An African wild dog (Lycaon pictus, left) compared to a spotted hyena (Crocuta crocuta, right). Both photographed at the Bronx Zoo.
It never fails. Whenever I visit a zoo’s African wild dog exhibit someone inevitably asks “Are those hyenas?”, and when I visit spotted hyena enclosures I often hear the question “Are those dogs?” These carnivores, known to scientists as Lycaon pictus and Crocuta crocuta (respectively), are only distant cousins, but the vague similarities shared between them often cause people to confuse one with the other.
There are a few quick and dirty ways to tell them apart. Spotted hyenas, as their name indicates, have a coat flecked with solid spots while the fur of each African wild dog carries a distinctive pattern of caramel, white, black, and dark brown. They are also shaped a little bit differently; hyenas are stockier, with relatively shorter midsections, while African wild dogs have a longer, more lanky appearance. And, if you are really an astute observer, you might notice that African wild dogs lack something your more familiar domestic dogs have; a fifth toe, or dewclaw, on the forelimb. It is thought that this loss might be an adaptation which allows African wild dogs to more efficiently run after prey over long distances, but when did this happen, and how do these canids relate to other dogs?
The partial skeleton of a fossil canid referred to the new species Lycaon sekowei. From Hartstone-Rose et al., 2010.
To figure out the history of Lycaon we need to turn to the fossil record, and a report just published in the Journal of Paleontology proposes that a recently-discovered fossil dog may hold the key to he origins of the painted carnivores. In the 1-2 million year old deposits of Sterkfontein, South Africa (not far from where Australopithecus sediba was found), paleontologists Adam Hartstone-Rose, Lars Werdelin, Darryl de Ruiter, Lee Berger, and Steven Churchill recovered the remains of a previously unknown fossil dog. It shows some peculiar similarities with living Lycaon.
The new canid, named Lycaon sekowei, is represented by several specimens from two different time periods. The first group of fossils, dated to about 1.6-1.9 million years ago, consists of several bits of jaw with the teeth still anchored inside. The second, appraised to be about 1 million years old and tentatively referred to the new species, together make up nearly 40% of a skeleton, meaning that the anatomy of the carnivore is about 70% known (i.e. once you have the right femur, you also know what the left one looks like.) It appears to have been the largest canid, living or fossil, ever found in Africa, but what really makes it special are the details of its teeth and limbs.
The premolar teeth (RP2, RP3) of Lycaon sekowei (top), Lycaon pictus (second from top), Xenocyon (third from top), and Canis lupus (bottom) compared. From Hartstone-Rose et al., 2010.
As vertebrate paleontologists know well, a tooth can tell you a lot about a fossil mammal. Despite the fact that animals with similar diets often have similar teeth, the distinctive patterns of cusps and ridges are often useful in determining what kind of animal a fossilized tooth represents. In the case of Lycaon sekowei, it has peculiar accessory cusps on its premolars that are only seen in the canid genus Lycaon, and in a direct comparison the premolars of the new species more closely resemble those of Lycaon pictus than the gray wolf (Canius lupus) or the fossil wolf Xenocyon.
The dental resemblances between Lycaon pictus and Lycaon sekowei places the fossil species in a good position to be a potential ancestor of the living species, but if this is correct then there was a significant change elsewhere in the skeleton during the transition. When the scientists looked at the skeleton of the tentatively referred specimen they found part of the first metacarpal, or part of the digit which has been lost in living African wild dogs. Supposing that Lycaon sekowei is the ancestor of Lycaon pictus, the 1 million year old specimen is correctly referred to the new fossil species, and the loss of the first digital is an adaptation to hunting behavior centered around running after prey for significant distances, then the presence of this bone in Lycaon sekowei may mean that the cursorial hunting techniques of African wild dogs were relatively recent developments.
There are a lot of assumptions packed up into this hypothesis, however, and the ancestral status of Lycaon sekowei cannot be taken as a certainty. Based upon the evidence reviewed by the paleontologists it appears that Lycaon sekowei was a close relative of living African wild dogs. It certainly had a very similar dentition well-suited to a diet consisting mostly of meat, but the rarity of fossil canid remains from Africa, as well as the tentative referral of the more complete skeleton to the species, makes me wary of saying it was an ancestor of living African wild dogs just yet. Lycaon sekowei is the best candidate for an ancestor of African wild dogs discovered to date, but without a more complete array of fossil material we cannot yet be sure whether it was truly an ancestor of African wild dogs or instead a close relative of that as-yet-undiscovered ancestor.
ADAM HARTSTONE-ROSE, LARS WERDELIN, DARRYL J. DE RUITER, LEE R. BERGER and STEVEN E. CHURCHILL (2010). THE PLIO-PLEISTOCENE ANCESTOR OF WILD DOGS, LYCAON SEKOWEI N. SP Journal of Paleontology, 84 (2), 299-308 : 10.1666/09-124.1