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Geology 1023 – Lab #11, Winter 2014
Mesozoic & Cenozoic invertebrates life forms, and hominids
This week’s laboratory will complete the study of the major invertebrate fossil groups by
focusing on the echinoderms (stelleroids, echinoids, crinoids, and blastoids), molluscs (clams,
snails, and cephalopods) and bryozoans. We will also have a brief look at hominid and primate
fossil skulls and some of the parameters used in the study of hominid evolution.
Phylum Echinodermata: Echinoderms include sea stars, sand dollars, sea urchins, sea
cucumbers, and crinoids (“sea lilies”). Echinoderms all show 5-fold symmetry best shown by sea
stars. However, close examination shows that one of the 5-fold rays is different and, strictly
speaking, echinoderms are bilaterally symmetrical — some obviously so (e.g., Micraster).
Class Echinoidea (Sea urchins): Echinoids are hemispherical or disc-shaped (sand dollars)
with 5-fold symmetry around the apex of the hemisphere (or disc). They are mobile and
benthic. Many have spines (urchins). Some burrow into sediment (e.g. sand dollars). They
are not abundant in fossil record but are best preserved in late Mesozoic and Cenozoic rocks.
Class Stelleroidea (Sea stars and brittle stars): Five-rayed, benthic, mobile forms that are
rare in the fossil record.
Class Crinoidea (“sea lilies”): Sessile benthic forms consisting of a globular body (calyx) of
tightly fitting calcite plates with five-fold radial symmetry and branching, tree-like “arms”.
The calyx is attached to the seafloor by a stem of variable length. The stems consist of
stacked, circular or pentagonal calcite plates called columnals. The arms also consist of
calcite plates, which are usually very small and are rarely preserved. Occasionally the calyx
is preserved intact, but typically the plates disarticulate after death. Separated columnals are
the most common crinoid fossil. Rock that consists mostly of crinoid debris is called
crinoidal limestone.
1. Study and compare the labelled drawing of a generalized crinoid (in handout) with the lab
display specimens 305–307. Make a drawing of one specimen, with scale. Label arms, calyx
and stem.
Variable drawing showing:
Arms
Calyx
Stem
Scale
Mesozoic & Cenozoic Life & Hominids – Winter 2014
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2. Display specimen 304 is a limestone made of crinoid debris.
a) What part(s) do you recognise (use handlens)?
Columnals and stems
b) What proportion of the grains is derived from crinoids?
>50%
c) Thus, what is the name for this kind of limestone?
Crinoidal limestone
3. Echinoid specimens 299–301, 339, 340 have 2 different symmetries. Make a labelled
drawing of a bilateral form with a scale and indicate its plane of symmetry and name.
Drawing of echinoid showing:
Bilateral symmetry
Scale
Name
4. Examine display specimen 302 (sea star). Does it truly have 5-fold symmetry?No, bilateral
5. Draw a labelled sketch of specimen 302 with a scale showing its symmetry.
Drawing of sea-star showing:
Bilateral symmetry (one arm
shorter than others)
Scale
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Phylum Mollusca: A very diverse group of invertebrates containing many extinct classes, three
of which are important fossils and also account for most aquatic invertebrates alive today. These
are Class Bivalvia (modern clams, mussels), Class Gastropoda (snails) and Class Cephalopoda
(octopus, squid and Nautilus).
Class Bivalvia: Bivalves are aquatic and live in both fresh and salt water. All are benthic,
some are sessile (e.g., mussels), others burrow into soft sediment (e.g., clams, razor-shells),
and others bore into harder substrates (including rock and wood, e.g., “shipworms”).
Bivalves have a hinged, calcareous, bivalved shell. Bivalves use a single set of muscles to
close the shell and an elastic ligament to open it. Thus, on the death of the organism the
valves pop open. As a result, fossil bivalves are usually preserved as separated shells (or
parts thereof). Brachiopods, in contrast, use two sets of muscles to open and close their shells
and are commonly preserved intact. IF a bivalve species has a plane of symmetry it passes
between the valves (in contrast to the brachiopods). Some bivalves are asymmetrical (e.g.,
oysters).
Class Gastropoda: Gastropods (snails) are the most abundant molluscs today (> 100,000
known species). They are found in terrestrial and aquatic (fresh and salt water) environments.
