19 March 2016

Fossil Vertebrate(s) of the Month: Glyptodontinae

Glyptodon clavipes & other South American megafauna
Field Museum
It's an old adage that one of the joys of paleontology is that you never know what you're going to find in the field.  It could be something fantastically bizarre or gorgeous, or it could be something that changes our understanding of a group's evolution.  As paleontology itself evolves into a more analytical field, new and improved research methods lead mean that game-changing discoveries now happen in the lab at least as frequently as they do in the field.  A prime example of this is a subfamily of South American mammals known as the glyptodontines.  Were I writing this a month ago, I'd have referred to them as glyptodontids, members of their own distinct family related to, but distinct from, sloths, anteaters, and armadillos.  Glyptodonts are as far from a recently-discovered taxon as you can get, having been named in 1879 and even before that having been the subject of study by such luminaries as Darwin and Owen.  Likewise, they are anything but obscure, having long been the focus of both scientific and public attention, due in no small part to their size (the largest are often compared to VW Beetles), their massive shells composed of hexagonal plates (the size and bulkiness of which leading to relatively high rates of preservation and a very good fossil record), and their armored (and in some cases weaponized) tails.  And yet, there's still a lot we don't know about even such a seemingly well-understood group.  Until now, I've used glyptodonts as prime examples of convergence, evolving armor similar to that of armadillos despite being from a separate xenarthran lineage.  Last month, though, a study by Frederic Delsuc and colleagues showed that armadillos and glyptodonts are similar not due to convergence, but because they are very closely related.  In fact, using mitochondrial DNA recovered from a 12,000 year old specimen of the spike-tailed glyptodont Doedicurus, Delsuc et al. showed that not only do glyptodonts belong to the same order (Cingulata) as armadillos, they can actually be placed in the armadillo family Chlamyphoridae.  This family does not include armadillos of the genus Dasypus so familiar to Texans and Floridians, but it does include, among other species, the pink fairy armadillo and the giant armadillo (competitor and, sadly, early-round upset victim in March Mammal Madness).  That such a well-studied group can still surprise us as we develop new methods of study is not only a testament to the data-driven, non-dogmatic nature of science, but nicely illustrates why it's so much fun to study fossils: be it on the pampas of Argentina or in a genetics lab in Montpellier, you really never know what you're going to find.

25 December 2015

Fossils 'Neath the Tree

Of course, one of the joys of any advent calendar is the payoff at the end, so here's my gift to you: lots and lots of lagerstätten set to Tchaikovsky.  Note that I only used my photos, so not every site I highlighted is included and there's a strong emphasis on Neogene mammals.  Happy Holidays!

24 December 2015

24. Frozen Mummies of the Far North

Frozen Siberian Cave Lions Cubs
National Geographic
Location: Siberia, Russia & Alaska, USA
Age: Pleistocene

Over the last 24 days, we've seen lagerstätten preserved in many different ways, all of which have in some way helped tell the story of how climate change through the Cenozoic has affected life on land.  Today, to close out the advent calendar, we're ending with specimens that share not a particular locality but rather a particular environment of preservation, one that only exists because of the cold climate of the Pleistocene.  Original soft tissue - muscles, organs, skin, and hair - are not unheard of from the Pleistocene.  Mummies have been preserved in dry caves across the globe: moas in New Zealand, thylacines in Australia, ground sloths in Patagonia and the Mojave Desert.  Even more spectacular are those animals that have been frozen in the permafrost of the far reaches of the Northern Hemisphere.  Permafrost is the frozen soil that underlies the tundra of Siberia and Alaska and, if any organism is buried in either region's sediments before being significantly scavenged or decomposed, it can become preserved in the subsurface ice.  Melting during warmer periods or, more recently, mining brings these remains to light with surprising frequency.  Because they consist of original organic material, these permafrost mummies do not qualify as fossils by everyone's definition.  For those of us that do consider them to be a part of the fossil record, though, the Siberian and Alaskan permafrost constitute what has been referred to as "the ultimate lagerstätte." Frozen woolly rhinos have been unearthed, as have bison (see the University of Alaska's "Blue Babe" for a particularly well-known example), horses, and numerous other animals.  Very recently, a discovery of frozen Siberian cave lion cubs made major waves, but historically (and as with many sites profiled in the last week) the real stars of the show are mammoths.  In fact, a frozen woolly mammoth brought back to St. Petersburg at the end of the 18th Century was one of the first fossils of any type of organism to pique the interest of the general public.  Today, permafrost mummies are sources of hugely valuable information about life in the subarctic regions of the world during the Pleistocene (they have also, unfortunately, become lightning rods for creationists, who have frequently made the claim that the specimens show evidence for rapid freezing, allegedly falsifying gradualist explanations for the history of Earth and its life - I need hardly remark that such evidence is, in fact, nonexistent).  Organisms and ecosystems from the polar regions of the world are the first to feel the effects of climatic change, so the light that permafrost mummies can shed on how life has responded to periods of warming and cooling in the past could be invaluable for illuminating the future of modern subarctic organisms.

