Geology 3020

The PALEOZOIC has been called the "age of marine invertebrates". The animals that characterize the lower Paleozoic evolved from earlier soft-bodied METAZOANS of the Precambrian. The record of life is more evident in the Paleozoic due to the development of hard body parts that were more readily fossilized; for example, calcium carbonate shells; chitinous external skeletons (modern examples are crabs, insects). Virtually all lower Paleozoic life was MARINE - the land was almost entirely devoid of plants and animals (at least until Silurian time).

MODES OF LIFE
Certain terms define the way in which an organism lives. BENTHONIC organisms are marine bottom dwellers. Benthonic animals may be sessile (attached), vagrant (move around), or burrowing (dig in). Pelagic organisms may be either NEKTONIC (free swimmers) or PLANKTONIC (floaters). TERRESTRIAL animals live on land.

KINGDOM ANIMALIA
The Kingdom Animalia is defined as animals that are multicellular and use other organisms for food.

PHYLUM ARTHROPODA
The arthropods are the most abundant and diverse group of animals known today. Included in this phylum are the lobsters, spiders, insects, centipedes, and many other such animals. It is estimated that there are over a million species and that this group of animals comprises over 80 percent of all known living animals. They exist in all terrestrial, fresh-water, and marine environments and move about by all forms of locomotion. Arthropods posses CHITINOUS exterior skeletons, segmented bodies, paired and jointed appendages, and highly specialized nerve and sensory organs. Only a few groups have left a significant fossil record. Even insects, so numerous and diverse today, left few fossils because preservation is difficult for animals that die in terrestrial environments.

SUBPHYLUM CHELICERATA
These arthropods have pincer-like claws, and include scorpions, king crabs, and the extinct EURYPTERIDS

1. Visit the University of California at Berkeley Museum of Paleontology Eurypterida page 
   
   http://www.ucmp.berkeley.edu/arthropoda/chelicerata/eurypterida.html

1. Were Eurypterids grazers, scavengers or predators?
2. How big did they grow?
3. When did they appear?
4. When did they become extinct?
5. Why are Eurypterids commonly referred to as "sea scorpions"?

SUBPHYLUM TRILOBITA
TRILOBITES were the most important fossil-forming arthropods. They were entirely marine, and most forms were vagrant bottom dwellers. Trilobites first appeared about 600 million years ago. New species of trilobites appeared at a rapid rate during the Cambrian and Ordovician periods, but thereafter began to decline, finally becoming extinct in the Permian period.

The name trilobite means "three lobes" and refers to the division of the carapace into three longitudinal portions: the axial lobe and two pleural lobes. The three major body segments of trilobites are the CEPHALON (head), THORAX (segmented body), and PYGIDIUM (tail).

1. Three different species of early Paleozoic trilobites are on display in the lab:

Peronopsis interstrictus from the Cambrian of Utah

Elrathia kingi from the Cambrian of Utah

Phacops speculator from the Ordovician(?) of Utah(?)

 
Visit the Virtual Fossil Museum:

 http://www.fossilmuseum.net/index.htm

 and click on Fossils and then Trilobites.  Use the images and descriptions to identify the trilobites in the lab (body size, body shape and eye shape are all helpful identifiers).

a.

b.

c.

PHYLUM BRACHIOPODA
Brachiopods are found throughout the geologic record back to the Cambrian period. However, during the Paleozoic era, they were far more abundant and diverse than they are today.

Brachiopods are composed of two shells (valves) and are similar in appearance to the bivalves (clams, etc.). However, the two valves of the brachiopods are not the same size: the larger valve, called the PEDICLE VALVE, somewhat overlaps the smaller valve, called the BRACHIAL VALVE.

