Sunday, May 26, 2019

Your Friends The Titanosaurs, part 12: Futalognkosaurus, Gondwanatitan, and Hypselosaurus

For today's entry in the ongoing series, we have a big sauropod that used to be even bigger, a small sauropod that appears to have been lost in a fire, and a small sauropod of historical interest which is a bit of a humbug.

Sunday, May 19, 2019

Trilobites and strange fate

For reasons that will become abundantly clear in a few months, I've been immersed in the paleontology and geology of Grand Canyon National Park for work. We've been doing a lot of projects in that general area over the past few years (Glen Canyon National Recreation Area, Lake Mead National Recreation Area, Tule Springs Fossil Beds National Monument, Walnut Canyon National Monument [check out the public report], Wupatki National Monument, and Zion National Park), and it's only fitting that we take on Grand Canyon. This particular story includes both Grand Canyon and Lake Mead.

Boulder Dam Recreation Area, later renamed Lake Mead National Recreation Area, was established in the 1930s to administer the reservoir Lake Mead that was filling behind Hoover Dam, at the time known as Boulder Dam. As originally conceived, the recreation area extended quite a bit farther east, into what is now part of western Grand Canyon National Park. This is because at the time it was planned that another dam, the Bridge Canyon Dam, was going to be constructed in that area, and the recreation area was sized to accommodate the anticipated reservoir. Obviously, unless you are a reader who has stumbled in from another timeline, no such dam was ever built, and in 1975 the park boundaries were reconfigured, with most of eastern Lake Mead NRA (Grand Wash Cliffs and east) being transferred to Grand Canyon National Park.

This area, as a matter of fact, looking due south into the Grand Wash Cliffs (photo taken from small plane, hence the plane structures and the whole "up in the air" thing).

Anyway, we were still back in the 1930s. The NPS had a few people on staff in the 1930s who specialized in geology, such as H. Donald Curry at Death Valley and Edwin McKee at Grand Canyon. Working at Boulder Dam Recreation Area was Ed Schenk, who had the challenge of contending with a field area that was steadily shrinking by the day as the reservoir filled. A substantial portion of his work at Lake Mead remains unpublished, but his research on the Cambrian escaped that fate (Schenk and Wheeler 1942). His counterpart at Grand Canyon, McKee, was also working on the Cambrian, and published a rather more famous work a few years later (McKee and Resser 1945). You may not recognize the citation, but if you've studied geology at the college level you may well have run into material that's been derived from this publication, in which McKee described the facies changes of the Cambrian formations in terms of marine advances and retreats: very briefly (and simply), there's the nearshore Tapeats Sandstone, the shallow marine Bright Angel Shale, and the deeper marine Muav Limestone.

As part of his work, Schenk collected fossils from about four dozen localities in and around the recreation area. About a quarter of the collections were from Cambrian rocks, all in that area which is now in western Grand Canyon NP. These collections included a fairly typical assortment of mid-Cambrian life, such as trilobites, brachiopods, and hyoliths. Several of these collections were cited in Schenk and Wheeler (1942). It is not immediately obvious, but the same collections are also cited in McKee and Resser (1945), with a few re-identifications. I only realized it when I thought to check because Schenk was noted as a collector in McKee and Resser (1945). Charles Resser, whom we met briefly earlier, also provided identifications for Schenk's paper. Essentially, the two papers were being worked on contemporaneously with contact between the groups of authors, and Schenk's shorter publication beat McKee's work into press by a couple of years (M&R '45 would also have been affected by wartime circumstances and Resser's passing in 1943).

If you're super-curious about these things, the collections definitely mentioned in both S&W and M&R are as follows, using M&R's stratigraphy ("F-" collections are Schenk's):
Peach Springs Member, Muav Limestone: fauna 73 = F-40
Bright Angel Shale tongue: fauna 74 = F-47
Spencer Canyon Member, Muav
Bright Angel Shale tongue
Sanup Plateau Member, Muav
Bright Angel Shale tongue: fauna 75 = F-37
Rampart Cave Member, Muav: fauna 76 = F-39
Flour Sack Member, Bright Angel Shale: faunas 46, 47 = F-16, F-17
Bright Angel Shale tongue
Tincanebits Tongue, Muav
Bright Angel Shale upper slope units: fauna 48 = F-44; fauna 49 = F.C. 761
Bright Angel Shale red-brown cliff unit?
Bright Angel Shale lower slope units: fauna 8 = F-15

Resser named several taxa from the F-# collections, and the holotypes for these taxa were sent to the USNM. These include Albertella schenki from F-44 (McKee and Resser #48; holotype USNM 108583), Lingulella mckeei from F-17 (M&R #47; USNM 108561a), Acrocephalops? arizonaensis from F-16 (M&R #46; USNM 108624), Kootenia simplex from F-37 (M&R #75; USNM 108591a), Kootenia schenki from F-40 (M&R #73; USNM 108586a), and Solenopleurella porcata from F-40 (M&R #73; USNM 108586a and 108626a). If you check the online USNM database, specimens with photos have the F-numbers on their slabs, showing their origin.

