The Face of Diamantinasaurus (and some other body parts)

One of the things that was frequently missing from "Your Friends The Titanosaurs" was heads. Sure, there were a fair number of lower jaws and braincases, but actual faces were few and far between. Skulls just don't seem to have stuck with the rest of the skeleton, and in general were not made of the sternest material in a titanosaur's body. (Bitey parts of the skull, yeah, those are more robust. Braincases, yeah, those are knots of bone. Stuff in between? Not so much.) Several entire continents are unrepresented by reasonably complete titanosaur skulls. We can now scratch Australia off that list, thanks to Diamantinasaurus matildae, as described in great detail by Poropat et al. (2023).

(...or can we? See below!)

The Conulariid Interior

Today we check in with one of the more unusual members of Paleozoic seafloor communities: Conulariida. The "four-sided herringboned ice cream cones" still hold many mysteries (including the mystery of the whereabouts of George Sinclair's collection; I'd still be interested in knowing more about that!). One of the major mysteries has been what exactly the soft parts of the animal looked like; if we knew that, we'd know a lot more about how conulariids are related to other animals, how they fed, how they looked, etc. It's generally assumed they are some kind of cnidarian (along with corals, jellyfish, sea anemones, and so on). Wikipedia has them potentially aligned with Staurozoa, which today is represented by stalked jellyfish (worth looking up if you've never heard of stalked jellyfish).

A cnidarian identity would imply stinging tentacles, but these have never been firmly identified. Soft parts in general are not particularly well-known for conulariids, which makes sense because preserving the soft parts of cnidarians is not something that just happens as a matter of course. (We could use a late Paleozoic amber-producing coastal forest that was flooded by a storm that dredged up all kinds of marine organisms.) There were some potential finds in the 1980s, as discussed in Babcock and Feldman (1986a) and Sendino et al. (2023) (see Figure 30 in Babcock and Feldman 1986b for internal casts and x-ray image of a conulariid's putative guts). Recently, Sendino et al. (2023) have applied X-ray micro-Computed Tomography (μCT) to a collection of well-preserved Pennsylvanian-age conulariids from the Wewoka Formation of Oklahoma and the Finis Shale Member of the Grand Formation of Texas.

What can μCT see in a conulariid? First off, it can see the concealed end of one conulariid partially within another conulariid. This is a good sign as a sanity check because we can confirm it can discern something that obviously should be there. With that encouraging information in mind, what else is there?

Figure 4 in Sendino et al. (2023); it's always good to see what you *ought* to see. CC BY 4.0.

Sendino et al. (2023) found "longitudinal bundles" in many of their specimens, i.e., oriented apex–aperture. The authors interpreted these as muscles for closing the flaps of the aperture. (This tells us a few things about the muscular and nervous systems of conulariids.) In some examples there was also an internal structure they interpreted as a possible gastric cavity. In other specimens, the internal sediment was clearly replaced, for example by sand, or contained other fossil material such as forams or a tiny drilled brachiopod. The internal sediment of some specimens appears to have been disrupted by later burrowing. A number of the conulariids also show scars from external attacks (conulariids seem to have been easy targets). The article, which is freely available, is heavily illustrated with μCT images, followed up by a series of supplementary files of large images.

And this is their basic interpretation (Figure 13). CC BY 4.0.

In other business: I'll be giving a talk for the Geological Society of Minnesota on Monday, May 8: "Snorkeling at Shadow Falls: Fossils of Minnesota". Non-members are welcome!

References

Babcock, L. E., and R. M. Feldmann. 1986a. Devonian and Mississippian conulariids of North America. part A. General description and Conularia. Annals of the Carnegie Museum 55:349–410.

Babcock, L. E., and R. M. Feldmann. 1986b. Devonian and Mississippian conulariids of North America. part B. Paraconularia, Reticulaconularia, new genus, and organisms rejected from Conulariida. Annals of the Carnegie Museum 55:411–479.

Sendino, C., B. Clark, A. C. Morandini, T. Salge, M. Lowe, and W. Rushlau. 2023. Internal conulariid structures unveiled using µCT. PalZ (2023). doi:https://doi.org/10.1007/s12542-023-00649-7.