Visit: Permafrost is widespread (though increasingly rare) beneath the tundras of Alaska, Canada, and Russia.  However, as a subsurface feature, it's not something easily observed.  The best opportunity I know of for doing so is the Permafrost Tunnel Research Facility near Fairbanks.  As a research site, it's not generally open to the public, but the Army Corps of Engineers does lead occasional tours.
Fossils: In the continental US, your best bet is the American Museum of Natural History, home to both a frozen mammoth and a frozen squirrel, nicely demonstrating that it's not just megafauna that were frozen.  The University of Alaska Museum of the North has an especially important collection, including the aforementioned "Blue Babe."  My lack of Russian language skills makes verification of this difficult, but the two museums that have historically housed permafrost mummies in that country are St. Petersburg's Zoological Museum and Moscow's Paleontological Museum.
Is there a relevant book full of gorgeous fossil photos that I can gift to a paleontologically-minded friend?: Several!  Enough, in fact, that I'll simply leave it to you all to search for one that suits your interests rather than linking to any in particular.

This post is part of my 2015 Paleontology Advent Calendar, a series of vignettes on lagerstätten - sites of exceptional fossil preservation - that document changes in climate and environments through the Cenozoic.  You can see the other posts here.

23 December 2015

23. Tanque Loma

Reconstruction & Skeleton of Eremotherium at the Museo Paleontologico Megaterio
University of California Museum of Paleontology
Location: Santa Elena, Ecuador
Age: Pleistocene (24,000-17,000 years ago)

While the North American megafauna consisted of animals such as mammoths and mastodons, horses and tapirs, bears and dogs, and bison and camels - all of which would have been, to varying degrees, familiar in Pleistocene Asia, Europe, or Africa - the megafauna of South America had very different roots.  Until late in the Cenozoic, it had been the most isolated of island continents, populated by birds and mammals that had evolved there and that had no close relatives anywhere else in the world (as well as, bizarrely, monkeys and rodents that apparently rafted to the continent on storm-tossed vegetation).  However, as temperatures cooled and sea levels dropped (and, even more importantly, as the volcanic Isthmus of Panama began to form late in the Miocene), a land bridge formed that would connect the Americas.  Over millions of years and in several waves, animals migrated across Central America in both directions.  The effect this had on North America is attested to by the success of now-extinct ground sloths, glyptodonts, and "terror birds," as well as by the continued prosperity of armadillos, opossums, and porcupines, all taxa with origins south of Panama.  Several South American sites document the effect that the so-called American biotic interchange on native ecosystems.  One of the most-recently described is a site that has drawn comparisons to Rancho La Brea: the asphalt beds of Tanque Loma in coastal Ecuador.  This site contains remains of North American migrants: mastodonts, horses, and deer.  Contrary to the traditional narrative that northern invaders outcompeted their austral counterparts, Tanque Loma also preserves a rich array of South American taxa, notably giant ground sloths, the most iconic of the native megafauna.  Among these, the huge Eremotherium is particularly abundant, leading to the suggestion that it may have been a gregarious animal that congregated in the area.  Unlike Rancho La Brea, though, they were not trapped there, or at least not by asphalt.  Unusually, the asphalt at Tanque Loma seems to have infiltrated the local sediments well after the fossils were deposited, helping to preserve the bone bed, but not to form it.

Visit: I'm not certain what the preservation status of this site is, but I'm fairly certain it is not open for visitation.
Fossils: The Museo Paleontologico Megaterio on the campus of the Universidad Estatal Península de Santa Elena was constructed specifically to house specimens from Tanque Loma.
Is there a relevant book full of gorgeous fossil photos that I can gift to a paleontologically-minded friend?: No, probably in large part because of how recently described the site is, but if you want more information on it you can check out Emily Lindsey's descriptive paper.

