A case of mite-on-mammal ectoparasitism from Eocene Baltic amber (Acari: Prostigmata: Myobiidae and Mammalia: Erinaceomorpha)

Tetrapods are rarely recovered from fossil resins, such as amber, and fossils of parasites are even rarer. We describe the first pre-Quaternary co-occurrence of ectoparasitic mites with hairs of their mammalian hosts, preserved in life-like detail from a piece of Eocene (∼ 40 Ma) Baltic amber. The mites, representing the oldest fossils of the family Myobiidae (Acari: Prostigmata: Eleutherengona), are described as <i>Protohylomysobia erinaceophilus</i> Sidorchuk &amp; Bochkov gen. et sp. nov. and belong to the generic group <i>Amorphacarus</i>. Recent members of this group parasitize small-sized insectivores – shrews, moles and gymnures (Mammalia: Eulipotyphla: Soricidae, Talpidae and Erinaceidae: Galericinae). The fossils indicate that the evolution of Myobiidae and their relationships with mammals were well underway by the Eocene. The hairs of the hosts are also described, and are morphologically compared with those of Recent mammals. This comparison suggests an early-derivative member from an array of mammalian groups, and provides clues to its habitus. Our data give a new perspective on a long discussion about the source of mammal hairs in Baltic amber. The combined mite, amber and hair evidence suggest a small, short- and fine-haired member of Amphilemuridae, sister family to hedgehogs, as a host for the mites and the source of at least some of the hairs preserved in Baltic amber. http://zoobank.org/urn:lsid:zoobank.org:pub:FB65DC5F-360E-4594-8153-6A04E732BF37

四足类动物化石在琥珀等化石树脂中鲜有发现，而寄生生物化石则更为罕见。本研究首次报道了产自一块始新世（约4000万年前）波罗的海琥珀的外寄生螨类与哺乳动物宿主毛发的共存化石，其保存细节栩栩如生，近乎活体状态。该螨类为肌螨科（Myobiidae，蜱螨亚纲Acari：前气门目Prostigmata：真气门下目Eleutherengona）已知最古老的化石标本，被正式命名为*Protohylomysobia erinaceophilus* Sidorchuk & Bochkov 新属新种，隶属于*Amorphacarus*属群。该属群的现生成员寄生于小型食虫类动物，包括鼩鼱、鼹鼠及毛猬（哺乳纲Mammalia：真盲缺目Eulipotyphla：鼩鼱科Soricidae、鼹科Talpidae及猬科Erinaceidae：毛猬亚科Galericinae）。化石证据表明，肌螨科的演化及其与哺乳动物的共生关系在始新世时期已进入成熟阶段。本研究同时对宿主毛发进行了形态描述，并与现生哺乳动物毛发开展形态学比对。比对结果显示该宿主属于某支哺乳动物类群中的早期衍生类群，同时为其生活习性提供了相关线索。本研究数据为长期以来关于波罗的海琥珀中哺乳动物毛发来源的学术争论提供了全新视角。综合螨类、琥珀及毛发的相关证据，本次发现的宿主应为猬科（Erinaceidae）的姐妹科两猬科（Amphilemuridae）中一种体型小巧、被覆短细毛发的物种，该物种既是此次螨类的宿主，也为波罗的海琥珀中至少部分保存的毛发提供了来源。http://zoobank.org/urn:lsid:zoobank.org:pub:FB65DC5F-360E-4594-8153-6A04E732BF37