Prasopora, with a comment on biostratigraphy

Prasopora, the "gumdrop bryozoan", is one of the most recognizable Ordovician fossils in Minnesota. Museum collections from Minnesota have boxes of the little darlings rattling around together. And I—I hardly ever see the dang things in the field.

Yes, one of these things; a bit more "chocolate kiss" than "gumdrop" but well within morphological variation.

While my competence in many fields is questionable at best, in this case you can be assured I would recognize a Prasopora if I saw one, even if it was years before I learned the stress goes on the second syllable rather than the third. (I have an unerring instinct for putting the stress on the wrong syllable for scientific names I've read but never heard.) No, the real issue here is one of biostratigraphy. My usual stomping grounds cap in the lower third of the Decorah, and Prasopora doesn't really kick in until the middle–upper Decorah. This has been recognized since the days of "The Geology of Minnesota" (Ulrich 1895; Winchell and Ulrich 1897). At that time eight species were recognized (P. affinis, P. conoidea, P. contigua, P. insularis, P. lenticularis, P. oculata, P. selwyni, and P. simulatrix), all of which were restricted to a range extending from the "Fucoid and Phylloporina beds" of the "Black River Group" (roughly Sardeson bed 5, middle–upper Decorah) to the "Fusispira and Nematopora beds" of the "Trenton Group" (as high as Sardeson bed 8, in the Prosser Limestone) (Winchell and Ulrich 1897; approximate correlations after Sloan 1987). None of them are listed in equivalents to Sardeson beds 3 and 4, in the lower Decorah, and only P. conoidea, P. contigua, P. lenticularis, and P. simulatrix were reported from the closest "Fucoid and Phylloporina beds".

Same specimen as above, which has a convenient break showing a partial cross-section; it's not solid all the way through.

Forty years later Stauffer and Thiel (1941) were not quite as dainty in their stratigraphic divisions, simply having a Decorah Shale Member of the Galena Formation and a Spechts Ferry Member of the Platteville Formation (approximately the Carimona Member of the Decorah). The "Spechts Ferry" gets Prasopora grandis, which had been Monticulipora grandis back in 1897, when it had been reported from the Stictoporella bed (lower Sardeson bed 3). P. grandis also appears in S&T's Decorah Shale Member list along with the four "Fucoid and Phylloporina beds" species, Stauffer presumably having stratigraphically higher specimens of P. grandis than W&U. Whether or not grandis pertains to Prasopora has been a matter of some dispute, and it seems to have wandered back to the metaphorical arms of Monticulipora. More importantly, it doesn't look like classic gumdrop Prasopora, instead being "irregularly massive, often tending to become lobate or subramose" (Ulrich 1895). In other words, it's not the kind of thing the typical fossil enthusiast would associate with the genus.

Wee little discoidal Prasopora.

My personal experience with Prasopora is limited to a few pieces in the Valentine box that appear to represent P. conoidea and a small discoidal species, a couple of small discoidal specimens that blur the line between early-stage Prasopora and "less famous bryozoan encrusting the external surface of an inarticulate brachiopod in an aesthetically pleasing Prasopora-like way", and one great honking lopsided hoof of a colony I found a few years ago at a basement excavation. I don't generally attempt to assign species to bryozoan fossils, but P. simulatrix is the only species described by Ulrich (1895) to attain dimensions even vaguely like it, so I'll go with that.

A top view of an unfortunately resolutely three-dimensional object.

And the underside, showing the distinctive layering and a few bits of other things that became part of the structure.

Bonus news: for those of you who've had your fill of gumdrop bryozoans, the spring 2023 edition of the NPS Park Paleontology newsletter is now available.

References

Sloan, R. E. 1987. History of study of the Middle and Late Ordovician rocks of the Upper Mississippi Valley. Pages 3–6 in R. E. Sloan, editor. Middle and Late Ordovician lithostratigraphy and biostratigraphy of the Upper Mississippi Valley. Minnesota Geological Survey, St. Paul, Minnesota. Report of Investigations 35.

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

Ulrich, E. O. 1895. On Lower Silurian Bryozoa of Minnesota. Pages 96–332 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(1). Johnson, Smith & Harrison, state printers, Minneapolis, Minnesota.

