Look at the links from the earlier post on Fossils (yesterday). At https://www.sciencedaily.com/releases/2017/03/170308145343.htm … we find the ancient fish fossil found in southern China probably came from the back end of the Silurian period (which preceded the Devonian which is well known for the number of jawed fishes found in fossil beds). The Silurian period is not overly endowed with fish fossils but the Chinese is the second one in recent finds. However, there were fragmentary pieces of what looks like fish in the Silurian, most notably at the end of Silurian extinction event. On that interpretation jawed fish would have evolved in the Silurian and were able to diversify quickly in the Devonian, filling niches vacated following the end of Silurian event (assuming a catastrophe of some kind was global).
The great catfish story comes from http://news.nationalgeographic.com/2017/03/ancient-egypt-catfish-fossil-… … it was found in a dry wadi in a desert SW of Cairo and was six and a half feet long. It was not gigantic as catfish of a similar size occur in the Mekong in the modern era, and the Wels (a European member of the catfish family) can grow to a similar size. It dates to the Eocene period and this part of the Sahara was once submerged, it is thought, even though nowadays there are eroded sandstone cliffs and sandstone buttes eroded by the wind (and sand storms). It has had a varied history over geological time and is full of whale bones. There are other remains too – such as sharks, crocodiles, rays, turtles and all kinds of marine creatures. Where the catfish fits into that is unclear but it may have inhabited an estuary situation.
The article at http://link.springer.com/article/10.1007/S00531-009-0491-8 … is interesting as it says sequencing in geology is basically a matter of convenience for geologists to differentiate phases of layering in sedimentology (as in ripples and waves etc). The research, from Holland, appears to claim this was logic in the manner of the layering that was related to cycles, order rather than randomness. As an argument, it has promise of flowering more with greater research. One to watch.