariids, plus I finally got the hang of horn corals), plus for my job I got to sleep under the stars at Death Valley and see part of the Grand Canyon by small plane. All in a day's work, I say. Having had some good luck in the Platteville this year, I plan to pay more attention to it this year. My "white whale" would be finding an equivalent to the old "Johnson Street Quarry" echinoderm locality; I've been looking out for Hidden Falls Member exposures lately. I'd love to see an edrioastroid or a "cystoid".

I continue to update the Compact Thescelosaurus; if you have something you'd like me to correct, just let me know. Here's a few things I expect for dinosaurs in 2016 (nothing too serious, of course):

North American camels: not the run-of-the-mill Christmas camels

In North America and Europe, camels generally keep a low profile except for December, when they show up as part of Christmas iconography: the Three Wise Men, Nativity scenes, etc. The general scarcity of camels in these landmasses makes them exotic. Camels and llamas today evoke specific areas: camels bring to mind deserts from north Africa into central Asia, and llamas are shorthand for the Andes. However, camelids (including camels, llamas, alpacas, and so forth) are actually a North American innovation, circa middle Eocene. Through no particular fault of their own, there are now no longer any native camel species in North America, although as recently as the late Pleistocene, about 126,000 to 11,700 years ago, camels were common. The two flagship models at this time were Camelops hesternus, which translates to the evocative "yesterday's camel", and Hemiauchenia macrocephalus, also known as the "North American llama". The exact taxonomy, of course, is somewhat more bushy when you get into it, but this isn't bad for broad strokes. The camel family filled a number of niches in North America over the Cenozoic, from what we would recognize as roles similar to modern camels and llamas, to giraffe analogues like Aeypcamelus, to plus-sized forms like Megacamelus and Titanotylopus, to analogues of deer and gazelle, such as Poebrotherium (also of note as the first fossil organism named from the White River Badlands; Prout's "Palaeotherium" doesn't count because he didn't actually name it). Here are a couple of examples from the now-vanished North American empire of camels:

The three wells of Fort Monroe, and why they didn't pan out

Fort Monroe at Old Point Comfort in southeastern Virginia, today the namesake attraction of Fort Monroe National Monument, has a long and distinguished history. It also hosts an odd little geologic story. If you're familiar with Chesapeake geology, you may guess the punchline, but don't spoil it for everyone else, okay?

Fort Monroe, during the early stages of the Civil War. Not pictured: somebody contemplating where to sink a well, never dreaming that by the time they stopped in 1869, the war would be long over, the current President would be assassinated, his replacement would be impeached, and the well would only turn up salt water. (image found at NPS monument site).

For understandable reasons, it is useful for a fort to have a secure water supply. Logically enough, the staff at Fort Monroe decided to address theirs by drilling an artesian well. Thus it was that in 1845, work began on a well. Drilling continued until July 1846, at which time a pipe broke at 189 ft (58 m). In terms of getting water, this effort was unsuccessful, but for those of us interested in geology and paleontology, the attempt was a rousing success. The pioneering American microscopist Jacob Whitman Bailey identified a number of fossils, particularly from a unit of fine-grained greenish gray sand 48 to 108 ft (15 to 33 m) down). Identifiable material included coal, foraminifera, stratigraphically useful bivalves and scaphopods, and echinoid spines (Fontaine 1882). The mollusks are typical of the Yorktown Formation, now known to be Pliocene.

By the time of the Civil War, the fort (which remained in Union hands throughout) was still reliant on a cistern. Another attempt to sink a well was begun in 1864, within the walls of the fort (Woolman 1899). This time they reached 907 ft (276 m) (Rogers 1882) before running out of money in September 1869 (Fontaine 1882). Again, a number of marine fossils were found in the sediments, this time also including abundant diatoms, shark teeth, and whale bones (Rogers 1882). Also, like the first well, there was a distinct lack of potable groundwater. The only significant water was struck at 599 ft (183 m), and it was reportedly very saline (Sanford 1913).

There is no sense in doing things halfway, so in 1902 a third attempt was made. This time, they didn't stop until they penetrated crystalline bedrock at 2,254 ft (687 m) (Darton 1902). In eastern Virginia, there aren't a lot of places to view long columns of strata, so this and the 1864 well have attracted a fair amount of interest, popping up from time to time in the literature (e.g. Richards 1945, 1947; Cederstrom 1945, 1957; Powars 2000). Interestingly, Darton (1902) thought there was quite a bit of Cretaceous coastal plain sediments below the fossil-bearing Cenozoic marine sediments, but Cederstrom (1945, 1957) thought it was Cenozoic all the way down. In the end, the well has been quite informative for geologists. In terms of water? The third and final attempt was just as fruitless as the others. When water was tested, it proved to be saline (Sanford 1913).

