Biology subjects

Sanchez-Villagra, M. R.

Publications and source records attributed to Sanchez-Villagra, M. R..

5 recordsLinked to original sources

bioRxiv2026

Revisiting Cucuruchu, a Late Pleistocene site on the Venezuelan Caribbean coast with megafauna and lithic association

The study of historical documents from the original excavation led by J. M. Cruxent, of museum collections, as well as results of fieldwork, are combined to provide a revised assessment of the archeologically site of Cucuruchu, which together with those of Taima-Taima and Muaco, document megafaunal lithic remains associated from the Late Pleistocene in northern Venezuela. Six vertebrate taxa are reported for Cucuruchu: five megaherbivores (a giant sloth, Eremotherium laurillardi.; a glyptodontid, Glyptotherium cf. G. cylindricum; a macrauchenid, cf. Xenorhinotherium bahiense; a proboscidean, Notiomastodon platensis; and an equid, Equus sp.), and a turtle (Kinosternon sp.). Two fragments of El Jobo projectiles were found in situ lying among megaherbivores bones, while another unidentified projectile fragment was also found in the same layer. Although no direct evidence of human exploitation on these megaherbivores remains has been found, the presence of El Jobo projectiles in the undisturbed fossil-bearing layer some of which are associated with fossil remains, could be a suggestive of such interaction. Two new radiocarbon dates indicate ages of at least ca. 15.3-16.0 kyr cal BP for the fossil-bearing layer, contrasting with the mid to late Holocene age originally reported. Cucuruchu is a window to the past and supports the presence of hunter-gatherers of the El Jobo culture in the region at the end of the Pleistocene.

paleontology↗

bioRxiv2026

PALAEOROBOTICS UNCOVERS DEVASTATING MAMMALIAN TAIL STRIKE DYNAMICS

Extant animals occupy only a fraction of evolutionary design space, leaving many extinct morphologies without living analogues for functional testing. We combined comparative anatomy of 32 glyptodont species with a life-sized palaeorobotic tail rig to determine strike severity in club-tailed giant from the Pleistocene megafauna Doedicurus. The robophysical model, informed by fossil geometry and inertia, matched simulated fossil-tail collision momentum (98-105%) and generated peak forces of 81.1 kN at 6.4 m{middle dot}s-{superscript 1}, with an impulse of 427 N{middle dot}s, far exceeding equine extremity fracture forces. Peak force scaled near-linearly with strike velocity, implying [~]183 kN at projected top speed of 15 m{middle dot}s-{superscript 1}. Measurements suggest Doedicurus delivered high-severity strikes, supporting antipredator defence as primary selective driver of extreme tail weaponization, and establish palaeorobotic validation of extinct animal biomechanics.

bioengineering↗

bioRxiv2026

Diverse megamammals exploited by humans, chronology and palaeoecology at Taima-Taima, Late Pleistocene, South America

The arrival of humans to the Americas at the end of the Pleistocene has been one of the foundations of the hypothesis that hunter-gatherer groups had a direct role in the extinction of megafauna. However, empirical evidence of the exploitation of megafauna by humans and associated chronological context are still scarce, especially in South America. Using evidence of modifications on osteological remains, we provide a reassessment of the megafauna that was exploited at the classic Taima-Taima site (Venezuela), with an updated chronology and paleoenvironmental inferences. Our results show that, at least, five species of extinct megaherbivores were probably exploited at the site, expanding the previous records, restricted to the proboscidean Notiomastodon platensis and the giant armadillo Glyptotherium cf. G. cylindricum. The new data of the other exploited taxa include the terrestrial sloth Glossotherium, the macrauchenid cf. Xenorhinotherium bahiense and a toxodontid; both killing and slaughtering activities were likely practised at the site. Seven new enamel radiocarbon dates show an age of 15.3-17.8 cal kyr BP for the fossiliferous strata, although this is likely to be a minimum age given the materials propensity for modern carbon uptake. The study of phytoliths and starch grains from the dental calculus of N. platensis identified five plant taxa from the phytoliths: arboreal dicotyledons, Poaceae, Marantaceae, Asteraceae and Arecaceae. Ecometrics studies of dental diversity reveal how no other single site on the continent preserves such a diversity of grazing and browsing megaherbivores exploited by humans.

paleontology↗

bioRxiv2020

Variation and mechanisms of life history evolution in insular dwarfism as revealed by a natural experiment

Islands are a classic focus for evolutionary studies. One subject of much interest has been the evolution of "dwarfs", significantly smaller island mammals relative to their continental counterparts. Although a consensus has been achieved that multivariate ecological causes are behind body size changes, the processes involved remain largely unexplored. Life history variables, including the age of first reproduction, growth rate, and longevity, are probably key to understanding the process of insular dwarfism. The Japanese Archipelago with numerous islands offers a unique natural experiment of evolution into different sizes within the same group of organisms, deer. Thus, we investigated eight deer populations with a total number of 52 individuals exhibiting body size variation, both extant and fossil, to clarify the effect of insularity on life history traits. We applied several methods to both extant and extinct populations to resolve life history changes among deer populations. Skeletochronology, using lines of arrested growth formed in long bones (femur and tibia), successfully reconstructed body growth curves and revealed a gradual change in growth trajectories reflecting the degree of insularity. Slower growth rates with prolonged growth periods in more isolated deer populations were revealed. An extensive examination of bone microstructure further corroborated this fact, with much slower growth and later somatic maturity evident in fossil insular deer isolated for more than 1.5 Myr. Finally, mortality patterns assessed by demographic analysis showed variation among deer populations, with a life history of insular populations shifting toward the "slow life".

evolutionary biology↗

bioRxiv2017

Bayesian divergence-time estimation with genome-wide SNP data of sea catfishes (Ariidae) supports Miocene closure of the Panamanian Isthmus

The closure of the Isthmus of Panama has long been considered to be one of the best defined biogeographic calibration points for molecular divergence-time estimation. However, geological and biological evidence has recently cast doubt on the presumed timing of the initial isthmus closure around 3 Ma but has instead suggested the existence of temporary land bridges as early as the Middle or Late Miocene. The biological evidence supporting these earlier land bridges was based either on only few molecular markers or on concatenation of genome-wide sequence data, an approach that is known to result in potentially misleading branch lengths and divergence times, which could compromise the reliability of this evidence. To allow divergence-time estimation with genomic data using the more appropriate multi-species coalescent model, we here develop a new method combining the SNP-based Bayesian species-tree inference of the software SNAPP with a molecular clock model that can be calibrated with fossil or biogeographic constraints. We validate our approach with simulations and use our method to reanalyze genomic data of Neotropical army ants (Dorylinae) that previously supported divergence times of Central and South American populations before the isthmus closure around 3 Ma. Our reanalysis with the multi-species coalescent model shifts all of these divergence times to ages younger than 3 Ma, suggesting that the older estimates supporting the earlier existence of temporary land bridges were artifacts resulting at least partially from the use of concatenation. We then apply our method to a new RAD-sequencing data set of Neotropical sea catfishes (Ariidae) and calibrate their species tree with extensive information from the fossil record. We identify a series of divergences between groups of Caribbean and Pacific sea catfishes around 10 Ma, indicating that processes related to the emergence of the isthmus led to vicariant speciation already in the Late Miocene, millions of years before the final isthmus closure.

evolutionary biology↗