This post is part of my 2015 Paleontology Advent Calendar, a series of vignettes on lagerstätten - sites of exceptional fossil preservation - that document changes in climate and environments through the Cenozoic.  You can see the other posts here.

22 December 2015

22. The Mammoth Site

The Mammoth Site
Location: South Dakota, USA
Age: Pleistocene (26,000 years ago)

The Waco Mammoth Site, profiled a couple of days ago, is a moment (or, to be precise, three moments) frozen in time.  Catastrophic events that entomb numerous animals simultaneously, as happened at Ashfall as well as at Waco, are one way to get a konzentrat lagerstätte.  Rancho La Brea illustrates the other way to generate a bone bed: have some kind of natural trap in which specimens build up over time.  This method is also nicely illustrated by a second mammoth-rich locality a few states north of Waco.  On the southern edge of the Black Hills, a sinkhole opened up roughly 26,000 years ago.  A lake formed in this sinkhole that served as a home to invertebrates and fish and as a pitfall trap to terrestrial organisms.  While these range from rodents to bears (including some of the best remains of the giant short-faced bear Arctodus ever found outside of Rancho La Brea), the majority of the animals preserved here are mammoths.  Delightfully to those of us who enjoy exposing the "everything's bigger in Texas" mantra for the lie it is, more than twice as many individuals have been uncovered from the South Dakota site, representing both Columbian and woolly mammoths.  As has been clearly established by the last couple of posts, Columbian mammoths are widespread across North America, but the presence of their cold-adapted relative in the Black Hills illustrates an important trend in Pleistocene climate.  While the "global hothouse" of the Eocene is a bit of an oversimplification (see the earlier posts on the Okanogan and Florissant), it is true that the difference in climate between the poles and the equator was smaller early in the Cenozoic than it is today.  However, the presence of a species usually associated with tundra and other cold environments - and its absence from a site less than a thousand miles to the south - demonstrates that the strong latitudinal gradients associated with temperature today were solidly in place by the Pleistocene (though with the caveat that, because it sits at a relatively high altitude, the Mammoth Site is not a perfect analog for lower-lying localities at the same latitude).  This increase in the difference in climate between more polar and more equatorial ecosystems may seem somewhat trivial, but it's long been suggested that this difference plays a major role in driving several ecological and evolutionary trends.  Not only was climate in the Pleistocene abnormally cold and variable, then, but life on land was affected by huge climatic extremes even within the confines of a single continent.  Lagerstätte such as the Mammoth Site and Rancho La Brea show how North American organisms and ecosystems responded to this new climatic regime, but things looked quite different one continent to the south.

Visit: If you live in the US, at some point in your life you'll make the requisite trip to Mt. Rushmore.  Spend as little time as possible there and head south to the sites that really should be headlining your Black Hills itinerary: Custer State Park, Wind Cave, and Hot Springs, where the Mammoth Site has been developed into an excellent on-site museum.
Fossils: Most of the mammoths from the Mammoth Site remain in situ, and anything that's been excavated has remained on-site at the museum.
Is there a relevant book full of gorgeous fossil photos that I can gift to a paleontologically-minded friend?: There is, published by the museum in Hot Springs, whose web site seems to be temporarily down, meaning I can't link to it.

This post is part of my 2015 Paleontology Advent Calendar, a series of vignettes on lagerstätten - sites of exceptional fossil preservation - that document changes in climate and environments through the Cenozoic.  You can see the other posts here.

21 December 2015

21. Rancho La Brea

Dire Wolf Skulls
Page Museum
Location: California, USA
Age: Pleistocene-Holocene (55,000 years ago-Recent)

