Marine Invertebrate Paleo

1. Marine Invertebrate Paleo Phylum Conodonta

2. Phylum Conodonta • Late Precambrian- Triassic • Conodonts are an extinct group of marine animals whose skeletal parts consisted of microscopic mineralized elements, many of which were arranged in patterns or apparatuses. • More or less complete apparatuses are called natural assemblages. • Many of the elements occurred in symmetrical pairs (i.e., right and left members) • Some Conodonts contained a single type of element, but most possessed a number of differently shaped elements. • The elements disarticulated from internal soft body parts, and are commonly only what is preserved.

3. Conodont elements • Known worldwide • Recovered from a variety of marine sedimentary rocks • Conodonts evolved rapidly so they are superb index fossils • Worldwide Biostratigraphy • Upper Cambrian-Triassic • Over 140 Conodont biozones • Conodonts are assumed to be metazoans at a coelomate level of organization, there exact biology has not been determined. • Most of what we know is based on mineralized elements from bedding planes with symmetrical natural assemblages. • Bilateral symmetrical animals • Small (few cm in greatest dimension) • Important soft parts only inferred from a few very unusual details of size and shape from body impressions found in 1982.

4. Details from this Mississippian specimen from Scotland include: • Elongate worm-like animal (4 cm in length) • Has impression of a mid-line • Terminal tail-like structure • Almost complete assemblage of elements in the head region of the impression. • Elements may have been part of some grasping or tentacle structure associated with the mouth.

5. Morphology and Microstructure of skeletal elements • Elements composed of a form of carbonate apatite (known as Francolite) laid down in layers or lamellae around an initial point of growth • Very sturdy mineral that is easily freed from sedimentary rocks by dissolving the rock with organic acid • Elements recovered from insoluble residue • Three basic types of Conodont elements have been recognized: • Coniform elements – cone shaped structures consisting of a base and a cusp. • Ramiform elements – include a main cusp flanked by posterior-anterior and/or laterally directed processes that posses denticles • Petiniform elements – bear denticles on platforms of laterally expanded processes.

6. Inferred Paleoecology • Most paleontologists agree that Conodonts were: • Pelagic and ubiquitous in the marine environment • Rare in extremely shallow water • Rare in far-offshore and deep basinal environments • Common in nutrient rich shelf waters • Most abundant in sediments bearing stenohaline organisms • No brackish water occurrences have been reported • Evidence suggest preferred warm water near equatorial belts rather than high latitudes. • Conodont feeding patterns have not been established • Elements jaw-like structures fed on plankton

7. Color alteration of elements used in oil and gas production • Color Alteration Index (CAI) • An important application of Conodonts as a tool in geologic interpretation • Indicates the depth and duration of sediment burial and geothermal gradient of the rocks in which the elements occur • Normal unaltered Conodont elements are pale yellow to brown (CAI=1) • Intensely altered elements are colorless (CAI=8) • The gradation from 1 to 8 is easily identified under a microscope