Sunday, November 27, 2022

Musings on Hanyusuchus

Every year a handful of new croc taxa are described. If you're strictly in this business for the dinosaurs, you ought to see what the croc side of Archosauria has been up to from time to time; they were quite versatile in palmier days. Even though they aren't quite as diversified as they used to be, it turns out they had hitherto-unsuspected tricks up their sleeves even as recently as a few hundred years ago. This spring a new genus and species of gavialid was described from the Holocene of south China: Hanyusuchus sinensis. This is fascinating, for many reasons. The obvious is that here we have a species of [insert expletive of choice] 20-foot-long gavial that existed up to perhaps a few hundred years ago in full contact with one of the most thoroughly documented civilizations in history, and it was completely overlooked. It may not have gone extinct until the time of the Ming dynasty. This is something like discovering that bears in Greek and Roman mythology were actually Arctodus, only if Arctodus was the size of a pickup truck. China, of course, is noted for the extant Alligator sinensis, but although the Chinese alligator is many things, not even on its best days has it been a 20-foot-long gavial.

Figure 2(s) from Iijima et al. (2022). Depicted: Hanyusuchus sinensis (composite, scaled to holotype) and 1.8 m (5.9 ft) tall human. Not pictured: Alligator sinensis (to imagine, mentally scale the Hanyusuchus to be about the same size as the human). CC BY 4.0.

Another fascinating aspect is the namesake. Han Yu was a significant writer, philosopher, and politician of the Tang dynasty. At one point in his life, he got in trouble at court and was packed off to Chaozhou in Guangdong, southeastern China to serve as prefect. In this capacity, he issued a proclamation in 819 concerning the crocodilian population. This in itself is not remarkable, except for the audience: he issued it to the crocodiles themselves. A translation of the statement can be found here (well worth a read). The icing on the cake is that the crocodiles reportedly did as instructed and departed, although we can presume that if they *did* indeed vanish from the area, strong hands wielding metal implements (like the Bronze Age weapons that left marks on some specimens) were more important in enforcing the departure. The reader may suppose that Han Yu's action was just a quaint old-time delusion; after all, there is a long history of animals being prosecuted for crimes. However, as the author of the translation notes drily, "Tang prefects did not habitually make formal verbal addresses to the local fauna" (footnote 7, p. 60). One wonders if perhaps Han Yu, who was noted for a sense of humor, had his tongue firmly in cheek.

There's also a melancholic existential aspect to the discussion. H. sinensis was part of the fabric of life in southern China for thousands of years. Descriptions of the species can be identified in historical sources, now that we know what to look for. Dynasties, cultural flowerings and renaissances, wars, conquerors, travelers like Marco Polo and Ibn Battuta, all came and went while 6-m gavials patrolled the southern rivers. They took livestock and killed people. They were apparently very noisy, probably the source of reportedly "thunder-like sounds in the night". Then they were driven into extinction and basically forgotten for hundreds of years.

References

Iijima M, Qiao Y, Lin W, Peng Y, Yoneda M, and Liu J. 2022. An intermediate crocodylian linking two extant gharials from the Bronze Age of China and its human-induced extinction. Proceedings of the Royal Society B: Biological Sciences 289:20220085. doi:10.1098/rspb.2022.0085.

Sunday, November 20, 2022

Your Friends The Titanosaurs: Caieiria allocaudata

This edition of "Your Friends The Titanosaurs" is a little different in that not only are we welcoming a new friend, we are saying goodbye to an old friend. The latter is something that should come as no surprise; with well over a hundred species, notorious for incomplete material, some of them are eventually going to turn out to be the same.

(Also, I should have mentioned this, but I moved the external links to a separate page to conserve space on the sidebar.)

Sunday, November 13, 2022

Quick Guide to Fossils at Uŋčí Makhá Park

So I went back to Uŋčí Makhá Park last weekend and spent a couple of hours taking photos of fossils, because it makes such an ideal place to see the upper Platteville fauna. After all, a winter of freezes and thaws may not leave these new exposures looking as nice as they do now. Here's a quick guide to what can be seen there. (Let's see how many photos I can squeeze into one post, and how many species I can misidentify!)

