CBS 4 Special Report – A Giant Oyster Discovery

Special Reports
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An estuary of giant oysters over 43 million years old remains perfectly preserved outside Roma in Starr County. (Source: Alex Herbst, CBS 4 News)

Deep in the trees and brush along the Rio Grande in Roma, you can find some of the oldest remaining fossils in the entire Rio Grande Valley.

“This is for the southernmost counties, this is as old as rocks get,” explains UTRGV Geology Professor Dr. Juan Gonzalez.

These fossils tell us a story tens of millions of years in the making.

“Geologically speaking we are back into the Eocene, which is somewhere around 43 million years.”

Before the Rio Grande Valley became the landscape we know it as today, the ocean once reached as far inland as the Roma Cliffs. The Lagunas and bays along the coast today could be found nearly 100 miles inland.

“If you face the ocean, you are looking at the open Gulf of Mexico. If you face to the Laguna Madre, you see a lagoon or an estuary. If you were to look below the sandstone here, you’d see clays and finer grain sediments that contain different fossils. If you look into those, you will find giant oysters.”

Those fertile grounds for giant oysters continue to hold their past together today.

“This reef is pretty well preserved. We see animals in living positions. In other words, they were not transported or reworked by water. This is how they were living.”

When we say giant oysters, we mean giant.

“It’s about eight to ten times larger and thicker than the modern oysters we have today.”

Ranging from a few inches to more than a foot in size, these giant oysters easily dwarf the types found living along the coast today.

“Chances are this is a different species from what modern oysters are today.”

Hundreds of these giant oysters are perfectly preserved as rocks that line where the Rio Grande met the former bay, showing the size and texture of these creatures.

“We are standing on it. We are standing on oyster shells and oyster hash from that far back in time.”

It’s a find that Gonzalez tells us is unique to Starr County.

“For south Texas, I think it’s pretty unique.”

Despite many people associating oysters with pearls, the fossilization process would have likely prevented any pearls in these oysters from surviving or being able to be salvaged.

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