In the oceans, the Carboniferous is called the Golden Age of Sharks, and ray-finned fish arose to a ubiquity that they have yet to fully relinquish. Ray-finned fish probably prevailed because of their high energy efficiency. Their skeletons and scales were lighter than those of armored and lobe-finned fish, and their increasingly sophisticated and lightweight fins, their efficient tailfin method of propulsion, changes in their skulls, jaws, and new ways to use their lightweight and versatile equipment accompanied and probably led to the rise and subsequent success of ray-finned fish in the Carboniferous and afterward. , which are amoebic protists, rose to prominence for the first time in the Carboniferous. Reefs began to recover, although they did not recover to pre-Devonian conditions; those vast Devonian reefs have not been seen again. did not appear until the . Trilobites steadily declined and nautiloids familiar today, and straight shells became rare. The first , which were ancestral to squids and octopi, first appeared in the early Carboniferous, but some Devonian specimens might qualify. Ammonoids flourished once again, after barely surviving the Devonian Extinction. This essay is only focusing on certain prominent clades, and there are many and . The early Carboniferous, for example, is called the Golden Age of , which are a kind of , which is a phylum that includes starfish. The crinoids had their golden age when the fish that fed on them disappeared in the end-Devonian extinction. Earth’s ecosystems are vastly richer entities than this essay, or essay, can depict.
So far in this essay, mammals have received scant attention, but the mammals’ development before the Cenozoic is important for understanding their rise to dominance. The , called , first , about 260 mya, and they had key mammalian characteristics. Their jaws and teeth were markedly different from those of other reptiles; their teeth were specialized for more thorough chewing, which extracts more energy from food, and that was likely a key aspect of success more than 100 million years later. Cynodonts also developed a secondary palate so that they could chew and breathe at the same time, which was more energy efficient. Cynodonts eventually ceased the reptilian practice of continually growing and shedding teeth, and their specialized and precisely fitted teeth rarely changed. Mammals replace their teeth a . Along with tooth changes, jawbones changed roles. Fewer and stronger bones anchored the jaw, which allowed for stronger jaw musculature and led to the mammalian (clench your teeth and you can feel your masseter muscle). Bones previously anchoring the jaw were no longer needed and . The jaw’s rearrangement led to the most auspicious proto-mammalian development: . Mammals had relatively large brains from the very beginning and it was probably initially . Mammals are the only animals with a , which eventually led to human intelligence. As dinosaurian dominance drove mammals to the margins, where they lived underground and emerged to feed at night, mammals needed improved senses to survive, and auditory and olfactory senses heightened, as did the mammalian sense of touch. Increased processing of stimuli required a larger brain, and . In humans, only livers use more energy than brains. Cynodonts also had , which suggest that they were warm-blooded. Soon after the Permian extinction, a cynodont appeared that may have ; it was another respiratory innovation that served it well in those low-oxygen times, functioning like pump gills in aquatic environments.
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Here is a brief summary of this essay. Ever since more than three billion years ago and about a billion years after the Sun and Earth formed, organisms have continually invented more effective methods to acquire, preserve, and use energy. after three billion years of evolution and, pound-for-pound, it used energy . The story of life on Earth has been one of , and in turn influencing them. During the eon of complex life that began more than 500 million years ago, there have been many brief for some fortunate species, soon followed by increased energy competition, a relatively stable struggle for energy, and then cleared biomes and set the stage for another golden age by organisms adapted to the new environments. Those newly dominant organisms were often marginal or unremarkable members of their ecosystems before the mass extinction. That pattern has characterized the journey of complex life over the past several hundred million years. among some animals, which provided them with a competitive advantage.