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Pheidole chaan
| †Pheidole chaan Temporal range: middle Miocene Mexican amber, Chiapas, Mexico | |
|---|---|
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Insecta |
| Order: | Hymenoptera |
| Family: | Formicidae |
| Subfamily: | Myrmicinae |
| Tribe: | Attini |
| Genus: | Pheidole |
| Species: | †P. chaan |
| Binomial name | |
| †Pheidole chaan Varela-Hernández & Flores-Zapoteco, 2024 | |
Pheidole chaan is the first Pheidole species with two individuals of different castes, one soldier and one worker, found in the same syninclusion (Carpenter 1930; Wilson 1985a; Baroni-Urbani 1995; Casadei-Ferreira et al. 2020; Varela-Hernández and Riquelme 2021).
Photo Gallery
Varela-Hernández & Flores-Zapoteco, 2024, Figure 1. (A) complete piece of amber showing Holotype CPAL.469 (soldier) and Paratype CPAL.470 (worker) of Pheidole chaan. (B) Micrograph of soldier (in lateral view) and worker (oblique view) of Pheidole chaan. (C) Head, in frontal view, of soldier of Pheidole chaan.
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Identification
Soldier/Major worker
The holotype can be recognised by the following combination of characters:
- head longitudinally striated, except vertexes that are punctured in frontal view
- area between vertex of head and posterior margin of clypeus and close to the frontal carenas, scooped-off
- dorsal surface of mandibles smooth, lateral surface of mandibles longitudinally striated
- promesonotum continuously arched in lateral view
- internal margin of scapes sinuous
- propodeal spines well-developed with basal area as width as tall
- node of petiole angled (acute) in lateral view, bifurcated in oblique view
- postpetiole angled posteriorly
Minor Worker
With the following combination of characters:
- vertex of head concave
- entire head with coarse punctures
- compound eyes protruding laterally from margin of head
- mesonotal groove deep, forming a U-shape concavity
- propodeal spines long and slender
- petiole forming a thin triangular-shaped node
Pheidole chaan differs notably from the other fossil Pheidole species as follows: it can easily be separated from both Pheidole tethepa and Pheidole primigenia because these last species are spiny ants, that is, they have pronotal spines, while P. chaan has not pronotal spines. Pheidole tertiaria is a female 7.0 mm long, with head coarsely and reticulately rugose, in contrast, P. chaan has a maximum body length 1.3 mm long, almost entire head with thick longitudinal striae. Pheidole chaan differs from Pheidole anticua in that P. anticua has pronotum, in lateral view, flat, katepisternum areolate, node of petiole smoothie rounded, while P. chaan has pronotum, in lateral view convex, katepisternum with bottom half longitudinally striated, top half smooth and node of petiole angled posteriorly. Pheidole chaan also differs from Pheidole pauchil because P. pauchil has a pronotum with a well-developed neck, anterior and posterior margins of node of petiole meeting apically forming a more or less triangle, extensor surface of hind femur flattened forming an acute angle while P. chaan does not form any pronotal neck, the node of petiole is angled posteriorly and hind femur is cylindrical, not forming any angle.
Pheidole chaan has some affinities with the punctatissima group (sensu Wilson 2003) because it shares the following combination of characters. Small species, head width of major 0.7–1.0 mm; major with medium to long antennal scapes, such that when the tip of the scape is touched to the lateral border of the head in full-face view, it reaches halfway between the eye and occipital border, or farther; antennal scape of the minor moderately long, so that when laid across the occipital corner the scape in full face view exceeds the corner by at least 4X the maximum scape width; its posterior dorsal half completely foveolate with no other sculpturing except, at most short carinulate on the antennal fossa. However, Pheidole chaan can be separated from all species of the punctatissma group because of the presence of a deep median impression on head of the soldier in Pheidole chaan and absent in all species of the punctatissima group. The species of the punctatissima group have propodeal spines short and relatively slender in comparison to P. chaan which has well developed and thick propodeal spines. Most species of the punctatissima group have a promesonotal concavity well-defined, instead P. chaan has no promesonotal concavity. The exception to this character in the punctatissima group are Pheidole onyx and Pheidole citrina. In both species, major´s bottom half of head is devoid of any sculpturing, in short, this area is smooth and shiny, in contrast this area is densely striated in P. chaan.
Distribution
This taxon was described from Mexican amber, Chiapas, Mexico (Middle Miocene).
Castes
Nomenclature
The following information is derived from Barry Bolton's Online Catalogue of the Ants of the World.
- †chaan. †Pheidole chaan Verala-Hernández & Flores-Zapoteco, 2024: 2, figs. 1-3 (w.s.) CHIAPAS AMBER (Mexico, Oligocene-Miocene).
Type Material
The complete piece of amber (Figure 1A) includes a syninclusion with the Holotype CPAL.469 and paratype CPAL.470 (Figures 1A, 1B). The complete piece of amber is housed in the Colección de Paleontología (CPAL-UAEM), Morelos, México.
- Locality: Simojovel, Los Pocitos mine, Simojovel, Chiapas, México.
- Horizon: Mazantic shale and Balumtum sandstone strata, Early Miocene (Riquelme et al. 2014b, 2015).