Bonapartenykus – Late Cretaceous Predator from Argentina

Bonapartenykus – Late Cretaceous Predator from Argentina

Welcome to a journey back in time, to a world dominated by magnificent creatures whose stories are etched in the Earth’s geological layers. Among these ancient beings, one stands out for its unique attributes and mysterious past: Bonapartenykus. Named in tribute to the renowned paleontologist José F. Bonaparte, this theropod dinosaur offers a fascinating glimpse into a bygone era.

Let’s embark on an exploration of this incredible creature, piecing together its history, lifestyle, and the world it inhabited. Through fossil records and scientific deduction, we will reconstruct the life of Bonapartenykus, offering insights not just into this particular dinosaur but also into the broader tapestry of life during the Late Cretaceous Period.

Bonapartenykus Key Facts

Meaning of nameJosé F. Bonaparte’s Claw
Type SpeciesBonapartenykus ultimus
When it Lived83.5 to 66.0 MYA
PeriodLate Cretaceous
EpochCampanian to Maastrichtian
Length8.2 feet
HeightApproximately 5.5 feet
Weight159.0 pounds
MobilityMoved on two legs
First Discovery2010 by Argentine-Swedish Dinosaur Expedition
Described by2012 by Federico Agnolin, Jaime Powell, Fernando Novas, and Martin Kundrát
HolotypeMPCA 1290
Location of first findAllen Formation, Patagonia, Argentina

Bonapartenykus Origins, Taxonomy, and Timeline

Bonapartenykus, meaning “José F. Bonaparte’s Claw,” is a nod to José F. Bonaparte’s significant contributions to the field. The Latin suffix “onykus,” meaning claw, highlights one of its most striking features. It’s like a small acknowledgment to the past, etched into the nomenclature of this ancient creature. As for the specific name “ultimus”, it derived to the Latin word “ultimus”, meaning “the latest”. At the time of the discovery, Bonapartenykus ultimus was the youngest alvarezsaurid from South America.

Illustration of Bonapartenykus, a small theropod dinosaur from the Late Cretaceous period, depicted with a slender body, long legs, and a distinctive crest on its head. This dinosaur, known for its bird-like features and likely insectivorous diet, is shown in a walking posture.

As a member of the Theropoda and the Alvarezsauridae (and more particularly the Patagonykinae), it shares lineage with some of the most well-known predators of the dinosaur world, such as Patagonykus puertai. Its type species, Bonapartenykus ultimus, is the sole member of the genus at this date.

The timeline of Bonapartenykus spans a fascinating era. Roaming the Earth during the Late Cretaceous Period, specifically from the Campanian to the Maastrichtian, it witnessed a world in flux, a world that was about to undergo monumental changes. This timeline, approximately 83.5 to 66.0 million years ago, situates our subject in one of the most dynamic periods in Earth’s history.

Discovery & Fossil Evidence

The discovery of Bonapartenykus in 2010 by an Argentine-Swedish Dinosaur Expedition in the Allen Formation, Patagonia, Argentina, opened a new chapter in our understanding of alvarezsaurids. The expedition unearthed a wealth of information, allowing us to piece together a more complete picture of this creature’s life and environment.

Black and white image showing the left femur of Bonapartenykus ultimus, the holotype specimen. The bone is labeled with various anatomical features, including the greater trochanter (gt), caudal trochanter (ct), and medial shaft (ms). This image highlights the detailed fossilized structure of this small theropod dinosaur from the Late Cretaceous period.
Left femur of Bonapartenykus ultimus (holotype, MPCA, 1290) in A, lateral, B, cranial and C, medial views.
Picture by Federico Agnolin

Fossil evidence, primarily the holotype MPCA 1290, were found in a fluvial sandstone and provide invaluable insights into Bonapartenykus. The locality, as the Upper member of the Allen Formation (Salitral Ojo de Agua, Patagonia, Argentina), delivered numerous non-avian dinosaur remains: ornithischian hadrosaurids, ankylosurs, titanosaurids, and several but incomplete theropods.

The preservation state of Bonapartenykus, though not complete, allows us to reconstruct its physical characteristics and potential behaviors. This evidence, while not as extensive as for some other species, is crucial for painting a portrait of this intriguing theropod.

Bonapartenykus Size and Description

Bonapartenykus ultimus, a notable member of the Alvarezsauroidea, was a unique dinosaur of the Late Cretaceous Era. This creature’s body shape was relatively streamlined, adapted for its lifestyle. It possessed a well-proportioned head atop a flexible neck, which likely aided in foraging or predatory activities. The vertebrae, particularly the mid-dorsal ones, were characterized by distinctive spinopostzygapophyseal laminae. Bonapartenykus had sturdy limbs, indicative of a bipedal locomotion style. Its tail, proportionate to its body size, might have been used for balance. The skin texture remains largely speculative. As for its movement, it was likely swift, befitting its build.

Size and Weight of Type Species

Colorful illustration showing various dinosaurs from the Allen Formation fauna. Different species are depicted in vibrant colors, with a human silhouette for scale in the center. The image includes a range of dinosaurs from small to large, showcasing the diversity of the Late Cretaceous period
PaleoNeolitic, CC BY-SA 4.0, via Wikimedia Commons

Bonapartenykus ultimus was a considerable size for an alvarezsaur. Measuring about 2.5 meters (8.2 feet) in length and weighing around 72.0 kilograms (159.0 pounds), it stood as the largest known member of its clade. This size estimate is particularly significant considering the generally smaller stature of alvarezsaurs. The weight and length give us a glimpse into the physical presence of Bonapartenykus in its habitat, suggesting a robust yet agile dinosaur capable of varied physical activities, be it hunting or scavenging.

