Sunday, October 10, 2021

Compact Thescelosaurus Year Six

The time has come again for the annual review of The Compact Thescelosaurus. This year's new page is on aetosaurs and their close relatives, with the classification diagram page updated. (Don't forget, Wednesday the 13th is also National Fossil Day!)

Aetosaur Desmatosuchus spurensis is one of the subjects of the NPS Prehistoric Life Coloring Book. Coincidentally, an aetosaur also featured in the 2014 National Fossil Day artwork.

Sunday, September 26, 2021

Your Friends The Titanosaurs: Menucocelsior arriagadai

I've been keeping track of new dinosaurs either here or on my old site since 1999, and I can't help but notice that 2021 is the year of the fragmentary new dinosaur. Is this a reflection of COVID restrictions at museums and so forth, i.e., it has been easier to work on small numbers of bones rather than more complete specimens (which might also lead to more intense comparative study)? Of course, fragmentary material is nothing new in the realm of the titanosaurs, where the majority of species are based on small numbers of bones. (2021 has been pretty good for titanosaurs.) Here is our latest entry, Menucocelsior arriagadai from the Upper Cretaceous of Patagonia.

Genus and Species: Menucocelsior arriagadai. "Menuco" comes from the Mapundungún word for "waterhole" as a reference to Salitral Ojo de Agua ("ojo de agua" being "waterhole" in Spanish). "Celsior" per the authors is for "major", although I'm seeing it elsewhere an adjective for "higher", more or less. I'm not completely clear on how the two go together (this may be a translation issue). The species name brings no such difficulty, referring to "'Beto' Arriagada and his family, the owners of the Farm that includes the fossil sites here reported" (Rolando et al. 2021).

Citation: Rolando, M. A., J. A. Garcia Marsà, F. L. Agnolín, M. J. Motta, S. Rozadilla, and F. E. Novas. 2021. The sauropod record of Salitral Ojo del Agua: An Upper Cretaceous (Allen Formation) fossiliferous locality from northern Patagonia, Argentina. Cretaceous Research 105029. doi: 10.1016/j.cretres.2021.105029.

Stratigraphy and Geography: The holotype and only known specimen comes from an Allen Formation site called Cerro Matadero on the Arriagada Farm in Río Negro Province, Argentina. The area is known as Salitral Ojo de Agua (Rolando et al. 2021). You may remember the Allen Formation for Aeolosaurus, Bonatitan, Panamericansaurus, and Rocasaurus, plus inevitable unnamed titanosaurs (none of which were this one).

Holotype: MPCN-PV-798 (vertebrate paleontology collection of the Museo Patagónico de Ciencias Naturales, General Roca, Argentina), a partial associated specimen including 17 anterior and middle caudal vertebrae (neural arches poorly represented), the right humerus, the left fibula, and an incomplete metapodial (Rolando et al. 2021).

Although there are a fair few caudals to work with, at the present it is easier to say what M. arriagadai isn't than what it is. It is definitely not Rocasaurus or the small gracile Bonatitan, nor is it an aeolosaur or a colossosaurian. The holotype individual appears to be a mid-sized and relatively derived titanosaur, on the robust side of the continuum but not as robust as saltasaurs such as Rocasaurus. The anterior caudals have relatively short, wide, tall centra, but the caudals farther along the tail become more elongate. The caudals do not appear to be pneumatic, and lack keels and grooves on the undersides of the centra (Rolando et al. 2021). For now, M. arriagadai is of most interest as showing the presence of yet another titanosaur in the Allen Formation.

But that is not where the paper ends, not at all. M. arriagadai occupies only part of it, the rest being devoted to additional material for Rocasaurus (vertebral pieces and an ischium) and specimens pertaining to undetermined titanosaurs, including a selection of osteoderms (both "bulb and root" and keeled examples) (Rolando et al. 2021). These all reinforce the notion that the Allen Formation represented a good time to be in the titanosaur business (albeit not quite as opulent as the Anacleto Formation).

References

Rolando, M. A., J. A. Garcia Marsà, F. L. Agnolín, M. J. Motta, S. Rozadilla, and F. E. Novas. 2021. The sauropod record of Salitral Ojo del Agua: An Upper Cretaceous (Allen Formation) fossiliferous locality from northern Patagonia, Argentina. Cretaceous Research 105029. doi: 10.1016/j.cretres.2021.105029.

Sunday, September 19, 2021

Minnesota's state fossil revisited

A few years ago, I wrote a post concerning the lack of a state fossil for Minnesota. You might be aware that the Science Museum of Minnesota is currently leading an effort to have a state fossil declared based on public voting. You can check out the candidates and vote here. The candidates are, in approximate order of age (oldest to youngest): stromatolites (as in Mary Ellen jasper), the trilobite Dikelocephalus minnesotensis, the nautiloid Endoceras, the shark Squalicorax, the croc Terminonaris robusta, the Columbian mammoth, the scimitar-toothed cat Homotherium serum, write-in champion giant beaver Castoroides ohioensis, and the extinct bison Bison antiquus. Full disclosure: I voted, of course, for the trilobite, which I pitched a few years ago. Voting closes September 30, so there's still time to participate.

Sunday, September 5, 2021

Bryozoan Overload

Sometimes you look at a slab, and you notice one special thing about it. "That's a nice Isotelus hypostome." "Neat strophs." "Look at that Phycodes!" In this case, it's "Gee, that's a lot of bryozoans!"

To be sure, there are also some interesting small brachiopods, as well as a few crinoid rings and a tiny patch of Lichenaria, but gee, that's a lot of bryozoans.

(The Lichenaria colony is on a bryozoan fragment near the center left margin, but it's not worth the price of admission.)

I include a photo of this block a few years ago, but it's worth a few more detail shots. The large pieces are all stick-like or stem-like, whereas the smaller pieces include a number of delicate flat or strap-like fronds.

Branching straps plus a few different brachiopods.

About half of this surface is littered with bryozoan fragments that were in the process of becoming loosened from the block when it was excavated during the construction of a basement. Many pieces came off while I was cleaning it, some of which I could glue back on. (Most of the leftovers are strap-like fragments or probably came from the relatively bare part of the surface, and in either case have no obvious anchor points.) Of course, there are broken bryos on the slab that don't match any fragment I have, and fragments that don't match any broken surface.

Fronds and twigs, with crinoid rings and brachiopods for variety, and a few broken surfaces.

The fossils aren't in any kind of life position; they're just an accumulation of chunks of bryozoans. Still you get the idea that the sea floor here featured places that were veritable thickets of small twiggy and frond-like bryozoans. To all you time travelers: probably not recommended for bare feet.

It's bryozoans almost all the way through, as well.

Sunday, August 29, 2021

Further thoughts on the location of Finn's Glen

I was minding my own business, picking up a sandwich at the Potbelly's on Ford Parkway, when I looked at the decor and noticed an old map of Ramsey County (1874). Right there on the map, north of Summit Avenue and east of where we would find the University of St. Thomas today, is "Wm. Finn". William Finn. Finn of Finn's Glen.

Forgive the flare. It was a dramatic moment.

Bingo. Meaning what, exactly? (Unfortunately, it doesn't identify the glen.) Years ago I wrote about Finn's Glen in conjunction with Shadow Falls. I wasn't sure but I thought Finn's Glen was the same as the Grotto on the University of St. Thomas campus, south of Shadow Falls. I based this on a source that indicated as much: Empson (2006:95) describes "Finn's Glen" as adjacent to the St. Paul Seminary, south of Summit Avenue, and a place of meditation. As a University of St. Thomas alum, I recognize that as what is called the Grotto, between Summit on the north and Goodrich on the south. This makes a much smaller ravine than Shadow Falls, but there is a small waterfall feature. Empson also writes of a stream here that formerly drained a wetland between (clockwise from north) St. Clair, Snelling, Randolph, and Fairview. We can see this in Winchell's "Falls of St. Anthony" map (1877). But...