Determining where you are stratigraphically

First of all, I'd just like to reiterate the stratigraphy. Most of the vertical extent is in the Magnolia Member of the Platteville Formation, with the upper part composed of the Carimona Member of the Decorah Shale. I'm thinking more or less the entire extent of the Carimona is exposed, based on thickness; at any rate the next thing up would be the shaly part of the Decorah, and there isn't a trace of it to be seen. I'm suspicious because the difference is just so darn clear, but at this site there is an unmistakable color change between the two units: the Carimona is the upper blue-gray interval and the Magnolia is the light tan-gray interval below. The Deicke K-bentonite is the lower and thicker of the two bentonite gaps in the Carimona. (Note that the Carimona is sometimes supplemented or replaced by landscaping, but this is pretty obvious.) As you walk from south to north, the "floor" goes up stratigraphically, so it's not all one bedding plane but a gently rising series of planes, until by the exit you're close to the color change.

The color change is quite evident here. The Deicke K-bentonite is the cut-in about halfway up the blue-gray Carimona (above the scale bar in the center of the photo).

Here we've gone north, and the floor has risen. The Deicke is still the seam in the middle of the blue-gray rocks.

Sunday, October 30, 2022

Strolling on the Magnolia Member by Hidden Falls

If you're looking for something geological to do in the Twin Cities while we're still under our unseasonably warm and dry weather, may I suggest paying a visit to the new park area above Hidden Falls? [Update, 2022/11/01: this park is called Uŋčí Makhá Park.] As part of the conversion of the former Ford Plant environs, part of the area of the creek into Hidden Falls has been daylighted. The landscaping has produced a mini-bedrock gorge that exposes significant vertical and bedding-plane surfaces of the Magnolia Member of the Platteville and the overlying Carimona Member of the Decorah.

There's nothing quite like this kind of exposure in the Twin Cities; we don't have a lot of exposed non-vertical bedrock in the first place, and this particular stratigraphic interval tends to be out of reach. The closest might be the platform below the overlook at Shadow Falls, but that's more limited in extent and has more of a stair-step profile.

Bonus points for spotting the Deicke K-bentonite.

Many of the exposed bedding plane surfaces reveal the shell beds the Magnolia is known for. The fossils are almost entirely brachiopods (with a few snails) and are represented by dolomitized molds and casts, giving them that characteristic sugary appearance.

See the little bumps? Brachs.

Enlarge for a world of brachiopods.

Here's a closer view showing a few nice examples, representing multiple species.

Also, just for fun, some of the stones used for landscaping are loaded with burrows.

If you stop by, please don't attempt to remove the fossils; it's a park, after all, and the fossils aren't really going to come off in one piece because they're molds and casts. Just enjoy the experience of walking on the seafloor without ever getting wet!

Sunday, October 23, 2022

Abbott and Costello Meet the Hyolith

I seem to have missed doing a hyolith post last year, which is really a shame and is all on me. Honestly, where else are you going to get the latest information on hyoliths? Social media? Cable news? Public radio? No, of course not! This is really a public service I'm running here, and you'll thank me for it someday. With that out of the way, what's been going on in the world of hyoliths over the past couple of years? A few thoughtfully curated highlights:

If you've ever spent time looking at the origins and relationships of gastropods, you'll be familiar with the seemingly endless debates about whether such-and-such is a gastropod or something that just happens to have a shell that looks like a snail shell (like monoplacophorans, helcionelloids, and maybe bellerophonts). We've had a bit of that with the local snail-oids, although by the Late Ordovician most of the hard cases had been cleared out. Down in the Cambrian things are more complicated. One example is Protowenella, an itty-bitty (smaller than 1 mm long) shell thing that looks kind of like a Phrygian cap. (Okay, fine, it looks like an exaggerated Smurf hat.) Is it a gastropod, a monoplacophoran, or a helcionelloid? According to Peel (2021), it is none of these. Instead, it is... a hyolith.

