FOSSIL AQUATIC ORIBATID MITES (ACARI: ORIBATIDA: HYDROZETIDAE: HYDROZETES) FROM THE PALEOCENE OF SOUTH-CENTRAL ALBERTA, CANADA

Extract

Fossil oribatid mites were recovered from the Paskapoo Formation exposed along the Red Deer River valley near Blackfalds (fossil insect site 1, 12UUP 171 030). The fossils are Late Paleocene (approximately middle Tiffanian) in age (Fox in press). Other adult and immature fossil insects collected from the same locality reported by Mitchell and Wighton (1979) inhabited a mixed forested environment with associated low-energy, shallow, fresh water. The climate at the time of deposition is suggested by Wighton (1980, 1982) to have been warm-temperate to subtropical. The 11 adult and seven immature fossil mites (Fig. 1 specimen no. UAPC6186) are associated with an unidentified fossil insect larva and two chironomid fly pupae on the underside of a compression-impression fossil leaf of “Viburnum” cupanioidea (Newbeq) R. W. Brown (Caprifoliaceae). Most structures on the larvae are obscured, but the size (length 220–240 μm, width 140–150 μm), absence of dark pigmentation, presence of 3 pairs of legs, and general appearance closely resemble oribatid mite larvae (Fig. 2a,b). The adult specimens have several characteristics in common with the extant genus Hydrozetes. The triangular prodorsum lacks microsculpture and narrows to a pointed rostrum (Fig. 2c,d). Examination of the bothridial area in two specimens indicates that the bothridium is reduced and the sensillus is not present. The legs are monodactylous (Fig. 2d,e) and pteromorphae are absent. The notogastral margin is incomplete anteriorly and bears a round, concave area that probably represents the lenticulus. The size (length 495–520 μm, width 325–355 μm) and general habitus of the fossil mites closely resemble those of extant Hydrozetes species.