Apart from the obvious fact that they are both members of the Panthera genus (i.e. the largest members of the feline family), recent studies have shown that, based on mitochondrial DNA, tigers and snow leopards are actually considered sister species, whereas (believe it or not) lions are more closely related to jaguars and common leopards.
It all comes down to evolution: as seen in the phylogenetic tree above, tigers and snow leopards diverged from their common Panthera ancestor (whose identity remains unknown to this day) around approximately 3.9 million years ago – by that time, lions, leopards and jaguars were just starting to branch off from that same ancestor
, and split from other felines around 4.3–3.8 million years ago, each eventually becoming their own species.This basically means that tigers and snow leopards have more of a recent evolutionary history when compared to other big cats. After that, the striped felids evolved into a unique species towards the end of the Pliocene, before becoming generalist predators that began to conquer a wide variety of Asian habitats – from South Asia’s tropical rainforests and mangroves to cold, temperate forests further north, and even grasslands in some places –; whilst their spotted cousins became specialists, evolving to exclusively occupy Asia’s frigid montane regions, including the Tibetan Plateau and the Himalayas.
Plus, one can see the relation when taking a closer look at these animals’ faces. Sure enough (and I have fellow Quoran Simon Javenic to thank for providing this info in his answer to What are some interesting facts about tigers?), as shown in the picture above, tigers and snow leopards seem to have a more circular face as well as a longer and narrower snout; while lions, jaguars and common leopards have a bit more ovular face, along with a broader and flatter muzzle.
Last but not least, tigers can roar like the rest of the Panthera members, but snow leopards lack that characteristic due to the structure of their throat (see all about it in my answer to Do larger felines – lions, tigers, leopards, cheetahs, cougars, etc. – purr the same way house cats do?). However, they both share the ability to emit a vocalization called prusten, a form of communicative behavior that manifests itself through chuffing (see video below), notably when these animals close their mouth and blow air through the nostrils, thus producing a breathy snort that is usually issued to say hello or to signal good intentions.
Utterly mind-blowing, eh? All this time, we thought that the world’s largest felid, the tiger, was closely related to the second biggest cat, the lion, due to their similarities in size, build and behavior.
And yet, just like so many other cases in zoology, taxonomy proves us wrong, and instead establishes that the tiger’s closest relative is actually the fluffy, spotted winter cat, the snow leopard, which is on top of that much smaller, weighing approximately 27–54 kg (60–120 lbs), which is pretty lightweight for a big cat, especially when compared to a 220–300 kg tiger.
In that context, snow leopards should have their name reconsidered and be called “snow tigers”! Though in this case, we’re gonna have to come up with other names so as to not confuse them with the real snow tigers out there, particularly the Siberian/Amur tiger…