Dwarf goat more reptile than mammal

Myotragus balearicus, also known as the "mouse goat," is shown in a reproduction at CosmoCaixa in Barcelona.
Myotragus balearicus, also known as the "mouse goat," is shown in a reproduction at CosmoCaixa in Barcelona.Xavier Vazquez
/ Source: Discovery Channel

What had bones like a crocodile and grew like a crocodile, but was a goat? The answer, according to a new study, was the now-extinct Myotragus, also known as "mouse goat."

The tiny goat, which stood about 19 inches tall at the shoulder, took on characteristics of cold-blooded reptiles, a first for a mammal, in order to survive life on the island of Majorca, where food sources were few and far between.

In doing so, the Plio-Pleistocene goat left behind at least five attributes associated with many warm-blooded mammals: relatively fast movement, high growth rates, keen senses, high metabolism and fairly big brains.

"(Myotragus) not only decreased aerobic capacities and behavioral traits, but also flexibly synchronized growth rates and metabolic needs to the prevailing resource conditions as do ectothermic reptiles," researchers Meike Kohler and Salvador Moya-Sola wrote in a study published in the latest Proceedings of the National Academy of Sciences.

"Although frequently thought of as primitive, (cold-blooded animals) are actually specialists in coping with low levels of available energy," the researchers noted. In other words, the goat wasn't somehow de-evolving into a lower reptilian state, but instead did what it had to do for survival on the near food-less Mediterranean island.

For the study, Kohler and Moya-Sola, both Autonomous University of Barcelona paleontologists, analyzed bones for the now-extinct goat, as well as bones for crocodiles and deer, all from the same general time period and location.

The bones of cold-blooded reptiles, such as the crocodiles, have parallel growth lines that cyclically come to a halt before starting up again characterizes. Similar to tree rings, these lines match the growth cycles of animals.

Warm-blooded species, on the other hand, exhibit uninterrupted, fast bone growth.

High magnification revealed the dwarf goat's bones were more like those of a crocodile, so Myotragus grew low and slow.

The bone microstructure further indicates the goat attained sexual maturity late, at around age 12, according to the scientists, and had an extended life span.

In addition to shedding light on what was once called the "odd goat," the findings may also help to explain other dwarf mammals, such as elephants and hippos, which have also been found on islands.

These mini-sized animals seem to have evolved in environments that had few predators, yet also few resources. Unlike most mammals, the tiny island dwellers probably didn't need to evolve highly attuned senses and swift moves to elude predators.

Since much of the brain handles the five senses, their brains may have shrunk to fit their requirements.

Maria Rita Palombo of Sapienza University of Rome led an earlier study that determined the small goat did indeed undergo "a significant reduction in relative brain size, especially affecting the vision and locomotor centers."

The petite, slow-moving and small-brained goats persisted for 5.2 million years on Majorca, but one encounter forever wiped them off the face of the earth.

"Myotragus did not survive the arrival of a major predator, Homo sapiens, some 3,000 years ago," Kohler and Moya-Sola conclude.