Exercise 10 Fossil Lab Part 5: Crinoids, Blastoids, Fusulinids, Plants

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1 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. Figure 1. Restoration of a crinoid. 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 10 1

2 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. branches arms Figure 2. Enlarged view of a crinoid calyx. Note that the five arms split upward to produce a large number of smaller branches. columnals 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). ambulacrum anus Deltoid plates Radial plates Basal plates Figure 3. Enlarged view of blastoid calyx (side and top views). 10 2

3 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 10 3

4 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). 10 4

5 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. 10 5

6 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? 10 6

7 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). 10 7

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). Late Paleozoic ferns seemingly differed little from their modern counterparts. We have for your viewing pleasure some examples of fossil ferns (Figure 8). Figure 8. Artist s reconstruction of fossil fern leaves preserved in a concretion. 10 8

9 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 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 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. 10 9