Graptolites: gone yesterday, here today?

Graptolites are one of the less-heralded members of the local Ordovician menagerie, probably because they don't seem to be all that common around here. Graptolites were colonial animals (and I use "were" and other past-tense terminology with implied quotation marks, because of the shocking twist yet to come). The colonies, called "rhabdosomes", are made up of branches called "stipes", which support cup-like structures called "theca" that housed the individual animals. (See also here for official terminology.) The overall effect is that stipes often resemble saw blades, with the "teeth" being the theca. Early graptolites were apparently attached to the seafloor and formed densely branching (dendritic) colonies (see for example several of the specimens here and here), whereas later forms were apparently planktonic and attached to floats of their own device or other floating things, such as seaweeds [2020/11/11: no! It appears that there is no evidence for floats or attachments; see Maletz 2015 for the gory details]. The rapid taxonomic turnover of graptolites, coupled with the ease of distribution for planktonic forms, make them excellent index fossils. Planktonic distribution also has the neat side effect of getting graptolites into rock formations that otherwise lack much for fossils, usually because of low oxygen levels in the water column precluding a great deal of life while the formation was being deposited. While low oxygen would limit bottom dwellers, it wouldn't stop things from drifting through higher up the water column. Fossils of graptolites are found from the Cambrian into the Carboniferous. This may not be where the story ends, though: it has been known for a while that graptolites are most similar to pterobranchs, a living group of tube-dwelling often-colonial worm-like hemichordates. There is evidence that pterobranchs are, in fact, living graptolites (e.g. Mitchell et al. 2013; Discovery Magazine ran an article on this topic back in 1993). Should this be the case, it would appear that only the planktonic forms truly disappeared; seafloor forms persisted, albeit in much reduced circumstances (only a handful of pterobranch genera and species are known). All of the species reported from the Twin Cities appear to be of the planktonic persuasion.

As mentioned, graptolites are an uncommon component of the local fauna. They do pop up from time to time, though, and their thin dark saw blade fossils are quite distinctive if you get a large enough chunk. Reports of graptolites in the Twin Cities go back almost to the beginning of local geology, actually. Shumard (1852) reported graptolites from a bluff about a half-mile downstream from Fort Snelling, in what would now be considered the lower Platteville Formation. Winchell and Schuchert (1895) provided illustrations for three species, Climacograptus typicalis, Diplograptus pristis?, and Diplograptus putillus. All of their cited specimens came from outside the metro, and apparently from higher stratigraphically than virtually all metro rocks, with C. typicalis from what would now be the Cummingsville Formation and the other two from what would now be the Dubuque Formation, per the stratigraphic table in Winchell and Ulrich (1897). Stauffer (1930) found abundant black fragments of graptolites in a particularly calcareous layer low in the Decorah Shale in rocks recovered from a heating shaft dug for Northrop Auditorium. Stauffer and Thiel (1941) observed C. typicalis in what would now be the Mifflin Member at Lock and Dam 1, on the Ramsey County side. Their lists reported three following species in the Platteville Formation and Carimona Member (their Spechts Ferry). All three were listed under Hydrozoa, the group that includes relatives of corals and jellyfish, which was a reasonable enough hypothesis at the time (before the discovery of pterobranch affinities, graptolite relationships were a free-for-all):

Climacograptus typicalis (Pl, Ca)
Climacograptus (Mesograptus) putillus (Pl)
Diplograptus amplexicaulis? (Pl)

(More graptolites are known from older rocks a bit farther afield in Minnesota. Ruedemann [1933] described several species from the Upper Cambrian St. Lawrence Formation of Afton.)

From Winchell and Schuchert (1895). This looks kinda like at least one of the examples in the following photo, but you should always be wary of diagnosing your fossils via photos and plates.

A University of Minnesota piece with a few graptolites (look for the things that look like saw blades on sticks. Mouse-sized hacksaws.).

References

Maletz, J. 2015. Graptolite reconstructions and interpretations. Paläontologische Zeitschrift 89:271–286.

Mitchell, C. E., M. J. Melchin, C. B. Cameron, and J. R. Maletz. 2013. Phylogenetic analysis reveals that Rhabdopleura is an extant graptolite. Lethaia 46(1):43–56.

Ruedemann, R. 1933. The Cambrian of the upper Mississippi Valley, part III, Graptolitoidea. Milwaukee Public Museum Bulletin 12(3):307–348.

Shumard, B. F. 1852. Geological report of local, detailed observations, in the valleys of the Minnesota, Mississippi, and Wisconsin rivers, made in the years 1848 and 1849, under the direction of David Dale Owen, United States Geologist, by B. F. Shumard, head of subcorps. Pages 481–531 in Owen, D. D. Report of a geological survey of Wisconsin, Iowa, and Minnesota; and incidentally of a portion of Nebraska Territory. Lippincott, Grambo & Co., Philadelphia, PA. 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.

Stauffer, C. R. 1930. Conodonts from the Decorah Shale. Journal of Paleontology 4(2):121–128.

Stauffer, C. R., and G. A. Thiel. 1941. The Paleozoic and related rocks of southeastern Minnesota. Minnesota Geological Survey, St. Paul, MN. Bulletin 29.

