Brunellopteron norradi, Béthoux, Deregnaucourt & Norrad, 2021

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), pp. 207-221 : 215-219

Brunellopteron norradi BØthoux, Deregnaucourt and Norrad, sp. nov.

( urn:lsid:zoobank.org:act:F29F7AC2-5624-4786-B842-7CD22C0E4B3E )

( Figs. 6 , 7 )

Material

Holotype, specimen NBMG 21589 , a positive imprint of a left hindwing, deposited at the New Brunswick Museum (palaeontology collection; Saint John, New Brunswick, Canada).

Etymology

The species epithet composes a dedication to Donald B. Norrad, co-discoverer of the holotype (and father of the second author).

Diagnosis

Hindwing: area between anterior wing margin and ScP broad; MP branched, or area between MP and CuA filled with alternating convex and concave intercalaries; several cross-veins connecting (i) MP and the median free portion of CuA, (ii) the basal free portion of CuA, MP + CuA and the median free portion of CuA on one hand, and the basal free portion of CuP on the other, and (iii) the basal free portion of CuP and AA; area between AA and the posterior wing margin well developed, filled with numerous concave intercalary veins; occurrence of intercalaries of second order (i.e. having the same elevation as that of the main vein delimiting the corresponding area).

∗

Description

Holotype specimen ( NBMG 21589 ): basal half of a hindwing, positive imprint, most convex veins eroded; length about 93 mm as preserved, 145–155 mm as estimated; maximum width 36.9 mm as preserved, 38.6 mm as estimated; area between anterior wing margin and ScP broad in basal area; R (or R + MA) not preserved but position of basal portion inferable based on slope elevation; course of basal portion of MA not preserved, either fused with R from the wing base or more distally (dotted lines in Fig. 6d ); origin of RP + MA and split of this vein (into RP and MA) not preserved; RP rectilinear, with a fork about 66 mm distal to wing base; MA (distal to the RP–MA split) not preserved but a short portion of its course, opposite the posterior bending of MP, inferable based on slope elevation; MP fusing with CuA for 2.3 mm, then diverging from MP + CuA somewhat obliquely, directed anteriorly; then, MP with a marked posterior arching, inflexion point 27.5 mm distal of the MP – CuA split; first MP fork (or, first concave intercalary arising) 54.3 mm distal of the MP –CuA split; area between the anterior stems of MP and CuA broad; Cu with a distinct basal stem splitting into CuA and CuP; CuA 3.5 mm long before it fuses with MP; CuA portion distal to the split of MP + CuA (into MP and CuA) about 7.4 mm long before it fuses with CuP (itself emerging from CuP + AA); CuA + CuP fusion about 3.0 mm long; distal to the CuA–CuP split, courses of the anterior stem of CuA and of its first posterior branch inferable based on slopes elevations; anterior-most branch of CuA with a posterior arching, more or less opposite to that of MP; basal portion of CuP 9.7 mm long before it fuses with AA; CuP presumably with a short free portion distal to the CuP-AA split and basal to its fusion with CuA; CuP posteriorly pectinate, with 5 terminal branches; course of the anterior stem of AA inferable, to some extent, based on slopes elevation; AA fused with CuP for about 2.0–2.5 mm; in the area between AA and the posterior wing margin, course of actual AA branches barely preserved; cross-venation generally scalariform, forming intercalary veins of elevation opposed to that of surrounding main veins, at least within the CuA, CuP and AA areas; MP and median free portion of CuA, median free portion of CuA and basal free portion of CuP, and basal free portion of CuP and AA connected by several cross-veins; at least in the CuP area, occurrence of an intercalary vein of second order (bordered by two intercalary veins; ∗ in Fig. 6d ).

Locality and horizon

Robertson Point, Grand Lake, New Brunswick, Canada; Sunbury Creek Formation.

