Be Kind to Rocks Week

by Carl Strang

St. James Farm Forest Preserve has a scattering of stones, large and small, in its forests and open areas. Some of these are chunks of local Silurian dolomite bedrock that were gouged out by the most recent continental glacier. Others are glacial erratics, stones likewise left by the glacier but picked up by it where the bedrock was different. These generally source back to Canada. Though much of the glacier’s Lake Michigan Lobe route followed that lake bed, the bedrock there is a soft shale that the ice ground to clay, with occasional surviving pieces up to a couple inches across, but nothing that could be called a boulder.

Recently my eye was caught by a trailside erratic split by the temperature changes that the seasons bring.

This appears to be a rock type known as gneiss, which started out as granite but was subjected to stresses that altered its structure into a banded pattern. Such bedrock is common around the east end of Lake Superior, where our glacial lobe exited Canada.

This appears to be a rock type known as gneiss, which started out as granite but was subjected to stresses that altered its structure into a banded pattern. Such bedrock is common around the east end of Lake Superior, where our glacial lobe exited Canada.

There was no indication that the rock had been struck by anything to create the break. Freezing and thawing were sufficient. I photographed the rock and left it as is. A week later, passing that way again, I saw that someone had replaced the fragment.

Gravity works, and the pieces were fitted precisely, so a human agent is indicated.

Gravity works, and the pieces were fitted precisely, so a human agent is indicated.

So, what motivation are we tracking here? Was it simply a matter of orderliness? Or, did someone want to make sure that the fragment did not become someone’s souvenir? Or, was this putting-back-together an act of kindness to the rock? I am reminded of one of the most widespread traditional stories west of the Mississippi River, with every Native American tribe having at least one version, in which an animated rock teaches Coyote (or his trickster equivalent, depending on the version) a lesson of respect.

 

Exploring the Interior

by Carl Strang

Now that the leaves are down from the trees and shrubs, I have been exploring the areas between the forest trails at St. James Farm Forest Preserve. Those areas are large enough that I cannot cover the forest adequately from the trails. I have found deer runs and old equestrian paths that will provide sufficient access for routine monitoring. Along the way I have found some interesting places. One foggy day I zig-zagged my way through part of the western forest.

This area has been cleared of invasive honeysuckles and other shrubs. Part of it is young second growth with a few clearings where perennial herbaceous plants are growing.

This area has been cleared of invasive honeysuckles and other shrubs. Part of it is young second growth with a few clearings where perennial herbaceous plants are growing.

Elsewhere there are old trees, many of them red oaks.

Elsewhere there are old trees, many of them red oaks.

Among the occasional boulders was this outwash-rounded fossiliferous one.

Among the occasional boulders was this outwash-rounded fossiliferous one.

The chunk of local Silurian dolomite appears to have been a spot on the ocean floor, adjacent to a reef, where there was a crinoid colony.

The chunk of local Silurian dolomite appears to have been a spot on the ocean floor, adjacent to a reef, where there was a crinoid colony.

A morainal depression held a huge fallen red oak.

A morainal depression held a huge fallen red oak.

The tree had lost the grip of most of its roots in the soil.

The last roots that were holding the tree up still show the relatively fresh color where they fractured.

The last roots that were holding the tree up still show the relatively fresh color where they fractured.

The orientation of the trunk relative to those broken roots suggests that a very strong wind from the west was the culprit.

 The oak didn’t go down alone. Broken stems reveal the trees it took out on either side. The force of the fall split the oak’s stem lengthwise.

The oak didn’t go down alone. Broken stems reveal the trees it took out on either side. The force of the fall split the oak’s stem lengthwise.

Each day in this exploration has brought its own delights.

Here, a beautiful moss colony became established on an old burn scar.

Here, a beautiful moss colony became established on an old burn scar.

One day when I was the preserve’s only human visitor, I saw one of St. James Farm’s coyotes. The fat belly and good coat indicate that this animal is a successful hunter.

One day when I was the preserve’s only human visitor, I saw one of St. James Farm’s coyotes. The fat belly and good coat indicate that this animal is a successful hunter.

