The rivalry between dogs and cats have raged on for centuries, with no clear indication of how things even began in the first place, but according to new research conducted by an international team of scientists, this age-old competition between the two species has played a key role in the evolutionary history of canines.

In a study featured in the Proceedings of the National Academy of Sciences journal, researchers from the University of Gothenburg in Sweden, the University of São Paulo in Brazil and the University of Lausanne in Switzerland examined more than 2,000 fossil specimens and discovered that the introduction of Asian felids to the continent of North America had particularly devastating effect on the diversity of local dog families.

Evidence from these analyzed fossils suggests that the felids contributed to the eventual extinction of as many as 40 different species of dogs.

Lead investigator Daniele Silvestro at Gothenburg's biological and environmental sciences department explained that while it was initially assumed that changes in the climate played a significant role in the development of biodiversity, their findings point to competition among various species of carnivores to be the more crucial for the evolution of canids.

The first family of dogs originally came from North America around 40 million years in the past. They were able to reach their maximum diversity approximately 22 million years ago, which was characterized by the spread of over 30 different dog species in the continent. Modern analysis, however, show that there are only nine members of the original dog family left in North America.

These dog species evolved to have larger bodies and became more adept at being large predators to other animals. Some dogs even reached sizes of about 30 kilograms (66 pounds), becoming one of the largest known carnivores on the continent of North America.

While modern-day species of large carnivores are threatened with a higher rate of extinction compared to smaller animals, the researchers did not find any evidence that could pertain to a similar pattern among ancient species of canid.

The success in the evolution of carnivorous species is ultimately tied to their ability to hunt for their own food. Limited sources of food, however, often result in stiff competition among different carnivores in a region.

The study suggests that carnivores in North America could have potentially followed similar survival dynamics in which competition among species of ancient dogs and felids.

Despite the significantly negative impact of the introduction of felids in the continent, the same cannot be said regarding the effects of dogs on the survival of ancient cats. The study shows that felids could have been more adept predators compared to other extinct species included in the family of dogs.

Photo: Jeffrey W | Flickr