The ArcBuilder Universe

 

TimeLine of the ArcBuilder Universe

 

The Pre-Galactic Civilization

390 to 363 million years ago

 

390 million years ago:  A group of fresh-water fish, the Sarcopterygii, evolve lobed fins to aid them in moving about on the bottom of lakes and rivers in order to search for food.  Living in largely shallow water habitats that were choked with plants and detritus, as well as possessing upward facing eyes atop a wide and flat skull, they were finely adapted to this ecological niche, feeding on everything from plants to mud-dwelling creatures to other fish.  In time, however, these lobed fins would evolve into very early primitive legs, allowing for more efficient movements under water as well as providing limited mobility on the shoreline, where more untapped food sources might be found.  While the legs were small and weak, they were nonetheless true limbs, and represented the earliest method of vertebrate terrestrial habitation, however transitory.

The earliest known genus of transitory lobed-finned fish and tetrapods  was Pandericthys.  Its habitat extended from fresh water to tidal flats and estuaries, where it preyed on a wide variety of creatures, including jawless fish and other lobed-finned fish.  Indeed, its pursuit of the latter may have aided in its further adaptations for terrestrial movement.  This genus of animal, and the Sarcopterygians in general, were capable of drawing oxygen from the air as well as the water.  Because of the relatively low oxygen levels of the time, this would have been a decided evolutionary advantage. 

375 million years ago:  The lobe-finned fish Tiktaalik evolves, and represents a clear link between the former Pandericthys and later tetrapod forms.  Unlike previous forms, this genus possessed basic wrist bones and simple rays very reminiscent of fingers.  Their fins were weight bearing structures, with large scapular and coracoid elements.  These adaptations allowed the animal to live at the bottom of water bodies with fast currents.  An expanded and more robust rib cage, as well as the earliest form of a true neck would have aided the animal while outside of the water as far as breathing and hunting were concerned.  Living in swampy environments, Tiktaalik could easily move out of the water and over mudflats for fair distances, in search of both prey and other bodies of water.  This was a major evolutionary step in the exploitation of the land.
365 million years ago:  One of the earliest known true amphibians, Acanthostega, evolves.  It possessed four recognizable limbs, though they were poorly developed and not capable of supporting the animal's weight while outside of the water.  As such, its habitat tended to be weed-choked swampland, where it used its limbs for bottom-dwelling locomotion.


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The ArcBuilder Universe is a science fiction project established, authored, and copyrighted ©
by John M. Dollan 2002-2016
This page first uploaded in February 13, 2016
Most recent update for this page February 13, 2016