Fossil reptiles and amphibians from eastern Spain reveal how modern Iberian herpetofaunas took shape 16 million years ago

Some 16 million years ago, the shallow lakes and muddy floodplains of an intramontane basin in what is now Castelló, eastern Spain, were patrolled by freshwater crocodiles, haunted by forest-dwelling glass lizards and, remarkably, stalked by chameleons. A new study published in the journal Fossil Record has catalogued the amphibian and reptile fossils from 42 Early Miocene sites in the Ribesalbes-Alcora Basin, painting the most detailed picture yet of how the ancestors of today’s Iberian lizards, snakes, salamanders and toads assembled themselves into a recognisably modern cast.

The research team examined 4,690 disarticulated bones and teeth, recovered between 2008 and 2012 by screening-washing sediment from seven sections along the Campisano Ravine, including sites such as Mas dels Coixos, Barranc de Campisano and Corral de Brisca. Based on the accompanying small mammal faunas, the deposits date to the Early Aragonian, roughly 16.49 to 15.98 million years ago, corresponding to mammal zone MN 4. The remains were sorted and identified under binocular and scanning electron microscopes and compared with modern skeletons held in museum collections in Madrid, Paris and Valencia.

In total, the assemblages yielded 21 taxa, and their composition remained remarkably stable throughout the sequence. Among the amphibians, the team identified a newt belonging to the genus Lissotriton, the group that includes today’s palmate and Bosca’s newts, along with a toad of the family Bufonidae. The reptile roster is far richer: indeterminate crocodylians represented by nearly 300 conical teeth and bony armour plates, probable tortoises, terrapins, geckos, skinks, lacertid lizards, worm lizards of the family Blanidae, glass lizards of the genus Ophisaurus, the legless lizard genus Pseudopus, blind snakes, a natricine snake of the extinct genus Palaeonatrix and tentative vipers.

Two discoveries stand out. The first is a fragmentary lizard dentary from the Corral de Brisca 1 site that closely resembles Pyrenasaurus evansae, a scincoid previously known only from late Eocene sites in north-eastern Spain and southern France. If the identification holds, Pyrenasaurus would qualify as a Lazarus taxon, a lineage that vanishes from the fossil record only to reappear millions of years later. Its apparent survival across the Grande Coupure, the dramatic faunal turnover at the Eocene-Oligocene boundary around 33.5 million years ago when Asian immigrants swept into Europe and many endemic lineages died out, hints at unusual ecological stability in this corner of Iberia. A similar pattern has been documented for the choristoderan Lazarussuchus, which outlived its supposed extinction by tens of millions of years.

The second surprise concerns the skink genus Chalcides. Molecular studies had suggested the genus diversified around 10 million years ago in the Moroccan region and colonised Europe only during the Messinian Salinity Crisis, roughly 5 to 6 million years ago, when the Mediterranean nearly dried out. The new fossils, however, are far older, and their teeth lack the expanded crowns seen in Central and Eastern European and Asian relatives. This suggests two distinct Miocene morphotypes: an expanded-crown form across Central and Eastern Europe and Central Asia, and a non-expanded form confined to south-western Europe. The authors propose a provocative alternative scenario in which Chalcides actually evolved in Europe, dispersed to Africa and Asia, later vanished from Eurasia, and then re-colonised southern Europe from north-western Africa, mirroring patterns seen in geckos and freshwater turtles.

Equally striking is the probable chameleon. A single fragmentary tooth-bearing bone from Corral de Brisca 0B shows the acrodont, laterally compressed teeth characteristic of Chamaeleonidae, though such features are shared with some agamid lizards, so the attribution remains cautious. Chameleons are thought to have entered Europe through Anatolia via the Gomphotherium Landbridge, the terrestrial corridor linking Eurasia and Africa that opened around 23 million years ago, and the new specimen, together with recent finds from Catalonia and re-discovered material from Agramón, confirms that the group reached the Iberian Peninsula during the Early Miocene. Because chameleons with non-contacting tooth bases are associated with closed habitats, the animal may have lived in forest or dense shrubland.

Reptiles and amphibians, with their ectothermic physiology, are acutely sensitive to temperature, rainfall and humidity, making them excellent palaeoclimate proxies. The team applied the Herpetological Ecophysiologic Groups method, which assigns each taxon to one of six groups based on thermoregulation, water balance and gas exchange strategies inferred from living relatives, and converts the resulting index into an estimate of mean annual precipitation. Today the basin receives about 432 millimetres of rain per year. The fossil assemblages told a different story: every site except one yielded precipitation estimates above the modern value, ranging from roughly 401 millimetres at Mas d’Antolino 0A to a remarkable 890 millimetres at Corral de Brisca 0B.

Rather than a simple trend, the sequence reveals an alternating rhythm of humid and dry phases. The oldest site, Mas dels Coixos 3, suggests open forest with a moderate 565 millimetres; rainfall then surged to over 800 millimetres at Mas de Torner 2, dipped at Barranc de Campisano 1, plunged to the sequence’s lowest value at Mas d’Antolino 0A, where gypsum layers independently signal aridity, and then climbed through two more humid peaks before falling again at Corral de Brisca 1. This cyclical pattern echoes reconstructions based on small mammals, gastropods and isotopes, although the herpetological estimates do not always align perfectly with the other proxies, a discrepancy the authors attribute to the limitations of actualistic methods, which assume that the climatic tolerances of modern relatives apply to fossil forms.

The snake fauna adds its own chapter to the story. The presence of Palaeonatrix marks the genus’s first record in the Iberian Peninsula, extending a lineage known mainly from the Early and Middle Miocene of Eastern Europe. Meanwhile, the absence of archaic ophidian taxa suggests the sites belong to the late MN 4, after the so-called MN4-event, when modern snake families such as colubrids, vipers and elapids flooded into Central and Western Europe, displacing the older constrictor-dominated fauna as climates warmed and humidified.

Taken together, the study fills a conspicuous gap. While Early Miocene mammals of Iberia have been intensively studied, fossil amphibians and reptiles of this age remain poorly documented, leaving researchers without key information about how a fundamental component of modern ecosystems took shape. The Ribesalbes-Alcora assemblages show that by 16 million years ago, the groundwork of the modern Iberian herpetofauna was already being laid, complete with forest-dwelling glass lizards, aquatic natricine snakes, burrowing amphisbaenians and even a chameleon that had crossed continents to reach a lakeshore in eastern Spain.

Subject of Research: Early Miocene fossil amphibians and reptiles from the Ribesalbes-Alcora Basin in eastern Spain

Article Title: Early Miocene herpetofauna from the Ribesalbes-Alcora Basin (Castelló, eastern Spain): a first step towards modern herpetofaunas in the Iberian Peninsula

Article References: Marquina-Blasco, R., Montoya, P., Ruiz-Sánchez, F. J., & Crespo, V. D. (2026). Early Miocene herpetofauna from the Ribesalbes-Alcora Basin (Castelló, eastern Spain): a first step towards modern herpetofaunas in the Iberian Peninsula. Fossil Record, 29(2), 533-574. https://doi.org/10.3897/fr.29.189879

Image Credits: AI Generated

DOI: 10.3897/fr.29.189879

Keywords: Early Miocene, herpetofauna, Ribesalbes-Alcora Basin, paleontology, Iberian Peninsula, chameleons, Chalcides, Pyrenasaurus, palaeoclimate, Grande Coupure, fossil reptiles, Spain