Triceratops, the last dinosaur?


From Discovery News:

Triceratops Was Last Dinosaur Standing

The 65 million-year-old find suggests a meteor may have wiped out the dinosaurs in a sudden catastrophic event.

By Jennifer Viegas

Tue Jul 12, 2011 07:00 PM ET

THE GIST

The world’s last known surviving non-avian dinosaur was a Triceratops from Montana’s Hell Creek Formation.

The discovery suggests dinosaurs did not gradually die out before 65 million years ago, but that they went suddenly extinct.

Hoofed mammals and rodent-like species were among the animals that flourished after the extinction event.

A Triceratops may have been the last dinosaur standing, according to a new study that determined a fossil from Montana’s Hell Creek Formation is “the youngest dinosaur known to science.”

The Triceratops, described in the latest Royal Society Biology Letters, dates to 65 million years ago, the critical period of time associated with the Cretaceous-Tertiary (K-T) extinction event that wiped out all non-avian dinosaurs and many other animals and plants.

Since this rhinoceros-looking, three-horned dinosaur lived so close to the mass extinction moment, it could negate an earlier theory that dinosaurs gradually died out before 65 million years ago.

“Our paper suggests that dinosaurs did not go extinct prior to the impact,” lead author Tyler Lyson told Discovery News. “The fact that this dinosaur is so close to the K-T boundary lends support to the idea that they went extinct as a result of a meteorite impact.”

Lyson, a researcher in Yale University’s Department of Geology and Geophysics, and his team discovered the remains of the Triceratops, including its over 1.5-foot-long horn, just 5 inches below the pollen-calibrated K-T boundary at Camel Butte, a hill at the Hell Creek Formation in southeastern Montana.

By studying the region’s geological layers, the scientists can see how dinosaurs suddenly disappeared after the catastrophic event, which Lyson and many other experts believe was a meteorite strike that directly hit Earth at Mexico’s Yucatan Peninsula.

Lyson said that “we don’t fully understand the kill mechanism,” but other researchers “have a proposed a nuclear winter, while others have proposed a thermal pulse.”

The prior theory that dinosaurs gradually died out before 65 million years ago was often based on what is known as the “3-meter gap,” which referred to an apparent geological zone devoid of dinosaur fossils before the K-T event.

The Hell Creek Triceratops, however, was not only found within that 3-meter region, but it also exists at the upper reaches of it, proving that at least one dinosaur and presumably more were still alive when the meteorite blasted into Chicxulub, Mexico.

Co-author Stephen Chester of Yale’s Department of Anthropology told Discovery News that the Camel Butte site is important both because it has “the most recent dinosaur specimen” and “because we are finding a great diversity of small mammals that are first documented directly after the extinction event.”

Chester continued, “Although the K-T mass extinction event is mainly known for the disappearance of the non-avian dinosaurs, it is also an extremely important event in mammalian evolution because once the dinosaurs vanished, mammals underwent a large adaptive radiation and began occupying diverse ecological niches in the Paleocene.”

These mammals included condylarths, which were hoofed animals proposed to be ancestral to some modern orders of hoofed mammals. They also included multituberculates, which Chester described as being “extinct rodent-like animals with a very specialized dentition.”

It remains unclear why certain mammals, turtles and other animals survived the K-T extinction event, but Lyson explained that species with generalist, rather than specialized, diets tended to fare better, as did smaller animals and water dwellers.

Kirk Johnson is vice president of Research & Collections and chief curator at the Denver Museum of Nature & Science.

Johnson told Discovery News that he agrees the Triceratops is indeed “the last known non-avian dinosaur of the Cretaceous.” He said, “The 3M Gap is a weak concept to begin with,” and that his own work on plants and insects supports the idea that the meteor impact was the “direct and immediate cause of habitat destruction and extinction of more than 50 percent of North American plant and insect species.”

Peter Sheehan, curatorial chair of the Milwaukee Public Museum‘s Department of Geology, also agrees with the new findings. He and all of the other researchers, however, suspect that more recent dinosaurs even closer to the K-T boundary will be found in the future.

For now, however, the 65-million-year-old Triceratops is the world’s last known surviving dinosaur.

See also here.

