Rhynchocephalians — members of a sister group of squamates (lizards, snakes, and worm lizards) that includes the living tuatara (Sphenodon punctatus) — from the Late Jurassic Solnhofen Archipelago have been known for almost two centuries. The number of their specimens and species is constantly increasing, but little is known about the development of these animals. The well-documented marine rhynchocephalian genus Pleurosaurus, which lived during the Late Jurassic epoch some 150 million years ago, is one of such cases. With over 15 described (and many more undescribed) specimens, there were no unambiguous juveniles — until now.
Pleurosaurus, a remarkable, long-bodied swimming rhynchocephalian that lived during the Late Jurassic epoch, some 150 million years ago, in what is now Germany. Image credit: Roberto Ochoa.
“The genus Pleurosaurus is the most abundant rhynchocephalian in the Late Jurassic deposits of Canjuers and Cerin, France and the Solnhofen Archipelago, Germany,” said Dr. Victor Beccari, a researcher at the SNSB-Bayerische Staatssammlung für Paläontologie und Geologie and the Ludwig-Maximilians-Universität, and his colleagues.
“The genus is defined as a pleurosaurid with an elongated, triangular skull, a recurved premaxilla, absence of postfrontal, low anterior flange on the teeth, reduced forelimbs etc.”
“There are currently two species in this genus, Pleurosaurus goldfussi and Pleurosaurus ginsburgi.”
“Specific distinction is based on differences in the number of presacral vertebrae (50 and 57, respectively), skull versus appendicular bone proportions, and the development of the pelvis, being more developed, that is, with a more robust dorsal process of the ilium, in Pleurosaurus goldfussi.”
“Although extensive research has been done on Pleurosaurus, with over 15 published specimens, no unambiguous juvenile specimen of this taxon has been described so far.”
Pleurosaurus cf. P. ginsburgi: (a) photograph in standard light; (b) photograph under UV light; and (c) interpretative illustration of the specimen. Image credit: Beccari et al., doi: 10.1002/ar.25545.
In new research, the authors described the first unambiguous post-hatchling juvenile of Pleurosaurus.
The specimen came from the Mörnsheim Formation close to Mühlheim, near Solnhofen, Bavaria, Germany.
“This fossil is particularly interesting because it clearly shows characteristics of a young animal,” the paleontologists said.
“Its teeth are small and show no signs of wear, the bones are not fully developed, and the vertebrae are still in the process of forming.”
“Its small size, along with other features, makes it the first clearly identified juvenile Pleurosaurus specimen, filling an important gap in the understanding of the growth and development of these extinct reptiles.”
The discovery of a young Pleurosaurus has significant implications for the classification of another genus, Acrosaurus.
“In the past, some paleontologists suggested that Acrosaurus might represent a juvenile Pleurosaurus, but until now, there was no solid evidence to support this hypothesis,” the researchers said.
“The new fossil shows many similarities to those previously attributed to Acrosaurus, suggesting that the latter may not be a separate genus but simply a hatchling of Pleurosaurus.”
“For years we tried to understand how these animals grew and developed, but we had never found such a young and well-preserved specimen,” added Dr. Andrea Villa, a researcher at the Institut Català de Paleontologia Miquel Crusafont.
The team’s paper was published in the March 2025 issue of The Anatomical Record.
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Victor Beccari et al. 2025. A juvenile pleurosaurid (Lepidosauria: Rhynchocephalia) from the Tithonian of the Mörnsheim Formation, Germany. The Anatomical Record 308 (3): 844-867; doi: 10.1002/ar.2554
