The Weirdest Animals on Earth: 12 Amazing Facts About Seahorses

A seahorse in all its glory. Photo by Gustavo Gerdel at Wikimedia Commons.

1. Seahorses are fish. They include about 54 different species of fish and are closely related to sea dragons and pipefish. But seahorses are not your typical fish! A baby seahorse is called a fry (like in other fish), but a group of seahorses is called a herd (like in horses).

2. Seahorses have skeletons unlike any other fish. Unlike other bony fish, seahorses have a neck, an exoskeleton, and a prehensile tail. Seahorses do not have pelvic fins, ribs or scales. Instead, their skin is stretched over a series of bony plates arranged in rings.

3. Seahorses are terrible swimmers and can die of exhaustion if the sea is rough or the current is too strong. The only fin they have to get around with it the tiny one in the middle of their back (the dorsal fin). They use even smaller pectoral fins on the sides of their head to steer. Seahorses and razorfish are the only fish to swim upright, because it is horribly inefficient. It is a good thing they have a prehensile tail to hang on to whatever is nearby.

A pygmy seahorse in camouflage.
Photo by prilfish at Wikimedia.

4. Seahorses are experts at camouflage and can change color. They are even able to grow fleshy appendages (called cirri) that help them with camouflage by giving them a weed-like appearance.

5. Seahorses have terrible smell but amazing vision. They have the fewest genes for olfactory receptors (used in other animals for smell and taste) of any ray-finned fish species known. But seahorses have excellent vision and their eyes can work independently, meaning they can look forward and backward at the same time!

6. Seahorses eat weird. They have a toothless, tubular snout, which they use to suck up small fish and crustaceans. They swallow them whole. Seahorses do not have stomachs and don't digest very well, so they have to eat constantly.

7. Seahorses are one of the ocean's deadliest predators, with a 90% kill rate. Because of the shape of their head and their slow, finless method of movement, seahorses move with near hydrodynamic silence, barely moving the water as their stealthily sneak up on their prey. Once they are within striking distance, they snap their heads and suck up their prey. 

8. Seahorses click when they're courting and growl when their stressed. 

9. Seahorses are monogamous and pair for life. Their courtship begins with a daily dance between the couple that they do for days. The final courtship dance can last eight hours before the female "impregnates" her partner.

10. Male seahorses get "pregnant". They are the only males that take on the full responsibility of pregnancy, carrying up to 2,000 babies at a time! Although they don’t have a mammalian womb and placenta, they do have an enclosed abdominal pouch specifically for the purpose of incubating the babies. The female deposits her eggs in his brood pouch, in which he fertilizes them and incubates them for 10-45 days (depending on the species). During this time, his body undergoes a number of hormonal and physiological changes. When the babies are ready to emerge as fully developed little seahorses, seahorse dads even experience contractions as they give birth! 

11. Seahorses are evolving faster than any other group of bony fishes. Scientists have sequenced the entire genome of a tiger tail seahorse, a threatened tropical seahorse species.

12. Seahorses are under threat because of the traditional Chinese medicine trade, the pet trade, and the curio trade, all of which capture seahorses from the wild, and because of habitat depletion and pollution.

The Olympic Athlete of the Animal Kingdom: The Circulatory System of a Horse (A Guest Post)

By Emily Fandrey


How do you judge the abilities of an athlete? Is it all about speed? What about endurance? Strength? How would you judge an animal that can run up to 48 kilometers per hour (30 mph), cover 48 kilometers (30 miles) in a day, or clear a 2.4 meter (8 foot) jump, all while carrying a human on its back? Because of these abilities, the horse (Equus caballus) is often considered to be one of the animal kingdom’s best athletes. The major factor behind horses’ advanced athleticism is their unique circulatory system, specialized for delivering large amounts of oxygen throughout the body.

Image by Paul Kehrer at Wikimedia Commons.

A horse’s circulatory system has three major players: the heart, the spleen, and the frog (and no, this has nothing to do with the animal frog, but rather a specialized unit of a horse’s hoof). Due to these three components, horses have one of the best aerobic capacities in the animal kingdom. Let’s look at a racehorse for example: During a race, a thoroughbred can reach a maximum oxygen capacity (the amount of oxygen the blood can carry) of 200 milliliters per kilogram per minute, meaning 200 milliliters of blood per kilogram of weight (or 3.1 ounces per pound) are transported to the body every minute! This is more than twice the oxygen capacity of the most elite human athlete!

This diagram illustrates the horse’s circulatory system,
including the heart, arteries, veins, and spleen. Diagram by Emily Fandrey.

