Ordovicium ~455 million years ago.

Dr. Rooves presses his hand against the glass. One of the Estonioceras's notices the movement and attempts, in vain, to introduce its beak to the doctors fingers. The crinoid forests sway silently around the underwater research facility as orthocones slowly pass by above them.

Silurian, ~427 million years ago

The research boat came to a stop near a group of vertically-oriented cephalopods and got ready to set up camp. They lost their first drone quite unexpectedly, when the Pterygotus impacatus swam out as if from nowhere, grabbing ahold of the machine as if taking it for a meal. It's not like there was nothing else to eat - the coral reef teemed with life, full of trilobires, nautiloids, primitive armored jawless fish and multiple genera of sea scorpions.

Devonian, ~380 million years ago

Luckily the shapes of humans are too alien for the massive Homostius to register as prey. However, the presence of these strange, bubble-emanating creatures is enough to make the fish stir fom its hiding place at the bottom of the sea, the' sudden movement scaring off a group of Psammolepis's.

Devonian, ~373 million years ago

This time the group has come ashore on a floodplain, on the edge of an early forest. Flying drones are being deployed, prototaxites are being examined and Panderichthys's are getting bothered.