A New Last Occurrence

Headlines in paleontology usually center on the oldest or first find of a fossil species. However, determining the youngest or last occurrence of a now-extinct species is just as important.

A youngest occurrence was recently confirmed for an extinct group of echinoderms, the phylum that includes starfish, sand dollars, and brittle stars.

Edrioasteroids are one of a number of bizarre echinoderms that went extinct by the end of the Paleozoic Era for reasons not yet understood. These silver-dollar sized, disc-shaped animals lived attached to shells or other hard surfaces on the sea floor.

This discovery comes as paleontologists focus their energy on looking for these fossils in younger rocks to answer questions about the reason for their demise.

Photo credit: drydredgers.org

For more pictures of edrioasteroids click on today's title.

Reference: Journal of Paleontology November, 2009, First definite record of Permian Edrioasteroids: Neoisorophusella from Russia

Great Fossil Faunas, V: The La Brea Tarpits

All the previously described lagerstatte are deposits of organisms from a marine environment. The fifth and final pick for "greatest fauna" is something completely different: The fossils encased in the La Brea tarpits were land-dwellers who became entrapped in a natural asphalt spring, and if for no other reason, the unique environment and fossilizing agent earn the La Brea tarpits a place on our list of top 5 fossil faunas.

How can an animal be so stupid as to fall into an asphalt pool? These were probably not steaming or bubbling pits like the mudpots and geysers of Yellowstone, but still pools of dense oil muck camoflaged by plant debris and perhaps even holding a pool of water.

Animals that came to take a drink got stuck, their distress cries were heard by predators who themselves became ensnared, and finally scavengers that came along for the easy pickings became mired in the muck—leaving a record of the whole food chain, from plants to insects to mammoths to saber tooth tigers and vultures—650 species of plants and animals so far identified, on the basis of 3.5 million fossils recovered, an astonishing diversity of animals that gives us an unprecedented window into an ice-age ecosystem.

Photo from www.papermag.com/blogs/2008/11/mr_mickeys_mustsee_guide_to_la_1.php

Great Fossil Faunas, IV: Solnhofen Limestone

This famous lagerstatte from southern Germany is an obvious choice for a “greatest fossil fauna” list because it is in these fine-grained limestones representing the deposits of an ancient lagoon that the fossils of Archaeopteryx were found.

Archaeopteryx was the first evidence for a link between birds and reptiles, and the discovery of the first specimen came only a few months after Charles Darwin published Origin of Species, in which he made the case for a common ancestry for all organisms.

One of Darwin’s most vexing problems was the apparent lack of the transitional forms between major groups that his theory predicted, and the discovery of Archaeopteryx was an answer to this dilemma.

The lagoon that preserved Archaeopteryx down to its feathers also preserved insects, crustaceans, and echinoderms in exquisite detail, and give us a glimpse into a 150-million-year-old nearshore ecosystem.

For more info on Archaeopteryx click on the title of today's blog.

Great Fossil Faunas, III: The Burgess Shale

You have to love an animal named Hallucigenia, an animal so strange that paleontologists have flipped the original reconstruction of the animal (lower picture, tottering on stiff spines) upside-down (upper picture, with the spines on the back).

Hallucigenia is only one of a menagerie of odd animals known from the Middle Cambrian Burgess Shale of British Columbia. It keeps company with the five-eyed Opabinia, skeletal trilobite-like Marella, and Wiwaxia, a strange enough animal with a truly weird name.

The discovery of the Burgess Shale fauna was another paradigm-breaker. This fauna represented a virtual explosion of body plans early in the history of multicellular life, some of which were culled as experiments in evolutionary design, others that can be traced to groups that left descendents.

new Hallucigenia pic copyright 2003 by Karen Carr

For more information on the Burgess Shale animals, click on today's blog title.

Great Fossil Faunas, II: The Ediacara Fauna

The oldest known fossils of multicellular organisms are known from rocks of what was formerly called the Precambrian Eon.

The Precambrian was long regarded as a time before life appeared, as there were no known fossils from the ancient rocks. The appearance of abundant shelly fossils was taken to mark the end of the Precambrian and the beginning of the subsequent Cambrian Period.

Because of the presumption that Precambrian rocks contained no fossils, the first discovered Ediacarian organisms were not recognized as being organic remains. It was only after multiple similar faunas from Newfoundland, Africa, Australia, and England were discovered that the true significance of these strange creatures was appreciated.

For smashing one of the earliest paradigms of fossil distribution, the Ediacara biota earns a spot on our list of 5 great fossil faunas.

For more information on the Ediacaran organisms click on the title, above.

Great Fossil Fauna, I: Gunflint Chert Flora

The Gunflint chert is part of a sequence of 1.8 billion-year-old rocks exposed in the Gunflint Range of northern Minnesota and western Ontario along the north shore of Lake Superior.

These rocks contain stromatolites, organo-sedimentary structures formed by cyanobacteria trapping and binding sediment, and when examined under the microscope, small spheres, rods and filaments less than 10 micrometers in size are visible in the chert layers--microfossils preserved in near-pristine 3-D.

The discovery of the Gunflint chert caused a paradigm shift in paleontology, as it proved that under exceptional conditions, even very ancient lifeforms could be preserved.

For its role in opening our eyes to the presence of life in very ancient rocks, the Gunflint chert earns a place on our list of “top 5 fossil lagerstatte”

Photo credit: http://www.fas.org/irp/imint/docs/rst/Sect20/A12.html

Fossil "Mother Lodes"

The history of life on Earth is a story told in photographs made of stone--the rocks and fossils preserved when and where conditions were favorable. Some of these photos are time exposures in which events blur together, others, much rarer, are snapshots of an instant in time. These snapshots commonly are the result of the sudden, rapid burial of the organisms living in the environment, as through an ocean storm surge or river flood or avalanche or entrapment in a mucky bog or sticky pit of natural asphalt. These snapshots are characterized by exquisite preservation of anatomical details not usually fossilized, and fossil deposits of this sort are referred to by a German word, lagerstatte, which is a mining term that refers to a "mother lode" or abundance of ore. Fossil lagerstatte are "mother lodes" of exceptionally preserved fossils. The Pennsylvanian (320-286 million year old) Mazon Creek fauna, from which the bizarre Tullymonstrum (the state fossil of Illinois, seen here from the side of a U-Haul truck) is known is one example.

This week's GeoLog challenge is to describe the 5 most significant fossil faunas or lagerstaette, fossil "mother lodes." Despite the relative rarity of exceptional preservation, the list of lagerstaette, for example the list posted on the Wikipedia website, takes up a whole page, so some selection criteria need to be imposed. My "top 5" lagerstaette were chosen to include different geological periods, different depositional or geological environments, and a variety of organisms, from microfossils to dinosaurs, and for their historical significance.

Paleontologically, all lagerstaette are important, because we've learned things from each of them about the variety and diversity of life that we would not have known otherwise.