Finn's Glen is clearly marked...

...Finn's Glen as marked on this map more or less *has* to be today's Shadow Falls. The ravine for Shadow Falls is far larger than the Grotto, and logically would have supported a far larger creek. Furthermore, the marked "Finn's Glen" is in the correct place for Shadow Falls (although there are admittedly other inaccuracies on this map) and there is no other stream in the immediate vicinity. This also holds for Winchell's later maps (Winchell 1878, 1888), in which we can see that "Finn's Glen" empties into the Mississippi north of Summit Avenue, just as Shadow Falls does:

From Winchell (1878).

From Winchell (1888).

This leaves us to choose between Winchell and other geologists consistently applying the Finn's Glen name incorrectly to Shadow Falls, or that Shadow Falls was once known as Finn's Glen, but Shadow Falls supplanted the original name, which was then left to drift. Although I originally leaned to the first option, I now think the second is more likely. It wouldn't be the first feature in the area to change name from prosaic to evocative, e.g., Brown's Falls becoming Minnehaha Falls. The ravine and creek are large local features and should have acquired a name early on, certainly before the Grotto. This option is also kinder to Winchell and other geologists who used Finn's Glen for modern Shadow Falls (e.g., Sardeson and Ulrich). Does it fit with the timeline?

Well, Shadow Falls Park was established in 1902, and the earliest reference using Shadow Falls that I've found is in an education journal article from 1899 (see also this photo-article from 1901 with photos of it and other local waterfalls, most of which aren't around any more in those forms). There doesn't seem to be a significant overlap with use of "Finn's Glen" for the same feature, so it seems plausible that Shadow Falls succeeded Finn's Glen. Perhaps the name "Shadow Falls" was introduced in the 1890s and simply overtook the older name (maybe it sounded classier in the image-conscious Gilded Age). Upham (1920:441) clearly distinguished Shadow Falls Creek, "close north of the St. Paul Seminary," from Finn's Glen "about a mile farther south". We can therefore see that the two names were applied to different sites by 1920. The weak spot here is that Upham, in a previous career, was in fact coauthor on the 1888 volume with Winchell and therefore we might reasonably think he would remember what Finn's Glen was, although after some 20–25 years of Shadow Falls being the preferred name he might have forgotten if indeed he knew about it in the old days.

Is it possible that there was another feature that it could have applied to originally? Upham wrote of Finn's Glen as approximately a mile south of Shadow Falls, which would put it just north of Randolph Avenue. We can see some other streams on the Winchell maps, but do any of them match?

Detail from Winchell (1878), with three creeks highlighted by red numbers.

#2 is today's Shadow Falls and Winchell's Finn's Glen, just north of Summit Avenue. #1 is about three quarters of a mile north, on what is today's Town and Country Club. (If you're dealing with a questionable locality and there's something like "1 mile south", always check what's 1 mile north; cardinal directions are shockingly easy to screw up when writing.) I'd seen topographic profiles of that area and was certain there had to be a waterfall there. Well, there was, but it's been gone a long time. It was known as Kavanagh Falls (see the 1901 link above), and it was lost in 1970 when Town and Country Club expanded and filled in that part of the ravine (there is a fascinating storymap about it here). (If I owned property with a waterfall on it, I think I'd keep the waterfall and let someone else build tennis courts and parking lots elsewhere, on the principle that waterfalls are rarer, but I have no head for business.)

#3 is more of a mystery. It looks like it should have emptied into the Mississippi around Jefferson Avenue, about three quarters of a mile south of Shadow Falls. This is not a mile, but it's not unconscionably off, either. This one is even harder to account for than Kavanagh Falls. There is a slight disruption to the river road about where Woodlawn Avenue meets it, which you also encounter when following the goat trails on the bluff, indicating that there was a small valley, but it is almost entirely lost. Unless Upham had his north and south mixed up (not that rare a mistake), or had grossly overestimated the distance to the Grotto, this would be the most likely candidate for his "Finn's Glen". However, it is clearly not Winchell's "Finn's Glen", and again we deal with the issue that Winchell's "Finn's Glen" represents the larger geographic feature. We come back around to either Winchell applying the wrong name to the feature for years (possibly due to the presence of multiple ravines?), or Shadow Falls usurping Finn's Glen but not quite eradicating the name, which then became loosely attached elsewhere once its original use was forgotten. (Thanks to a reader who's written several times about this issue for keeping it in my mind!)

References

Empson, D. L. 2006. The street where you live: a guide to the place names of St. Paul. University of Minnesota Press, Minneapolis, Minnesota.

Upham, W. 1920. Minnesota geographic names: their origin and historic significance. Collections of the Minnesota Historical Society 17. Minnesota Historical Society, St. Paul, Minnesota.

Winchell, N. H. 1877. The geology of Hennepin County. Minnesota Geological Survey, St. Paul, Minnesota. Annual Report 5:131–201.

Winchell, N. H. 1878. The geology of Ramsey County. Minnesota Geological Survey, St. Paul, Minnesota. Annual Report 6:66–92.

Winchell, N. H. 1888. The geology of Ramsey County. Pages 345–374 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.

Sunday, August 15, 2021

Your Friends The Titanosaurs: Hamititan xinjiangensis

As far as I'm concerned, 2021 has been relatively quiet for new dinosaurs (great year for ophthalmosaurid ichthyosaurs, though; I might even learn to spell "ophthalmosaurid" correctly the first time through). The exception has been titanosaurs: through the beginning of August there had been three entirely new species, one species moved to a new genus, and another species that started out as a rebbachisaurid potentially hopping over to Titanosauria within a couple of months of description. Hamititan xinjiangensis makes another new addition. It was published this week (Wang et al. 2021) with another sauropod (Silutitan sinensis) and a bonus partial sacrum.

Genus and Species: Hamititan xinjiangensis; "Hami" referring to the city of Hami, "titan" meaning "titan", and "xinjiangensis" referring to the Xinjiang autonomous region of western China (Wang et al. 2021). Together they mean something akin to "Hami titan from Xinjiang".

Citation: Wang, X., K. L. N. Bandeira, R. Qiu, S. Jiang, X. Cheng, Y. Ma, and A. W. A. Kellner. 2021. The first dinosaurs from the Early Cretaceous Hami Pterosaur Fauna, China. Scientific Reports 11:14962. doi:10.1038/s41598-021-94273-7.

Stratigraphy and Geography: H. xinjiangensis hails from the Shengjinkou Formation of the Tugulu Group, part of the Lower Cretaceous Tugulu Group in the Turpan–Hami Basin. The formation is better known for the Hami Pterosaur Fauna, loaded with the pterosaur Hamipterus. The holotype and only known specimen of H. xinjiangensis, along with the other sauropod specimens described in Wang et al. (2021), came from lacustrine sandstone. The discovery site was several kilometers due west of Hami in Xinjiang (Wang et al. 2021).

Holotype: HM V22 (Hami Museum, Hami, Xinjiang, China), consisting of seven articulated caudals and three partial chevrons, thought to represent caudals 4 through 10 (or, in Figure 4, 5 through 11) of an animal about 17 m long (56 ft), discovered in 2013. A small theropod shed tooth was found nearby (Wang et al. 2021).