So let’s break down this superior aerobic system, starting with the horse heart. Typically, a horse’s heart weighs 1% of its total body weight; meaning if a horse weighs 450 kilograms (1000 pounds), its heart will be roughly 4.5 kilograms (10 pounds). If this was true for humans, a 68 kilogram (150 pound) human’s heart would be 0.68 kilograms (1.5 pounds), although the average human heart is only about 0.23 kilograms (half a pound). The horse’s heart functions very similarly to a human heart. It contains four chambers and is responsible for getting oxygen to the body by pumping the oxygen-filled blood. After the body systems have used the oxygen in the blood, this deoxygenated blood enters the heart and is sent to the lungs where the blood is resupplied with oxygen from breathing air. This oxygenated blood reenters the heart and is pumped back out to the body. Because of the size of their hearts, horses are able to supply large amounts of blood with oxygen to the body with each heartbeat, averaging a combined 38 liters (10 gallons) per minute (this is about ten times as much as a human).

Horses also have very different heart rates than humans during rest and exercise. A horse’s resting heart rate is 28-44 beats per minute (bpm), compared to the average human’s, which is 60-80 bpm. During exercise, a human’s heart rate is 90-170 bpm, depending on age. A horse’s heart rate, however, rises to 80 bpm during a walk, 130 bpm during a trot, 180 during a canter, and 240 bpm while galloping. At top speed, the fast beating heart of the horse is what allows the heart to pump much more blood to the body than a human, increasing their athletic abilities.

A diagram of how the horse’s frog sends blood back to heart quickly,
working against gravity. Diagram by Emily Fandrey.

With the long legs of horses, the heart also has to work against gravity to get blood from the limbs back to the heart. To combat this, the horse has its “frog”. For a horse, the frog is a vessel-filled tissue structure on each of its four hooves. When weight is placed on the frog, this structure can help the heart work against gravity. How? When the horse’s hoof meets the ground, the ground will push up on the frog, resulting in the frog being compressed and squeezing blood in the vessels out and rapidly up the leg. The frog helps heart work against gravity by sending the blood up the leg and back to the heart, allowing for faster blood circulation, increasing the athleticism of the horse.

The last key factor to the horse’s circulatory system is the spleen. This organ improves aerobic capabilities and the horse’s athleticism. Now, the primary function of the horse’s spleen is to remove damaged blood cells. However, when a horse is relaxed, their spleen will fill with up to 30 liters (8 gallons) of oxygen-filled blood. And then, once the excitement of activities like running or jumping sparks, the spleen will contract and send up to 25 liters (6.6 gallons) of this stored blood back into circulation in mere seconds! So in seconds, the spleen is capable of almost doubling the maximum amount of oxygen the blood can carry, increasing the athleticism of the horse as well.

So if you ever need an excelling athlete on your team, consider an animal with a superior circulatory system: the horse. With a large and powerful heart capable of pumping large amounts of blood, a spleen to provide an extra burst of blood in seconds, and a “frog” to work against gravity, there is no wonder why horse is considered to be one of the world’s superior athletes.


References

Allen, K.J., Young, L.E., and Franklin, S.H. (2016). Evaluation of heart rate and rhythm during exercise. Equine Veterinary Education 28: 99-112. DOI: 10.1111/eve.12405.

Cardiovascular System (2007). In EQUINAvet.

Circulatory System of the Horse (2010). In Helpful Horse Hints.

Equine Circulatory System Vet, Horse First Aid (2012). In Equestrian and Horse.

Norton, J. (2013). The equine circulatory system. In EquiMed: Horse Health Matters.

The Physiology of Your “Sense of Self”

Quick! Name all of your senses!

Now, close your eyes and wave your arms over your head. Which of those senses are helping you know where your arms are in space?

The answer is the often-forgotten sense of proprioception. Proprioception (derived from the Latin for “sense of self”) is an animal’s sense of its body’s position in space. We have several different specialized receptor cells that all detect a change in body position in different ways.

Grays muscle picture by Mikael Haggstrom
at Wikimedia Commons.

If you raise your arms over your head as if you are going to grab a pull-up bar, then some muscles in your back (like your trapezius muscles), shoulders (like your deltoids and rotator cuff muscles), and arms (like your triceps) will contract. Muscles are all connected with tendons to the bones they pull on. When a muscle contracts, its tendons are stretched. Specialized proprioceptor cells called Golgi tendon organs merge with tendons and detect when their corresponding muscle is being stretched. Together, they inform the brain about muscle tension in muscles all across the body.

Grays muscle picture by Mikael Haggstrom
at Wikimedia Commons.

However, while some muscles will contract during your movement, other muscles in your chest (like your pecs) and arms (like your biceps) will stretch. Each muscle contains muscle spindles, another kind of specialized proprioceptor cell. Muscle spindles are wrapped around individual muscle fibers within the muscles. They send signals to the brain to let it know when the muscle is stretched and by how much.

Joint receptors are specialized proprioceptor cells located between bones in the capsular tissue of joints. When the angle of a joint changes, the bones and tissues put pressure on the joint receptor, causing it to send a signal to the brain. Your brain collects information from all of your Golgi tendon organs, muscle spindles and joint receptors to know the angle of each joint and the tension and length of each muscle in your body, and thus, your body’s position in space.

gif by Extremistpullup at Wikimedia Commons.

Some animals, and some individuals, are better at this than others. This guy should be pretty proud of his proprioceptive abilities (and strength). But then again, let’s see him try this:

Body Armor is Not Always for Protection

When we see an animal covered in scales and plates, we assume that it has this armor to protect itself from predators. It seems obvious, which is probably why scientists had not really tested it… until now. And they found that it is not necessarily true.

