18 August 2011

Alabama predators

One of my (too) many science passions is paleontology.  In my student days I was fortunate to have various opportunities to collect fossils including plants and fish from Wyoming, ancient crocodiles and amphibians from west Texas, and extinct marine invertebrates from Ontario, Canada.  I recently was able to revisit those days and went on a short fossil trip.  This trip, about an hour from my home, was special as I was able to take my daughter along (who always likes a road trip).  

We collected with several members of the Alabama Paleontological Society out of Birmingham and until the rain started we had a great couple of hours collecting along the Tombigbee River.   

The site is part of the Upper Lisbon Formation and dates from the Middle Eocene - Bartonian at 40.4 - 37.2 million years old.  Among the various small solitary corals, gastropods, and oysters, we got lucky and found some shark and ray teeth.  The teeth are really cool (and sharp, after 37+ million years!).   
Shark teeth surrounding a ray tooth.  Rays consume crustaceans and bivalves through crushing.
  
Having just taught a course in Zoology it’s really amazing to compare these teeth to ones from extant sharks and see how little has changed with these predators.

This also made me think about another predatory group  closer (literally) to home.  We live near wetlands and this time of year we have large populations of various species of dragonflies zooming around our neighborhood.  I’ve seen at least 5 species, including Darner’s, Saddlebags, and I believe some Seaside Dragonlet’s (the only dragonfly to develop in salt water).  If I stand long enough in my yard I can watch various individuals go after each other, hunt, and mate.   After catching a damselfly (a cousin of the dragons) I let it go only to have a dragonfly swoop down and grab it and carry it off to an unfortunate end.  
 An unknown Libellulidae dragonfly takes a rest in my front yard.

Dragonflies, both as larvae and adults, are superb predators, and like the sharks I mentioned above have not changed much in the last 325 million or so years.  Odonates in general are thought to have descended from protodonates (the “griffenflys”), which first appeared during the Palaeozoic, and were large (think 1 foot wingspan), and probably hunted anything they wanted to.