* Triassic Period: The Triassic Period was a time of significant change and diversification in life on Earth. It occurred between 252 and 201 million years ago.

* Red Sandstone: Red sandstone typically forms in environments where iron minerals are abundant and oxidized (rusted). This often indicates arid or semi-arid conditions.

* Fossil Clues: To identify fossils that might be found in Triassic red sandstone, consider the following:

Likely Fossils:

* Therapsids: These mammal-like reptiles were diverse and abundant in the Triassic. Some examples include Cynodonts (close relatives of mammals) and Dicynodonts.

* Early Dinosaurs: The first dinosaurs evolved during the Triassic. Early forms like Herrerasaurus and Coelophysis could be present.

* Archosaurs: This group includes crocodiles, pterosaurs, and dinosaurs.

* Early Mammals: While small and relatively rare, the first mammals evolved during the Triassic.

* Fossil Plants: Red sandstone environments might contain fossilized remains of drought-resistant plants like ferns, conifers, and cycads.

Less Likely Fossils:

* Marine Fossils: Red sandstone is typically formed on land, so marine fossils like fish or trilobites would be unusual.

Important Note: The specific fossils found will depend on the exact location and geological history of the red sandstone deposit.

To give a more accurate answer, I would need more information:

* Location: Where was the red sandstone layer found?

* Other Clues: Are there any other fossils or geological features present in the layer?

Let me know if you have more details, and I can help you narrow down the possibilities!