Syntonopteroidea, Kukalova-Peck, 1985

Tenny, Jakub Prokop André Nel Andrew, 2010, On the phylogenetic position of the palaeopteran Syntonopteroidea (Insecta: Ephemeroptera), with a new species from the Upper Carboniferous of England, Organisms Diversity & Evolution (New York, N. Y.) 10 (4), pp. 331-340 : 337-339

Relationship between Syntonopteroidea and other major palaeopteran groups

A group (Triplosobida+( Syntonopteroidea +Ephemerida)) (= Ephemeridea Latreille, 1810 sensu Rasnitsyn 2002) was defined by Rasnitsyn (2002: 88). In the following, we discuss four main aspects of that proposal.

(1) Affinities of Syntonopteroidea with the Triplosobida (= Triplosobidae , only including Triplosoba pulchella (Brongniart, 1883)) . Prokop and Nel (2009) excluded this option, as this family has been transferred from the Hydropalaeoptera to the Rostropalaeoptera (= Palaeodictyopterida).

group including the Syntonopteroidea (under the name “Syntonopterida”) and Ephemerida, on the basis of the supposed presence of a costal brace. As the Syntonopteridae have no costal brace, Rasnitsyn probably based that grouping on the alleged presence of a costal brace in Bojophlebia , after an assumption of Kukalová-Peck (1985). However, as we noted above both the phylogenetic position of Bojophlebia and its possession of such a costal brace are very uncertain. Consequently, there is no potential synapomorphy supporting the grouping of Syntonopteroidea with Ephemerida.

(3) Affinities of Syntonopteroidea with the Ephemeroptera (and possibly Bojophlebiidae ?). These taxa share the presence of a distinct anterior curve or ‘zigzag’ of AA1+2, although this can be pronounced to a varied extent ( Kukalová-Peck 1985: fig. 2, 1997; Willmann 1999: fig. 1b; Zhou 2007). The feature is absent in Odonatoptera and constitutes a potential synapomorphy of the former groups.

(4) Affinities of Lithoneura with Odonatoptera, Ephemeroptera , and Protereismatidae . Several potential synapomorphies (items a–c below) have been proposed by various authors to support a grouping comprising these taxa. One should keep in mind here that, considering extant taxa alone, a clade Odonatoptera+ Ephemeroptera receives some support from molecular studies but is at least debatable from a morphological viewpoint ( Bechly 1996; Hovmöller et al. 2002; Kjer 2004; Klass 2009; Wheeler et al. 2001).

(a) Willmann (1999: fig. 12) listed four potential synapomorphies. Three of them concern structures unknown from Lithoneura . The fourth putative synapomorphy is a composite character state “simple CuP (plesiomorphic character?), with MA and RP being fused over a short distance and with intercalary veins (character state uncertain).” While this is true for Miracopteron and Lithoneura among the Syntonopteroidea , MA only touches RP in one point (but is not fused) in Anglolithoneura (T in Fig. 1 ), suggesting that this character is subject to reversals or homoplasy. Still the one-point touch in Anglolithoneura could be an initial state of longer fusion, and this could be a synapomorphy of a clade Syntonopteroidea +Odonatoptera+ Ephemeroptera , together with the presence of intercalary veins.

(b) Absence of an archedictyon and presence of a regular pattern of cross-veins are similar in Syntonopteridae and in Odonatoptera and Ephemeroptera , suggesting a possible synapomorphy. proposed by Kukalová-Peck (1985, 1991) as a synapomorphy for a clade Ephemeroptera +Odonatoptera+ Bojophlebiidae + Syntonopteridae . Concerning Syntonopteroidea , Kukalová-Peck’ s (1985) opinion was based on the assumption that AA1+2 should always separate in two branches. In Lithoneura , the presence of one point of contact between the convex AA1+2 and the concave CuP, and the fact that these veins maintain their respective convexity in their distal parts, support the hypothesis of Willmann (1999: fig. 1b) that there is no fusion CuP+AA1, contrary to Kukalová-Peck (1985: figs. 11, 14) ( Fig. 5a, b ). The only argument favouring the possible fusion of AA1 with CuP is the presence in Miracopteron of a distal posterior branch of CuP that seems to be less concave than the main CuP (see Fig. 6 ). This branch would be (?) AA1 re-emerging from CuP. But this vein is clearly not as convex as the genuine branches of AA; its interpretation as AA1 is uncertain. In Anglolithoneura AA 1+2 separates near the posterior wing margin into two convex branches that can be interpreted as AA1 and AA2, without any capture of a branch by CuP ( Fig. 1 ). Thus, the situation greatly varies among Syntonopteroidea .

