In a groundbreaking study published in Nature on September 10, 2025, researchers from the University of Bristol have unveiled a remarkable fossil that rewrites our understanding of the earliest members of the lizard lineage. This extraordinary discovery sheds fresh light on the origins and evolutionary adaptations of lepidosaurs, the reptilian clade that encompasses modern lizards, snakes, and the distinctly unique tuatara from New Zealand. The fossil, dating back approximately 242 million years to the Middle Triassic period, provides unexpected anatomical details that challenge long-held assumptions about the morphology and feeding adaptations of these ancient reptiles.
Lepidosaurs have long been recognized as one of the most diverse and successful land vertebrate groups, currently boasting over 12,000 species — a number that surpasses both birds and mammals. Central to their ecological success is the remarkable flexibility of their skulls and jaws, enabling them to capture and process a wide range of prey items with innovative feeding mechanisms. Prior to this discovery, paleontologists believed that the earliest lepidosaurs possessed a combination of key features now characteristic of modern lizards and snakes. These included a partially hinged skull that allowed for expansive gape, an open lower temporal bar facilitating this mobility, and a plethora of palatal teeth used to apprehend elusive, small prey.
The lower temporal bar, a bony rod that historically bridged the cheekbone to the jaw hinge, is notably absent in present-day lizards and snakes, though preserved in the tuatara, thus presenting a living snapshot of a more primitive architecture. This ancestral condition has been pivotal in interpreting lepidosaur evolution. Palatal teeth, too, have been assumed to be standard in early lepidosaurs, functioning as vital tools to grip and manipulate prey items. These morphological traits have long been accepted as integral to the feeding strategy that propelled lepidosaurs to ecological dominance.
However, the newly identified specimen, Agriodontosaurus helsbypetrae, disrupts this narrative. Contrary to expectations, this fossil exhibits no palatal teeth and shows no clear evidence of the specialized cranial hinge that facilitates wide mouth opening. Remarkably, it retains the open lower temporal bar, a feature common among lizards and snakes, thus possessing only one out of these three previously assumed ancestral traits. Of particular interest is the presence of unusually large, triangular-shaped teeth, far surpassing those found in closely related taxa. This unexpected dental morphology implies a different feeding strategy that likely involved piercing and shearing hard, chitinous exoskeletons of insects—a niche feeding strategy somewhat analogous to the modern tuatara.
The minute size of the fossil, with a skull merely 1.5 centimeters in length, initially posed significant challenges to the research team. Traditional X-ray scanning techniques, although valuable, offered insufficient resolution for detailed anatomical assessment. To overcome this, the team harnessed cutting-edge synchrotron X-ray computed tomography (CT), employing powerful beamlines at both the European Synchrotron Radiation Facility in France and the Diamond Light Source in the UK. These advanced imaging methods allowed the researchers to visualize fossil intricacies at unprecedented resolution without inflicting damage, unlocking fine anatomical detail hidden within the tiny fossilized skull.
Through painstaking reconstruction of the scan data, scientists could explore the internal and external morphology of Agriodontosaurus with newfound clarity. This detailed visualization revealed the absence of palatal teeth and the lack of a cranial hinge mechanism that modern lizards employ to manipulate prey. Instead, the fossil’s prominent and sharp teeth suggest a specialized feeding mode adapted for handling tough insect exoskeletons, possibly representing an evolutionary experiment distinct from the pathways leading to contemporary lepidosaur feeding architectures. The divergence between Agriodontosaurus and its modern relatives highlights a previously unappreciated plasticity in early lepidosaur dietary adaptations.
Moreover, the discovery enriches our understanding of the evolutionary trajectory of the tuatara lineage. Despite often being dubbed a “living fossil,” the tuatara’s modern form masks a complex evolutionary history embedded within a once-diverse array of ancient lepidosaurs. The presence of the lower temporal bar in tuatara—a retention of an archaic skeletal feature—contrasts with the trend toward its reduction or loss among other lepidosaurs, as evidenced by this new fossil. These nuances underscore the evolutionary experimentation within Lepidosauria during the Middle Triassic and prompt a reevaluation of skeletal and feeding adaptations’ roles in shaping their success.
The ecological context of Agriodontosaurus further amplifies its significance; it roamed landscapes shortly prior to the rise of the dinosaurs, an era characterized by dynamic faunal turnovers and niches ripe for exploitation. Its specialized insectivorous dentition and compact size imply a lifestyle deeply intertwined with the undergrowth, taking advantage of insect prey resources that would have been abundant yet challenging to capture. Such intricate ecological interactions reveal the adaptive versatility underpinning lepidosaur proliferation in terrestrial ecosystems, emphasizing the predatory nuances that predate the dinosaur ascendancy.
The fossil birthplace—the Helsby Sandstone Formation of Devon, England—has long been a fruitful paleontological site, famous for a multitude of fossil discoveries spanning over 150 years. The serendipitous recovery of this specimen in 2015, by Dr. Rob Coram, epitomizes the continual surprises the field of paleontology holds and exemplifies how even well-explored localities can yield transformative finds when revisited with advanced technology and fresh perspective. This extraordinary find not only offers a vivid glimpse into ancient lepidosaur anatomy but also places a critical reference point within the broader narrative of reptilian evolution.
Collectively, the research reshapes fundamental concepts about lepidosaur origins and their feeding apparatus’ evolutionary history. The identification of Agriodontosaurus helsbypetrae underscores the mosaic nature of morphological evolution, where traits may emerge, disappear, or co-exist in surprising combinations rather than following a linear progression. This discovery calls for renewed scrutiny of fossil specimens worldwide, employing high-resolution imaging to detect subtle anatomical features that might have been overlooked or misinterpreted previously.
Furthermore, the study exemplifies how multidisciplinary collaboration and technological innovation catalyze breakthroughs in paleobiology. From MSc student investigators meticulously analyzing scan data to senior scientists synthesizing these findings within an evolutionary framework, the project embodies the future trajectory of vertebrate paleontology. It bridges the microscopic world of fossilized remains with grand evolutionary patterns, illuminating pathways that have led to modern reptilian diversity.
As a species, lepidosaurs now include a dazzling array of adaptations—flexible jaws, venomous capabilities, diverse locomotor styles—yet this fossil reminds us of their humble and enigmatic beginnings. Agriodontosaurus stands as a testament to the evolutionary experiments that have shaped the lepidosaur lineage, a powerful narrative woven through the fossil record and now revealed in stunning detail through the marriage of nature’s remnants and human ingenuity.
Subject of Research: Animals
Article Title: The oldest known lepidosaur and origins of lepidosaur feeding adaptations
News Publication Date: 10-Sep-2025
Web References:
http://dx.doi.org/10.1038/s41586-025-09496-9
Image Credits: Credit: Bob Nicholls
Keywords:
Paleontology, Fossils, Earth sciences, Vertebrate paleontology