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.

Brooksella: what are star cobbles?

Back in the far-off year of 2012, when I was helping to compile instances of paleontological type specimens found in National Park Service units, we had to make decisions about various edge cases. One of these was how to handle names for what later turned out to be pseudofossils. We decided to record the information as historically relevant but did not include the "taxa" in any counts. On this blog we've actually covered a couple of them already, "Lingula calumet" and "Paradoxoides barberi" from within or very near Pipestone National Monument. Another is "Brooksella canyonensis", a putative jellyfish from the Proterozoic Nankoweap Formation of Grand Canyon National Park. It was first reported as such in Van Gundy (1937) and then named, not entirely enthusiastically, in Bassler (1941). "B. canyonensis" has fared poorly as a jellyfish, but has had its supporters as an organic feature (e.g., Glaessner 1969; Kauffman and Steidtmann 1981; Kauffman and Fursich 1983; tentatively Ciampaglio et al. 2006). However, I favor an inorganic interpretation. Admittedly, there are several to choose from: gas-escape structures or compaction (Cloud 1968), "sand-volcano"-type fluid escape (Ford and Breed 1977; Ford 1990), and mud rolls (Fedonkin and Runnegar 1992).

"B. canyonensis" was not the first species in the genus Brooksella, though. Brooksella was named by Charles Walcott for "star cobbles" from the Coosa Valley of Alabama (Walcott 1896), now attributed to the middle Cambrian-age Conasauga Formation (Nolan et al. 2023). In fact, he named three taxa for different forms of cobbles: B. alternata, B. confusa, and Laotira cambria (Walcott 1896). Star cobbles got their name because at their best they look like the stereotypical twinkly pointed things you might doodle. Some of them even have five rays, although six is more typical and they are more lobed than pointed, so it's not a perfect match.

Brooksella (A–D, K) and Laotira (E–H, J) as illustrated by Walcott (1898) and reproduced as Figure 1 in Nolan et al. (2023) (which see for full caption). CC BY 4.0.

Walcott interpreted the objects as representing jellyfish, which are probably not the first thing you think of when fossils come to mind, but jellyfish fossils are in fact known elsewhere. In this case, though, the interpretation hasn't proved tremendously popular over time, and numerous alternatives have been proposed. These alternatives, though, generally involve some kind of organic origin, either as a true body fossils or a trace fossil of some sort. It's not hard to see why: they look like something that *ought* to be organic, even if the identity of that something is unclear. (Anyone who has gone out fossil hunting will probably recognize this feeling. Sometimes you're right, sometimes you're wrong.)

Nolan et al. (2023) have published a detailed reassessment of Alabama Brooksella. As part of it, they prepared a lovely supplemental figure of various hypotheses, with thumbnail evaluations (discussed at greater length in the text). (*Warning*: Hold off on clicking the link if you'd rather not get their solution immediately.) Studies of Brooksella from the past couple of decades have interpreted it as a trace fossil (either a feeding burrow or a coprolite) or a glass sponge (hexactinellid). Nolan et al. subjected star cobbles to about as many tests as can legally be done to rocks in their analysis of the various possibilities, and came to several conclusions, including:

• Brooksella specimens do not have a sponge's anatomy. There aren't spicules, features previously interpreted as ostia (pores) bear a strong resemblance to pitting left behind when lichen are cleaned off, and lobes do not feature opening at their ends for radial canals (which were also not found).
• The orientation of the specimens when found in situ was with the putative central osculum (excurrent vent) down in the sediment, which is an inconvenient place for an osculum. Furthermore, many examples did not even have an "osculum".
  
• The specimens include internal voids and tubes, but these spaces do not correspond to the external form, unlike primary burrows (although this does not preclude the specimens having "captured" parts of burrows that were passing through). Furthermore, the internal features do not include common burrowing structures such as backfill.
  
• The specimens have the same composition as silica concretions from the same rocks, and are very comparable overall, with the same kind of weathering rings, lichen pitting, and random internal voids and tubes.
  

