The Arctic Cretaceous revisited

One of the earliest posts here, way back in March 2014, was about an assemblage of high-Arctic Late Cretaceous coprolites that had been part of my graduate work. We did quite a bit with them (Chin et al. 2008), but there's always more that can be discovered. One of the things Chin et al. (2008) noticed was the rarity of body fossils for large potential coprolite producers. They broached the idea that the producers were only around part of the time, living elsewhere during the polar winter and only turning up to feed during the long sunny summer days. Duffy et al. (2026) takes this idea and runs with it.

You may recall that back in 2014 we discussed two major categories of coprolites, those with a dominantly greensand composition and those with a dominantly phosphatic composition. The greensand coprolites had various kinds of inclusions, including crustacean carapaces, bivalves, and squid hard bits* and such (interestingly without evidence of processing by teeth), suggesting consumers that were bottom-feeders, whereas the phosphatic coprolites were loaded with planktonic microfossils, suggesting filter feeding (or feeding on soft-bodied filter feeders) (Chin et al. 2008). The division is nuanced a bit more this time around, with an intermediate group with greensand embedded in phosphate. At the time, we could easily see that the phosphatic coprolites had spiral structures, as in shark excrement. As it turns out, at least some greensand coprolites also have internal tubular structures, although usually not as easy to spot (Duffy et al. 2026). What that means is that most of the coprolite producers therefore had spiral intestinal valves like sharks.

*I had the hardest time figuring out those squid-pen bits when I was working with the fossils. I thought they might be horseshoe crab tails.

There is one group that fits quite well for producing the whole range of coprolites while also not producing abundant body fossils: sturgeons. Sturgeons have spiral valves. The adults don't have teeth to shed, so they aren't leaving hundreds of potential fossils, and they aren't crushing or cutting prey. Rather, they are bottom-feeders that suck in prey items (and sediment). They are also big enough to produce the size range of greensand coprolites. Meanwhile, young sturgeons have small teeth (but they lose them), and they feed on zooplankton. Finally, there are sturgeons today that migrate from marine water to estuaries or shallow marine settings to feed on seasonal food blooms before spawning in freshwater (Duffy et al. 2026). They're about as perfect of "poopetrators"** as we could ask for.

**I still regret nothing! 

It's the migration part that particularly interested Duffy et al. Most behaviors are pretty darn difficult to fossilize clearly; or, if you want to get philosophical about it, all behaviors are reflected somewhere in anatomy, but most of them produce effects that are too subtle to pick out or are swamped by the effects of other behaviors. We can look for evidence for migration in certain large land animals such as mammoths by studying stable isotopes in bones. These animals were big enough to travel long distances (and thus drink water in places with different isotopic signatures, for example) and had nice big bones that allow sampling for time sequences. The Devon Island situation is not quite so convenient, but a few lines of evidence are suggestive (Duffy et al. 2026):

1. The microfossils in the coprolites suggest plankton blooms during long polar summer days, which is a pretty common high-latitude pattern; make hay when the sun shines, after all. Blooms of one kind of organism attracts populations of other organisms to consume them. This is a pretty simple way to establish a migratory pattern. (The flip side is that everything would clear out during the polar winter. Think of an Old West boom town, except for having annual booms and busts.) This is the strongest line of evidence in my mind.
2. There are lots of coprolites and not much skeletal evidence for what made them. This is interpreted as evidence for producers that only lived there part of the time. I think this is a bit weaker, as there are always going to be more turds than bodies, but it's worth noting.
3. Sturgeons, as likely producers for some large percentage of the coprolites, are known to be migratory today, and anatomically haven't changed much since the Late Cretaceous.
4. Finally, many of the vertebrates inhabiting the Western Interior Seaway and neighboring areas have distributions that are pretty darn cosmopolitan in this region, consistent with migratory patterns. Like the second point, I don't think this is as strong as the first, but again it's worth noting.

