Marine Invertebrate PaleoPhylum Conodonta

Phylum ConodontaLate Precambrian- TriassicConodonts 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.

Conodont elementsKnown worldwideRecovered from a variety of marine sedimentary rocks Conodonts evolved rapidly so they are superb index fossilsWorldwide Biostratigraphy

Upper Cambrian-TriassicOver 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 animalsSmall (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.

Details from this Mississippian specimen from Scotland include:Elongate worm-like animal (4 cm in length)Has impression of a mid-lineTerminal tail-like structureAlmost 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.

Morphology and Microstructure of skeletal elementsElements composed of a form of carbonate apatite (known as

Francolite) laid down in layers or lamellae around an initial point of growthVery sturdy mineral that is easily freed from sedimentary rocks by

dissolving the rock with organic acidElements recovered from insoluble residue

Three basic types of Conodont elements have been recognized:1. Coniform elements – cone shaped structures consisting of a

base and a cusp.2. Ramiform elements – include a main cusp flanked by

posterior-anterior and/or laterally directed processes that posses denticles

3. Petiniform elements – bear denticles on platforms of laterally expanded processes.

Inferred PaleoecologyMost paleontologists agree that Conodonts were:

Pelagic and ubiquitous in the marine environmentRare in extremely shallow waterRare in far-offshore and deep basinal environmentsCommon in nutrient rich shelf watersMost abundant in sediments bearing stenohaline

organismsNo brackish water occurrences have been reportedEvidence 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

Color alteration of elements used in oil and gas productionColor 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