Hands on Activities for Understanding Ammonite

Sutures

Clint Cowan Carleton CollegeOn the Cutting Edge - Professional Development for

Geoscience Faculty

Teaching Paleontology in the 21st Century

Goals

• Short term / Lower Level goals– Spatial reasoning / Visualization– Implicit or Explicit:

• 2D to 3D Reasoning• Using biological actualism• Understanding shell growth in Molluscs• Understanding preservation (steinkerns,casts &

original material)

– “Complexity” in a simple system

Supplies

• Fossil Ammonites www.stonesbones.com– Between $50 - $150 per (depends size, etc.)

• Nautilus shells: www.SeaShellCity.com– Between $15 - $50 per (depends size, etc.)

• Glass plates from local handyman• Play-Doh, food coloring (Kmart)• Tubing, syringes, cover slips, Glycerol - lab

supplies

For complex sutures, many students have trouble physically relating the septum to the suture

It helps to go back and forth between the Nautilus and the ammonoid…

Prove you know it by building it…

Making a fluted or convolute edge to your chamber wall really drives the concept home

“Oh yeah!” The sutures are only visible where the phragmacone has been chipped/worn away

One year, a student simply couldn’t get it… until we buffed away part of the phragmacone of the Nautilus to expose the edge of a chamber wall, and that did it…

Filling some chambers with Play-Doh helps get the steinkern point across, too.

Jordy, show me how and where the animal adds new shell material to grow…

SHOW ME:

growth lines

sutures

ornamentation (?)

What are the relationships (if any) between these?

How are color

(or for a clam, a periostracum)

secreted ?

Then I hit them with a 20 minute ppt presentation about biomineralization, with an emphasis on the Mollusks.

How do sutures get to be dendritic ? (NOTE: this is not the same question as what is the purpose of dendritic sutures)

complex shape = complex explanation?

The Hele-Shaw CellTechnique borrowed from: The Center for Polymer Studies at

Boston University “Exploring Patterns in Nature” website Two glass plates, one with a hole drilled in the center

Cover slips

Plastic tubing that fits snugly in the hole in the glass plate, and syringes that fit snug-but-easy inside the tubing

Glycerin, Food Coloring

Binder Clips

Windex and Paper Towels (critical)

2 glass plates

~ 8” square

Two stacked micro cover slips in each corner (2 x 150 µm = 300µm gap

top plate has holedrilled in it

put a piece of white paper underneath for better visibility

1 regular binder clip at each corner keeps the whole thing together

QuickTime™ and aMotion JPEG OpenDML decompressor

are needed to see this picture.

Did ammonites somehow run the biological equivalent of a Hele-Shaw experiment?

Goals

• Long term Higher Level goals (Essay)– Functional Morphology– Natural Selection– Driven vs. Passive Trends– Argument Construction– Familiarization with Peer-Reviewed

Literature (sources)

What would the biological parts be that are analogous to our experimental Hele-Shaw apparatus?

You have: cameral fluid, visceral fluid, membrane between them, and space between inside of phragmacone and body membrane

This always comes up: What did the ‘backside’ of the soft animal look like? How do organisms “secrete” minerals?

Thinking more about complex sutures:

Did the animal re-run a Hele-Shaw experiment each time it scooted forward?

… or … did the animal run a Hele-Shaw only the first time it scooted forward and created the first septum, and then the rump remembers the shape (was cast in that fluted configuration)?

How do sutures increase in length to accommodate increased circumference of phragmacone as creature grows?

S-t-r-e-t-c-h-i-n-g ?

or

Adding new bits ?

Is the dendrite shape (in detail) coded for genetically?

isn’t this how ammonite species are recognized?

So … yes….it must be… but what is coded?

8 Teams in lab each ran a Hele-Shaw experiment using the same fluids and set-up….

Were the dendrites identical between the teams ?

(close enough to recognize them as the same species?)

(… or is the Hele-Shaw not really a good analogy?)

•What benefit (if any) did complex sutures impart ?

• They must be coded for if they are selected for…

• If they are selected for, then they must provide some benefit (increased fitness)

• Is the data on ancestor-decendent lineages robust enough to be able to say complexity increases? Where does this data come from?

• If sutures start out simple, is there any way to change except toward more complex ? (random walk away from a left wall S.J. Gould’s “Full House”)

Questions for further study

Why did the more simply-sutured Nautilus survive?

(rules of the game during ‘normal’ times and at times of environmental perturbation (at extinction events))