A unique, large-sized stem Odonata (Insecta) found in the early Pennsylvanian of New Brunswick (Canada)

This dataset contains the digitized treatments in Plazi based on the original journal article BØthoux, Olivier, Norrad, Rowan E., Stimson, Matthew R., King, Olivia A., Allen, Luke F., Deregnaucourt, Isabelle, Hinds, Steven J., Lewis, Jake H., Schneider, Jörg W. (2021): A unique, large-sized stem Odonata (Insecta) found in the early Pennsylvanian of New Brunswick (Canada). Fossil Record 24 (2): 207-221, DOI: 10.5194/fr-24-207-2021, URL: http://dx.doi.org/10.5194/fr-24-207-2021Abstract. A stem relative of dragon- and damselflies, Brunellopteron norradi BØthoux, Deregnaucourt and Norrad gen. et sp. nov., is documented based on a specimen found at Robertson Point (Grand Lake, New Brunswick, Canada; Sunbury Creek Formation; early Moscovian, Pennsylvanian) and preserving the basal half of a hindwing. A comparative analysis of the evolution of wing venation in early odonates demonstrates that it belongs to a still poorly documented subset of species. Specifically, it displays a MP + CuA fusion, a CuA + CuP fusion, and a CuP + AA fusion, but it lacks the “extended” MP + Cu / CuA fusion and the “extended” (CuP / CuA + CuP) + AA fusion, the occurrence of which is typical of most Odonata, including Meganeura -like species. The occurrence of intercalary veins suggests that its closest relative might be Gallotypus oudardi Nel, Garrouste and Roques, 2008, from the Moscovian of northern France.1 IntroductionConjecture of primary homology in wing venation of extant dragon- and damselflies (Odonata) remained a matter of debate for most of the 20th century. Despite the ancient Meganeura -like insects being known, attempts to relate the wing venation of stem and crown Odonata to other insect groups abutted a number of issues. Among them was the propensity, in odonate wings, of cross-veins to convert into main-vein-like elements, including so-called “intercalary veins”, which can prove difficult to distinguish from surrounding genuine main veins. Confusion also arose from persisting gaps in the documentation of venation patterns which had experienced intense modifications since the Pennsylvanian.A landmark in this debate was the proposal made by Tillyard (1925b), who, at that time, had adopted the view that the insect wing venation ground plan is composed of a number of primary veins sharing the same branching pattern, specifically a convex, anterior branch and a concave, posterior one, also known as the serial ground plan (Lameere, 1922, 1923; contrast with Tillyard, 1925a, in which the author expressed doubts on the adequacy of the Comstock–Needham terminology, he used previously). It is relevant to first emphasize that even though Tillyard (1925b, p. 42) stressed that Protodonata (including, in his opinion, Meganeuridae and a few other species) and Odonata were two clearly distinct taxa, he also stated that MP and CuA (his Cu 1) were not only present as free veins beyond the wing base in Meganeuridae but also in species he regarded as stem Zygoptera, i.e. crown Odonata. It follows that Tillyard, in some respect, regarded a subset of Protodonata as stem Odonata (and see Tillyard and Fraser, 1938).The key point in Tillyard’s thesis from 1925 (Tillyard, 1925b) is the presumed loss of MP and CuA as free veins, beyond the wing base. He derived this view from the study of a remarkable specimen of a Meganeura -like species composed of a negative imprint of a hindwing recovered from Elmo (Kansas, USA; Wellington Formation; Artinskian, early Permian; Fig. 1a, b, d, e). Unlike previously known species, vein elevations were preserved in a pristine manner in this material. Tillyard recognized a fusion of M with R, owing to the occurrence, after ScP, of two closely adjoined veins. The resulting vein further splitting into a convex vein (certainly RA), a concave vein (certainly RP) and a convex vein (likely MA), the concave MP had to have vanished. He observed what he believed was a remnant of it (besides R and MA?), basal to the split of RA and RP + MA (red-filled broad arrow on Fig. 1d), but we could not corroborate his observation (only two veins occur). Tillyard also noted a loop, near the wing base, he regarded as formed by CuA and CuP diverging and fusing shortly afterwards. The resulting