Marine Fossils Modes of Life or Habitat

Fossils provide crucial insights into past environments and ecosystems, helping scientists understand how life and the Earth itself have changed over time.

Fossils are the remains or traces of once living organisms. Our introduction to paleontology (the study of fossils), will be limited to those forms that are commonly preserved and geologically useful. For Historical Geology purposes, we will be concerned with two aspects of paleontology

Fossils as indicators of relative age (using the Principle of Floral and Faunal Succession. fossils as indicators of environment. All organisms are dependent on their environments for survival. Some organisms, however, can survive only in restricted environments.

Fossil Types

Body Fossils:

• Skeletal Structure: Bone shape and size reveal locomotion (running, swimming, flying), diet (teeth, beaks), and even social behavior (horns for display).
• Muscle Attachments: Scars on bones indicate muscle size and strength, hinting at movement patterns and prey capture.
• Soft Tissue Preservation: Rare cases of preserved skin, feathers, or internal organs offer direct insights into appearance, physiology, and diet.

Trace Fossils

• Footprints: Trackways reveal information about posture, gait, speed, and social behavior (group movement).
• Burrows: Shape and size indicate burrowing habits, potential social structures, and adaptations to specific environments.
• Coprolites (fossilized feces): Content analysis reveals diet and ecosystem interactions.
  

Marine Fossils Modes of Life

1. Benthic Organisms (Seafloor Dwellers)

Organisms living on or within the seafloor sediment:

Epifaunal (Surface Dwellers)

• Sessile: Permanently attached to the substrate. Examples: Corals (reef-builders), crinoids ("sea lilies"), brachiopods.
• Vagrant: Mobile crawlers/grazers. Examples: Trilobites (mostly surface grazers), gastropods (snails), sea urchins.

Infaunal (Burrowers)

• Shallow Burrowers: Live near the sediment surface. Examples: Clams (Mya), burrowing bivalves.
• Deep Burrowers: Permanent dwellers in deeper sediment. Examples: Worm tubes, some bivalves (e.g., Lucina).

2. Pelagic Organisms (Water Column Dwellers)

Organisms inhabiting open water, away from the seafloor:

Planktonic (Passive Drifters). Examples: Radiolarians (silica skeletons), foraminifera (calcareous shells), jellyfish (rare soft-tissue fossils).

Nektonic (Active Swimmers). Examples: Ammonites (extinct cephalopods), fish (shark teeth, bony fish fossils), ichthyosaurs (marine reptiles).

3. Specialized Modes of Life

Unique adaptations to niche environments:

Demersal: Swim near the seafloor (e.g., flatfish, some cephalopods).

Neustonic: Float at the water’s surface (e.g., Velella, colonial cnidarians).

Reef-Builders: Sessile colonial organisms creating structures (e.g., corals, stromatoporoids).

Chemosynthetic Communities: Thrive near hydrothermal vents/seeps (e.g., fossilized tube worms).

Interstitial: Microscopic organisms in sediment pores (e.g., ostracods, micro-crustaceans).

Marine fossils provide a fascinating glimpse into the life habits of ancient sea creatures. Here's how these fossils can be categorized based on the lifestyles of the organisms they once were:

Marine fossils can be further described in terms of their life habits. These habits are shown in Figure A2.  Corals, for example tend to be attached to the bottom and are thus referred to as benthic (bottom dwelling) sessile (fixed). Lobsters, however, move along the ocean bottom and although still benthic, are also considered vagrant. Swimming and floating organisms are referred to as nektonic and planktonic, respectively. In our example above, some fish might represent the nektonic pelagic environment.

Feeding Habits:

Filter Feeders: Organisms like brachiopods, some bivalves, and crinoids that filtered food particles from the water.

Predators: Fossils like those of sharks or large marine reptiles indicate predatory behavior.

Scavengers: Creatures that fed on dead organic material; some trilobites might have been scavengers.

Herbivores: Less common in the marine fossil record directly, but some marine reptiles or fish might have fed on marine plants or algae.

Deposit Feeders: These organisms, like certain types of worms, ingested sediment to extract nutrients.

Social Behavior:

Solitary: Many fossils indicate organisms that lived alone.

Colonial: Some fossils like those of graptolites or certain corals show they lived in colonies.

Environmental Adaptations:

Reef Builders: Corals and certain ancient organisms like stromatoporoids created habitats for other marine life.