James' World 2

Click the link below the picture

.

Alone, Tyrannosaurus rex sniffs the humid Cretaceous air, scenting a herd of Triceratops grazing beyond the tree line. As the predator scans the floodplain, its vision suddenly snaps into focus. A single Triceratops has broken off from the herd and wandered within striking distance. Standing motionless, the T. rex formulates a plan of attack, anticipating the precise angle at which it must intersect its target before the Triceratops can regain the safety of the herd. The afternoon silence is shattered as the predator crashes though the low branches at the edge of the forest in hot pursuit.

T. rex has hunted Triceratops in so many books, games, and movies that the encounter has become a cliché. But did a scene like this one ever unfold in real life? Would T. rex identify its prey by vision or by smell? Would the Triceratops be warned by a loudly cracking branch, or remain oblivious because it was unable to locate the source of the sound? Could T. rex plan its attack like a cat, or would it lash out indiscriminately like a shark?

Ever since dinosaurs were first described in the early 1800s, paleontologists have debated their intelligence, sensory capabilities, and behavioral complexity. Early investigations relied on natural endocasts, which are casts formed when sediment fills the empty space in a skull. These casts replicate the shape of the braincase’s contents in life. The conventional wisdom long held that all dinosaurs had tiny brains and therefore unsophisticated behaviors. Perhaps the most amusing example of this view of dinosaur intelligence came from 19th-century paleontologist Othniel Charles Marsh, who hypothesized that the armored dinosaur Stegosaurus had a second brain near its rump to supplement the walnut-size brain in its skull. This idea was based on a vaguely braincase-shaped expansion of the spinal canal near the dinosaur’s pelvis. The mysterious expansion is now thought to represent a glycogen body—a structure that stores energy-rich glucose and occurs in a similar position in some modern birds.

Present-day paleontologists remain unconvinced that Stegosaurus was capable of much higher reasoning. But in recent years, scientists’ appraisal of the cognitive capacity of some other dinosaurs has improved, particularly that of members of the theropod lineage that gave rise to birds. With the advent of new technologies, such as micro computed tomography (CT) scanning, we can now reconstruct the volume and surface topography of brains without having to depend entirely on rare natural endocasts, greatly expanding the number of species available to study. Advanced imaging is also teaching us how dinosaurs might have used their brains. We now have the tools needed to answer the question of how long-­vanished animals perceived the world around them and what really happened when predator met prey in the age of dinosaurs.

Where did T. rex fall on the intelligence spectrum between dim-witted Stegosaurus and tool-using ravens? In a high-profile paper published last fall, neuroscientist Suzana Herculano-Houzel of Vanderbilt University suggested that a T. rex was about as smart as a baboon—a startling conclusion because primates, with their large brains, are some of the cleverest animals around. Having spent long hours pondering the way brain volume scales with body size and what this relation means for brain function in extinct dinosaurs and birds, we were intrigued to see the headlines about this study. Superficially, the brain of the tyrant lizard king looks fairly puny compared with its body size. Weighing in at less than a pound, the brain of this six-ton dinosaur is diminutive next to the 11-pound brain of the African elephant, which, despite being the largest living terrestrial mammal has a smaller body than T. rex.

Herculano-Houzel argued that the relation be­­tween brain size and body size is unimportant when it comes to intelligence. What matters, she said, is the raw number of neurons in the telencephalon, a region in the front of the brain that includes not only the olfactory bulbs that process smell but also the cerebrum, where higher cognitive functions such as decision-making occur. Scientists previously had only an imprecise understanding of how many neurons were present in vertebrate brains because in different species they can be more or less densely packed in different parts of the brain.

A T. rex with the intelligence of a primate would be terrifying. We think some caveats are in order, however.

Herculano-Houzel and Roberto Lent of Federal University of Rio de Janeiro invented a technique for counting neurons called the isotropic fractionator method. It uses special chemicals to dissolve a brain, essentially making brain soup. A fluorescent dye stains the nuclei of neurons so that they glow and are easily visible. Researchers can precisely count the glowing nuclei in a small, homogeneous sample of the soup and then extrapolate the total number of neurons in the living brain. Using this method, Herculano-­Houzel and her colleagues calculated that human brains have approximately 100 billion neurons, confirming earlier estimates.

.

Beth Zaiken

.

.

Click the link below for the article:

.

__________________________________________