Belated Tree-following at Fossil Lake

A lake in southwest Wyoming, lined with palm trees!

This month there's little to report about the trees I'm following aside from a bit of green in the aspen canopy—emerging leaves I think (forgot binoculars). Instead I have news about a tree I tried to follow five years ago, a Wyoming palm. This was not an extreme cultivar able to survive -10º to -40 °F average annual minimum temperature but a native. However, Wyoming palms went extinct millions of years ago, and now exist only as fossils.

Powell Palm, Sabalites powellii, at the U. of Wyoming Geology Museum (also called Palmites sp.).

That year (2017) I had hoped to visit Fossil Butte National Monument in southwest Wyoming, where the palms used to grow. I would go after finishing a field project nearby. But a June blizzard intervened. Three weeks ago, there was another opportunity, on my return trip from the Great Paleozoic Sea, but again a blizzard threatened. This time I ignored it, for awhile.

Above, Fossil Butte National Monument in the high dry desert of southwest Wyoming (NPS, Tyra Olstad photo). Below, same general area 52 million years ago.

Lotus plants (Nelumbo sp.) in foreground; click to view dragonfly and mosquitos.

My first stop was the Visitor Center, small but packed with fossils and information. A ranger greeted me and offered a tour. "Absolutely!" I replied. "Can we start with plants?" I followed him to the Plant Wall. In addition to the familiar palm leaves, there was a palm inflorescence and many other plant fossils, with modern genera surprisingly (to me) well represented.

Plant Wall at Fossil Butte NM (NPS photo). Below left of the palm leaf on the right is a palm inflorescence.

Like today's palms, those at Fossil Lake had large inflorescences with hundreds of tiny flowers.

Fossilized palm inflorescence.

Fossilized palm flower (NPS photo), c. 8 mm across.

Fifty-two million years ago, in what would become southwest Wyoming and adjacent Utah and Colorado, there were three large lakes, larger even than our Great Lakes. These were Lake Gosiute, Lake Uinta, and Fossil Lake. The last was the smallest, but its sediments were especially rich in plant and animal remains. The now-lithified sediments of Fossil Lake are famous for abundant well-preserved fossils.

Petrified Fish Cut near Green River, Wyoming, excavated in 1868 during construction of the transcontinental railroad. William H. Jackson photo, 1869 (Hayden Survey) (source).

Fossil Lake's Knightia (the many small fish in this photo) is said to be the most common of vertebrate fossil in the world. It's also the state fossil of Wyoming (photo by Mike Nelson).

This ray fossil is an example of the exceptional preservation at Fossil Lake (NPS photo). As I learned on my visit, rays usually aren't well preserved because they have cartilage rather than true bones.

We finished the tour at a diorama showing southwest Wyoming 52 million years ago. Dioramas of ancient worlds have enchanted me since I saw my first, 60+ years ago. I've never outgrown them, though I now know there can be a fair amount of informed speculation involved.

The many diverse creatures and plants preserved in Fossil Lake sediments indicate the climate was warm and humid. Vegetation along the shoreline was lush, with forests of palm, cinnamon, maple, and oak inhabited by mammals small and large, including some of our ancestors.

Yikes! Is that a giant oreodont approaching upper left?

As we finished, I asked the ranger about his background. Just five days earlier he graduated from university in California, then drove for two days to Wyoming, and went to work the next day. He was eager to share the joy of visiting the distant past, and his enthusiasm was contagious. Lucky me!

Next I hiked the nature trail, past high desert cushion plants blooming profusely in light snow and howling wind. The blizzard was closing in. I decided to skip the old quarry, where I would have seen remnants of Wyoming palm habitat up close. That and much more await another visit. I raced home ahead of the storm, easy to do on Interstate 80 with a ferocious tailwind. Good mileage too.

Sources

Grande, L. 2013. The lost world of Fossil Lake. University of Chicago Press.

McGrew, PO, and Casilliano, M. 1975. The Geologic History of Fossil Butte National Monument and Fossil Basin. NPS Occasional Paper No. 3.

