Number of Dinosaur Species May Be Overestimated

New analyses of fossils is leading scientists to question our understanding of dinosaur species.

We’ve finally figured out why there were no medium-sized dinosaurs (New Scientist). The bluffing headline by Riley Black glosses over the difficulty of figuring out where one dinosaur species ends and another begins. Researchers at the University of New Mexico aren’t so sure. Their new idea—that juvenile dinosaurs outcompeted one another—flies in the face of earlier explanations, such as the idea that juveniles didn’t fossilize well or have not yet been found. Any dinosaur hatched from an egg would have to spend some time as a youngster. Why are so few of them found? It doesn’t make sense.

In a study of 43 dinosaur communities spanning 136 million years of prehistory, Katlin Schroeder at the University of New Mexico and her colleagues found that carnivorous dinosaur species estimated to have had an adult body weight of between 100 and 1000 kilograms were rare to non-existent in many dinosaur communities.

This contrasts with the way carnivorous species of different sizes carve out niches in today’s ecosystems. In places like the Serengeti in East Africa, carnivorous species form a continuous size gradient of small to large – from the tiny bat-eared fox to mid-sized African wild dogs to burly lions – without the break seen among predatory dinosaurs.

Medium-size dinos are missing from the fossil record. Here’s why. (Live Science). Another bluffing headline, this one by Laura Geggel, doesn’t really answer the “here’s why” claim or solve the problem of the missing middlings. She only gives the researchers’ idea as a possibility:

Donning their detective hats, the researchers soon found a suspect; megatheropods — the largest of the meat-eating dinosaurs, like Tyrannosaurus rex and Gorgosaurus, which weighed over 2,200 pounds (1,000 kilograms) as adults. It’s possible that juvenile megatheropods edged out the middlings, the researchers said. 

“Juvenile megatheropods may have outcompeted other medium-sized dinosaurs, resulting in deflated global dinosaur diversity,” study lead researcher Katlin Schroeder, a doctoral student in the Department of Biology at the University of New Mexico, told Live Science in an email.

Geggel notes that not everybody agrees with the new idea. Why would Tyrannosaurus juveniles survive to adulthood? Wouldn’t they be facing the same competition from the big adults? The explanations offer little more than suggestions: for instance, that the adults shared their kills with their youngsters, or the youngsters went after different prey till they grew up. Or, maybe it’s the paleontologists’ fault for misidentifying the bones.

It’s also possible that some dinosaur species in the study were misidentified. Only recently have paleontologists begun to assess bone microstructure, which can reveal a dinosaur’s age at death. “This can show that some small dinosaur individuals belonging to one species were simply juveniles of other species, or conversely, that some small dinosaur individuals thought to be juveniles of one species are instead adults of new dwarf species,” D’Emic said.

This leaves readers wondering if dinosaur species have been overestimated or underestimated. A different project gives support to the former.

Credit: By Nobu Tamura email:nobu.tamura@yahoo.com

Dinosaur species: “Everyone’s unique” (University of Bonn). Is it the case that dinosaur hunters have been too eager to call every specimen a new species? Their analysis of plateosaur skulls suggests that is a real problem.

Plateosaurus lived during the Late Triassic, about 217 to 201 million years ago. “With well over 100 skeletons, some of them completely preserved, it is one of the best known dinosaurs,” says Dr. Jens Lallensack, who researched dinosaur biology at the University of Bonn and has been working at Liverpool John Moores University (UK) for several months. The herbivore had a small skull, a long neck and tail, powerful hind legs and strong grasping hands. The spectrum is considerable: Adult specimens ranged from a few to ten meters in length, weighing between about half a ton and four tons.

The variability in plateosaurs, in other words, is much greater than thought. They call this “natural variation between individuals.”

Dinosaurs have been preserved for posterity mainly through bones. Paleontologists rely on anatomical details to distinguish different species. “A perpetual difficulty with this is that such anatomical differences can also occur within a species, as natural variation between individuals,” Lallensack reports. Researchers at the University of Bonn and the Dinosaur Museum Frick (Switzerland) have now been able to show that Plateosaurus anatomy was significantly more variable than previously thought – and the validity of some species needs to be re-examined.

Natural variation may reflect differences between individuals, but also differences within individuals – changes in appearance as they grow up. Whatever the causes of natural variation, it means that some species may have to be recombined into fewer species. The U Bonn researchers believe they have debunked the splitters and supported the lumpers (taxonomists who multiply species vs those who combine them, respectively).

The way these plateosaurs were buried will be of interest to creationists and flood geologists:

The first bones of Plateosaurus were found as early as 1834 near Nuremberg, making it the first dinosaur found in Germany, and one of the first ever. Between 1911 and 1938, excavations unearthed dozens of skeletons from dinosaur “graveyards” in Halberstadt (Saxony-Anhalt) and Trossingen (Baden-Württemberg). A third such cemetery was discovered in the 1960s in Frick, Switzerland. “It’s the only one where there are still digs every year,” Lallensack says.

illustration by Brett Miller

What kind of ordinary, uniformitarian process would bury dozens of dinosaurs in a mass grave? These “dinosaur graveyards” occurred in three different locations, the paragraph above indicates. Just one such graveyard would surely be considered strange and unique, requiring very special conditions to bury large beasts together. But three? Halberstadt is some 280 miles from Trossingen, and Frick is approximately 50 miles farther south. Would similar catastrophic burials occur so distant from each other?

Look how big that Plateosaur is! Imagine dozens of them buried together. Today’s large animals do not die together in mass graves. They lie on the surface and are picked apart by scavengers. What would scientists say if they saw dozens of elephants buried together? They would say a major catastrophe like a flood had occurred. How much more when large dinosaurs are found buried together in three scattered locations?

When you look at evidence like this without Darwin glasses on and without moyboy assumptions, it fits the Biblical timeline. There were not as many dinosaur species as often claimed; they lived at the same time, and a flood buried them all. This explanation also fits the discovery of soft tissue, proteins and DNA inside dinosaur bones.

The explanation with the lowest perhapsimaybecouldness index should be favored. The Darwinians routinely add “may have” or “could have” or “possibly” to their explanations, trying to keep their precious millions of years protected from falsification.