Sample exam now on web
Soft parts from hard parts – putting the flesh back on
living representatives
analogy
soft part preservation
flattened faunas
soft part impressions on hard parts
muscle scars
bivalve and brachiopods
Form and function
Inferring function:
analogy with living representatives
model making and experimentation
direct analysis of fossil remains
Major points:
Morphological feature may not be “optimally-designed for several reasons:
1. Morphological features may have more than one function, preventing optimal functioning for any one particular task.
2. More than one feature may be involved with a particular function; organisms need to be functionally integrated.
3. Morphological features may look the way they do for reasons of ancestry (phylogeny), mode of construction, as well as function.
1. Analogy with living representatives.
Fossils probably have soft parts similar to their living representatives. If same species, then soft parts probably the same.
May not work so well with distant relatives.
Example: weighing dinosaurs
How can you estimate weight when the soft, fleshy parts of the dinosaur aren't preserved?
Most estimates of weight are based on scale models.
Scale model ankylosaur is 1/40th the length of a life size ankylosaur.
Now, we need to figure out the volume of the model. We can do this by seeing how much water it displaces when submerged.
volume without ankylosaur:
volume with ankylosaur:
The difference is the volume of the ankylosaur =
Now, volume is the cube of a linear dimension, so a 1/40 length (or width or height, i.e. any linear dimension) model is a 1/40 x40x40, or 1/64,000 volume model,
So, the volume of a full-size ankylosaur is equal to volume of scale model x 64,000
Dividing by 1,000 to get liters = 2,880 liters = volume of the ankylosaur
Living crocodiles have a density of 0.9 kg/liter, so a full sized ankylosaur weighed
0.9 kg/l x 2,880 l = 2592 kg
= this is 2.592 metric tons, or 5,702 pounds, or 2.85 US tons
sources of error/assumptions:
1. model is correct
2. measurements are correct
3. density estimate is correct (armor higher density?), croc not typical?
2. Rare preservation of soft parts. Frozen, amber, carbon films, pyrite replacement of soft tissue. Often like trying to deal with a flattened fauna.
Example: trilobite appendages. Extinct group of arthropods, known best from their exoskeltons. In few localities, the soft parts are preserved as thin films of carbon or as pyrite. Overheads
Burgess Shale Olenoides; middle Cambrian, British Columbia; carbon films
pair of antennae from head (cephalon); pair from rear (pygidium)
Limbs extending from below thorax and pygidium
Utica Shale Triarthrus, upper Ordovician, NY, pyrite replacement
Antennae at cephalon only
Note biramous (branched) limbs; walking below, gills above
3. Impression of soft parts on preserved hard parts (most common approach)
muscle scars on bones
muscle scars on shells
Example - bivalve mollusks and brachiopods (handout)
comparative anatomy: two major fossil groups of shelled, bottom-living filter-feeders
planes of symmetry, brachs: thru both valves. Bivalves, between the two valves
Mineralogy brachs:calcite. Bivalves mostly aragonite,
Diversity Brachs Paleozoic; Bivalves post-Paleozoic
hard parts and soft parts
brachiopods: soft part features vs. hard part features
bivalve molluscs: soft part features vs hard part features
Inferring function:
analogy with living representatives
most common, large sharp teeth in carnivores, eyes in trilobites, etc
model making - sometimes it prove useful to make physical or computer models in order to figure out the function of some structures.
1. Consider . U-shaped burrows - very common, but most are not exactly U-shaped
Usually slightly higher on one end;
Prairie dog burrows
Marine worm and arthropod burrows
ventilation of air or fluid - respiration or feeding
Bernoulli's Principle OVERHEAD; note areas of high and low pressure
Direct analysis - sometimes it’s possible to work with the fossil material directly and learn a lot about function
1. Pelycosaur sail. Recall that the area of the sale increased in proportion to the volume of the animal - evidence in support of a thermoregulatory function.
2. Trilobite eyes. OVERHEAD
By analogy with living arthropods, these are clearly eyes, compound eyes composed of
individual lenses.
Each lens is a single crystal of calcite, with the C-axis perpendicular to the surface of the eye.
Can look thru a calcite crystal in this direction.
What was the trilobite's field of vision? Direct analysis.
Project each lens onto a stereo net.
Field of vision almost 180 degrees front to back.
And from 10 degrees to about 20 degrees. Approach detected by progressive darkening: bottom to top - from below or the side; from top to bottom - from above