A turnover of the pinniped fauna took place in the Southern Hemisphere during the Pliocene, based on evidence from South America and South Africa. This resulted in the extinction of early phocids, which were replaced by otariids dispersing from the North Pacific. There is currently a lack of evidence of a similar event from Australia, with the only confirmed phocids from the Miocene–Pliocene boundary and the earliest confirmed otariids from the late Pleistocene. Here, we report a fossil monachine tooth from the Pliocene Whalers Bluff Formation of Portland (Victoria). The tooth represents an extinct monachine seal; it does not resemble either crown lobodontins or miroungins. This is the geologically youngest pre-Holocene occurrence of Phocidae in Australia, and one of the youngest pre-Pleistocene records of phocids in the Southern Hemisphere. It extends the maximum known geochronological range of monachines in the fossil record of Australia to between 6.2 and 2.67 Ma. It is possible that pinniped faunal turnovers in the Southern Hemisphere all occurred during the late Pliocene, with the turnover in Australia occurring sometime after 4.31 Ma. The description of additional Australasian fossil pinnipeds will further constrain this faunal turnover event.

根据南美洲和南非的证据，上新世期间，南半球出现了夹脚动物区系的翻转。这导致了早期灭绝，被从北太平洋散布的otariids取代。目前，澳大利亚缺乏类似事件的证据，只有中新世-上新世边界的确凿的phocids，以及来自更新世晚期的最早的otariids。在这里，我们报道了来自波特兰（维多利亚州）的上新世捕鲸崖组织的化石莫纳辛齿。牙齿代表已灭绝的莫纳辛密封。它既不像冠状罗伯顿汀也不像米洛宁。这是澳大利亚新世时代地质上最年轻的全新世，也是南半球最年轻的更新世前记录之一。它把澳大利亚化石记录中已知的莫纳肯内斯的最大地质年代范围扩大到6.2至2.67 Ma之间。南半球的针尖动物区系更新可能都发生在上新世晚期，而澳大利亚的更新期发生在4.31 Ma之后的某个时间。对其他澳大利亚化石的捏制的描述将进一步限制这种动物更新事件。