Tree-following: Wildlife

Sabalites in the hallway to the University of Wyoming Geology Museum.

We tree-followers have gathered once again to report on the status of our trees, the ones we’ve chosen for the year. Mine is a Sabalites palm tree that grew in southwest Wyoming 50 million years ago, and then went extinct. It must have been common around ancient Fossil Lake, and fairly close to shore, because many intact frond fossils have been found in lake sediments now turned to rock—the Green River Formation.

I won’t visit Sabalites in its native habitat until it's warm enough for an outdoor vacation, and our local Sabalites, on display in the Geology Museum, doesn’t change from month to month. So what to report? Sometimes tree-followers write about wildlife seen on or near their trees; this month I’ll do the same.

Knightia and Sabalites. Courtesy CSMS Geology Post.

My wildlife sighting was a school of Knightia, small herring-like fish. They were swimming around a large Sabalites frond that was floating in warm subtropical water near the lushly-vegetated shore of Fossil Lake. But wait … there’s something wrong with this idyllic scene. The fish weren’t swimming … they were dead!

Mass mortality slab, University of Wyoming Geology Museum.

How ironic that mass die-off was preserved in exquisite life-like detail! (NPS photo; click to view).

Fossil Lake occupied the southwest corner of Wyoming early in the Eocene Epoch.

Fossil Lake was the smallest of the large Eocene lakes of southwest Wyoming and adjacent states, yet it’s exceptional in terms of the number of Knightia fossils it left behind. In some “death layers” there are 100+ per square meter—over an area of tens of thousands of square meters! Millions of Knightia fossils have been excavated—it’s the most common fish fossil in the world! In 1987, it was designated the state fossil of Wyoming.

Most common vertebrate fossil or fish fossil? Both claims are out there.

The Fossil Butte Member of the Green River Formation includes many mass-mortality layers, representing multiple events scattered across thousands of years. Apparently die-offs were not rare catastrophes, but something that occasionally happened under specific conditions. But those conditions remain a mystery. Maybe fish were poisoned by cyanobacteria, or suffocated by super-blooms of algae, or killed by changes in water temperature or chemistry or both. Maybe Knightia was especially susceptible. Its modern-day relatives, the herring, are known to die off en masse in response to sudden environmental change. Fortunately herring recover quickly—one fish can lay 200,000 eggs at a shot! Maybe Knightia was equally fecund.

Knightia had more than environmental change to worry about. Given its abundance, it probably was the main food for predator fish, like Diplomystus dentatus below. This fossil is not from a mass mortality bed, so what killed it? “It most likely died from starvation or suffocation because it could not spit the Knightia out” (NPS).

Did Diplomystus' dinner do him in? (NPS photo; click to view the remarkable preservation).

For more tree-following news, check our virtual gathering. And consider joining us ... it's amazing what we learn when we follow trees. There's always something interesting, and never any pressure or obligation :-) Thanks to The Squirrelbasket for hosting!

Sources  (in addition to links in post)

Grande, L. 2013. The lost world of Fossil Lake. University of Chicago Press.

National Park Service. Geology Field Notes, Fossil Butte National Monument.

Virtual Museum of Geology. Green River Formation.

Northwest Nebraska during Peak Mammal

A Paleocastor walks into a phone booth … (already heard this one?)

Take Nebraska Highway 29 from Mitchell north to Harrison and you will drive through miles and miles of rolling grasslands beneath skies that seem to go on forever. You might see occasional cattle, or pronghorn antelope. Make the same trip twenty million years ago and you would drive for miles and miles through rolling savannas beneath skies that seem to go on forever but … instead of the occasional animal you’d see multitudes of mammalian creatures—some huge, some kind of familiar, others quite strange. This was northwest Nebraska during Peak Mammal, an American Serengeti.

Answer to recent geo-challenge: Agate Fossil Beds National Monument 20 million years ago (early Miocene). Diorama by Jay Matternes; source & source.