Now for the punchline: they never turned up potable groundwater for the simple reason that they couldn't. What they had no way of knowing at the time was that during the Eocene, approximately 35 million years ago, an object from space blasted into North America about where the tip of the Delmarva Peninsula is today. Fort Monroe happens to be within the area directly affected by the impact. The sediments down to bedrock were rearranged in the blink of an eye and the preexisting aquifers were completely disrupted. In the impact zone, no matter how far down you go, you turn up salty water (Powars and Bruce 1999; Powars 2000).

References:

Cederstrom, D. J. 1945. Structural geology of southeastern Virginia. Bulletin of the American Association of Petroleum Geologists 29(1):71–95.

Cederstrom, D. J. 1957. Geology and ground-water resources of the York-James Peninsula, Virginia. U.S. Geological Survey, Washington, D.C. Water-Supply Paper 1361.

Darton, N. H. 1902. Norfolk folio, Virginia-North Carolina. U.S. Geological Survey, Washington, D.C. Folio of the Geologic Atlas 80.

Fontaine, W. M. 1882. The artesian well at Fort Monroe, Va. The Virginias 3(2):18–19.

Powars, D. S. 2000. The effects of the Chesapeake Bay impact crater on the geologic framework and the correlation of hydrogeologic units of southeastern Virginia, south of the James River. U.S. Geological Survey, Reston, Virginia. Professional Paper 1622.

Powars, D. S., and T. S. Bruce. 1999. The effects of the Chesapeake Bay impact crater on the geological framework and correlation of hydrogeologic units of the lower York-James Peninsula, Virginia. U.S. Geological Survey, Reston, Virginia. Professional Paper 1612.

Richards, H. G. 1945. Subsurface stratigraphy of Atlantic Coastal Plain between New Jersey and Georgia. Bulletin of the American Association of Petroleum Geologists 29(7):885–955.

Richards, H. G. 1947. Invertebrate fossils from deep wells along the Atlantic Coastal Plain. Journal of Paleontology 21(1):23–37.

Rogers, W. B. 1882. Infusorial deposit of Virginia in the Fort Monroe artesian well. The Virginias 3(10):151–152. Reprinted in Geology of the Virginias, 1884, pp. 733-736.

Sanford, S. 1913. The underground water resources of the coastal plain province of Virginia. Virginia Geological Survey, Charlottesville, Virginia. Bulletin 5.

Woolman, L. 1899. Artesian wells in New Jersey. Pages 59–144 in Annual report of the State Geologist for the year 1898. Geological Survey of New Jersey, Trenton, New Jersey.

Nodosaurus: more than a corduroy armadillo

Ankylosaurians, be they clubbed or club-less, labor in relative anonymity among dinosaurs, bundles of roughage trundling along, only briefly intersecting the limelight of flashier dinosaurs. A few get a bit more press, enough to put them in a respectable second tier of popularity (Ankylosaurus and Gastonia, particularly). Despite being the traditional namesake for the club-less ankylosaurs*, Nodosaurus is not one of them. Instead, it fills a role not unlike a venerable distant relative who occasionally shows up at family functions to hover on the sidelines. We know he or she is there and we show due deference, but there's no particularly warm connection of familiarity. The closest it's gotten to a star turn since it was named in 1889 was as a John Sibbick illustration in the "Normanpedia", where it is depicted as a sort of vaguely armadillo-like creature suspiciously eyeing the reader and bearing a precise gridwork of button-like armor pieces, without a hint of spikes or plates. Oddly, the skeletal restoration on the next page shows a distinctly different pattern of armor, featuring alternating bands of large scutes between the ribs and smaller pieces over the ribs, which unintentionally give it a sort of corduroy texture. As we shall see, there does indeed appear to a corduroy pattern over part of the animal, but there was also a lot more going on.

*This great tradition goes back all the way to the 1970s (Coombs 1978). Prior to this, ankylosaurs were just kind of there as one sort of mash. After this, ankylosaurs were still just kind of there, but now there were two flavors.