Lithopsyche antiqua

Jong, Rienk De, 2017, Fossil butterflies, calibration points and the molecular clock (Lepidoptera: Papilionoidea), Zootaxa 4270 (1), pp. 1-63 : 16-18

antiqua . Lithopsyche antiqua Butler, 1889

Incertae sedis.

United Kingdom, England, Isle of Wight, Gurnet Bay, Bembridge Marls ; late Priabonian , late Eocene. Depository: BMNH (holotype, I.19984).

Published figures: Butler (1889: Pl. XXXI Figs 3 , 6); Jarzembowski (1980: Figs. 44, 77).

Butler identified the fossil on the basis of traces of spots, which he considered similar to those in members of the “Euschemidae” ( Geometridae ). Jarzembowski (1980) redescribed the specimen (part and counterpart) and gave a more detailed description, including the venation, based on the left pair, since the right pair are superimposed and their anterior parts are missing. Body and wings preserved. Body without much detail; long palps visible; head and thorax relatively slender. Two cubital and three median veins visible, M2 slightly closer to M1 than to M3; parts of three radial veins can be seen, but apical part and much of the front margin of the forewing is missing, Cu2 branching off cell at about one-third from base. In both wings, cell probably closed. In forewing udc in missing anterior part, mdc not visible, ldc weak; 2A weakly indicated, terminating on 1A. Hindwing with long curving humeral vein, making a sharp angle with Sc+R1; humeral angle rounded with margin thickened on inner side.

According to Jarzembowski (1980) wing shape and venation are close to those of a number of extant Neotropical Riodinidae species, such as Metacharis ptolomaeus (Fabricius) , Mesene phareus (Cramer) and Anteros formosus (Cramer) . However, either M1 originates from the upper end of the cell next to R3+(4+5) or it branches off R3 before R4+5 branches off. In Riodinidae R5 tends to move distally, branching off R4 increasingly closer to the apex, disappearing altogether in a number of genera. Since much of the apex is missing, it cannot be decided which radial veins are visible, but they do not appear to branch off each other. Extrapolating the vein trajectories representing the radial veins in Jarzembowski's figure towards the cell, an arrangement could be established typical for Hesperiidae , with all veins originating from the cell separately. In extant Riodinidae the palps are not long. Moreover, in Riodinidae as well as in other butterflies Cu2 generally originates at or (well) beyond the middle of the cell. There appears to be a general evolutionary trend of the origin of Cu2 moving distally. This is apparent in Hesperiidae , where in the Coeliadinae , the first subfamily branching off, Cu2 generally originates well before the middle of the cell, while in the crown group, the Hesperiinae , it may originate well beyond the middle of the cell. Thus, the venation of the forewing is reminiscent of Hesperiidae , in particular Coeliadinae , but the long curving humeral vein in the hindwing is unknown among Hesperiidae , and what is left of the head seems too narrow for Hesperiidae . In addition, extant Hesperiidae do not have long palps.

The hindwing venation is indeterminate for an identification. The origin of Cu1 and M3 from the same spot at the lower outer corner of the cell can be found in a number of Hesperiidae , many Nymphalidae (if the cell is closed), Riodinidae and Lycaenidae . Considering all these observations, the identification of the fossil cannot be more precise than a butterfly of unknown affinities, thus of no utility for calibrating a molecular clock.

Butler (1889) thought to see so much of the spots on the wings that he reconstructed the insect (Pl. XXXI Fig. 6) as a dark brown, white-spotted geometrid-like moth with filiform antennae (no antennae visible in the fossil), but according to Jarzembowski (1980), what is left of wing design is difficult to see and indeterminate. It does not imply that Butler's (1889) observations were incorrect. Particularly in older compression fossils—especially those collected during the 1800's or before—some of the fine details, such as wing eye spots and bars or even delicate veins may have preservationally deteriorated or even lost, rendering modern observations less accurate than the old descriptions taken over 100 years ago.

Figures

FIGURES 3 – 4. Wing venation of (A) Pareronia Bingham, 1907 (Pieridae), and (B) Hasora Moore, 1881 (Hesperiidae). See text for explanation.