Napakimyrma paskapooensis

LaPolla and Barden (2020) - The Paskapoo Formation in Alberta, Canada is of Paleocene age, and has yielded a variety of fossil arthropod specimens (Wighton 1980; Kevan et al. 1981; Baker and Wighton 1984; Wighton and Wilson 1986). Mitchell and Wighton (1979) first reported on a possible ant specimen from the Paskapoo Formation, but over the subsequent decades no further study was completed on the fossil. Here we describe this ant specimen. The specimen is of particular interest with respect to fossil ants because the age of the Paskapoo Formation has been estimated to be of Tiffanian to late Paleocene (60.2–56.0 million years old) (Fox 1990; Lerbekmo and Sweet 2000), placing it well within a critical time period after the Cretaceous—within the 23-million-year long gap between the last window into ant evolution in the Cretaceous and the heretofore earliest Cenozoic ants known from the Fur Formation.

Identification
LaPolla & Barden (2018) - Large worker ant (TL: 6.8 mm) with extended anterior petiolar peduncle comprising approximately 50% of total petiole length and distinct angular dorsal propodeal margin; dorsal face of the propodeum long; petiolar node very high, ~2/3 of petiole length; petiole with gradually rounded ventral margin.

Because the gastral cuticle is significantly less rigid than that of thoracic segments in ants, the large size of the gaster appears to be largely preservational. The femur is probably distorted too, appearing wider than it would have been in life. This species is diagnosable from all other North American fossil ants by an extended anterior peduncle, sinuous ventral margin of petiole and angular dorsal propodeal margin.

Distribution
Described from the. Stratigraphic and geographic range - Type locality and horizon only.

Biology
The paleoclimate of the Alberta Plains of the Paleocene was likely warm-temperate, for which Fox (2011) speculated a similar modern habitat would be the current humid coastal plain of the southeastern United States. Based on a collection of largely aquatic adult and larval insect fossils, Mitchell and Wighton (1979) suggested the Blackfalds site where the fossil ant was discovered was a forested backswamp.

Nomenclature

 * † paskapooensis. †Napakimyrma paskapooensis LaPolla & Barden, 2018: 436, fig. 2 (w.) ALBERTA, CANADA.

Worker
TL, 6.8; HL, 1.57; LHW, 0.55; ML, 2.42; PRH, 1.14; PDH, 0.72; APS, 0.33; PPS, 0.35; GW, 2.39; GL, 2.81.

Laterally compressed worker specimen; overall large (TL: 6.8 mm), but due to preservation details of the cuticle such as sculpturing or setal patterns are not visible. Most head features are not clear but head may have been longer than broad based on appearance in lateral view, antennae not preserved; distal end of mandible visible along with part of an apical and an immediate subapical tooth which appear to be equal in size; anterior face of pronotum rises steeply toward dorsum (at ca. 45° angle); pronotum with prominent rounded dorsum; propleuron appears faintly visible as preserved in lateral view; metanotal area distinctly “v-shaped” with sharp posterior declivity; anterior portion of propodeum with distinct right angle leading to long, flat dorsal face; junction of dorsal and declivitous posterior propodeal faces meet at an obtuse angle; declivitous margin long and steep; propodeum height and length approximately equal. Portions of a single putative foreleg preserved as disarticulated femur, tibia, and portion of the tarsus; femur wide, approximately 2× width of tibia; single tibial spur visible. Metacoxa present and articulated behind and underneath the petiole as preserved. Petiole with long anterior peduncle inclined ventrally; petiolar node large and triangular; ventral margin of petiole slightly concave underneath node; petiole height at its greatest approximately 2/3 petiole length; gaster large and rotund; G1–G3 are visible on specimen.

Type Material
Holotype: UAIPC 6300, part and counterpart (the part holds nearly the entire specimen; the counterpart consists of a small portion of the gaster and the faintest outline of part of a leg). Worker specimen laterally compressed. Type locality: Blackfalds Insect and Plant Site, Dennis Wighton site 1, downstream from confluence with Blindman River on left bank of Red Deer River, Alberta, Canada.

Type horizon
Tiffanian to late Paleocene (Fox 1990; Lerbekmo and Sweet 2000).

Etymology
Toponym for the Paskapoo geological formation.