The newly unveiled Labrujasuchus expectatus disrupts traditional notions of crocodilian evolution. Emerging from the lineage that gave rise to modern crocodiles—known for their quadrupedal stance and formidable teeth—Labrujasuchus defied expectations by evolving a bipedal locomotion, tiny arms, and most strikingly, a toothless beak. Its morphology startlingly resembles ornithomimosaurs, those swift, bipedal theropod dinosaurs often compared to modern ostriches, yet it belongs unmistakably to a different archosaur clade. This astounding case of convergent evolution illustrates how environmental pressures can shape drastically different evolutionary branches to arrive at similar solutions.

The significance of Labrujasuchus lies not only in its physical form but also in its ecological implications. The Late Triassic was a crucible of evolutionary innovation, where many modern animal strategies first emerged. Archosaurs were diversifying into a myriad of forms, from the gliding pterosaurs, descendants of bipedal cousins called lagerpetids, to the arboreal oddity Drepanosaurus with its grasping claws and prehensile tail. The presence of a bipedal crocodilian relative further underscores the adaptive experimentation rampant during this period.

Dr. Alan Turner, the lead author of the study published in the Journal of Vertebrate Paleontology, emphasizes the evolutionary uniqueness of Labrujasuchus. “The transition to bipedalism in crocodile relatives is exceptionally rare, making Labrujasuchus a fascinating subject for studying locomotor evolution. While bipedality is well-documented in dinosaurs and birds, uncovering a crocodile-line archosaur that adopted this mode of movement challenges our preconceived narratives,” he explains. This convergent evolutionary path highlights the plasticity of archosaur morphologies in response to ecological pressures.

This discovery fills an essential gap in the fossil record of shuvosaurs, a family of archosaurs with enigmatic body plans that have only recently begun to be understood. Prior to this find, two shuvosaur species from the same geological region delineated a broad evolutionary bracket. Labrujasuchus now elegantly occupies the intermediate phase, bridging temporal and morphological gaps in this intriguing lineage. The precise timing and morphology of this shuvosaur highlight the meticulous unfolding of archosaur diversity during the Triassic.

The species’ nomenclature carries both scientific and folkloric significance. Derived from “Ranchos de los Brujos”—Spanish for “Ranch of the Witches”—the genus name Labrujasuchus pays homage to the Ranch of the Witches site, also known as Ghost Ranch, where the fossil was discovered. The species name, expectatus, meaning “expected,” creatively references how paleontologists anticipated an intermediate shuvosaur species would eventually be found, validating predictive models based on earlier fossil records. This thoughtful naming encapsulates the intersection of scientific rigor and local cultural history.

Ghost Ranch itself holds a special place in paleontology, renowned not only for its dramatic red badlands immortalized by artist Georgia O’Keeffe but also as a treasure trove of Triassic fossils. This multi-quarry site has contributed immensely to our knowledge of Late Triassic ecosystems. The ongoing excavation project, co-led by co-author Dr. Nate Smith of the Natural History Museum of Los Angeles County (NHMLAC), continues to unearth a diverse cast of prehistoric creatures, enriching our understanding of this enigmatic era.

The broader implications of studying Labrujasuchus extend far beyond taxonomy. The Triassic period’s evolutionary experiments provide vital context for modern biodiversity crises. Many creatures from this epoch developed global survival strategies, some of which still underpin ecosystems today. By examining these ancient life forms, scientists can glean insight into resilience, adaptation, and extinction—lessons profoundly relevant as contemporary species face accelerating environmental changes.

Modern crocodilians are often stereotyped as relics from a bygone era, seemingly unchanged for millions of years. However, Labrujasuchus reminds us that their evolutionary history is far more complex and dynamic. The physiology and anatomy of these prehistoric relatives underscore evolutionary plasticity and innovation rather than static stasis. As paleontologists continue to unravel these threads, the narrative of crocodilian evolution gains nuance and depth.

The Natural History Museum of Los Angeles County plays a pivotal role in this research frontier. Their Dinosaur Institute curates an extensive collection of Mesozoic tetrapod fossils, encompassing not only dinosaurs but a wide array of contemporaneous vertebrates including early mammals, amphibians, and other archosaurs like Labrujasuchus. This resource allows scientists and students alike to investigate evolutionary patterns and functional morphologies with unprecedented detail.

The discovery of Labrujasuchus imparts a profound message about the Triassic world: it was an era of unpredictable evolutionary experimentation, where lineages diverged and converged in extraordinary ways. The peculiar yet elegant adaptations of this shuvosaur exemplify the dynamic interplay of environment, physiology, and ecology that shaped modern vertebrate diversity. It is a testament to the enduring power of fossils to surprise us and rewrite the textbooks.

As research continues, the combination of field excavation, detailed anatomical analysis, and comparative phylogenetics will likely illuminate more aspects of shuvosaur evolution. Each new find stitches together the complex tapestry of life’s grandeur during the Mesozoic. Labrujasuchus expectatus stands as a remarkable milestone in this journey, offering a window into a world where crocodile ancestors roamed on two legs, challenging our assumptions and broadening our scientific horizons.

