Sunday, January 23, 2022

Bruce Erickson

This week saw the end of an era in Minnesota paleontology with the passing of Bruce Erickson. Bruce had been the curator of paleontology at the Science Museum of Minnesota from 1959 to 2017, where he was most famous for his work on the Paleocene fossils of Wannagan Creek. Much of his research was on crocodilians (several examples of which were featured in this post), but he also worked on many other topics, including the dinosaurs of the Poison Creek Quarry (Morrison Formation), champsosaurs, and turtles. Examples of many of these fossils can be seen in the paleontology exhibit area of the Science Museum, which includes a Wannagan Creek section (one of the few large Paleocene exhibits you'll find in a museum), several Morrison dinosaurs, and an enormous Triceratops (a composite of two partial skeletons he collected early in his tenure). If you'd like to know more, many of his publications and other paleontological publications from Science Museum collaborators can be downloaded here.

Sunday, January 16, 2022

Passing thoughts on Struthiosaurus (and Silvisaurus!)

I saw the headline "Surprising Dinosaur Discovery: Ankylosaur Was Sluggish And Deaf" and was indeed surprised, not so much by the "sluggish" part but by the "deaf" part. Hearing is generally pretty lightweight in terms of anatomical investment and it's useful wherever there is a medium to communicate sound. Even snakes can perceive sounds via vibrations. We're not talking about something like flight, a costly adaptation that requires a body specifically dedicated for it. It's not difficult to understand why, in the absence of natural pressure to maintain it, many lineages of birds have become flightless on islands. Hearing, though... I was having trouble coming up with a selective scenario that would eliminate it. So I thought I'd have a look at the actual paper (Schade et al. 2022).

...And it turned out the headline overstated things. Schade et al. (2022) described the holotype braincase of the diminutive Late Cretaceous European nodosaur Struthiosaurus austriacus. As part of their study, they measured the areas of the braincase associated with hearing. They calculated the mean hearing frequency as 1230 Hz and the bandwidth as between 296 and 2164 Hz. For the musicians among us, that works out to keys 42 (D above middle C) to 76 (double high C), centered just below key 67. Judging by a helpful chart on Wikipedia, this range is comparable to that of a chicken. [Update, 2022/01/17: Lead author Marco Schade has sent me an article, Hill et al. 2014, that shows chickens have a wider hearing range: 9.1 Hz to 7.2 kHz at 60 dB. This honestly makes more sense than the Wiki range, which seemed pretty constricted for a bird. The next closest match on the chart is the bullfrog, provided of course that the range is accurate; Heffner and Heffner 2007 give a slightly more constricted range than the Wiki chart, of 100 Hz to 2.5 kHz.] Schade et al. also commented that "the auditory acuity of S. austriacus seems somewhat superior to that of turtles". Thus, the paper did not find S. austriacus to be deaf, although it appears that they did not enjoy an especially rich range of sounds. [2022/01/20: To be completely fair to the headline writers, there seems to have been some difficulty with the German word "schwerhörig", which as Schade informed me means something like "barely able to hear".] (We must of course remember that this is one braincase, and it's possible that we happened to have stumbled on one individual with poor auditory capabilities, violating our unspoken assumption that fossilized organisms tend to the average rather than the extremes. More braincases would help to tell.)

 Struthiosaurus austriacus, the perfect nodosaur for around the house. Just don't call for it in a low-pitched voice. Figure 1 from Schade et al. (2022) (which see for full caption). CC BY 4.0.

There is also an intriguing counterpoint featuring the somewhat larger and earlier North American nodosaur Silvisaurus condrayi. In the original description (Eaton 1960), Eaton noted the presence of inflated nasal sinuses, which he interpreted as resonating chambers. With a diameter of approximately 50 mm (2 in), the chambers were postulated to have produced a sound "about E or F four octaves above middle C". This is surprisingly high-pitched, at keys 101 or 102 on an extended piano, or 5274.041 or 5587.652 Hz. (In fact, it's so high-pitched something doesn't seem right. Either Eaton or I have misinterpreted something in the sound physics, those aren't resonating chambers, or Silvisaurus went through life projecting the majestic sound of tinnitus.) Either would be well beyond the postulated hearing range of S. austriacus.

