FOSSIL 1: BRACHIOPODA AND PELECYPODA

In paleontology lab sessions (specifically when dealing with animal fossils in the form of body fossils), we are typically asked to draw the organism in 3D, showing three different views and including a scale. Let’s break this down:

1. The 3D representation must include dimensions of length, width, and height.

2. In general illustrations, the views we usually use are top, bottom, back, front, and side. However, when identifying animal body fossils, this doesn’t apply, as we use different anatomical terms for the views. These are:

   • Dorsal: Refers to the underside of the organism when it was moving.

   • Ventral: Refers to the top side of the organism when it was moving.

   • Posterior: The end opposite to the direction of movement.

   • Anterior: The end in the direction the organism was moving.

3. The "scale" refers to the actual measurements of the original fossil taken using tools such as a ruler. The length, width, and height are measured and then noted on the drawing.

Now, I will begin this session's fossil discussion with brachiopoda and pelecypoda fossils.

BRACHIOPODA

A. Definition

• Etymology: Brachion – arm and Pous – foot
• Scientific Definition: Brachiopoda are marine animals that possess hard valves (shells) on both their upper and lower surfaces.

B. Definition

• Sessile organisms, either attached to a substrate or burrowed into sediment.
• Typically found in calm marine environments, avoiding strong currents.
• Exhibit bilateral symmetry when viewed from the top (left and right sides are symmetrical).

C. Taxonomic Level

• Phylum: Brachiopoda

D. Classifications

a. Inarticulata (without hinge)

• Shells are usually composed of organic material such as chitin or horny substances.
• They lack a hinge and supporting structures for the lophophore (feeding organ).
• Fossils from this group are mostly found in rocks dating from the Cambrian to the Silurian periods.

b. Articulata (with hinge)

• Shells are typically composed of calcium carbonate.
• Equipped with a hinge mechanism and usually have internal structures to support the lophophore.
• First appeared in the Cambrian period, with their peak abundance occurring from the Ordovician to the Carboniferous.

E. Morphology

• Pedicle: A stalk-like structure used to anchor the organism to the sediment or substrate.
• Pedicle valve: The valve through which the pedicle emerges; typically the ventral (lower) valve.
• Brachial valve: The opposite valve, typically housing the lophophore; usually the dorsal (upper) valve.

F. Index Fossils

• Spirifer: Lived from the Ordovician to the Triassic period.
• Terebratula: Commonly found in rocks from the Devonian period.

PELECYPODA

A. Definition

• Etymology: Pelecys – small axe and Podos – foot
• Scientific Definition: A flat-footed organism, with limbs shaped like a small axe blade.

B. Characteristics

• Inhabit freshwater environments.
• Exhibit bilateral symmetry when viewed from the side (the upper and lower shells are symmetrical—equivalved).

C. Taxonomic Level

• Class: Pelecypoda (also known as Bivalvia)

D. Morphology

DIFFERENCES BETWEEN BRACHIOPODA AND PELECYPODA

A. Shell Appearance

• Symmetrical from left to right, but lateral appearance is asymmetrical (Brachiopoda).
• Asymmetrical from left to right, but lateral appearance is bilaterally symmetrical (Pelecypoda).

B. Interior and Posterior Orientation

• Determined based on the vertical direction (Brachiopoda).
• Determined based on the horizontal direction (Pelecypoda).

C. Shell Differentiation Criteria

• Shell size and the presence of a pedicle opening (Brachiopoda).
• Presence of a beak projection (Pelecypoda).

D. Beak Orientation

• Upright (Brachiopoda).
• Slanted (Pelecypoda).