Figure 4 in Wang et al. (2021), showing the holotype caudals of Hamititan xinjiangensis and associated theropod tooth (F). Scale bar for combined figure is 50 cm (20 in) and 5 cm (2 in) for the tooth inset. See here for full caption. CC BY 4.0.

Is H. xinjiangensis indeed a titanosaur? It's a fair question, given both the historical difficulties surrounding Early Cretaceous titanosaurs and the particular difficulties classifying East Asian Early Cretaceous sauropods, which seem to be doing their own thing. First things first: H. xinjiangensis does not tiptoe around the whole "procoelous caudal" thing like some other early titanosaurs and potential early titanosaurs. It is boldly, proudly procoelous. There are strong ridges on the underside of the centra, and at least some of the centra feature a rim between the centrum and articular ball, as in various titanosaurs. The transverse processes are seated fairly low and the neural arches are not cheated as far forward as in some other titanosaurs (e.g., aeolosaurs). The bones do not feature spongy texture (Wang et al. 2021). Despite some quibbles, it's certainly got more going for it than some other putative early titanosaurs (although I certainly would not be surprised if within a few years someone argued it was not a titanosaur, just another East Asian Early Cretaceous sauropod with a titanosaur-like tail).

Is it Silutitan? Well, we can be reasonably certain that the holotype of H. xinjiangensis is not from the same individual as the holotype of S. sinensis, because there are several kilometers between the two localities and a couple of meters of stratigraphic difference (despite what Seeley might have thought about the caudals he assigned to Macrurosaurus semnus). To look at this phylogenetically, Wang et al. (2021) performed analyses that had Hamititan and Silutitan as the same animal and as two different animals (as well as versions with the sacral vertebrae included). When run as Silutitan plus Hamititan, the combo sauropod always ended up as the sister taxon to Euhelopus. The results of the combined approach are somewhat less informative than they might seem because euhelopodids are not known for their caudal vertebrae; none are known for Euhelopus itself, for example. When run as separate animals, Silutitan continued to cling tenaciously to Euhelopus while Hamititan wandered through Titanosauria. Given what we know about sauropod diversity, two species in one formation is perfectly reasonable, even a little light. (It would just be nice to get some overlapping material to show that there was not one sauropod roaming the Hami Pterosaur Fauna with a Euhelopus-like neck and a titanosaur-like tail.)

References

Wang, X., K. L. N. Bandeira, R. Qiu, S. Jiang, X. Cheng, Y. Ma, and A. W. A. Kellner. 2021. The first dinosaurs from the Early Cretaceous Hami Pterosaur Fauna, China. Scientific Reports 11:14962. doi:10.1038/s41598-021-94273-7.

Sunday, August 8, 2021

Geranosaurus atavus

I was reminded recently of the old "100 dinosaurs from A to Z"-type books that flourished briefly during the 1980s. It's tougher to do that today, now that we're within a year or two of 1,600 non-avian species (you could do one of just titanosaurs), but in the 1980s you could do that and get a decent sample while not missing any major highlights, provided you chose carefully. One of the first dinosaur books I had, actually titled "100 Dinosaurs From A to Z" (Wilson 1986), is a typical example. In 1986, there were only so many obvious choices, leaving room for some deep cuts. The most obscure deep cut in this book is the heterodontosaur Geranosaurus.

Sunday, August 1, 2021

Practical applications of Chesapecten, early 19th century

"Fossil pectens of a large size, some of them ten inches wide, are found abundantly in the lower part of Virginia. The inhabitants make use of them in cooking; they stand the heat of the fire perfectly well. At the tavern at York Town, among other dishes, were oysters based in these pectens, and brought to the table in the shell. I wanted the company of a few scientific friends to enjoy the treat. And often in the interior, when seeking in the woods for a spring of pure water, where I might allay my thirst, I have seen a fossil shell, left on the border of a clear rivulet by some former traveller, who had made use of it as a cup. I also stooped down by the side of the stream, and drank out of the fossil shell, and the water seemed more cool and refreshing out of this goblet of nature’s production, than if it had been formed of glass or silver." (Finch 1833)

Chesapecten madisonius, not quite as famous as C. jeffersonius but still quite nice.

References

Finch, J. 1833. Travels in the United States of America and Canada. Longman, Rees, Orme, Brown, Green, and Longman, London, United Kingdom.

Sunday, July 18, 2021

A fossiliferous Prairie du Chien block

The Prairie du Chien Group is great for stromatolites, but not much for other fossils except for localized occurrences of molds and casts of mollusks; see for example the second photo here or the second photo here. You do get lucky occasionally, though. I did not collect the following block myself, nor was it found in situ, but I would be very, very surprised if it did not originate in the Prairie du Chien Group. The most notable aspect about it is this spiral feature:

What is it? A few thoughts:

If you had to pick a second group to find in the Prairie du Chien after stromatolites, it would be snails, and the Prairie du Chien snails do include some large forms that are flat-coiled or coiled in a low spiral, such as Helicotoma and Rhachopea. They're even of comparable size to this.

Some trace fossils spiral, but we can see that the width of the spiral passage increases as it goes out, and animals do not generally increase in girth like that over a short distance unless they handle matter like the Incredible Hulk, so that's not what we have.

Finally, although we usually think of early Paleozoic nautiloids as straight-shelled, there were a few coiled forms, including one known from the Prairie du Chien: Eurystomites. We can see that this spiral seems to separate from the inner coil near the end, and conveniently enough, Eurystomites also gets lax at the end of its coil. However, there's no clear indication of chambers.

What do I think? Without being able to see the entire fossil, you could make an argument that this is an internal cast (steinkern) or external cast of a snail (in which the outer whorl shows separation either because we're looking at the inside or because the plane of exposure isn't low enough to show that the whorl is actually just flaring), or a poor-quality external cast of a Eurystomites or similar nautiloid (can't be internal, because there's no evidence of chambers).

Operating on the principle that where you find one body fossil in the Prairie du Chien, you might find more, I examined the rest of the block, which turned out to have several more easily interpreted molds of much smaller and more obvious snails:

Low-coiled snail, coiling into the block.

A more elongate form; the shell may be slightly sculptured, but relatively coarse mineralization in the mold makes it hard to tell. A similar but less easily photographed example looked much smoother.

A pair of shell molds exposed at an awkward angle.

Sunday, July 11, 2021

The Short Life and Unnecessary Death of the Devils Lake Formation

Edward Oscar Ulrich was previously featured here as one of the main players in the brachiopod noir "The Great Brachiopod Caper of 1892", on the side of the "victors". Decades later, though, he seems to have come out on the short end with a formation he named from one of the more geologically notable areas in Wisconsin: Devil's Lake in the Baraboo Range. Devil's Lake itself is more than worthy of a post in its own right, but for the moment I'll just plant that seed for future reference.

A brief bit of exposition is in order, though. The Baraboo Range is an exhumed area of early Paleozoic topography, with a core of Proterozoic Baraboo Quartzite. The range is elliptical and oriented east-west, with a north range and a more complete south range; during the Cambrian and Early Ordovician, before it was buried, the range was oriented north-south instead of east-west. Similar to Taylors Falls, where basalt withstood the advancing seas, the ancient quartzite of the Baraboo Range formed islands in the Cambrian sea. Also like Taylors Falls, there is a conglomeratic sandstone that formed adjacent to the resistant Precambrian rocks, only in this case the conglomerate is composed of material shed from Baraboo Quartzite rather than Midcontinent Rift basalt. It is this flanking sedimentary unit, well-exposed near Devil's Lake, that Ulrich named the Devils Lake Formation.

