Sunday, April 5, 2020

Trilophosaurus and Ophthalmothule

For this post, we highlight two extinct reptiles that have been the subjects of publications in the past few days. Other than that, they don't have much in common. One is a short-necked terrestrial herbivore less than three meters long that lived during the Late Triassic in what is now Arizona, the other is a long-necked marine carnivore between five and six meters long that lived at about the Jurassic–Cretaceous boundary at what is now an Arctic island (not quite so arctic at the time).

Sunday, March 29, 2020

George Washington's dolphins, and other NPS paleontology news

Here are a few recent items from the world of National Park Service paleontology:

Fossil Dolphins at George Washington Birthplace National Monument

You may remember from a couple of months ago the announcement of shark fossils from within the cave system of Mammoth Cave National Park, embedded in the Mississippian-aged rocks which host the caves. Here's another announcement of a marine nature, this time coming from George Washington Birthplace National Monument in eastern Virginia. At this park, dolphin fossils including two skulls were recently excavated from the Miocene-aged Calvert Formation bluffs along the Potomac. I'm particularly proud and pleased about this news, because I have been going to GEWA annually since 2014 to conduct monitoring of fossil resources. (I am also jealous because I wasn't available to participate!) There are two things going on here that threaten fossil resources: the Potomac can rather effectively batter the poorly lithified Calvert Formation bluffs when it gets churning; and there has been a long-time culture of collecting, which we've been trying to change.

March 2015, on part of the Potomac shore.

November 2019, somewhere close to the same place as the previous photo. The colors seem to be a seasonal thing (the colorful surfaces are scrubbed off during winter storms). Note the trees looming above.

When you're at a park, remember to leave the fossils where they are. Tell park staff if you come across something interesting. Maybe another dolphin will turn up!

Park Paleontology News, spring 2020

A couple of years ago we resumed the Park Paleontology newsletter as a collection of short online articles, published in the spring and fall. This venue gives us a chance to put out short pieces on our various projects, covering a variety of aspects of NPS paleontology from a range of viewpoints. The spring 2020 collection was recently made public and includes the following:


Feel free to also check out the back issues from the past few years, too!

Grand Canyon NP and Chaco Culture NHP virtual museums

One of our favorite methods of documenting fossils is through the use of photogrammetry to create 3D models. The basic concept is that you take a number of overlapping photos of something and then use dedicated software to stitch the photos into a digital 3D model. (This can also be used to print tangible 3D models as well.) Our interest started with documenting fossil vertebrate tracks; they don't always lend themselves to collecting (size of track surface, fragility, tracks being part of the scenery) and casting can damage them. Led by crack photogrammetry specialist Jack Wood, we've since expanded to a wide variety of fossils. We've recently made two collections of photogrammetric models available for viewing. One set captures examples of the wide variety of fossil organisms found at Grand Canyon National Park. The other, for Chaco Culture National Historical Park, is focused on the Western Interior Seaway.

Sunday, March 22, 2020

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.

Sunday, March 15, 2020

Your Friends The Titanosaurs, part 22: Paludititan, Panamericansaurus, and Paralititan

The inexorable march of the titanosaurs continues, bringing us to the letter "P" (which for whatever reason is a popular letter for starting off titanosaur names, like "A" and "M"). For variety, we have a small species from Europe (Paludititan nalatzensis), a small species from South America (Panamericansaurus schroederi), and a large species from Africa (Paralititan stromeri). If you're looking ahead, the next couple of anticipated posts are heavy on South American species, and include two of the largest known titanosaurs (Patagotitan mayorum and Puertasaurus reuili).

Sunday, March 8, 2020

Stromatolite Sunday

I happen to know a place along a shore where the riprap includes a small percentage of stromatolitic blocks, and given the nice weather on Saturday, I thought I'd stop by and take some pictures. I have not asked about the source, but I have a pretty good idea that the provenance is one or more quarries in the area working the Shakopee Formation (Prairie du Chien Group). The rocks look like the Shakopee Formation (including that which is exposed in outcrop nearby), and there are no fossils beyond stromatolites and burrows. Stromatolites can be subtle features, but not these examples. Not only is the layering very distinct, once you get used to the appearance of the stromatolitic blocks it is possible to reliably pick them out from the other blocks at a distance of a few meters/yards. The simplest way to describe it is that the non-stromatolitic blocks are sandier and thus reflect light differently. Here's a side of a stromatolitic block, as you might see it as you approach.

