The Late Miocene hippopotamid, <i>Archaeopotamus pantanellii</i> nov. comb., from the Casino Basin (Tuscany, Italy): paleobiogeographic implications

Fossil remains from the latest Messinian of Casino Basin (Tuscany, Italy) are known since the beginning of the nineteenth century. Among the others, the mammal assemblage includes <i>Mesopithecus pentelicus, Tapirus arvernensis, Propotamochoerus provincialis</i> and scarce and poorly preserved remains of a hippopotamid, consisting of a mandibular symphysis fragment, an apical fragment of a lower canine, some isolated lower incisors, a fragmented second upper premolar and a second lower molar. These specimens were initially referred as <i>Hippopotamus hipponensis</i> and later ascribed to the new species <i>Hippopotamus pantanellii</i> (recently reported as <i>Hexaprotodon? pantanellii</i>). However, this attribution has been disputed during the past years. The hippopotamid remains from the Casino Basin are revised here in order to clarify their systematic position and to infer paleobiogeographic and evolutionary patterns within the Mediterranean fossil record of Hippopotamidae. The morphology of the remains collected from the Casino Basin more closely resembles the African than the Asian hippopotamids’ lineage and therefore the Tuscan remains should be more properly referred as <i>Archaeopotamus pantanellii</i>. The latter species probably dispersed into Tuscany from the Iberian Peninsula where the presence of <i>Archaeopotamus crusafonti</i> is well documented.自19世纪初起，意大利托斯卡纳（Tuscany）卡西诺盆地（Casino Basin）的最新墨西尼期（Messinian）化石遗存便已被学界所知。该地点的哺乳动物组合中包含梅氏中猴（Mesopithecus pentelicus）、阿弗尔貘（Tapirus arvernensis）、省原河猪（Propotamochoerus provincialis），以及一件保存零散且状态欠佳的河马科动物遗存，其标本包含下颌联合部碎片、下犬齿尖段碎片、若干孤立下门齿、一枚残破的上前第二前臼齿与一枚第二下臼齿。这批标本最初被归为希波纳西斯河马（Hippopotamus hipponensis），之后又被划归为新种潘塔内利河马（Hippopotamus pantanellii）（近期被标注为？六齿河马（Hexaprotodon? pantanellii））。然而，这一分类归属在过往数十年间一直存在争议。本文对卡西诺盆地出土的河马科动物遗存展开重新厘定，旨在明确其系统发育位置，并推断河马科在地中海区域化石记录中的古生物地理格局与演化模式。经研究发现，卡西诺盆地出土的河马科遗存形态更趋近于非洲河马科支系，而非亚洲类群，因此托斯卡纳的这批遗存更适宜被归为潘塔内利古河马（Archaeopotamus pantanellii）。该物种可能经由伊比利亚半岛（Iberian Peninsula）扩散至托斯卡纳，而伊比利亚半岛已有克鲁萨丰蒂古河马（Archaeopotamus crusafonti）的明确化石记录。