A remarkable discovery in paleontology sheds new light on the early evolutionary history of squamates, the diverse group encompassing lizards and snakes. Researchers have examined a partial skeleton, designated NMS G.2023.7.1, recovered from the Early Cretaceous Purbeck Limestone Group, preserved in exquisite detail within a limestone matrix. This specimen stands out for its mosaic anatomical features that bridge gaps in our understanding of squamate evolution during a critical period in reptilian history.
The disarticulated fossilized bones of NMS G.2023.7.1 are dispersed over an area approximately 19 centimeters in diameter on a rippled bedding surface. This arrangement mirrors similar preservation patterns seen in related specimens attributed to Parviraptor estesi, supporting their relative contemporaneity and depositional environment. Detailed examination reveals an impressive array of skeletal elements, including parts of the skull such as the right mandible and braincase, an extensive suite of vertebrae and ribs, and several components of the appendicular skeleton like humeri and femora, albeit all incomplete to varying degrees.
Critical to validating the specimen’s integrity as a single individual is the morphological consistency among all preserved squamate elements and the absence of anatomical duplication. The spatial pattern of the bone scatter aligns with expected anatomical distribution, arranging cranial features and anterior vertebrae on one side of the block, with hindlimb and caudal vertebrae on the other, bridged by dorsal ribs and forelimb elements. Importantly, no other squamate remains were found within a two-meter radius, which significantly reduces the likelihood of mingled individuals or post-mortem transport from other sources.
Taphonomic analysis highlights the selective preservation dynamics experienced by the skeleton prior to burial. The presence of numerous foraminiferal Group 1 elements—primarily vertebrae and ribs, which are easily displaced by water currents—suggests depositional conditions characterized by moderate currents insufficient to dislodge these lighter bones yet inadequate to introduce large, allochthonous Group 2 and 3 elements such as limb bones or skull fragments. The sedimentary context indicates a lagoonal environment wherein bone fragments from non-squamate vertebrates were commonly deposited alongside the squamate remains, likely representing the local faunal assemblage rather than introduced material.
Reconstruction efforts utilizing advanced 3D modeling software, such as Blender and Meshlab, facilitated detailed anatomical mapping of the skull and body proportions. The assembled skull model, estimated at 41.4 millimeters in length, reveals a long and low cranial profile consistent with known parviraptorid morphologies. These reconstructions integrated comparative data from known specimens like the holotype of Parviraptor estesi to project accurate biological contours. Vertebral column measurements and limb bone lengths obtained from digital models informed plausible estimates of total presacral length and overall body morphology, critical for life restoration representations by skilled paleo-artists.
The fossil preparation was an interdisciplinary endeavor incorporating chemical preparation techniques and high-resolution imaging. The block housing NMS G.2023.7.1 was carefully extracted and subsequently prepared using acetic acid baths to remove matrix material without damaging delicate bones. Innovative imaging modalities, including micro-computed tomography (μCT) scanning at multiple resolutions and synchrotron-based phase-contrast X-ray tomography at the European Synchrotron Radiation Facility, produced unparalleled three-dimensional visualizations. These imaging methods have enabled detailed segmentation and digital excavation of individual bones, facilitating both morphological and histological analyses with unprecedented clarity.
Osteohistological investigations were conducted on thin sections obtained from the humerus, femur, and rib shafts. Specimens were manually extracted and embedded in low-viscosity epoxy resin, then precision sectioned and ground to optical thickness. Microscopic examination under plane-polarized light disclosed microstructural features indicative of growth patterns, vascularization, and bone remodeling processes, providing insight into the life history and developmental biology of this early squamate. High-resolution photomicrographs supplement these data, enabling future comparative studies.
Phylogenetic analyses employed Bayesian inference with fossilized birth–death models to evaluate the evolutionary placement of the specimen within squamate lineage trees. Three comprehensive morphological character matrices were utilized, incorporating wide taxon sampling including extant and extinct squamates, rhynchocephalians, and early reptiles. The analyses featured stringent topology constraints derived from molecular phylogenies and permitted testing across different hypotheses of toxicoferan relationships—a clade including anguimorphs, iguanians, and snakes. The parviraptorid specimens, including NMS G.2023.7.1, consistently emerged within early branches, illuminating unresolved aspects of squamate diversification.
Each dataset incorporated a variety of protocols to ensure convergence and robust statistical support. These included long-chain Markov Chain Monte Carlo runs exceeding 100 million generations, meticulous monitoring of effective sample sizes, and multiple replicates to confirm reproducibility of topology estimations. This rigorous approach against confounding phylogenetic signals lends credence to the evolutionary interpretations proposed, underscoring the specimen’s significance in understanding squamate ancestry.
The cumulative evidence affirms that NMS G.2023.7.1 represents a unique glimpse into early squamate morphology and ecology. Its mosaic anatomical features, combining primitive and derived traits, exemplify evolutionary experimentation within this lineage during the Jurassic-Cretaceous transition. The specimen not only enriches paleontological records but also provides a vital calibration point for molecular clock models, potentially realigning timelines for reptilian evolutionary events.
This investigation also highlights the power of integrating multidisciplinary scientific approaches in paleontology. From meticulous field discovery and chemical preparation to state-of-the-art imaging and computational phylogenetics, each methodological element plays a crucial role in uncovering the complexities of ancient life. The ability to digitally reconstruct complete anatomical structures from fragmentary fossils elevates our capacity to visualize extinct ecosystems and evolutionary trajectories.
Future research prospects include more refined biomechanical modeling of limb function based on these anatomical reconstructions, alongside further histological studies to elucidate growth rates and life history strategies. Additionally, expanding phylogenetic datasets with newly discovered fossils will continue to sharpen our understanding of squamate diversification dynamics and their responses to paleoclimatic shifts during the Mesozoic.
In summary, the comprehensive study of NMS G.2023.7.1 propels not only squamate paleontology but also broader vertebrate evolutionary biology. By revealing a unique blend of morphology and preserving rich histological and phylogenetic data, this fossil stands as a keystone discovery, promising to inspire further investigations into the early origins and adaptive radiations of Squamata.
Subject of Research: Early fossil squamate anatomy and phylogenetics
Article Title: Mosaic anatomy in an early fossil squamate
Article References:
Benson, R.B.J., Walsh, S.A., Griffiths, E.F. et al. Mosaic anatomy in an early fossil squamate. Nature (2025). https://doi.org/10.1038/s41586-025-09566-y
Image Credits: AI Generated