Many Cenozoic lagerstätten have produced more fossils (Fossil Lake, for example) and many have higher quality of preservation (such as Messel), but none is as widely known as the "tar pits" of Rancho La Brea.  Part of the reason for this fame is likely the location of the site, on Wilshire Boulevard in the middle of Los Angeles.  Part of it is due to the unusual method of preservation, in which animals were trapped and eventually buried in asphalt seeps.  The bulk of La Brea's fame, though, is due to the fossils uncovered there, which include megafaunal mainstays - mammoths, sloths, camels, and horses - as well as rarer large mammals, such as tapirs, and a wide variety of small-bodied animals.  The most spectacular fossils from La Brea are its predators, which are found in huge numbers (in the thousands, in the case of especially common species).  Coyotes (originally described as their own species, Canis orcutti, sadly no longer recognized as distinct from the living C. latrans) and dire wolves are particularly abundant, as is Smilodon, the saber-toothed cat that has such wide appeal that it was designated California's state fossil.  Other big predators that show up at Rancho La Brea include the extinct American lion Panthera atrox, the scimitar-toothed cat Homotherium, and the giant short-faced bear Arctodus, as well as still-living predators such as cougars, timber wolves, and black bears.  It's not just mammalian predators that are abundant at the site: a wide variety of raptors have been found here in larger numbers that anywhere else, including familiar taxa such as hawks, eagles, and condors, but also the extinct Teratornis (which besides being impressive in and of itself, has a fantastic name that translates as "Monster Bird").  Why so many predators?  It's long been hypothesized that prey animals trapped in asphalt would have served as lures for carnivorous animals, many of which would have then become trapped themselves, providing ever more carrion to be had.  Recent research (including, at the risk of indulging in self-promotion, some of my own) has supported this hypothesis, further suggesting that the abundance of large and/or social predators at La Brea implies that animals particularly adept at defending carcasses from other scavengers were frequently preserved at the site.  This is just one example of how Rancho La Brea fossils have been used to reconstruct the biology of Pleistocene organisms.  Other long-standing areas of study have been whether or not Smilodon was social (a highly unusual trait among living cats) and, more relevant to the theme I've been following all month, how climate change through the Pleistocene and Holocene have affected the La Brea biota.

Visit: The LA area is home to several of the world's great museums, and even among that distinguished milieu, the George C. Page Museum of La Brea Discoveries in Hancock Park is a standout.  Besides the museum itself, several asphalt pools, excavation sites, and megafaunal statues are on view in the park.
Fossils: Almost every major natural history museum has a few Rancho La Brea specimens.  The Page Museum is the best spot to see them in the LA area, but several specimens are on display at its parent museum, the LA County Museum, as well.
Is there a relevant book full of gorgeous fossil photos that I can gift to a paleontologically-minded friend?: There is!

This post is part of my 2015 Paleontology Advent Calendar, a series of vignettes on lagerstätten - sites of exceptional fossil preservation - that document changes in climate and environments through the Cenozoic.  You can see the other posts here.

20 December 2015

20. Waco Mammoth

Columbian Mammoths from the Waco Mammoth Site
Larry D. Moore, Wikimedia
Location: Texas, USA
Age: Pleistocene (68,000-53,000 years ago)

Snowmass is known for its mastodons, proboscideans - members of the same order of mammals as elephants - that were early stars of the North American fossil record.  In time, though, their status in the popular imagination as iconic megafauna would be usurped by another type of proboscidean: mammoths.  Mammoths are much closer relatives of elephants (they are, in fact, more closely related to Asian elephants than are African elephants) and while the most famous of them is Mammuthus primigenius (the woolly mammoth), the most widespread species in North America is the Columbian mammoth, Mammuthus columbi.  They are well-represented at several sites across the continent and have figured prominently in the debate over whether human activity or climate change played a larger role in the extinction of megafauna at the close of the Pleistocene.  In at least one case, though, the death of several mammoths can be clearly attributed to natural causes.  In what is now Waco, Texas, a flash flood 68,000 years ago killed and buried a herd of Columbian mammoths, making the site, like Ashfall, a snapshot of a moment in time.  Unusually, many of the individuals at the Waco Mammoth Site are juveniles, leading to the suggestion that the group killed in the flood was a nursery herd.  Other layers at the site preserve younger, less fatal floods, that preserved more mammoths and, among other things, remains of another icon of the Ice Ages: the saber-toothed cat Smilodon.  As with all mammalian predators, Smilodon tends to be much less common than its prey at most localities, and were this true everywhere, it might remain a somewhat enigmatic animal.  Fortunately, just as the Waco Mammoth Site preserves huge concentrations of herbivores, other sites have done the same for the animals that preyed upon them.

Visit: This July, President Obama designated the Waco Mammoth Site a national monument, preserving the locality - and guaranteeing its visitability - in perpetuity.
Fossils: To the best of my knowledge, all of the fossils from Waco remain on-site.
Is there a relevant book full of gorgeous fossil photos that I can gift to a paleontologically-minded friend?: Not that I'm aware of.

This post is part of my 2015 Paleontology Advent Calendar, a series of vignettes on lagerstätten - sites of exceptional fossil preservation - that document changes in climate and environments through the Cenozoic.  You can see the other posts here.