Postcranial osteology of Boverisuchus vorax from the middle Eocene of Wyoming, USA : Implications for terrestrial adaptation in eusuchian crocodyliforms

Boverisuchus, a mid-sized eusuchian crocodyliform from the middle Eocene of Europe and North America, has long been regarded as more terrestrial than extant crocodylians and is often portrayed as one of the apex predators in Laurasian terrestrial ecosystems during the middle Eocene. Although Boverisuchus has been studied extensively since the nineteenth century, its skeletal osteology warranted re-examination based on three-dimensionally preserved materials to better understand its anatomy, function, and ecology. Our revised description of the North American Boverisuchus vorax provides new insights into previously poorly known aspects of the postcranium, including the configuration of the manus and pes. Comparative analyses of skeletal proportions incorporating phylogenetically informed allometric corrections indicate that B. vorax possesses elongated fore- and hindlimbs, elongated proximal carpals, and shortened metacarpals and digits-features that enhance the stance phase support and propulsive capacities, increase stride lengths, and reduce the cost of leg swing. The short, hoof-like terminal phalanges are integral to the overall shortening of the manual and pedal phalanges, reducing distal limb mass and improving swing phase energetics at the expense of stability. Additionally, the diagonal accessory keels and ridges on the paravertebral osteoderms likely functioned to resist torsional stresses on the trunk while trotting. Taken together, these skeletal proportions and postcranial specializations suggest increased terrestriality and improved locomotor capabilities in B. vorax.