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 Type

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

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:

Pelagic Organisms:

These lived in the water column, away from the bottom. They are divided into:

Planktonic:

These organisms floated in the water column. Fossils of planktonic life forms include:

• Foraminifera: Tiny, often shelled protists.
• Radiolarians: Another group of protists with intricate mineral skeletons, usually made of silica.

Nektonic:  

These were active swimmers. Fossils indicating a nektonic lifestyle include:

• Ammonites: Extinct cephalopods with coiled shells.
• Fish: Including both bony fish and sharks, with their cartilaginous skeletons often preserved as fossils.

Benthic:  

Benthic: Organisms that live on or near the bottom of the ocean. This can include both sessile (non-moving, like corals) and vagrant (mobile, like crabs) species.

Epifaunal: Organisms that live on the surface of the seafloor or on other organisms.

• Brachiopods: Look similar to clams but are entirely different phylogenetically.
• Crinoids: Often called sea lilies, they are filter feeders with a stalk anchoring them to the substrate.

Infaunal:  Organisms that live within the sediment of the seafloor.

• Bivalves: Like clams or mussels, which burrow into the sand or mud.
• Trilobites: Although some could swim, many species lived on or burrowed slightly into the sea floor.

Mobility:

Sessile: Refers to organisms that are permanently attached to a substrate and do not move from one place to another.

• Corals: Both solitary and colonial forms that build reefs.
• Sponges: Simple multicellular organisms often found as fossils with their porous structure.

Vagrant: Organisms that are mobile but live on or near the seabed. These are mobile bottom-dwellers:

• Gastropods: Snails that crawled along the ocean floor.
• Echinoderms like sea urchins and starfish: Many species move around to graze or hunt.

Symbiotic or Parasitic: Some marine fossils show evidence of symbiotic relationships or parasitism:

• Certain brachiopods or bivalves might be found in association with other organisms, suggesting a symbiotic relationship.

Burrowing: An animal that lives in a burrow, either digging into the sediment for protection or to find food.

By studying the morphology of fossils, the sedimentology of the rock they're found in, and associated fauna and flora, paleontologists can infer these life habits. These insights help reconstruct ancient marine ecosystems, understanding not just what creatures lived, but how they lived, interacted with their environment, and with each other.

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.