Aquatic gastropods are mobile, benthic forms and are both carnivores and herbivores.
Typically, gastropods have a single shell that is coiled in a helical (screw) spiral. A few
species have planar spirals. The shell is not chambered (c.f. cephalopods). Some forms do not
have shells (e.g., the common garden slug) and some do not have coiled shells. Gastropods
are important Mesozoic fossils.
Class Cephalopoda: Cephalopods are tentacle-bearing invertebrates that include octopus
and squid. Cephalopods are pelagic and move rapidly. Most are predators. Note also that
cephalopods are the largest invertebrates (e.g., modern giant squid as well as many fossil
forms). Modern cephalopods do not have an external skeleton with one exception, Nautilus.
The important fossil forms have a shell, which is divided into chambers by cross-cutting
walls (septa). The shell is commonly coiled though there are some “straight” forms (most of
which are early forms). The organism secreted new chambers as it grew and the soft tissues
occupied the last (largest) chamber. In contrast to gastropods, cephalopod shells are usually
coiled in a plane (planispiral) not a helix.
Where septa and outer wall join, “suture lines” develop. Suture lines can have simple or
complex shapes and that variability makes distinguishing species relatively easy. In addition,
suture lines showed marked changes with evolution. Thus, cephalopods are extremely
important zone fossils in the Mesozoic.
Sutures in shelled cephalopods are described by holding the cephalopod with the plane of
Mesozoic & Cenozoic Life & Hominids – Winter 2014
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symmetry (coiling) vertical and with the aperture on top and pointing away. Viewed this
way, sutures are variably wavy lines that are symmetrical across the plane of symmetry (see
morphology handout).
Cephalopods are divided into three orders. Two orders are shelled cephalopods and the
distinction is based on the suture shape. Shelled cephalopods are divided as follows:
1. Order Nautiloidea: Sutures are straight or gently curved.
2. Order Ammonoidea: Sutures have complex crenulated shapes.
The third order is different.
3. Order Belemnoidea. Belemnites were similar to the modern squid. They had an internal
skeleton (modern squid have “cuttlebones”). Belemnites (all extinct) had an internal,
translucent, honey-brown, bullet-shaped, rod of calcite called a “guard”. The guard is
very distinctive in shape and colour. Well-preserved guards show a conical opening at
one end called the phragmocone.
6. Display specimen 317 is a modern bivalve, Mercenaria. Using your handout as a guide, draw
a sketch with scale. Label at least 3 of: teeth/sockets, ligament area, muscle scars, palial line,
and palial sinus.
Drawing of bivalve showing (at least three of):
Teeth/sockets, ligament pit, muscle scars, palial
line, palial sinus
Scale
7. Give two features of 317 that indicate it is a clam not a brachiopod.
Two of: Not symmetrical, ligament pit, no pedicle
opening, one set of muscle scars, …
8. Two of the fossil specimens in your specimen drawer are bivalves. Which ones are they?
F17
F24
One of: Not symmetrical across shell, muscle scars, etc.
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What feature(s) indicate that they are bivalves not brachiopods?
9. Specimens 308, 309, 310, and 312 are “snails”. Draw a sketch of one of them with scale.
Label the “apical angle”, an important distinguishing feature. (See morphology handout).
Drawing of snail showing:
Apical angle
Scale
10. Specimen 310, and F19 (from your drawer) is a snail, but both are somewhat unusual for
snails in one respect. What is it?
Coiled in a plane not a helix.
11. Specimens 322–329 and 341–345 are cephalopods. List which one(s) is (are):
Nautiloids:
322, 326(?), 343
Ammonoids: 323, 324, 325, 326(?), 327, 329, 341, 342, 344, 345
Belemnites:
328
12. Note that specimen 323 is somewhat unusual for a cephalopod. What feature makes it so?
[Hint: this is the reverse of question 10.]
Coiled in a slight helix.
Phylum Bryozoa: Bryozoans are colonial, mostly marine, tentacle-bearing, filter-feeding,
benthic invertebrates. Individuals are very small or microscopic. Each individual secretes it own
individual, calcareous or chitinous tubes (zoecia) that joins with others to form a twig-like,
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branching, or frond-like colony called a zoarium. The colonies commonly have a lacy sheet-like
structure (fenestrate), and may exist separately or be an encrustation on other organisms
(including plants). One form (Archimedes) occurs as a lacy sheet twisted in a corkscrew shape.