An armadillo girdled lizard has some impressive body armor, but does it do what we think it does?
Image by Handre Basson at Wikimedia Commons.

Today at Accumulating Glitches, I talk about new research on the functions of plates and scales in cordylid lizards. Check it out here.

And to learn more, check this out:

Broeckhoven, C., Diedericks, G. and le Fras Mouton, P. What doesn’t kill you might make you stronger: functional basis for variation in body armour, Journal of Animal Ecology, 84, 1213–1221 (2015). DOI: 10.1111/1365-2656.12414.

Loony Locomotion (A Guest Post)

By Emma Doden

For those of us who have worn fins while snorkeling or swimming before, we know how much faster you are able to cut through the water with them on your feet. But as soon as you try to walk on land with those big flippers on, that grace and speed turns into awkward and ungainly steps. You have to concentrate very hard on not falling flat on your face and find yourself thinking that your own two small feet are much more convenient for walking on land than the flippers.


The common loon in flight. Notice how far back on the body its feet are placed!
Photo by Ano Lobb from Wikimedia Commons.

The common loon is a familiar flipper-footed bird for those of us residing in the Northern Midwest. Found on many lakes in the North Woods from late March to September, their black and white plumage, ruby red eyes, and haunting calls make them unforgettable. However, just like any other waterbird, as soon as they come onto land, all of their beauty and poise vanish. Loons do not have the luxury of removing their flippers when they come onto land. Instead they flip and flop clumsily on their bellies, probably feeling just as frustrated as any person frog-stepping with flippers on.

So why do loons have so much trouble walking on land?

Because most of their lives are spent in water, the common loon’s legs and feet are located extremely far back on their bodies, allowing them to swim and dive more efficiently. Loons don’t use their wings to aid in propulsion while underwater, so they need all the power they can get from their legs and feet to catch tasty fish.

The placement of their legs means that they must slide on their belly while on land. Their legs can’t support the weight of their body and so they instead use them to push off of the ground and slide forward. The only time you will find a loon on land is for mating or nesting. Common loons will build their nests on the shore, usually no more than 5 meters from the water, because it takes a lot of effort to belly flop even that short distance!

Watch the video below to see how comical a loon looks when stranded on land:

Though loons are strong fliers as well as divers, coming in for a landing can also be challenging. Their legs are too far back to thrust forward and use as landing gear, so they stick them straight back and make a splash-landing on their bellies, penguin style!

But what makes their legs and flippers so good for swimming and diving?

Common loons propel themselves through the water with sideways strokes of their legs and feet, similar to oars on a boat. Diving birds have leg bones with a long spike-like extension at the knee where very strong muscles connect. This part of their leg acts like a lever when a loon paddles, allowing the leg and foot to be powerfully propelled through the water. Each foot is fairly large with webbing between each toe. When a loon paddles through the water, the webbing fans out and the foot rotates slightly in relation to the body on the downstroke, allowing the maximum surface area to push off of the water. On the upstroke the toes will compress together and the webbing will bunch up so that there is minimal resistance cutting through the water. The motion of the foot splaying out and compressing in with each stroke creates an efficient mode of transportation for the water-loving loon. With legs and feet like these, they are able zoom through the water as fast as fish and dive up to 200 feet!

Loons rarely come onto land, and so it is not often that you will find one of these majestic creatures floundering through the mud of a lakeshore. You are much more likely to see them gliding effortlessly across a lake, until they disappear below the surface. Then you can imagine them easily hunting fish using their powerful legs and feet to propel them while diving. Even more so than wearing flippers to help you swim, just think how much faster you could be in the water with the streamlined body and strong legs and feet of a common loon!

To learn more about common loons and their flipper-foot conundrums visit these websites:

Piper, Walter. The Loon Project.

The Cornell Lab of Ornithology. 2011. Common Loon, Life History. All About Birds.

Evers, David C., James D. Paruk, Judith W. Mcintyre and Jack F. Barr. 2010. Common Loon (Gavia immer), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; The Birds of North America Online.

Michigan Department of Natural Resources. 2014. Common loon (Gavia immer).

Shearwater Seabird Osteology. 2013. Divers/loons: Osteology.

Caught in My Web: Memory Regeneration, Fish Sex, and the Physics of Swimming

For this edition of Caught in My Web, we explore the science of swimming and other underwater oddities.

1. If you are pondering great questions in life, such as "How is swimming different between a sperm and a sperm whale?", then you are in luck. The physics of how size influences the ability to swim is explained by Aatish Bhatia on TEDEd.

2. Neil Hammerschlag, a shark scientist and blogger for National Geographic, discusses the use of satellite tags for shark research.

3. Phys.org explains the science of side-to-side fish movement.

4. Robert Krulwich at NPR talks about headless planarians that regenerate their heads and their memories.

5. And the Beckman Institute tells you why Nemo would have become a girl if he had not found his dad: