#lagerstatte

What were those bird-dinosaurs up to /j

It’s not as rare as you’d think, but yeah it’s rare. And things can go wrong

[Image: A sea star, beautifully preserved in pyrite, all five limbs spread out, showing the soft tissue which joins the arms together, prepared out of mid grey slate.]

Fossil flower

The exceptional preservation of this Eocene (56-34 million years ago) flower is due to the fine grained nature of the limestone in which it was entombed. The specimen comes from the Green River Formation covering parts of the North American Midwest towards the end of the uplift of the Rocky Mountains. The formation was deposited in the intermontane basins between the chains of growing peaks, and includes a mixture of terrestrial swamp and river sediments and deep lake sequences, which were surrounded by swampy areas with a profusion of warm climate plants. The formation is world famous for its fossil freshwater fish and the formation dates from between 53.5 and 48.5 million years ago.

Some of these plants turned into coal seams, while the spring algal blooms in the lakes produced oil shales in the anoxic lake bottom oozes. Some of the lake sediments are varved, with fine laminations that record seasonal changes between organic rich dark sediments from the short mountainous growing season and thin layers of light coloured sediment deposited in winter from suspended particles in the lake water. The best preserved fossils are found in these varved oozes, which are made of very fine grained limy mud. The fossils are well dated due to layers of volcanic ash interleaved in the sediments that were erupted from the nearby Yellowstone caldera and San Juan volcanic field. The area is designated as a Lagerstatte, a German word used to denote an area of rock with exceptional or important fossils.

Loz

Image credit: NPS

http://geology.com/articles/green-river-fossils/[_

Just over a hundred years ago, in 1909, the noted American palaeontologist Charles Doolittle Walcott discovered something strange in the Canadian Rockies. Ghostly imprints were etched into the rock, faintly delineating the twisted filaments of legs or antennae. A myriad of ancient organisms, five hundred million years old, were pressed between the layers of shale, their soft tissues intricately preserved. In many ways, Walcott had hit the palaeontological jackpot, as the fossil beds in what became known as the Burgess Shale formation contained some of the oldest, most diverse and best-preserved fossils known at the time. Soft tissue preservation was unprecedented in rocks of this immense age, and the Burgess Shale allowed scientists to examine an ancient ecosystem almost as it would have appeared when the animals were alive. The fossils were numerous and bizarre; along with the ones shown in the photos, Marella and Canadia (trilobite and annelid worm ancestors respectively) stranger forms were found, such as Opabinia, with a cluster of five eyes and a proboscis, and Hallucigenia, with a double row of long spines down its back. Derek Briggs and Simon Conway Morris, later to become famous as influential writers and theorists, concluded that a lot of the species in the Burgess shale had no modern descendants, and represented ancient groups - phyla - unknown from any other period in time. Based on these findings, the evoluntionary biologist Steven Jay Gould wrote a famous book (Wonderful Life) postulating that the animals had been failed evolutionary 'experiments' which died out as more well-adapted forms emerged.

Study of the site has been ongoing into the present day, and a better understanding of the species has led to the evolutionary experiment hypothesis to be largely abandoned, as many of them have now been fitted into existing groups. In 2014, a new Burgess Shale outcrop was announced: by the time the find went public, at least fifty species had already been found, and species new to science are still being discovered.

-TJT

Solnhofen Plattenkalk - rare and beautiful.

For large parts of the Jurassic about 155 million years ago, areas of western Europe were covered by warm, shallow seas. Associated with these is one of the most valuable fossil sites known on Earth. The Solnhofen Plattenkalk or Solnhofen Limestone in Bavaria, Germany, is a Late Jurassic ‘Konservat- Largerstätte’ that preserves a rare and unique assemblage of fossil biota.

During the Late Jurassic the area occupied by the Solnhofen Plattenkalk was an archipelago at the edge of the Tethys Ocean. Extensive coral and sponge reef systems created numerous protected lagoons with limited recharge from the open ocean. As salinity in the lagoons rose high enough for the resulting brine to be toxic to life and since the deepest waters were anoxic, many ordinary scavengers were absent. In this environment of soft, fine sediments the remains of animals living around the lagoons are exceptionally well preserved.

The fossil assemblages are highly diverse, with jellyfish, worms, ammonites, bivalves, prawns, shrimp, lobsters, barnacles, crinoids, echinoids and fish all preserved. Horseshoe crab fossils are also preserved and often found at the distal end of their own tracks, formed as they walked to their demise.

Although there is great diversity from the marine species there is also an abundance of terrestrial life preserved. Fossils of insects, plants, small dinosaurs, lizards, crocodilians, and pterosaurs are all found. The fossils from the Solnhofen Plattenkalk are not numerous, but they are exceptional, including delicate dragonfly wings and over 600 identifiable species of dinosaur. This Konservat-Largerstätte gives an unprecedented view of a complete Jurassic ecosystem.

Does anyone have any kind of fossils of their own? Add some pics into the comments below, we would love to see them.

~ JM

First - I shared a couple shots of crinoids yesterday - make sure to note that crinoids aren’t squid, they actually form columns of hard, fossilized parts.

But, to answer your question, an area of exceptional fossil preservation is called a Lagerstätte. They are rare, but there are dozens of them known around the world. To form one requires some unique set of details in the way the area is formed.

For example, rapid sediment accumulation could contribute, particularly in the precambrian as there were few to no burrowing organisms that long ago. Once a body was buried in the sediment, it would leave an impression on the sediment as it hardens into rock.