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It is possible to gain a good estimate of the height and weight of an aurochs by scaling up the bones of the fighting bull to match the fossilized bones of the primordial ox. The usual comparison is made of the large metatarsal bone, the bone between the hock and the hoof. The results are astonishing.

Size comparison of a modern bull,
an aurochs, and a bullfighter

A basic principle involved in weighing an imagined (but once very real) aurochs involves the rule of calculating volume in three-dimensional objects. The surface area of an animal (think of its skin stretched out flat for easy measurement) increases by the square of the dimensions (a hide or a rug two feet square equals four square feet; a four-foot-square rug or hide totals 16 square feet, etc.). A measurable change in the height or length or an animal will increase its surface area by the square of the proportional increase. But volume is another matter; volume changes by the "cube" of the dimensions. A one-foot-square block of ice is, of course, one cubic foot. A two-foot block has 8 cubic feet and a three-foot block has 27.

The same principle applies to very complicated shapes, like cows, if the proportions among all the parts remain constant. And since animals have a specific gravity approximately equal to one (1) no matter what their size, the cow scales up in weight almost as neatly as a geometric solid like a block of ice. That makes it possible to re-create, and then "weigh," an aurochs. Paleontologists do this by considering the relative length (or width or circumference, it doesn't matter) of bones that are anatomically identical in "toro" and aurochs.

To estimate the overall dimensions of an aurochs, we need to assign an average height and weight to the fighting bull. For convenience, and to err on the side of underestimating the size of an aurochs, a fighting bull will be defined as one meter (39 inches) tall, which is very tall for the breed. This will actually "underestimate" the size of an aurochs because it will decrease the proportional, scalable differences. The British aurochs is one and two-thirds larger in height than the one-meter fighting bull; the continental ones are from one and three-quarters to twice the height. But we are also interested in the sheer volume (and the weight) of our aurochs, and for that, we have to remember to cube the difference in the dimensions. Fighting bulls vary, but 500 kilograms (1,100 pounds) is a convenient and reasonable number. The legal minimum to enter the ring in Spain is 470 kilograms, or 1,036 pounds, on the hoof. To estimate the weight or mass of an aurochs, multiply the modern animal's weight by the difference in dimensional proportions "cubed."

Fossils reveal that the aurochs' size varied a little from region to region and by conflicting interpretations of scientists. English aurochs seem to have been a little smaller than continental animals. The average English male beast was some 1.6 meters (5 feet 3 inches) tall. Various European aurochs have been estimated (again, for the male beast) at 1.75 meters (5 feet 9 inches) to as large as 2.0 meters (6 feet 6 inches).

The British aurochs, smallest of the ancient ones, would have weighed about four times (1.6 cubed, or 1.6 X 1.6 X 1.6 = 4.096) as much as a "toro," or 2,048 kilograms, 4,514 pounds, a whopping two and one quarter tons of mobile and hostile beef. The continental aurochs, by the same formula (dimensional proportion cubed), weighed from 2,680 kilograms to 4,000 kilograms -(from almost 6,000 pounds to some 8,000 pounds). It appears that Julius Caesar was not exaggerating when he said they were just a little smaller than an elephant.

Using bone size to estimate a whole animal's size and particularly its weight may seem a little theoretical, but Aberdeen-Angus breeders know it is practical. Every spring and fall, all across North America, some breeders will do precisely what the paleontologists do, measure a bone and define a weight based on that bone. One of the many tedious tasks in raising registered beef breeds is the obligation to keep a record of birth weight for each animal and the beast's weight at weaning. (The second weighing shows rate of growth.) These are important numbers because the perfect beef animal for breeding turns out calves with a fairly low birth weight (this makes for easier calving) and a high wean weight (which demonstrates a genetic tendency for quick growth). Newborn calves, less than two days old, are reasonably easy to catch and hold for tasks like putting a numbered tag in their ear. (After a day or two, some serious foot chases take place.) Tagging goes smoothly most of the time; the calf is pinched between the rancher's legs for the few seconds it takes to pin the tag through the ear. Weighing is harder. The calf has to be placed in a sling or have two legs tied together so that a scale can be hooked onto the critter. Hoisting it clear of the ground is not fun: The rascals weigh anywhere from 75 to 110 pounds (34 to 50 kilograms), and their longish legs make it necessary to hold the scales almost up at eye level to get them off the ground.

Researchers in Ames, Iowa, developed a simple cloth tape measure for newborn Angus calves--one side for bull calves, the other for heifers. The rancher can use it to measure the outside diameter of a rear leg "ankle" (just above the hoof where the metacarpal and the proximal seismoid bones overlap), and the tape measure gives the weight in pounds. The Ames researchers guarantee getting the weight within three pounds every time. This is the same conversion technique paleobiologists would use to calculate the mass of an extinct animal.

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