So now the stage is set for routine coverage of St. James Farm’s ongoing natural history story.

 

Literature Review: Pleistocene and Holocene

by Carl Strang

Today’s notes are from last year’s literature on the recent ice ages and subsequent prehistoric times. Some are biological in focus, others relevant to past and present climate change.

Coyotes once were bigger and more carnivorous than they are today, according to the following study.

Coyotes once were bigger and more carnivorous than they are today, according to the following study.

Meachen, J.A., A.C. Janowicz, J.E. Avery, and R.W. Sadleir. 2014. Ecological changes in coyotes (Canis latrans) in response to the ice age megafaunal extinctions. PLoS ONE 9(12): e116041. doi:10.1371/journal.pone.0116041 They measured coyote skulls from 29,000 years ago (La Brea tar pits) to present day, and found a transition from features associated with predation specialization to the present-day omnivory. Another study had found in addition a decrease in body size. They interpret this as a change in predator interactions. When the much larger dire wolf was the other dominant canid, and megafauna were abundant, coyotes could make a good living as specialist predators. Megafauna loss, and associated dire wolf extinction, opened the door for gray wolf immigration from Europe. This new, smaller predator was similar ecologically, but at the same time larger than the coyote, forcing a coyote niche shift to a more generalized diet.

Maher, K., and C.P. Chamberlain. 2014. Hydrologic regulation of chemical weathering and the geologic carbon cycle. Science 343:1502-1504. Kerr, Richard A. 2014. How Earth can cool without plunging into a deep freeze. Science 343:1189. The Kerr news article was based on the Maher and Chamberlain paper. The study looked at the mechanism that limits ice age cooling, preventing it from running away to a pole-to-pole glaciation. Volcanoes add carbon dioxide to the atmosphere, warming climate but also dissolving in rainwater, the resultant carbonic acid dissolving rock. The products flow to the sea, are taken up by plankton for skeleton building, and ultimately are buried. This removal process limits carbon dioxide buildup. Most of the dissolved rock is in mountains, and mountain uplift as in the Andes and Himalayas thus is tied to a global thermostat turndown. However, cooling slows the weathering reactions, allowing carbon dioxide to build back up.

Pena, Leopoldo D., and Steven L. Goldstein. 2014. Thermohaline circulation crisis and impacts during the mid-Pleistocene transition. Science 345:318-322. They found evidence for a profound change in oceanic circulation patterns corresponding to the change in glacial cycling from 41-thousand-year to 100-thousand-year durations. They conclude that “North Atlantic ice sheets reached a milestone in size and/or stability” that led to the ocean circulation change, resulting in a greater carbon dioxide drawdown, increased polar glaciation, and setting the pattern for the following 100,00-year cycles.

Guil-Guerrero, J.L., et al. 2014. The fat from frozen mammals reveals sources of essential fatty acids suitable for Paleolithic and Neolithic humans. PLoS ONE 9(1): e84480. doi:10.1371/journal.pone.0084480 They analyzed the fat chemistry of frozen woolly mammoths, horses and bison from Siberia. The fats were judged to be nutritionally good for human hunters of the time (41,000-4400 years ago). Furthermore, the fats of mammoths and horses were like those of hibernating mammals. The authors suggest that the mammoths and horses hibernated in similar fashion to present-day Yakutsk horses, which move little and mainly stand in sleeping positions during the coldest weather. The mammoth fatty acids suggest derivation from certain lichens in the diet.

Willerslev, Eske, et al. 2014. Fifty thousand years of Arctic vegetation and megafaunal diet. Nature 506 (7486): 47. DOI: 10.1038/nature12921 A large, multi-national team went into Pleistocene sediments and mummified gut contents, and used reference DNA from herbarium specimens to characterize vegetational changes over the past 50,000 years. They found that the last ice age caused a significant alteration of northern plant communities, greatly reducing forbs while increasing grasses and woody plants. Many of the megafauna herbivores such as woolly rhinoceros and woolly mammoth depended on the forbs for their protein content, and the authors believe that the failure of forb-rich communities to re-form after the ice receded contributed to or even caused megafaunal extinctions. No mention was made of human hunting in the ScienceDaily article describing the study.

