Lagerstätten!
/by Carol Hasenberg
Unidentified bird species from the Fossil Butte Member in southwestern Wyoming (Green River Shale), USA, Field Museum of Natural History, Chicago, Illinois, by Matt Mechtley from Tempe, Arizona.
Dr. William Orr, curator of the University of Oregon Condon Fossil Collection and frequent GSOC speaker, entertained and amused the GSOC crowd on Friday, May 13. He also provided an informative lecture about the prima donnas of the fossil world, those that come from lagerstätten. Lagerstätten is a German word meaning “storage places.”
In these sites, fossils are characterized by one or more of the following:
Outstanding preservation: mummies, frozen carcasses, fossils from tar pits, oil shales, or other anoxic media
Complete representation of the ecosystem: predators and prey, producers and consumers
Uninterrupted continuous fossil record: steady rapid sedimentation over eons of time.
A brief glimpse into a time where we have no fossils at all.
Orr has not had the privilege of working with such fossils very often; his work usually involves identifying “marker species” such as tiny foraminifera, which characterize particular times, depth, latitude, and other key features of geological strata.
La Brea Smilodon fatalis (saber tooth tiger) skull cast with jaws at maximum gape, photo by Bone Clones.
For his lecture Orr took us through a tour of lagerstätten, from the familiar to the remote. First stop was at the La Brea Tar Pits in California, which are 20-40 thousand years in age. Bill proclaimed that “petroleum is the best embalming fluid nature has devised.” At the La Brea Tar Pits, thousands of ice age creatures were trapped in the sticky tar and over time their skeletons were preserved in a jumble of bones due to the natural stirring of the tar. Bones taken from the site were often assembled into “chimera” skeletons which came from the bones of many animals.
Normally in geological strata, remains of herbivores far outnumber the carnivores due to the coincidence of the food pyramid biomass ratios with the preservation of the fossils. Not so here. Predators were attracted to other animals trapped in the tar, so the food pyramid became inverted at this site.
Arctodus simus (short faced bear) reconstruction, photo by Dantheman9758, June 26, 2007.
Amongst Orr’s favorite denizens of the tar are the following species:
Dire wolf, a “pony sized dog.”
Saber tooth "tiger" was really a “bobcat on steroids.”
Short faced Bear was a “super predator.” Could run fast and was very large.
Fossil of typical Ediacaran fossil Kimberella quadrata, photo by Aleksey Nagovitsyn, February 27, 2009.
Next stop on this tour of the world through time was from Southern Australia, the earliest known metazoans (multi-celled critters) dated 550 mybp from the Ediacaran Period. Scientists are hard pressed to classify these creatures that evolved into body types not represented by today’s species. Dickinsonia: Worm? Lichen? Spriggina: arthropod? Tribrachidium: three legged or triskelion-shaped animal. Mawsonites: jellyfish? They all have a quilted, i.e., segmented body types with hydrostatic inflation, similar to a water-filled mattress.
Fossil of freshwater stingray, Heliobatis radians, from Fossil-Lake, Kemmerer, Wyoming, is a Green River Shale fossil, photo by Didier Descouens.
Orr’s third example was the Green River Shale lagerstätte from Wyoming, Colorado, and Utah, dated 50 mybp. About a dozen sites of this oil shale produce fossils. The stratum occurs in flat uniform layers from an ancient Eocene lake. Green River Shales are varved, i.e., contain alternating winter and summer layers. Green River fossilized fish are very famous and found in many museum collections. It is presumed that schools of fish swam into anoxic layers of water and died suddenly. The finds include outstanding fossils of fish eating other fish that presumably choked and died. Freshwater stingrays are found in these sites, and other freshwater species, including turtles and crocodilians, lizards and snakes.
Green River Shales contain much more than fish fossils, and this lagerstätte produced fossils representing an entire ecosystem. The shales record the transition from a moist subtropical to drier temperate climate. Birds fossils are articulate with feathers. More land animal finds include a five toed horse, bats, and squirrels. Insects with colors patterns are preserved. Also included are flora from the era, which tells botanists a lot about the climate.
Fossil jewel beetle from Messel Pit, still showing color of the exoskeleton, photo by Torsten Wappler, Hessisches Landesmuseum Darmstadt.
The next lagerstätte on the tour was of a similar time range; the Messel Pit in Germany dated at 47 mybp is a maar crater filled with water. This outstanding site was mined for brown coal and oil shale in the nineteenth century, and then saved from being converted into a sanitary landfill in the twentieth. In 1995 it was designated as a UNESCO World Heritage site. Petroleum seeped into the bottom of the crater, preserving animals which died and fell in. The site is famous for its amazing preservation of articulated animal skeletons. Entrails were preserved as well as other soft tissue remains. Primates, horses, squirrels, frogs, gar, crocodiles and other reptiles were found, and some were preserved three dimensionally. Birds, bat, and insects fossils show color variations preserved.
The first complete Anomalocaris fossil found from the Burgess Shale, photo by Keith Schengili-Roberts.
Orr’s next example was the famous Burgess Shale in British Columbia, Canada. This lagerstätte contains fossils of the earliest known animals, dated to 508 mybp. The formation represented the base of a middle Cambrian reef and preserved remains of many animals, including soft tissue remains. Lace crab, trilobites, and other soft bodied forms were well preserved. One outstanding species was the super predator of its day, Anomalocaris. It grew to six feet long, and ate trilobites. This creature’s fossils were found in bits and pieces, thought to be separate species, until a complete fossil was discovered. Another outstanding fossil, Piakia, was the earliest known vertebrate.
Dr. Orr saved his favorite lagerstätte for last, and of course that is Oregon’s own John Day fossil beds. The John Day Fossil Formation is dated 50-5 mybp coming from a single basin, and comprised of shales and silts. Enormous quantities of volcanic ash kept this formation forming over such a long period of time. It is the “styrofoam popcorn of geological formations.” The biggest contributor of volcanic ash was the Crooked River caldera centered in Prineville. Also contributing were the nearby Wildcat Mountain and Tower Mountain Calderas, all of which have been recently toured by GSOC.
Orr reviewed his favorite animals from the formation, which captured the John Day ecosystem over time. The species Ekgmowechashala, named for the Sioux word “little cat” was a little lemur that looked like a man. Borophagus “the bone eater” was a scavenger that ate bones. Also Osteoborus, which was another bone eater. Entelodon was the “terminator pig”, a super predator. Another Orr favorite was a gopher the size of a tomcat - Epigalus the “gopher from hell.” “They should have used him on Caddyshack,” Orr joked.