Prehistoric mammals have been largely upstaged by the dinosaurs with their over-the-top charisma. This is naive, and a real shame. After all, it was mammals that underwent “one of the most spectacular evolutionary radiations ever documented” (Prothero 2006). With the extinction of non-avian dinosaurs (birds are dinosaurs) 65 million years ago, small mammals came out of the shadows and begin to diversify—a diversification that accelerated into an explosion. We know of only only eight species of placental mammals from 65 million years ago, mostly tiny shrew-like creatures. But just ten million years later, there were on the order of 100 groups of species (genera), including all major orders in existence today—“from shrews and rodents to giant whales and flying bats” (Prothero 2006).

The best record of these exciting evolutionary times is contained in 60-million-years-worth of sediments eroded from the Rocky Mountains and carried east to form the Great Plains. A good amount of wind-borne volcanic ash from Utah and Nevada ended up in the mix, and lots of mammalian carcasses were buried.

Three major pulses of deposition created the Great Plains from Rocky Mountain debris. Source.

Then about 130 years ago, a man was visiting his sweetheart on the upper Niobrara River when he spotted a fossilized leg bone sticking out of a rock. James Cook soon married his sweetheart, bought the Agate Springs Ranch from his father-in-law, and continued to find bone fragments and curious inexplicable features.

A Devil’s corkscrew or daemonhelix.

Cook contacted paleontologist Olaf A. Peterson of the Carnegie Museum in Pittsburgh, Pennsylvania. Peterson visited the ranch in 1904, starting paleontological studies that have continued off and on to the present. The ranch (now a National Monument) turned out to be a key site in the amazing record of prehistoric life on the Great Plains. “The great bonebed at the Monument remains one of the most impressive and scientifically interesting paleontological sites in North America” (Graham 2009).

Entrance to Agate Fossil Beds National Monument in northwest Nebraska. NPS photo.

Why so many bones in one place? Paleontologists think that during an extended drought, thirsty starving dying animals gathered at the muddy remains of waterholes. Carcasses accumulated, were torn apart by scavengers, and trampled by the still-living. Then the river flowed again, burying dismembered skeletons in sediment. Eventually the sand, silt, volcanic ash, and bones became rock. When the Niobrara River carved its valley, it exposed bone-filled sandstone and siltstone.

Bone slab from Carnegie Hill—part of a diorama in the Visitor Center.

University Hill in the distance, so-named because the University of Nebraska had a fossil quarry there.

Even though Agate Fossil Beds National Monument is a key site for the best record of one of the most spectacular evolutionary radiations ever documented, visitation is light. I met only one person on the trails, the Artist-in-Residence. It was a cool calm spring day, brilliant in the sunshine. I walked through rolling grasslands beneath blue sky that seemed to go on forever. Sometimes I could just make out a ghostly multitude of mammalian creatures—some huge, some kind of familiar, others quite strange—chalicotheres, rhinoceroses, entelodonts, beardogs, … oh my!

Devil’s corkscrews turned out to be fossilized burrows of the dry-land beaver, Paleocastor.

Tracks of ancient mammals in ashy lime mud, dog tail for scale.

Rhinos were really common. Diceratherium niobrarense on left, and the smaller Menoceras.

The dreaded beardog, Daphoenodon, was the largest carnivore in the area, about the size of today's wolf. It was neither a bear nor a dog, but a member of the extinct family Amphicyonidae.

Scavenger Dinohyus, the “terrible pig." It was not a pig but an entelodont. Some stood six feet tall at the shoulder, about the size of a male American bison (our “buffalo”).

Dinohyus today.

In the distance, a herd of Morupus approaches the muddy remains of a water hole, filled with carcasses and bones. Moropus was a chalicothere, an extinct group related to horses and rhinos.

Three chalicotheres stand in air-conditioned comfort.

A beardog, two entelodonts, and three chalicotheres meet at the waterhole … (you supply the punchline).