All in all, I like it, and I think it's great to learn new tricks from old turds. You never know what will turn up once you start looking at these humble fossils!

References

Chin, K., J. Bloch, A. Sweet, J.Tweet, J. Eberle, S. Cumbaa, J. Witkowski, and D. Harwood. 2008. Life in a temperate Polar sea: a unique taphonomic window on the structure of a Late Cretaceous Arctic marine ecosystem. Proceedings of the Royal Society B 275(1652): 2675–2685. doi: 10.1098/rspb.2008.0801.

Duffy, F., K. Chin, S. Cumbaa, and L. Wilson. 2026. Coprolite evidence for marine vertebrate migration in the warm Cretaceous Arctic. Historical Biology. doi: 10.1080/08912963.2026.2670771.

Journey Somewhat Nearer to the Center of the Earth: fossils in cores

Most of the time, when people are looking for fossils, they find them at the surface or just below. However, this is hardly the limit of where they can be found. After all, a fossiliferous formation found at the surface in one location may be buried hundreds to thousands of feet beneath other rocks and sediments somewhere else, and it doesn't stop being fossiliferous just because it's buried that far down. It just becomes much less accessible. We can get glimpses of the buried fossils through core samples.

The Lives of the Strophs

As mentioned a few years ago, strophomenid brachiopods must have had a different lifestyle than your typical brachiopod. With no pedicle to attach to anything, they would have been loose on the seafloor. Their strongly concave-convex shell anatomy seem likely to have been inconvenient in several ways. If you place them convex-up, the opening between the valves is liable to be in the sediment, which doesn't help a filter-feeder. If you place them concave-up, the shell is liable to be flipped over if it is not partially sunk into the sediment, and even if it's clear, the narrow gape would make the intake prone to fouling. Clearly, though, they must have been doing something right, at least for a few million years in the Late Ordovician if the rocks in the Twin Cities have anything to say about it.

A stroph in the Magnolia Member of the Platteville. See, I can always find ways to use even more photos from Uŋčí Makhá Park!

A new publication by Dattilo et al. (2024) offers a lifestyle reconstruction of the stroph Rafinesquina that may resolve these issues: in brief, rather than a narrow valve gape, these brachiopods may have lived with their valves wide-open.

Perhaps like this, as restored by Kyle Hartshorn for Figure 15, not unlike some modern brachiopods. CC BY 4.0.

Dattilo et al. present several lines of evidence leading to the conclusions that Rafinesquina had a typical gape around 45 degrees and could potentially open wider. The major area of focus was the anatomy of the hinge, including both the hard structures and the inferred musculature. The assembly, as it turns out, is rather more complex than one might suspect just looking at Stroph #46893 in a random Platteville surface. (It's also rather more complex than can be explained in a couple of sentences, so fortunately there is the paper to refer to.)

Although to be fair, Stroph #46893 has its charms.

The possibility of widely gaped strophs leads to some other potential implications. For instance, once the ability to make a respectable gape is admitted, there is also the possibility for mobility. A stroph buried by sediment could have used valve clapping to escape. (And if we're doing that, why not a bit of clap-swimming, like modern scallops?) Clapping is also a great way to quickly clear sediment from the feeding organs, and we may have evidence of this in the form of "moats" around some stroph fossils. A natural wide gape also helps explain how stroph internal anatomy worked: a stroph with a narrow gape has a cramped area for its lophophore to function in, while a stroph with a wide gape doesn't have to worry about this as much, as long as there's enough space to stow the lophophore when the valves are closed. Finally, a wide gape does not settle the concave-up or convex-up question, as the brachiopod can function in either mode. Dattilo et al. suggest that convex-up is more stable and protective for the stroph's soft parts.

