One of the most common memes in our popular understanding of zoology is that the thylacine of Tasmania was the marsupial equivalent of the gray wolf. This idea comes from a rather superficial understanding of its morphology, and lots of speculation about its behavior have stemmed from this popular understanding. One idea is that they were pack-hunters like wolves and dingoes, and they would have been murder on Tasmania’s sheep industry. Therefore, the final extinction of the thylacine was largely predicated upon a rational fear that the creatures would have been detrimental to sheep husbandry.
A lot of these speculations come from a belief that the thylacine was quite large. As I have discussed before on this space, larger carnivores are largely forced to hunt larger prey to survive. Otherwise, the larger size is of no benefit to the animal. Ecologists have found that the mass of 21 kg (about 46 pounds) is the size at which a carnivorous mammal can no longer subsist on smaller prey alone.
Thylacines were estimated to have weighed 29. 5 kg (about 65 pounds), which meant that their diet would have been larger prey. However, really big prey species are almost absent from Tasmania. The largest kangaroo in Tasmania is the Tasmanian Eastern gray kangaroo, which weighs is roughly the size of the smaller forms of white-tailed deer in the US. Further, analysis of Thylacine skulls revealed that they could not withstand very much force. So the thylacine would not have been a very effective predator of prey the size of an Eastern gray kangroo, and it would have had a lot of trouble grappling with a fully grown sheep.
The fact that thylacines would have had problems killing large prey creates a contradiction in their supposed larger size. If thylacines really did weigh 65 pounds on average, then they would be a major exception to the rule that larger predators must hunt larger prey to survive.
Well, a new analysis by researchers at Monash University has revealed that traditional estimates of thylacine size were greatly exaggerated. Using complex morphometric analyses on various preserved specimens, the researchers revealed that the mean weight of a male thylacine was 19.7 kilograms (43 pounds). The mean weight of a female was 13. 7 kilograms (30 pounds).
These animals would have been roughly the same size of an Eastern coyote. Now, Eastern coyotes can live on large prey or small prey, and they can scavenge quite well. But they have skulls that can withstand blunt force from a sheep or a deer that a pack of them has run down. The Eastern coyote can live as a fox or a wolf, depending upon the conditions of the ecosystem in which it lives.
A thylacine would have been a smaller prey specialist, and because its weight did not exceed 21 kilograms, its subsistence on smaller prey did not violate the “costs of carnivory” rule.
Indeed, the only predatory mammal I can think of that does come close to violating this rule is the maned wolf, which sometimes weighs 22 or 23 kg. It lives almost entirely on small prey and fruit. This species has been persecuted for its attacks on livestock, but like the thylacine, it is not much of a threat to them.
Of course, there will be debate about this finding. Many historical accounts of thylacines suggest or imply or even outright claim that they were killing sheep and dogs left and right.
But the truth is that Europeans had their own concept of what a creature like this could do or was likely to do, and they merely transposed these ideas onto a creature that had the superficial appearance of a wolf or hyena.
We should by now stop trying to pigeonhole the thylacine into a marsupial wolf and should try to appreciate it for what it was.
Or might still be.*
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*I don’t believe they still exist, but I certainly wish they did!
Natural History 
given that some were captured and kept in zoos, weren’t any of them actually weighed?
I read reports of this research with interest but some scepticism. Historical photographs of thylacines seem to show a larger animal.
The large range of sizes calculated by the researcher could reflect inaccuracies in the techniques used or could have resulted if some or all of the specimens were juveniles.
Marsupials, including Tasmanian devils, typically have much lower temperatures and basal metabolic rates than placental mammals. What effect would this have on the size at which they could subsist on smaller mammals?
Incidentally, I am quite familiar with Eastern Grey Kangaroos. They weigh up to 60kg and have powerful hindquarters. I can’t imagine a weak-jawed 15kg predator pulling down an adult Eastern Grey Kangaroo.
i am also put in mind of the issues regarding the “saber toothed tiger” (Smilodon) I reference the PNAS article on the animal which states “Our results demonstrate that bite force driven by jaw muscles was relatively weak in S. fatalis, one-third that of a lion (Panthera leo) of comparable size, and its skull was poorly optimized to resist the extrinsic loadings generated by struggling prey. ” Yet it’s well documented that Smilodon was a major predator of it’s time. Perhaps the issue is HOW the thylacine hunted.
https://www.pnas.org/content/104/41/16010/