Sources (in addition to links in post)

The beautiful scenes and portraits of Miocene fauna come from the Monument’s trail signs and Visitor Center.

Graham, J. 2009. Agate Fossil Beds National Monument Geologic Resources Inventory Report. Natural Resource Report NPS/NRPC/GRD/NRR—2009/080. National Park Service, Denver, Colorado. PDF here.

Maher, HD, Jr., Egelmann, GF, and Shuster, RD. 2003. Roadside geology of Nebraska. Mountain Press Publishing Company.

Prothero, DR. 2006. After the Dinosaurs, the Age of Mammals. Indiana University Press.

Trimble, DE. 1980. The geologic story of the Great Plains. U.S. Geological Survey Bulletin 1493. Available online.

Geo-challenge in Space and Time

The American Serengeti. Where are we ... and when?

Be forewarned, happy scavenger—good times never last.

The rolling land is covered in grass, for as far as the eye can see. Hackberry trees, tall grasses and lush forbs line the streams … usually. But not now. Instead, there are hordes of thirsty starving animals. Predators feast upon easy prey, but soon they die too, as do the scavengers—all victims of a terrible drought. Yet it was because of climate change that they lived at all.

The bones pile up, are buried in sediment, become encased in rock. Then a cattle rancher finds some sticking out of a hillside, leading to a remarkable fossil quarry with millions of well-preserved bones. The animals rise again, to dwell in air-conditioned comfort.

“The valleys … although largely uninhabitable, are full of interest to the geologist. Located along these rivers is one of those grand cemeteries of extinct animals which have excited the wonder of intelligent men all over the world.” — Ferdinand Vandeveer Hayden, 1871

Where on Google Earth?

The Record Keeper

Several weeks ago I posted a geo-challenge, What do these deposits have in common?, with photos of four diverse accumulations of organic matter:  a mass of amber-like gunk containing stems and seeds, a pile of leaves and twigs, more amber-ish gunk plastered on the wall of a rock crevice, and sticks and pieces of cow manure in a rock cavity.

And the answer is (~fanfare~) ... this guy (or one like him).

Each was deposited by a packrat (Neotoma sp.), also called woodrat.  Above, bushy-tailed woodrat at Chaco Canyon, New Mexico.  Courtesy USGS and NOAA.

Packrats are not true (Old World) rats, as are the infamous rats of urban ecosystems (Rattus rattus and R. norvegicus).  Rather they are members of the Cricetidae family, along with other New World mice and rats, for example deer mice, voles, lemmings and muskrats.  Packrats weigh in at 100-600 g (i.e. up to a pound), and have long tails, prominent ears and eyes, and strong feet for climbing trees and rocks (and rafters in the attic).  Twenty-one species inhabit North America, from Canada close to the Arctic Circle south to Nicaragua.  They live in diverse habitats -- boreal forests, tropical forests, chaparral, lava fields, alpine tundra, deserts of various kinds, and the nooks and crannies of human habitation.

In all environments, packrats depend on moist plant matter for both food and water, and so spend a lot of time foraging.  They have a strong propensity to collect non-food items as well, hence their name.  Collectibles in the mind of a packrat include plant fragments, bones, dung and a wide variety of "interesting" items, especially anything shiny.

Packrat den with nest found under outdoor grill.  Note pieces of aluminum foil.

Source, Mr. Pack Rat (control).

It’s the packrat’s curious house-building that is of interest to us.  They construct dens in various styles, depending on the species, utilizing structures and materials available in their particular habitat.  For example in the chaparral of coastal California, the dusky-footed woodrat (Neotoma fuscipes) builds large mound-like dens of leaves, twigs and other debris (photo below) that provide protection from rain and predators, and insulation against temperature extremes.  Inside, the den is subdivided into chambers, including one for a nest, several pantries, and one on the periphery or just outside that serves as an outhouse and garbage dump -- a midden.  As we'll see shortly, some packrat middens are of great interest to humans.

