Two new pygmy mole cricket relatives from 99-million-year-old amber reveal evolution caught in the act

Deep inside a piece of amber that solidified from tree resin roughly 99 million years ago, two tiny insects have been waiting with their evolutionary secrets intact. Researchers at the Leibniz Institute for the Analysis of Biodiversity Change in Hamburg have now described both specimens as new genera and species of Tridactyloidea, the superfamily of orthopterans that includes pygmy mole crickets and their relatives. One of the new fossils fits neatly into the known family Ripipterygidae. The other, however, carries a combination of anatomical features that should not coexist according to the textbook diagnosis of any living lineage, and the authors suggest it may represent an ancestor of two entire families before their evolutionary separation had been completed. The study, published in the journal Evolutionary Systematics, adds to a growing body of evidence that the mid-Cretaceous amber forests of what is now Myanmar harbored an astonishing diversity of these minute jumping insects, far exceeding what survives today.

Tridactyloidea is a superfamily within the suborder Caelifera of the order Orthoptera, the group that contains grasshoppers, locusts and crickets. Three families belong to it. The Cylindrachetidae are heavily adapted to a fossorial, almost worm-like lifestyle and comprise 16 species distributed across Australia, New Guinea and parts of South America; they are not known from the fossil record. The remaining two families, Ripipterygidae and Tridactylidae, look superficially similar but can be told apart by a set of consistent morphological characters. The cercus, a paired appendage at the abdominal apex, is one-segmented in Ripipterygidae and two-segmented in Tridactylidae. The mesotibia, the middle segment of the middle pair of legs, is roughly the same width as the mesofemur in Ripipterygidae, whereas in Tridactylidae it is distinctly inflated and wider than the mesofemur. Female Ripipterygidae retain a visible ovipositor, while in Tridactylidae it is too reduced to be seen. The paraproctal lobes of Ripipterygidae bear a distinct array of setae at their tips and often take on an elaborate modified shape, while those of Tridactylidae resemble a second pair of cerci and lack such setae.

The fossil record of both families is sparse overall, but the last 15 years have seen remarkable findings in Burmese amber from the mid-Cretaceous. Both families appear to have been incredibly diverse in this ancient fauna. Seven genera of Tridactylidae have been reported from Burmese amber, compared with ten extant genera, and seven genera of Ripipterygidae, compared with only two extant genera. The new study, based on two amber pieces in the collection of the Leibniz Institute in Hamburg with the collection numbers GPIH07231 and GPIH07232, was excavated at mining sites near Tanai village in Kachin State or Hkamti village in Sagaing Division. The two sites differ in age by roughly 10 million years: amber from Tanai is estimated at 98.79 plus or minus 0.62 million years old, while amber from Hkamti is approximately 110 million years old. The authors also explicitly acknowledge the severe humanitarian situation currently in place in Myanmar and follow the position taken by Haug and colleagues in 2020 regarding the scientific use of amber specimens from Kachin State, wishing to recognize the fossils’ origin by giving them names that connect them with their home country.

The first new taxon, a well-preserved male specimen, has been named Abaddonella nwarrngaal gen. et sp. nov. The genus name derives from Abaddon, the angel of the abyss from the Book of Revelation, combined with the diminutive suffix -ella, yielding something like little demon. The name refers to two small bumps on the vertex of the head in front of the compound eyes, which remind the authors a little of demon horns. The species epithet nwarr ngaal is Burmese for little cow, a nod to the conspicuous light and dark color markings on the head and pronotum. The specimen is assigned to Ripipterygidae on the strength of two diagnostic characters: its cercus is one-segmented, and its mesotibia is not significantly wider than the mesofemur. Imaging was conducted with a stacking system using a Canon EOS 5Dsr camera with a 65 millimeter lens at 2.5 times magnification, with individual photographs stacked in Zerene Stacker and drawings created in GIMP by direct layer copying.

Abaddonella nwarrngaal is a fully preserved specimen except for the left metathoracic leg, with a body length of approximately 1.83 millimeters. The antenna is 10-segmented and moniliform, with the pedicel and scape wider than the remaining antennomeres. A lighter area crosses the compound eye, dividing it into two equal parts and continuing onto the dorso-lateral portion of the head. The pronotum, more or less quadrangular in shape, carries a light base color scattered with several dark spots, and both forewings and hindwings are present, the hindwings slightly longer than the abdomen. The prothoracic leg bears hairs across the entire tibial surface and terminates apically in three strong dactyls, the longest measuring 0.05 millimeters. The metafemur is inflated along its entire length, and the metatibial fin shows distinct serration. At the abdominal apex, the cercus is one-segmented, cylindrical and heavily setulose, while the paraproctal lobes are much shorter than the cercus, inconspicuous and without setae, and the subgenital plate is elongated with long hairs, including one especially long hair at its apex.