Nolan et al. concluded that Brooksella is no different from the local concretions except for the lobes, and should therefore "be considered a pseudofossil until proven otherwise." A consequence of this conclusion is that Brooksella, not being a glass sponge, would not have been a source of silica for preservation of fossils in the Conasauga. (It's not stated, but it seems that it would have been a sink instead.) It further goes to show that you shouldn't trust strange things in the Cambrian.

Brooksella (A–E) and concretions (F–K) collected from the Conasauga Formation by Nolan et al. (scale bar 1 cm, or 0.4 in); Figure 5. CC BY 4.0.

References

Bassler, R. S. 1941. A supposed jellyfish from the pre-Cambrian of the Grand Canyon. Proceedings of the United States National Museum 89(3104):519–522.

Ciampaglio, C. N., L. E. Babcock, C. L. Wellman, A. R. York, and H. K. Brunswick. 2006. Phylogenetic affinities and taphonomy of Brooksella from the Cambrian of Georgia and Alabama, USA. Palaeoworld 15:256–265.

Cloud, P. E., Jr. 1968. Pre-metazoan evolution and the origins of the Metazoa. Pages 1–72 in E. T. Drake, editor. Evolution and environment. Yale University Press, New Haven, Connecticut.

Fedonkin, M. A., and B. N. Runnegar. 1992. Proterozoic metazoan trace fossils. Pages 389–395 in J. W. Schopf and C. Klein, editors. The Proterozoic biosphere: A multidisciplinary study. Cambridge University Press, Cambridge, United Kingdom.

Ford, T. D. 1990. Grand Canyon Supergroup: Nankoweap Formation, Chuar Group, and Sixtymile Formation. Pages 49–70 in S. S. Beus and M. Morales, editors. Grand Canyon geology. Oxford University Press, New York, New York.

Ford, T. D., and W. J. Breed. 1977. Chuaria circularis Walcott and other Precambrian fossils from the Grand Canyon. Journal of the Palaeontological Society of India 20:170–177.

Glaessner, M. F. 1969. Trace fossils from the Precambrian and basal Cambrian. Lethaia 2(4):369–393.

Kauffman, E. G., and F. Fursich. 1983. Brooksella canyonensis: A billion year old complex metazoan trace fossil from the Grand Canyon. Abstracts with Programs - Geological Society of America 15(6):608.

Kauffman, E. G., and J. R. Steidtmann. 1981. Are these the oldest metazoan trace fossils? Journal of Paleontology 55:923–947.

Nolan, M. R., S. E. Walker, T. Selly, and J. Schiffbauer. 2023. Is the middle Cambrian Brooksella a hexactinellid sponge, trace fossil or pseudofossil? PeerJ 11:e14796. doi:https://doi.org/10.7717/peerj.14796.

Van Gundy, C. E. 1937. Jellyfish from Grand Canyon Algonkian. Science 85(2204):314.

Walcott, C. D. 1896. Fossil jelly fishes from the Middle Cambrian Terrane. Proceedings of the United States National Museum 18:611–614.

Walcott, C. D. 1898. Fossil Medusæ. U.S. Geological Survey, Washington, D.C. Monograph 30.

Your Friends The Titanosaurs: Chucarosaurus and (maybe) Ruixinia

We check in again with titanosaurs with one new genus and species that is definitely titanosaurian, and another that falls into the hazy uncertainty of potential Early Cretaceous titanosaurs.

Chucarosaurus diripienda

It's been a thing the past couple of years for dinosaurs to take the winter off, with few new names in December, January, and February, and 2023 has continued the tradition. Also, oddly enough, titanosaurs seem to strike during the winter; not that any time of the year is safe from them, but you can count on them taking up the slack left by tyrannosaurs and duckbills and so on.

Where was I? Anyway, the first publicized non-avian dinosaur of 2023 is our first guest, the titanosaur Chucarosaurus diripienda.

Genus and Species: "Chucaro" is a Quechua word for a "hard and indomitable animal", while "diripienda" is Latin for "scrambled" (Agnolin et al. 2023), giving us something like "scrambled indomitable lizard".

Citation: Agnolin, F. L., B. J. Gonzalez Riga, A. M. Aranciaga Rolando, S. Rozadilla, M. J. Motta, N. R. Chimento, and F. E. Novas. 2023. A new gigant titanosaur (Dinosauria: Sauropoda) from the Upper Cretaceous of northwestern Patagonia, Argentina. Cretaceous Research (preprint). doi:https://doi.org/10.1016/j.cretres.2023.105487.