Below, a dusky-footed woodrat den at the base of a sprawling coastal live oak, Montaña de Oro State Park, California.  For an entertaining tour of dusky-footed woodrat dens, including interior shots, see Living in the Sticks at nature of a man.

In areas with rock outcrops, packrats take advantage of natural structures and construct dens in crevices and cavities, requiring less effort and resources.  Plant fragments, bones and the usual collectibles are added.  Large mammal dung is popular in some places.

A packrat lined this rock cavity with sticks and pieces of cowpies (the Honeycombs in western Utah).

The middens of rock-outcrop-dwelling packrats, especially in arid environments, are the ones we value most.  Some are spectacular.  Protected from the elements deep in a crevice or cavity, large masses of packrat debris can accumulate, cemented together with highly-concentrated urine to form a hard, durable amber-like material called amberat (or occasionally "ratite").  In such a situation a packrat’s refuse pile may remain undisturbed for thousands of years, growing with each generation of residents.  The giant midden below is at least 28,000 years old (orange notebook is 7” x 4”).  Courtesy USGS.

Lovely golden amberat covers a crevice wall in volcanic tuff; Hickison Summit, central Nevada.

As you can see above, amberat can be beautiful ... and maybe even appealing:

"we came to a high cliff and in its face were niches or cavities as large as a barrel or larger, and in some of them, we found balls of a glistening substance looking like pieces of variegated candy stuck together ... It was evidently food of some sort, and we found it sweet but sickish, and those who were hungry ... making a good meal of it, were a little troubled with nausea afterwards" (party of Gold Rush miners headed for California in 1849, from Betancourt et al. 1990, p 3).

Amberat may be a terrible food substitute, but it’s invaluable nonetheless, for it contains a record kept by all packrats that ever lived in the den.  Plant fragments are well-preserved in amberat, and can be identified even after many thousands of years (photo below).  In the dry environs common in the American West, middens are a major source of evidence for reconstructing past vegetation and environments, from the Pleistocene (last glacial advance) through the Holocene (post-glacial time through the present).  Some middens have been found dating to at least 40,000 years before present.

A mummified 12,500-year-old snakeweed flower from a packrat midden is easy to identify.  Source.

Fossil middens, with the collections of many many many generations of packrats from prehistoric times to the present, allow us to look back on the vegetation of yesteryear and the way it has changed over time.  The Colorado Plateau is especially amenable to such paleoecological reconstruction.  In the arid environs of the Plateau, many fossil middens have been preserved.  The Plateau also is an area of high topographic relief, where vegetation can shift up and down in elevation in response to climatic change.  Vegetation and climate change from glacial times to the present have received a lot of attention.

Diagram courtesy USGS and NOAA (click on illustration for larger view).

During the last glacial period, boreal and montane forests were common on the Colorado Plateau.  Now these trees are restricted to montane sites, having moved up in elevation as much as 3000 feet (diagram above).  In other cases, plants responded by shifting their distribution along a north-south gradient.  For example, the piñon-juniper woodlands that are so common on the Colorado Plateau today were absent during the last glacial period, when they grew much further south.  They invaded northward as the climate warmed.

Modern-day piñon-juniper woodland; San Rafael Swell in central Utah. 

Interpreting a packrat’s record requires caution and a good understanding of the critter itself.  Though a great collector, a packrat’s foraging range is limited to within 30-100 m of its den.  And they can be picky, especially those that are dietary specialists.  For example, Stephen’s woodrat eats little aside from juniper, while a bushy-tailed woodrat living in the same area will have a much more diverse diet.  All packrats prefer moist plant parts (at least 50%  water by weight) as food is pretty much their only source of water.

Thus a packrat’s tastes distort the relationship between the record kept in its midden and the surrounding vegetation.  While middens may reveal some of the plant species that grew in the area, we can’t easily conclude that there weren’t others as well, even some that were common.  Perhaps the packrat just wasn’t interested (which seems to be the case for grasses, for example).