Hoffecker, J. F., S. A. Elias, and D. H. O’Rourke. 2014. Out of Beringia? Science 343 (6174): 979. DOI: 10.1126/science.1250768 They reviewed cores taken from the Bering Sea and found that Beringia was not a barren grassland through the glacial times but had significant areas of tundra shrubs and trees. Animals including elk and moose likely lived there, and the likelihood of long-term human occupation seems good. This could provide a way that the ancestors of Native Americans could have been isolated from Asians for the 10,000 years, between 25,000 and 15,000 years ago, accounting for the genetic differences comparisons show. Beringia was not glaciated, and summers may well have been like those of today, though winters would have been severe. When the glaciers opened a way by melting, the 15,000-year Native American presence in the continent began as the Beringians moved in.

Literature Review: Paleozoic Era

by Carl Strang

The first animals which unambiguously connect to present day forms appear in the fossil record early in the Paleozoic Era, which began 542 million years ago, billions of years after the planet first formed. Here are some notes from studies of this era published in 2014.

American alligator. One of the following studies places the split between the reptilian crocodile-dinosaur-bird group and the lizard-snake group at the very end of the Paleozoic Era.

American alligator. One of the following studies places the split between the reptilian crocodile-dinosaur-bird group and the lizard-snake group at the very end of the Paleozoic Era.

Cong, Peiyun, et al. 2014. Brain structure resolves the segmental affinity of anomalocaridid appendages. Nature, DOI: 10.1038/nature13486 They studied the brain structure of Lyrarapax unguispinus, a fossilized relative of Anomalocaris, and found it was both simpler than those of its contemporary prey, and very similar to those of today’s onychophorans, or velvet worms, terrestrial southern hemisphere forest floor predators with unusual antennae that connect to the brain in the same way that the pair of grasping appendages connected to the brain of Lyrarapax. The similarities suggest a common ancestry.

Jourdan, F., et al. 2014. High-precision dating of the Kalkarindji large igneous province, Australia, and synchrony with the Early-Middle Cambrian (Stage 4-5) extinction. Geology 42 (6): 543. DOI: 10.1130/G35434.1 From a ScienceDaily article. The first major extinction event, which took out 50% of species in the Middle Cambrian, was caused by a mass volcanic eruption in Australia according to this study.

Morris, Simon Conway, and Jean-Bernard Caron. 2014. A primitive fish from the Cambrian of North America. Nature, DOI: 10.1038/nature13414 New Burgess shale fossils from the Cambrian of 505mya (million years ago) show detail in one of the earliest fishes, Metaspriggina, in which branchial arches are revealed as paired, with the first pair slightly thicker than the others (a step toward the first jaw). They had large eyes, and probably were good swimmers.

Shubin, Neil H., Edward B. Daeschler, and Farish A. Jenkins, Jr. 2014. Pelvic girdle and fin of Tiktaalik roseae. PNAS, DOI: 10.1073/pnas.1322559111 From a ScienceDaily article. They describe the anatomy of the rear part of this fish, previously known only from anterior portions. This animal was transitional toward terrestrial life, living in a delta environment where the ability to cross over land from stream to stream was advantageous. It was large, as much as 9 feet long, with large teeth making it somewhat reminiscent of a crocodile. It was lobe-finned, had a flexible neck, and rudimentary lungs. Its well-developed shoulder girdle previously was known, but it had been assumed that it crawled with only its front fins. The surprise was that the pelvic girdle also is developed, with a ball and socket joint and strong hind fins, so these fish had rudiments of four, rather than just two legs.

Ezcurra, M.D., T.M. Scheyer, and R.J. Butler. 2014. The origin and early evolution of Sauria: reassessing the Permian saurian fossil record and the timing of the crocodile-lizard divergence. PLoS ONE 9(2): e89165. doi:10.1371/journal.pone.0089165 They took a close look at Permian fossils in an attempt to resolve debate on when the split happened between the reptilian line leading to crocodiles, dinosaurs and birds on the one hand (archosauromorphs) and lizards and snakes on the other (lepidosauromorphs). They concluded that only the former have been found in the Permian, and place the earliest possible time for the split at 254.7 million years ago (very late Permian).

Literature Review: Proterozoic Eon

by Carl Strang

The Proterozoic Eon spanned the immense period of time from 2.5 billion to 542 million years ago. It has captured the imaginations of many researchers, because its rocks have teased them with clues that hint at amazing stories, such as the first eukaryotic life forms, a billion-year stall-out of life’s evolution, a globe-covering ice age (“snowball Earth”), and the first appearance of multicellular organisms, which may or may not be connected to those we have today. Here are my notes from last year on some studies of that eon.

There was no terrestrial life in the Proterozoic, but this was the time when the Chicago region’s crust joined the North American continent, appending itself to the southern boundary of the Canadian Shield.

There was no terrestrial life in the Proterozoic, but this was the time when the Chicago region’s crust joined the North American continent, appending itself to the southern boundary of the Canadian Shield.

Northwestern University. 2014. “Mysterious Midcontinent Rift is a geological hybrid.” ScienceDaily, <www.sciencedaily.com/releases/2014/10/141016132850.htm>. This article described a collaborative project, still unpublished, focusing on the mid-continent rift that left Lake Superior as its most visible feature. The rift was underway in the mid-Proterozoic when it filled with magma and stopped opening. More magma subsequently poured out on top of it, pushing the original body down and thickening the crust there. The feature thus combines rift characteristics with those of a large igneous province, and contains more volcanic rock than any other mid-continent rift on the planet. Incidentally the pieces of volcanic rock we find in local glacial drift came from that source.

Sánchez-Baracaldo, Patricia, Andy Ridgwell, and John A. Raven. 2014. A Neoproterozoic transition in the marine nitrogen cycle. Current Biology, DOI: 10.1016/j.cub.2014.01.041  From a ScienceDaily article. They used molecular clock estimation to place the appearance of nitrogen fixing by cyanobacteria at 800 million years ago. This may have removed the nutrient limitation that was holding life back, setting the stage for proliferation both of biomass and of evolutionary potential. However, this timing also is just before the Snowball Earth glaciation event, and the authors suspect that the algal bloom might have sequestered enough carbon to be a trigger for that event.

Hoyal Cuthill, Jennifer F., and Simon Conway Morris. 2014. Fractal branching organizations of Ediacaran rangeomorph fronds reveal a lost Proterozoic body plan. PNAS, DOI: 10.1073/pnas.1408542111  From a ScienceDaily article. They looked at the 3-dimensional structure of Ediacaran life forms (referred to as rangeomorphs), and found that their fractal designs efficiently filled the space around them. They argue that these were animals, living too deep in the sea for photosynthesis, which absorbed dissolved nutrients directly from the water. This was possible until predators, filter feeders and more mobile life forms rendered this subsistence style unsupportable.

Liu, Alex, et al. 2014. Haootia quadriformis n. gen., n. sp., interpreted as muscular Cnidarian impression from the Late Ediacaran period (approx. 560 Ma). Proceedings of the Royal Society B, DOI: 10.1098/rspb.2014.1202  From a ScienceDaily article. They described an Ediacaran fossil from Newfoundland, 560 million years old, concluding that it was a cnidarian with muscle tissue, the earliest animal with muscle.

Literature Review: Hadean and Archean Eons

by Carl Strang

Today’s post begins a series of weekly updates from last year’s literature on prehistoric life and the associated geology. In this one I include selected studies of our planet’s first two eons, covering the first 2 billion years (out of 4.6 total) of the Earth’s existence. The Hadean Eon is defined by the lack of surviving crust. It is known mainly from moon rocks, which along with certain deep-Earth data have told of a collision between the early Earth and a Mars-sized object named Theia. The moon was a product of that collision. The following Archean Eon brought the first-formed planetary crust, oceans, and the origin of life.

