Presentation on theme: ""— Presentation transcript:
CAMBRIAN SYSTEM in Minnesota Upper Cambrian – St. Croixian In Minnesota and Wisconsin unconformable on PreCambrian strata Cross-bedded sandstones
Spectacular trace fossils (Ichnofossils) Climactichnites resemble tracks made by a motorcycle both is size and character. Described by Sir William Logan in 1860, Climactichnites was believed at that time to come from the oldest sedimentary formation known; the Canadian formation is now known to be Upper Cambrian. The fossil caused considerable controversy among paleontologists, and speculation regarding the track maker's identity abounded. Arthropods with soft bodies were denied by the lack of footprints. The possibility of a snail was denied by the V-shaped ridges, and that no known Cambrian snail or worm (even today) can account for the tracks that can be six or more inches wide.
More recently, Getty and Hagadorn, have suggested that Climactichnites fossils are body impressions of a slug- like creature that crawled across the surface – preservation dependent on a biofilm of alga on the sand flats. Getty, P. R.; Hagadorn, J. W. (2008). "Reinterpretation of Climactichnites Logan 1860 to Include Subsurface Burrows, and Erection of Musculopodus for Resting Traces of the Trailmaker". Journal of Paleontology 82 (6): 1161–1172. doi: / doi /
Scyphozoans Jellyfish medusae
The Cambrian was of great evolutionary innovation, with many major groups of organisms appearing within a span of about forty million years. Trace fossils made by animals also show increased diversity in Cambrian rocks, showing that the animals of the Cambrian were developing new ecological niches and strategies -- such as active hunting, burrowing deeply into sediment, and making complex branching burrows. Almost every metazoan phylum with hard parts, and many that lack hard parts, made their first appearance in the Cambrian. Although almost all of the living marine phyla were present, most were represented by classes that have since gone extinct or faded in importance. The Brachiopoda for example, were represented by the relatively primitive inarticulate brachiopods.
Other Cambrian invertebrates with mineralized skeletons included: Trilobites, archeocyathids, inarticulate brachiopods, monoplacophorans, echinoderms. Cambrian echinoderms were predominantly unfamiliar and strange-looking types such as early edrioasteroids, eocrinoids, and helicoplacoids. Starfish and sea urchins had not yet evolved. In addition there were problematic conical fossils known as hyolithids.
Plate of Upper Cambrian fossils from Mt. Jubillee, Columbia River Valley, British Columbia, described by Teiichi Kobayashi,1938 Trilobites General morphology skeletal parts (from the Treatise of Invertebrate Paleo) Mostly members of the benthos Bottom-dwellers Olenellus
Upper Cambrian trilobites and lingulids from Wisconsin
Inarticulate brachiopods lack interlocking hinge mechanisms and have the valves held together only by muscles. Modern forms e.g. Lingula, burrow in soft, muddy, dark-colored sediments and move up and down within their burrows on a long leathery or fleshy stalk-like extension (pedical). They are found in marine or brackish water in poorly - oxygenated estuaries and mud flats. Inarticulate Brachiopods ‘living fossils’ Subphylum Linguliformea (L. Camb. - Rec.) chitonophosphatic shells Fossil In burrow, organism retractile on a pedicle Spatula-shaped shell with fleshy pedical projecting from between The two valves
Prior to 1952, the monoplacophorans were known only from fossil shells from the Cambrian and Devonian. Then in that year the 'Galathea' expedition dredged up 10 living specimens of Neopilina galathea. These two species are the only known living representatives of this class Monoplacophorans – primitive molluscs Possess segmented muscles and organs ancestral to later mollusc classes
Phylum uncertain Class HYOLITHA Marek, 1963 Family HYOLITHIDAE Nicholson, 1872 Genus Hyolithes Eichwald, 1840 Fossils of Hyolithes Reconstruction of the hyolithid animal
Paper No LATE CAMBRIAN TRILOBITES (SAUKIIDAE) AND THEIR IMPLICATIONS FOR PALEOGEOGRAPHY AND PALEOENVIRONMENTAL RECONSTRUCTIONS HENDERSON, Wayne G.HENDERSON, Wayne G., Univ California - Riverside, 1432 Geology Bldg, Riverside, CA , and HUGHES, Nigel C., Department of Earth Sciences, Univ California - Riverside, Riverside, CA Late Cambrian trilobites of the family Saukiidae occupied a variety of shelfal environments across Laurentia and much of core and outboard Gondwanaland. Such widespread distribution is rare among polymerid Cambrian trilobites, and stands in marked contrast with the distribution of their closest relatives, the exclusively Laurentian Dikelocephalidae. Preliminary comparisons of Saukiidae from widely dispersed landmasses show that several supposedly endemic species are morphologically indistinguishable from forms found on separate landmasses, and thus likely constitute synonyms. Given this, a comprehensive, morphology-based revision of the saukiid systematics is now required in order both to better understand relationships within the group, and to refine understanding of the biogeographic distribution of this group. A character matrix for phylogenetic analysis of all well-preserved saukiids has been constructed based strictly on morphological criteria. Character analysis using the PAUP program have been undertaken in order to clarify saukiid relationships and apply this knowledge to Late Cambrian paleogeography. A preliminary cladogram is presented and defended Denver Annual Meeting (October 27-30, 2002) Session No. 120