Silvisaurus condrayi

You wait long enough, and history starts to pile up, like falling snow (only history doesn't melt away and has a way of churning back to the surface). In paleontology, we've just passed two centuries with Megalosaurus (1824) and Iguanodon (1825). I was thinking about the topic of this post and how it was a relatively recent name, even though it felt old, but then realized that 1960 is not quite as recent as it was when I first read about Silvisaurus in the mid-1980s. I'm not tracking stats to any great degree, but it's probably safe to say there aren't a lot of people reading this who were mid-career when the scientific description of Silvisaurus condrayi was published.

Vectipelta barretti

Last week we had a look at almost-hadrosaur Gonkoken nanoi. This week we're hopping over to another branch of Ornithischia for the ankylosaur Vectipelta barretti. I'm always up for ankylosaur news, and took particular interest in this case because I've long had a deep and irrational fondness for Polacanthus, going back to the 1980s.

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.

The gut contents of Borealopelta

Seems like we just had Borealopelta markmitchelli as a major part of a post. Unlike back in March, this time around the famously well-preserved nodosaur doesn't have to share space with any other ankylosaurs. The occasion is the publication of Brown et al. (2020), which describes plant material found inside the carcass of the ankylosaur. This publication is freely available, and if you have any interest in dinosaur paleobiology you ought to snag it (and its supplementary material; never forget the supplements!).

On the nuances of ankylosaurs

Restoring an ankylosaur is not the easiest thing in the world, because usually they died without bothering to keep their armor together. This makes it all the more disheartening when details are missed when working from the few well-preserved examples. For example, with Borealopelta, even though photos abound and there are two publications with many illustrations (both of which can be freely accessed), many restorations don't accurately reproduce the armor pattern. For reference:

The pattern of osteoderms over the torso is composed of transverse bands of distinct single rows of osteoderms. The bands alternate between wider, more prominent rows of larger, modestly keeled osteoderms and narrower rows of much smaller, unkeeled, roughly equant osteoderms. Significantly, the long axes of the larger scutes are oriented transversely to the body (i.e., they appear wider than long), not parasagittally, as they are frequently restored (the CollectA Borealopelta, which gets other details right, fudges on this, as well as the next thing). This pattern is not unlike the articulated armor known for Nodosaurus.

The pattern of osteoderms over the hips is not an extension of the torso armor, but is composed of generally polygonal pieces in a more tightly fitting mosaic, with an irregular distribution of filler osteoderms. This is not unlike the pattern seen in the pelvic armor of Stegopelta.

Figure 3 from Brown (2017). CC-BY-4.0.

It's such a lovely specimen, let's look at it some more! Figure 1 from Brown (2017). CC-BY-4.0.

It should also be noted that placing an osteoderm pattern found on one ankylosaur onto another, more poorly known ankylosaur is a crapshoot. Known articulated ankylosaur torso armor varies widely:

Kunbarrasaurus has a scattering of very small osteoderms between the shoulders and hips, and several relatively large pointed osteoderms situated at the hip-tail transition.

Borealopelta has the pattern described above, which also incorporates large spikes and large keeled osteoderms in the neck and shoulder region.

Edmontonia has three bands of large keeled scutes on the neck and shoulders, a lateral fringe of spiky osteoderms to just past the shoulders, and then small osteoderms in a groundmass of minute pieces. (Restorations that show Edmontonia or "Palaeoscincus" often mix the correct anterior armor with an imaginary post-shoulder pattern of a brickwork of large scutes, derived ancestrally from Barnum Brown's hypothetical skeletal restoration of Ankylosaurus as a sort of cobblestone Stegosaurus with the short tail of a ceratopsid.)

No cobblestones on the back of Edmontonia.

Sauropelta is something like a lazy Borealopelta, with vague transverse bands of larger circular or ovate osteoderms separated from each other by abundant groundmass osteoderms.

Round, slightly peaked, and loosely aligned osteoderms on Sauropelta.

What we have of Pinacosaurus indicates bands of large strongly keeled scutes on the sides and tail.

Pinacosaurus is about as close to the classic cobblestone pattern as is known at this time.