References

Dattilo, B. F., R. L. Freeman, K. Hartshorn, D. Peterman, A. Morse, D. L. Meyer, L. G. Dougan, and J. W. Hagadorn. 2024. Paradox lost: wide gape in the Ordovician brachiopod Rafinesquina explains how unattached filter-feeding strophomenoids thrived on muddy substrates. Palaeontology 67(2): e12697. doi:https://doi.org/10.1111/pala.12697.

Regarding forams

Life started out microscopic (at least to humans) and most of it has stayed that way. Of course, many microscopic organisms have poor fossil records, due to factors like lack of hard parts and the whole "microscopic" thing (finding and studying microfossils takes special equipment and expertise that aren't used for collecting, say, brachiopods). However, a subset of microscopic organisms have very significant fossil records. We saw the ostracodes a few years ago, but there are also a number of groups of single-celled organisms that produce hard parts suitable for fossilization. Among the most important are: coccolithophores, phytoplankton which form skeletons of scale-like objects known as coccoliths, micron-scale structures that make up chalk (and which are sometimes called nannofossils because they're so darn small); diatoms, phytoplankton with cell walls made of silica; dinoflagellates, which form organic-walled cysts; radiolarians, protozoans that form body structures of silica; and the subjects of today's entry, the foraminifera, which can be described glibly as "amoebas with shells".

A living foram, the brackish-water benthic calcareous species Ammonia tepida, showing strands of pseudopodia surrounding the coiled test. What do all these terms mean? Read on! (Photo from Wikimedia Commons; unfortunately, no scale, but you'll get an idea of the size of what we're dealing with in the photos to come.)

Subsurface paleontology of Lafayette Square and the Washington Monument

Washington, D.C. is not generally ranked in the first order of fossiliferous areas. It can hardly be considered a bust, though. The "Middle" Cretaceous Potomac Group (due to a tragic geologic oversight, there is no formal Middle Cretaceous) has been reasonably kind for plants; see Fontaine (1889, 1896), Knowlton (1889), Ward (1895), Ward et al. (1905), and Sinnott and Bartlett (1916) for some of the gory details. Something you may notice from that list is that all of those publications are at least a century old. The obvious problem is that Washington is a city first and foremost, so it's not like there are a lot of outcrops for prospecting any more. The Potomac Group has also produced some scrappy dinosaur remains, and anywhere that the Potomac River once flowed is liable to have cobbles with Skolithos tubes, eroded from Cambrian rocks up in the mountains. The classic Potomac Skolithos cobbles are rounded pieces of orangeish quartzite with simple vertical Skolithos burrows, similar to skinny pencils and with a tendency to stand out from the host rock. Washington is also blessed with a profusion of fossiliferous building stone, particularly the inevitable "Indiana Limestone" (Salem Limestone). But I digress. In a city, we cannot come to the outcrop, so the outcrop must come to us. This is where subsurface explorations come in handy. We talked about taking cores from lake sediments a few weeks ago. The subsurface of Washington, like any major city, has been picked at innumerable times, uncovering fossils from places such as just north of the White House and near the Washington Monument.

Kirchner Marsh and the use of lake sediments

As we've seen from time to time with packrat middens, there are many ways of looking at past ecological conditions. A common method in more humid environments that the deserts and mountains of the Southwest is studying lake deposits, which is quite well-suited to the Land of 10,000 Lakes. Many types of paleoecologically useful fossils can be extracted from lake sediments, ranging from diatoms ("algae" with silica cell walls), to spores and pollen, to mollusks, to ostracodes, to the jaw parts of certain midge larvae. (There are, of course, other kinds of fossils that can be found in lakes, but they aren't as commonly used for paleoecological work. A single mammoth, while certainly of great interest, is not as versatile for this kind of thing as innumerable pollen grains spread over thousands of years.) Spores and pollen are part of a group of fossils known as palynomorphs, organic-walled microfossils. There are several other types of palynomorphs, including various cysts and so forth, but for the purposes of upper Pleistocene and Holocene lake sediments in Minnesota, spores and pollen are clearly the stars of the show.

