I've heard of conjoined twins, but why do conjoined animals always seem uncommon?

Humans have conjoined twins, but it seems that we rarely hear of such cases in animals. However, this does not mean that there are no cases of conjoined twins in animals. It is just that most animals live in the wild and the living environment is harsh. It is difficult for the individuals to survive after being conjoined, so we rarely see conjoined animals.

X-ray of thoracic and abdominal conjoined twins, image source: Wikipedia. In fact, ever since humans began raising animals (whether for livestock breeding or rescue in zoos), cases of conjoined animals have occurred from time to time. For example, conjoined lambs have appeared in many ranches.

Image source:vipanimalcare

Some time ago, a pair of conjoined turtles were hatched at a wildlife center in Massachusetts. Their bodies (including their shells) were connected, but they had independent heads and limbs.

Conjoined sea turtles, photo courtesy of New England Wildlife Center

According to the Wildlife Center, the conjoined turtles are diamondback terrapins, which are native to the northeastern and southern United States. They are one of the most widely distributed sea turtles in North America, with their range extending south to the Florida Keys and north to Cape Cod.

The diamondback terrapin is widely distributed in North America. Image source: gbif. The name of the diamondback terrapin refers to the pattern on the top of its shell. Their shell color ranges from brown to gray, and the body color can be gray, brown, yellow or white. There are unique black markings on the body and head. The shell of males can grow to 13 cm in length, while that of females can reach 19 cm.

Diamondback terrapin, image source: gbif

The Wildlife Center said the conjoined diamondback terrapins are thriving. They are very active, alert to their surroundings, and appear to be in good condition. Generally speaking, conjoined animals have a shorter lifespan and a lower quality of life, but these two little guys seem to be doing well overall. Genetic or environmental factors that affect embryonic development can lead to "dicephaly," a condition in which the bodies of the two individuals are connected but their heads are separate, making them appear to share a single body. Reports of "dicephaly" in animals are very rare (because such special individuals are unlikely to survive), and in addition to these two two-headed turtles, other known cases of "dicephaly" in animals include a two-headed venomous snake found in Virginia, a dead two-headed deer found in Minnesota, and a two-headed dolphin accidentally caught by fishermen.

Two-headed rattlesnake. Photo credit: Bob Zappalorti/Herpetological Associates

This pair of conjoined fawns has two heads and two hearts. Photo credit: Gino D'Angelo et al/University of Georgia

Conjoined dolphins accidentally caught by Dutch fishermen, photo courtesy of nationalgeographic

The conjoined turtles were hatched in a protected nesting site and then cared for by a wildlife center. They have now survived for more than two weeks. By taking X-rays, staff at the wildlife center found that the conjoined turtles had independent spines, but the two spines seemed to be fused together at the back of the body. In the first few days of hatching, the conjoined turtles obtained nutrition from the same yolk. They had their own independent digestive tracts, but the stomach and intestines of one of them seemed to be more developed, but in any case both turtles were able to eat and digest food. At present, the two conjoined turtles can swim to the surface of the water to breathe in a coordinated manner. They eat and swim normally, and their weight is gradually increasing. Researchers said that when the conjoined turtles grow up a little more, more physical examinations will be carried out to understand their shared internal organs and their respective body structures. It is hoped that this rare pair of conjoined turtles will grow up smoothly.

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