Why is the tail of the hippocampus square?

Cats, dogs and dogs may see more tails, but do you know what the tail of the hippocampus looks like?

Why is the tail of the hippocampus square?


Just as they look amazing in fish, the hippocampus also has a different tail structure from most animals – its cross section is square. Four sets of L-shaped plates surround the square tail shape, protecting the middle vertebrae. What’s so special about a square tail compared to a circular one? In the latest issue of science, Michael M. Porter of Clemson University and his team have solved the mystery [1].

“I started hippocampal research in a team at the University of California, San Diego, and my team was working on a series of armored biomaterials — and the hippocampus was armored, so we started with the skeleton of it.” “With a certain understanding, I began to be more interested in its tail,” Porter told the scientist. According to him, in the whole animal kingdom, only a few groups, such as hippocampus and sea dragon, have evolved square tails. Their research found that such a tail structure can help the hippocampus to better resist external compression and distortion, and improve the grasping ability of the hippocampus tail.

Why is the tail of the hippocampus square?

I am a seahorse. I have a sharp square tail. Photo Source: Michael M. Porter/Clemson University

Firstly, Porter observed the flexibility of the tail of the hippocampus and the structure of the bone plate. The smaller the bone plate that makes up the tail of the hippocampus is, the smoother it can bend its tail into a logarithmic spiral and achieve the maximum curvature near the tip of the tail. After measurement, Porter found that the tail end of the hippocampus could bend as much as 850 degrees to the ventral side, and 290 degrees to the dorsal side and 570 degrees to the bilateral side, respectively. The size, tilt angle and overlapping degree of each hippocampal plate can affect its bending ability.

According to the details of the hippocampal tail bone plate, Porter 3D prints the square tail model of the hippocampus, and at the same time constructs the corresponding round tail model for comparison. “3D printing enables us to imitate the wonderful design in nature, and at the same time to construct new models that have not yet been found in nature. We can compare these models with each other to provide inspiration for engineering design and explain some evolution processes of organisms.”

Compared with the 3D printing model, the quadrate tail structure of hippocampus shows better compression resistance: when facing external shocks, the bone plate can slide sideways to absorb the impact force and protect the spine better. In extreme cases, the square plate of the hippocampus can deform up to 50% without causing permanent damage to the spine.

Deformation effects of rapid impact on Square Prototype and Cylindrical Prototye models (slow lens). Video Source: Research Papers

In terms of bending ability, the square-tail model and the round-tail model are similar, but because the square-tail model provides a larger circumference of cross-section, thus expanding the contact area with the outside world, the hippocampus tail shows a stronger grasping ability than the round-tail model in bending grasp. In addition, the maximum distortion angle of the circular tail model can reach 30 degrees, while that of the square tail model is only about 15 degrees. This relatively narrow distortion range can also better protect the hippocampus from external distortion.

Bending and twisting performance tests of hippocampal square tail model and round tail model. Video Source: Research Papers

“The square tail is the morphological feature of the ancestors of the family Hymenopteridae and the family Hymenopteridae. These fish are covered with skeletal armor, which is unmatched. Only some of them have grasping ability, while others do not. Because square structures are more resistant to compression, we suspect that such structures are more likely to be adapted to the characteristics of armor function, rather than to increase grip ability. Potter’s colleague, morphologist Dominique Adriaens, said, “However, the results show that square tails also have mechanical advantages in grasping. It is conceivable that the rigid bones of these fish may also evolve in a more dexterous direction, with additional grasping functions.”

Why is the tail of the hippocampus square?

“When we need to take both defensive and grasping functions into account, this square cross-section structure is superior to the design.” Potter said. He believes that this research will contribute to innovation in robotics. “This structure of the hippocampus can be applied to the design of robotic arms, which may be quite useful in industrial, military and pharmaceutical fields. In the design of tentacles or snake-like robots, such a bone plate structure is lighter and more flexible than the traditional hard structure, and more resistant to pressure than the soft structure. In addition, the square tail of the hippocampus can also provide valuable reference for R&D personnel in the exploration and acquisition of oil and gas, the design of human armor in military industry, the design of prosthetic limbs and scaffolds in medical treatment, etc.