Scolosaurus, represented by one of the earliest known well-articulated armor patterns, has had an outsized influence on ankylosaur restorations, along with Edmontonia/"Palaeoscincus" and the cobblestone Ankylosaurus. It is known for a relatively small number of large conical or keeled scutes set in broad transverse bands of smaller osteoderms. Photos of Zuul indicate something similar but with even larger osteoderms. The boundaries of the bands are often depicted as stark and well-defined, with the animal having a sort of jointed carapace, but photos show more subtle boundaries. In hindsight, Scolosaurus can be seen as the prototype for "banded Hylaeosaurus" restorations made popular by the "Illustrated Encyclopedia of Dinosaurs". It's not clear why Scolosaurus should have been chosen as the model given that the known armor of Hylaeosaurus consists of large elongate spiky osteoderms and flattened plates from the neck and shoulders, quite unlike that of Scolosaurus.

Click to zoom and see for yourself: the bands are not starkly delimited. Photo by "the paleobear", found at Wikimedia Commons. CC-BY-2.0.

A casual look at ankylosaur restorations will show that exaggerated armadillo-like bands derived from Scolosaurus are one of the more popular patterns chosen for restoring ankylosaurs. This pattern at least has the benefit of being based on an actual specimen, unlike the cobblestone or "brick house" of adjoining large osteoderms, or the "undifferentiated sea of small pointed bits".

References

Brown, C. M. 2017. An exceptionally preserved armored dinosaur reveals the morphology and allometry of osteoderms and their horny epidermal coverings. PeerJ 5:e4066. doi:10.7717/peerj.4066.

Three weeks of ankylosaurs and pterosaurs

March has been busy over at The Compact Thescelosaurus, with ten new entries adding three ankylosaurs, four pterosaurs, and three theropods. There's still a week to go, too. Sometimes people talk about following taxonomy as another kind of stamp collecting. I have a more artistic point of view, with each specimen as more along the lines of tiles in an incomplete mosaic or notes in an unfinished song, each contributing to a greater whole. It just so happens that the currency of the realm is in species and genera. (I also keep track because you can't tell the players without a program!) As usual, I'll leave the theropods to others, except to say that it's nice to see Arkansaurus finally graduate from informal name to the big leagues, thanks to Hunt and Quinn (2018) (the name has figured in print since 1983, after all). A few comments on the ankylosaurs and pterosaurs:

Jinyunpelta

Ankylosaurs have had a good few weeks, publicity-wise. First we get some actual science done on the long-held belief that they were prone to "bloat and float" (if you don't like to contemplate recently deceased animals, I will simply say yes, it looks pretty good; if you'd like a less-technical summary, go here). We've also now got the oldest record of a true tail club, wielded by the newly minted Jinyunpelta sinensis.

Borealopelta

At last, the "Suncor ankylosaur" takes its place among the described! With the description of Borealopelta, I can cross off one more from "Coming Attractions". (That's four and a half down, with half-credit on Daspletosaurus, and eighteen and a half to go.) The first thing I recommend that you do is to download the description and the supplemental information from here.

Borealopelta, photo borrowed from Wikimedia Commons.

Hoplitosaurus

With the recent coverage of Zuul and the Suncor nodosaur, it seems like a good time for another entry on North American armored dinosaurs. We've already visited with Nodosaurus textilis, Stegopelta landerensis, and Hierosaurus sternbergii. Today's star is another species of similar vintage, Hoplitosaurus marshi. Like our other three subjects, Hoplitosaurus was initially described around the turn of the 20th century from a single armor-heavy specimen found in Cretaceous rocks of the American West. Also like the other three, Hoplitosaurus received barely a blurb for its initial description and had to wait for someone else to spare a little more time and ink.

Regarding Liaoningosaurus

By now you may have heard about the new paper by Ji Q. et al. on Liaoningosaurus, proposing some surprising things about the paleobiology of this ankylosaur. Andrea Cau already had a go at it over at Theropoda. I'm afraid I won't be as concise or insightful, but possible gut contents are involved, and having fought my own gut-content dinosaur to a truce, I think I can bring a distinct perspective to this paper. 