We come now to strange fate. Around 1960, with Schenk having long since left the NPS, staff at Lake Mead sent his old collections to the USGS for taxonomic identification. The USGS used to have a system where field geologists could send material for identification, usually to determine the relative age of rock units for mapping and resource projects. The resulting files were called "Examine & Report" (E&R) files. I've seen the files for the Lake Mead project, which took a while to complete for various reasons. Trilobite specialist A.R. "Pete" Palmer was sent the Cambrian samples for identification. Naturally enough, given the rock units involved, he used McKee and Resser (1945) for reference, as he remarked in the memo. Given that most of the fossils in McKee and Resser (1945) were only mentioned in lists, and type and figured specimens that might have given away the tale were retained from the collections by the Smithsonian, there was very little way of knowing that this exercise was actually about using McKee and Resser (1945) to identify fossils from some of the collections in McKee and Resser (1945).

References

McKee, E. D., and C. E. Resser. 1945. Cambrian history of the Grand Canyon region. Carnegie Institution of Washington Publication 563.

Palmer, A. R. 1963/10/17. O-60-55. USGS internal memo to M. B. Ingham (E&R file).

Schenk, E. T., and H. E. Wheeler. 1942. Cambrian sequence in western Grand Canyon, Arizona. Journal of Geology 50(7):822–899.

Sunday, May 12, 2019

Stillwater tusk(s): Minnesota's first

Stillwater, Minnesota is not the kind of place that comes to mind when thinking about good elephant country. If you've never been there, there's a bit of a drop from the top of the St. Croix Valley to the river (the map coming up will make this clear). Furthermore, Stillwater is not noted for its broad floodplain, so a proboscidean wouldn't have much space if it did come down. However, the deep valley of the St. Croix itself is of geologically recent vintage, a parting gift of the most recent ice age sending meltwater through an area marked by billion-year-old faults. This is all a long-winded way of saying that compared to today, it would have been much easier to have mammoths and mastodons wandering around the future area of Stillwater right after the ice had cleared out, only where they were wandering wouldn't have looked very much like how it looks like today.

In fact, what appears to be the first documented find of mammoth or mastodon fossils in Minnesota was made in Stillwater in 1856 (Anonymous 1860; Stauffer "1945"). The find was briefly mentioned in a description of the Minnesota Historical Society ("Already we find it its museum the remains of the first mastodon found in the State, presented by A. [Abram or Abraham] J. Van Vorhes, esq., of Stillwater"; Anonymous 1860), but a fuller account would not be made until Newton Horace Winchell took an interest in it.

According to Winchell, who met with Van Vorhes, the find came from coarse river gravel (actually the base of a bed of fine sand 30–40 feet thick [9–12 m] according to the included stratigraphic section) "far above the present river, but within the main valley" and consisted of a single mastodon tusk (Winchell 1878). Obviously, as an isolated find there's really no way to be certain where the tusk was when its services were no longer required by its owner, but we take our tusks where we find them. (There are differences between mastodon and mammoth tusks, but I don't know if these were known in the mid-1800s, or if this is just a case of "mastodon = generic American proboscidean".) Van Vorhes also reported pottery fragments at the top of the sand bed. Eight feet (about 2.5 m) of the tusk went to the Academy of Sciences of St. Paul (Winchell 1878), and would have been lost in the 1881 fire (mentioned previously).

Winchell also included an extensive quotation from Van Vorhes, who reported multiple tusks "were found about eight or ten feet [about 3 m] above the base of the hill: the hill at this point rises at an angle of about 45°. After excavating in the base of the hill on the grade of Myrtle Street about 37 feet [11 m], the tusks were found, consequently 37 feet below the surface. At this point the hill was about 90 feet high [27 m].

The crockery I found some thirty feet [9 m] farther into the hill and some six or eight feet [about 2 m] higher in the strata. This hill is a continuous tongue of land lying between the Florence mill stream and a spring run. The two streams run parallel and some 350 feet [107 m] apart. The hill is so steep on the Florence mill side as to be inaccessible except by clinging to roots and brush growing on it. The material at the base is sand and small gravel. Where the tusks were found the strata were pure sand ten or twelve feet thick [about 3 m], exhibiting clearly the direction of the current in an eastward inclination one or two degrees."

