Exceptional Preservation
Somerockbedshaveproducedexceptionalfossils. Fossilsfromthesebedsmayshowevidence
of soft body parts that are not normally preserved. Two of the most famous examples of
soft organism preservation are the Burgess Shale in Canada and the Solnhofen Limestone
in Germany. The Burgess Shale is 505 million years old and records the first explosion of
shelled organisms in Earth’s oceans. Many of the Burgess Shale fossils are bizarre animals
thatseemunrelatedtoanyotheranimalgroup. TheSolnhofenLimestoneis145millionyears
old and contains fossils of many soft-bodied organisms that are not normally preserved, such
as jellyfish. The most famous Solnhofen fossil isArchaeopteryx, one of the earliest birds.
Although it resembles a dinosaur fossil, impressions of feathers can clearly be seen (Figure
11.7).
Figure 11.7: Fossils from Lagerstätten: Archaeopteryx(left) andAnomalocaris(right). Ar-
chaeopteryx was an early bird. Anomalocariswas an enormous predator (one meter long)
that lived 500 million years ago. ( 13 )
Index Fossils and Living Fossils
The fossil record shows clearly that over time, life on Earth has changed. Fossils in relatively
young rocks tend to resemble animals and plants that are living today. In older rocks, fossils
are less similar to modern organisms.
As scientists collected fossils from different rock layers and formations, they discovered that
they could often recognize the rock layer by the assemblage of fossils it contained. Some
fossils proved particularly useful in matching up rock layers from different regions. These
fossils, calledindex fossils, are widespread but only existed for a relatively brief period