chapter 8—stuff to know

Fossils & Evolution—Chapter 8 1

Chapter 8—Stuff to know

• Marine bathymetry zones– Neritic / bathyal / abyssal / hadal

• Environmental limiting factors (know all)– Salinity categories– Stenohaline /euryhaline taxa

• Evolutionary paleoecology– tiering; escalation;


Chapter 8—Paleoecology

• Ecology = the study of the interactions between organisms and their environment

• Paleoecology = ecology applied to the study of fossils and ancient environments

• Evolutionary paleoecology = study of ecologic phenomena that operate on the scale of millions of years (and are invisible to ecologists of the living biota)

• Main applications of paleoecology are in (1) reconstructing ancient depositional environments and (2) assessing environmental influences on evolution


Marine ecosystem

• Modern marine ecosystem is used by paleontologists as an analogue for ancient marine ecosystems

• Drawbacks to uniformitarian approach– Past climates generally have been warmer than today’s– Past sea levels generally have been higher than today’s

• Few modern epicontinental seas• No modern tropical epicontinental seas

Fossils & Evolution—Chapter 8 4Devonian(360 Ma)


Marine bathymetry zones• Neritic = continental shelf (from sea level to ~200 m)

– Intertidal– Subtidal zone

• Bathyal = continental slope and rise (from ~200 m to ~2000 m)

• Abyssal = deep ocean floor (from ~2000 m to ~ 6000 m)• Hadal = very deep ocean (> 6000 m)• Photic zone = depth to which light penetrates

– Highly variable, depending on water clarity– Photosynthesis usually takes place in upper 100 m of water

column


Marine environments


• Ecologic limiting factors = physical, chemical and biologic properties of the environment that limit the distribution and abundance of a particular species– Temperature– Oxygen– Water depth and depth-related variables– Salinity– Substratum– Food


Limiting factors:Temperature

• Probably the single most important limiting factor governing large-scale distributions (biogeographic provinces)


15°C

15°C

Modern symbiont-bearing corals and foraminifers occur mainly in water that is warmer than 15°C (winter sea surface temperature)


Limiting factors:Oxygen • Black Sea: direct relationship between dissolved

oxygen in water and faunal diversity– As dissolved oxygen decreases with increasing depth,

so too does diversity– First animals to disappear are large, heavily calcified

invertebrates– Small, weakly calcified to uncalcified taxa extend to

greater depths (taxa unlikely to be preserved as fossils)


Limiting factors:Oxygen

soft-bodied


Limiting factors:Oxygen


Limiting factors:Water depth • Depth, in and of itself, exerts very little influence

over distribution of organisms, but depth-related factors are very important– Hydrostatic pressure– Light wavelength and intensity– Salinity– Temperature– Nutrients– Dissolved oxygen


Limiting factors:Water depth (light)

• Light is attenuated as it penetrates through water– Intensity of light

decreases– Different

wavelengths of light are absorbed at different rates

green algaeuse red light

red algaeuse blue light


Limiting factors:Salinity• Stenohaline species have little tolerance

for salinity fluctuations• Euryhaline species have greater tolerance

for salinity fluctuationsTerm salinity (‰)Freshwater 0–0.5Brackish 0.5–30Seawater 30–40Hypersaline 40–80Brine > 80


Limiting factors:Salinity• Stenohaline groups include:

– Corals, cephalopods, articulate brachiopods, and echinoderms

• Euryhaline groups include:– Inarticulate brachiopods (Lingula), pelecypods,

gastropods, and ostracodes


Evolutionary paleoecology

• Evolutionary paleoecology = study of ecologic phenomena that operate on the scale of millions of years (and are invisible to ecologists of the living biota)



• Tiering = degree to which organisms in a community occupy/exploit different levels above and below the sea bottom– Partitioning of space above the seafloor increased in

Ordovician time with advent of tall crinoids, etc.– No equally tall filter feeders since Jurassic time– Partitioning of space below the sea bed increased in

Late Paleozoic time (and continues to this day)– end-Permian extinction caused a temporary reduction

in tiering (throw-back to Precambrian)


Tiering: infaunal tropical shrimp


Tiering:tall crinoid


Tiering



• Escalation = “arms race” in the evolution of predation and defense capabilities– Triassic increase in kinds of shell-crushing

predators led to decline of lightly protected shellfish and preferential survival of forms with robust shells, burrowing, swimming, or other defense adaptations


Evolutionaryfaunas

weakly skeletonized taxa(e.g., trilobites) and few predators

increase in calcification of skeletons,but fauna dominated by sessilefilter-feeders

modern fauna dominated by taxawith robust shells and/or burrowing,swimming, or other defense adaptations


Predation scars on gastropod shell


Escalation: increase in “crushers” through time


Escalation: decrease in umbilicate and/or thin-shelled snails through time


Escalation: increase in heavily fortified snails through time

chapter 8—stuff to know

Documents

water depth depth

ecologic limiting factors

depthrelated factors

water depth lightlight

increasing depth

important limiting factor

study of fossils

water clarityphotosynthesis