The fate and status of the supposed fossil tick Ixodes tertiarius Scudder, 1885

J.A Dunlop

doi:10.1051/acarologia/20112021

Abstract

A fossil described as Ixodes tertiarius Scudder, 1885 from Wyoming, USA represents the only non-amber record of a tick (Acari: Ixodida) from the Eocene. The original illustration does not include characters indicative of any particular modern tick genus; or even Ixodida in general. Unfortunately, efforts to track down the type specimen were unsuccessful and it is almost certainly lost. Confusion about the original place of publication is addressed, and given that there is an illustration associated with the original mention of the name it is not a nomen nudum. However, since it is impossible to verify the accuracy of this illustration against a type specimen – and given the absence of convincing taxonomic features in the figure – Ixodes tertiarius is considered here a nomen dubium which should be excluded from the tick fossil record.

Highlights

Given that oldest part of the Green River formation marginally predates Baltic amber, Ixodes tertiarius has occasionally been explicitly listed as the oldest putative record of the family Ixodidae
Looking at the inflated anteriormost appendages, if these were leg 1, a case could be made for the fossil being something like a large velvet mite (Trombidiidae), but again this would be based on the outline appearance of the animal rather than diagnostic characters
While Ixodes tertiarius could conceivably be a mite of some description, in the absence of a type, and in light of the equivocal nature of the drawing, an exact assignment to any particular group seems to be impossible

Summary

INTRODUCTION

Given that oldest part of the Green River formation marginally predates Baltic amber, Ixodes tertiarius has occasionally been explicitly listed as the oldest putative record of the family Ixodidae (cf Petrunkevitch 1955; Selden 1993) Most recently, in their discussion of problematic tick names Guglielmone et al (2009: 307) suggested that I. tertiarius could be a nomen nudum – see Guglielmone and Nava (2011) – but concluded that they had not seen the original material and that: "It would be worthwhile to locate this fossil, whose study may shed light on tick evolution." In light of this – and as part of a wider project to stabilise fossil arachnid nomenclature – an attempt was made to track down Scudder’s type specimen; without success as documented below

MATERIALS AND METHODS

DISCUSSION