The “Inside” Scoop: Hippo

Happy Sunday Y’all!

I hope you’re excited about another installment of The “Inside” Scoop! Today I selected the majestic hippopotamus! Despite their generally docile appearance (and adorable footage of the new, premature hippo baby, Fiona, at the Cincinnati Zoo), these semiaquatic giants are not pushovers, and they have the anatomy to back it up! This episode of Inside Nature’s Giants took place in a park in Zambia. (Video has graphic content. The following timestamps are provided to help people navigate the video depending on their gore preferences.) The hippo was culled as part of the park’s population management program, and the meat from the animal was given to the nearby village.

4:26 – The episode begins with an introduction by Richard Dawkins about the geographic range of hippos. Although these “river horses” are localized to Subsaharan Africa today, they used to roam across Asia and Europe.

5:06 – Adult hippos are too big to have natural predators, which is why they have adopted a laid-back lifestyle. However, they are still territorial and aggressive, especially when drought threatens their survival. The clip at 7:45 shows an emaciated male who was rejected from the main pod, and footage at 9:22 depicts just how fierce these animals can be.

10:00 – The investigation into the hippo’s anatomy begins by analyzing the skull, teeth, and skin. Hippos have extremely large, sharp teeth. However, their skin may be the most fascinating aspect (in my opinion). It can get up to 2 inches thick! At 14:00, the scientists explain the amazing properties of hippo skin. Hippos secrete “blood sweat.” The secretion is generated by sebaceous glands and is actually colorless but turns a pinkish red hue after contact with air! The best part is that this sweat acts as a natural sun protectant AND antibiotic. The antibiotic properties are key for the health of hippos because they frequently receive wounds from fights and also spend their days wading around in a pond of their own feces. Not a great combination for avoiding infection…

16:00 – It may come as no surprise then that a favorite snack of hippos is “sausage fruit.” This fruit is toxic to humans when eaten raw, but hippos love it. The fruit happens to possess medicinal properties and is a common ingredient in several human healthcare products, including sun care creams.

17:15 – The integument system is clearly crucial to the survival of hippos, so they also welcome the aid of avian assistants. Birds are known to remove ticks and parasites from the skin and wounds of hippos. Because hippo skin can dry out quickly, one never finds hippos far from a water source.

19:10 – Necropsy begins! The stomach is the first organ removed. It takes up a whopping 2/3rds of the abdominal cavity! The semi-digested grass (Note: hippos don’t eat fish even though they spend a lot of time in the water) found in the hippo’s stomach weighed just under 158kg, that’s almost 350 pounds (26:16)!

21:45 – When do hippos consume all this food when they are floating around all day? At night! When the sun goes down, hippos emerge from the water to forage, and the camera crew caught some rare footage of this.

27:07 – Hippos have a multi-chambered stomach with different textures to help store and ferment grass. At 29:26, Richard Dawkins explains that hippos are even-toed ungulates, or Artiodactyls, and their closest relatives are actually WHALES! Despite being carnivores, fin whales also have multi-chambered stomachs, which is characteristic of herbivores. This trait supports the relationship between hippos and whales (more to come).

31:45 – Due to its sizeable stomach, hippos possess a relatively short large intestine, which means that not much water absorption occurs. Consequently, hippos have moist feces and actually fling it around with their tail. The meaning of the feces flinging in water is thought to be territorial. However, on land, hippos leave feces trails to help them remember their way back to water.

34:42 – Not much is known about what hippos do while underwater, but researchers have discovered that they give birth and nurse underwater. Furthermore, they also have a symbiotic relationship with fish that clean their mouths and gums.

 

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Hippos underwater (note that they don’t float!) Brian Snelson, Hockley, Essex, England – HipposUploaded by Snowmanradio, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=12185287

35:53 – Anatomists dissect out the lungs and the heart. The lungs provide more support for the evolutionary link between hippos and whales as both animals have lungs that are not divided into lobes. This feature allows hippos (and whales) to forcefully exhale and inhale rapidly. However, this begs the question, How do hippos not float if they just inhaled 5 minutes worth of air? Evidently, the limb bones of hippos do not have a marrow cavity. They are literally just solid bone and act as ballast for the hippo to compensate for the rapid air intake. Consequently, hippos do not technically float or really know how to swim. Instead, they more walk or gallop while underwater.

39:25 – The last aspect of the hippo highlighted was sound. Scientists dissected out the hippo’s larynx or “voice box.” It was incredibly huge and, again, shared characteristics with the larynxes of whales. The vocal folds found in hippos (and baleen whales) are oriented 90 degrees from what is usually seen in terrestrial animals. This helps aquatic animals project their sounds into the water rather than primarily out of their mouth. There is some cool footage of researchers using a hydrophone to listen to hippo noises underwater (40:50). Among other noises, hippos make “click” noises that have been compared to the click noises produced by killer whales!

Super fun necropsy video today in my opinion! One of the least gory out of all of the Inside Nature’s Giants videos that I have reviewed so far, but still super interesting. I loved learning about the blood sweat and the multiple overlapping characteristics seen between whales and hippos! Have a great week!

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