It's like "A Sound of Thunder" but when the guy goes back from the past to the present, his superiors ask him if anything worrying happened during the trip. He says, No. But they are all in tanks of liquid now. Not humans anymore. And they all agree that nothing in the trip affected the present. The End. It was a short story I read maybe 40 years ago. Not sure when exactly. Has anyone heard of this story?
I think this is William Tenn's short story "Brooklyn Project", first published in Planet Stories, Fall 1948
Early in the story, the inventor explains: "In a few moments, man’s first large-scale excursion into time will begin. Not by humans, but with the aid of a photographic and recording device which will bring us incalculably rich data on the past. With this experiment, the Brooklyn Project justifies ten billion dollars and over eight years of scientific development." As such, it is not a person going back to the "Age of Reptiles", but a camera.
The story ends as follows:
They all agreed, and their bloated purpled bodies dissolved into liquid and flowed up and around to the apparatus. When they reached its four square blocks, now no longer shrilling mechanically, they rose, solidified, and regained their slime-washed forms.
“See,” cried the thing that had been the acting secretary to the executive assistant on press relations. “See, no matter how subtly! Those who billow were wrong: we haven’t changed.” He extended fifteen purple blobs triumphantly. “Nothing has changed!”
The story can be read in its entirety here.