The Devils Lake Formation first popped up in Ulrich (1920), as a name in a table. It did not get a proper description until Thwaites (1923), where it was described as a "more or less glauconitic sandstone" with quartzite pebble conglomerate. Ulrich (1924) added a little more, emphasizing the well-developed conglomerate found on the flanks of the quartzite ridges and noting its presence in nearby Parfrey's Glen. Never the subject of much discussion, the Devils Lake Formation was laid to rest in the literature following Wanenmacher et al. (1934). The authors regarded the formation as a geological chimera, because it was not coherent in terms of biostratigraphy. (It was also mixed up in Ulrich's doomed effort to establish the Ozarkian and Canadian periods between the Cambrian and Ordovician, which didn't help its reputation.) In light of the push to define formations by their rocks rather than their fossils that came about not long after Wanenmacher et al. (1934), this is a fatally flawed argument: formations live or die on the distinctiveness of their lithology, not because of how many trilobite zones they span. The Devils Lake Formation should have been expected to span multiple zones, because it represents unusual depositional conditions that persisted adjacent to the range beginning with the arrival of the Cambrian seas until the range was buried during the Ordovician. However, going back and resurrecting the Devils Lake Formation was not a high priority for anyone.

The plot thickened when in 1990 Clayton and Attig named a new formation, the Parfreys Glen Formation, for quartzite conglomerate and conglomeratic sandstone found adjacent to the quartzite ridges of the Baraboo Range. The new unit encompasses the same kinds of rocks as the Devils Lake Formation and is present in the same areas. It is hard to avoid the conclusion that the Parfreys Glen Formation is the Devils Lake Formation under a new name. Oddly, even though all of the papers mentioned above are referenced several times in the 1990 publication, nowhere is the term "Devils Lake Formation" used, not even to dismiss it. (This is not the only example of something about Devil's Lake geology going missing; for some reason the Cambrian fossils found near the lake are basically absent from the literature since Resser 1942. For a further "devilish" aspect, no two geologic maps of the area map the Cambrian rocks in exactly the same places around the lake; compare Wanenmacher 1932 [in Raasch 1935], Dalziel and Dott 1970, Clayton and Attig 1990, Baumann and Abrams 2013, and Stewart and Stewart 2021.)

Conglomerate in Parfrey's Glen; is it the Parfreys Glen Formation, or the Devils Lake Formation in disguise? Found on Wikimedia Commons, taken by user Wackybadger. CC BY-SA 3.0.

References

Baumann, S. D. J., and M. J. Abrams. Geologic map of Devils Lake, Sauk County, Wisconsin, United States, T11N R6E and R7E. Midwest Institute of Geosciences and Engineering, Chicago, Illinois. Publication M-072013-1A. Scale 1:12,000.

Clayton, L. and J. W. Attig. 1990. Geology of Sauk County, Wisconsin; with a section about the Precambrian geology by B. A. Brown and an appendix naming the Rountree Formation by J. C. Knox, D. S. Leigh, and T. A. Frolking. Wisconsin Geological and Natural History Survey, Madison, Wisconsin. Information Circular 67. Including geologic map, scale 1:100,000.

Dalziel, I. W. D., and R. H. Dott, Jr. 1970. Geology of the Baraboo District, Wisconsin: a description and field guide incorporating structural analysis of the Precambrian rocks and sedimentologic studies of the Paleozoic strata. Wisconsin Geological and Natural History Survey, Madison, Wisconsin. Information Circular 14. Scale 1:62,500.

Raasch, G. O. 1935. Paleozoic strata of the Baraboo area. Kansas Geological Society, 9th Annual Field Conference Guidebook:405–415.

Resser, C. E. 1942. Fifth contribution to nomenclature of Cambrian fossils. Smithsonian Miscellaneous Collections 101(15).

Stewart, E. K., and E. D. Stewart. 2021. Geologic map of the Baraboo 7.5-minute quadrangle, Sauk County, Wisconsin. Wisconsin Geological and Natural History Survey, Madison, Wisconsin. Open-File Report 2021-02. Scale 1:24,000.

Thwaites, F. T. 1923. The Paleozoic rocks found in deep wells in Wisconsin and northern Illinois. The Journal of Geology 31(7):529–555.

Ulrich, E. O. 1920. Major causes of land and sea oscillations. Journal of the Washington Academy of Sciences 10(3):57–78.

Ulrich, E. O. 1924. Notes on new names in table of formations and on physical evidence of breaks between Paleozoic systems in Wisconsin. Transactions of the Wisconsin Academy of Sciences, Arts and Letters 21:71–107.

Wanenmacher, J. M. 1932. The Paleozoic strata of the Baraboo area, Wisconsin. Dissertation. University of Wisconsin, Madison, Wisconsin.

Wanenmacher, J. M., W. H. Twenhofel, and G. O. Raasch. 1934. The Paleozoic strata of the Baraboo area, Wisconsin. American Journal of Science (5th series) 28(163):1–30.

Sunday, July 4, 2021

Fossil Crocodylomorphs of the National Park Service

For this year's National Park Service fossil group inventory, I've chosen crocodylomorphs, which for convenience I'm going to refer to as "crocs". Crocodylomorpha encompasses the true crocodilians and their closest extinct relatives, which over the years has been defined to exclude major groups of allied Triassic archosaurs (rauisuchids, poposaurs, prestosuchids, etc.). (Technically speaking, traditional Crocodilia is closer to the clade Crocodyliformes, but I have a soft spot for "sphenosuchians" and it's my blog.) Non-crocodilian crocodylomorphs were big players throughout the Mesozoic but came to peter out in the Cenozoic, with holdouts into the Miocene (Sebecosuchia). Some of these non-crocodilian crocodylomorphs looked basically like modern crocodilians and presumably filled very similar niches, but by definition weren't crocodilians*. Others were quite a bit different; for example, small, long-legged terrestrial crocs had a wide distribution from the Late Triassic through the Jurassic, and there were multiple groups of marine forms.

*I have certain misgivings about crown groups, particularly that future stability of usage relies on groups not going extinct (or there would have to be backdating, like radiocarbon dates are pegged to 1950), although at this point I might as well complain about the decline in use of Etruscan.

The NPS record of croc fossils turns out to be sparser than I expected: there are 17 park units with solid records (albeit two of these being reworked or washed up, making them hard to place stratigraphically), and another couple potential records. Here is the requisite map and its accompanying long caption:

Click to embiggen. The sites mentioned in this post are: 1. John Day Fossil Beds National Monument; 2. Bighorn Canyon National Recreation Area; 3. Fossil Butte NM; 4. Dinosaur NM; 5. Colorado NM; 6. Curecanti NRA; 7. Bryce Canyon National Park; 8. Glen Canyon NRA; 9. Petrified Forest NP; 10. Chaco Culture National Historical Park; 11. Theodore Roosevelt NP; 12. Badlands NP; 13. Agate Fossil Beds NM; 14. Niobrara National Scenic River; 15. Big Bend NP; 16. Waco Mammoth NM; 17. Gateway NRA; 18. Fort Washington Park; 19. Cumberland Island National Seashore.

These 19 units are primarily in the Colorado Plateau and northern Great Plain, and these two areas correlate in large part to temporal distribution: the Colorado Plateau records are mostly Jurassic and Cretaceous, and the Great Plains records are Cenozoic. A couple of compact diagrams will show this:

Part 1 shows the Mesozoic, Paleocene, and Eocene records, which make up the bulk of the reports.

