Geology 1023

Lab #11

Mesozoic and Cenozoic life, and hominids

3 major invertebrate phyla• Echinodermata (spiny skinned)

– Class Echinoidea– Class Stelleroidea– Class Crinoidea

• Mollusca– Class Gastropoda– Class Bivalvia– Class Cephalopoda

• (Bryozoa)

Phylum Echinodermata

• Class Echinoidea (urchins and sand dollars)– Internal but peripheral skeleton (most of the

soft tissue is internal to the skeleton)– Mobile, benthic– 5-fold radial symmetry (actually bilateral in

detail)– not abundant in fossil record, and best

preserved in Mesozoic and Cenozoic

Echinoid morphology

Phylum Echinodermata

• Class Stelleroidea– Star-shaped forms– Mobile, benthic– Apparent 5-fold symmetry (actually bilateral)– Rarely preserved as fossils

Phylum Echinodermata

• Class Crinoidea– Sessile– Holdfast, stem, calyx, arms– Radial symmetry– All components made of calcite plates

• stems plates (columnals) are circular or pentagonal

• calyx plates are polygonal (hexagonal)

– Some limestones composed almost entirely of crinoid material (crinoidal limestone)

Crinoid morphology

Modern crinoid: Antedon

Phylum Mollusca

• Three very important classes– Gastropoda (snails)– Bivalvia (“clams”)– Cephalopoda (octopus, squid & Nautilus)

• Very important fossils of the Mesozoic and Cenozoic

Class Gastropoda

• Very abundant (80,000 known living species, perhaps up to 250,000 in total)

• Terrestrial and aquatic• Shell (if present)

– Single– Coiled in a helical spiral (i.e., no plane of

symmetry)– Unchambered

• Important in Mesozoic

Apical angle

Large apical angle

Small apical angle

Class Bivalvia• Shells

– Two– If symmetry is present, plane of symmetry between

the shells (c.f. brachiopods)– Some forms have no symmetry (e.g., oysters)

• No internal hard parts (c.f., brachidium)

• No pedicle opening

• Ligament area (pit)

• Simple muscle scars (1 or 2, only)

• Palial line (± sinus)

Bivalve morphology

Class Cephalopoda• Pelagic • Tentacle bearing• Shells

– Shells are coiling in flat spiral (i.e., plane of symmetry) – Divided by septa into chambers

• Shelled cephalopods – Very common and very important in Mesozoic (zone

fossils)– Most modern forms have no shell (octopus, squid);

largest invertebrate animals alive today

Class Cephalopoda

• Shelled forms divided into 2 orders on the basis of the shape of the suture– Nautiloidea (straight or gently curved sutures)– Ammonoidea (convoluted sutures)

• Belemnoidea = A squid-like order with an internal skeletal element called a “guard”– Guard is cigar-shaped, honey-brown calcite rod

Nautiloid

A straight nautiloid

Ammonite

Ammonite morphology

Belemnite guards

Belemnites and ammonites

Phylum Bryozoa

• Colonial

• Marine (mostly), benthic, filter-feeders

• Individuals (zoids) are microscopic and occupy minute structureless cavities (zoecia) on lacy frond-, sheet- or mound-shaped colonies (zoaria)

An ancient

bryozoan

Hominins• Most of the prominent skeletal differences

are visible in the skull

• Many different parameters that can be measured– Position of the foramen (condylar position

index – high in hominins)– Angle of the forehead (high in hominins)– Brow ridges (small)– Sagittal crest or keel (absent)– Enlarged canines and canine diastema (absent)

Condylar position index• C = occipital

condyle (boney knob beside the foramen)

• CD/CE x 100• CD = 6.3 cmCD = 6.3 cm• CE = 16.2 cmCE = 16.2 cm• CPI =

6.3/16.2x100 = 39

Forehead angle

• Forehead angle = J

• Measured from plane of the orbits (eye sockets)

• Relatively small (<20°) in modern humans

Other features as seen in a gorilla skull

• Sagittal crest

• Brow ridges

• Canine diastema

• Enlarged canine

Questions?

Reminder!

• Final lab exam next week!