EUGENE M. MCCARTHY, PHD
Things you don’t expect happen more often than things you do.
In the fall of 1897, a report (quoted below) appeared in many U.S. newspapers. It describes a strange animal born at the Cincinnati Zoo, a rat that had large tusks and grunted like a pig.
The only pig with recurved tusks like of the rat in the picture below is the small Indonesian pig known as the babirusa (see image at right). Thus, if this strange creature was in fact a pig-rat hybrid—a type of cross that, seemingly, has never been reported—then the specific type of pig in question would have been a babirusa (Babyrousa babyrussa).
The transcript copied here is from page 2, column 1, of the December 9, 1897, issue of the Appomattox and Buckingham Times, a newspaper published in Appomattox, Virginia (source).
The ordinary white rat is merely an albino brown rat (Rattus norvegicus).
There is, of course, the question of how a babirusa would inseminate a rat. Even though babirusas are smaller than most pigs, at first glance such a mating might seem impossible. However, in some crosses, even ones occurring in a natural setting, there can be very large differences in the size of the male and female. Moreover, many animals do not require penetration for fertilization, especially when the distance between the entrance to the reproductive tract and the ovary (the location of unfertilized eggs) is short, as it is in small animals (this distance is only about an inch in rats). For example, during copulation most birds simply touch their cloacae together; there is no penetration because the male has no a penis. Among birds, penises are present only in members of Order Anseriformes (ducks, swans, geese, etc.), and in a few others, such as ostriches and emus. So, even though in the present case it is unknown what actually occurred, one can imagine various scenarios. Perhaps two babirusas were confined in a crate stacked on top of the cage where the mother rat was being held. Then, perhaps they had sex and, after withdrawal, maybe the male slopped semen onto the mother rat below so that she ended up with babirusa semen in her reproductive tract. This is just one possibility, of course.
Another question is whether this case might be due to overgrowth of the incisors, a fairly common condition in mice and rats. Incisors grow continuously in rodents, but the grinding action of the lower incisors against the upper always maintains their proper length. However, overgrowth of these teeth takes a long time to develop, whereas the quoted report says that the animal in question was only a week old. Moreover, the length of the teeth pictured in the accompanying illustration far exceeds that seen in rodents with overgrown incisors and it can be seen in the picture that the teeth emerge from the sides of the mouth like tusks, not from the front as would incisors, and that they are shaped like tusks. And besides, why would abnormal tooth growth cause a rat to “grunt like a pig”?
One reader suggested this might be a case of malocclusion, a fairly common malady in rats. However, as was the case with overgrowth of the incisors, malocclusion does not produce huge tusks “fully twice the length of the head.” Nor does malocclusion cause teeth to emerge from roots at the sides of the jaw. Nor does it cause a rat to grunt.
Thus, it would seem either that this creature was in fact a babirusa-rat hybrid or that the whole thing was a hoax. The latter option seems unlikely given that the Cincinnati Zoo would likely have demanded a retraction from the many newspapers that printed this story if it were false.
This would be an interordinal cross (Order Artiodactya × Order Rodentia), which might lead many readers to suppose that it is too distant to be possible. However, this website lists many other interordinal crosses among mammals, some of which are quite well documented.
By the same author: Handbook of Avian Hybrids of the World, Oxford University Press (2006).
Human Origins: Are we hybrids?
On the Origins of New Forms of Life
Cat-rabbit Hybrids: Fact or fiction?
Georges Cuvier: A Biography
Prothero: A Rebuttal
Branches of Biology