The bushy-tailed woodrat (Neotoma cinerea) is not a picky eater, and so its midden is a better indicator of the surrounding vegetation.  Photo courtesy MT Fish, Wildlife & Parks.

The abundance of a given plant species in a midden does not necessarily reflect its abundance in the surrounding area.  Trees are especially prone to over-representation because it’s not uncommon for trees to grow adjacent to rock outcrops in areas otherwise tree-less (more water, shade available).

Another confounding factor is change-in-ownership.  One can’t assume that the same species of packrat has occupied a den for thousands of years, especially if the climate changed during that time.  Indeed, some investigators found that when they removed a packrat from a den and a different species moved in, the new midden deposits changed noticeably ... due to change in packrat tastes rather than in the surrounding vegetation.

In spite of these complications, middens continue to be valuable indicators of paleovegetation, especially when multiple middens are used, and in conjunction with pollen data.  Fossil middens and fossil pollen provide complementary information.  Plant fragments from middens generally can be identified to species, but represent just the vegetation close to the den.  Pollen records come from larger areas, but most source plants can’t be identified beyond genus or even family.

The Pleistocene - Holocene transition is the most popular focus of midden study, but recent changes in vegetation also have been clarified using records kept by packrats, for example the contentious topic of whether juniper invasion has been facilitated by recent livestock grazing and fire suppression.  In the Pacific Northwest, midden data from lava tubes, combined with pollen analyses, indicate this trend is related to post-glacial warming, having begun long before humans, cattle and sheep arrived (Mehringer and Wigand, in Betancourt et al. 1990).

Piñon-juniper woodland possibly invading sagebrush.  For more detail, see Utah's Rangelands.

Cole et al. (1997) used midden data to look at historical changes in high-desert vegetation in Capitol Reef National Park.  Presettlement middens consistently contained a suite of palatable (to livestock) plant species that are now absent or greatly reduced, for example winterfat and Indian ricegrass.  Unpalatable species now present, such as snakeweed and Russian thistle, were not found in middens older than 200 years.  The authors concluded that “the most severe vegetation changes of the last 5400 years occurred during the past 200 years”, i.e. with introduction of livestock grazing.

Known packrat midden sites in western North America; last updated 05/20/2013; courtesy USGS.

Packrat middens are so common in the deserts of the American West that it seems all one has to do to find one is peek into enough crevices and cavities.  They are worth seeking out.  Amberat is distinctive and curious, and even beautiful in some cases.  If you're lucky, a midden will be close enough to the ground to examine its contents.

Stems and seeds preserved in amberat in a crevice in the Sevier River Formation, southern Utah.

Attentive readers will remember that amberat is not edible.  However there are claims (mainly by vendors) that it possesses healing properties due to “a unique complex of bioactive substances” (of course!).  But before you start scraping amberat off rock walls and ledges, you might want to read this recent post at The Eekosphere.

The beloved Eek.  Photo by T. Walsh, 2013; from The Eekosphere.

P.S.  While I was putting together this post, I happily stumbled upon The Eekosphere, a great blog about Eek, a dusky-footed woodrat (packrat) whose best friend is Scribble, a Norwegian rat.  No, this is not a children's book ... it's a true story! ... and highly-recommended.

Sources (in addition to links in post).

Betancourt, J.L., Van Devender, T.R., and Martin, P.S.  1990.  Packrat middens.  The last 40,000 years of biotic change.  Tucson:  Univ AZ Press.

Cole, K.L., Henderson, N., and Shafer, D.S.  1997.  Holocene vegetation and historic grazing impacts at Capitol Reef National Park reconstructed using packrat middens.  Great Basin Naturalist 57:315-326.

US Geological Survey in cooperation with Northern Arizona University.  2008.  Prehistoric Packrats Piled Up Clues to Climate Change (PDF).

USGS and NOAA.  Paleo Slide Set: Packrat Middens: Vegetation & Climate Variability in the Southwestern United States.  Last modified 12 October 2001.