X-ray scans reveal the wing secrets of a tiny 100-million-year-old singing cricket

Deep inside a piece of completely opaque amber from Charente-Maritime, France, lies one of the smallest singers in the fossil record: a cricket barely 3.3 millimetres long that lived roughly 100 million years ago, during the Late Albian to Early Cenomanian. The species, named Picogryllus carentonensis, is the smallest cricket ever found with a complete stridulatory apparatus, the specialised wing equipment that male crickets use to chirp. Now, for the first time, researchers have produced a full three-dimensional reconstruction of the forewing venation of a fossil cricket, using powerful X-ray imaging to see through the amber and map every vein of a wing that has been hidden for 100 million years.

The achievement, published in the journal Fossil Record, matters because cricket wings are notoriously difficult to interpret in fossils. Most ancient insects survive only as flattened imprints in rock, and even the lucky specimens preserved in amber often have incomplete wings or veins whose trajectories are impossible to follow. In Picogryllus carentonensis, the right forewing is damaged, but crickets habitually fold their right wing above the left one, so the left forewing underneath was almost fully complete. The team used propagation phase-contrast X-ray synchrotron microtomography at the European Synchrotron Radiation Facility in Grenoble, scanning the specimen at beamline ID19 with 30 keV X-rays, 2,500 projections over 180 degrees, and a voxel size of just 20.24 micrometres. From those scans, more than 3,600 two-dimensional slices across three spatial planes were assembled into a digital 3D model of the wing.

Why go to such lengths over a wing the size of a grain of rice? Because insect wing venation is one of the most hotly debated subjects in palaeontology. For over two centuries, scientists have argued about how many main veins insect wings contain and how to identify them, and no single system has ever been universally accepted. A recent framework proposes seven main veins in neopteran insects: the costal, subcostal, radial, median, cubital, postcubital and anal veins. Crucially, microtomography gives researchers access to the very base of the wing, where veins emerge from structures called basivenalia, allowing veins to be identified by their origins rather than by superficial appearance. This is what makes a 3D reconstruction so much more powerful than a photograph of an imprint.

The reconstruction revealed that the general structure of the forewing of Picogryllus carentonensis is strikingly similar to that of modern crickets. The wing is divided into a lateral field, running vertically along the body, and a dorsal field, lying flat over the insect’s back, separated by a median fold. The lateral field carries three main veins, Sc, R and M+CuA, with the subcosta pectinate, bearing at least eight oblique branches directed toward the anterior edge. Between the radial and median veins lies the long, narrow lanceolate cell, roughly 4.5 times longer than wide, a hallmark of singing crickets. The dorsal field contains the cubital, postcubital and anal veins, including the harp, a triangular resonating cell, and the mirror, the rounded cell that plays a key role in projecting cricket song.

The researchers identified features that are recognised synapomorphies, shared derived characters, of the Orthoptera: the fusion of the media and cubitus anterior veins, and the fusion of CuA with the first anterior branch of CuPa. The two postcubital veins run near the posterior margin of the wing, forming the so-called chord veins of crickets, and an arculus, a distinctive crossvein structure associated with sound production, is present. The pattern matches almost perfectly the general venation scheme proposed for crickets in 2023, which was built on precise homology criteria rather than guesswork. This validation means the fossil can now be placed on a firm morphological footing alongside its living relatives in the family Oecanthidae.

But the tiny cricket also holds a surprise. Its mirror, the cell central to sound radiation, is crossed by two strong, parallel crossveins, a rare feature in extant crickets. Few living species show more than one crossvein in this cell, although some phalangopsid crickets, such as Paragryllus and Paragryllodes, have up to six concentric crossveins, and winged Phaloriinae typically have two transverse ones. Applying the new venation pattern to the genus Oecanthus shows that what looked like two crossveins in that group is actually a single crossvein plus a highly modified c1 cell, making the two-crossvein mirror of Picogryllus genuinely unusual.

Why would a singing cricket need extra crossveins in its mirror? The researchers propose a functional hypothesis: in many contemporary crickets, the mirror is involved in sound propagation, and the crossveins may reinforce the wing membrane against the stresses of vibration. Large, flexible forewings may need such reinforcement to withstand repeated vibration during calling. There is an intriguing size angle as well. In extant crickets, the frequency of the calling song increases as body size decreases, and the smallest living singing crickets are much larger than Picogryllus. The extra crossveins may have allowed the call of this miniature species to remain in relatively low frequencies despite its tiny sound-producing apparatus, effectively stiffening the vibrating surfaces in a way that shifted its acoustic output.

The fossil’s affinities add another layer to the story. The extinct families Baissogryllidae and Protogryllidae show crossveins in the homologous region, but their cell there is open and not closed by a reinforced s1 crossvein as in true crickets, and they also possess a diagonal crossvein and an ant-mirror cell that Picogryllus lacks. The connections of the crossveins in Picogryllus are identical to those in the living phalangopsid Lerneca fuscipennis, which could support a hypothesis of primary homology, but given that these lineages are not closely related to the Oecanthidae, the crossveins are most probably homoplastic, features that evolved independently in different lineages rather than being inherited from a common ancestor.

Microtomography has its limits at this scale. The stridulatory file, the row of teeth on a wing vein that scrapes against the other wing to produce sound, could not be reconstructed, which prevents any estimate of the frequency of the calling song of Picogryllus. The authors suggest that nanotomography might increase resolution, but caution that the regions in question appear damaged, so finer scanning would probably not recover the missing structures. Even so, this is the first time an almost complete 3D venation pattern has been reconstructed in a fossil Orthoptera, and the technique is proving transformative for studying falsely-flat structures like wings, in both fossil and living taxa.

The implications reach well beyond one tiny cricket. Precise morphological information from fossils is exactly what is needed for modern phylogenetic analyses, including tip dating and total-evidence approaches that combine molecular data from living species with morphological data from extinct ones. Fossils lack DNA, but a validated venation pattern like this one allows accurate placement of extinct species in the tree of life. Two other Cretaceous oecanthid crickets recently described from Myanmar amber, Crassicorpus maculatus and Ordicalcaratus inconditus, are congruent with the new interpretations, though their mirror cells will need closer checking. With this exquisitely preserved 100-million-year-old wing now fully mapped, palaeontologists have a validated morphological basis for reconstructing how cricket wings, and the songs they produce, evolved over hundreds of millions of years.

Subject of Research: Paleontology

Article Title: First 3D reconstruction of a forewing of a fossil Orthoptera : Interpreting the venation pattern in the smallest known cricket with a stridulatory apparatus, † Picogryllus carentonensis ( Orthoptera , Grylloidea , Oecanthidae )

Article References: Ferreira, J., Josse, H., Denadai de Campos, L., Nel, A., & Desutter-Grandcolas, L. (2024). First 3D reconstruction of a forewing of a fossil Orthoptera: Interpreting the venation pattern in the smallest known cricket with a stridulatory apparatus, †Picogryllus carentonensis (Orthoptera, Grylloidea, Oecanthidae). Fossil Record, 27(1), 101-110. https://doi.org/10.3897/fr.27.113100

Image Credits: AI Generated

DOI: 10.3897/fr.27.113100

Keywords: paleontology, crickets, orthoptera, amber fossils, microtomography, evolution, bioacoustics, Cretaceous, First, reconstruction, forewing, fossil