vein being concave, and therefore presumably composed of CuP, the convex CuA had to have vanished. Finally, a strong oblique structure, his “anal crossing”, located between CuP (his Cu 2) and AA (his 1A), was not regarded as part of the main veins scheme, despite its strength. This proposal was further formalized in Tillyard and Fraser (1938) and was followed for decades, including prominent textbooks (e.g., Carpenter, 1992; Rohdendorf, 1962).This paradigm was challenged by Riek and KukalovAE-Peck (1984; and see Riek, 1976), who described two critical, early Pennsylvanian species, Eugeropteron lunatum Riek in Riek and KukalovAE-Peck, 1984 and Geropteron arcuatum Riek in Riek and KukalovAE-Peck, 1984, displaying (i) at the wing base, a set four well-delimited veins between ScP and AA (there are three in Meganeura -like species, two in extant Odonata), interpreted as RA, RP, M and Cu, successively, and (ii) in the distal area, a complete set of MA, MP, CuA, CuP and AA veins. These insects could be related to Odonata owing to a sequence of vein fusions where they compose the earliest configurations. Under this scheme, a MP + CuA fusion was acquired in early stem Odonata, then further extended into a MP + Cu / CuA fusion. This made Tillyard’s CuP and AA available for being interpreted as the supposedly missing MP and CuA, respectively, and his “anal crossing” interpretable as secondarily fused CuA and CuP, an unusual configuration among Meganeura -like species (this stem then fuses with AA; Fig. 1c, f). This evolutionary scheme definitely reconciled the wing venation of Odonata with the serial insect wing venation ground plan: at the wing base, all extant Odonata possess a R + MA stem and a MP + Cu (or MP + Cu + AA) stem. This proposal was applied at the scale of the entire order by Bechly (1996), who also provided an extensive systematic framework derived from the new conjectures of primary homology. These conjectures were corroborated by detailed analysis of wing base structures in extant Odonata (Jacquelin et al., 2018) and are widely accepted nowadays. A recent proposal made by Trueman and Rowe (2019a; and see associated debate; Nel et al., 2019; Trueman and Rowe, 2019b) lacks relevance as a consequence of ignoring Eugeropteron -like species, arguably the most important ones to address the question of wing venation homologies in Odonata.Aspects of comparatively minor importance remained unclear, notably the actual course of M and MA in Eugeropteron -like species. BØthoux (2015) proposed an alternative to Riek and KukalovAE-Peck’s interpretation of the four veins located between ScP and AA at the wing base in these odonates, as follows: RA (as opposed to R), MA (as opposed to RP), MP (as opposed to M), and Cu (unchanged). In other words, instead of assuming an R system splitting into RA and RP at the very wing base, as proposed by Riek and KukalovAE-Peck, BØthoux assumed that the M system, instead, is split at the very wing base. This is more consistent with the prediction by Riek and KukalovAE-Peck that, in extant Odonata, MA is fused with R, and MP with Cu, from the wing base (which implies a very early split of the M system indeed). Another alternative was proposed by Petrulevičius and GutiØrrez (2016), with RA, RP + MA, MP, and Cu composing the four veins of interest, but this implies that both R and M systems are split at the wing base and is therefore a less parsimonious conjecture.Despite the abundance of Late Palaeozoic strata in Atlantic Canada (Gibling et al., 2019), evidence of fossil insects is rare, with examples preserved in the Pennsylvanian strata at the UNESCO World Heritage site at Joggins, Nova Scotia (Calder et al., 2006; Prokop et al., 2017; Faulkner et al., 2017); Sydney Mines, Nova Scotia (Dawson, 1878; Copeland, 1957); and Fern Ledges, New Brunswick (Matthew, 1909). A single unpublished specimen has been collected from the early Permian strata of Brule, Nova Scotia (Van Allen et al., 2005). Herein we report the discovery of a hindwing from the Sunbury Formation (New Brunswick) displaying a wing venation pattern known to occur in a subset of yet poorly documented stem Odonata. Owing to its combination of character states and its large size, it composes a remarkable addition to the group.

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