In its abdominal and external genitalia morphology, Abaddonella is most similar to Burmaripipteryx, a genus described from Burmese amber in 2023, but it differs from that genus and from all other Ripipterygidae by the two small bumps on the vertex in front of the eyes, as well as by the coloration pattern of the head, pronotum and external genitalia. The only species of Burmaripipteryx, B. oblongus, has cerci with the basal half light and the distal half dark, a completely light subgenital plate, and no noteworthy color pattern on the head or pronotum. Interestingly, the underdeveloped paraproctal lobes of Abaddonella and Burmaripipteryx, much smaller than the cerci, of no distinct shape and lacking apical setae, are rather unusual for Ripipterygidae. According to a molecular time estimate by Song and colleagues published in 2015, the split between the lineages of Ripipterygidae and Tridactylidae occurred around 153.45 million years ago, roughly 50 million years before the formation of the Kachin amber from Tanai. The authors speculate that perhaps at some point in time the separation of the two families had not yet been fully completed and a third lineage, ancestral to both, still existed, a question they say will be answered with more findings of Tridactyloidea from Kachin amber in the future.

The second new taxon is where the story becomes genuinely puzzling. Naginipteryx pinna gen. et sp. nov., based on a female holotype, exhibits external genitalia with a distinctly ripipterygid-like morphology: the cercus is one-segmented, cylindrical and setulose; the paraproctal lobes are two-segmented, longer than the cerci, apically swollen and clavate with distinct long hairs; and the ovipositor is visible, approximately as long as the cerci, with a rather thick valve. By these characters alone, the species should be assigned to Ripipterygidae. But the mesotibia tells a completely different story. It is very inflated with a marked triangular shape, looking as if it is made up of two triangles, with the distal half inserted into the bigger, both wider and thicker, proximal half. This feature is usually considered diagnostic of Tridactylidae, and in Naginipteryx the inflation actually surpasses what is common for that family, exceeding even the pronounced mesotibiae of Burmese amber tridactylids such as Latedactylus longapedi or Burmadactylus tenuicerci.

The genus name Naginipteryx honors the nagini, the female of the naga, a mythological half-human, half-serpent creature from Asian religions including Hinduism and Buddhism that also appears in the mythology of Myanmar, the name chosen because the triangularly shaped mesotibia recalls a classical dragon’s tail. The species epithet pinna is Latin for fin, referring to the fin-like ventral appendages on the abdomen, which remind the authors of the dorsal fin of fish such as male sea goldies or the threadfin butterflyfish. The well-preserved female specimen, with a body length of 2.52 millimeters from head to abdominal apex, has most of the head and thorax somewhat contorted due to internal damage of the amber structure. The prothoracic leg terminates in four dactyls, the longest 0.05 millimeters, and the metatibial fin carries serration, with apical spurs slightly longer than the subapical ones and bearing four conspicuous hairs on their ventral margin. Proximal to the abdominal apex are three fin-like appendages, the anterior two each with a single inserted hair. The external genitalia are very similar to those of Yakkhapipteryx gracilis, described in 2022, but Naginipteryx differs from that genus by the distinctly inflated and triangular mesotibia, by ventral abdominal appendages with an inserted hair, and by a blunt rather than pointed metatarsus bearing one row of serration and one row of hairs.

Because of this strange combination of characters, the taxonomic position of Naginipteryx pinna is genuinely difficult, and the authors have for now placed the species outside both families, Ripipterygidae and Tridactylidae, suggesting it may be an ancestor of both lineages, prior to the evolutionary separation being completed. Some Burmese amber species previously assigned to Ripipterygidae were noted to have untypical mesotibiae, as when the authors of Kallosripipteryx zhangi remarked in 2024 that its mesotibia was slightly fusiform rather than slender as typical of ripipterygids, but in Naginipteryx this character is extremely pronounced. The authors suggest that this strange combination may indicate the presence of an ancestral lineage, or perhaps several ancestral lineages, of Tridactyloidea in the Burmese amber forest that had not yet completed the evolutionary separation between Tridactylidae and Ripipterygidae. The increasing number of Ripipterygidae genera described from Burmese amber, now including Abaddonella and Naginipteryx alongside Archaicaripipteryx, Burmaripipteryx, Ciconipteryx, Kallosripipteryx, Magnidactylus, Ozymandipteryx and Yakkhapipteryx, prompted the authors to provide an up-to-date identification key to the family’s genus-level diversity known from this locality, restricted to the genus level since most genera are currently monotypic. As more Tridactyloidea emerge from the amber, the picture of how these two families diverged may become clearer, and fossils like Naginipteryx pinna stand as rare snapshots of evolution caught in the act, midway between the lineages we know today.

Subject of Research: New species of Tridactyloidea from mid-Cretaceous Burmese amber show an intermediate evolutionary state between extant lineages

Article Title: New species of Tridactyloidea ( Orthoptera , Caelifera ) from mid-Cretaceous Burmese amber show an intermediate evolutionary state between extant lineages

Article References: Schall, O.-K. O., Heads, S. W., & Husemann, M. (2025). New species of Tridactyloidea (Orthoptera, Caelifera) from mid-Cretaceous Burmese amber show an intermediate evolutionary state between extant lineages. Evolutionary Systematics, 9(2), 173–181. https://doi.org/10.3897/evolsyst.9.154534

Image Credits: AI Generated

DOI: 10.3897/evolsyst.9.154534

Keywords: Burmese amber, Tridactyloidea, Ripipterygidae, Tridactylidae, Orthoptera, paleontology, Cretaceous, fossils, evolution, taxonomy, species, Caelifera