"The first appearance of trilobites in the fossil record defines the base of the Atdabanian stage of the Early Cambrian period (521 million years ago), and they flourished throughout the lower Paleozoic era before beginning a drawn-out decline to extinction when, during the Devonian, all trilobite orders except the Proetids died out.
Trilobites finally disappeared in the mass extinction at the end of the Permian about 250 million years ago. The trilobites were among the most successful of all early animals, roaming the oceans for over 270 million years.[4]"
https://en.wikipedia.org/wiki/Trilobite
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"Platystrophia is an extinct genus of brachiopod that lived from the Ordovician to the Silurian in Asia, Europe, North America, and South America. It has a prominent sulcus and fold. It usually lived in marine lime mud and sands."
https://en.wikipedia.org/wiki/Platystrophia
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Devonian 419-359 million years ago
Silurian 443-419 million years ago
Ordovician 485-443 million years ago
Cambrian 541-485 million years ago
I'm not disagreeing with you. I have not studied anything at all about Trilobites or the Cambrian period. . . and everyone in my family disowns grandma. When her kid got together the way they spoke about her was "Do you know what YOUR mother has done now?" She was a battle axe of an old lady. She could very well have been wrong about it all. LOL! The way she treated my grandfather, who was a saint, should not have happened to a mean junk yard dog. She do things like burn half of his socks. The left half. Truth. I recall sitting at breakfast when we were on one of our rare visits in Southern Indiana when she yelled out "AMOS! Do I have to BEG for the butter?" She had not even asked for it. Typical. Another example, is when her sister, my great aunt Goldie died, she had my grandfather TEAR DOWN Aunt Goldie's house and store the wood and other parts in the garage out of spite. She and Aunt Goldie never got along, and this was her way at getting back at Goldie's kids. She'd somehow gotten title to the house, but not the land, and while the kids got the land, she wouldn't let them have the house!
For some reason she liked me over all the other grand kids so would send me gifts out of the blue all the way to California. These fossils were just a couple of them.
However, I hold no protective instinct for my Grandmother, either one of them. They were not nice ladies. My grandfathers, on the other hands, were real saints to put up with either of them.
My grandparent's house was supposedly the oldest house in Posey County Indiana, with part of it built in 1803. However, I have crawled all around the basement and attic of that house, and read everything I could get my hands on, and I think it's sorta like the guy who claims he owns the hatchet that George Washington chopped down that cherry tree with. He is absolutely certain it's the original hatchet. It's only had the handle replaced five times and the head three times, but it's the original hatchet, sure as shootin'. At some time in the past, there may have been a cabin built on that site that was the first house in Posey County, and MAYBE that rock, over there in the basement, was part of the foundation of that cabin, but sure as shootin' this house is the oldest structure in Posey County!
My mother inherited the house from her sister and I was her sister's executor, my mom had me sell it. The buyers tore it down and turned it into a parking lot for the auto-garage across the street which WAS the oldest railroad round-house in Southern Indiana. . . except it isn't round, it's rectangular, and is no longer a railroad engine storage shed. Oh, well.