Some fossils feel like old friends. As happy as I am to encounter petrified skeletons I’ve never seen before in museum halls, there’s something comforting about rounding a corner to find a cast of AMNH 5027 – the first Tyrannosaurus I ever met – or see Stenomylus, a little North American camel that I’ve encountered in exhibits from New Haven to Los Angeles.
The ancient rhino Teleoceras recently joined the club, too. Paleontologists have exhumed so many of these squat, tubby rhinos that almost every major museum in America seems to have one. And, because of its stubby-legged, barrel-shaped body, the 17-4.5 million year old herbivore has often been cast as “the rhino that lived like hippo”. A life ambling between lake and shore seemed to be the only sort that made sense for such an oddly-proportioned mammal, and I repeated the traditional story when I tweeted a photo of the beast during a visit to Harvard’s Museum of Natural History.
But looks can be deceiving. Paleontologist Bobby Boessenecker – expert on aquatic and semiaquatic fossil mammals – jumped in on Facebook to point out a 1998 study that cast Teleoceras in a different way. (This is the nice thing about being friends with paleontologists – they’ll catch your errors and will immediately proffer citations to get you back on track.) According to the Paleobiology paper by Bruce MacFadden, at least some of the rotund rhinos stayed high and dry.
Different species of Teleoceras used to range across the span of North America, from Oregon to Florida. In some places – like the 10 million year old Ashfall Beds of Nebraska – they’ve been found by the dozens. MacFadden chose to focus on specimens found in the 9.5 to 4.5 million year old rock of the sunshine state, as well as those of its neighbor Aphelops – a rhino with longer legs that has often been reconstructed as a relatively swift species that browsed for soft plants in open habitats. And to investigate this “tale of two rhinos”, MacFadden turned to geochemical traces locked inside the rhinos’ teeth.
You are what you eat. That’s the basis for a branch of fossil research that focuses on geochemical isotopes. In short, different pathways in plant photosynthesis leave distinct signatures of the isotope 13C. That trace ends up becoming incorporated in teeth as they grow, and, by comparing these signatures in fossil teeth to those of living animals with known diets, paleontologists can narrow down what prehistoric mammals were munching on. Similar logic applies to other geochemical indicators. The water prehistoric animals imbibed, for example, left geochemical signposts in the form of 18O, and this isotope can be used to determine whether an animal in question had a more or less aquatic lifestyle.
By analyzing these carbon and oxygen isotopes in the fossil rhinos, MacFadden was able to check what had often been assumed on the basis of skeletal shapes. What he found didn’t fit the traditional Teleoceras tale.
In the oldest part of the sample, in teeth 9.5 and 7 million years old, MacFadden didn’t find much difference in diet between Teleoceras and the leggier Aphelops. They had similar carbon isotope signatures, indicating a diet of what are called C3 plants that included trees, forbs, shrubs, and some grasses.
By 4.5 million years ago, though, the rhinos were definitely picking off different parts of the menu. Aphelops appears to have been a browser, nibbling on soft plants, while Teleoceras was a “mixed feeder” with a large proportion of C4 grasses – which had spread into the region by that time – in its diet. This seemed to be in accord with evidence from elsewhere. At Nebraska’s Ashfall site, for example, plant material found around the throats and stomachs of Teleoceras hinted that the rhino snarfed down bushels of grass.
From diet, Teleoceras seemed more at home out in the grasslands than in the water – an idea mooted decades before by paleontologist William Diller Matthew. And the oxygen isotope signatures seemed to cinch it. Teleoceras didn’t have an oxygen isotope profile like that of a hippo, but instead seemed to match mammals that spend most of their time in the terrestrial realm. “While the δ18O results cannot rule out the possibility that Florida Teleoceras spent a small percentage of its daily life cycle in water,” MacFadden wrote, “the data do not support the previous hypothesis that this species was principally aquatic.”
