Cambrian Shadows: A Fossil Mall Theme Park

about the ichnofossils of Blackberry Hill, Elk Mound Group, Wisconsin

With the sun high overhead, the ichnofossils of this quarry are nearly invisible. Late in the day, however, when shadows are long, these fossils leap to life. These are the Cambrian Shadows of central Wisconsin.

 

 

 

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Of all the periods in Geological History, Cambrian Time is perhaps the most alluring and mysterious, because of an apparent burst of evolutionary creative design. While much is known about the Cambrian, much also remains shrouded in mystery. Over a period of merely a few tens of million of years there appeared numerous novel designs. Animals appeared with hard outer parts that not only protected them from ever more capable predators, but provided the structural support allowing adaptation to larger size. Darwin believed evolutionary adaptation proceeded in a smooth continuous manner, in contrast to the fossil record known during his time that appeared to abruptly end at the Lower Cambrian. The fossils bridging the mysterious gap from the Precambrian into the Cambrian were not discovered until the middle of the 20th century. Thus, the mystery known as the Cambrian Explosion has persisted for 150 years. While there are different theories that are plausible and rational, there is no theory that enjoys a total consensus. What caused biology's most profound and rapid period of diversification of life? Why have similar bursts of diversification not occurred since the Cambrian? Why have no new phyla appeared after the Cambrian? These are questions not yet answered by science.

When one thinks of the migration of animals from the marine environment to land, Devonian-time comes to mind. But, in fact, this critical adaptation may have already begun in the Cambrian. Ichnofossils such as Climactichnites, Diplichnites, and Protichnites support the hypothesis that animals were venturing unto shore, though not yet far from the sea. Many of these fossils are almost as enigmatic today as they were during the time of Darwin. Fossils from the Blackberry Hill Site (Krukowski Flagstone Quarry) in Central Wisconsin were intensely studied by paleontologists and may shed light on mysteries that worried Darwin, and that persist today. The recent and exciting discovery of arthropod body fossils in the Krukowski quarry may shed light on some of the mystery of earliest terrestrialization by animals during Cambrian time.

With the sun high overhead, the ichnofossils of this quarry are nearly invisible. Late in the day, however, when shadows are long, these fossils leap to life. These are the Cambrian Shadows of central Wisconsin.

Blackberry Hill, and its fossils: