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| Trilobite and Sea Scorpion Fossil Trackways |
What makes this block especially tasty to the fossil-loving eye is that it preserves both a lovely Cruziana trilobite trackway alongside what may be a eurypterid — a sea scorpion — or horseshoe crab trackway, all dancing together across the same bit of ancient seabed.
It is a proper prehistoric traffic jam.
Now, when we say Cruziana, we are not talking about the trilobite itself, but the style of the trace fossil — the shape and pattern left behind by the critter as it shuffled, ploughed, scraped or scooted along the sediment.
In this case, we see elongate, bilaterally symmetrical furrows preserved along the bedding plane with repeated oblique striations running at jaunty little angles.
I always picture some tiny Paleozoic artist armed with a wee putty knife making rhythmic cuts through wet clay. Alternatively, imagine an overly enthusiastic trilobite showing off its Olympic-level skate skiing skills across the seabed.
Sadly, no medals were awarded in the Carboniferous. While Cruziana traces are most commonly linked to trilobites, other arthropods could make similar marks, so there is still a little mystery woven into the mud.
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| Trilobite and Sea Scorpion Fossil Trackways |
The study of trace fossils is called ichnology — from the Greek ichnos, meaning “track” or “footprint” — and it is one of the best ways we have of decoding the behaviour of ancient life long after the critters themselves have vanished.
Trace fossils are marvellous things because they preserve behaviour rather than bodies.
These are the footprints, furrows, resting spots and feeding trails of ancient marine life — little snapshots of daily business on the ocean floor hundreds of millions of years ago.
They tell us who was bustling about, how they moved, where they paused, and sometimes even what mood they might have been in.
Alright, perhaps not mood exactly, but definitely purpose.
Every groove and scratch here records a living creature interacting with its world in real time, long before dinosaurs, birds or mammals ever appeared on the scene.
This busy little block — measuring 4 1/2" x 3 1/2" x 1 1/4" — comes from the Tar Springs Formation of Perry County, Indiana, USA, and resides in the collections of the deeply awesome David Appleton.
The Tar Springs Formation stretches across parts of southern Indiana and is known both from surface outcrops and subsurface deposits extending from central Martin County southwestward toward the Ohio River.
In Indiana, the formation is primarily shale, though scattered limestone beds and chunky local sandstone lenses also appear, including the handsome Tick Ridge Sandstone Member described by Gray in 1986. Thickness varies considerably, from about 70 feet (21 m) to more than 150 feet (46 m) in places like central Posey County and southwestern Gibson County.
Where the formation thickens, sandstone tends to dominate, hinting at shifting ancient shorelines, changing currents and the restless pulse of long-vanished Carboniferous seas.
