This week we return to the Paleozoic and examine developing marine communities, followed by a discussion of the causes of the Permian Mass Extinctions — the greatest disaster in the History of Life. Paleogeographic maps of Pangaea at the end of the Permian can be found on the Paleomap website (note that it was not “99% of all life” which went extinct). Wikipedia has a good Permian Extinctions article, although the topic is controversial enough that some parts of it may be biased by partisan editors of one cause or another. The latest in this Very Bad Time for life is a calculation of the volatiles released by the massive volcanism, including chemicals that eroded the ozone layer. The End-Permian Extinction happened much more rapidly than we previously thought. In fact, from this study, it was geologically instantaneous. Life was doing OK until quite suddenly a tipping point was reached to throw it into catastrophe.
Probably on Friday our vertebrate cousins will appear in our narrative. The best place on the Web for simple and thorough descriptions of the chordates and their history is at the University of California Museum of Paleontology. Check out their pages on the urochordates (tunicates), cephalochordates, and chordates in general. The Berkeley tetrapod (four-legged) webpage is especially useful for us. I like this website lovingly devoted to the ancient coelacanth fish Latimeria. It has many illustrations and an extensive history of what we know about this remarkable evolutionary survivor. The Tree of Life page on terrestrial vertebrates will show you current ideas about the relationships of fish and early amphibians. It is a rich source of further links. You might like the short Japanese 3-D animation of Eusthenopteron (an ancient bony fish near the origin of the amphibians) embedded in this link.
Here is a good general page from Wikipedia on amphibians.
Your first test results: The average for Test #1 was 85%. The breakdown was 90s (12), 80s (8), 70s (6) 60s (2), below 60 (1). The highest score was 98.5%. Two-thirds of the scores were essentially A or B, which is very good. here are the Spring 2019 student HOL test #1 answers.
A pycnodontid fish tooth, Menuha Formation (Upper Cretaceous), southern Israel. Collected by Andrew Retzler. (Click to enlarge.)
Geology in the News –
The insect apocalypse is upon us. We are in the midst of a terrible Mass Extinction equivalent to some of the worst we’ve seen in the fossil record. Insect losses signal ecosystem collapse. Yikes.
Hummingbirds, little sweet hummingbirds, have a fantastic evolutionary history of violent competition with their elaborate beaks. This is a well-written and illustrated account in the New York Times.
It’s not very often we see evidence of cancer in the fossil record. Recently a leg bone of one of the earliest turtles (Triassic) was found to show signs of bone cancer. Most unusual.