The Dinosaur in Detail

Bonapartenykus set itself apart with several unique features. Its mid-dorsal vertebrae, for instance, exhibited distinct laminae ending abruptly above the postzygapophyses, a characteristic not commonly observed in other dinosaurs. The underside of the coracoid was uniquely deflected, featuring grooves similar to those found in Xixianykus, which might indicate similar muscle attachments or movements. Furthermore, the fused scapulocoracoids and the wide notch on the scapula’s posterior margin are reminiscent of traits found in Ceratonykus. These morphological peculiarities not only distinguish Bonapartenykus within the Alvarezsauroidea clade but also shed light on its evolutionary adaptations, suggesting a creature well-adapted to its ecological niche.

Each of these features reflects an evolutionary adaptation, contributing to the dinosaur’s survival and prowess. The discovery of Bonapartenykus, especially in association with eggshells, provides crucial insights into the reproductive behavior and developmental stages of alvarezsaurs, deepening our understanding of this intriguing species.

Contemporary Dinosaurs

In the diverse landscapes of the Late Cretaceous, Bonapartenykus thrived amidst a fascinating cast of contemporaries. Imagine the majestic Barrosasaurus, a giant among giants, traversing the lush Cretaceous forests. Larger than Bonapartenykus, this sauropod might have roamed in herds (“They move in herds, they do move in herds!” … try to guess the movie!). In the shadow of these gentle giants, Bonapartenykus could have lurked, calculating and agile. Was it a predator to these colossal vegetarians, or did it scavenge what predators like Unquillosaurus left behind?

Unquillosaurus, a sleek and possibly formidable predator, may have shared hunting grounds with Bonapartenykus. Could there have been a silent competition for prey or territory between them? These two hunters, possibly similar in size and agility, might have engaged in a stealthy dance, each marking its dominion and showcasing its hunting prowess. Bonapartenykus, with its unique adaptations, may have had to be cunning and strategic to coexist with such a competitor.

Then there was Pitekunsaurus, another titanic sauropod, a peaceful giant that lumbered through the same realms as Bonapartenykus. Perhaps larger than both Bonapartenykus and Unquillosaurus, it presents a contrast to the predatory lifestyle. Was it simply too large for Bonapartenykus to consider as prey, or did it present an opportunity for scavenging? The presence of such herbivores would have greatly influenced the ecosystem, providing sustenance for a range of predators and scavengers alike.

In this vivid tableau of the Late Cretaceous, each dinosaur played a role in the grand scheme of life. Bonapartenykus, with its distinctive features and hunting style, coexisted with these giants and hunters, each influencing the other’s survival and behavior. The interactions amongst them – be it in competition, predator-prey dynamics, or cohabitation – shaped the environment they thrived in.

Interesting Points about Bonapartenykus

Bonapartenykus in its Natural Habitat

Bonapartenykus, a formidable presence in the Late Cretaceous, roamed the diverse landscapes of the Allen Formation. This geological setting, spanning the Campanian to Maastrichtian Stages, was not just a backdrop but an active participant in the life of this theropod. The formation’s fluvial sandstones tell stories of rivers that meandered through ancient lands, shaping the habitats and influencing the lives of the creatures that dwelled within them.

Varied Environments of the Late Cretaceous

The Allen Formation’s rich tapestry of environments ranged from ephemeral lakes and wind-swept aeolian systems to coastal marine settings that morphed into estuaries and tidal flats. While found in a fluvial sandstone, this variety of landscape created a dynamic environnement for Bonapartenykus. The hybrid coastal systems, influenced by strong storm events in some areas, were linked intricately with aeolian systems, creating a landscape both challenging and rich in resources for the predators and prey alike.

Interactions within the Ecosystem

In such a rich and varied environment, interactions between different species were inevitable. The relationship between Bonapartenykus and its contemporaries likely included predator-prey dynamics, competition for resources, and possibly even scavenging behaviors. The presence of large herbivores would have provided ample hunting opportunities, while the presence of other predators could have led to territorial disputes or competition for the same food sources.

The Allen Formation, with its diverse environments and range of inhabitants, provided a perfect setting for Bonapartenykus to exhibit its hunting prowess, adaptability, and survival strategies. This Late Cretaceous ecosystem, teeming with life, was a world where Bonapartenykus played a pivotal role, influencing and being influenced by the land and its cohabitants.

Frequently Asked Questions

What era did this dinosaur live in?

Bonapartenykus lived during the Late Cretaceous Period, approximately 83.5 to 66.0 million years ago.

What type of dinosaur was it?

It was a theropod, belonging to the Alvarezsauridae (and more precisely to the Patagonykinae).

Where was this dinosaur first discovered?

The first fossils were found in the Allen Formation, Patagonia, Argentina, in 2010.

What did it eat?

As a carnivore, it likely preyed on smaller animals.

How did it move?

Bonapartenykus moved on two legs, indicating a bipedal locomotion style.

Is there much known about its size?

While exact measurements are not available, it’s believed to be a medium-sized theropod.


The information in this article is based on various sources, drawing on scientific research, fossil evidence, and expert analysis. The aim is to provide a comprehensive and accurate overview of Bonapartenykus. However, please be aware that our understanding of dinosaurs and their world is constantly evolving as new discoveries are made.

Article last fact checked: Joey Arboleda, 03-09-2024

Featured Image Credit: Miracusaurs, CC BY-SA 4.0, via Wikimedia Commons

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