Revision of Varanus marathonensis (Squamata, Varanidae) based on historical and new material: morphology, systematics, and paleobiogeography of the European monitor lizards

Monitor lizards (genus Varanus) inhabited Europe at least from the early Miocene to the Pleistocene. Their fossil record is limited to about 40 localities that have provided mostly isolated vertebrae. Due to the poor diagnostic value of these fossils, it was recently claimed that all the European species described prior to the 21st century are not taxonomically valid and a new species, Varanus amnhophilis, was erected on the basis of fragmentary material including cranial elements, from the late Miocene of Samos (Greece). We re-examined the type material of Varanus marathonensis Weithofer, 1888, based on material from the late Miocene of Pikermi (Greece), and concluded that it is a valid, diagnosable species. Previously unpublished Iberian material from the Aragonian (middle Miocene) of Abocador de Can Mata (Vallès-Penedès Basin, Barcelona) and the Vallesian (late Miocene) of Batallones (Madrid Basin) is clearly referable to the same species on a morphological basis, further enabling to provide an emended diagnosis for this species. Varanus amnhophilis appears to be a junior subjective synonym of V. marathonensis. On the basis of the most complete fossil Varanus skeleton ever described, it has been possible to further resolve the internal phylogeny of this genus by cladistically analyzing 80 taxa coded for 495 morphological and 5729 molecular characters. Varanus marathonensis was a large-sized species distributed at relatively low latitudes in both southwestern and southeastern Europe from at least MN7+8 to MN12. Our cladistic analysis nests V. marathonensis into an eastern clade of Varanus instead of the African clade comprising Varanus griseus, to which it had been related in the past. At least two different Varanus lineages were present in Europe during the Neogene, represented by Varanus mokrensis (early Miocene) and V. marathonensis (middle to late Miocene), respectively.巨蜥属（Varanus）蜥蜴至少在中新世早期至更新世时期就已栖息于欧洲。其化石记录仅见于约40个化石点，产出的化石多为孤立的脊椎骨。由于这些化石的分类鉴别价值较低，近期有研究指出，21世纪前描述的所有欧洲巨蜥物种均不具备分类学有效性，而基于希腊萨摩斯岛晚中新世地层中包含头骨骨骼在内的破碎材料建立的新种Varanus amnhophilis则被认定为有效物种。我们重新检视了采自希腊皮克尔米晚中新世地层的Varanus marathonensis Weithofer, 1888模式标本，认为该物种为有效且可鉴别的类群。此前未发表的伊比利亚地区标本分别来自巴塞罗那巴列斯-佩内德斯盆地Abocador de Can Mata的阿拉贡期（中中新世）地层，以及马德里盆地Batallones的巴列斯期（晚中新世）地层，基于形态学特征可明确归为同一物种，这也为该物种提供了修订后的鉴别诊断标准。Varanus amnhophilis实为V. marathonensis的主观次同物异名。 基于迄今已描述的最完整巨蜥骨骼化石，我们通过分支系统学分析（cladistic analysis）对80个分类单元进行了研究，共编码495个形态学性状与5729个分子性状，进一步厘清了巨蜥属的内部系统发育关系。Varanus marathonensis为大型物种，分布于欧洲西南与东南的低纬度区域，地质时限至少覆盖MN7+8至MN12。我们的分支系统学分析显示，V. marathonensis隶属于巨蜥属的东部演化支，而非此前认为的包含Varanus griseus的非洲演化支。新近纪时期欧洲至少存在两支巨蜥演化支系，分别以早中新世的Varanus mokrensis与中-晚中新世的V. marathonensis为代表。