Mark Wilson March 18th, 2012
Since Melissa Torma and I recently returned from our expedition to southern Israel (see immediately previous posts), I thought our weekly fossil highlight should be one of our specimens collected from the Middle Jurassic Matmor Formation of Makhtesh Gadol.
This is a colonial scleractinian coral, a group that first appeared in the Triassic. It was originally made of aragonite and is now recrystallized to calcite. The exterior is well preserved, but the interior is coarsely crystalline. You can just make out faint outlines of the individual corallites that make up the colony.
The distinctive feature of this specimen is that it shows different growth directions. Apparently it was disturbed on the seafloor as it grew, so it periodically had to change its direction to keep growing upwards towards the sunlight. It needed the light because it had photosynthetic symbionts in its tissues.
This coral is one of many indications of the shallow paleoenvironment we’ve proposed for the Matmor Formation. It is also encrusted by a variety of sclerobionts, so it is a bit of a community all on its own.