Carnotherium

The domesticated dwarf giraffes gave rise to 2 extremely popular and successful branches: the Kryotheres and the Carnotheres. After many members of Carnivora died out, there was a huge niche. These were filled in with many groups and one of them being the Carnotheres. They filled in the roles of so many predators and diversified for so long that they could be the most successful group of predatory mammals ever. Here is the common species.
The size of a horse, these carnivores can run at up to 40 miles per hour for 2 miles. The upper front of their body is unusually stocky, allowing them to bring down prey 3 times their own size. Yet the lower half is very lean and resembles a greyhound build. Their heads are large and muscular. Their "canines" are actually bone protruding from the actual skull and the canines on the bottom are are modified incisors.
Carnotheres, of this particular species are solitary and give birth to 3 or 4 calfs that resemble wooly dog pups. At a young age they learn to swim quite well. By adulthood, prey in the water is an option.