Discussion

The nearly complete lack of preserved convex elements (main veins or intercalaries), a consequence of weathering, could be partly circumvented by considering the elevation of the preserved slopes. For example, the course of the basal portion of AA can be easily traced ( Fig. 7a ). The reconstruction of the course of AA distal to its fusion with CuP was elaborated considering that the concave element indicated by ◦ on Fig. 6d is separated from CuP by an elevated section ( Fig. 7a ), and therefore it cannot be a branch of CuP. It is therefore a concave intercalary branch located within the AA area. It follows that the elevated section must be AA. Then, given the orientation of the basal and inferred distal portions of AA, the occurrence of a short, free portion of CuP (emerging from CuP + AA and basal to its fusion with CuA) was inferred, but its reconstructed length is speculative. The course of several other portions of convex elements remains more or less speculative. Notably, whether MA fuses with R at the wing base, or more distally, cannot be appreciated. In some cases, conditions known in related species allowed plausible reconstruction, such as the length of the RP + MA stem. Finally, portions of a concave element were observed between genuine CuP branches (∗ on Fig. 6d ; purple-filled broad arrows on Fig. 7b ). It is delimited by two elevated areas, interpreted as remains of convex intercalaries. It follows that this concave structure is an intercalary sharing the same elevation as that of the main vein delimiting the corresponding area (here, CuP), this qualifying an intercalary of second order. The occurrence of a comparatively broad area between AA and the posterior wing margin makes it patent that it is a hindwing.

Based on the above, the new specimen displays the configuration schematized in Fig. 5c . Specifically, it displays the derived character state “occurrence of a MP + CuA fusion, of a CuA + CuP fusion (after both veins had first diverged) and of a CuP + AA fusion” (as opposed to “in both wing pairs, MP and CuA distinct, CuA and CuP distinct, and/or CuP and AA distinct”). As a consequence, close relationships with the following species can be excluded: Eugeropteron lunatum , Geropteron arcuatum , Tupacsala niunamenos Petrulevičius and GutiØrrez, 2016 , Kirchnerala treintamil , and Aulertupus tembrocki . Conversely, the new species clearly displays a basal free portion of CuA (dark-green-filled arrow on Fig. 5c ), a plesiomorphy indicating that close relationships with Erasipteroides valentini and Euodonatoptera (as delimited by Bechly et al., 2001) can be excluded.

The remaining species are Erasipteron larischi , known from a single forewing whose apex is missing, and Zessinella siope Brauckmann, 1988 , known from body remains associated with fore- and hindwings whose venation could be deciphered at their bases only. Piesbergtupus hielscheri Zessin, 2006 , known from the basal half of a single forewing, is also considered as it likely displays a free median portion of CuP and, possibly, a free basal portion of CuA ( Fig. 8 ). The same applies to Gallotupus oudardi Nel, Garrouste and Roques, 2008 , known from a single, almost complete forewing, creased in several areas.

Erasipteron larischi and Zessinella siope are herein regarded as essentially similar. Both species have a similar size (forewing about 15 mm wide in the former, about 9 mm in the latter), comparatively large cells, and a very short CuP + AA fusion (at least in the forewing). The main difference is, in the forewing, the number of rows of cells in the area between AA and the posterior margin (two in the former, one in the latter), a trait which could be a mere consequence of the size difference. Interestingly, while the three typical fusions ( MP + CuA, CuA + CuP and CuP + AA) occur in the forewing of Zessinella siope , it is not evident that it is the case in the hindwing, for which a possible interpretation is that CuP and AA are connected by a cross-vein. This should be further investigated, but if this were the case, the new specimen would then strongly differ from Zessinella siope and, by extension, from Erasipteron larischi . Additionally, intercalary veins are absent in the area between AA and the posterior wing margin in the forewing of these two species (condition unknown in hindwing). Even though comparison with the new specimen is hindered by the fact that it is a hindwing, given the important development of intercalary veins in this area, it can be reasonably assumed that such structures occurred in the corresponding forewing. Notably, such intercalary veins occur in the known forewing of Gallotupus oudardi .

The occurrence of a seemingly branched MP in the new specimen is a very unusual feature among Odonata . This vein is simple in Erasipteron larischi (the distal half of MP is unknown in Zessinella siope and Piesbergtupus hielscheri ) and in virtually all Odonata indeed. Among Euodonatoptera, the Permian and Triassic Zygophlebiida possess a wide area between MP and the anterior stem of CuA that is filled with alternating convex and concave vein-like structures. However, the latter, which could be regarded as MP branches, are believed to be intercalaries instead (see Nel et al., 2001, and references therein). Such organization can also be found in some extant forms, for example some Polythoridae (see Garrison et al., 2010). Then, it cannot be completely ruled out that it is also the case in the new specimen (i.e. that it possesses a simple MP and alternating convex and concave intercalaries between MP and CuA). This condition might also be present in Gallotupus oudardi . Yet, the character state “area between MP and CuA broad, filled with intercalary veins” would allow differentiating the species the new specimen belongs to from Erasipteron larischi (and, by extension, Zessinella siope ).