This all still leaves room to play with that original headline. How could we get a lineage of deaf nodosaurs? It has been suggested that snakes have reduced auditory capabilities because they evolved from burrowing ancestors. This doesn't seem especially feasible for nodosaurs; if nothing else they would have lost their spikes and plates long before their hearing had they been doing serious full-body burrowing. There's another possibility, though: S. austriacus is thought to have been an island endemic. If the founding population included an individual with reduced auditory capabilities, and that individual contributed disproportionately to the gene pool, we have a route for this trait becoming prevalent in at least this population of nodosaurs. A similar phenomenon could happen later in the island population's history as well, although it would be more difficult for any one mutation to spread with a larger population. Unfortunately, it would be very difficult to test this hypothesis without a whole lot of braincases from multiple stratigraphic horizons.

References

Eaton, T. H., Jr. 1960. A new armored dinosaur from the Cretaceous of Kansas. The University of Kansas Paleontological Contributions: Vertebrata 8:1–24.

Heffner, H. E., and R. S. Heffner. 2007. Hearing ranges of laboratory animals. Journal of the American Association for Laboratory Animal Science 46(1):20–22.

Hill, E. M., G. Koay, R. S. Heffner, and H. E. Heffner. 2014. Audiogram of the chicken (Gallus gallus domesticus) from 2Hz to 9 kHz. Journal of Comparative Physiology A 200:863–870.

Schade, M., S. Stumpf, J. Kriwet, C. Kettler, and C. Pfaff. 2022. Neuroanatomy of the nodosaurid Struthiosaurus austriacus (Dinosauria: Thyreophora) supports potential ecological differentiations within Ankylosauria. Scientific Reports 12:article 144. doi:10.1038/s41598-021-03599-9.

Friday, December 31, 2021

Stromatolites in the snow

To close out 2021, here are some stromatolites in the snow.

A big stromatolitic eye; no scale bars today (I couldn't reach this one anyway, but it's a couple of feet across).

At this location there's a large wall of Prairie du Chien Group rocks that was exposed a few years ago during the construction of a bike trail. The bike trail descends from north to south, exposing more of the section as you go until a few dozen feet of the Lower Ordovician are visible. There is a distinct stratigraphic break near the top of the section, and just above this break is a stromatolitic interval with some large colonies, like the eye-shaped example above. I haven't seen any definite fossils below the break, but there might be some (there are numerous small voids, at least some of which could represent dissolved shells). There are some nice sedimentary structures, though, such as cross-bedding and planar bedding (sand grains in the carbonate).

The center of this photo shows a sort of bi-lobed pillow that smooths out into a single mound. It is not far from the eye-like stromatolite in the previous photo. In both cases, the large colony is about a foot above the stratigraphic break.

There are also some blocks that have fallen. In fact, I suspect that the stromatolitic interval is more prone to shedding blocks than the rest of the interval, because the stromatolitic interval has more opportunities for fracturing.

Sunday, December 19, 2021

Theory and Application of Hypsibema

The dance of splitting and lumping will go on as long as there are two people and something to classify. On the one hand are the creators of new names. Are they revealing the hidden biological diversity of the past and present, or are they necessary evils at best, scurrilous egotistical rogues who turn taxonomy into tacky monuments to their own questionable genius at worst? On the other hand are the lumpers. Are they providing clarity against confusing multiplicity, or are they cranky reactionary gatekeepers who secretly (or not-so-secretly) flatter themselves as lonely upright crusaders against disorder and incompetence? Well, fellas, you can make questionable decisions splitting or lumping!

Consider, for a moment, the case of Hypsibema:

Late in 1869, Edward Drinker Cope presented a group of bones from North Carolina to the Academy of Natural Sciences of Philadelphia. He proposed to name the assortment Hypsibema crassicauda. The description takes up a grand total of 112 words (no illustrations, of course) and is reprinted below in its entirety:

"He [Cope] exhibited a number of remains of fossil reptiles, from Sampson Co., North Carolina, of cretaceous age, which were intrusive in miocene beds. Among these were humerus, tibia, fibula, metatarsus, caudal vertebra, and perhaps cervical vertebrae and ungueal phalange of a Dinosaur, discovered together by Prof. W. C. Kerr, Director of the Geological Survey of North Carolina. The remains indicated a species having the same general form and size as the Hadrosaurus foulkei. The caudal vertebra was of very different form, and resembled more that of Hylaeosaurus, minus the diapophyses. This vertebra was elongate, depressed and angulate. The animal presented various other points distinguishing it from Hadrosaurus, and was named Hypsibema crassicauda."

