Episode 159 – Giraffes – COMMON DESCENT

Listen to Episode 159 on PodBean, YouTube, Spotify, or wherever you listen to your favorite podcasts!

Some animals are so familiar and famous that it’s easy to forget how utterly strange they are. This episode, we discuss the relatives, ancient history, and big questions surrounding the evolution of Giraffes.

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Long Mammals

There are only two living members of the family Giraffidae: the antelope-shaped okapis, which inhabit certain forests of the Congo and which stand a perfectly reasonable 1.5 meters (5 feet) tall at the shoulder; and the preposterously proportioned giraffes, whose very long necks and even longer legs can hoist their heads nearly 5.8 meters (19 feet) off the ground.

**Left**: A modern giraffe photographed in Zambia. Image by Jpatokal , CC BY-SA 3.0
**Right**: A modern okapi, photographed in a French zoo. Image by Daniel Jolivet, CC BY 2.0

The heads of both giraffes and okapis are adorned with bony projections called ossicones. These probably serve multiple functions, but their most dramatic use is in combat between males. Giraffe fights can be surprisingly violent, as you can see in this video.
**Left**: Two male giraffes in combat. Image by Steve Garvie, CC BY-NC-SA 2.0
**Right**: Giraffe skull with a prominent third ossicone. Image by Nikkimaria, CC BY-SA 3.0

So Long, Giraffes

Certainly the most famous feature of giraffes is their height, which – to reiterate – is ridiculous. They are by far the tallest living animals, and their bodies feature numerous adaptations to accommodate their unusual body shape, including enlarged bones, muscles, and ligaments in the neck, as well as specializations in their cardiovascular system to allow blood to flow efficiently and without issue along the full length of their neck and legs.

The question of why giraffes evolved such height has intrigued scientists for centuries. Numerous benefits might have nudged natural selection in that direction, including the ability to see farther across the landscape and the ability to access high-growing leaves beyond the reach of other herbivores. Their long necks are also great for efficient feeding – they can use their flexible necks to reach plenty of food without having to move their bodies much – and for violently bashing their heads into each other, most often during competition over mates or territory. Any of these factors, and others, are likely to have been important during the evolutionary history of giraffes.

Giraffes’ efficient feeding is also helped by the fact that they have very long, mobile tongues, as Will is discovering first-hand in these photos.

And to complete the pun in this subsection header, giraffes and okapis are both experiencing population declines and are highly vulnerable to extinction due to the rapidly changing modern world.

Giraffe Evolution

Giraffes and okapis belong to a group called Pecora, the “horn-bearing” members of the even-toed hoofed mammals (artiodactyls), which also includes the likes of cows, sheep, deer, and pronghorns. The ancestors and ancient relatives of giraffes include a variety of mammals with flashy headgear distributed across Asia, Europe, and Africa during the Miocene and Pliocene Periods.

Numerous early members of the giraffe lineage (or perhaps close cousins) had quite ostentatious ossicones.
**Top left**: *Xenokeryx amidalae*. Image by Israel M. Sánchez, CC BY 2.5
**Top right**: Ampelomeryx ginsburgi. Image by Muséum de Toulouse, CC BY-ND 2.0
**Bottom:** *Prolibytherium.*Image by Nobu Tamura, CC BY-SA 4.0

The giraffe lineage eventually began to feature more okapi- and giraffe-like species.
**Left**: The elephant-sized *Sivatherium giganteum*. Image from Basu et al 2016. CC BY 4.0
**Right**: The okapi-like *Palaeotragus*. Image by Jonathan Chen, CC BY-SA 4.0

**Left**: The quite giraffe-like *Samotherium.* Image by Natural History Museum, London, CC BY 4.0
**Right**: The large-ossiconed *Honanotherium*. Image by Ryan Somma, CC BY-SA 2.0

African giraffes as we know them appeared around seven million years ago, descended from Asian ancestors. Changing climates at that time gave rise to the widespread grasslands that modern giraffes inhabit.

Learn More

Short-necked giraffe relative discovered in China

Seeing Quadruple? Discovering Four Giraffe Species

The Remarkable Cardiovascular System of Giraffes (technical, open access)

Giraffe neck evolution:
Why sauropods had long necks; and why giraffes have short necks (technical, open access)
Giraffe Stature and Neck Elongation: Vigilance as an Evolutionary Mechanism (technical, open access)

On the origin, evolution and phylogeny of giraffes (technical, paywall)

And here’s that article Will mentioned during the Patron question: How Many Atoms Do We Have In Common With One Another?

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llewelly February 19, 2023 / 3:11 pm

Since you mentioned sauropod necks in the podcast, one of the more interesting articles on why giraffes have the necks they do has the amusing title: _Why Sauropods Had Long Necks; and Why Giraffes Have Short Necks_ https://peerj.com/articles/36/

It is, naturally, by two paleontologists who work on sauropods, Michael Taylor and Matt Wedel, from the blog svpow.com

For those who want something easier than the paper, there’s a nice talk on youtube:

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Aamir March 22, 2023 / 9:30 pm

Another close relative to giraffes and kin is the pronghorn found in the Americas!

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