Torosaurus Is Not Triceratops: Ontogeny in Chasmosaurine Ceratopsids as a Case Study in Dinosaur Taxonomy: here.

Austrian dinosaur: here.

A tough river turtle, Boremys, not only survived the meteorite impact that likely wiped out the dinosaurs, but it also seemed completely unfazed by the catastrophic event, according to a new Society of Vertebrate Paleontology paper: here. And here. And here.

Many dinosaurs and pterosaurs were active both by day and night, and some were entirely nocturnal, a new study suggests: here.

THE fate of the dinosaurs may have been sealed half a billion years before life even appeared, by two geological time bombs that still lurk near our planet’s core. A controversial new hypothesis links massive eruptions of lava that coincided with many of Earth’s largest extinctions to two unusually hot blobs of mantle 2800 kilometres beneath the crust. The blobs formed just after the Earth itself, 4.5 billion years ago. If the hypothesis is correct, they have sporadically burst through the planet’s crust, creating enormous oceans of lava which poisoned the atmosphere and wiped out entire branches of the tree of life: here.

15 thoughts on “Triceratops, the last dinosaur?

  1. Extinction and radiation: how the fall of the dinosaurs led to the rise of mammals by J. David Archibald . Baltimore : The Johns Hopkins University Press , 2011 . 108 pp. Hardback. ISBN 13: 978-0-8018-9805-1 ISBN 10: 0-8018-9805-6. £39 .

    It’s more than 40 years since I listened to undergraduate lectures on this topic, so I thought I might get myself updated. I was also interested in the whole issue of evolutionary transitions – how does a reptile become a mammal when every stage of the process has to be a functionally coherent and fully adapted to its ecological environment? This book is nicely discursive and readable, but doesn’t seem to address that question.

    From the start it does make two good points: first that palaeontologists tend to focus on a single geological era and not the transition between them and second, that there were mammals living alongside dinosaurs (albeit not the familiar taxa that we see today). Even a six year-old knows the dinosaurs and their long names, even if they can’t spell anything else, but nobody seems very aware of the contemporary mammals. Eutherians do not appear in the North American fossil record until the late Cretaceous, but recent studies on fossils from central Asia apparently extend their existence back much earlier and I recall lectures about Morganucodon from even earlier still. This was a ‘missing link’, a mammal with remnant reptilian features, but it is not mentioned here. Nor is the recent discovery of ‘the first mammal’, Juramaia, or its discoverer, so I feel slightly confused rather than updated on the origin of fossil mammals, although this book is focussed on the later Cretaceous-Tertiary transition.

    What caused the extinction of dinosaurs is discussed of course. The various challenges (meteorites, acid rain, vulcanism, climate change, overexploitation by aliens, etc.) killed off dinosaurs, large and small, terrestrial and aquatic, yet so many other taxa survived, including mammals, but why? It’s not clear what was actually wrong with being a dinosaur. Moving swiftly on, it is firmly (and reasonably) asserted that their removal opened the way to a rapid expansion of mammals into the groups we know today. However, ‘the molecular clock model’ apparently suggests that diversification actually occurred before the extinction of dinosaurs. The author explains away this awkward anomaly by suggesting that the cataclysms occurring at the end of the Cretaceous must have somehow caused the molecular clock to speed up. Exactly how is not explained.

    What actually is a mammal? This surely is a central question. The presence of mammae to produce of milk has to be the prime feature, but is not evident in fossils. Fur and homeothermy are also difficult to study in the fossil record. They are what enabled mammals to colonise many extreme environments, but only at the expense of increased energy consumption. The relevance and significance of all this is not discussed. Two slightly incongruous pages at the end suggest that a single species (our own) achieving a population of 9 billion in the next 40 years will constitute a major extinction threat for many extant mammals (and much else). Good point, it took millions of years to see off the dinosaurs.

    Overall, this book forms a commentary on the author’s own research and the context in which it was carried out. Its narrow focus on molars and the application of cladistics to establish relationships between fossil taxa and their immediate ancestors will appeal to the few who are similarly engrossed. But ultimately the book doesn’t really answer the question posed by its subtitle. It doesn’t tell us HOW the fall of the dinosaurs led to the rise of mammals, only that it did.

    http://onlinelibrary.wiley.com/doi/10.1111/j.1096-3642.2012.00807.x/full

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