A Curious Piece of Coral

As I was riding my bike on a trail not far from my house, I stopped, as I sometimes do, to check for fossils at a creek bed. During the summer, the creek is often nearly dry where it crosses the trail, and rocks that have been washed from the limestone hills are deposited in the bed and on the banks. In the past I've found small bivalve fossils, but this time I was rewarded with a sizable chunk of fossilized coral.

I was curious what type of coral I had found, and what time period it had come from. As I couldn't make it to the library at the time, I began some highly sophisticated Internet research. I learned from this interesting site that many of Missouri's fossils come from the Carboniferous, a period of the Paleozoic Era.

This map, from the Paleontology Portal, shows
the areas of Missouri whose surface fossils are
from the Carboniferous Period. The darker blue
is for the early Carboniferous (Mississippian)
and the lighter blue is for the later
Carboniferous (Pennsylvanian.)

 The Carboniferous is often treated as two periods, the earlier Mississippian and later Pennsylvanian. In Missouri and near St. Louis, Mississippian fossils are common along the river that gives the period its name. However, fossils from both periods can be found in the area. During these periods, as in others, a warm, shallow sea often covered Missouri. It retreated and returned throughout the Paleozoic Era. The St. Louis metro area was alternately coastline, shallow ocean, and marshland.  The result is that one can find both terrestrial and marine fossils here. A research project investigating Pennsylvanian fossils from a road cut of I-170 found a coral the researchers identified as being from the genus Michelinia, which bore a passing resemblance to my find. 


I wondered if I may have found a different species of Michelinia. A quick consultation with Internet colleagues has me fairly convinced that it is a species of Michelinia, perhaps favosa. Checking some fossil guides at the library seems to confirm this, mainly based on the honeycomb structure and the Carboniferous age of St. Louis's soil. Until someone more knowledgeable can tell me otherwise, that's what I'll believe.


I'm fascinated by the idea that this area was once a shallow sea, home to early fish. I was about 5 or 6 years old the first time I heard that Missouri was once underwater. I think I was spooked by that thought at the time. Later, I found the St. Louis Science Center's life-size display of just such a shallow sea from the Paleozoic. My high school was right next to the Science Center, and occasionally after school I'd wander around the museum. The shallow sea display meets you when you turn a corner in the natural history exhibit. You find yourself at eye level with strange tubular early sharks, ammonites, and trilobites. The lighting is dimmed, and the display casts a  deep blue haze. Sometimes I'd imagine as I looked at the display that the indigo haze swept across the whole of the state and that St. Louis was still covered by the prehistoric sea. The fact that this coral I found probably once grew from a coastal reef and that breaking waves could once be heard in South County is endlessly thought-provoking for me.