Part 2 shows the few younger records; the two that can't be pinned down are added to keep them company.

You can probably guess a lot of the story if you have some familiarity with the stratigraphy of western North America. As so many other groups of terrestrial vertebrates, the place to go in the NPS for Triassic crocs is Petrified Forest National Park, where "sphenosuchians" have been found in the famous Chinle Formation. (Ignore the phytosaurs; they only look like crocs.) After that, possible early croc tracks have been found in the Navajo Sandstone of Glen Canyon National Recreation Area; with all of the Early Jurassic tracks in the Colorado Plateau parks, there are likely other track records. We have no body fossil records in the parks' rocks yet, though (the facies aren't as forgiving as elsewhere). Four parks have records for the Late Jurassic: Bighorn Canyon National Recreation Area has swim traces attributed to crocs in the Sundance Formation, and no points for guessing what's represented at the other three. (It's the Morrison Formation.) NPS Morrison crocs are best known from Dinosaur National Monument, which primarily has the well-represented Amphicotylus (formerly Goniopholis), but also produced the type specimen of the diminutive Hoplosuchus kayi.

The Cretaceous is more sparsely represented, with nothing confirmed from the Early Cretaceous. Ot the Late Cretaceous records, neither Bryce Canyon NP (Straight Cliffs and Wahweap microvertebrate remains) nor Chaco Culture National Historical Park (Menefee isolated material) have much to speak of. Big Bend NP, on the other hand, has the most impressive croc record in the NPS. Granted, that's an easy call when you can point to the type specimen of the suitably Texas-sized Phobosuchus riograndensis (now a species of Deinosuchus), but the park also has by far the longest record of crocs in the NPS. Five formations are represented: the Aguja Formation and Javelina Formation, both Late Cretaceous; the overlying Black Peaks Formation, which straddles the Cretaceous and Paleocene; the Early Eocene Hannold Hill Formation; and the Middle Eocene Canoe Formation. Recently a second croc species has been named from Big Bend NP fossils: Bottosaurus fustidens, from the Paleocene part of the Black Peaks Formation. Other taxa are present, but have not been studied in as much detail.

Looking elsewhere in the Paleocene, there is a single record of a partial bone from the Aquia Formation at Fort Washington Park, and Theodore Roosevelt NP has crocs in the Bullion Creek and Sentinel Butte Formations, comparable to nearby Wannagan Creek (only not quite so concentrated). The Eocene is fairly good for NPS crocs. Apart from Big Bend, we have croc fossils in: the Wasatch Formation at Fossil Butte NM; the Clarno Formation at John Day Fossil Beds NM; and the Chadron Formation at Badlands NP. The type specimen of Caimanoidea visheri (now considered a synonym of Alligator prenasalis) may have come from Badlands NP.

And that's almost the end. Crocs disappeared from the drying interior of North America during the middle Cenozoic. For the Miocene, we have one *very* sketchy potential record from the early Miocene Anderson Ranch Formation of Agate Fossil Beds NM and better records of crocs from the middle Miocene Valentine Formation of Niobrara National Scenic River (including the type specimen of Nordenosaurus magnus, originally described as a big lizard but now identified as a small crocodilian). At Waco Mammoth NM there is late Pleistocene alligator material, but we are otherwise lacking Pleistocene crocodilian records. Two units have material of uncertain provenance: a scute found in dredge material at Cumberland Island National Seashore and various croc fossils that have washed up at Gateway NRA.

Sunday, June 20, 2021

Your Friends The Titanosaurs, part 37: Conclusions

After three years of monthly (and sometimes more frequent) entries, I've finally finished what I set out to do: provide a short description of every titanosaur. That was enough time for eleven new genera and species to be described, and one species covered in the second post to be moved to a new genus (Aeolosaurus maximus to Arrudatitan). To make it easier to navigate the whole shebang, I've created a new page, "Your Friends The Titanosaurs", that collects them all. I've also flipped branches on The Compact Thescelosaurus: macronarians now come after diplodocoids, instead of the other way around.

After all that work, I feel I've earned the right to wave my arms through one last post, to summarize some general considerations that didn't have a place in the other posts.

Sunday, June 13, 2021

Your Friends The Titanosaurs, part 36.5: Australotitan

After three years and dozens of posts, the titanosaurs have issued a lovely parting gift before the wrap-up. (Isn't the title of this series "Your Friends The Titanosaurs", after all?) Here we have Australotitan cooperensis from the Winton Formation of Australia, joining Diamantinasaurus matildae, Savannasaurus elliottorum, and part-time titanosaur Wintonotitan wattsi.

Sunday, June 6, 2021

The elusive arms of the ammonite

Paleontology is littered with unsolved questions. Some can be answered, but just not now; maybe additional specimens are needed, or new techniques. Others are bound to remain unanswered because they require evidence that can't be obtained (for example attributes that can't be fossilized, or organisms that lived in times and places that neglected to leave a depositional record). One longstanding question is what did the business end of an ammonite look like? Presumably they had some kind of appendages appropriate to cephalopods; it's been assumed that they had ten arms, based on their closest living relatives, but they've been coy about leaving direct physical evidence.

A paper just published by Smith et al. (2021) aims to shed light on the brachial apparatuses of certain Late Cretaceous ammonites in the Scaphitidae. If you're mildly conversant in Upper Cretaceous marine rocks but not an ammonite fanatic, "Scaphitidae" will probably put you in mind of the famous Scaphites and its lazy outer whorl, but other members of the family were more traditional in appearance. Over the years, little hook-like bits have been found with specimens of a couple of scaphitid genera, specifically Hoploscaphites and Rhaeboceras. There was initially some thought that these were radular "teeth" (the radula being the molluscan's scraping food processor), but they seemed to be too large, and then genuine radular teeth turned up.

This still left the hook-like bits without an identity. Smith et al. used CT-scanning on several ammonites to show the numbers and locations of the objects within the shells. They differ significantly between Hoploscaphites and Rhaeboceras. In Hoploscaphites they are all a few mm long and have two paired tips, a bit like someone making air quotes. In Rhaeboceras, they range in length from 1 mm to more than 1 cm and come in nine different shapes. Six of them have two cusps, but they are generally strongly unequal in shape, whereas other are tricuspid, pointed, or rounded. They were found in clusters in the shells, with no pattern to distribution except that they were not found inside the jaws in those shells with jaws preserved. The different morphologies of the Rhaeboceras bits are arranged in straight or curved longitudinal rows with the cusps pointing in one direction (straight row) or outward (arc), and certain morphotypes tend to be found in association. The number of elements in a shell can be as many as 168.

Figure 2 from Smith et al. (2021). A shows a specimen of Rhaeboceras halli with hooks, B is a detail image of the hooks in situ, C shows examples of radular teeth, and D and E show eight of the nine hook morphologies. CC BY 4.0.

Smith et al. interpreted the elements as belonging to a pair of tentacular clubs, and provided a reconstruction of Rhaeboceras in life with the clubs extended. Hooks are known from belemnoids and squids, but there is evidence that belemnoid hooks and squid hooks derive from different tissues. The presence of hooks in scaphitid ammonites would show that a third cephalopod group acquired them. They also provide some resolution on the arrangement and nature of ammonite arms.

Rhaeboceras in action; interestingly, this ammonite would have had more diverse hooks than belemnoids and squids. A wider range of prey? Figure 6 in Smith et al. (2021). CC BY 4.0.

