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Exercise 10

Fossil Lab—Part 5:

Crinoids, Blastoids, Fusulinids, Plants

ECHINODERMS (CRINOIDS AND BLASTOIDS):

Echinoderms are an extremely diverse group of advanced invertebrates

including such familiar forms as starfish, sand dollars, urchins, and sea

cucumbers. The name echinoderm means “spiny skin.” Apart from their

spiny skin, all echinoderms are united in exhibiting five-fold (pentameral )

symmetry. There are a large number of classes of echinoderms, many of

which have good fossil records. In this lab, however, we will focus only on

the crinoids and blastoids because of their abundance in Upper Paleozoic

rocks. These stalked echinoderms were so pervasive during the

Mississippian and Pennsylvanian periods, that their remains make up the

dominant particles in many bioclastic limestone deposits.

Crinoids and blastoids both share a common overall morphology consisting of

a calyx (or “head”), stem, and holdfast (or “root”) (Figure 1). The stem is

made up of a stack of disc-shaped elements called columnals. The calyx

Figure 1. Restoration of a crinoid.

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consists of a number of polygonal plates, with arms typically extending

upward for filtering nutrients from sea water.

All crinoids possess five arms attached to the calyx (Figure 2). The arms

typically split into a much larger number of smaller branches. Upon death of

an individual, the plates making up the calyx and arms usually disarticulate to

become isolated sedimentary particles. Preservation of intact specimens is

uncommon.

Blastoids possess a large number of small erect arms in life, but the arms

are almost never preserved in fossil specimens. Rather, the calyx of a fossil

blastoid is distinguished by its very obvious pentameral symmetry and the

presence of 13 plates. There are three basal plates, five radial plates, and

five deltoid plates. A feeding structure called the ambulacrum is positioned

within each radial plate. The mouth and anus are located at the top of the

calyx, with the anus being the largest of the five pores (Figure 3).

Figure 3. Enlarged view of blastoid calyx (side and top views).

Figure 2. Enlarged view of a crinoid calyx. Note

that the five arms split upward to produce a large

number of smaller branches. arms

branches

Deltoid plates

Radial plates

Basal plates

ambulacrum

columnals

anus

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Paleoenvironmental Range:

During the Paleozoic Era stalked echinoderms lived in continental shelf

environments in tropical and temperate latitudes. Crinoidal and blastoidal

skeletal debris is present in almost all bioclastic limestones of Mississippian

and Pennsylvanian age. Today, stalked echinoderms occur mainly in very deep

water (bathyal and abyssal depths). Highly specialized stalkless crinoids live

today in shallow water reef environments.

Stratigraphic Range:

Crinoids originated in the Cambrian Period and still exist today, although

their golden age was in the Late Paleozoic. Blastoids originated in the

Ordovician Period and became extinct at the end of the Permian Period.

Crinoid Examples:

1. Crinoid calyces with arms intact. Specimen ECL 20 exhibits very

delicate arms with fine “pinnules.” Note the bifuraction (splitting) of

of arms just above the calyx. Specimen PEL 2 has five arms, each of

which has split into just two branches.

2. Crinoid with arms and fine “pinnules.”

3. Basal part of crinoid calyx. The calycal plates are well preserved on

this specimen. Note the large number of plates and their polygonal

shape.

4. Examples of partial crinoid calyces.

5. Basal part of a crinoid calyx. Examine this specimen closely. What is

unusual about it?

6. Sawed block of limestone with intact crinoids. These crinoids have

both the calyx and parts of the stems preserved. Make sure you can

identify the columnals.

7. Another example of a crinoid calyx with arms attached.

8. Assorted crinoid calyces, stems, and holdfasts. This assemblage is

extraordinary in that holdfasts are rarely preserved so nicely. The

holdfast is that part of the animal’s body that anchors the animal in

sediment (superficially analagous to the roots of a plant). Note the

columnal making up the stem.

9. Crinoidal limestone. Usually crinoids fall apart upon death and their

disarticulated remains accumulate as carbonate sediment. The

columnals are most abundant. Mississippian and Pennsylvanian age

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crinoidal limestones are common and very thick in many parts of the

world, including Iowa.

Blastoid Examples:

1. Blastoid calyx exhibiting well preserved ambulacra.

2. Assorted blastoid calyces. Feel free to remove specimens from vials,

but please don’t get them mixed up. Make sure you can recognize

ambulacra, radial plates, and the position of the anus. The mouth was

situated in the middle of the five pores in the center of the upper

calyx.

3. Pentremites. You will be asked to identify this genus on the Lab Exam. Examine the specimen carefully, noting the ambulacra, anus,

etc. Can you distinguish basal, radial, and deltoid plates?

4. Another Pentremites. This specimen is very well preserved. Note

that the upper part of the stem is still attached to the calyx. Can you

see individual plates?

5. Unidentified blastoid. Look at this specimen carefully. Can you tell

which end is the top and which is the base?

FUSULINIDS: The order Foraminiferida includes single-celled animal-like protists that

secrete mineralized skeletons. “Forams” are among the biostratigraphically

most useful of all fossil groups because of their abundance, widespread

distribution in marine deposits, and rapid rates of evolution. As a group,

forams range from Cambrian to today. Both benthonic and planktonic types

exist today, but the planktonic types originated in Mesozoic time and

probably are only distantly related to the benthonic types.

