Taphonomy

Taphonomy is the study of all the changes that take change or alter the carcass or body of a plant or animal from the time it dies to the time that it may be dug up as a fossil. Often, a taphonomic study of shells, skeletons, pollen, leaves, wood, etc. will reveal a lot of information on the pre-mortem and post-mortem environments at the burial site. Consider some hypothetical examples and answer these questions: A collection of two separate species of clam shells is measured. The two species are close to the same size and thickness and their general shape is about equal. Curiously, one species is almost invariably found with both of the valves (shells) intact and whole (unbroken) while clams of the other species are almost always in small pieces. The two fossil species are found at very near the same level in the rock layers thus they are roughly the same age.
Write up a short narrative to suggest two reasons why one clam species might be represented by whole, unbroken specimens, while the other is fragmented. Small rodents such as squirrels, rats, mice, voles and gophers are the most diverse (most different) and abundant (most specimens) of all mammals. Rodents are moreover “keystone taxa” the food staple for huge numbers of predators including hawks, owls, eagles, crows, heron, opossum, skunks, wolves, foxes, coyotes, bobcats, cougars, raccoons, weasels, mink and badgers. Clearly to sustain themselves in the face of such an appalling number of predators, rodents must have A. large litters of young, B. very short gestation period and C. almost unbelievably high numbers of specimens (high “biomass”). When a small rodent is caught and eaten the skeletal parts are, at best, crushed or macerated, or at worst, entirely dissolved in the gastrointestinal tract of the predator/scavenger. In spite of this, the bones of small fossil rodents are easily the commonest vertebrate fossil in comparison to any ungulate (larger hoofed mammal) or predator. Write a short narrative to explain this apparent enigma.
When an extant (modern) ungulate (hoofed mammal) such as a deer, elk, moose, camel, buffalo, etc. dies, small as well as large rodents (porcupines) almost always chew up the bones for their calcium content even as the carcass is decomposing. Skeletal parts that are particularly rich in calcium, such as antlers, are usually destroyed entirely. In the fossil record however, we often find ungulate fossils within yards of each other where the bones of one group will be thoroughly chewed or worked over by rodents, while another close by will be pristine, without a mark on them.
Write up a short narrative that might explain this disparity. In dealing with vertebrate fossils, such as mammals or reptiles, the teeth are the only skeletal parts that are almost invariably preserved. Thus many classifications of fossil mammals rely heavily on teeth. Even after passing through a gastrointestinal tract, teeth are usually in perfect condition while bone from the same skeleton will be variously broken, crushed or even dissolved. What you would suppose teeth have that bone lacks? If we divide sedimentary environments into two separate realms: marine (oceanic) and non-marine (land and fresh water) we see a huge contrast in the quality and quantity of the fossil record. Scavengers that pick over a carcass abound in both environments, but they are much more diverse and thorough in marine settings. If we examine the energy of the sedimentary environments, we find that on land, with the exception of lake deposits, most environments are of relatively high energy or rapidly moving water as streams, rivers, etc. In contrast, the ocean environment has high energy along the shorelines in the surf, but offshore in deeper water, most of the environments are very low energy, quiet settings. If we look at the fossil record of the two, we find that the ocean settings are far more complete and representative of the ocean biota than the non-marine record. Marine fossils moreover, unless they lived in the turbulent surf zone don’t bear nearly as much abrasion and wear as those in non-marine settings.

With this summary in mind, would you expect a lake floor to have as complete and well preserved a fossil record as an ocean floor? Also speculate as to why most non-marine fossils are usually badly abraded (worn) , eroded and scattered. Finally, if we consider the relatively unlikely happenstance of a fully articulated (whole) skeleton in the fossil record, such as a fish or an elephant, speculate as to the conditions that might be necessary to preserve an animal or a plant in such a fully assembled or articulated state. Would these conditions be more easily met in a marine or non-marine setting? Why?

 

 

 

 

 

 

 

 

Sample Solution

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