References

Smith, C. P. A., N. H. Landman, J. Bardin, and I. Kruta. 2021. New evidence from exceptionally "well-preserved" specimens sheds light on the structure of the ammonite brachial crown. Scientific Reports 11:article 11862. doi:10.1038/s41598-021-89998-4.

Sunday, May 30, 2021

Your Friends The Titanosaurs, part 36.2: Coming Attractions (Europe and South America)

Here we go: Apart from next month's wrap-up (and anything that gets named before then), this is the last time down the titanosaurian rabbit hole. We're going to visit the unnamed titanosaurs of Europe and South America, complementing the visit last time to the rest of the world. Some of the best examples are in this post, such as MAU-Pv-LI-595, MAU-Pv-AC-01, and MUCPv-1533, all from the vicinity of Rincón de los Sauces/La Invernada.

Note: This is another long one. On the other hand, it's split into many paragraph-sized chunks, so it's good for skipping around.

Sunday, May 16, 2021

Your Friends The Titanosaurs, part 36.1: Coming Attractions (outside of Europe and South America)

Here we have a few of the many, many unnamed and/or undescribed titanosaurs. Some of their common habitats are abstracts, dissertations, press releases, and offhand comments in publications. Sometimes they're the subject of a paper describing some particular anatomical topic, or a geographic range extension. In other cases they're among five different morphotypes in a bonebed, and you can only hope that this pans out, because otherwise there's no negotiating with a von Huene puzzle. All the while you grit your teeth because you despair of ever seeing the really notable specimens published, especially so long as there's a theropod knuckle left to be described...

Anyway, this is not quite like "Coming Attractions in Dinosauria", which was based primarily on unnamed species with nicknames in long use. This is more like the original Addendum II in "The New Dinosaur Dictionary", except with specimen numbers and more references. It is certainly not exhaustive, and would take a lot more than a few weeks to make so. I am omitting embryonic forms (note that titanosaur nests have been found in several areas, including Argentina, India, and Spain), tracks, and named forms that need further description (Ampelosaurus, Futalognkosaurus, etc.). I've organized this by continent, and then by country; it turns out that if a country has terrestrial Cretaceous rocks, there is an excellent chance it has titanosaurs. Because of the sheer number of entries, I opted to split the post, with Europe and South America to come later.

I don't know if this will impress anyone, but I had a lot of fun writing this post.

Sunday, May 9, 2021

Your Friends The Titanosaurs, part 35.5: Arrudatitan and Dzharatitanis?

Here's a quick update on some breaking news, with a new genus for an existing species and a putative rebbachisaur potentially hopping over from Diplodocoidea.

Arrudatitan maximus

This series has now gone on long enough that a species from one of the earliest entries has been transferred to a new genus. What we first came to know as Aeolosaurus maximus, third species of Aeolosaurus, is now Arrudatitan maximus (Silva et al. 2021). Confusingly, or conveniently, it remains A. maximus, but if you're facing a situation where using just one letter might cause confusion, the usual way to solve the problem is to go to two letters: Ar. maximus instead of the old Ae. maximus. The type specimen and provenance have not changed since Santucci and Arruda-Campos (2011) named Ae. maximus. For reference (repeating from the original entry), this species is based on a partial associated skeleton collected in 1997 and 1998 by staff of the Museu de Paleontologia de Monte Alto, Brazil, mentioned as early as Santucci and Bertini (2001). The skeleton, MPMA 12-0001-97, includes two partial posterior cervicals, fragments of several dorsals, parts of nine caudals, seven partial cervical ribs, twelve partial dorsal ribs, eight chevrons, a fragmentary scapula and arm bones, the left and partial right femur, the left ischium, and fragments. This specimen was found in sandstone at the top of the Adamantina Formation 12 km (7.5 mi) southwest of Monte Alto in São Paulo State. Croc and theropod teeth were found with the titanosaur, but no tooth marks were observed (Santucci and Arruda-Campos 2011). Brusatte et al. (2017) estimated the type individual as on the order of 14 to 15 m long (46 to 49 ft), but it seems to have grown since then: Silva et al. (2021) suggested it was 19 to 22 m long (62 to 72 ft), which is a bit more "maximus". The complete femur measures 1.55 m (5.09 ft) long, but is slender for its size (Santucci and Arruda-Campos 2011). The new genus name honors the now-deceased Professor Antonio Celso de Arruda Campos (Silva et al. 2021), one of the two authors of the original description. Originally the name would have translated as something like "greatest Aeolosaurus", but it would now be more akin to "Antonio Celso de Arruda Campos's greatest titan".

Future Arrudatitan maximus caudals, from Figure 1 in Martinelli et al. (2011). Scale bar is 5 cm (2 in). (License apparently CC, but iteration not stated.) If the second and third in sequence were articulated more closely at the centrum, more of the droop apparent farther back would be visible.

"Aeolosaurus" maximus had never been entirely comfortable in Aeolosaurus. Martinelli et al. (2011) regarded the caudal vertebrae of the type specimen (then "MPMA/without number") as more like those of other Brazilian aeolosaurinids than Aeolosaurus, a distinction observed quantitatively in Filippi et al. (2013): "A." maximus plotted with the great unwashed masses of aeolosaurinids rather than A. rionegrinus and A. colhuehuapensis in some details of placement of vertebral features. Bandeira et al. (2016), in their description of Austroposeidon magnificus, found A. maximus to plot rather distantly from the other two Aeolosaurus species in their phylogenetic analysis, and therefore referred to it as "A." maximus throughout the paper. The same result came up in Silva et al. (2019) and Hechenleitner et al. (2020) (and, it goes without saying, in Silva et al. 2021).

Given it hasn't been that long since the 2018 post, you might think that there hasn't been a lot of other news on this species. However, last year a paper was published devoted to its tail (Vidal et al. 2020). The articulated tail segment as discovered had a significant droop, as if Ar. maximus never got the memo about how dinosaurs didn't let their tails drag. This is not simply taphonomy, either; the vertebrae quite comfortably articulate in a downward curve. (This is also reportedly the only case of sauropod protony, as opposed to the well-known phenomenon of opisthotony in dinosaur skeletons leaving the neck and tail arched over the back.) Regrettably, at this point we only have a few vertebrae from one individual to work with.

(This also seems like as good a place as any to mention that the rock unit that produced Baurutitan britoi, Trigonosaurus pricei, and Uberabatitan ribeiroi has been differentiated from the Marília Formation as the Serra da Galga Formation, described in Soares et al. 2021 and alluded to in Silva et al. 2021.)

Dzharatitanis kingi

At the end of February 2021, Averianov and Sues published a description of a new sauropod, Dzharatitanis kingi, the first rebbachisaurid from Asia. At the end of April, in one of the faster turnarounds in memory, Lerzo et al. (2021) published a re-evaluation of the type and only known specimen that found it to be a titanosaur.

But we haven't been properly introduced yet. D. kingi is based on a well-preserved and nearly complete anterior caudal, USNM 538127 (U.S. National Museum of Natural History, Washington, D.C.). This fossil was found in 1997 during an URBAC (Uzbek/Russian/British/American/Canadian; think "Urbacodon") expedition in Uzbekistan. It came from the Turonian-age Bissekty Formation of Dzharakuduk in Navoiy Region. The genus name refers to Dzharakuduk and the species name honors the late Dr. Christopher King, giving us something like "Christopher King's Dzharakuduk titan" (Averianov and Sues 2021). USNM 538127 is one of a number of sauropod fossils from Upper Cretaceous rocks of central Asia, many of which are described in some detail in Sues et al. (2015) and Averianov and Sues (2017). There are two minor issues with the material that have held back greater understanding: the great majority of the specimens are teeth, and so far there isn't much in the way of associated specimens. USNM 538127 was obliquely referred to a couple of times before being unveiled in Sues et al. (2015) (Sues and Averianov 2004; Wilson 2005; you're not missing a whole lot if you don't go check them out, as the presence of USNM 538127 is only made clear by following Sues et al. 2015 back).

