A Turtle-seal Hybrid?

Mammalian Hybrids

EUGENE M. MCCARTHY, PHD GENETICS, ΦΒΚ

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But in the seas, spread out as they are far and wide, forming an element at once so delicate and so vivifying, and receiving the generating principles from the regions of the air, as they are ever produced by Nature, many animals are to be found, and indeed, most of those that are of monstrous form; from the fact, no doubt, that these seeds and first principles of being are so utterly conglomerated and so involved, the one with the other, from being whirled to and fro, now by the action of the winds and now by the waves.

—Pliny the Elder
The Natural History (9.1)

A reconstruction of the animal described in the news report quoted on this page. (Image: Matthew Crow)

Note: Any claim that hybrids can be produced from this highly disparate cross would require confirmation from a specimen.

What may have been a turtle-seal hybrid was reported on page 4, column 3, of the August 11, 1840, issue of the Oneida Whig, a newspaper published in Utica, New York (source):

From the Baltimore Sun.

    The Sea Serpent Caught.— On Sunday evening about 6 o'clock, as the schooner Wasp, Captain Williams, and the schooner Independent Eagle, Captain Owens, were coming up the bay, they descried, about three miles below North Point, a strange looking fish or serpent to leeward. A boat from each schooner was manned and a chase for the prize took place. A harpoon was driven into the creature and away it flew, dragging the boat for nearly eight miles, like a ship down a cataract. It was found necessary at length to stop the speed of this marine locomotive, and a couple of balls being shot into it, the death flurry came on, and it soon floated a lifeless carcass. It was borne in triumph to the foot of South Street wharf, where it was visited by most of the old cruizers about town, who had been to every part of the globe, and knew every thing that partook of the nature of fish, flesh, or fowl, like a book. They all declared they had never seen such a nondescript. It measures twelve feet in length, and nine feet from fin to fin [i.e., in width?]; it has a head like a seal, with teeth, and its back is covered with a hard shell. It has four fins or flippers, and its general appearance bears some resemblance to a turtle, or rather a monstrosity of that species of fish, which nature in one of her freaks had created. How came it to the Chesapeake Bay is a mystery. It can be seen at South Street wharf.
    The Baltimore American says:
    “The creature would be a curiosity, we should suppose, any where, from its enormous size, but it is certainly a rarity in our waters. Its weight is supposed to be about 1000 pounds.”^†

† The Leatherback Sea Turtle, which is one of the largest extant reptiles, can attain an overall length of 7.2 feet (2.2 meters) and a corresponding weight of some 1,500 lbs (680 kg). Therefore, a similarly proportioned animal with a length of 12 feet, as indicated in the report, would tip in at around 7,000 lbs (3,175 kg). Calculations: [(12/7.2)³] x 1500 lbs = 6,944 lbs. This huge size would help to account for its “dragging the boat for nearly eight miles, like a ship down a cataract,” a seeming impossibility for any known sea turtle. However, the 1,000-pound weight of the animal as stated in the report would be entirely inconsistent with its supposed length. Perhaps it its weight was merely estimated from its appearance and not with an actual scale?

Are turtle-seal hybrids possible?

Leatherback Sea Turtle
Dermochelys coriacea

The Leatherback Sea Turtle (Dermochelys coriacea) has various characteristics that seem to connect it with mammals, in particular its scaleless skin and ability to maintain body temperature above ambient conditions, even in arctic waters (Frair et al. 1972; Paladino et al. 1990). It also lacks a bony shell. In a study of its skeleton, Rhodin et al. 1981 found that the “chondro-osseous morphology of Dermochelys is unlike that of any other known extant turtle or reptile but is more similar to that of marine mammals.” Moreover, leatherbacks have an extensive covering of brown adipose tissue (Goff and Stenson 1988), a characteristic otherwise associated with mammals, not reptiles, because it plays an essential role in warmbloodedness. Tsatsanis et al. (2015) state this specifically:

The Swiss naturalist, botanist, physician and classical linguist Conrad Gesner was the first, in 1551, to describe adipose tissue as a separate entity. He recognized two types of adipose tissue: white adipose tissue (WAT) and brown adipose tissue (BAT). We now know that WAT stores excess energy and that, evolutionarily speaking, it first appeared in the teleost fish. On the other hand, the main function of BAT is energy expenditure as heat (non-shivering thermogenesis) and it first appeared later in evolution as a characteristic of mammals.

In a study of leatherbacks Paladino et al. (1990) reported that "metabolic rates of adults at rest and while nesting are intermediate to those predicted by allometric relationships for reptiles and mammals,” which is what one would expect from the product of a reptile-mammal cross.

Is it possible, then, that the leatherback sea turtle represents a hybrid between some type of more conventional sea turtle and a marine mammal such as a seal? If so, then the seal-headed creature described in the report above might conceivably have been a hybrid between a leatherback (or some other sea turtle) and a seal, which was perhaps oversized due to heterosis.

The mere fact that this cross is so distant would be enough to convince many people of its impossibility. After all, seals and sea turtles belong to two different vertebrate classes, Mammalia and Reptilia, respectively. However, there is, in fact, quite a bit of evidence that interclass crosses do occasionally occur. Indeed, there are various reports about other mammal-turtle crosses, both turtle-cow hybrids and turtle-sheep hybrids. And there are even reports about turtle-human hybrids.

Chicken-pigeon hybrids

A similar cross >>

Bird-mammal hybrids >>

Table of contents >>

Bibliography >>

Biology Dictionary >>

By the same author: Handbook of Avian Hybrids of the World, Oxford University Press (2006).

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