The 366 daily episodes in 2014 were chronological snapshots of earth history, beginning with the Precambrian in January and on to the Cenozoic in December. You can find them all in the index in the right sidebar. In 2015, the daily episodes for each month were assembled into monthly packages, and a few new episodes were posted. Now, the blog/podcast is on an occasional schedule with diverse topics, and the Facebook Page showcases photos on Mineral Monday and Fossil Friday. Thanks for your interest!

Saturday, April 5, 2014

April 5. More trilobites



Trilobites continued a remarkable diversification during the Silurian. Some, such as Staurocephalus murchisoni, had these big bulbous things like noses at the front of their bodies. It’s actually the glabella, which in turn is the central, axial portion of the cephalon, or head. The sketches here give you an idea how bizarre it looks. 
Staurocephalus murchisoni (left); Deiphon forbesi (right)

Many trilobites have a simple dome-like glabella, slightly raised above the side parts of the cephalon, or head, where the eyes are. The glabella apparently covered and contained some of the trilobite’s forward digestive organs – the stomach, which was above and forward of the mouth. Exactly how it worked isn’t clear, at least not to me after checking around – if any trilobite specialist hears this and can enlighten us, please contact me at rigibson@earthlink.net. But at a first pass, it seems that the glabella is more or less the stomach, or maybe part of the intestine. It’s been speculated that larger glabellas indicate more complex food sources, which some infer to mean that the trilobite in question might have been carnivorous – but that seems to be a bit of a stretch to me.

How and why did these bulbous glabellas evolve into knob-like protrusions extending away from the animal’s body? Beats me.
—Richard I. Gibson
See also:

Richard Fortey, Lifestyles of the trilobites (PDF)
The drawings above are from a 19th century textbook.

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