Hadean Eon

Arpita, Roy, et al. 2014. Earthshine on a young moon: explaining the lunar farside highlands. Astrophysical Journal Letters, DOI: 10.1088/2041-8205/788/2/L42 The far side of the moon has hardly any maria, unlike the familiar near side which has large areas covered by those ancient lava flows. This paper provides an explanation as to why the far side crust is so much thicker, so that meteor strikes did not so readily punch through. It is built on the collision that formed the moon. Both Earth and moon were much closer together at first, and the moon became tidally locked, so that the one side always faced the Earth. The heat of the Earth kept the near side hotter and molten longer, so that aluminum and calcium compounds cooled sooner and fell out more thickly on the far side, ultimately combining with silicates to form a thicker, feldspar-rich crust there.

Herwartz, D., A. Pack, B. Friedrichs, and A. Bischoff. 2014. Identification of the giant impactor Theia in lunar rocks. Science 344 (6188): 1146-1150. Data casting doubt on the Theia collision hypothesis were based on lunar rocks that had been contaminated through contact with Earth. New measurements taken from samples returned by NASA missions from the moon confirm that the proportion of Earth material in the moon is low enough to fit collision models.

Valley, John W., et al. 2014. Hadean age for a post-magma-ocean zircon confirmed by atom-probe tomography. Nature Geoscience, DOI: 10.1038/ngeo2075  They found zircon crystals in certain Australian rocks that formed 4.4 billion years ago, pushing back the earliest crust formation time and potentially permitting the formation of life earlier than had been thought. They suggest a hydrosphere may have existed as soon as 100 million years after the Theia collision.

Stromatolite fossil, Kakabeka Falls Provincial Park, Ontario. Stromatolites were colonial photosynthetic bacteria, responsible for the initial buildup of oxygen in the Archean atmosphere.

Stromatolite fossil, Kakabeka Falls Provincial Park, Ontario. Stromatolites were colonial photosynthetic bacteria, responsible for the initial buildup of oxygen in the Archean atmosphere.

Archean Eon

Russell, Michael J., et al. 2014. The drive to life on wet and icy worlds. Astrobiology 14 (4): 308. DOI: 10.1089/ast.2013.1110  From a ScienceDaily article. They are examining one way life could make a start, around alkaline thermal vents at the bottom of an otherwise acidic (carbon dioxide rich) ocean. “Life takes advantage of unbalanced states on the planet, which may have been the case billions of years ago at the alkaline hydrothermal vents,” said Russell. “Life is the process that resolves these disequilibria.” The article describes two possible geological analogs to processes that go on in mitochondria. One imbalance is in protons, or hydrogen ions, which would have been more concentrated on the outsides of vent chimneys. The other would be the gradient from the methane and hydrogen in the vent to carbon dioxide in the surrounding ocean, which could have produced an electron transfer. The mineral analogs to enzymes are thought to have been “green rust” (not further identified in the article; its participation could have stored energy from the proton imbalance in a phosphate-containing molecule) and molybdenum (known to transfer two electrons at a time in physiological processes). They point out that these are processes that could be common on other watery planets.

Martin, William F., Filipa L. Sousa, and Nick Lane. 2014. Energy at life’s origin. Science 344:1092-1093. They compare the energy-releasing chemical reactions common to living things and find them to be similar to those going on at alkaline hydrothermal vents, suggesting that such places were where life began.

Literature Review: Inside the Earth

by Carl Strang

Sea cliffs, Adak Island. Formations like this have inspired scientists to discover the dynamics of the Earth that produced them.

Sea cliffs, Adak Island. Formations like this have inspired scientists to discover the dynamics of the Earth that produced them.

Naif, S., K. Key, S. Constable, R. L. Evans. 2013. Melt-rich channel observed at the lithosphere–asthenosphere boundary. Nature  495 (7441): 356 DOI: 10.1038/nature11939  As described in a ScienceDaily article. They found a previously unknown layer of magma in the upper mantle which apparently is the lubricant for tectonic motion of crustal plates.

Livermore, P.W., R. Hollerbach and A. Jackson. 2013. Electromagnetically driven westward drift and inner-core superrotation in Earth’s core. PNAS, DOI: 10.1073/pnas.1307825110  From a ScienceDaily article. The solid iron inner core of the Earth, about the size of our moon, rotates to the east but at a faster speed than the planet as a whole. The outer core, also of iron but liquid, rotates slowly to the west. These dynamics result in the planet’s geomagnetic field, which itself rotates very slowly to the west. At the same time, the field produces the observed motions of the two parts of the core.

