September 5, 2002
Taphonomy (in conclusion)
A common approach to see how well the fossil record reflects the animals that were alive at that time is to look at Recent habitats and faunas, and to compare the diversity and composition of the living faunal with that of the accumulating dead remains:
The Mugu Lagoon and Tijuana Slough studies mentioned earlier, for example.
Another example: marine mammals in the northern Gulf of California
Live fauna known from boat and aerial surveys
Skeletal remains from the beaches on the Colorado River delta – bones on the beach
Examined about 4 km of beaches,
Found 470 individual bones plus three carcasses
Identified species from skulls: 28 skulls found
Found 8 or 18 species known in northern Gulf. Why so few?
Some bones more common than others in living marine mammals
Skull:vertebrae:ribs:phlanges:girdle/limbs ratio is 1:74:30:68:16 (the expected ratio if everything preserved)
Among the dead (the observed ratio): 1:12:3:1:1 What bones are not well-represented? Why?
Record of activity and behavior of past life
Some species can leave body fossils, some trace fossils, and some both
Main types of trace fossils A. Traces on bedding planes
1. tracks. Discrete footprints (arthropods, vertebrates)
2. trails. Continuous traces of moving organism (worms, mollusks, arthropod)
B. Structures within the sediment
1. Burrows – structures formed within soft sediment by moving grains out of the way (vertebrates, mollusks, arthropods, worms).
2. Borings – structures formed in hard substrates such as shell, coral, limestone, wood, bone. Cutting through the grains mechanically or chemically. Mollusks, sponges, algae, worms.
C. Marks on body fossils
1. Drillholes - predation usually by snails on other molluscs
2. Repair scars – from sublethal injury (the animal recovered), the injury is
repaired in some way. Healed bones, repair scars on shells.
3. Feeding damage. Marks on bone, shell, leaves, left by herbviores and
predators . Munch marks.
D. Excrement
1. fecal pellets and fecal strings (<10 mm diameter). Crabs, snails, insects
2. coprolites. “Discrete fecal masses” = turds >10 mm in size. Vertebrates
E. Other
1. Root traces
2. Non-fecal pellets - owl pellets, hair balls, excavation pellets of crustaceans
Naming trace fossils – after distinctive morphology of the trace; not after the maker of the trace.
Skolithos – vertical tubes
Cruziana – trilobite crawling traces?
Ophiomorpha/Thalassinoides
Zoophycos
Same trace can be made by different organisms.
Different organisms can make the same trace.
Behavioral classification
Locomotion - repichnia
Resting traces - cubichnia
Dwelling traces – domichnia
Grazing traces – paschichnia
Feeding traces – fodichnia
A. Paleoenvironmental reconstruction
“ichnofacies” (0verhead and figure in lab handout): groups/assemblages of trace fossils that are indicative of particular environments.
Records of behaviors that are typical of certain environments (even though the maker of the trace may be different at different times)
B. Paleobiology
Compare relative abundance of species (potential prey) with relative abundance of drilled individuals. Prey is being selected if the proportions differ.
a. Posture in dinosaurs.
Sprawling (feet wide apart) vs upright (feet directly beneath). Bipedal and quadrapedal
b. Relative speed. Within a trackway, an increase in stride length indicates an
increase in speed.
c. Absolute speeds. But we can’t use stride length to compare different speed in different species of dinosaurs. Why not? Because smaller animals moving at the same speed as a larger animal need to take more strides. Their stride length will be smaller only because their legs are shorter. – more in lab later in the semester.