Many forms are featureless but velvety small mounds or encrustations on rocks, seaweed and
other sessile organisms.
13. Display samples 278 to 281 are bryozoans. Examine them and then look at the specimens in
your sample drawer. Using the display specimens and the identification charts indicate which
specimens in your drawer are bryozoa (there are four, including a modern one).
F7
F8
F9
F23
Humans (and their nearest relatives).
In paleoanthropology (study of fossil humans and their relatives), we must classify hominid
species on the basis of aspects of their skeleton. We must be aware however, that much of what
makes (or made) humans different from their ancestors and modern related species is not readily
seen in our skeletons. We focus particularly on the one aspect that does seem to show the most
difference, the size and shape of the skull. Paleoanthropologists use a wide variety of skull
measurements to distinguish between various species of hominids. We will make a few
measurements (and calculate ratios) to compare the 11 skulls in our collection. Of particular
importance are: braincase size, whether the foramen is under the skull or at its back, the presence
(and size) of brow ridges, the slope of the forehead, etc.
The diagram at the left shows some of the dimensions we will
use to calculate various ratios.
a. The condylar position index (CPI) = CD/CE x 100. “C” is the
occipital condyle, a boney knob beside the foramen (the hole
where the spinal chord emerges from the skull). The CPI is
highest in humans (where the foramen is far forward).
b. The angle of the forehead, “J”, is measured relative to the
plane of the eye sockets (orbits). In modern humans this is
around 20°, in apes and more ancient humans the forehead
slopes backwards considerably (i.e., J is larger).
c. Eyebrow ridges (supraorbital torus) are a prominent feature of ape and
many hominid skulls. The function of the ridge seems to be to distribute the
forces associated with chewing a largely vegetarian diet.
d. Apes and some early hominids have/had a bony crest along the top of the
skull (sagittal crest). This is present in forms that had very large jaw muscles
(for a vegetarian diet perhaps). Some modern humans have a relict of this, a
sagittal keel. Looking face-on (and provided they are bald) they have a
“pointy-headed” appearance (e.g., Patrick Stewart, a.k.a. Jean-Luc Picard).
Mesozoic & Cenozoic Life & Hominids – Winter 2014
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e. Many apes and other primates have large canine teeth. The larger canine requires a gap (called
a canine diastema) in the opposing jaw into which it fits. Enlarged canines and associated
diastemas disappeared early in humans.
14. Measure the CPI and forehead angle for the specimens. Indicate if brow ridges are Absent,
Slight, Prominent or Extreme. Indicate if the specimen has a sagittal crest (Y/N). Determine
(if possible) if there are Enlarged canine teeth (≥ 50% larger than the other teeth) and if there
is an associated canine Diastema. Some of the specimens are damaged and don’t show every
feature (particularly the teeth and any associated diastemas).
Indices/traits
Brow ridges
(Absent,
Slight,
Prominent,
Extreme)
Sagittal crest
(Y/N)
Enlarged
canines, canine
Diastema (or
Neither)
E
N
E
≈30-50°
S
N
No
4/12.5 x 100
=30–50
≈35-55°
P
N
cannot see
H04
cannot
measure
≈40-70°
E
Y
cannot see
H05
6/14 x 100
=30–50
≈40-60°
P–E
Y
No
H06
5/9.5 x 100
=40–60
≈25-45°
S
N
No
H07
6/11.5 x 100
=40–60
≈45-65°
P
N
No
H08
8/11.5 x 100
=65–85
≈50-60°
S–P
N
No
H09
7.5/10.5 x
100 =65–85
≈10-30°
A
N
No
H10
2/15.5 x 100
=10–30
≈40-60°
P–E
Y
E+D
H11
5/19.5 x 100
=20–40
≈55-75°
E
Y
E+D
Skull #
CPI
(condylar
position index)
Angle of
forehead
H01
4.5/12.5 x
100 =25–45
≈70-90°
H02
4/11.5 x 100
=25–45
H03