Note that Cope had received them second-hand, with no other information about their association other than they were "together". He was young at this time, not yet 30 and just getting started in this dinosaur business, but this was just one example of a worrying tendency that would show up again in his career: despite all of his undoubted paleontological acumen, he never seemed to twig to the idea that perhaps collections of bones found in the same general area did not necessarily belong to the same species or even genus. (See also Monoclonius.)

Because H. crassicauda was thought to have hadrosaurian affinities, Lull and Wright (1942) naturally included it in "Hadrosaurian Dinosaurs of North America". By that point Cope's bounty had been reduced to a caudal vertebra, the distal end of a humerus, a tibial shaft, and a partial metatarsal II, catalogued as USNM 7189 (National Museum of Natural History, Washington, D.C.). Lull and Wright passed the following judgment: "The material is too meager and uncharacteristic to permit a real definition of the genus and species, and the form must therefore be considered a nomen nudum [as mentioned here, basically a nomen dubium as understood today]. It indicates, however, the presence in North Carolina of Cretaceous hadrosaurs of uncertain affinities." Well, hallelujah, and so forth; insert your own uproar as the mood strikes. (One slightly disconcerting note: Lull and Wright thought the caudal resembled the caudal of fellow North Carolina form Hadrosaurus tripos. Hadrosaurus tripos is now regarded as a Pliocene whale.)

In hindsight it is very easy to say that Cope shouldn't have bothered naming Hypsibema crassicauda. The material isn't great and there is no real evidence that any of the bones belong to the same thing. It can be counter-argued that he didn't know any better and was acting within the bounds of mid-19th century vertebrate paleontology, but it still is not his finest hour. (None of the surviving bones can even articulate, for crying out loud. Even if they'd been found in an area the size of a square foot they could still easily be a hydraulic concentration of random fauna, and here he is thinking they're the same thing after getting them second-hand at best?)

So much for the 19th century.

Elsewhere and elsewhen, in 1942 geologists of the Missouri Geological Survey were studying clay units in southeastern Missouri. One of them, Dan Stewart, came into contact with Lulu Chronister, who told him about bones found on the Chronister farm during the digging of a well. One thing led to another, and in early 1945 Stewart and Charles Gilmore (of Thescelosaurus and Alamosaurus fame around here) published a description of 13 caudal centra (neural arches apparently lost around the time of discovery) and two fragments, catalogued as USNM 16735. They used the bones as the basis of new sauropod Neosaurus missouriensis (Gilmore in Gilmore and Stewart 1945). If you've never heard of Neosaurus missouriensis, it's because Neosaurus turned out to be preoccupied, and Gilmore quickly substituted Parrosaurus (Gilmore 1945). Gilmore (in Gilmore and Stewart 1945:25) commented that "[t]he specimen on which the present paper is based consists only of caudal centra that in the ordinary course of events would be considered too meager for generic designation, but in view of the uniqueness of both its geographical and geological occurrence the name Neosaurus missouriensis is proposed for its reception."

Neither Hypsibema crassicauda nor Parrosaurus missouriensis garnered much attention over the next few decades. Then, in 1979 Donald Baird and Jack Horner published a review of Cretaceous North Carolina dinosaurs. Things did not go well for Hypsibema crassicauda at first; Baird and Horner determined that the type material was chimeric. They restricted the type to just the caudal vertebra, because Cope had based the species name ("thick-tailed") on it, and identified it as belonging to a sauropod. They then pulled the tibial and metatarsal fragments as hadrosaurian, and identified the "humerus" as the distal end of a tyrannosaurid femur. So far, this is just another case of the clinical dissection of an obscure questionable name.

Then, though, the authors brought out Parrosaurus missouriensis. Technically speaking, with a publication title of "Cretaceous dinosaurs of North Carolina" they could have ignored P. missouriensis and nobody would have felt shortchanged, but they opted to go the extra mile. In fact, they went farther than the extra mile, sinking Gilmore's species into Cope's species: "Now that Hypsibema has been freed of hadrosaurian encumbrances its genetic identity with Parrosaurus becomes obvious. Every morphological feature cited for the Missouri vertebrae can be matched in those from North Carolina. Indeed, the possibility of specific identity cannot be dismissed..."