Winchell, N. H., and C. Schuchert. 1895. Sponges, graptolites, and corals from the Lower Silurian in Minnesota. Pages 55–95 in Lesquereux, L., C. Schuchert, A. Woodward, E. Ulrich, B. Thomas, and N. H. Winchell. The geology of Minnesota. Minnesota Geological and Natural History Survey, Final Report 3(1). Johnson, Smith & Harrison, state printers, Minneapolis, MN.

Winchell, N. H. and E. O. Ulrich. 1897. The lower Silurian deposits of the Upper Mississippi Province: a correlation of the strata with those in the Cincinnati, Tennessee, New York and Canadian provinces, and the stratigraphic and geographic distribution of the fossils. Pages lxxxiii–cxxix in L. Lesquereux, C. Schuchert, A. Woodward, E. Ulrich, B. Thomas, and N. H. Winchell. The geology of Minnesota. Minnesota Geological and Natural History Survey, Final Report 3(2). Johnson, Smith & Harrison, state printers, Minneapolis, Minnesota.

Coming Attractions in Dinosauria?

One more trip to the well... In the spirit of Addendum II, here is my own compilation of undescribed dinosaurs. I am deliberately avoiding repeating entries from the 1982 list (sorry, "Thotobolosaurus" [2020/04/19: now Kholumolumo], Archbishop, Cleveland-Lloyd ankylosaur, and Monoclonius recurvicornis). In the spirit of that list, I full expect some of these to be named next week and some to be still hanging around, say, thirty-three years from now, like some from 1982 are still waiting in 2015. This is not an exhaustive list, but more of a "greatest hits". It is biased to reports with some history behind them, and also biased to reports that I think will eventually be substantiated, so there's none of the "[random place] [random dinosaur represented by a single bone]". Let me know if they ever get around to "Ngexisaurus".

Where are they now: 1980s dinosaur rumors, ornithischians

We now reach the final section, the part dealing with ornithischians (links to theropods and sauropodomorphs). The ornithischian portion of Glut (1982)'s Addendum II is a real mixed bag. It's not just because people seem to forget about ornithischians, especially when the ornithischians come without bearing horns or plates. There's some really scrappy stuff listed and some really vague entries, as well as two genera that had been named and had entries in the rest of the book, and a third that had been named but hadn't made the book.

Where are they now: 1980s dinosaur rumors, sauropodomorphs

And now we return to 1982. We have seen the future of theropods, now let us turn to the future of sauropodomorphs. One future was that of Supersaurus and Ultrasaurus, a future of every large sauropod having to out-superlative the sauropod before it. This future petered out before it got any farther, kneecapped by an honest mistake half a world away and a terminal case of bonebed chimerism. Another future was that of Roccosaurus, the fanged prosauropod, and it was a terrible bleak cheesy early-'80s dystopian future, with leather and chains and synthesizers. That future never came to pass. Others involved overlooked fossils from Portugal and central Asia taking their rightful places, or promises of skulls from India, or an unusual elongate cervical vertebra from Wyoming, or a skeleton from Tendaguru.

Where are they now: 1980s dinosaur rumors, theropods

One of the great mantras of paleontology is "wait for the paper" (occasionally with choice adjectives between "the" and "paper"). Paleontology is, after all, a science of delayed gratification. First you have to find the fossils, then prepare them, then write and submit a manuscript, and then see it published. This process is measured in years in the best of times, and often some information gets out, either intentionally (talks, posters, news releases) or unintentionally (unredacted information in other publications, gossip, etc.). We went over part of this ground before. Here's a group of concrete examples.

All of the other echinoderms

If you thought that echinoderms have a variety of seemingly unrelated body plans today (sea stars, crinoids, sea urchins, sea cucumbers...), you should have seen them during the Paleozoic, when several now-extinct classes populated the oceans. The group with probably the most recognition are the blastoids, or sea buds, which had stalks like crinoids but with a nut-like structure instead of a cup-like structure as the business end. The rocks of the Twin Cities area are not known to have produced blastoids, but they have produced rare examples of four other groups not including the crinoids we saw before. They are: asteroids (sea stars), rhombiferan cystoids, edrioasteroids, and stylophorans (a.k.a. carpoids, a.k.a. homalozoans). Three of these groups are extinct, and it doesn't take much to guess which. This diversity of echinoderms is not particularly unusual; Cincinnatian rocks have all the same classes as well as brittle stars and cyclocystoids (extinct and known mostly from their ring-like outer structures), and the Bromide Formation of Oklahoma, of comparable age, outdoes the Minnesota rocks handily. But for the luck of the cosmic draw, any of these extinct groups might be around today.

World of Stone

This is part of Devil's Parlor in the Minnesota side of Interstate Park, on the St. Croix River. I was at the park on Saturday for a park geology program, and following work I wandered through the Glacial Gardens section. Interstate Park, as its name suggests, has units in two states, in this case Minnesota and Wisconsin. The two parts are state parks, associated with but not part of St. Croix National Scenic Riverway (the Wisconsin side is also the western trailhead for the Ice Age National Scenic Trail, as well as one of the nine parts of the Ice Age National Scientific Reserve). Interstate Park is known for its glacial landforms, imprinted primarily on Precambrian bedrock.