At https://archaeologynewsnetwork.blogspot.com/2020/02/boom-and-bust-for-an… … the sea dragons in question are ichthyosaurs – fish like reptiles that filled an evolutionary niche in the oceans equivalent to modern dolphins and porpoise. They first appeared in the record of the rocks at 250 million years ago, it is said. They went on to diversify into a broad range of sizes and occupied a variety of marine ecologies. However, around 200 million years ago, we are told, there was a bottleneck through which only one lineage of ichthyosaurs survived. They do not seem to have evolved greatly thereafter. This is presented as a problem – for the ichthyosaurs (as well as modern science).
What exactly was the bottleneck? Well, it was the end of Triassic mass extinction event. No wonder some varieties of ichthyosaurs died out. However, there is also a problem as they later say that between 250 and 90 million years ago there developed some 200 species of ichthyosaurs. However, during the Jurassic we are told ichthyosaurs remained common but displayed less variation …
… the researchers went on to say it was perhaps this loss of variation that led to their extinction (in the late Cretaceous period). It is dated 90 million years ago and represents another indicator the Cretaceous has been stretched too far as the extinction event itself, at the K/T boundary, is dated 65 million years ago.