The bit about sauropod (mis)identification is a topic for another time and place. For the moment, the critical piece is sinking one poorly known species into a different poorly known genus on the basis of exactly one piece of overlapping material: the caudal of H. crassicauda, with remnants of the neural arch (which you don't even get with P. missouriensis). Even if they are very similar, that's asking a lot out of dinosaurian caudal centra, which are not generally noted for having unusually high concentrations of apomorphies. Implicitly this classification is saying that the rest of the body of the two forms will not differ significantly, a bold statement all around. Whether or not you agree with the synonymization, I suspect you'd probably agree that it's not an ideal situation.

Because for many years there was little interest in the disposition of H. crassicauda and P. missouriensis (although missouriensis became the state dinosaur of Missouri during that time frame), the generic synonymization has persisted. Recent developments in Missouri bode fair to spur a reassessment, though.

[Note: despite the url for this entry, I did not write it in August 2018, I only started working on a post with a couple of the ideas and gave it a custom url because I didn't like the automatic version. (For that matter, the present entry owes much more to another and even older post idea.) Of course, I had long forgotten about the custom link when I dusted it off. Seeing as there's no critical reason to change it, I'll let it stay.]

References

Baird, D., and J. R. Horner. 1979. Cretaceous dinosaurs of North Carolina. Brimleyana: The Journal of the North Carolina State Museum of Natural History 2:1–28.

Cope, E. D. 1869. [Remarks on Hypsibema crassicauda and Hadrosaurus tripos.] Proceedings of the Academy of Natural Sciences of Philadelphia 21:192.

Gilmore, C. W. 1945. Parrosaurus, n. name, replacing Neosaurus Gilmore 1945. Journal of Paleontology 19(5):540.

Gilmore, C. W., and D. R. Stewart. 1945. A new sauropod from the Upper Cretaceous of Missouri. Journal of Paleontology 19(1):23–29.

Lull, R. S., and N. E. Wright. 1942. Hadrosaurian dinosaurs of North America. Geological Society of America Special Paper 40.

Saturday, December 11, 2021

A reflection

December 4, 2021:

It's the early afternoon on one of those gray days that Minnesota churns out from about the time the leaf show is over to about the time that snowfall gets serious; it's as if Mother Nature, not quite sure what weather to go with, simply throws the gray blanket over the state until she makes up her mind. I am wandering the Mississippi River gorge in St. Paul and Minneapolis.

The view from the Shadow Falls overlook.

Saturday, November 27, 2021

The green rocks of home revisited (now with stromatolites!)

Almost exactly five years ago I posted on a visit to Cottage Grove Ravine Regional Park. I was in the area and thought I'd stop again. There's been a lot of work at the park since then, and I wanted to check that the abandoned stream channel and dry waterfall were still visible. Also, over the past five years I've become much better at finding stromatolites, so I thought I'd try my luck.

Were the landforms still there?

That's a dry waterfall, all right. The lowest interval seems to have some weathered cross-bedding; perhaps a somewhat sandier bed in the Prairie du Chien?

I'd say yes, the old channel is still there.

How about stromatolites?

We have stromatolites!

That's the stuff.

Separation has occurred within a stromatolitic interval here.

At the beginning, I was seeing them in loose blocks, which led to the question "where are they coming from?" This was more complicated. The stromatolitic blocks were much lighter-colored and less weathered, indicating fresh faces. There were no obvious fresh faces on the surrounding walls, though. Had large stromatolitic blocks broken up in the dry stream bed fairly recently? Or were these "plants", Prairie du Chien blocks that had been brought in for landscaping and culvert riprap, then declared surplus and deposited here? The walls were not helping.

Features like the wavy lines give a general biotic impression, but I'd really want to see some light-colored patches indicating fallen blocks to cinch a relationship.

Fine lines are visible behind the dull gray and moss.

Then I saw this enormous fallen block.

Do you see them? They're near center. If not, hold on.

There they were.

How about now?

A proverbial bull's eye.

This block is too large and too well-mossed to have been placed here in the past few years. Clearly at least some of the stromatolites are local. I'm still wondering where the loose "clean" blocks came from, though.

Sunday, November 14, 2021

Issi saaneq and Brighstoneus simmondsi

A couple of new non-theropod names have come down the pipe since the beginning of November, and I thought I'd cover them together. Let's tackle the earlier of the two (both geochronologically and publication-wise) first.