One of the peculiarities of Piesbergtupus hielscheri is the straight to slightly concave shape of its posterior wing margin in the basal third of the forewing ( Fig. 8 ). In Odonata , but also in many Megasecopteromorpha, this trait is part of a petiolation syndrome that very generally occurs in both foreand hindwing. Judging from the development of the AA area in the new specimen, the species it belongs to most likely had forewings with a broad base or a very short petiole at best. This excludes close relationships with Piesbergtupus hielscheri . The new specimen is also larger than this species (estimated lengths 145–155 mm vs. 100 mm).

It occurs that Gallotupus oudardi is possibly the closest relative of the species to which the new specimen belongs. Further comparison is made difficult because several critical areas are creased in the only known specimen of the former. In particular, the point where MP fuses with the cubital system (either with CuA or Cu) is unknown. Judging from the distance between the point of fusion of CuA and CuP on one hand, and the first fork of RP on the other, preserved in both specimens, the new one is about 1.6 times as long as the known wing of Gallotupus oudardi , this precluding an assignment of the new specimen to this species.

Finally, a trait absent in the species considered above is the occurrence of several cross-veins connecting (i) MP and the median free portion of CuA, (ii) the basal free portion of CuA, MP + CuA and the median free portion of CuA on one hand, and the basal free portion of CuP on the other, and (iii) the basal free portion of CuP and AA ( Figs. 6 , 7a ). This trait is present in Aulertupus tembrocki , presumably remotely related to the species the new specimen belongs to, as it lacks the CuP + AA fusion (see above).

Observed differences between the new specimen and known species legitimate the erection of a new species and of a new genus.

Figures

Figure 5. Transformation series of the relation between MP (red), the cubital system (green) and AA (orange) in early stem Odonata: (a, c, e, g) schemes and (b, d, f) transformations allowing transition from one scheme to another; (a) condition in Eugeropteron lunatum Riek in Riek and KukalovAE-Peck (1984), considered as ground plan; (b) transformation from (a) to (c), MP and CuA fuse, CuA and CuP fuse (after they had first diverged), and CuP and AA fuse; (c) condition in Erasipteron larischi Pruvost, 1933, Brunellopteron norradi BØthoux, Deregnaucourt and Norrad gen. et sp. nov. (darkgreen-filled arrow indicates the basal free portion of CuA, basal to its fusion with MP; dark-green-bordered arrow indicates the median free portion of CuA; light-green-bordered arrow indicates the basal free portion of CuP; light-green-filled arrow indicates the median free portion of CuP); (d) transformation from (c) to (e), the point of fusion of MP and CuA reaches the point where CuA and CuP diverge, with the consequence that CuA has no basal free portion (dark-green-filled arrow in c); (e) condition in Namurotypus sippeli Brauckmann and Zessin, 1989; (f) transformation from (e) to (g), the point of fusion of MP with the cubital system is relocated further basally, and the fusion of AA and CuP continues beyond the point where CuA and CuP fuse, with the consequence that CuP has no median free portion; (g) condition in Meganeura-like species.

Figure 6. Brunellopteron norradi BØthoux, Deregnaucourt and Norrad gen. et sp. nov., holotype (NBMG 21589, New Brunswick Museum; positive imprint of a left hindwing): (a) drawing of visible structures, with indication of convex, weathered portions; (b) photograph (dryethanol composite, flipped horizontally), with indication of the location of items in Fig. 7; (c) same as in (a) but with portions reconstructed based on convex, weathered portions and the morphology of known related species; (d) same as in (c) with colour-coding and legend (◦ indicates a particular concave intercalary vein; see text; indicates an intercalary of second order).

Figure 7. Brunellopteron norradi BØthoux, Allen, Norrad and Deregnaucourt gen. et sp. nov., holotype (NBMG 21589, New Brunswick Museum; positive imprint of a left hindwing), details as located in Fig. 6b, RTI extracts, normals visualization (all flipped horizontally; bottom left corners, normals visualization colour code as applied to a hemisphere): (a) basal area; (b) detail of the concave intercalary of second order (purple arrows) located between CuP branches.

Figure 8. Piesbergtupus hielscheri Zessin, 2006, holotype (private collection), redrawn based on data in original description (as for CuA, CuP and AA, only the anterior stem colour-coded; lightgreen-filled arrow indicates the median free portion of CuP).