(Thank you to Matias Motta for providing a pdf!)

Stratigraphy and Geography: C. diripienda is to date known only from the lower Upper Cretaceous Huincul Formation of the Pueblo Blanco Natural Reserve, northwestern Río Negro Province, Argentina (Agnolin et al. 2023). The site is rather better known for a variety of theropods representing several lineages (Tralkasaurus, Aoniraptor, Gualicho, Taurovenator, Overoraptor) (Agnolin et al. 2023).

Holotype: MPCA (Museo Provincial "Carlos Ameghino", Cipolletti, Río Negro, Argentina) PV 820, consisting of a left humerus, most of a left radius, left metacarpal II, left ischium, somewhat eroded left femur, the shaft of the left fibula, the proximal end of the right tibia, and the distal end of an anonymous metapodial, found disarticulated but associated and interpreted as representing one individual (Agnolin et al. 2023). A left femur and tibia (MPCA PV 821) represent another individual.

You might notice right away that, unlike most titanosaurs, we're not dealing with vertebrae here. This is a little inconvenient for comparative purposes, but on the other hand it does focus attention on areas of titanosaurian anatomy that do not receive as much attention. The limb bones indicate a large but relatively gracile form, with an estimated femur length of 200 cm (78.7 inches) (Agnolin et al. 2023).

Two other titanosaurs have been named from the Huincul Formation, the redoubtable Argentinosaurus huinculensis and the somewhat less famous Choconsaurus baileywilsoni. Limb bones of A. huinculensis and C. diripienda can be distinguished by several details, as well as A. huinculensis being more robust overall (although I suppose that shouldn't be too surprising). There is very little overlap with C. baileywilsoni, only metacarpal II, which is much more elongate in C. baileywilsoni. The phylogenetic analysis places C. diripienda as a colosssaurian but not quite a lognkosaurian, hanging out in the area of Bonitasaura salgadoi and Notocolossus gonzalezparejasi (Agnolin et al. 2023).

Ruixinia zhangi

Oddly enough again, the last non-avian dinosaur of 2022 was a potential titanosaur, Ruixinia zhangi. It falls into the grand tradition of Early Cretaceous East Asian titanosaur-ish sauropods, and as such is well worth an entry.

Genus and Species: The entire name is an allusion to Ruixin Zhang, a benefactor of the Erlianhaote Dinosaur Museum (Mo et al. 2023). As such, a translation isn't really applicable.

Citation: Mo, J., F. Ma, Y. Yu., and X. Xu. 2023 (preprint 2022). A new titanosauriform sauropod with an unusual tail from the Lower Cretaceous of northeastern China. Cretaceous Research 144:article 105449. doi:https://doi.org/10.1016/j.cretres.2022.105449.

(Cretaceous Research could almost be sub-headed as "The Journal of Titanosaurian Research" these days. They're all over it.)

Stratigraphy and Geography: R. zhangi hails from the famous Yixian Formation and was found at Batuyingzi, Beipiao, western Liaoning Province, northeastern China (Mo et al. 2023).

Holotype: ELDM (Erlianhaote Dinosaur Museum, Inner Mongolia, China) EL-J009, an articulated partial skeleton featuring most of the vertebrae (14 cervicals, dorsals, several sacrals, and 52 caudals), several dorsal ribs, 36 chevrons, left hip minus the ischium, left femur, left tibia, left astragalus, left metatarsal V, and a possible pedal phalanx (Mo et al. 2023).

Going from the description of the holotype, you'll note that we're dealing with a nearly complete vertebral column. Unfortunately, the other side of the coin in this case is that the precaudals are rather smooshed (Mo et al. 2023). From a visual inspection the cervicals seem kind of chunky, suggesting a relatively thick neck. R. zhangi has a rather odd tail; some of the highlights are as follows. The anterior caudals are strongly procoelous. The last six caudals are fused into a rod, simple in structure unlike the club of Shunosaurus and the cockscombs of Mamenchisaurus hochuanensis (Mo et al. 2023). (If it's just a rod, I wonder if it's just a one-off pathology.) The caudal neural spines are notably low and mildly split at the tops in the anterior caudals; the supporting neural arches are not cheated anteriorly in the first part of the tail like most titanosaurs but do have an anterior bias later on (Mo et al. 2023).

