This is Trilobite Tuesday post #14.
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Olenellus nevadensis: An elegant member of one of the oldest trilobite families.
Trilobites were a very successful group of arthropods that existed on Earth from the early to middle Cambrian to the Permian mass extinction events. That's a span of about 275 million years. By the end, there were just a few species left and the Permian extinction swept them away along with more than 90% of species on Earth at that time. But where did the trilobites come from and when did they emerge? The American Museum of Natural History has a page on the "First Trilobites". It's an interesting page, which names possible ancestors (Spriggina floundersi) and the oldest known species (Profallotaspis and Bigotina) from remote outcrops in eastern Russia. There's also a discussion of Snowball Earth and how it potentially caused the Cambrian Explosion.
Trilobites emerged fully formed upon the Cambrian scene. By the time, some 521 million years ago, that the initial members of this ancient line of arthropods began filling oceanic environments around the globe, they were already creatures with highly developed eyes, complex digestive systems and admirably functional calcite carapaces. Quite simply, at that moment trilobites were the most advanced life forms that Planet Earth had ever produced.
Despite their sudden and dramatic appearance in the fossil record, it is obvious that trilobites evolved from earlier, more primitive organisms. Many of these ancestral creatures may have more resembled segmented worms or articulated jellyfish than the distinctive three-lobed animals that we all recognize today. Those possible early ancestors, such as Spriggina floundersi -- found in the 550 million year old Ediacaran-age rocks of Australia -- appear to have possessed rudimentary body segments and even primitive genal spines. But despite such somewhat recognizable evolutionary advances, these primeval life forms were a far cry from the Redlichid trilobites that some 30 million years later would dominate the world's seas.
The truth is that the fossil record has guarded the secrets of early trilobites -- and their immediate predecessors -- with a steadfast passion. Indeed, only a scarce few locations across the face of the planet have so far revealed themselves to be the cradles for these early “experiments” with complex life. In recent years, discoveries made in outposts such as the fossil-rich Chengjaing formation of southern China and the trilobite strongholds of central Nevada have cast additional light on this poorly understood period of earth history. But the hunt for the World's Oldest Trilobites rages on.
Cambroinyoella wallacei: Similar to the species above, this example from Nevada shows that early trilobite radiation was a wide occurrence.
Jakutus primigenius: A Siberian species that represents one of the oldest lines of trilobites.
Redlichia chinensis: This attractive pair of early trilobites provides evidence of the species' prolific nature.
Bolbolenellus brevispinus: An unusual member of the Olenellid line.
Gabriellus kierorum: A magnificently preserved Lower Cambrian trilobite found in British Columbia, Canada.