Subject of Research: Animals
Article Title: A NEW SHUVOSAURID (ARCHOSAURIA, POPOSAUROIDEA) FROM THE LATE TRIASSIC (NORIAN) HAYDEN QUARRY OF NEW MEXICO, U.S.A.
News Publication Date: 26-May-2026
Web References: http://dx.doi.org/10.1080/02724634.2026.2618182
Image Credits: Credit to Jorge Gonzalez

Keywords: Triassic, Labrujasuchus expectatus, Shuvosauridae, Archosauria, Convergent Evolution, Bipedal Crocodile Relatives, Hayden Quarry, Natural History Museum of Los Angeles County, Dinosaur Institute, Paleoecology, Fossil Discovery, Evolutionary Biology

Researchers from the University of Washington’s Department of Biology, in conjunction with scientists at the Burke Museum, have unveiled these findings in the Journal of Vertebrate Paleontology, presenting a meticulous osteological analysis of Sonselasuchus fossils unearthed since 2014. These fossils belong to the Sonsela Member of the Upper Triassic Chinle Formation, a geologic unit richly endowed with well-preserved archosaur remains that continue to shed light on Late Triassic ecosystems. Analyzing over 950 specimens from this species, the team observed a differential growth pattern affecting limb proportions that strongly suggests a shift in locomotor strategy during ontogeny.

Elliott Armour Smith, the study’s lead author, articulates the fundamental observation: juveniles possessed relatively balanced forelimbs and hindlimbs, consistent with quadrupedal locomotion. However, as these animals reached adulthood, their hindlimbs elongated and thickened disproportionately relative to the forelimbs. This ontogenetic transformation, realized through changes in limb skeletogenesis and muscle attachments inferred from bone morphology, indicates a functional shift toward bipedalism. Such developmental plasticity is extraordinary among pseudosuchians, which traditionally are understood to have retained sprawling or semi-erect quadrupedal postures throughout life.

This bipedal tendency in Sonselasuchus is particularly compelling given its phylogenetic position within Poposauroidea, a clade of croc-line archosaurs often overshadowed by their bird-line contemporaries—namely theropod dinosaurs. Morphologically, shuvosaurids, including Sonselasuchus, exhibited convergent evolution toward traits reminiscent of ornithomimid (ostrich-like) dinosaurs: a toothless beak, extensive hollowing of bones, and enlarged orbital regions. Yet, these features arose independently on the croc-line evolutionary trajectory, underscoring a fascinating example of ecological convergence as archosaur lineages exploited similar niches within Late Triassic terrestrial ecosystems.

The ecological implications of Sonselasuchus’ locomotion and morphology are profound. Its denizen status in densely forested habitats, dominated by coniferous flora such as cedar-like trees hence the species epithet cedrus, suggests selective pressures favoring agile bipedal movement possibly for foraging or predator avoidance. The toothless beak hints at an omnivorous or herbivorous diet, diverging from the carnivorous norms seen in many contemporaneous pseudosuchians. Hollow bones, a trait typically associated with weight reduction in high-mobility animals, further denote an adaptation towards increased locomotive efficiency.

The Petrified Forest bonebed from which Sonselasuchus fossils derive is a paleontological treasure trove, amassing over 3,000 bones that chronicle an intricate snapshot of Late Triassic biodiversity. This rich assemblage includes fishes, amphibians, and various reptiles and dinosaurs, allowing researchers an unprecedented window into ecosystem dynamics. The collaborative effort over the past decade between the University of Washington, Burke Museum, and the National Park Service, involving students and volunteers, continues to yield new species and refine our understanding of the evolutionary pathways of archosaurs.

The elucidation of Sonselasuchus’ anatomical and functional characteristics advances broader questions about the evolutionary origins of bipedalism, a hallmark locomotor pattern significantly impacting vertebrate diversification. While bipedality is well-documented in bird-line archosaurs (dinosaurs and their avian descendants), its independent emergence on the croc-line challenges previous assumptions about muscular and skeletal constraints within pseudosuchians. Morphometric analyses in this study emphasize the critical role of ontogenetic trajectories in facilitating such locomotor shifts.

Moreover, the discovery underscores the complexity of convergent evolutionary processes in ecosystems where multiple archosaur clades coexisted and competed. The parallel acquisition of features such as toothless beaks, large orbits, and bipedal stance across these distinct lineages testifies to similar selective pressures shaping their morphology and behavior, despite divergent ancestries. This reinforces the notion that analogous ecological roles can drive remarkably similar evolutionary outcomes.

This research not only enriches the taxonomic and functional understanding of shuvosaurids but also prompts reevaluation of Late Triassic archosaur diversity and adaptive strategies. As ongoing excavations at Petrified Forest National Park unearth more skeletal elements, refined biomechanical modeling and histological studies are anticipated, potentially unveiling further insights into growth patterns, metabolism, and phylogenetic relationships within Poposauroidea.

Ultimately, Sonselasuchus cedrus embodies a fascinating chapter in archosaur evolution, illustrating how developmental plasticity and ecological opportunity can lead to atypical locomotor adaptations. Its story, emerging from Arizona’s fossil-rich strata, resonates with the broader quest to decode the evolutionary experiments that predate the more familiar dinosaur-dominated Mesozoic landscapes. With its blend of croc-line ancestry and dinosaur-like morphology, Sonselasuchus challenges our conventional paradigms and invites deeper inquiry into the multifaceted nature of archosaur diversification.

Subject of Research: Evolutionary osteology and locomotor adaptations of the Late Triassic shuvosaurid Sonselasuchus cedrus from the Chinle Formation.

Article Title: Osteology and relationships of a new shuvosaurid (Pseudosuchia, Poposauroidea) from the Upper Triassic Chinle Formation of Petrified Forest National Park, Arizona, U.S.A.

News Publication Date: 9-Mar-2026

Web References: https://tandfonline.com/doi/full/10.1080/02724634.2025.2604859

Image Credits: Artwork by Gabriel Ugueto

Keywords: Sonselasuchus cedrus, shuvosaurid, Pseudosuchia, Triassic, bipedalism, archosaur evolution, Petrified Forest National Park, Chinle Formation, convergent evolution, limb ontogeny, osteology, croc-line archosaurs