Sciency Thoughts: Xyelydid Sawflies from the Middle Jurassic of Inner Mongolia.

Monday, 23 November 2015

Xyelydid Sawflies from the Middle Jurassic of Inner Mongolia.

The Xyelydidae are an extinct group of Sawflies, Pamphilioidea, known from the Middle Jurassic to Early Cretaceous of Eurasia. They are possibly ancestral to other members of the group, though their relationships are poorly understood, though since Sawflies are thought to be ancestral to all other Hymanopterans (Wasps, Bees and Ants), the Xyelydidae are of particular interest to palaeoentomologists (scientists that study fossil Insects).

In a paper published in the journal Alcheringa on 1 October 2015, Mei Wang of the Key Lab of Insect Evolution & Environmental Changes at Capital NormalUniversity in Beijing, Alexandr Rasnitsyn of the PaleontologicalInstitute of the Russian Academy of Sciences and the Invertebrate Palaeontology Department at the Natural History Museum in London and Chungkun Shih and Dong Ren, also of the Key Lab of Insect Evolution & Environmental Changes at Capital Normal University describe a series of fossil Xyelydid Sawflies from the late Middle Jurassic Jiulongshan Formation of Inner Mongolia. All of the specimens are assigned to the enigmatic genus Ferganolyda, whose morphology has proved hard to interpret.

The first specimen described is assigned to the species Ferganolyda scylla, which has previously been described only from a single male specimen. The new specimen is somewhat smaller, at 11.4 mm in length compared to 18 mm for the original, and since members of the genus Ferganolyda are known to be sexually dimorphic, generally with larger males than females, this specimen is considered to be female (all Hymenopterans undergo radical metamorphosis upon reaching maturity, with a grub-like larval stage quite unlike the adult, so all adult specimens are known to be fully mature).

Ferganolyda scylla, latest Middle Jurassic, Inner Mongolia, China. (A) Photo of specimen. (B) Line drawing. Scale bars = 2 mm. N1, pronotum; psc2, mesoprescutum; na, notaulus; scl2, mesoscutellum; v1, valvulae 1. In all figures, cell symbols are bold and vein symbols are in regular lettering. Wang et al. (2015).

The second specimen is assigned to the previously described species Ferganolyda chungkuei. The specimen is estimated to have been 21.2 mm in length in life, though it lacks its head. It is partially covered by a film of white carbonate material, making some features hard to observe, though it is otherwise well preserved.

Ferganolyda chungkuei, latest Middle Jurassic, Inner Mongolia, China. (A) Photo of part. (B) Photo of counterpart. (C) An additional crossvein on M+Cu of right wing of part. (D), A stub on M+Cu of left wing of part. (E) Line drawing of counterpart. Scale bars = 2 mm in A, B and E; 0.5 mm in C and D. PN2, mesopostnotum; cn, cenchrus; scl3, metascutellum. Wang et al. (2015).

The third and fourth specimens described are assigned to a new species, Ferganolyda eucalla, meaning ‘beautiful’, a reference to the excellent preservation of these specimens. Both specimens are thought to be female, being 11.7 and 11.8 mm in length respectively.

Ferganolyda eucalla, latest Middle Jurassic, Inner Mongolia, China. Photo of specimen. Scale bar is 2 mm. Wang et al. (2015).

The final two specimens are assigned to another new species, Ferganolyda insolita, meaning ‘strange’, a reference to the morphology of the species. The two specimens are considered to be a male 14.3 mm in length and a female 16.9 mm in length. In this case the female is larger than the male, but can be clearly identified by the presence of an ovipositor.

Ferganolyda insolita, female specimen, latest Middle Jurassic, Inner Mongolia, China. (A) Photo of part. (B) Photo of counterpart. (C) Line drawing of part. (D) Line drawing of forewing of part. (E) Line drawing of hind wing of part. Scale bars = 2 mm in A–E. pp, propleura. Red arrows indicate a crustacean shell. Wang et al. (2015).

All members of the genus Ferganolyda have enlarged, broad heads. This is particularly true of the males, which also have long and thin antennal flagella. The purpose of these antennae is unclear, as the group has no living representatives. Males of the living Dipteran (True Fly) family Deuterophlebiidae have similar antennae, which they use to search for females while patrolling over fast-moving water. However no similar behaviour is known in any living Sawfly (or other Hymenopteran), and the enlarged head-capsule of Ferganolyda makes it unlikely that the males could have performed acts of sustained flight.