Paleontologists have unveiled an exciting discovery: a new genus and species of ancient gecko, identified as Carinasquama rusmithii, found in two pieces of amber from a 99-million-year-old (Middle Cretaceous) deposit in Kachin State, Myanmar. Notably, one specimen features a bulge at the base of its tail, indicative of a male lizard’s hemipenis, suggesting the presence of copulatory organs.
Ventral views of the holotype (A) and paratype (B) of Carinasquama rusmithii. Image credit: Daza et al., doi: 10.3897/sjp.145.188227.
The Carinasquama rusmithii gecko inhabited the tropical forests of what is now Myanmar about 99 million years ago.
This species had a snout-to-mouth length of 1.6 to 2.2 cm, placing it alongside some of the tiniest living geckos.
What distinguishes this discovery is the prominent bulge at the base of one specimen’s tail.
Paleontologist Juan Daza from Sam Houston State University and his team interpret this feature as a hemipenile ridge, suggesting the presence of copulatory organs, or hemipenes, that are often retracted into the tails of male squamates (including lizards and snakes).
This finding is significant as it represents one of the oldest lizard fossils that can be confidently classified as male, given that soft tissue structures rarely survive fossilization.
“While paleontologists typically use skeletal features for sex determination, this process can be complicated by the incompleteness of fossil remains,” the researchers stated.
“In fossil assemblages, sexual dimorphism may manifest through ornamentation or can be detected via multivariate analysis.”
“Gender estimation might occur if embryos or eggs are found within or associated with female specimens, but other sex-specific traits are seldom preserved in fossils.”
“Squamates exhibit a hemipenile protuberance observable externally in males.”
“These structures generally leave no trace in hard rock fossils, yet they can be preserved in amber.”
Carinasquama rusmithii detailing integument features: (A) Dorsal view showing head and back scales. (B) Ventral view illustrating hemipenes at the cloaca. (C) Closer look at the multi-carnation scale. (D) Tail view showcasing spotted scales. Image credit: Daza et al., doi: 10.3897/sjp.145.188227.
To visualize their skeletons in three dimensions, the scientists employed micro-CT technology on two specimens. Carinasquama rusmithii has remarkable preservation, where the surrounding integument (scales, skin texture, and even cloacal outlines) remains detailed despite much of the enclosed space being hollow.
“Carinasquama rusmithii‘s characteristics, such as lack of frontal scales, absence of frontoparietal scales, homogeneous head scales, fused eyelids, and uniform scale size throughout the body with visible interstitial skin, are common in modern Gekkotan,” the authors highlighted.
The precise phylogenetic placement of Carinasquama rusmithii remains ambiguous, yet it is tentatively classified within the broader Pan-Gekkota group.
“Genetic studies have positioned Scottish lizards as members of the Pan-Gekkota family, which includes one of the earliest fossil lizards with clear male identification,” the researchers noted.
“This hemipenile bulge found in one of the fossils evidences the presence of hemipenes in mid-Cretaceous squamates, but its origins likely predate this group’s emergence.”
The research team’s findings will be published in the Swiss Journal of Paleontology. You can access their paper here.
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JD Daza et al., 2026. Evidence of male anatomy in a dwarfed amber gecko from mid-Cretaceous Burma. Swiss Journal of Paleontology 145: 785-799; doi: 10.3897/sjp.145.188227
Source: www.sci.news
