Human Dinosaurs Psittacosaurus Went from Moving on Four Feet to Two

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Christian Science Monitor reports that new research suggests that the Psittacosaurus, or “parrot dinosaur,’” went from moving on four feet to two about 100 million years ago, in a region now part of China. Walking upright on two legs might have made human dinosaurs.

Qi Zhao, a Ph.D. student at the University of Bristol and also a researcher at the Institute for Vertebrate Paleontology in Beijing, studied a total of 16 fossil specimens of Psittacosauses that generally varied in age from 1 to 10 years old. Specimens of the 1-year-old Psittacosauses show that they might have developed like a modern human being, starting on all fours and then standing and walking.

The findings were published in the scientific journal Nature Communications. Indications are that Psittacosauruses had evolved over time from four-legged adults to two-legged adults, adapting to environmental pressures.

The Psittacosaurus has been dubbed: the Lizard King,” after a song by Jim Morrison and the Doors on the album “Waiting for the Sun,” which contains the couplet “I am the Lizard King / And I can do anything.”

We know that a significant event in evolution occurred when animals climbed out of the water to live on the land.  Mammals started out as tetrapods, or four-legged animals.  Most mammals are still traveling on four legs.  But a bipedal species has evolutionary advantages.  It has a better view of approaching predators, can wade into deeper water for fish, and reach up higher to snag fruit from the trees.  In order to stay upright (and keep moving), the hipbones in humans needed to be changed from a locomotive device (helping to use the back legs to travel) to a load-bearing one (keep the top half on top).  Bipedalism allowed reduce the amount of skin exposed to the tropical sun, which helped to avoid hyperthermia. It freed up our hands and arms for tool making.  This practice is s estimated to have started about 2.6 million years ago.

Bipedalism saved energy during locomotion, enabling long distance running and hunting.  Humans had to walk, because climatic conditions forced them to come down from the trees to the savannas in order to search for water and food. They had to hurry in order to evade predators. Or at least try to.

Bipedalism caused humans to develop bigger brains.  Encephalization refers to the tendency for a species to increase brain size through evolutionary time. The rapid increase in brain size occurred about 500,000 years ago.

But bipedalism may have preceded encephalization.  It may have started when Homininae, the tribe that includes the human clan, disassociated themselves from the Panini tribe.  The Panini tribe was composed of chimpanzees. Compared to the chimpanzee brain, the human brain is not only larger, but certain brain regions were particularly altered during human evolution. In any event, humans are the only Homininae that survived.

Dinosaurs might have been human, and humans dinosaurian, in their ability to stand up, but how did bipedalism make us particularly human?

The early bipedals eventually evolved into the australopithecines and later the genus Homo. Australopithecines lived between the Pliocene (5.332 to 2.588 million years ago) and the Pleistocene (2,588,000 to 11,700 years ago) epochs.  Homo is the genus of great apes that includes modern humans and species closely related to them. The genus is estimated to be about 2.3 to 2.4 million years old.

The best advantage of walking upright is that it provided more energy for brain development.   About two percent of body weight uses 20% of the body’s energy.  More available energy had the effect of developing the prefrontal cortex in humans, the area of the brain that governs executive functions, such as solving problems and inhibiting emotional impulses.  It permitted humans to interpret life and make predictions based on past experiences.  It also allowed them to ascribe motivation to others, which helped in the socialization process.  (John Medina, Brain Rules).  Humans began to gather together between 1 million to 800,000 years ago.  They were communicating by means of symbols 250,000 years ago.

Bipedalism may have been the time of sexual dimorphism in humans, which concerns the differences in the sexes.  Dimorphism is particularly evidenced by variances in their brains.  Men have larger brains on average than women, but women have a higher percentage of gray matter.  Comparing size to gray matter, the differences even out.  Still, recent studies have shown that men use more of their brains than women in the same mental tasks.

Strutting along on two legs might have increased the adaptive abilities of both humans and dinosaurs, and made them cousins, but dinosaurs gained extinction, and the human population grew from a few thousand to seven billion.


By:  Tom Ukinski


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