Sunday, July 23, 2017

Graptolites of Afton

"Saw Clinton R. Stauffer, with a big rock in his hands
Says he found the graptolite site again
Gonna celebrate at Selma's Ice Cream Parlour
Send 'em off to Rudolf Ruedemann

[imitation of the sound of a graptolite]
Graptolites of Afton..."

(I apologize for nothing!)

University of Minnesota Paleontological Collection (UMPC) 4093, a particularly photogenic paratype of Callograptus staufferi, also depicted as Figure 5, Plate 55 in Ruedemann (1933).

Graptolites are a distinctive minor part of St. Croix Cambrian fossil faunas. So far their fossils are more or less limited to the St. Lawrence Formation of Afton on the Minnesota side and Osceola on the Wisconsin side (with a stray report from the Reno Member of the Tunnel City Group of Afton in Hughes and Hesselbo 1997). It's unlikely that this reflects a real geographic limitation, but it's what we have to work with. The first report was made by Hiram Prout in 1851. (Prout also gets trivia credit for the oldest report of a fossil from the Badlands, which probably outweighs the first St. Croix graptolite in the eyes of most people.) Prout's description is unfortunately vague about the circumstances and has a confusing habit of using the royal "we", but there are two suspects that come to mind as his source: his acquaintance Benjamin Shumard, from the David Dale Owen surveys, and James Hall, one of the lords of 19th century invertebrate paleontology, who was part of an 1850 survey in Wisconsin. The species name Prout chose suggests Hall had something to do with it, as does the omission of graptolites from the Owen survey report (Owen 1852). At any rate, Prout's fossils, obtained from "a thin seam of calcareo-aluminous shale, fifty feet above the water level" (=St. Lawrence Formation) at "Osceola Mills" (=Osceola), were dubbed Graptolithus hallianus (later to become Dendrograptus hallianus). The American Museum of Natural History has a specimen, AMNH FI 289, which is sometimes given as the holotype, but it doesn't look much like either figured specimen. However, it and another piece (AMNH FI 35989) may well be from the original collection, as suggested by some anonymous soul on the specimen cards.

Prout's original illustrations of Graptolithus hallianus, as well as two other kinds of graptolites from the same site (the "a" object in 1 and the asterisked object in 2, which Ruedemann (1933) recognized as an example of his new species Dendrograptus edwardsi.

And there matters rested until Clinton R. Stauffer, who hasn't had a starring appearance here in a while, pair a visit to Afton in 1930 and came back with a clutch of graptolite-bearing rocks. These were sent to graptolite specialist Rudolf Ruedemann for description, and he obliged with a publication in 1933. Stratigraphically, we have a good idea where they came from: a "light buff sandstone", "31 feet below the base of the Jordan (Norwalk) sandstone". The geographic location is kind of vague and confusing from source to source, but you can get a general sense for it. Unfortunately, the site is no longer extant; as mentioned in Robert Sloan's unpublished autobiography, it was lost due to highway relocation (kind of a kick, considering the state government recorded the site as of interest back in 1980 when looking at power transmission corridors). Having seen a later collection from the site, I suspect that Stauffer got the best stuff, and probably did considerable high-grading.

Ruedemann described the Afton graptolites as including six species: Acanthograptus priscus, Callograptus staufferi, Dendrograptus edwardsi, Dendrograptus hallianus, Dendrograptus sparsus, and Dictyonema minnesotense, which for some reason he kept forgetting about in his tables and lists (it happened in both his 1933 and 1947 publications). Three of them, Acanthograptus priscus, Callograptus staufferi, and Dictyonema minnesotense, were named from Afton specimens. Their type material can be found along with figured specimens of the other three species in the paleontology collections of the University of Minnesota, which is my cue to shut up and post pictures of some of the specimens.

Holotype (UMPC 4084) of Acanthograptus priscus, depicted in Figures 5 and 6, Plate 51 of Ruedemann (1933). Black bar is 1 cm.

Holotype (UMPC 4088) part and counterpart of Callograptus staufferi (circled) among numerous other graptolites, depicted in Figures 2 and 5, Plate 50 of Ruedemann (1933).

Dendrograptus hallianus (UMPC 4094), depicted in Figure 4, Plate 55 of Ruedemann (1933). Black bar is 1 cm.

Examples of two species on one piece. UMPC 4092 is a colonial stalk and basal disk of Dendrograptus edwardsi, depicted in Figure 6, Plate 49 of Ruedemann (1933). UMPC 4097 is Dendrograptus sparsus, depicted in Figures 8 and 9, Plate 49 of Ruedemann (1933).

Holotype (UMPC 4090) of Dictyonema minnesotense, depicted in Figure 3, Plate 55 of Ruedemann (1933). Black bar is 1 cm.

References:

Hughes, N. C., and S. P. Hesselbo. 1997. Stratigraphy and sedimentology of the St. Lawrence Formation, Upper Cambrian of the northern Mississippi Valley. Milwaukee Public Museum Contributions in Biology and Geology 91.

Owen, D. D. 1852. Report of a geological survey of Wisconsin, Iowa, and Minnesota; and incidentally of a portion of Nebraska Territory. Lippincott, Grambo & Co., Philadelphia, Pennsylvania. Available at http://archive.org/details/mobot31753000174885 (plates not included), https://archive.org/details/reportofgeologi00owen (full plates) or http://books.google.com/books?id=Y_ZYAAAAYAAJ.

Prout, H. A. 1851. Description of a new graptolite found in the lower Silurian rocks near the Falls of St. Croix River. The American Journal of Science and Arts (2nd series) 11:187–191.

Ruedemann, R. 1933. The Cambrian of the upper Mississippi Valley. Part III, Graptolitoidea. Bulletin of the Public Museum of the City of Milwaukee 12(3).

Ruedemann, R. 1947. Graptolites of North America. Geological Society of America Memoir 19.

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