Hi, The scenario that emerges, conclude the researchers, is of all the Alcedo tortoises getting blown off the volcano at the time of eruption except for the lone, lucky lineage, which could have been as small as a single pregnant tortoise, but probably a group of related individuals. (This comes from October 2, 2003 Did Galápagos Turtle Lineage Survive Ancient Blast? in National Geographic.) I think this sentence means the scenario is all tortoises died execpt for one which could have been a pregnant tortoise. But I don't understand the structure of the bold part. What is the subject? What is the relation between it and its preceeding sentence? Thanks in advance!