The Wonderful Net: How Camels and Penguins Are So Chill

Now let’s consider the adaptations of modern camels to a life in the harsh extremes of the desert. The most obvious adaptations are the humps, large fat deposits, which the camel can withdraw water from when food and drink are scarce. When they do find it, camels are capable of drinking water very quickly, with some sources indicating as many as thirty gallons in thirteen minutes! Their thick lips allow the animal to go after any vegetation it comes across, including hardy desert plants that are equipped with all sorts of large spikes and thorns. Thick, luscious eyelashes help to block the blowing sand from their eyes, and they can seal off their nostrils to prevent sand from getting in their, as well.* Their feet are broad, equipped with fleshy footpads that help distribute the weight of the camel over a broader surface area, just like a snowshoe.

Dromedary camels Camelus dromedarius in the Sahara Desert in Morocco, a comparison of four ungulate legs, a horse Equus sp., white tailed deer Odocoileus virginianus, fossil camel Paleolama, extinct bison Bison antiquus Photo Credit Zack Neher

A number of camel adaptations.  On the top left and bottom right, check out the luscious eyelashes and the thick lips.  On the bottom left, we have a comparison of four different species of ungulate.  From left to right, we have a horse (Equus sp.), a white-tailed deer (Odocoileus virginianus), an extinct camel (Paleolama), and an extinct bison (Bison antiquus).  Compare the skinny camel foot bones with the enormous, spreading foot in the picture on the top right.  Large, fleshy pads allow the camel to distribute its weight over a larger surface area.

While doing research for this blog post, I stumbled across two words that quickly caused this simple post on camels to spiral into a three part extravaganza: “rete mirabile.” Rete mirabile is Latin for “wonderful net,” and refers to a network of veins and arteries that are in close contact to one another. The close proximity of the different blood vessels allows heat to transfer from one to the other, in a process known as countercurrent heat exchange.

A diagram of a wonderful net rete mirabile counter current heat exchange by Zack Neher

A diagram of a rete mirabile, explained in the paragraph below.

What’s the point of the rete mirabile, or countercurrent heat exchange? A number of warm-blooded animals have some sort of “wonderful net” at work in their bodies, and it aids in thermoregulation. I first came across the term a few years ago while reading Daniel Ksepka’s blog on fossil penguins. Most penguins swim in waters that are colder than their body temperature, and since penguins are birds and birds are warm-blooded, that can be a problem. The large surface area and the low volume of the flipper means that it’ll lose heat to the environment fairly rapidly, faster than the rest of the body. As warm, oxygenated blood is pumped out of the heart and into the wing, the blood immediately begins to cool. The blood, now cold, is then pumped back into the body of the penguin. To help keep the flippers warm, the hot, outgoing blood vessels are in close proximity to the colder, incoming blood vessels. As the blood passes through, some of the heat from the outgoing blood is transferred to the colder blood returning from the flipper to the body of the bird. This ensures that the overall temperature of the flipper doesn’t drop too low, and means that the blood returning to the heart is warmed slightly. The flipper can remain colder, while the core body temperature of the penguin can remain stable.**

A trio of African Penguins Spheniscus demersus on the beach at Simon's Town in Cape Town South Africa with Michael Collett and Teddy Castro Photo Credit Zack Neher

A trio of African penguins (Spheniscus demersus) at Simon’s Town near Cape Town, South Africa.  Hidden within their flippers are rete mirabile, that help keep their core temperature warm.

Turns out, the rete mirabile is a pretty common occurrence, and it seems to crop up all over the place, especially in diving and burrowing mammals, both of which tend to suffer from a lack of oxygen. Some studies suggest that allowing the temperature of the limbs to cool means that they need less oxygen anyways, which is of further benefit for these divers and burrowers. Seals and sea lions have them in their flippers, and they can be found in the tails of whales, as well. In 2015, it was discovered that the opah, a large species of sunfish, employ the use of rete mirabile in their gills to help keep their heart warmer than the surrounding water temperature. Arboreal animals, or animals that live in trees, are sometimes found with these wonderful nets, as well, where they are called “vascular bundles.” Some scientists believe that the presence of these bundles is to reduce oxygen consumption in clinging animals, like sloths, pottos, the slow loris, and tree anteaters. They suggest that, since these clinging animals are flexing their muscles (which can restrict bloodflow), the lowered limb temperatures means that less blood flow is required altogether (O’Dea, 1989).  Another fascinating example of a mammalian rete mirabile is in the neck of the giraffe. To prevent the blood vessels in the head of a giraffe from bursting when the animal lowers its head below its heart to drink, the blood vessels in the rete mirabile expand, decreasing the pressure of the blood entering the brain!