R. zhangi is not particularly large, with a femur 137 cm (53.9 inches) long and an overall body length on the order of 12 m (39 ft), but it is the current champion of the Yixian Formation sauropods (followed by Dongbeititan with a femur length of about 114 cm [44.9 inches] and Liaoningotitan slightly smaller at 108 cm [42.5 inches]). The phylogenetic analysis finds it well within Titanosauria (Mo et al. 2023), which is promising, but it's also closely associated with two taxa that are questionably titanosaurian per other authors (Daxiatitan and Xianshanosaurus), which is not so promising.

References

Agnolin, F. L., B. J. Gonzalez Riga, A. M. Aranciaga Rolando, S. Rozadilla, M. J. Motta, N. R. Chimento, and F. E. Novas. 2023. A new gigant titanosaur (Dinosauria: Sauropoda) from the Upper Cretaceous of northwestern Patagonia, Argentina. Cretaceous Research (preprint). doi:https://doi.org/10.1016/j.cretres.2023.105487.

Mo, J., F. Ma, Y. Yu., and X. Xu. 2023 (preprint 2022). A new titanosauriform sauropod with an unusual tail from the Lower Cretaceous of northeastern China. Cretaceous Research 144:article 105449. doi:https://doi.org/10.1016/j.cretres.2022.105449.

Hunting the wild stromatolite at Vermillion Falls

The gorge at Vermillion Falls, as seen before, is cut through quite a bit of the Prairie du Chien Group. Therefore, it is entirely reasonable to suppose that somewhere in all of those oodles of outcrop, there are some stromatolites. It should be just a matter of walking down and having a look, right? We-e-ll, easier said than done. A few factors are pushing against going from "predicted" to "established":

1) The classic booby prize of vertical exposures—sure, there's a lot of surface, but you don't get to see most of it up-close;

1b) Furthermore, for many of the places where you *can* examine the walls, you can't change your vantage point because backing up a foot or two puts you a foot or two lower or in open space (and that never helps). What makes this annoying with stromatolites is they can be expressed in various scales, and what you can't see with your nose on the rocks may be perfectly apparent from a couple of arm's lengths away except for that whole "absence of footing" thing, or a promising feature may disappear as you clamber up the slope to inspect it;

2) The surfaces have been fried to a crisp by weathering, which for our purposes disguises the fine layering and other subtle features.

The existing literature is not especially illustrative. Stauffer and Thiel (1941) included a section taken at the railroad bridge (now a footbridge), which describes the walls as 58.5 ft (17.8 m) of Shakopee Dolomite over 1 ft (0.3 m) of Root Valley Sandstone over 47 ft (14 m) of Oneota Dolomite, with nary a stromatolite mentioned (to be fair, the lithological descriptions are also very slim). The site has made it into a few theses and other student papers (Shea 1960; Squillace 1979; Robins 2005), but that seems to be about it. Maybe this limited documentation is a recognition of the above limitations by wiser heads than mine, but I have the faith of a gambler that something will turn up if I look long enough, so down we go back into the gorge.

Besides, why would I want to sit around inside when I could see things like this?

My strategy involves *not* looking directly for stromatolites, at least not the classic laminated features. I would never see them here except on fresh breaks. Instead, I'm looking for a couple of other features: bedding planes that are undulating rather than horizontal, and anomalously recessive intervals (I've seen elsewhere that stromatolitic intervals may be relatively erosion-prone compared to non-stromatolitic intervals). These two features should be visible even through the stain of weathering that began before the most recent Ice Age.

Down near the falls, in some of the lowest accessible beds, something very promising is apparent.

Left

Center

Right

We've definitely got an undulating surface that is appropriately stromatiform* in appearance, as well as being within an interval that is recessed. (In fact, the interval above is recessed in comparison to the interval above that, so this is not for people who don't like rocks poised above their heads [or, for that matter, people who have a phobia of birds pooping on them, because there are pigeons roosting in cavities above].)

