Science

How to Make a Hippogriff Fly and Other Flights of Fancy

Fantastic creatures appear in myths and legends from cultures around the world. These beings take many forms. Some of them run, slither, swim or burrow. Many of them fly. As a paleontologist who studies fossil birds and pterosaurs (Habib) and an illustrator who designs creatures for books and films (Whitlatch), we are especially interested in the biomechanics of flight and how to portray flying beasts believably. We recently teamed up to produce a book on this topic called Flying Monsters: Illustrating Flying Vertebrates (to be published in 2021 by Design Studio Press), which covers both real and imaginary animals. In the pages that follow, we riff on three fanciful creatures depicted in the book and explain the science that lifts them up while grounding them in reality.

REMAKING A CLASSIC: Flying Horses

Credit: Terryl Whitlatch

Flying horses abound in myths and stories. The most famous is probably Pegasus, the winged horse of Greek legend that sprang from the blood of the snake-haired monster Medusa when the hero Perseus beheaded her. Somewhat lesser known is the hippogriff, a part-equine, part-avian predator capable of galloping on the ground like a horse and then launching into the air to fly like an eagle.

We reimagined the classic hippogriff as a blend of horse and pterosaur. This mix would enable the animal to take flight at horse size. Several factors appear to have been instrumental in allowing giant pterosaurs such as Quetzalcoatlus, Cryodrakon and Hatzegopteryx to attain their great sizes while maintaining the ability to fly: their bones were light for their strength, their wings were formed by a membrane of muscle and skin rather than by comparatively heavy feathers, and they probably used both their folded wings and their hind limbs to push off from the ground and launch themselves into the air—a much more powerful leap than one executed by the hind limbs alone. Like these pterosaurs, our hippogriff (really a hippoptero) can use its wings as leaping limbs to execute takeoff.

This launch style works for both a quadrupedal winged horse in which the forelimbs double as wings and a hexapodal one in which the wings are a third pair of limbs. In the latter case, the wings push against the ground in a more extended position in tandem with the four running limbs. The two configurations have different considerations: building a flight-capable hexapod requires stacking the shoulder blades, whereas the quadruped requires a complete rebuild of the shoulder because real horses cannot lift their forelimbs out to the sides, much less over their back.

Flying horses art concept.
Credit: Terryl Whitlatch

Placing the wings in contact with the ground for takeoff to make the wing muscles do double duty is the most realistic way to get a horse-size fantasy creature into the air. With muscle physiology and bone strength typical of vertebrate animals and with a vaguely pterosaurlike quadrupedal build, 800 pounds is probably about the maximum such a creature could weigh while still being able to fly. If the flying horse had lots of air spaces in its bones, as the giant pterosaurs did (and as many birds do today), then it could weigh less than 800 pounds and still bear a full-size horse exterior. Alternatively, adding bigger muscles or longer limbs for leaping than giant pterosaurs possessed could raise the size limit. With the right anatomy, even a 1,200-pound winged horse could fly.

In our hippogriff, the muscles of the back drive the upstroke, and the muscles of the chest power the downstroke, just as in living bats and long-extinct pterosaurs. Birds, in contrast, have both sets of muscles in the chest. With a batlike or pterosaurlike arrangement of the flight muscles, the chest could be a reasonable size. With a birdlike arrangement, in contrast, the chest would have to be so large as to be ungainly. The bat or pterosaur condition is also a more realistic option for the hexapodal body plan, in which the stacked shoulder blades make a birdlike musculature impossible.

DEPICTING THE METAPHYSICAL: Angels of the Bible

Despite their centrality in Judeo-Christian stories, art and traditions, angels are rarely described in any physical detail in surviving religious texts. In modern interpretations, these heavenly beings are often shown as humans with wings, but the few written descriptions of angels in the Bible suggest much more complex forms: many are described as terrifying to behold, and any human being who encountered them is said to have been overwhelmed by fear. Two books of the Bible—Revelation and Ezekiel—contain the most detailed physical descriptions. Both seem to depict the same four angels, sometimes referred to as the Four Living Creatures.