A fusion of CuP with AA is obviously present in the Meganisoptera (and more advanced Odonatoptera) (see, e.g., Nel et al. 2009), where the concave CuP ‘vanishes’ into the main longitudinal convex AA to separate again further distally into a convex AA and a concave CuP. In the most basal Odonatoptera— Eugeropteron Riek in Riek & Kukalová-Peck, 1984—there is a brace between AA, CuP and CuA, but no obvious fusion of a branch of CuP to AA.

In Ephemeroptera , Bojophlebiidae (after Kukalová-Peck’ s 1985: fig. 2), there is a strong convex brace between AA and CuP, but there is no CuP fused to a convex AA, and also no direct evidence of a branch of AA completely fused with a concave CuP.

The presence of a strong convex brace or a contact between AA and CuP is a possible synapomorphy of Ephemeroptera, Syntonopteroidea, and Odonatoptera , which would separate them from the Palaeodictyoptera [Note that nothing similar to a strong convex brace between AA and CuP can be found in the Palaeodictyoptera , in which AA is completely separated from CuP ( Kukalová 1969a, 1969b, 1970). The only known exception is a rather strong cross-vein between AA and Cu, aligned with a crossvein between Cu and M, occurring as a kind of arculus in the eugereonid Dictyoptilus sepultus ( Kukalová 1969b) . This is clearly not homologous to what can be observed in Ephemeroptera, Odonatoptera , and Lithoneuridae .] Kukalová-Peck (1997: 265) proposed a “cup-aa1” brace as a “strong” synapomorphy of the Ephemeroptera and Odonatoptera. This potential synapomorphy supports the hypothesis of Kukalová-Peck (in Wootton and Kukalová-Peck 2000) of a basal division of Palaeoptera in two taxa, Hydropalaeoptera ( Ephemeroptera and Odonatoptera) and Rostropalaeoptera (Palaeodictyopterida).

However, a similar connection between veins CuP and AA1 is also present in the modern Plecoptera (e.g. Béthoux 2005). Haas and Kukalová-Peck (2001: fig. 14) interpreted this brace as AA1 distally fused and vanishing in CuP, but Kukalová-Peck and Lawrence (2004) did not.

New data on other body structures and/or on larval characters shall be necessary to definitely solve the problem of classification of the Palaeopterous insects.

Palaeogeographical significance

Anglolithoneura magnifica is the first syntonopterid described from the Upper Carboniferous of Europe. It exhibits a pattern of wing venation similar to that in Lithoneura lameeri (Westphalian D/Cantabrian; Mazon Creek, Illinois, USA). The close affinities between these two taxa support the well-known Euramerican connection during the Late Carboniferous. Other insects, such as Anglopterum magnificum Prokop, Smith, Jarzembowski & Nel, 2006 ( Palaeodictyoptera : Homoiopteridae ) and chelicerates such as Euproops danae (Meek & Worthen, 1865) , Pleophrynus verrucosa (Pocock, 1911) and Adelophthalmus imhofi Jordan & Meyer, 1856), are known from Late Carboniferous basins both in the UK and at Mazon Creek, supporting a Euroamerican connection as well ( Anderson 1994; Dunlop 1994; Proctor 1999; Prokop et al. 2006).

Figures

Fig. 1 Anglolithoneura magnif- ica gen. et sp. n., holotype; composite line drawing of hind wing. Scale bar 10 mm. For abbreviations of wing veins, see the “Material and methods” section

Fig. 5 Lithoneura lameerei Carpenter, 1938, holotype (No. MCZ 4537, Museum of Com- parative Zoology at Harvard University, Cambridge, MA, USA). a Detail photograph of left hind wing base. b Line drawing of left hind wing base. Scale bars 5 mm

Fig. 6 Miracopteron mirabile Novokshonov, 1993, holotype (No. 2/ 135, Paleontological Institute, Russian Academy of Sciences, Moscow); photograph of counterpart. Scale bar 10 mm