USNM 538127 in posterior (A), right lateral (B), and anterior (C) views. Scale bar 10 cm (4 in). Figure 1 in Averianov and Sues (2021). CC0 1.0.

USNM 538127 is kind of an odd piece, actually. It's notably short anterior-posterior for a titanosaur caudal, and notably short vertically for a rebbachisaur caudal. The centrum is advertised as opisthocoelous, but it's very modest about it. Lerzo et al. (2021) ran the rescored specimen in two data sets, including that used by Averianov and Sues (2021), with further tweaking based on whether or not the caudal is the first caudal or farther back. In all cases, they found it more likely to be a somphospondylan than a rebbachisaurid, well within Titanosauria in their first data set. The Averianov and Sues result is not illustrated, but stated to be a somphospondylan titanosauriform. This and some other information make me feel a slight twinge about diving in with a titanosaurian identification, though. Sues et al. (2015) and Averianov and Sues (2017) noted similarities between USNM 538127 and Baotianmansaurus henanensis and Dongyangosaurus sinensis, currently existing not quite in and not quite out of Titanosauria (Mannion et al. 2019). I have a sneaking suspicion that D. kingi may be something similar.

References

Averianov, A., and H.-D. Sues. 2017. Review of Cretaceous sauropod dinosaurs from central Asia. Cretaceous Research 69:184–197. doi:10.1016/j.cretres.2016.09.006.

Averianov, A., and H.-D. Sues. 2021. First rebbachisaurid sauropod dinosaur from Asia. PloS ONE 16(2), e0246620. doi:10.1371/journal.pone.0246620.

Bandeira, K. L. N., F. Medeiros Simbras, E. Batista Machado, D. de Almeida Campos, G. R. Oliveira, and A. W. A. Kellner. 2016. A new giant Titanosauria (Dinosauria: Sauropoda) from the Late Cretaceous Bauru Group, Brazil. PLoS ONE 11(10):e0163373.

Brusatte, S. L., C. R. A. Candeiro, and F. M. Simbras. 2017. The last dinosaurs of Brazil: the Bauru Group and its implications for the end-Cretaceous mass extinction. Anais de Academia Brasileira de Ciências 89(3):1465–1485.

Filippi, L. S., A. G. Martinelli, and A. C. Garrido. 2013. Registro de un dinosaurio Aeolosaurini (Sauropoda, Titanosauria) en el Cretácico Superior (Formación Plottier) del norte de la provincia de Neuquén, Argentina, y comentarios sobre los Aeolosaurini Sudamericanos [Record of an Aeolosaurini dinosaur (Sauropoda, Titanosauria) in the Upper Cretaceous (Plottier Formation) of northern Neuquén Province, Argentina, and comments on the South American Aeolosaurini]. Revista Brasileira de Paleontologia 16(1):147–156.

Hechenleitner, E. M., L. Leuzinger, A. G. Martinelli, S. Rocher, L. E. Fiorelli, J. R. A. Taborda, and L. Salgado. 2020. Two Late Cretaceous sauropods reveal titanosaurian dispersal across South America. Communications Biology 3:article number 622. doi:10.1038/s42003-020-01338-w.

Lerzo, L. N., J. L. Carballido, and P. A. Gallina. 2021. Rebbachisaurid sauropods in Asia? A re-evaluation of the phylogenetic position of Dzharatitanis kingi from the Late Cretaceous of Uzbekistan. Publicación Electrónica de la Asociación Paleontológica Argentina 21(1):18–27. doi:10.5710//PEAPA.24.03.2021.389.

Mannion, P. D., P. Upchurch, X. Jin, and W. Zheng. 2019. New information on the Cretaceous sauropods of Zhejiang Province, China: impact on Laurasian titanosauriform phylogeny and biogeography. Royal Society Open Science 6(8):191057. doi:10.1098/rsos.191057.

Martinelli, A. G., D. Riff, and R. P. Lopes. 2011. Discussion about the occurrence of the genus Aeolosaurus Powell 1987 (Dinosauria, Titanosauria) in the Upper Cretaceous of Brazil. Gaea 7(1):34–40.

Santucci, R. M., and R. J. Bertini. 2001. Distribuição paleogeográfica e biocronológica dos titanossauros (Saurischia, Sauropoda) do Grupo Bauru, Cretáceo Superior do sudeste brasileiro. Revista Brasileira de Geociências 31(3):307–314.

Santucci, R. M., and A. C. de Arruda-Campos. 2011. A new sauropod (Macronaria, Titanosauria) from the Adamantina Formation, Bauru Group, Upper Cretaceous of Brazil and the phylogenetic relationships of Aeolosaurini. Zootaxa 3085:1–33.

Silva, J. C. G. Jr., T. S. Marinho, A. G. Martinelli, and M. C. Langer. 2019. Osteology and systematics of Uberabatitan ribeiroi (Dinosauria; Sauropoda): a Late Cretaceous titanosaur from Minas Gerais, Brazil. Zootaxa 4577(3):401–438. doi:10.11646/zootaxa.4577.3.1.

Silva, J. C. G. Jr., A. G. Martinelli, F. V. Iori, T. S. Marinho, E. M. Hechenleitner, and M. C. Langer. 2021. Reassessment of Aeolosaurus maximus, a titanosaur dinosaur from the Late Cretaceous of southeastern Brazil. Historical Biology advance online publication. doi:10.1080/08912963.2021.1920016.

Soares, M. V. T, G. Basilici, T. S. Marinho, A. G. Martinelli, A. Marconato, N. P. Mountney, L. Colombera, A. F. Mesquita, J. T. Vasquez, F. R. Abrantes Jr., and L. C. B. Ribeiro. 2021. Sedimentology of a distributive fluvial system: the Serra da Galga Formation, a new lithostratigraphic unit (Upper Cretaceous, Bauru Basin, Brazil). Geological Journal 56(2):951–975. doi:10.1002/gj.3987.

Sues, H.-D., and A. Averianov. 2004. 2004. Dinosaurs from the Upper Cretaceous (Turonian) of Dzharakuduk, Kyzylkum Desert, Uzbekistan. Journal of Vertebrate Paleontology 24(supplement to 3):119A–120A.

Sues, H.-D., A. Averianov, R. C. Ridgely, and L. M. Witmer. 2015. Titanosauria (Dinosauria, Sauropoda) from the Upper Cretaceous (Turonian) Bissekty Formation of Uzbekistan. Journal of Vertebrate Paleontology 35(1):e889145. doi:10.1080/02724634.2014.889145.

Vidal, L. D. S., P. V. L. G. da Costa Pereira, S. Tavares, S. L. Brusatte, L. P. Bergqvist, and C. R. dos Anjos Candeiro. 2020. Investigating the enigmatic Aeolosaurini clade: the caudal biomechanics of Aeolosaurus maximus (Aeolosaurini/Sauropoda) using the neutral pose method and the first case of protonic tail condition in Sauropoda. Historical Biology advance online publication. doi:10.1080/08912963.2020.1745791.

