Zigrasimecia tonsora Barden & Grimaldi, 2013

Abstract, Júlio Cezar Mário Chaul, 2023, A revision of the Cretaceous ant genus Zigrasimecia Barden & Grimaldi, 2013 (Hymenoptera: Formicidae: † Zigrasimeciinae), Zootaxa 5325 (3), pp. 301-341 : 324-326

Zigrasimecia tonsora Barden & Grimaldi, 2013

Diagnosis (queen). Frons with a shallow V-shaped groove; vertex with a pair of cuticular ridges or protuberances (see comment below). Mandible apical tooth strongly offset from mandible's outer margin. Compound eyes ovoid (in relation to Z. goldingot ). Pilosity on dorsum of head composed of abundant, thin, flexuous setae ( Fig. 1 , E of Barden & Grimaldi, 2013, better observed in Antweb's high-resolution version than in the article's figure in the pdf), similar setae also present on dorsum of pronotum, mesothorax and propodeum. Dorsal propodeal surface relatively long (in relation to Z. goldingot ). Petiolar node forming a distinct, truncate dorsal surface, apex transversally apparently without lateral protuberances (or apparently not bilobed).

Comments. The holotype of Z. tonsora , Zigrasimecia genotype, is not a perfectly preserved specimen and, for this reason, and for being a queen rather than a worker, creates a taxonomical challenge in ascertaining conspecificity between it and any worker specimen. The reasons why the new species described here do not belong to Z. tonsora are presented above (see above in Z. goldingot Comments ).

The holotype head appears slightly desiccated and wrinkled; the "coronal rugosities", a pair of vertexal cuticular ridges, could be a preservational feature ( Cao et al., 2020a: note 7), although an anonymous reviewer called attention to the note by these authors claiming the paired structure is, in fact, symmetrical. By the illustration in the original publication the ridges are not perfectly mirrored, but considering how much compression and stretching forces the fossils are subjected to, that degree of displacement of one ridge in relation to the other is still acceptable to account for them as a symmetrical paired structure, if they are a natural trait of the specimen. Indeed, most burmite ants observed by the author are not free from at least a minimal amount of assymetry due to preservation in at least one part of the body. So, whether the vertexal ridges are a natural trait of Z. tonsora is an open question that might be solved as more specimens are discovered. In addition, a drawing of the toruli ( Fig. 2 , C of Barden & Grimaldi, 2013) is not in perfect accordance with the image presented ( Fig. 1 , C of Barden & Grimaldi, 2013), so the tubular shape of the illustration is here considered a misinterpretation. Instead, the toruli appear to have a regular ring-like shape, as in most ants, being, at most, slightly raised. The mesosoma is well-preserved. In the metasoma, only the petiole is preserved, the gaster being entirely covered by an internal fracture of the amber; the shape of the petiole, especially the flat dorsal surface of the node, is better seen in photo of Fig.1 , B than in drawing of Fig.2 , A of Barden & Grimaldi (2013).

All characters of the diagnosis, except the ones compared to Z. goldingot (eye shape and propodeum shape), are expected to be shared between the queen and worker.

Figures

FIGURE 1. Schematic drawings of most of the measurements taken from the specimens (presented in the species descriptions or in Appendix 1). See Materials and Methods or Appendix 1 for a detailed explanation of the measurements. Codes: a, head length; b, head length 2; c, head width; d, head width 2; e, head width 3; f, head maximum depth; g, mesosoma length (see also Fig.6); h, mesosoma height; i, propodeal spiracle length; j, petiole anterior face length; k, posttergite 3 length; o, posttergite 4 length. Measurements a, g, j, k, and o summed equal total length (TL). Gaster measurements l, m, n, and p are additional metasomal measurements that are useful if the measurements k and o are blocked (see Appendix 1).

FIGURE 2. Masticatory margin of mandible in Gerontoformica and Zigrasimecia. A, Gerontoformica sp. (ANTWEB1032629); B, Z. ferox (ANTWEB1008126); C, Z. chuyangsui (ANTWEB1032660); D, Z. tonsora (ANTWEB11008098). Black triangles indicate incision between apical and basal teeth (or basal lamella). Image of Z. tonsora by Philip Barden and image of Z. ferox by Vincent Perrichot, courtesy of Antweb.org.