Since these are domes, way-up is toward the top of the photo.

You'll see what looks like numerous parallel series of stacked parentheses. Let's zoom in on them:

Note that the column near the center splits into two smaller columns going up.

Enhance!

There's been just enough weathering to make the layers stand out nicely.

The stacks aren't necessarily separate columns, because if you look closely you can see that layers can continue from stack to stack, but "column" is a handy quick descriptor. In life, the colony would have had a lumpy upper surface composed of a number of distinct but connected domes. We can see this in upper and lower surfaces of stromatolitic blocks.

The upper surfaces of stromatolite blocks (A) are lumpy, showing the tops of the small domes. Sometimes there is a nice bottom surface that's essentially a negative of the upper surface (B). (These are definitely hollows, but your eyes may interpret the photo as domes.) Bottom surfaces can be easier to appreciate than the sometimes subtle upper surfaces.

In this case, weathering has partially removed some of the uppermost layers, "dissecting" the tops of the domes.

This photo, taken along the edge between an upper surface and a side, shows how the stacks translate into domes.

I am completely comfortable interpreting these lumpy stacked colonies as Stauffer's Cryptozoon rosemontensis, which he named from the Shakopee Formation not too far away. Almost all of the stromatolitic blocks I saw fall under this category, but there were a couple of examples that did not have stacks, instead having large hemispherical structures. These are much more typical of a variety named Cryptozoon minnesotensis.

These two photos show a much different flavor of microbial colony immortalized as stromatolites. A shows multiple lobes, while most of B is one big dome. These are in the vein of Cryptozoon minnesotensis.

Some of the blocks are well-preserved, even though they are now exposed to the elements. Others are now weathering, breaking down either by spalling at the tops of the dome stacks or by the stacks themselves beginning to fall out. The difference may have to do with how much sand was incorporated into the colony.

This group of photos shows a heavily eroded block, with columns beginning to spall out. A gives the overall appearance. B is a close-up of several such columns. The pockmarks mark where sand grains have eroded from the layers. C shows a closer view of pockmarks.

The Prairie du Chien Group is not noted for its non-stromatolitic fossils, although I have seen some snails in the Shakopee elsewhere. These blocks did not change that overall impression. There were a couple of cases of burrows or things that look very much like burrows, though.

A couple of examples of burrows or burrow-like features. A has a long feature from the lower left to near the center, plus other shorter similar features. B has what looks like a web of burrows.

Sunday, March 1, 2020

Stictoporellina cribrosa, saltine bryozoan

I've never put much emphasis on identifying bryozoans beyond their basic forms. There are, though, a few which are quite distinctive and worth differentiating. One that most fossil enthusiasts in Minnesota will be familiar with is the "gumdrop" or "Hershey kiss" Prasopora. Another notable example is Stictoporellina cribrosa, which can be identified as the "saltine" bryozoan if you don't mind extending the food comparison. S. cribrosa is the Decorah bryozoan known for broad thin colonies with perforations ("fenestrules").

As pictured here. If you enlarge it, you'll be able to more clearly see the tiny pores that were the living spaces of the bryozoan animals.

Sunday, February 23, 2020

Your Friends The Titanosaurs, part 21.5: Abdarainurus barsboldi

Abdarainurus barsboldi marks the first non-theropod dinosaur described in 2020. More importantly, it also represents an apparent titanosaur from part of the alphabet I've already covered, so I'm looping back to catch it, following the Baalsaurus mansillai precedent. It actually fits in well with last week's discussion of Opisthocoelicaudia skarzynskii, being another Mongolian sauropod with unusual caudal vertebrae, although in this case caudals (and some chevrons) are all that's there.