Palaeontological Principles

© Craven & Pendle Geological Society

Brachiopod, Trilobites and Worms!

Fossiliferous limestone (Silurian) from Shropshire

Fossils are useful to geologists for three main reasons:

1.  Their presence helps to determine the age of rocks in which they are found.

2.  They provide a means of establishing environmental conditions at the time of burial and therefore helps with palaeogeographic and palaeoecological reconstructions.

3.  Fossils provide data to plot the evolution of past organisms.

Having collected some fossils you are left with the daunting task of sorting them out in order to make some scientific sense of your collection.  The three common terms that you may come across are TAXONOMY (the science of identification and classification of organisms), SYSTEMATICS (a synonym of Taxonomy) and CLASSIFICATION (the division of organisms into a hierarchical series of groups).

An ordered and natural group of organisms is referred to as a TAXON (plural TAXA).  Classification methods often use hierarchy of taxa: example below.

HEIRARCHY
Phylum
Subphylum
Class
Subclass
Order
Suborder
Genus
Species

CLASSIFICATION
Echinodermata
Pelmatozoa
Crinoidea
Camerata
Monobathrida
Glyptocrinina
Pleurocrinus
tuberculatus

A Rostroconch

A Rostroconch
Upper Bowland Shales,
Weets Hill, Barnoldswick

A local find!

This curious fossil is a Rostroconch. The Rostrochonchia are a group of Palaeozoic bivalved molluscs that in early times were considered Bivalves. Further research by palaeontologists' concluded that they warrant a distinct class of their own, the Rostrochonchia. The Rostrochonchia are divided into two orders:

Order Ribeirioida
(Early Cambrian to Early Silurian)

Order Conocardioida
(Late Cambrian to Late Permian)

They probably lived a sedentary semi-infaunal lifestyle.

Pseudomytiloides dubius

Pseudomytiloides dubius
Whitby Mudstone Group, Lower Jurassic,
Runswick Bay, East Yorkshire

Identifying Fossils!

Sometimes sorting out fossils can be a problem. A good example is Pseudomytiloides dubius - originally described in the early 19th century I think, by J. Sowerby.

Mytiloides is the modern mussel so I guess the original description thought it was dubiously like the mussel, hence Mytiloides dubius.

Later redescription assigned it to Inoceramus, then it got its own genus Pseudomytiloides.