(Admittedly, the surprise you are feeling is probably tempered by the fact that this is a post about hyoliths, so it wouldn't have made sense for it to be a chiton or graptolite or something.)

Peel based his conclusion on the presence of a bilaterally symmetric operculum (a mineralized cap that covers the shell aperture) with features consistent with a hyolith origin. Gastropods frequently have opercula, but they aren't symmetric, and hyoliths are the only thing known to have had opercula in the Cambrian. If this referral is accurate, it would be something of an unexpected expansion of hyolith morphological talents. Hyoliths, of course, are famous for having long triangular shells with triangular cross-sections, whereas Protowenella as mentioned looks like a curled-over pointed hat.

Now let's turn from something that doesn't look like a typical hyolith but has something that *is* typical, to something that looks like a typical hyolith but is missing something expected. Hyoliths are generally divided into two groups, the orthothecids and hyolithids. Orthothecids showed up first and have a flat, retracting operculum (rather than the more complex operculum of hyolithids) and no helens (the paired spiny appendages that make hyolithids look kind of like they have wide spindly mustaches). It turns out that there are some hyoliths with hyolithid anatomy except for no helens. Liu et al. (2022) examined one such example, "Ambrolinevitus" ventricosus, an early Cambrian form from China (which they moved to Paramicrocornus, also known to lack helens). The implication is that the hyolithid body shape evolved before helens. Therefore, whatever ecological specialization was held by hyolithids over their earlier cousins, it was underway before helens appeared.

Finally, I leave you with Sun et al. (2021), a description of some beautifully preserved Cambrian hyoliths from China. Assigned to the new species Novakotheca weifangensis, they're small (less than 2 cm at most, although some have even smaller brachiopods attached) and pretty typical in shape. The neat thing about them is the preservation of mineralized soft parts of the digestive tract, interpreted as including a pharynx, esophagus, stomach, U-shaped intestine, and possible digestive gland. The anatomy is more complex than previously thought, and suggests that at least some hyoliths were not simply filter feeders.

References

Liu, F., C. B. Skovested, T. P. Topper, and Z. Zhang. 2022. Hyolithid-like hyoliths without helens from the early Cambrian of South China, and their implications for the evolution of hyoliths. BMC Ecology and Evolution 22: article 64. doi:10.1186/s12862-022-02022-9.

Peel, J. S. 2021. In-place operculum demonstrates that the Middle Cambrian Protowenella is a hyolith and not a mollusc. Alcheringa: An Australasian Journal of Palaeontology 45(4):385–394. doi:10.1080/03115518.2021.2004225.

Sun H., Sun Z., and Zhao F. 2021. Exceptionally preserved hyolithids from the middle Cambrian of north China. Geological Magazine 158(11):1951–1959. doi:10.1017/S0016756821000510.

Sunday, October 9, 2022

Compact Thescelosaurus Year Seven

Here we are at the second weekend of October, which means it's time for three things: National Fossil Day; a new sheet for The Compact Thescelosaurus; and our annual roundup of what's been added to the spreadsheet. National Fossil Day falls on Wednesday, October 12 this year, although events occur throughout the month (especially the weekends before and after), so check your nearest museum or National Park System unit for events! Our fall Park Paleontology newsletter is also up for viewing (including more fun with packrats).

Saturday, September 24, 2022

Your Friends The Titanosaurs: Ibirania parva

It's been more than half a year since our last friendly titanosaur (Abditosaurus kuehnei), but September has brought us a new saltasaur. To be precise, our guest is Ibirania parva, hailing from the late Late Cretaceous of the Bauru Basin of southern Brazil. There is always room here for a sauropod that could have been transported in a standard shipping container,* so let's begin.

*Or, heck with that, in an Amazon van—curl the neck and/or tail and 5.7 meters/19 feet of sauropod can be yours with free shipping for Amazon Prime members. Or get a horse trailer and make allowance for your curious sauropod to poke its head out the sides.