Wilson, J. A. 2005. Redescription of the Mongolian sauropod Nemegtosaurus mongoliensis Nowinski (Dinosauria: Saurischia) and comments on Late Cretaceous sauropod diversity. Journal of Systematic Palaeontology 3(3):283–318.

Sunday, May 2, 2021

The Lost Fucoids of Edwin McKee

Okay, that's hyperbole. The fucoids were never lost, they were just overlooked.

Many of you have probably heard of Edwin "Eddie" Dinwiddie McKee, who was the park naturalist at Grand Canyon National Park from 1929 to 1940. He moved on to other positions, but the Canyon was never far behind him. By the end of his career he'd written monographs about almost all of the Paleozoic sedimentary formations of the canyon, missing only the Temple Butte Formation and Hermit Shale/Formation for a complete set. He doesn't seem to have focused much on the Precambrian sedimentary rocks, though. Maybe the logistics of access made them less appealing (you have to go all the way to the bottom to see them, after all). Maybe the relative paucity of non-microscopic fossils made them harder to interpret. Maybe he just wasn't interested in the Precambrian. We do, though, have an interesting assortment of Precambrian rocks collected and briefly described by McKee.

In May 1930, McKee paid a visit to the Chuar Creek/Lava Creek area of eastern Grand Canyon NP, returning with about two dozen specimens from the Dox Formation, part of the Mesoproterozoic Unkar Group (lower chunk of the park's famous Grand Canyon Supergroup). Several had intriguing spindle-shaped surficial pits and ridges. McKee gave a brief description of them in an article about "fucoides" at Grand Canyon (McKee 1932). "Fucoid" goes back to the 19th century proposition that what we now know as invertebrate burrow fossils were actually seaweed fossils. (Usually the plural is "fucoids", not "fucoides") By the early 1930s, this was pretty raggedy, as McKee acknowledged; he was using it as a term of convenience for "any structure of that general nature regardless of its origin." Among the "fucoides" he presented were spindle-shaped markings on two pieces of Dox Formation rock. A careful examination of the photo will reveal that the markings in the piece on the left are incised into the rock, and those on the right-hand piece project out of the rock. They're something like mud cracks, but are certainly not textbook cracks (McKee also notes that there *are* more typical mud cracks in the Dox).

"Grant" is noted NPS photographer George A. Grant. Somewhere there must be a higher-quality version of this photo, but I haven't found it yet (I've seen one of the next figure in the article, but not this one).

This is the last we hear of these Dox "fucoides" from McKee, and probably the last anyone who was not a Grand Canyon National Park museum curator thought about them until 2019, when we began the Grand Canyon National Park paleontological inventory. I was working on the Precambrian paleontology chapter, and I love the historical side of the science, so McKee's article was right up my alley. I included the photo in my draft, and one of the reviewers noted, quite accurately, that there was no scale. Well, I couldn't do much about it (there isn't even a "photo is 2/3rd actual size" or something like that, and my time machine is in the shop, plus I don't do temporal paradoxes). That fall, though, when I was at the park I had the opportunity to visit the museum collections, and there they were. I took them outside to mimic the original photo, which appears to have been taken in front of a step, retaining wall, or something along those lines (of course including a scale bar this time).

It's not quite the same, but you get the idea. The white object is a box I used to provide additional support for the piece on the left, which at some point had been broken in two with the two pieces given different specimen numbers (the new numbers have yellowish backgrounds, while the original numbers have white backgrounds; if you compare this to the original photo, you can see the same spots).

While I was working, a number of other paleontologists were also visiting the collections as part of our National Fossil Day event. Spencer Lucas observed that the specimens looked a lot like microbially induced sedimentary structures (MISS), and asked about writing a short paper about them, to which I agreed (Tweet and Lucas 2021). The specimens themselves turned out to be more complex than is apparent from either photo. They are actually part and counterpart: in the color photo above, the large gray redox spots on the margins of the two pieces are the same spot, and the concave and convex features fit quite nicely when the pieces are lined up properly. Furthermore, there is another piece that belongs to this group, not included in the original photo (perhaps it didn't fit the composition?).

Here's a group shot, with the redox spots lined up and the previously omitted piece included.

The matching surfaces are laced with spindle-shaped features, convex in the upper row in the previous photo, concave in the lower row. Most of them are around 20 to 30 mm long (a little more or less than an inch), about 5 mm across, and with less than 5 mm of relief. A gentle, roughly longitudinal warp is most evident in the two left pieces, which might be a ripple or something similar but is heavily obscured. Flipping them over revealed additional but different features, a combination of blebs and long stringy features.

Figure 5 in Tweet and Lucas (2021). The black arrows in A point to two potential generations of ripples, and the white arrow points to the edge of a bed. B, the lower row in the preceding photo, is particularly marked by equant convex blebs and long stringy features, but there are a few on A as well.

The spindle-shaped features on the part-counterpart surfaces are shrinkage cracks, but as noted they aren't your typical mud cracks. Mud and coarser-grained sediments respond to shrinkage differently; mud grains stick to each other until something gives and a fissure forms, but sand grains slide apart from each other and do not form cracks unless something else interferes. That "something else" can be abiotic or, more frequently, biotic, such as a sticky microbial mat (Seilacher 1999). Something that is counterintuitive about microbially mediated cracks is that they are often preserved as positive features (Eriksson et al. 2007): mat and substrate contract and fissure, sediment fills fissure (either from above or from below due to environmental pressure), mat decays, and presto!—positive cracks! The long linear features in the photo above are similar to a different kind of MISS, in this case rolled-up mat fragments (Donaldson 1967; Eriksson et al. 2007).

This is more of a preliminary assessment than a definitive study. We don't have much to go on for the original geologic context, for one thing, and for another, if you really want to cover all of your bases, you need to take thin sections; MISS and inorganic features can be easily confused. Regardless, the features are highly suggestive of MISS, and the Dox Formation is already known to have stromatolites in other beds (Stevenson and Beus 1982). The Precambrian of the Grand Canyon has produced many features that were originally reported as burrow-like or "fucoidal", but most non-stromatolite features were dismissed as inorganic in the 1960s and 1970s, a couple of decades before the study of MISS took off. I would not be surprised if new study of the various formations of the Grand Canyon Supergroup, attuned to the possibility of MISS, were to uncover them in intervals previously regarded as barren of fossils.

References

Donaldson, J. A. 1967. Precambrian vermiform structures: a new interpretation. Canadian Journal of Earth Sciences 4:1273–1276.

Eriksson, P. G., H. Porada, S. Banerjee, E. Bopuougri, S. Sarkar, and A. J. Bumby. 2007. Mat-destruction features. Pages 76–105 in J. Schieber, P. K. Bose, P. G. Eriksson, S. Banerjee, S. Sarkar, O. Catuneanu, and W. Altermann, editors. Atlas of microbial mat Features preserved within the clastic rock record. Elsevier, Amsterdam.

McKee, E. D. 1932. Some fucoides from Grand Canyon. Grand Canyon Nature Notes 7(8):77–81.

Seilacher, A. 1999. Biomat-related lifestyles in the Precambrian. Palaios 14:86–93.

Stevenson, G. M. and S. S. Beus. 1982. Stratigraphy and depositional setting of the upper Precambrian Dox Formation in Grand Canyon. Geological Society of America Bulletin 93:163–173.

Tweet, J. S., and S. G. Lucas. 2021. Re-evaluation of Precambrian “fucoids,” microbially induced sedimentary structures in the Proterozoic Dox Formation, Grand Canyon National Park, Arizona. New Mexico Museum of Natural History and Science Bulletin 82:427–435.