Eight lyouns and an hundred egles

Mandeville's Travels (late 14th century) gives this description of the griffins of Bactria:

In þat contré ben many griffounes, more plentee þan in ony other contree. Sum men seyn þat þei han the body vpward as an egle, and benethe as a lyoun: and treuly þei seyn soth þat þei ben of þat schapp. But o griffoun hath the body more gret, and is more strong, þanne eight lyouns, of suche lyouns as ben o this half; and more gret and strongere þan an hundred egles, suche as we han amonges vs.

The average weight for a golden eagle is 4.91 kg for a female or 3.48 kg for a male. Both sexes have an average wingspan of 2.04 m. Multiplying the weights by 100 and the wingspan by the cube root of 100, we can estimate that a bird "more gret and strongere þan an hundred egles" would weigh over 491 kg (female) or 348 (male) and have a wingspan of 9.47 meters. This is close to the estimated wingspan (10-11 meters) of Quetzalcoatlus, the largest known animal ever to have flown.

The Asiatic lion -- presumably the closest subspecies to such lions as would have "ben o this half" in the past -- averages 175 kg (male) or 115 kg (female). Thus, eight lions would weigh about 1400 kg, and eight lionesses 920 kg -- far heavier than 100 eagles. A hundred male eagles weigh about as much as two lions, and 100 female eagles about as much as four lionesses. Surprisingly enough, Mandeville's numbers don't add up.

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What wingspan would be necessary to support a flying creature "more gret . . . þanne eight lyouns"? This is probably an extreme oversimplification, but the lift generated by wings should be a function of their area. This is why a large bird like an albatross needs much larger wings relative to its body size than a small one like a sparrow. If we keep a bird's structure the same but enlarge it so as to double its wingspan, its wings would generate 4 times as much lift as those of the smaller bird -- which would be insufficient since, weight being a function of volume rather than area, the bird's weight would have increased by eight times.

Let's say, based on the golden eagle numbers, that a 2-meter wingspan can support a 5-kg bird. Eight lions weigh 280 times that, so an animal that large would require a wingspan of 33.5 m. A merely Quetzalcoatlus-like wingspan of 11.8 m would only be enough to support the weight of a single lion. (Paleontologists estimate that Quetzalcoatlus weighed 200-250 kg, so my calculations seem to be in the ballpark.)