.96" Fossil Avisaurus ("Bird Lizard") Claw - Wyoming

About Avisaurus

Avisaurus was a genus of prehistoric bird that inhabited western North America during the Late Cretaceous, approximately 66–70 million years ago. Fossils attributed to this genus have been recovered from the Hell Creek Formation of Montana and the Lance (Creek) Formation of Wyoming, deposits famous for preserving dinosaurs such as Tyrannosaurus rex and Triceratops horridus. Avisaurus belonged to the Enantiornithes, a diverse group of early birds that flourished throughout the Cretaceous before disappearing during the mass extinction at the end of the Cretaceous Period. Although these birds possessed feathers and were capable of flight, they retained several primitive skeletal characteristics that distinguished them from modern birds, including teeth and claws on their wings.

Avisaurus is primarily known from fossilized hindlimb elements, particularly the tarsometatarsus, a fused bone of the lower leg and foot. Its robust proportions and well-developed muscle attachment structures suggest that it possessed powerful grasping feet, potentially adapted for perching and capturing prey. Some researchers have proposed that Avisaurus occupied an ecological niche comparable to that of modern birds of prey, although its exact diet and hunting behavior remain uncertain. Fossils of these ancient birds are exceptionally uncommon compared to the dinosaur remains found in the Hell Creek and Lance (Creek) formations, making identifiable Avisaurus material particularly significant for understanding the diversity of birds that lived alongside the last non-avian dinosaurs.

About The Lance Formation

The Lance Formation of eastern Wyoming is a Late Cretaceous (69–66 million years old) unit that represents the same geologic age as the famous Hell Creek Formation of Montana and the Dakotas. Although they are time-equivalent, the Lance and Hell Creek preserve subtly different environments. Hell Creek reflects a humid, forested coastal plain punctuated by volcanic ash deposits, while the Lance records a slightly drier, more open floodplain landscape with broader river systems and fewer ash layers. Together, they provide a complementary view of life in the final chapter of the dinosaur era.

Perhaps the most famous Lance resident would be Tyrannosaurus rex, the largest North American carnivore to ever live. However, other smaller theropods also roamed the American midwest in this subtropical coastal stream system, including the beaked Ornithomimus, a lanky running theropod with a build similar to a modern ostrich, as well as several small predatory troodonts such as Paronychodon and Pectinodon.

Herbivorous dinosaurs also took advantage of the abundance offered by this unique era. Armored ankylosaurs dwelt in herds, their safety assured by their numbers, their heavy bone plating protecting most of their bodies and even their eyelids, and huge bone clubs on the ends of their tails providing them with powerful offensive capabilities. Ceratopsians like the famous Triceratops also formed protective herds, guarding their necks with frills and horns. Their smaller relatives, the dome-headed pachycephalosaurs, were also well represented in the area. Hadrosaurs, duck-billed titans with huge batteries of plant-grinding teeth in elongated snouts, are also well known from the region.

In addition to dinosaurs, a wide variety of fishes, amphibians, lizards, snakes, turtles, champsosaurs, crocodilians, and pterosaurs have been found in the formation.