MoAW Weekly Spotlight - Ancestral Mammals During The Age Of Dinosaurs

January 29, 2021

Spotlight:

Ancestral Mammals During

The AGE OF DINOSAURS

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“Why has not anyone seen that fossils alone gave birth to a theory about the formation of the earth, that without them, no one would have ever dreamed that there were successive epochs in the formation of the globe.” ― Georges Cuvier, French Naturalist, 1769 - 1832

THE TRIASSIC PERIOD

from 230 million years to 195

million years ago

There were no flowers or grasses at the beginning of the Triassic Period (named for a tri-layered sequence of strata first discovered in southern Germany). Surrounded by a vast ocean, the supercontinent of Pangaea almost entirely circled the globe at the equator. Identical fossil remains found as far apart as Africa and North America suggest that the fauna of this period roamed freely across vast expanses of land that are now separated by the oceans. The Triassic marked the dawning of the Mesozoic (“Middle Life”) era or the Age of Dinosaurs. Because much of Pangaea lay along the equator, climates were generally tropical, and warm, ferny swamps teemed with primitive amphibians and crocodiles. In the arid desert regions, reptiles flourished with the extinction of mammal-like reptiles, producing the highly successful archosaur group which gave rise to crocodiles, pterosaurs, and a new kind of animal gradually appearing in the Late Triassic fossil record: the Dinosauria (“Terrible Lizards”), which continued to appear in increasing varieties for the next 140 million years. Due to the drifting of the Earth's crust and rising ocean levels, the gradual breakup of Pangaea beginning at the end of the Triassic globally separated dinosaur populations along with the first true mammals, tiny burrowing descendants of the mammal-like reptiles.

Order Therapsida,

Infraorder Cynodontia

Thrinaxodon liorhinus

Early Triassic, South Africa

The transition from synapsid reptiles to mammals was gradual rather than a quantum leap. Replacing gorgonopsids as the dominant predators of the Early Triassic, cynodonts were small, fox-like creatures with fewer reptilian characteristics than their ancestors. Although exhibiting tiny pits in their skulls which appear to have held whiskers and possessing a palate separating the nasal passages from the mouth, distinctly mammalian features, the primitive reptilian jaw structure of cynodonts retained certain prominent bones that became greatly reduced in mammals and incorporated into the inner ear. Extremely close to the ancestry of the mammals, this group included Thrinaxodon, an advanced therapsid of the forest of Antarctica and the South African Karroo.

Equipped with prominent canine teeth as well as other dental features characteristic of early mammals, Thrinaxodon is widely regarded as the original stock from which they arose. Two skulls from the Karroo Formation. University of California at Berkeley

Class Reptilia

Subclass Therapsida

Dicynodon grimbeeki

Middle to Late Permian, South Africa

For about 10 to 15 million years, great herds of these fat, little mammal-like therapsids inhabited South Africa, Russia, Scotland, Asia, and the Americas, apparently reproducing at an extraordinarily prolific rate. Found in the red beds of the South African Karroo Formation, these 3 specimens are the remains of creatures that once flourished throughout a region that was considerably closer to the South Pole during Permian times than it is now. In order to survive the severe Karroo winters, they may have evolved some kind of furry insulation.

Although they were probably the first successful group of herbivores among the vertebrates, equipped with horny beaks and tusk-like upper canines, by the end of the Permian Period to the Middle Triassic, the herds of Dicynodons (“Double Dog Tooth”) had dwindled to extinction, survived by a few relatives which evolved into early mammals. From the famous Karro Formation. University of California, Berkeley.

The Evolution Of The First Mammals

Fossilized glider takes the origin of mammals back to the Triassic.

MoAW's mission is to educate a diverse audience about the history of ancient civilizations and prehistoric life using fossils and artifacts from a variety of cultures and time periods; to enhance universal curriculum development for local and surrounding school districts, colleges, and universities while offering tourist incentive for the Coachella Valley's hospitality industry.

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