A giraffe Giraffa camelopardalis in Kruger National Park in South Africa Photo Credit Zack Neher

A giraffe (Giraffa camelopardalis) in Kruger National Park, South Africa.  To help keep the bloodvessels in the head from bursting when the animal bends down to drink, the giraffe has a rete mirabile in its neck that expand to accommodate the extra blood.

In my research on camels, I was initially surprised to discover that they possess a rete mirabile in their heads. My experience thus far had usually found rete mirabile associated with warm-blooded animals that needed to warm up, but never with warm-blooded animals that needed to cool down! Of course, the temperature of the blood in the blood vessels of the rete mirabile is all relative. In the cold waters off the shores of South Africa, the blood of the African penguin will of course be warmer than its surroundings. But in the scorching heat of the Sahara Desert, the blood of the camel might actually be cooler than the surrounding air temperature! Studies indicate that the rete mirabile in the heads of camels might serve to help decrease the temperature of the brain, allowing it to function in the deadly heat of the desert. More research suggests that a number of birds and mammals actually have some sort of rete mirabile in their heads to help cool the brain, including a number of large migratory seabirds, such as boobys and albatross in the Hawaiian Islands and Midway Atoll (watch for them in an upcoming blog post!).

A black footed albatross Phoebastria nigripes soars gracefully above the waves in the Pacific Ocean between Ensenada, Mexico and Honolulu, Hawaii Photo Credit Zack Neher

A black-footed albatross (Phoebastria nigripes) soars over the waves in the Pacific Ocean, between Mexico and Hawaii.  Like camels, as well as many other seabirds, albatross possess a rete mirabile in their head to help cool their brain.


*After spending just one night in the Sahara Desert, I can confirm Anakin Skywalker’s gripe about sand getting everywhere. It really does. Even after several showers, I was still picking sand out of my hair, ears, and nose for about a week. Even a month and a half later, I still have some sand stuck in my iPhone case.

**This counter-current heat exchange can be used in industry and man-made machines, as well. For example, aircraft sometimes will use heat generated in one part of the machine to heat cold fuel.


A Brief Fossil History of Camelids

What do World War I and II, penguin flippers, heat exhaustion and dehydration, Snowmass ski resort, the inspiration for Indiana Jones, warm-blooded fish, the accidental death of John Ainsworth Horrocks, the neck of the giraffe, luscious eyelashes, and Hawaiian seabirds all have in common? If you thought that they will all be featured in this three-part post about the dromedary camel, then you are correct.

Meredith Leung riding on the back of a dromedary camel Camelus dromedarius in the Sahara Desert in Morocco on Semester at Sea Spring 2016 with Michael Collett Kim Kassander Haley Collins and Emily Kaplan Photo Credit Zack Neher

Meredith Leung, one of my friends from Semester at Sea, riding on the back of a dromedary camel (Camelus dromedarius) in the Sahara Desert in Morocco.

While in Morocco, my friends and I got the chance to ride dromedary camels in the Sahara Desert, an opportunity that I was very excited about. The first thing that struck me as we rode out between the dunes was how barren and inhospitable the place was (which probably seems pretty obvious, but was still surprising to witness). I was, however, surprised at how many large shrubs and bushes could be found fairly frequently, a number I imagine would decrease the further into the desert you get. But even with the surprising amount of shrubbery where we were, it didn’t look like a place that would allow animals as large as a camel to survive. But survive they had, for millions of years, and that was one of the things that interested me the most.