The descriptions in the two texts agree on some details, but they differ in notable respects. In Revelation, these powerful angels are portrayed as resembling a lion, an ox, a man and an eagle. According to Ezekiel, in contrast, only their faces resemble these creatures. Revelation’s angels have three pairs of wings; Ezekiel’s have two pairs that are covered with eyes, and their flight is described as “hovering,” with abundant thunder, lightning and electrical plasma surrounding the angels as they flutter around the throne of God.

A prominent early interpretation, popularized by third-century bishop and Christian martyr Victorinus of Pettau, equated the four creatures with the Four Evangelists. In this understanding, the lion represents Mark, the ox represents Luke, the eagle represents John, and the man represents Matthew.

We depict Matthew, mostly as described in Ezekiel, though, with a single face as in Revelation (Ezekiel gives each angel four faces). And we dipped into the fossil record for real-world inspiration. For the body plan, we looked to Microraptor, a flying dinosaur that had four wings. Recent studies have concluded that Microraptor and its relatives probably flew by flapping their forewings and holding their hind wings under the body to help with stability and maneuverability. Accordingly, our Matthew has flapping, propulsive forewings, and he holds his hind wings vertically.

For the overall proportions, we turned to the largest airborne animals known: giant azhdarchid pterosaurs. These flying reptiles included animals such as Quetzalcoatlus and Cryodrakon, both of which grew to hundreds of pounds in weight and had wingspans in excess of 30 feet. These huge pterosaurs were oddly “front-loaded” animals, with massive heads, necks, chests and arms. Our rendering of Matthew features a humanlike (but distinctly alien) head atop a massive, Cryodrakon-style neck. An expanded chest accommodates large flight muscles, and a corresponding forward sweep of the wings aligns the center of lift with the center of mass. The resulting creature is at once magnificent and terrifying—and biomechanically feasible.

FLYING WITHOUT WINGS: Dragons of Asia

Asian dragons, particularly those of Chinese, Vietnamese and Japanese mythology, are challenging to represent in an anatomically believable way because these creatures are consistently shown flying without wings. They typically have a serpentine body plan, but they are not associated with snakes in traditional lore. Instead these dragons are often described as having features in common with both mammals and fish, especially carp, and they are associated with rivers, rain, lightning and storms.

To find good models from the real world to work with, we turned to living animals that fly without wings. Gliding snakes of the genus Chrysopelea do it beautifully, flying tens of feet at a time without any limbs at all. They perform a series of S curves and twisting motions in the air while gliding, which nicely approximates the winding paths flying dragons are often shown taking in traditional Chinese and Japanese art. (Dragon dancers in China work in teams of nine or more individuals to move a dragon on poles in flowing, curving patterns.) Chrysopelea also hails exclusively from Southeast Asia, which makes it a regionally appropriate group of snakes on which to model our dragon. Like Chrysopelea snakes, our anatomically plausible Asian dragon creates its primary flight surface by flattening its body and forming S curves in the air. To help account for the large size of the dragon, we have added some additional “webbing” along the body and limbs to enlarge the flight surface.

We looked to other unusual serpents from the real world, including the Malagasy leaf-nosed snake (genus Langaha), to develop the “whiskers” that are depicted on dragons in traditional art. These snakes have a long, flexible appendage projecting from their snout. By taking such a projection and splitting it, we have created a set of whiskerlike structures for our dragon. Asian vine snakes (genus Ahaetulla) inspired its narrow face, horizontal pupils and ridges over its eyes.

This dragon is associated with forest streams. It can swim, climb and glide, making it a fearsome and adaptable predator. All of the snakes we referred to for this build specialize in hunting lizards. Their fangs are located toward the back of the jaw, and their venom paralyzes other reptiles. In fact, the most important predators of lizards and snakes in many regions are other lizards and snakes. With that in mind, we have imagined that the greatest threat to young Western dragons (which is to say dragons with wings) is other dragons—specifically, serpentine, wingless ones from the East. Our use of biological inspiration has thus helped us fill in an entire ecology for our dragon. By considering the relations between form and function in real animals, we can imagine a creature of myth in a new light, in terms of both anatomy and behavior.


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