Kerr, Richard A. 2013. The deep Earth machine is coming together. Science 340:22-24. In this news review article, Kerr reports on progress geologists are making in understanding and mapping out details of the planet’s mantle. It is increasingly understood to be a complex mix of descending crustal slabs from plate boundaries, various masses of somewhat mysterious deep matter, and rising plumes from the deep mantle. This mapping is difficult and produces some contention over results, but consensus is growing. Plumes are recently accepted by many as existing, and accounting for a variety of phenomena including the Hawaiian Islands, the extraordinary eruption history of the Yellowstone area, Iceland’s volcanism, and the large volcanic traps eruptions involved in some of the massive species extinction events (most notably the end-Permian one). At present there are two very large “piles” of deep matter, one centering in the equatorial Pacific Ocean region, and one extending down the west coast of Africa and into the ocean to its south, with which are associated most of the active hot spots (mainly around their edges) and, in the African one, concentrations of diamond-bearing Kimberlites. The descending “curtains” of plate edges from subduction zones may be driving the movements and concentrations of different materials in various depths of the mantle. Heat from the core interacts with these materials in ways that remain to be determined.

Literature Review: Ice Ages and Climate

by Carl Strang

Today’s literature focus is on two studies from last year that increased our understanding of ice age dynamics and how our changes to the atmosphere may alter them.

Kokechik Bay, Alaska, late winter

Kokechik Bay, Alaska, late winter

Ballantyne, Ashley P., et al. 2013. The amplification of Arctic terrestrial surface temperatures by reduced sea-ice extent during the Pliocene. Palaeogeography, Palaeoclimatology, Palaeoecology, DOI: 10.1016/j.palaeo.2013.05.002  As described in a ScienceDaily article. Recent measures of carbon dioxide in the atmosphere have brought current levels into the range of the Pliocene, which was 3.5-9 degrees F warmer than today. A modeling study indicates that the difference may have been that the Arctic Ocean then was open year-round, a condition toward which we are trending now.

Kerr, Richard A. 2013. How to make a great ice age, again and again and again. Science 341:599. News article describing a study published in Nature that reports an advance in understanding the continental glacier cycle. That cycle corresponds to the 100,000-year stretching and shrinking of the Earth’s orbit around the sun, but that’s too weak to account for ice building and declining. The group led by Ayako Abe-Ouchi modeled in the 23,000-year wobble in the Earth’s spin axis, plus global climate modeling and data on northern ice sheets, which involve changing carbon dioxide levels and the mass of the ice. Simulated ice sheets expanded and contracted in close to the actual pattern. Ice gradually builds over the 100,000-year cycle, but then the 23,000-year cycle corresponds to the warming phase of the longer one, adding summer warmth. By then, crustal depression by the ice mass means that the ice is at a lower, warmer altitude (1 km of depression), and the glacier rapidly melts.

Literature Review: The Mesozoic Era

by Carl Strang

This week’s literature notes focus on selected papers from last year on the Mesozoic Era. These papers covered assorted topics; there were enough studies of early birds and feathered dinosaurs that I will treat them separately.

Some of this fellow’s relatives had cock’s comb-like head structures. See below.

Some of this fellow’s relatives had cock’s comb-like head structures. See below.

Jones, Marc EH, et al. 2013. Integration of molecules and new fossils supports a Triassic origin for Lepidosauria (lizards, snakes, and tuatara). BMC Evolutionary Biology 13 (1): 208 DOI: 10.1186/1471-2148-13-208  From a ScienceDaily article. Fossil jaws from the Middle Triassic show that reptiles representing the common ancestor of lizards, snakes and the tuatara were among the new groups to emerge in the wake of the end-Permian mass extinction.

Peter A. Hochuli and Susanne Feist-Burkhardt. 2013. Angiosperm-like pollen and Afropollis from the Middle Triassic (Anisian) of the Germanic Basin (Northern Switzerland). Frontiers in Plant Science, DOI: 10.3389/fpls.2013.00344  From a ScienceDaily article. This pollen, which appears to belong to an insect- (probably beetle-) pollinated plant, comes from a time 100 million years before the previous accepted evolution of flowering plants. It provides a fossil anchor for the earlier end of the range of molecular clock pointers from other studies.