*Google says it can come up with about 328,000 hits for "stromatiform". What it doesn't tell you is how many are useful and how many are just dictionaries, rhyming words, anagrams, pronunciations, and SEO things seeking to boost traffic with lists from dictionaries.

A little closer, between two apparent mounds

So stromatiform...

Obviously the next thing to do is to is to get close and look for finer details. That's where things become less clear. There are, conveniently, some fresh surfaces (not made by me!), and they do show alternating compositions. They are, however, rather thick layers.

Layers in one fresh surface.

Not quite as fresh, but you get the idea.

Layers on a spalled piece, frozen to the underlying moss.

I'd been hoping to find nice stacks of small columns beneath the undulating layers, but they aren't appearing (yet, at least). If we compare to Logan et al. (1964) and May et al. (2012), the latter also dealing with large Prairie du Chien stromatolites, it's as if we've skipped the columnar "Cryptozoon" stage and gone straight to broad "Collenia". This may say something about the local environment, or it may say that I'm just getting excited about some inorganic stromatiform-producing process.

Then there's whatever the heck is this. Bedded sedimentary rocks don't do things like this without a good reason.

If the issue is not immediately apparent, check the annotated version below and click to expand as necessary.

Too bad it was on the other side of the gorge. There's probably a way down somewhere...

References

Logan, B.W., R. Rezak, and R. N. Ginsburg. 1964. Classification and environmental significance of algal stromatolites. The Journal of Geology 72(1):68-83.

May, S. L., L. E. Davis, and D. G. Brown. 2012. Algal stromatolites in the Willow River Member of the Lower Ordovician Shakopee Formation near Chatfield, Minnesota, USA. The Compass: Earth Science Journal of Sigma Gamma Epsilon 84(1, Article 6):42–48.

Robins, C. 2005. The geology of the New Richmond Sandstone. Senior Integrative Exercise. Carleton College, Northfield, Minnesota.

Shea, J. H. 1960. Stratigraphy of the Lower Ordovician New Richmond Sandstone in the Upper Mississippi Valley. Thesis. University of Wisconsin, Madison, Wisconsin.

Squillace, P. J. 1979. The geology of the New Richmond Member of the Shakopee Formation (Lower Ordovician), Upper Mississippi Valley. Thesis. University of Minnesota, Minneapolis, Minnesota.

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

Roundup on Thunderstorm Ridge: keeping up with Petrified Forest NP

Last week's publication of the stem-caecilian Funcusvermis reminded me that I really ought to show off Petrified Forest National Park (PEFO) more often. Since the last spotlight, on the "biloph" trilophosaur Trilophosaurus phasmalophus in spring 2020, four more species of Triassic vertebrates have been described from fossils found in the park, to go along with a bushel of reports on anatomy, identifications of rare forms, vertebrate trace fossils, stratigraphy and geochronology, and other topics, to say nothing of conference abstracts and papers that mention PEFO fossils in wider contexts. (SVP conferences are usually good for a handful of PEFO topics.) Because we're talking the Late Triassic, the taxonomic diversity is wide. There's a little bit of almost everything.*

*Interestingly enough, that includes Paleozoic marine invertebrates: reworked fossiliferous cobbles of the Permian Kaibab Formation have been found in the park's Chinle Formation outcrops, particularly the Sonsela Member. There are also limited Neogene deposits with Hemphillian vertebrates.

Classically, as with most places that have produced vertebrate fossils for more than a century, big singular fossils were long the focus (e.g., skulls of phytosaurs). Although there is still interest in those kinds of fossils, increasingly study has focused on bonebeds and microvertebrates, with much more care given to stratigraphic placement. It turns out that PEFO holds a whole weird and wonderful landscape of everything that gave it a go in the Late Triassic, before a couple of groups of archosaurs took over land management for the rest of the Mesozoic. (And if you don't like vertebrates, the plants are just about as wild in their own way, and there are freshwater and terrestrial invertebrates as well.) It practically begs for a book like those on Florissant, Fossil Lake, the Morrison, and the White River Badlands.

Here's a strat column to help keep the geologic units straight, borrowed from the park website.

With all of that in mind, here are a few quick hits from the past few years of research at PEFO: