Aside from the rule of thumb that dinosaur posts attract more hits than non-dinosaur posts, I can't say that I can really predict what people will end up reading. I threw together "When ammonites got bored" at the last minute, knowing I was going on a trip, and it did surprisingly well. "An unfortunate snake" came together in about an hour, unpremeditated (inspired by a conversation with the other Science Museum prep lab volunteers the Tuesday before). I figured readership would be very light due to the holidays, but if I buy the in-house Blogger stats, it's the most-viewed new post since March, and perhaps earlier (for several months in late 2016 and early 2017, there was this weird thing going on where Blogger was counting 30 spurious hits every three hours). Meanwhile, I put a lot of time into "The News in Hadrosaur Dietary Paleobiology" and "Borealopelta", and the reactions were unspectacular compared to other dinosaur posts. Go figure.
Saturday, December 30, 2017
Saturday, December 23, 2017
An unfortunate snake
There's a lot of stress this time of year. It's also a time when people are often nostalgic about their childhoods. So, to relieve a little stress and appeal to your inner eight-year-old's sense of humor, I present a few paragraphs about an unfortunate fossil snake.
Sunday, December 17, 2017
Decorah crinoids revisited
Here in the Land of 10 Billion Crinoid Columnals, it's nice to be reminded that we do occasionally find a little more of the beast. I touched on the background of the metro crinoids in the crinoid post a couple of years ago. To quickly summarize: for whatever reason the paleontologists of the Minnesota Geological and Natural History Survey did not include echinoderms in the great monograph summarizing their work, although there were clearly plans to describe some crinoids, and Edward Oscar Ulrich did get to describe Cremacrinus punctatus; Frederick Sardeson described portions of the crinoid fauna in the first few decades of the 20th century; and the whole shebang was done up by Brower and Veinus in 1978. Their work was based around the University of Minnesota collections, largely collected by Sardeson. In his several decades of collecting, he amassed about 50 crinoid crowns and cups and several thousand plates (Brower and Veinus 1978), so if you're wondering why you haven't found any, it's because he got them all first. Here are a few highlights of the collection.
Sunday, December 10, 2017
Platteville moss
Sometimes it's hard to remember, but the early Paleozoic wasn't a complete water world. We've seen a bit of that up in Taylors Falls, where the sea surrounded basaltic islands during the late Cambrian. A less obvious example is at the contact of the Shakopee Formation and St. Peter Sandstone, which represents a few million years of exposure and erosion between marine cycles. The unusual thickness of the Decorah Shale in the Twin Cities has been interpreted as a result of nearby landmasses supplying sediment (the Transcontinental Arch, running northeast–southwest through the state). Land in the early Paleozoic gets a rap as an uninhabited wasteland (in fact, absence of land plants is sometimes put forward as one of the conditions necessary for the great sand sheets of the Cambrian into the Ordovician), and it's not like we have a lot of big showy fossils to dispute this perception. There are some hints, though.
Our oldest records of actual multicellular land plants are dominated by spores, which is not too surprising given that spores stand a much better chance of preservation than your typical terrestrial non-vascular plant (mosses, liverworts, etc.). These show that plants were colonizing the land by at least ~470 Ma, about the time of the Shakopee–St. Peter hiatus, and that vascular plants were around by the end of the Ordovician. It's been thought that these first land plants were not major influences on their environment, lacking roots and such, but modern mosses are no slouches at chemical weathering, and weathering from early plants may be implicated in Ordovician glacial cycles (quite a bit of debate there; see for example Lenton et al. 2012, Quirk et al. 2015, Porada et al. 2016). Early plants also appear to have given atmospheric oxygen the last kick toward the modern level, from the Ordovician into the Early Devonian, by causing more carbon burial (Lenton et al. 2016).
If plants were abundant enough to do these things, we ought to be able to find some body fossils to go with their spores. Where to look? In a recent study, Cardona-Correa et al. (2016) went to our old friend the Platteville, focusing on an outcrop in Dane County, southern Wisconsin. The formation and location were chosen for specific reasons. First, the Platteville was chosen because of the presence of fungal microfossils in the slightly younger Guttenburg Formation (roughly equivalent to the lower Decorah of the Twin Cities) (Redecker et al. 2000). These fungal microfossils appear to represent glomalean fungi, which are often symbiotic with plants today. The location is about 50 km (30 mi) from the ancient Baraboo Range, which was probably somewhat more imposing 455 million years ago when it was one of the few terrestrial areas in the region. That "terrestrial" bit is the important part, because the closer to shore, the more likely you could get transported plant remains.
Cardona-Correa et al. dissolved about 13 lb (6 kg) of rock in hydrochloric acid to retrieve organic microfossils. Among the foraminifera (basically "amoebas with shells") and acritarchs (a true "wastebasket" of organic microfossils that defy further classification) were a handful, fewer than 20, of multicellular fragments. Most of these fragments were polygonal arrays of cells in sheets, with a few flattened cylinders of cells. Cardona-Correa et al. compared these to the leaves and stems of peat moss, respectively (recognizing that moss leaves and stems aren't quite the same as the leaves and stems of vascular plants). If correct, not only do these fossils help to put a "face" to the early spore-producers, as well as confirm the general timing of plant groups diverging from each other as estimated through molecular clocks, but they are also evidence for very early peatlands.
These aren't the kind of fossils you're liable to stumble across, unless you too have access to facilities for treating samples as well as a good microscope and a lot of patience (13 pounds of rock for <20 fragments on the order of a few hundred microns across), but if they can be found once, it should only be a matter of time and effort to find more.
References
Cardona-Correa, C., M. J. Piotrowski, J. J. Knack, R. E. Kodner, D. H. Geary, and L. E. Graham. 2016. Peat moss–like vegetative remains from Ordovician carbonates. International Journal of Plant Sciences 177(6):523–538.
Lenton, T. M., M. Crouch, M. Johnson, N. Pires, and L. Dolan. 2012. First plants cooled the Ordovician. Nature Geoscience 5:86–89.
Lenton, T. M., T. W.Dahl, S. J. Daines, B. J. W. Mills, K. Ozaki, M. R. Saltzman, and P. Porada. 2016. Earliest land plants created modern levels of atmospheric oxygen. Proceedings of the National Academy of Sciences of the United States of America 113(35):9704–9709.
Porada, P., T. M. Lenton, A. Pohl, B. Weber, L. Mander, Y. Donnadieu, C. Beer, U. Pöschl, and A. Kleidon. 2016. High potential for weathering and climate effects of non-vascular vegetation in the Late Ordovician. Nature Communications 7, article 12113. doi:10.1038/ncomms12113.
Quirk, J. J. R. Leake, D. A. Johnson, L. L. Taylor, L. Saccone, and D. J. Beerling. 2015. Constraining the role of early land plants in Palaeozoic weathering and global cooling. Proceedings of the Royal Society B 282(1813):20151115. doi
Redecker, D., R. Kodner, and L. E. Graham. 2000. Glomalean fungi from the Ordovician. Science 289(5486):1920–1921.
Our oldest records of actual multicellular land plants are dominated by spores, which is not too surprising given that spores stand a much better chance of preservation than your typical terrestrial non-vascular plant (mosses, liverworts, etc.). These show that plants were colonizing the land by at least ~470 Ma, about the time of the Shakopee–St. Peter hiatus, and that vascular plants were around by the end of the Ordovician. It's been thought that these first land plants were not major influences on their environment, lacking roots and such, but modern mosses are no slouches at chemical weathering, and weathering from early plants may be implicated in Ordovician glacial cycles (quite a bit of debate there; see for example Lenton et al. 2012, Quirk et al. 2015, Porada et al. 2016). Early plants also appear to have given atmospheric oxygen the last kick toward the modern level, from the Ordovician into the Early Devonian, by causing more carbon burial (Lenton et al. 2016).
If plants were abundant enough to do these things, we ought to be able to find some body fossils to go with their spores. Where to look? In a recent study, Cardona-Correa et al. (2016) went to our old friend the Platteville, focusing on an outcrop in Dane County, southern Wisconsin. The formation and location were chosen for specific reasons. First, the Platteville was chosen because of the presence of fungal microfossils in the slightly younger Guttenburg Formation (roughly equivalent to the lower Decorah of the Twin Cities) (Redecker et al. 2000). These fungal microfossils appear to represent glomalean fungi, which are often symbiotic with plants today. The location is about 50 km (30 mi) from the ancient Baraboo Range, which was probably somewhat more imposing 455 million years ago when it was one of the few terrestrial areas in the region. That "terrestrial" bit is the important part, because the closer to shore, the more likely you could get transported plant remains.
Cardona-Correa et al. dissolved about 13 lb (6 kg) of rock in hydrochloric acid to retrieve organic microfossils. Among the foraminifera (basically "amoebas with shells") and acritarchs (a true "wastebasket" of organic microfossils that defy further classification) were a handful, fewer than 20, of multicellular fragments. Most of these fragments were polygonal arrays of cells in sheets, with a few flattened cylinders of cells. Cardona-Correa et al. compared these to the leaves and stems of peat moss, respectively (recognizing that moss leaves and stems aren't quite the same as the leaves and stems of vascular plants). If correct, not only do these fossils help to put a "face" to the early spore-producers, as well as confirm the general timing of plant groups diverging from each other as estimated through molecular clocks, but they are also evidence for very early peatlands.
These aren't the kind of fossils you're liable to stumble across, unless you too have access to facilities for treating samples as well as a good microscope and a lot of patience (13 pounds of rock for <20 fragments on the order of a few hundred microns across), but if they can be found once, it should only be a matter of time and effort to find more.
References
Cardona-Correa, C., M. J. Piotrowski, J. J. Knack, R. E. Kodner, D. H. Geary, and L. E. Graham. 2016. Peat moss–like vegetative remains from Ordovician carbonates. International Journal of Plant Sciences 177(6):523–538.
Lenton, T. M., M. Crouch, M. Johnson, N. Pires, and L. Dolan. 2012. First plants cooled the Ordovician. Nature Geoscience 5:86–89.
Lenton, T. M., T. W.Dahl, S. J. Daines, B. J. W. Mills, K. Ozaki, M. R. Saltzman, and P. Porada. 2016. Earliest land plants created modern levels of atmospheric oxygen. Proceedings of the National Academy of Sciences of the United States of America 113(35):9704–9709.
Porada, P., T. M. Lenton, A. Pohl, B. Weber, L. Mander, Y. Donnadieu, C. Beer, U. Pöschl, and A. Kleidon. 2016. High potential for weathering and climate effects of non-vascular vegetation in the Late Ordovician. Nature Communications 7, article 12113. doi:10.1038/ncomms12113.
Quirk, J. J. R. Leake, D. A. Johnson, L. L. Taylor, L. Saccone, and D. J. Beerling. 2015. Constraining the role of early land plants in Palaeozoic weathering and global cooling. Proceedings of the Royal Society B 282(1813):20151115. doi
Redecker, D., R. Kodner, and L. E. Graham. 2000. Glomalean fungi from the Ordovician. Science 289(5486):1920–1921.
Sunday, December 3, 2017
The News in Hadrosaur Dietary Paleobiology
I don't follow dinosaurs quite as avidly as I once did, but one topic I've kept an eye on is the paleobiology of hadrosaurs. If you're looking to work on paleobiology in dinosaurs, hadrosaurs are pretty much ideal. Many species are known from good remains of numerous individuals of various ages, giving about the best sample sizes you can get for nonavian dinosaurs. In addition, with all the bells and whistles like crests, soft tissue impressions, and the unique feeding adaptations, there's plenty of room for arguments. I've picked a few recent papers, focusing on feeding: what they ate and how they ate it.
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| Edmontosaurus at the Denver Museum of Nature and Science wonders how you get by with just two sets of teeth. |
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