| Geology 12 - Historical Geology | |||||
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The goal of this assignment is simply to survey the creatures of the early multicellular world. Your book has some text on these organisms; you should read that. At the Web sites that are listed, choose how much text you want to read, but do pay attention to the pictures.
The earliest evidence of multicellular life is the enigmatic acritarch, which probably represent a resting form of an algae (in stressful environments, some organisms grow a protein coat, forming a "cyst" and drop to the bottom to wait out the bad times).
University College London's microfossil Web site: read the Introduction and Lifecycle section
In the Latest Proterozoic (called the Vendian), some truly puzzling creatures appear - the Ediacaran Fauna. These creatures are often very flat, segmented, lack apparent organ systems. Some are difficult to link to any modern groups of animals.
UC Musuem of Paleontology Vendian page: Lots of pictures
On this page, just skim the text, but look at the pictures. What do these small shelly creatures have in common?
What are the characteristic organisms of the Cambrian? Visit the UC Museum of Paleontology and visit some of the links for the different organisms.
What these organisms tend to have in common is that they are generally:
- small
- phosphatic skeletons
- found within a few centimeters above or below the seafloor (i.e., shallow burrowers, live on the bottom, or on shallow stalks)
Investigate the soft-bodied organisms of the Burgess Shale (fossils and reconstructions). Their significance?
- insight into evolution among poorly preserved groups, such as worms
- multicellular organisms were complex from the beginning
- the earliest vertebrate-like organism appears (Pikaia)
In the textbook, read: p 230-238; p. 258-260; p. 273-277; 330-334.
1. Marine invertebrates: burst of new groups of organisms (Scroll down to Ordovician Life; skim through the text and sample the links)
Compared to the Cambrian fauna, these organisms are:
- larger
- more robust skeletons
- calcium carbonate
- using the environment in more ways (deeper burrowers, swimming farther from bottom)
- more diverse (more different kinds)
List and sketch at least four kinds:
2. Marine vertebrates: (LOTS OF TEXT at these sites - just skim a bit and look at the pictures)
Early fish were jawless with armored heads. Visit this site to see pictures (warning: the text is dense with technical terms): pteraspidmorphs, ostracoderms, anaspids.
Later fish had jaws and armored heads (placoderms).
In the Devonian, all the modern groups of fish are alive, including sharks, ray-finned fish (like trout and tuna) and the lobe-finned fish which give rise to amphibians.
What you should know about fish is how the lobe-finned are different from other fish.
In the textbook, read p. 262-268, 335-342
1. Plants appear in the Silurian. Forests in the Late Paleozoic create coal swamps.
2. Tetrapods emerge from the oceans in the Devonian.
Recent discovery of fish with legs: Tiktaalik
Other amphibian-like fish and fish-like amphibians: Acanthostega, Ichthyostega
What adaptations must a land animal have that a marine animal does not need?