Mammoth roundup

A couple of new publications concerning mammoths in National Park Service units have crossed my desk recently, so it seemed like a good opportunity to say a few further words on behalf of extinct proboscideans in the National Parks. I present to you first the finely wrought map below, which shows the various parks where body fossils of mammoths, mastodons, and their friends have been reported. At press time, there were 37 parks, monuments, and so forth with confirmed records, and another six with possible records (cases where the locality is not clear). This map has the novelty of differently colored and shaped symbols, which aside from providing a splash of color, show a preponderance of mastodons in the northeast and mammoths in the southwest. I've relied on the literature and such, so there's definitely the chance that some of the "mammoths" are mastodons, and vice-versa. Most of these records are from the Pleistocene, but there are a few that are older; notably, John Day Fossil Beds National Monument and Niobrara National Scenic River have both gomphotheres and mastodons of pre-Pleistocene age. The great majority of the mammoth reports in the lower 48 are likely Columbian mammoths, Mammuthus columbi (M. exilis of Channel Islands National Park being a notable exception), but given the ambiguities in North American mammoth taxonomy, I figured it wasn't worth the time to try to split them up.

I use the base map a lot, don't I? Definitely a "click to embiggen" this time, to enjoy the various colored symbols. Inventory of points: 1) Nez Perce National Historical Park, multiple states; 2) John Day Fossil Beds National Monument, Oregon; 3) Hagerman Fossil Beds National Monument, Idaho; 4) Lava Beds National Monument, California; 5) Golden Gate National Recreation Area, California; 6) Death Valley National Park, California–Nevada; 7) Tule Springs Fossil Beds National Monument, Nevada; 8) Lake Mead National Recreation Area, Arizona–Nevada; 9) Mojave National Preserve, California; 10) Channel Islands National Park, California; 11) Santa Monica Mountains National Recreation Area, California; 12) Joshua Tree National Park, California; 13) Noatak National Preserve, Alaska; 14) Kobuk Valley National Park, Alaska; 15) Bering Land Bridge National Preserve, Alaska; 16) Denali National Park and Preserve, Alaska; 17) Yukon-Charley Rivers National Preserve; 18) Arches National Park, Utah; 19) Glen Canyon National Recreation Area, Arizona–Utah; 20) Grand Canyon National Park, Arizona; 21) Wupatki National Monument, Arizona; 22) Colorado National Monument, Colorado; 23) Florissant Fossil Beds National Monument, Colorado; 24) Great Sand Dunes National Park and Preserve, Colorado; 25) Bent's Old Fort National Historic Site, Colorado; 26) Salinas Pueblo Missions National Monument, New Mexico; 27) White Sands National Monument, New Mexico; 28) Lake Meredith National Recreation Area, Texas; 29) Big Bend National Park, Texas; 30) Amistad National Recreation Area, Texas; 31) Waco Mammoth National Monument, Texas; 32) Padre Island National Seashore, Texas; 33) Big Thicket National Preserve, Texas; 34) Buffalo National River, Arkansas; 35) Vicksburg National Military Park, Louisiana–Mississippi; 36) Niobrara National Scenic River, Nebraska; 37) Mississippi National River and Recreation Area, Minnesota; 38) Mammoth Cave National Park, Kentucky; 39) Potomac Heritage National Scenic Trail, multiple states; 40) Valley Forge National Historical Park, Pennsylvania; 41) New Jersey Pinelands National Reserve (affiliated), New Jersey; 42) Fort McHenry National Monument and Historic Shrine, Maryland; 43) Colonial National Historical Park, Virginia.

A tale of two packrat species

This is Neotoma cinerea, the bushy-tailed packrat:

From Oregon Caves via Wikimedia Commons.

Welcome Waco Mammoth National Monument

July 10, 2015 saw the addition of a new National Park Service unit, Waco Mammoth National Monument. It's the second recent NPS unit to be established for Pleistocene fossils, after Tule Springs Fossil Beds National Monument, and has been a long time germinating. I'll probably have a more detailed post within a few weeks, but here's a quick introduction. 