Hierosaurus sternbergii

One of the notable quirks of nodosaurids is a predilection for washing out to sea. Nodosaurus textilis and Stegopelta landerensis are a couple of featured examples. We turn now to another species from the Western Interior Seaway: Hierosaurus sternbergii.

Stegopelta

After my years of puzzlement versus Leonardo, I have the greatest sympathy for the early generations of dinosaur paleontologists, being confronted with the often-scanty remains of beasts that had never been seen by anyone. We've already touched on Marsh dealing with Atlantosaurus and Cope dealing with Monoclonius recurvicornis. Ankylosaurians were no exception to the confusion. If a dinosaur skeleton is like a puzzle, a partial ankylosaur skeleton is like getting 300 pieces of a 2,000 piece puzzle, with the only guide being a hand-drawn copy of the box cover drawn by a right-handed person using their left hand, who is also in denial about the state of their vision. The puzzle, of course, is a stand of birch trees in a Great Lakes winter, in black and white. Small wonder that ankylosaurs spent most of the 20th century in the guise of magnified grouchy horned toads, covered in a pavement of armor laid out with enough regularity to satisfy the most tyrannical of 1950s suburb planners.

Nodosaurus: more than a corduroy armadillo

Ankylosaurians, be they clubbed or club-less, labor in relative anonymity among dinosaurs, bundles of roughage trundling along, only briefly intersecting the limelight of flashier dinosaurs. A few get a bit more press, enough to put them in a respectable second tier of popularity (Ankylosaurus and Gastonia, particularly). Despite being the traditional namesake for the club-less ankylosaurs*, Nodosaurus is not one of them. Instead, it fills a role not unlike a venerable distant relative who occasionally shows up at family functions to hover on the sidelines. We know he or she is there and we show due deference, but there's no particularly warm connection of familiarity. The closest it's gotten to a star turn since it was named in 1889 was as a John Sibbick illustration in the "Normanpedia", where it is depicted as a sort of vaguely armadillo-like creature suspiciously eyeing the reader and bearing a precise gridwork of button-like armor pieces, without a hint of spikes or plates. Oddly, the skeletal restoration on the next page shows a distinctly different pattern of armor, featuring alternating bands of large scutes between the ribs and smaller pieces over the ribs, which unintentionally give it a sort of corduroy texture. As we shall see, there does indeed appear to a corduroy pattern over part of the animal, but there was also a lot more going on.

*This great tradition goes back all the way to the 1970s (Coombs 1978). Prior to this, ankylosaurs were just kind of there as one sort of mash. After this, ankylosaurs were still just kind of there, but now there were two flavors.

Reports of gut contents in herbivorous dinosaurs

I generally avoid writing "nuts and bolts" posts about dinosaurs, because there's a lot of people already doing that who know what they're doing. There is, however, one topic on which I'm uniquely qualified to pontificate. In a previous lifetime I was a fresh-faced graduate student who wrote his thesis on possible gut contents in the "Leonardo" specimen of Brachylophosaurus. As such, I spent a fair amount of time considering the history of possible gut contents in herbivorous dinosaurs, which consists of an exclusive club populated by four hadrosaurs, one ankylosaur, and one sauropod. In retrospect, the Leonardo project was somewhat beyond my powers, but I battled on against overwhelming oddities and came out of it eventually. (For you folks playing along at home, by "herbivorous dinosaurs" I mean more or less classic dinosaurs that aren't theropods. I've got nothing against birds, which include many a herbivorous dinosaur, but they aren't why I got interested in these things, and I don't feel sentimental about them being dinosaurs, because "my" dinosaurs are almost all ornithischians and have all been dead for 66 million years.)

Chuanqilong and Tambatitanis

So I finish the Generic History of Dinosaur Paleontology series on July 20th, and four new genera come along. Of course, it's not quantity but quality, and a year with Anzu and Kulindadromeus will be remembered fondly. Every dinosaur should have its day, though, even if they aren't enormous crested caenagnathids or feathered ornithischians. Two of the most recent genera are in freely accessible publications and represent significantly different but still generally overlooked branches of the dinosaurian tree. They are the titanosauriform sauropod Tambatitanis and the ankylosaur Chuanqilong.