Cephalozygoptera Archibald, Cannings, Erickson, Bybee, and Mathewes, 2021

Nel, André & Jouault, Corentin, 2022, The odonatan insects from the Paleocene of Menat, central France, Acta Palaeontologica Polonica 67 (3), pp. 631-648 : 642-644

Order Cephalozygoptera Archibald, Cannings, Erickson, Bybee, and Mathewes, 2021

Remarks.—Archibald et al. (2021) grouped the two families Dysagrionidae + Sieblosiidae , and possibly Whetwhetaksidae (in which the head characters are unknown), in a new suborder Cephalozygoptera on the basis of a particular shape of the head. Nel and Zheng (2021) discussed this taxonomic treatment and considered that the particular shape of the head results from deformations due to the compression and overall a frontal projection of the head. Archibald and Cannings (2021) refuted the arguments of Nel and Zheng (2021), on the basis of the following arguments: the compound eyes of the specimen of Lestes ceresti chosen by Nel and Zheng (2021) would be absent, while after reexamination of the specimen it is not the case; they argued that if a distortion of the head occurs in Cephalozygoptera , the thorax has also to be deformed, and they considered the latter as normal. However, they did not manage to notice that also the thorax of the cephalozygopteran fossils are distorted and compressed. The major point to keep in mind is that the thorax deformation appears to be less pronounced due to its robustness and its sclerotization more important than in the head (partly due to the presence of the eyes creating huge soft areas).

Archibald and Cannings (2021) ignored the discussion in Nel and Zheng (2021) about Oligolestes stoeffelensis Nel, Poschmann, and Wedmann, 2020 , belonging to the stem-group of the Sieblosiidae and with a non-deformed head, of zygopteran type (due to its fossilization in lateral position). If we take into account their arguments O. stoeffelensis should have a head similar to that of Cephalozygoptera , which is not the case. They also ignored the important argument about the fact that the “cephalozygopteran” type of head is also present in the Epiproctophora and several more inclusive taxa, rendering this head pattern (even if not corresponding to deformations) a plesiomorphy, not sufficient to support a new suborder.

Here we repeat the list of characters that would be diagnostic of the Cephalozygoptera , after Archibald et al. (2021): head width across eyes about twice the length from anterior margin of antefrons to posterior of occiput ( Zygoptera : usually about three to five times as wide); compound eyes more or less adpressed to head, posterolateral corners protruding posteriorly to varying degrees, more or less rounded, sometimes acutely ( Zygoptera : distinctly bulging laterally from head capsule); compound eyes separated by about one eye’s width dorsally (ratio of width between eyes/width eye has a range of 0.8–1.9 and a mean 1.0), n = 11 ( Zygoptera : usually more than twice an eye’s width).

In the holotype of the lestomorphan Menatlestes palaeocenicus gen. et sp. nov., the head width across compound eyes is less than twice the length from anterior margin of antefrons to posterior of occiput, and the compound eyes are separated by less than one eye’s width dorsally ( Fig. 9A 1 ). These dimensions are clearly due to the deformation of the head, more important than that of the thorax that is simply compressed. Thus this taxon would fall in the Caphalozygoptera, while it clearly belongs to a different group.

The heads of several specimens of Lestes ceresti Nel and Papazian, 1985 , from the Oligocene of Céreste (Lubéron, France), are also strongly deformed while the thorax are simply compressed and projected forward. In specimen PNRL 2019 ( Fig. 11A ), the head width across eyes is 2.7 the length from anterior margin of antefrons to posterior of occiput; the compound eyes are oval, with posterolateral corners protruding posteriorly, and the ratio of width between eyes/width eye = 1.5. In specimen PNRL 2020 ( Fig. 11B ), the head width across eyes is twice the length from anterior margin of antefrons to posterior of occiput; the compound eyes are oval, with posterolateral corners protruding posteriorly, and the ratio of width between eyes/width eye = 1.1. In specimen PNRL 2021 ( Fig. 12A 2 , A 3 ), the head width across eyes is 2.4 the length from anterior margin of antefrons to posterior of occiput; the compound eyes are oval, with posterolateral corners protruding posteriorly, and the ratio of width between eyes/width eye = 2.

Indeed, it is clear that the heads of these specimens of Lestes ceresti are deformed, with the mouthparts anteriorly projected, while they should be below the head. Their thorax are clearly less deformed, even their prothorax and meso-metathorax are also frontally projected. Therefore we keep considering that the characters used to define the Cephalozygoptera are insufficient. Until a proper justification (allowing to define at least one clear apomorphy) of the suborder status, the Cephalozygoptera are treated as a synonym of the Zygoptera .

Figures

Fig. 9. Zygopteran odonatan Menatlestes palaeocenicus gen. et sp. nov., holotype MNT Nel Odo 2; from Paleocene, Menat, France. Head and thorax (A1), pterostigma (A2). Scale bars 1 mm.

Fig. 1. Anisopteran odonatan Macrogomphus menatensis sp. nov., holotype MNT Nel 4173; from Paleocene, Menat, France. Imprint (A1), counterimprint (A2), details of pterostigmata (A3, A4). Scale bars 1 mm.

Fig.11. Zygopteran odonatan Lestes ceresti Nel and Papazian, 1985, from Oligocene, Céreste, France.A. PNRL 2019, imprint (A1) and counterimprint (A2) of head and thorax. B. PNRL 2020, imprint of head and thorax. Scale bars 2 mm.

Fig.12. Zygopteran odonatan Lestes ceresti Nel and Papazian, 1985, PNRL 2021; from Oligocene, Céreste, France. Imprint (A1,A2), counterimprint (A3). Scale bars 2 mm.

Fig. 2. Reconstruction of forewing base of anisopteran odonatan Macrogomphus menatensis sp. nov., holotype MNT Nel 4173; from Paleocene, Menat, France.

Fig. 3. Zygopteran odonatan Menatagrion hervetae gen. et sp. nov., holotype MNT Nel Odo 1; from Paleocene, Menat, France. Imprint (A1, A2), counterimprint (A3). Scale bars 1 mm.