In place of the old model, MacFadden proposed that Florida’s ancient rhinos avoided competition for the salad bar by eating different plants – Aphelops being more of a browser, like today’s black rhino, and Teleoceras pioneering the grazing lifestyle embodied by the modern white rhino. The low-slung appearance of Teleoceras wasn’t because it lived like a hippo. Stumpy legs were an old, common trait amongst the rhinoceros lineage it belonged to, and it didn’t have to be particularly tall if – by MacFadden’s estimation – 60% of the herbivore’s diet was grass. Teleoceras was not so much a hippoceros as a living lawnmower.
Reference:
MacFadden, B. 1998. Tale of two rhinos: isotopic ecology, paleodiet, and niche differentiation of Aphelops and Teleoceras from the Florida NeogeneTale of two rhinos: isotopic ecology, paleodiet, and niche differentiation of Aphelops and Teleoceras from the Florida NeogeneTale of two rhinos: isotopic ecology, paleodiet, and niche differentiation of Aphelops and Teleoceras from the Florida NeogeneTale of two rhinos: isotopic ecology, paleodiet, and niche differentiation of Aphelops and Teleoceras from the Florida NeogeneTale of two rhinos: isotopic ecology, paleodiet, and niche differentiation of Aphelops and Teleoceras from the Florida Neogene. Paleobiology. 24 (2): 274-286.
Prothero, D. 2005. The Evolution of North American Rhinoceroses. Cambridge: Cambridge University Press. pp. 94-124
Go Further
Animals
- Fireflies are nature’s light show at this West Virginia state parkFireflies are nature’s light show at this West Virginia state park
- These are the weird reasons octopuses change shape and colorThese are the weird reasons octopuses change shape and color
- Why young scientists want you to care about 'scary' speciesWhy young scientists want you to care about 'scary' species
- What rising temperatures in the Gulf of Maine mean for wildlifeWhat rising temperatures in the Gulf of Maine mean for wildlife
- He’s called ‘omacha,’ a dolphin that transforms into a man. Why?He’s called ‘omacha,’ a dolphin that transforms into a man. Why?
Environment
- What rising temperatures in the Gulf of Maine mean for wildlifeWhat rising temperatures in the Gulf of Maine mean for wildlife
- He’s called ‘omacha,’ a dolphin that transforms into a man. Why?He’s called ‘omacha,’ a dolphin that transforms into a man. Why?
- The northernmost flower living at the top of the worldThe northernmost flower living at the top of the world
- This beautiful floating flower is wreaking havoc on NigeriaThis beautiful floating flower is wreaking havoc on Nigeria
- What the Aral Sea might teach us about life after disasterWhat the Aral Sea might teach us about life after disaster
History & Culture
- Scientists find evidence of ancient waterway beside Egypt’s pyramidsScientists find evidence of ancient waterway beside Egypt’s pyramids
- This thriving society vanished into thin air. What happened?This thriving society vanished into thin air. What happened?
Science
- Why pickleball is so good for your body and your mindWhy pickleball is so good for your body and your mind
- Extreme heat can be deadly – here’s how to know if you’re at riskExtreme heat can be deadly – here’s how to know if you’re at risk
- Why dopamine drives you to do hard things—even without a rewardWhy dopamine drives you to do hard things—even without a reward
- What will astronauts use to drive across the Moon?What will astronauts use to drive across the Moon?
- Oral contraceptives may help lower the risk of sports injuriesOral contraceptives may help lower the risk of sports injuries
- How stressed are you? Answer these 10 questions to find out.
- Science
How stressed are you? Answer these 10 questions to find out.
Travel
- How to make perfect pierogi, Poland's famous dumplingsHow to make perfect pierogi, Poland's famous dumplings
- The best long-distance Alpine hike you've never heard ofThe best long-distance Alpine hike you've never heard of
- Fireflies are nature’s light show at this West Virginia state parkFireflies are nature’s light show at this West Virginia state park
- How to explore the highlights of Italy's dazzling Lake ComoHow to explore the highlights of Italy's dazzling Lake Como
- Going on a cruise? Here’s how to stay healthy onboardGoing on a cruise? Here’s how to stay healthy onboard