TOKYO - New research is reshaping long-held assumptions about Tyrannosaurus rex, including suggestions that the giant predator may have lived to around 40 years rather than 28, while advances in fossil analysis are also offering new clues about dinosaur growth, posture and even color.
Makoto Manabe, a paleontologist who became director of the National Museum of Nature and Science in Tokyo's Taito Ward in April, explained the latest findings while introducing the museum's full-body Tyrannosaurus and Triceratops skeletons and genuine fossils.
One of the museum's Tyrannosaurus displays shows the animal crouching near a Triceratops. Manabe said the pose was chosen to illustrate one possibility for how the predator hunted. With its short arms, Tyrannosaurus may not always have chased and physically grabbed prey, but could instead have waited in ambush for animals such as Triceratops.
The Triceratops specimen on display is made up almost entirely of genuine fossil material apart from much of the tail. It is also exceptionally important because the skull and body were discovered connected, something known from only about three comparable specimens, Manabe said.
That preservation allows researchers to see the proportions of the head and body directly. It has also contributed to changing ideas about how Triceratops held its forelimbs. Older reconstructions often showed the elbows projecting outward because the hands were thought to have been placed on the ground in a way that forced the limbs into that position. More recent interpretations suggest the hands could have been oriented differently, allowing the elbows to remain closer to the body.
Tyrannosaurus, one of the best-known dinosaurs, continues to be the subject of intensive study. One major debate has concerned Nanotyrannus, a smaller tyrannosaur once widely interpreted as a juvenile form of Tyrannosaurus rex.
The prevailing view had been that young T. rex individuals were relatively small and lightly built before undergoing a rapid growth phase and developing into the massive adults familiar from fossils. Recent research, however, has revived the possibility that Nanotyrannus was actually a separate species.
That would mean North America about 66 million to 68 million years ago was home not only to Tyrannosaurus rex but also to another, smaller tyrannosaur.
Researchers have also refined estimates of dinosaur age and growth by examining microscopic structures inside fossilized bones. When fossils are sufficiently well preserved, scientists can cut thin sections from bones such as the femur and study them under a microscope.
The bone can contain striped patterns resembling tree rings. Counting these structures can provide clues to an animal's age and growth history.
In Tyrannosaurus rex, the evidence has suggested a major growth phase at roughly 12 to 15 years old, when the spacing between growth markers becomes wider. That rapid adolescent growth helps explain how the dinosaur reached such enormous size.
Earlier research based on these growth markers suggested T. rex reached adulthood at around 20 years old and may have had a maximum lifespan of about 28 years.
That estimate is now being reconsidered. Manabe said recent research has raised the possibility that some of the structures previously treated as annual growth markers may not correspond to only one year in the way once assumed. The latest work has therefore suggested that the lifespan of Tyrannosaurus rex could have extended to around 40 years.
Scientific advances are also changing assumptions about dinosaur appearance.
Fossil bones are commonly brown or black, even though living bone was originally white. The dark colors are thought to result from minerals and other substances entering the remains while they were buried in sediment.
For many years, scientists therefore assumed there was no reliable way to determine the original colors of dinosaurs. That began to change in 2010, when researchers showed that in exceptionally preserved fossils it can sometimes be possible to identify melanosomes, microscopic structures associated with pigmentation, using electron microscopes.
When such structures survive, scientists can estimate the colors and patterns of extinct animals.
Even so, the colors or markings of only around 10 to slightly more than 10 dinosaur species have been identified in this way, Manabe said.
No such evidence has yet been found that reveals the color of Tyrannosaurus rex.
As a result, illustrations of T. rex in dinosaur encyclopedias can vary widely. Some publishers and artists favor brighter reconstructions, while others depict the dinosaur in more subdued colors, partly as a way of distinguishing their books from competing titles.
For now, Manabe said, the true color of Tyrannosaurus remains unknown. If well-preserved pigment-related structures are eventually discovered in a suitable fossil, however, scientists may one day be able to determine what the world's most famous predatory dinosaur actually looked like.
Source: 産経ニュース
