On a day designated for celebrating canine companions, go behind the scenes at the American Museum of Natural History into the fossil dog collection—the largest of its kind in the world. Find dire wolves, bear-sized dogs, and more. These images and captions come to us from Jack Tseng, a National Science Foundation postdoctoral researcher in the Division of Paleontology at the American Museum of Natural History. He is a paleontologist interested in predators of all shapes and sizes, specializing in the hunting and feeding specializations of carnivorous mammals. Also, he love dogs.

The great diversity of sizes and shapes of domestic dog breeds is paralleled, if not surpassed, by what we see in the fossil record of dogs. Unfortunately for us, both the largest and smallest dog species known to science are extinct.

This is a photo of one of the earliest and smallest dogs, Archaeocyon pavidus, next to the largest and one of the most specialized canids, Epicyon haydeni. Archaeocyon lived 30-million-years ago, and was a small, Chihuahua-sized dog that sits near the base of the family tree branch that gave rise to all living dog species. Epicyon was a huge, bear-sized dog that has evolutionarily modified their skulls and teeth to adapt to a bone-crushing diet. At more than twice the body mass of living spotted hyenas (the best known bone-crusher and dog-like cat-relative), Epicyon could have crushed and eaten anything in its path during its reign as one of North America’s largest predators during the Age of Mammals.

Advertisement

This photo shows complete or partial forearm bones (the radius) of 15 individuals of the extinct dog Borophagus discovered at a single fossil site in Oklahoma, showing off the impressive number of specimens from a single type of bone that can be found from each of hundreds of fossil sites represented in our collections.

The vertebrate paleontology collection of the American Museum of Natural History is unparalleled in its diversity and quantity of fossil dogs, occupying more than 50 cabinets with total number of specimens estimated at between 5,000-10,000. This immense and diverse collection makes it a critical source of information for paleontologists and biologists.

Advertisement

The fossil skeletons of animals that you see on public exhibit are either extremely rare because of their completeness, or were assembled from parts of different individuals of similar sizes to create a composite skeleton demonstrating the animals’ proportions. The fossil dog collection at the American Museum of Natural History is not only the largest of its kind, but it also contains some of the most complete fossil skeletons known for dogs. This photo shows a nearly complete skeleton of the extinct hyena-like dog Aelurodon. Having more than just a skull or part of a leg allows paleontologists to reconstruct the proportions of these extinct predators, and in turn knowing something about their lifestyle and mode of hunting.

One of the most iconic fossil canines of all time has got to be the dire wolf. Known to science long before the similarly named animal characters in the Game of Thrones, today the best record of dire wolf populations comes from the tar pits of Los Angeles, California. This is a dire wolf skull excavated from the tar pits, one of several tar pit predator specimens in our fossil collection (the majority of Ice Age fossils from the tar pits is curated in California). The dire wolf was about the same size as modern grey wolves, but the former had a more robust skeleton. These top dogs represent the pinnacle of pursuit predators in the evolutionary history of dogs, having leg joints specialized for long-distance running, with a range of motion restricted to a single plane for increased efficiency. They lived in North America at the same time as large hoofed mammals such as camels, horses, bison, and gigantic ground sloths (a skeleton of which is visible in the background), none of which were easy prey. Evidence of the intensity of predation, or perhaps competition with other dire wolves, can be gleaned from healed injuries such the blow to the top of the braincase that this animal survived prior to being laid to rest in its asphaltic grave.

Advertisement

New research heavily based on the Museum’s fossil dog collection shows how dogs evolved in response to a cooling, drying climate in North America over the last 40 million years. Learn more about this research.