A dromedary camel Camelus dromedarius silhouetted against the horizon in the Sahara Desert in Morocco on Semester at Sea Spring 2016 with Michael Collett Kim Kassander Meredith Leung Emily Kaplan and Haley Collins Photo Credit Zack Neher

A domesticated dromedary silhouetted against the horizon.  The single hump on the back of the animal is plainly visible in this photograph.  The related Bactrian camel (Camelus bactrianus) has two humps.

Despite their absence on the continent today, the earliest camels actually evolved in North America, around 35 million years ago (MYA).  These small, early camels looked more like modern gazelle than today’s camels, as they were small, slender creatures with sharp hooves to aid in running.  Over time, they diversified from their small, goat-sized ancestors to a fantastic array of shapes and sizes, and inhabiting an equally diverse set of biomes, a much greater diversity than we see today. Some evolved similar to modern day gazelle, deer, and pronghorn, adapted for faster running in open areas. Others became huge, larger than modern day camels. Still others found their way northwards, inhabiting the most northern reaches of Canada in the frigid Arctic. It wasn’t until a few million years ago that the camelids found their way outside of North America. In one direction, we see the ancestors of the modern day guanaco, vicuña, alpaca, and llama cross the Isthmus of Panama into South America. Meanwhile, the ancestor of the modern dromedary and Bactrian camels dispersed from Alaska into Russia via the Bering Land Bridge (which humans would later use to cross in the opposite direction).

Mounted fossil skeleton of the extinct camelid Paleolama on display at the Houston Museum of Natural Science in Houston, Texas with Cian Kinderman Seamus Kieran Mikaila Bloomfield and Emily Barber Photo Credit Zack Neher

A mounted fossil skeleton of the extinct camelid Paleolama on display at the Houston Museum of Natural Science in Houston, Texas.  Paleolama was a mid-sized North American species that lived during the Ice Age.  You can see the resemblance in the overall body plan between Paleolama and the modern dromedary.

Humans would have actually encountered wild camels in North America when they first arrived during the last Ice Age.  Even in Colorado, we find the remains of Ice Age camels that would have lived alongside more famous and charismatic megafauna, such as the Columbian mammoth. In 2011, fossil bones of the genus Camelops were unearthed during the massive Ice Age dig at the Snowmass ski resort, discovered in the same layers as the bones of Columbian mammoth, deer, and bison. Although the exact cause of extinction is not entirely certain, there is a growing body of evidence that suggests that many of the large Ice Age mammals were driven to extinction by the arrival of early humans approximately 10,000 years ago, making the Ice Age Camelops another possible casualty of the spread of humanity.*

Fossil skull cast of the extinct camelid Camelops on display at The Living Desert Zoo and Gardens in Palm Desert California with Mark Julie and Dani Neher and Rick Nick and Sydney Carlson Photo Credit Zack Neher

This is a fossil skull cast of the extinct camelid Camelops, on display at The Living Desert Zoo and Gardens in Palm Desert, California.  Check out how large those nasty-looking front teeth are.  Unlike deer, camels evolved offensive weapons such as large, sharp teeth to combat potential predators.  Even a bite from today’s camels is nothing to joke about.

Even though we typically think of camels as exclusively desert animals, the fossil record shows us that in prehistory, the camel family had become adapted to a wide variety of habitats and niches. The development of a nomadic, desert lifestyle actually appears to be a fairly recent one!

Michael %22Big Mike%22 Collett riding on the back of a dromedary camel Camelus dromedarius in the Sahara Desert in Morocco on Semester at Sea Spring 2016 with Meredith Leung Kim Kassander Emily Kaplan and Haley Collins Photo Credit Zack Neher

Michael “Big Mike” Collett riding on the back of a dromedary in the Sahara.  See where the green rope is attached to the camel’s lower jaw?  If you look at the picture of the Camelops skull, you can see a large gap between the front teeth and the molars, called a diastema.  For these camels, many of the ropes were looped through here.

Join us next time, as we investigate an adaptation of the modern camel that helps keep it cool in the desert heat….and helps keeps penguins warm underwater!


* Unfortunately, the investigation is a bit of a COLD CASE.  Boom, Ice Age puns.