Leaving aside the question of one tusk or multiple tusks, the location of the find can be reasonably well established from Van Vorhes’s recollections (refreshing for a mid-19th-century find!). The Florence flour mill is long gone, and was not built until 1872, so Van Vorhes was using the then-current geography to describe the 1856 situation. However, as mentioned in the linked article, "The water for the mill was brought down from a dam located where the Pitman House once stood, now the northern portion of Trinity Lutheran Church, and supplied by a brook from McKusick’s Lake." The church is adjacent to Myrtle Street between 3rd Street N and 4th Street N, and a valley can be traced from this area to the lake. The "spring run" seems most likely to be related to a valley to the south, but the present-day distance is much greater than 350 feet. Given that Van Vorhes was an experienced surveyor, it's unlikely he would have been off by hundreds of feet or more; it seems more likely to me that the critical area has been so heavily modified in later years that the 1856 watercourses have been obscured or obliterated. My guess is that the find was made within 500 feet (150 m) of the present location of the church.

This map (helps to click) shows several of the landmarks mentioned above. As I said, I think the find was made in the vicinity of the modern church. (Here's a plug: I've found the Earth Point topo map overlay for Google Earth invaluable!)

The location was retransmitted incorrectly in Hay (1924:44), who placed it in Browns Creek. I suspect this stems from a misreading of a later report by Winchell. Winchell (1888:397) stated "In the fall of 1872 the writer [Winchell] first visited Stillwater, and in company with Mr. Abram Van Vorhes examined the deposit of tripoli in the valley of Brown's Creek. At the same time Mr. Van Vorhes pointed out the drift bank in which he had found ancient pottery and the remains of the mastodon." It's not hard to see how a reader may have come to the conclusion that the "drift bank" was in Browns Creek. This creek, though, is on the north side of Stillwater; Highway 96 borrows part of its valley. It is approximately 1.4 miles (2.3 km) north of the actual area of the find.

The loss of the specimen relegated it to a paper curio. Winchell returned to it once more, in 1910, which is notable because he hedged on the mastodon identification, acknowledging it could have been an "elephant" (mammoth). Aside from Hay (1924), the only other place it seems to have appeared in the literature since Winchell is Stauffer's inventory of Minnesota's Pleistocene fossils (usually given as 1945, but at least 1948). Winchell’s report is #17 in this publication, and Stauffer classified it as "Elephas sp.", which translates as "some kind of proboscidean". Stauffer included another Stillwater find, #6, a tusk found in terrace gravels “in the edge of Stillwater” at an unspecified time. With such little information, it is impossible to say anything else about it.

[An unrelated closing note: I really ought to plug the Geological Society of Minnesota more frequently for local readers; for example, there was a talk this week on Cretaceous fossils in Minnesota. This would have been the normal closing session of the spring lecture series, but an opportunity arose for the GSM to co-sponsor a presentation by Peter Brannen on "The Ends of the World", his book about extinction events, Monday, May 20th (see flyer below for more details). The fall lecture series will start up in September. The GSM staffs a booth during the State Fair in the Education building if you'd like to stop by and chat in person. Lectures are free and open to the public.]

Here's a flyer for the upcoming talk. Note: "Blue Line" should be "Green Line".

References

Anonymous. 1860. Minnesota. The Historical Magazine 4(5):141–142.

Hay, O. P. 1924. The Pleistocene of the middle region of North America and its vertebrated animals. Carnegie Institute of Washington Publication 322A.

Stauffer, C. R. “1945” [at least 1948 based on dates in the article]. Some Pleistocene mammalian inhabitants of Minnesota. Minnesota Academy of Science Proceedings 13:20–43.

Winchell, N. H. 1878. Primitive man at Little Falls. Minnesota Geological and Natural History Survey Annual Report 6:53–65.

Winchell, N. H. 1888. The geology of Washington County. Pages 375–398 in N. H. Winchell and W. Upham. The geology of Minnesota. Minnesota Geological and Natural History Survey, Final Report 2. Johnson, Smith & Harrison, state printers, Minneapolis, Minnesota.

Winchell, N. H. 1910. Extinct Pleistocene mammals of Minnesota. Bulletin of the Minnesota Academy of Science 4:414–422.

Sunday, May 5, 2019

Titanosaur osteoderms: distribution

My plan had been to wrap up everything in this post. (Well, originally it was to do everything in one post. Ha.) However, again the contents were beginning to sprawl, and I felt guilty about the lengths of a couple of recent posts. After all, this isn't a peer-reviewed journal article, is it? There are different expectations for a blog post. Therefore, we'll just have distribution here, and one more post for the functions and conclusion. For the previous installments, go here (introduction) and here (characteristics).