Identifying Fossils by Shape

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Fossils / Expeditions

Identifying Fossils by Shape


The shape of fossils may be used as a general guide in identification.

modified for Australian conditions based on a format
from the Geological Survey of Kentucky https://www.uky.edu/KGS/fossils/fossilid.php
line sketches with permission and courtesy of the Kentucky Geological Survey


OK so you have found a fossil and you haven't any idea what it is!
The following may be a helpful guide to at least get you started
Fossils in the field are generally poorly preserved, broken, or partially covered in the matrix of the surrounding rock so that their true size and shape is hidden.
Most commonly found fossils can usually be classified to their group by observing some simple shapes and features.

If your fossil has one of the shapes below, look down the guide for that shape and you will be presented with some possibilities of it's origins.
(Note: mobile phone users may need to view the fossil shape image map in landscape)
Click on the group of shapes on the image map below to get started... or scroll down to the desired shape

fossil shape Circle Circle Circle Circle Circle Circle Egg shapes Nut shapes Hammock shapes Hammock shapes Pentagonal shapes Pentagonal shapes C shapes Spiral shapes Spiral shapes Shell shapes Irregular mounds Peeling onion Cup shapes Cup shapes Cup shapes Tooth shapes Tooth shapes Tooth shapes Tooth shapes Flower/Needle shapes Flower/Needle shapes Honeycomb Honeycomb Tube shapes Tube shapes Tube shapes Tube shapes Tube shapes Tube shapes Tube shapes Tube shapes Tube shapes Tube shapes Chain shapes Sinuous shapes Bone shapes Bug shapes Tear shapes Tear shapes Net shapes Net shapes Scaly shapes Scaly shapes Scaly shapes Rope shapes
 
There are many shapes and fossils not shown on this diagram, but most of the common shapes are shown.

Circle

Circle
Small circular fossils (less than a few centimeters in diameter)
  1. Crinoid columnals are generally small circular fossils, a centimeter or less in width. They may have a hole toward the axis (bead shape) but are common without holes as well. Common in limestones and shales.





  2. Cross sectional views or views looking down on the tops or cups of horn corals can have a circular appearance. Most corals will have grooves or lines radiating out from the axis. They are generally less than 3 or 4 centimeters in width.





  3. Cross sectional views through some types of bryozoans are circular. Such sections are generally less than a centimeter in width and are common in Ordovician limestones.





  4. Atrypa brachiopods , Orbiculoidia brachiopods and some Productid brachiopods have circular shapes at certain orientations and do not have grooved ornamentation like many other shelled fossils. Look to see if you can see a tiny protrusion on one side of the shell that might be a hinge to the shell valves.





  5. Cross sectional views fossil plants such as ferns and the surface of fern trunks such as Lepidodendron






  6. trace fossils such as worm burrows



Larger circular fossils
  1. Some horn corals and tabulate corals are circular in cross section or when looking down from the top. Tabulate coral mounds may have diameters from centimeters to more than a meter across.


  2. fossil tree trunks


  3. backbones - individual backbones of mammals, reptiles, dinosaurs, fish, amphibians have a near circular cross-section



    Learn more about our discovery of an Ichthyosaur skeleton

Circle with a hole (bead)

Circle with Hole or Bead

Circle with Radiating Lines or Grooves

Circle with Radiating Lines or Grooves
  1. Cross sectional views or views looking down on the tops or cups of horn corals can have a circular appearance. Most corals will have grooves or lines radiating out from the axis. They are generally less than 3 or 4 centimeters in width.
  2. Cross sectional views through some types of bryozoans are circular. Such sections are generally less than a centimeter in width and are common in Ordovician limestones. Bryozoans have a different appearance in section from corals.
  3. Some crinoid columnals will also have radiating lines outward from center. Most will also have a hole or depression in the center, and will be small, generally less than a centimeter in diameter. They will be bead-like if separated from the rock they are found in.





    In contrast, bryozoans with circular cross sections will be tubular, and horn corals will often be conical or cup-shaped.

  4. Cordaite plant fossils


Bead with radiating lines or grooves

Circle with hole and radiating lines

Bead with hole and radiating lines

Circle with star axis

Circle with star axis

Bead with star axis

Egg shapes

Egg shape

Fossil eggs worldwide are very rare. In almost all cases an egg-shaped fossil is something else.

Nut shapes (flower-bulb shaped, bulbous)

Nut shapes

Pentagonal shapes (five-sided)

Pentagonal shapes

Pentagonal symmetry is common to echinoderms.

5-pointed star shapes

Stars are generally five-sided in fossils, and this type of symmetry is common to echinoderms. Several types of fossil echinoderms can be found in Kentucky.

NOTE: hexagonal shapes are more likely found to be fossilised mudcracks or basalt lava cooling columns




C shapes

C shapes

Cross sectional views through the valves of shelled animals such as brachiopods and bivalves are most common.

Spiral shapes

Spiral shapes

Small spiral fossils (less than a few centimeters in width)

Large spiral fossils (more than six centimeters across)

Shell shapes

Shell shape

Most shell shape fossils  are shells Found around coal deposits in many areas, in limestones, shales and sandstones and around the edges of Australia's ancient inland sea

Hammock shapes

Hammock shape

Irregular mounds (brain shapes)

Irregular mounds (brain shapes)

Peeling onion

>Peeling onion

Cup shapes

Cup shapes

Cup shapes with grooves in cup

Cup shapes with grooves in cup

Cup shapes with bulb on the bottom

Cup shapes with bulb on the bottom

Tooth shapes

Tooth shapes

Most of the tooth-shaped fossils found in Kentucky are not fossil teeth. Rather they are fossils of other animals.

Horn shapes

Horn shapes

Horn or tooth shape with segments

Horn or tooth shape with segments

Horn or tooth shape with transverse ribbing

Horn or tooth shape with transverse ribbing

Tube shapes

Tube shapes

Small tubes (less than a few centimeters in width)

Large tubes

Multiple, attached tubes

Multiple, attached tubes

Tube with holes

Tube with holes

Segmented tube

Segmented tube

Segmented tube with a rounded end


Segmented tube with a rounded end

Segmented tube that comes to a point


Segmented tube that comes to a point

Branching Tubes


Branching tubes

Screw shapes

Screw shapes

Saw-tooth shapes

Saw-tooth shape

Flower shapes

Flower shapes

Needle shapes

Needle shapes


Honeycomb

Honeycomb (wasp-nest and bee-hive shapes)

Mound with holes (bee hive shapes)

Mound with holes (bee hive shapes)


Chain shapes

Chain shapes

Sinuous shapes

Sinuous shapes

Bone shapes

Bone shapes

Many rocks and fossils may have bone-like shapes.

Bug-like shapes

Bug-like

Tear shapes

Tear-drop shapes

Tear-drop shape with segments


Tear-drop shape with segments

Net, fan, web, or mesh shapes

Net, fan, web, or mesh shapes

Scaly shapes, snake skin

Scaly shapes, snake skin



Chevron trails and Rope or loop shapes

Rope or loop shapes 

these shapes are usually traces of invertebrates on the bottom or in the sediment of an ancient water-body.


Microfossils





Some useful fossils are so small study requires a microscope
They exhibit bewildering variety and can be used as indicators of past sea temperatures, past oxygen levels and many other purposes.
See more about microfossils