Varricchio, David J., Frankie D. Jackson, Robert A. Jackson, Darla K. Zelenitsky. 2013. Porosity and water vapor conductance of two Troodon formosus eggs: an assessment of incubation strategy in a maniraptoran dinosaur. Paleobiology 39 (2): 278 DOI: 10.1666/11042  They found that this small carnivorous dinosaur incubated partly buried eggs, not burying them completely like crocodiles. This conclusion is drawn in part because of egg-in-nest fossils, and largely because the fossils’ relatively few, small eggshell pores that limit moisture loss are like those of incubated eggs and unlike buried ones.

Blackburn, Terrence J., et al. 2013. Zircon U-Pb Geochronology Links the End-Triassic Extinction with the Central Atlantic Magmatic Province. Science 340:941-945.  They have dated basalt samples around the edges of the Atlantic Ocean, looked at the rock just above and below those layers, and have connected the mass extinction that marked the end of the Triassic Period with a series of massive lava flows triggered by the rift that opened the Pangaea supercontinent and began to create the Atlantic Ocean as North America, South America and Africa split apart. They date the extinction at 201,564,000 years ago. The eruptions consisted of 2.5 million cubic miles of lava, in 4 major flows. Three of the flows occurred within 13,000 years, at the same time as the extinctions, which can be dated within 20,000 years at this point.

Bonnan, MF, et al. 2013. What lies beneath: sub-articular long bone shape scaling in eutherian mammals and saurischian dinosaurs suggests different locomotor adaptations for gigantism. PLoS ONE 8(10): e75216. doi:10.1371/journal.pone.0075216  Gigantic sizes were achieved more often in dinosaurs than in mammals. This study found that dinosaurs had relatively thick cartilage pads in load-bearing joints, making gigantism more frequently workable.

Bell, Phil R., Federico Fanti, Philip J. Currie, Victoria M. Arbour. 2013. A mummified duck-billed dinosaur with a soft-tissue cock’s comb. Current Biology DOI: 10.1016/j.cub.2013.11.008  From a ScienceDaily article. They describe a mummified fossil Edmontosaurus regalis with a previously unknowable soft-tissue “cock’s comb” structure on the top of its head.

Maiorino, L, A.A. Farke, T. Kotsakis, P. Piras. 2013. Is Torosaurus Triceratops? Geometric morphometric evidence of Late Maastrichtian ceratopsid dinosaurs. PLoS ONE 8(11): e81608. doi:10.1371/journal.pone.0081608  They did a comparative developmental study of fossils originally named Torosaurus and two species of Triceratops. Their measurements indicate different developmental trajectories for the two genera, and they reject the recent suggestion that Torosaurus is simply a more mature Triceratops.

A Tiny Dam

by Carl Strang

Back in April, a series of heavy rains resulted in some unusual flooding in DuPage County.

Water poured across the trail at Mayslake Forest Preserve.

Water poured across the trail at Mayslake Forest Preserve.

The swift waters had a scouring effect, and small streams county wide that previously had silt bottoms now were gravel bedded.

The stream at Mayslake was one example.

The stream at Mayslake was one example.

Now, more than 7 months later, the gravel continues to dominate wherever the water has continued to flow with any strength. It doesn’t take much to alter this, however. On a recent exploration of the lower part of Mayslake’s stream I found an elongate pool backed by a tiny dam.

The dam was formed by tree roots which captured a few sticks, with gaps filled by drifting leaves and other debris.

The dam was formed by tree roots which captured a few sticks, with gaps filled by drifting leaves and other debris.

Immediately below the dam, and above the pool, the stream remains gravel floored. In the pool, however, the gravel has become obscured by silt and organic detritus. This diversifies the ecology of the stream, as different invertebrates favor different substrates.

The pool above the dam

The pool above the dam

Little lessons in ecology, geology and change are always out there for us to discover and appreciate.

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