The reanalysis of a fossil found more than 20 years ago in New Mexico has resulted in the discovery of an entirely new species of horned dinosaur. Named Sierraceratops turneri, the Cretaceous beast is a sign that dinosaurs were more diverse than we thought — and that many new species are still waiting to be found.
During the late 1990s, CNN founder Ted Turner allowed a group of paleontologists to explore his ranch near Truth or Consequences, New Mexico. The billionaire chose a spot atop the Hall Lake Formation, which features sediments dating back to the Late Cretaceous. The paleontologists managed to find a partial dinosaur skeleton, which they identified as belonging to Torosaurus, a ceratopsid, or horned dinosaur, that lived some 66 million to 68 million years ago.
Recently, Sebastian Dalman, a paleontology student at the New Mexico Museum of Natural History & Science, along with his colleagues, decided to take another look at the fossil. The specimen consisted of the premaxilla (beak), brow horn, frills, shoulder girdle, ribs, and vertebrae. Upon closer inspection, the scientists came to realise that the bones had been misidentified — they were dealing with an entirely new species. Now designated Sierraceratops turneri, the new ceratopsid dino was named in honour of Sierra County and the media mogul. A comparative analysis with other known ceratopsids allowed the team to confidently declare the discovery of a distinct species. The team’s findings were published in the journal Cretaceous Research.
S. turneri lived around 72 million years ago during the Late Cretaceous, some 6 million years before the appearance of its famous horned relative, Triceratops. That the bones did not belong to Torosaurus is not a huge surprise, given that S. turneri lived millions of years earlier and a thousand miles away from Torosaurus’s known habitat. Updated radiometric dating allowed for a more precise chronology.
The four-legged plant eater had a combination of distinct features, including brow horns that were short and stout and frill bones that were “not quite like anything we’ve seen before,” as Nicholas Longrich, a paleontologist at the University of Bath and a co-author of the new study, explained in an email. S. turneri measured approximately 4.6 metres in length, including its 1.5 metre-long skull.
S. turneri likely lived in herds, while having to avoid its mortal enemy, the tyrannosaurs. Back then, New Mexico was quite warm, with rivers, swamps, floodplains, and palm trees.
An interesting thing that’s happening in dinosaur paleontology right now is that most of the low-hanging fossil fruit has already been taken. As a consequence, scientists are having to explore new areas and re-analyse old fossils. This has yielded positive results, however, as paleontologists are learning more about dinosaur diversity and how members of the same species weren’t as geographically dispersed as previously assumed. Longrich said there are two factors at play.
“For one, beds in different areas are often slightly different ages. So as you move across the landscape, you’re moving forward or backward in time, perhaps millions of years,” he explained. “Since dinosaur species are fairly short-lived — surviving a million years or less, on average — that means that you see different species just because you’re sampling different points in time.”
The other thing is that dinosaurs, while known for their size, don’t appear to have had large geographic ranges; very different species tend to appear across relatively short distances. Potential reasons for this include geographic barriers, climate, and access to plants, but Longrich suspects something else: competition among species. Longrich provided more detail at his blog:
[D]inosaurs and other animals might opportunistically move into an area because of some disturbance — a drought, warming, cooling, climate change, a disease — that decimates the local population. Once there, they would soon adapt to the local environment — adapting to the climate, to the plants, and (perhaps most importantly) to the local endemic diseases and parasites. This gives them a competitive advantage against competing species trying to move into the area.
At some point, however, an environmental disturbance creates an opening, or perhaps a species evolves some advantage that allows it to invade. Now, the invasives get a foothold.
The process repeats, over and over — dinosaurs spread out, evolve in different ways in different habitats, producing new species. This process — invasion, adaptation that prevents further invasion until a disturbance — could create barriers to dispersal without a geographic barrier, or a direct climate barrier…Your competitors are the biggest constraint on where you can live.
For S. turneri, its barrier-free environment was the edge of a huge inland sea known as the Western Interior Seaway. This coastal plain extended all the way up to Canada, allowing for a diversity of dinosaur species, according to the research. This could explain why different dinosaurs, from horned dinosaurs and duckbills through to tyrannosaurs and raptors, occupied different parts of the continent.
The good news is that, so long as paleontologists keep digging in North America, they should expect to find plenty more new species.