Quaternary paleontology at Channel Islands NP and Mammoth Cave NP

Here's a couple of quick entries on paleontological research going on in the National Parks. In this case, both examples are Quaternary. It's another case of serendipity: I was looking for the first article, and found the second article in the same volume. Neither Channel Islands National Park or Mammoth Cave National Park are slouches paleontologically, but they do get overshadowed. Places like Big Bend National Park, John Day Fossil Beds National Park, and Petrified Forest National Park get a paper or two every year, so it's nice to shine a light on some of the others.

Tule Springs Fossil Beds National Monument

I'm sorry about the gap there. I was traveling for work in the Southwest, and was unable to take the time to write anything. Here, though, is a piece about one of the places I saw, albeit briefly: one of the newest National Monuments, Tule Springs Fossil Beds National Monument. This site, north of Las Vegas, was declared in December 2014. It is noted for its abundant Pleistocene fossils, the depth of knowledge concerning its geologic and climatologic history, and historically notable investigations. Having just been established, there are no official National Park Service facilities quite yet.

Looking out across part of the southern end of the monument, facing north-northeast.

Packrat middens across (parts of) America: update to Tweet et al. 2012

A personal indulgence, but then what isn't with a blog? If you've got your copy of Tweet et al. (2012) handy, you'll see that the body of the paper describes 33 National Park Service units where there has been some reference to packrat middens. Two more were added in proof, and didn't get onto the map. I now have references for packrat middens in five additional NPS units, which will be described below, along with new information for one of the units added in press (City of Rocks National Preserve) and an updated map. There's nothing particularly earth-shaking, mostly anecdotal reports, but there's another geographic outlier in Glacier National Park (which can probably use all the climate proxies it can get). In further good news, the USGS/NOAA packrat midden database can once again be accessed, at http://geochange.er.usgs.gov/midden/.

On the Arctic Cretaceous

By now, those of you who follow paleontology news have probably heard of Nanuqsaurus hoglundi, the newly described genus and species of small Arctic tyrannosaur. The obligatory and nearly instantaneously produced Wikipedia article can be found here, and the scientific description can be found here. Nanuqsaurus comes from rocks of the North Slope of Alaska, and lived about 70 million years ago. It's just the "tip of the iceberg", so to speak, of the North Slope dinosaurs, which also include the hornless horned dinosaur Pachyrhinosaurus perotorum, a bonehead named Alaskacephale, the ubiquitous duckbill Edmontosaurus, and various small theropods. This is pretty typical for the latest Cretaceous of North America, give or take an armored dinosaur.

A road where the buffalo roamed

Personally, I don't have fond thoughts of I-35E. In my mind, it is indelibly associated with long back-ups at the interchange with I-94 in St. Paul, particularly I-94 eastbound in the evening rush hour. But enough of complaints; if the interstate could think and speak, doubtless it wouldn't be happy with traffic jams either. I-35E happens to run in an old river valley north of I-94. The drainage was known as Trout Brook, and it gradually disappeared from the surface between about the 1880s and the 1950s (an overview of the valley can be found here).

A brief meditation on the joys of packrat middens

One more trip to the Quaternary, for a personal favorite...

Imagine someone has asked you to describe what an area was like hundreds, thousands, perhaps tens of thousands of years ago. They're interested in the ecology, the climate, and so forth. What could you use to accomplish this? If there are lakes and marshes, you might start by taking sediment cores and looking for pollen, which tell you what kinds of plants were present, and how the flora changed over time. If you're on the coast, you might look for deposits of shells, which are useful for describing the conditions of the water (salinity, temperature, how energetic the setting was) and for stable isotope analyses. If there's a lot of ancient wood, you might get into tree-ring data. In dry protected places of western North America, there is another type of paleoecological indicator: middens constructed by packrats.