There are two major classes of brachiopods: Class Inarticulata and Class Articulata. In the articulate brachiopods, the valves are hinged along the posterior edge by teeth and sockets. Inarticulate brachiopods lack a definite hinge mechanism and the valves are held together only by muscles. The articulate brachiopods are greater in number and diversity and are very useful as index fossils. Brachiopods are marine, sessile and benthonic. Most attach themselves to the sea floor by a fleshy stalk, called a PEDICLE. Inarticulate brachiopods have a pedicle that emerges between the two valves, whereas in articulate brachiopods, the pedicle emerges from an opening in the pedicle valve, called the PEDICLE OPENING.

1. Two different types of early Paleozoic brachiopods are on display in the lab:

Ligula cuneata from the Silurian of New York

Orthida species (unknown origin)

Visit the University of California at Berkeley museum of paleontology Orthida page (http://www.ucmp.berkeley.edu/brachiopoda/orthida.html) and the Lingulata page

 (http://www.ucmp.berkeley.edu/brachiopoda/lingulata.html)  These pages only provide images of typical members of these groups.

Identify the lab specimens:

a.

b.

2. Why are lingulate brachiopods described as "living fossils"?

The graptolites are extinct colonial organisms that lived from the Cambrian period to the Mississippian period. They were most abundant in the Ordovician and Silurian periods, and their worldwide distribution and rapid evolution make them excellent index fossils for periods. Graptolites are typically preserved as carbon films in shales, where they resemble sawtooth-like pencil marks. Colonies of graptolites are called RHABDOSOMES, and consist of one or more narrow branches called STIPES. Stipes are formed from chains of cuplike THECA which are made of chitin.

Visit the University of California at Berkeley Museum of Paleontology Graptolite page:

http://www.ucmp.berkeley.edu/chordata/hemichordata.html

Find additional information at the Graptolite page of the British Geological Survey:

Graptolites - British Geological Survey (bgs.ac.uk)

5. What is the meaning of graptolite?

6. Some examples of Leptograptus flaccidus graptolites from the Ordovician of Oklahoma are displayed in the lab. Make a sketch of a typical example; label the stipe and the theca.

PHYLUM MOLLUSCA
Mollusks are probably the most familiar of the marine invertebrates: their shells are widely collected and the soft parts of some mollusks are eaten as food. Snails, slugs, clams, oysters, squids, and octopi belong to the phylum Mollusca. They are also of particular interest to geologists, as their shells are readily preserved as fossils.

Most members of this phylum possess external calcareous shells. The foot, a muscular portion of the body, provides for locomotion. In some forms, the foot is modified into tentacles. Gills accomplish respiration in most forms. Well-developed circulatory organs, digestive glands and a nervous system are evidence of advanced development.

Mollusks vary in size from microscopic to very large (a giant squid may grow to lengths of 15 meters). They can be found throughout both continental and marine environments.

CLASS CEPHALOPODA
This class includes the modern nautilus, squids, octopi, and the extinct ammonites. Members of this class are subdivided on the basis of the presence or lack of support elements. Some exist without appreciable internal or external hard parts (squid and octopus), some have an internal skeletal structure (belemnites), and some have an external shell (nautilus and ammonites). Cephalopods are marine and carnivorous, and characteristically have tentacles.

7. Some Ordovician nautiloids are displayed in the lab. Visit TONMO.com: The Octopus News Magazine Online to see a reconstruction of the anatomy of an Ordovician nautiloid https://www.tonmo.com/community/pages/nautiloids/

Sketch a nautiloid below; label the parts; indicate the body part that is represented by the lab specimens.

8. Reefs became important in the early Paleozoic. Visit the Virtual Silurian Reef at the Milwaukee Public Museum 

http://www.mpm.edu/content/collections/learn/reef/index.html

 Click on "Basic Concepts" and then "Reefs".

a. In what environmental conditions do reefs grow?

b. What are the five main types of reef organisms?

c. Go back to Silurian Reef home page, click on "Distribution of Silurian Reefs" and then "Global distribution of modern and Silurian reefs."

How do the modern and Silurian reef distributions compare?

d. Back up one page and click on "Silurian reefs in the Great Lakes region".

In what environmental setting did the two large belts of reefs occur?