A new Odonatan Insect from the Latest Triassic or Earliest Jurassic of Somerset, England.

Odonatopteran Insects, the group which includes the modern Damselflies and Dragonflies first appeared in the Carboniferous, with a variety of groups including the spectacular Griffenflies, Meganeuridae, which had wingspans of up to 71 cm, making them the largest flying Insects ever known to have lived. The crown group Odonata (a crown group includes all living members of a clade, the most recent common ancestor of all those members, and everything descended from that ancestor) first appeared in the Triassic, including the living Damselflies, Zygoptera, and Dragonflies, Anisoptera, as well as a number of extinct groups. One of these is the Liassophlebiidae, was first described in 1925 by palaeoentomologist Robin John Tillyard based upon specimens from the Late Triassic and Early Jurassic of Warwickshire and Worcestershire, England, which he assigned to the genus Liassophlebia. The Family Liassophlebiidae now includes five genera from the Triassic and Jurassic of Western Europe, Central Asia, and Antarctica, while the genus Liassophlebia includes five species from the Triassic of England and Jurssic of England and Germany.

In a paper published in the journal Historical Biology on 16 October 2023, Emily Swaby and Angela Coe of the School of Environment, Earth and Ecosystem Sciences, at the Open University, Deborah Hutchinson of the Bristol Museum & Art Gallery, Lee Riva of the Lovell Stone Group, and André Nel of the Institut de Systématique, Évolution, Biodiversité at the Muséum national d’Histoire naturelle, describe a new specimen of Liassophlebia from the White Lias Formation of Bowdens Quarry in Somerset, England.

The specimen was discovered at Bowdens Quarry in 2016 by Lee Riva, the quarry foreman, and subsequently donated to the Bristol Museum & Art Gallery. It comprises a split piece of fine-grained crystalline limestone with a partial forewing preserved as part and counterpart. Due to the fragmentary nature of this specimen it is ascribed to the genus Liassophlebia, but not to a specific species.

Liassophlebia sp., specimen BRSMG Cg3101 a+b: (A) BRSMG Cg3101 a, part; (B) BRSMG Cg3101 b, counterpart; (C) line drawing of BRSMG Cg3101 b, highlighting wing venation. Abbreviations: A×1, second branch of primary antenodal crossvein; CuA, anterior cubitus; DC, discoidal cell; MA, anterior median; MP , posterior median; N, nodus; Pt, pterostigma; RP3/4, third/fourth branch of posterior radius. Scale bars are 5 mm. Swaby et al. (2023).

The precise stratigraphic age of the deposits at Bowdens Quarry (and of the White Lias in general) is unclear. Bowdens Quarry comprises the uppermost part of the White Lias and the lowermost part of the overlying Blue Lias. Biostratigraphic data from the White Lias at Lavernock in Wales suggests that at least the uppermost part of the formation is Early Jurassic in age, whereas isotopic data from St Audrie’s Bay in Somerset suggests that the base of the White Lias coincides with the End Triassic Extinction Event (which actually comes slightly before the Triassic-Jurassic boundary, which is marked by the appearance of distinctly Jurassic forms during the post-extinction recovery).

(A) A geographic map highlighting the extent of Penarth Group in England and Wales (outcrop shown in purple), and location of Bowdens Quarry (red circle). Note that the outcrop has been simplified for clarity. B) Close-up of the study area (Langport, Somerset), indicating the location of Bowdens Quarry. (C) Simplified stratigraphic log of the Late Triassic-Early Jurassic succession from the Langport-Somerton area, showing the interval that BRSMG Cg3101 a+b came from. Based on lithology, the ‘lower’ White Lias is interpreted to be equivalent to the White Lias Formation on the Somerset coast and the ‘upper’ White Lias to the Watchet Mudstone Formation. MMG denotes the Mercia Mudstone Group and WL the White Lias. Swaby et al. (2023).

Robin John Tillyard described two species of Liassophlebia, Liassophlebia magnifica, from the Earliest Jurassic of Binton in Warwickshire, and Liassophlebia withersi, Latest Triassic of Strensham in Worcestershire. Unfortunately, Liassophlebia withersi was also described from extremely fragmentary material, so that, while it appears to come from a larger Insect that the new specimen, it cannot be confidently stated that the two are different species, with the effect that the new specimen does not help resolve the date of the White Lias at Bowdens Quarry.

An artist’s impression of Liassophlebia sp., resting on a frond of the Palaeofern species Phlebopteris muensteri. the forewings are based on the specimen BRSMG Cg3101 a+b. As the new specimen is incomplete, other specimens within the genera were used to create this artist’s impression as follows: the hindwing is based on the holotype specimen of Liassophlebia magnifica (NHMUK I.6648/I.10462); and the body proportions are based on the incomplete abdomens of the holotypes ‘Liassophlebia’ clavigaster (NHMUK I.10433) and ‘Liassophlebia’ hopei (OUMNH J.55084 a and b). The colour and body morphology, including resting wing posture is inferred from present day Anisoptera. Jules Kiely/Bristol Museum & Art Gallery in Swaby et al. (2023).

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