Abstract
BackgroundFossil ticks are extremely rare and Ixodes succineus Weidner, 1964 from Eocene (ca. 44–49 Ma) Baltic amber is one of the oldest examples of a living hard tick genus (Ixodida: Ixodidae). Previous work suggested it was most closely related to the modern and widespread European sheep tick Ixodes ricinus (Linneaus, 1758).ResultsRestudy using phase contrast synchrotron x-ray tomography yielded images of exceptional quality. These confirm the fossil’s referral to Ixodes Latreille, 1795, but the characters resolved here suggest instead affinities with the Asian subgenus Partipalpiger Hoogstraal et al., 1973 and its single living (and medically significant) species Ixodes ovatus Neumann, 1899. We redescribe the amber fossil here as Ixodes (Partipalpiger) succineus.ConclusionsOur data suggest that Ixodes ricinus is unlikely to be directly derived from Weidner’s amber species, but instead reveals that the Partipalpiger lineage was originally more widely distributed across the northern hemisphere. The closeness of Ixodes (P.) succineus to a living vector of a wide range of pathogens offers the potential to correlate its spatial and temporal position (northern Europe, nearly 50 million years ago) with the estimated origination dates of various tick-borne diseases.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0777-y) contains supplementary material, which is available to authorized users.
Highlights
Fossil ticks are extremely rare and Ixodes succineus Weidner, 1964 from Eocene Baltic amber is one of the oldest examples of a living hard tick genus (Ixodida: Ixodidae)
We examined all valid species of Ixodes s. str. and were unable to find a modern species with a combination of characters exactly matching those in the amber fossil
We cannot prove that Ixodes succineus carried bacteria, or other pathogens, but our study does confirm that at least one anatomically modern species of Ixodes was already present during the Eocene
Summary
Fossil ticks are extremely rare and Ixodes succineus Weidner, 1964 from Eocene (ca. 44–49 Ma) Baltic amber is one of the oldest examples of a living hard tick genus (Ixodida: Ixodidae). Fossil ticks are extremely rare and Ixodes succineus Weidner, 1964 from Eocene Previous work suggested it was most closely related to the modern and widespread European sheep tick Ixodes ricinus (Linneaus, 1758). Almost 900 living species of ticks in three families (Nutalliellidae, Argasidae and Ixodidae) are currently recognized [2] and their origins and evolution remain a topic of debate [3,4,5]. Key questions include whether ticks share a common ancestor with mesostigmatid mites – or a lineage thereof [6] – or alternatively with the large and rare holothyrid mites [7]. When did ticks originate, given that modern taxa require terrestrial vertebrate hosts, and on which palaeocontinent did they first appear?. Mammal-like reptiles, birds, and perhaps even feathered dinosaurs, would have been possible hosts for at least the Mesozoic species
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