Fig. 1

The range of common seadragons spans the southern Australian coast, including a known geogenetic break. a Sampling localities (purple dots) of Phyllopteryx taeniolatus along the entire known range (purple shade on map inset). The gray areas show the approximate location of the coastline during the Last Glacial Maximum, when sea levels were ca. 120 m lower than today. During sea-level lows, the Bassian Isthmus landbridge disconnected marine populations. The strait was long closed during the Penultimate Glacial Period (194–135 ka), followed by brief closures (76, 68–62, and 46 ka), and the most recent longer closure during the Last Glacial Maximum (43–14 ka) [18]. b Flooding sequence of the Bassian Isthmus with rising sea levels during the Last Glacial Maximum. Redrawn from [18]