Description of a new genus of primitive ants from Canadian amber, with the study of relationships between stem- and crown-group ants (Hymenoptera: Formicidae)

Abstract

A detailed study of the holotype of Sphecomyrma canadensis Wilson, 1985 from Canadian amber has led to the conclusion that the specimen belongs to a new genus, here named Boltonimecia gen.n. Since the taxonomy of stem-group ants is not well understood, in order to find the taxonomic position of this genus, it is necessary to review the classification of stem-group ants in a study of their relation to crown-group ants. In the absence of data for traditional taxonomic approaches, a statistical study was done based on a morphometric analysis of antennae. Scape elongation is believed to play an important role in the evolution of eusociality in ants; however, this hypothesis has never been confirmed statistically. The statistical analysis presented herein lends support to the view that antennal morphology reliably distinguishes stem-group ants from crown-group ants to determine whether a species belongs to one or the other group. This, in turn, may indicate a relationship exists between eusociality and scape elongation. A review of Cretaceous records of ants is made and the higher classification of Formicidae with definitions of stem and crown groups is proposed. Newly obtained data are discussed focusing particularly on the origin, evolution and diversity of ants. Examination of the amber inclusion.Photographs were taken with a Nikon D1X digital camera attached to the microscope Leica Z6 APO. The photographs were used to make drawings, which were then computer generated and adjusted using Adobe Photoshop. All measurements were made with an ocular micrometer and are in millimeters. The following measurements were recorded: HL -head length (measured in full-face view as a straight line from the anterior-most point of median clypeal margin to the mid-point of the posterior margin of the head), HW -head width (maximum head width in full-face view), SL -scape length (maximum length excluding articular condyle) F1L-F9Llength of flagellomeres (1 st -9 th ), AL -antenna length, ML -mandible length (maximum length of its horizontal part), WL -Weber's length (the distance from the anterodorsal margin of the pronotum to the posteroventral margin of the propodeum), TL -total body length.Taxon sampling and morphometry. I used all morphometric data on antennae and heads of stem-group ants available from the literature; also I either made measurements or used published data on antennae and heads of crown-group ants representing all extant subfamilies ( Тable S1). For the measurements, only species with both a detailed description in the literature and high resolution images available from AntWeb (Fisher 2002) were selected. I also aimed that the species would cover the broad phylogenetic diversity. All subfamilies in the data set are represented by one species, except for the largest ones (Ponerinae, Dolichoderinae, Formicinae, Myrmicinae), which are represented by two species. Recently, six subfamilies of the dorylomorph group have been subsumed into a single subfamily, Dorylinae (Brady et al. 2014), but here in order to cover bro...

Evolution and systematics of the Aculeata and kin (Hymenoptera), with emphasis on the ants (Formicoidea: †@@@idae fam. nov., Formicidae)

“…†Sphecomyrmines: †Zigrasimeciinae Borysenko, 2017. Comprises, according to Borysenko (2017), † Boltonimecia canadensis (Wilson, 1985) and species of † Zigrasimecia Barden & Grimaldi, 2013 (see also Cao et al . 2020b).…”

“…Identification supported by the following plesiomorphies: (o) cranioclypeal integration weak, i.e., clypeus projecting anteriorly, away from head (versus strongly integrated); (p) clypeus lacking chaetae ("traction setae"; apomorphically present in the sphecomyrmine clade and Amblyoponinae); (q) frontal carinae absent between antennal toruli (presence synapomorphic for total Formicidae); (r) head width, including eyes, usually wider than anteroposteriorly long (long head synapomorphic for total Formicidae); (s) propodeal spiracle located high and anteriorly on the segment (versus low and posterior position, synapomorphic for Formicidae); (t) fore wing Cu2 reaching 1A (occurs sporadically among stem and crown Formicidae). Bolton (2003) and pan Formicidae of Borysenko (2017). Synapomorphies: 2.…”

Sistemática y diversidad de las hormigas neotropicales

“…They recognize two clades, the basal Camelomecia clade and the total clade Formicidae, which in turn is divided into the clades Sphecomyrmines (with three Cretaceous subfamilies: Haidomyrmecinae, Zigrasimeciinae, and Sphecomyrminae) and Antennoclypeata (with Cretaeous Brownimeciinae and Crown clade Formicicidae). Borysenko (2017) compares plesiomorphic and autoapomorphic characters to separate "basal" ants (stem groups) from modern ants (crown groups) and performs a first statistical analysis of the scape lengths and flagellomeres of worker antennae to separate the basal (and extinct) groups of modern ants. This author uses criteria from the Phylum Code (PhyloCode) to define the "crown" group of ants such as Formicidae Stephens, 1829; the clade originated with the most recent common ancestor of Martialis heureka Verhaagh, 2008, andFormica rufa Linnaeus, 1761.…”

“…Pan-Formicidae Borysenko, 2017, is defined as "the total clade composed of the crown clade FormicidaeP and all extinct species that share a more recent common ancestor with FormicidaeP rather than with any living species that is not a member of FormicidaeP". Similarly, Borysenko (2017) defines all the subfamilies of Formicidae under the same criteria. One of the various consequences of the Borysenko (2017) study is that clades such as Armaniidae / Armaniinae could be included within Sphecomyrminae, and Cretaceous genera such as Brownimecia would remain in the main group of ants.…”

“…Similarly, Borysenko (2017) defines all the subfamilies of Formicidae under the same criteria. One of the various consequences of the Borysenko (2017) study is that clades such as Armaniidae / Armaniinae could be included within Sphecomyrminae, and Cretaceous genera such as Brownimecia would remain in the main group of ants.…”