Dear experts, how do you do?

Let me ask you a question about differences in thermoregulation of the Canidae and Hyenidae: there has been a clear trend of wiping out all actively hunting Hyenidae lineages probably under the competitive pressure by large and progressive wolf-like Canids for the last 2 and some million of years in the cold to temperate climatic zones - i.e. Eurasia and North America.
It may seem illogical since the hyenas are younger and thus they are supposed to be evolutionary more advanced than dogs. Anyway, the former failed and the latter won, the Chasmaportetes and relatives disappeared and wolves occupied the niche.
However, in Africa we still see a different picture - the huge spotted hyenas clearly dominate and hunt successfully taking down prey the size of African buffalo. The spotted hyena can attain weight of over 80 kg and it is able to run and hunt during a day under the African Sun. Local hunting dogs are extremely effective carnivores but they are limited in size being about 25 kg max. The same is true with the Asian hunting dog, the dhole, and with southern populations of grey wolf and with long-feral Australian dingo. All of them are limited with roughly the same size limit - about 25 kg.

One of the canid experts here said that this is the maximum weight, which still enables a canid to cool itself effectively under the tropical conditions. By passing it over a dog will inevitably have a heat attack during intensive activities like hunting.
On the other hand we see hyenas, which seem to have no problems with heat at all, even thouh they live a very similar life mode in the tropics as the dogs do in colder regions.
That guy unfortunately had no idea what kind of thermoregulation mechanisms the Hyenidae might have that enables them to be active cursorial carnivores and yet grow 4 time bigger than canids of the same region.

Could you, please, explain this strange difference between them?

Thank you!
Sincerely,
Gleb

Hi Gleb,

first of all I'd point out that the younger age of a lineage does not make it more advanced in terms of adaptations. Polarity in evolutionary lineages is determined by unique and shared changes in comparison to an outgroup. An older lineage can have a more functionally effective set of adaptations than a younger lineage in the same order.

My next point would be that hyaenas are predominantly nocturnal, so thermoregulation should not be a major issue with regard to heat loss. Canids are generally less nocturnal in their habits than hyaenas, so this might go some way to explaining the difference.

My final point is that there is considerable partitioning of resources in tropical ecosystems because there is much greater biomass - this leads to a lot of specialisation. This lessens as you move to more temperate regions. Hyaenas are obligate carnivores (and the aardwolf is an obligate termite-eater), whereas dogs are more generalist in their diet than hyaenas, which may partly explain the relative distributions. This also provides a reason for the larger size (and obligate communal living) of spotted hyaenas, since they are adapted to prey on large herbivores or compete with other large carnivores for their kill, whereas canids need to be small enough to subsist on small prey, insects, fruits, etc. for much of the time.