Fusulinids are a particular group of forams that lived during the

Pennsylvanian and Permian periods. They are unusually large for single-celled

organisms, sometimes reaching a length of 1 inch or more. They are easily

recognized by their distinctive “wheat-grain” shape. A fusulinid shell

consists of an initial spherical chamber followed by a spirally coiled

arrangement of successively larger and more elongate chambers. Partitions

between chambers are called septa. Folding and fluting of septa can give

rise to a complex internal appearance. Because fusulinids are characterized

on the basis of their internal anatomy, fusulinids are studied almost

exclusively in thin sections (Figures 4 and 5).

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Figure 4. Partially sectioned fusulinid showing external and internal structure.

Figure 5. Sectioned fusulinid showing spherical initial chamber and several additional volutions. Intense

folding of the septa gives rise to a complex internal appearance.

Fusulinids were extremely abundant in tropical and subtropical carbonate

environments, and like stalked echinoderms, they are major “rock-building”

fossils. Moreover, they evolved at very rapid rates, having diversified from

a single ancestral species in early Pennsylvanian time to well over 5,000

species by early Permian time, a span of about 30 million years. It is no

accident, then, that they serve as index fossils for correlating Pennsylvanian

and Permian rocks.

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Paleoenvironmental Range:

Fusulinid lived mostly in shallow water, tropical to sub-tropical carbonate

environments. Some were adapted for life in or near reefs.

Stratigraphic Range:

Fusulinids originated in the Pennsylvanian and became extinct at the end of

the Permian, coincident with the end-Permian mass extinction.

Fusulinid Examples:

1. Fusulinid limestones. Like crinoids, fusulinids were rock-building

organisms during the Late Paleozoic. The fusulinids that make up most

of these rocks are the relatively small, wheat-shaped objects.

Although small in absolute terms, fusulinids are very large by

comparison with most other protists.

2. Silicified fusulinids. This rock sample is a fusulinid limestone that has

been altered to chert. The fusulinids are white and the surrounding

matrix is black. Can you see any internal or external structures

preserved in the fusulinids?

3. Large fusulinids. These individuals are nearly an inch long (yikes!).

4. Isolated fusulinids in vial. Use the microscope to examine the

external surface of these shells. Can you see the septal furrows

between chambers?

5. Thin sections of fusulinids. Notice that the internal structure of the

shells is much more complex than the external surface you examined

at station 4. On the basis of size and internal complexity, which of

the specimens is more advanced evolutionarily?

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PLANTS:

In this lab we will focus on those plants that contributed to the

Carboniferous coal swamps (mainly lycopsids and ferns), as well as

sphenopsids.

Lycopsids typically are small spore-bearing plants, but during Carboniferous

time some grew to tree-scale proportions. The two most common genera of

tree-like lycopsids are Lepidodendron and Sigillaria. These plants are easy

to distinguish on the basis of leaf scars preserved as impressions. In

Lepidodendron, the leaf scars are arranged in diagonal rows, whereas in

Sigillaria they are arranged in vertical rows (Figure 6).

Figure 6. Reconstructions of Lepidodendron (left) and Sigillaria (right). Note arrangement of leaf scars.

Sphenopsids are distinctive plants that possess circular nodes along their

stems. The stems are ornamented by vertical ridges or ribs, and a ring of

leaf-bearing branches radiates from each node. Today the only remaining

sphenopsids are the scouring rushes known as “horse-tails” (Equisetum).

Probably the most common Carboniferous sphenopsid was the tree-size

Calamites. The leafy branches of the Calamites tree are given the name

Annularia. [Apparently, the tree and its branches were given separate

Linnean names before it was recognized that they are simply different parts

of the same plant.] (see Figure 7).

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Late Paleozoic ferns seemingly differed little from their modern

counterparts. We have for your viewing pleasure some examples of fossil

ferns (Figure 8).

Figure 7. Sphenopsid fossils. The trunk

of the large sphenopsid tree is known as

Calamites (left), characterized by circular

nodes and vertical ribs. The branches that

radiated from nodes are known as

Annularia (right). An entire plant is shown

in the reconstruction (below).

Figure 8. Artist’s reconstruction

of fossil fern leaves preserved in a

concretion.

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Plant Examples:

1. Fern impressions. Look closely to see the exquisite detail preserved in

these fossils.

2. More fern impressions. Again, the exception preservation shows the

details of leaf shape and even internal veins.

3. Modern sphenopsid Equisetum. Note the circular nodes on the stems

of these specimens. The ones preserved in leucite have small

branches radiating out from nodes.

4. Fossil sphenopsids. All of these specimens are trunk internal molds of

the tree-like Calamites. You will be asked to identify this genus on the Lab Exam. Note the nodes and longitudinal ribs.

5. Annularia (sphenopsid branches and leaves). You will be asked to

identify this genus on the Lab Exam. Each branch possessed a

series of circularly arranged leaves.

6. Modern ferns and sphenopsids. These specimens preserved in leucite

are typical small primitive plants. Contrast their size with that of

their Late Paleozoic relatives. Also, compare the “branches” of

modern Lycopodium with the fossil specimen at station 8.

7. Fossil lycopsids. Several examples of Lepidodendron internal molds.

You will be asked to identify this genus on the Lab Exam. The

distinctive characteristic of Lepidodendron is the diagonal

arrangement of leaf scars. Compare with Sigillaria (station 9).

8. Lepidodendron branch. Compare this specimen with the modern

lycopsid, Lycopodium, at station 6.

9. Sigillaria (fossil lycopsid). You will be asked to identify this genus

on the Lab Exam. In contrast to Lepidodendron, the leaf scars in

Sigillaria are arranged in vertical columns.

10. Lycopsid coal balls. Coal balls are masses of well preserved plant

tissue preserved in coal seams. By making thin sections of a coal ball,

the internal vascular structure of constituent plants can be

determined, thus enabling plant identification.