Evolution of the Aerial "Critter" fauna
The story of the first aerial organisms starts about 560 million years ago, just after the Cambrian explosion. At this time there was a high diversity of invertebrate life in the oceans, and this appears to have catalysed the very first steps towards the aerial fauna of today. Fossils recording this transition are very rare, so the current hypothesis is partly speculative.
It seems that the prevalence of aquatic predators in the Cambrian oceans forced some kinds of invertebrate to switch from a passive surface-swimming lifestyle, to that of an airborne floater. The first ancestral critters were various Ctenophore, Siphonophore, and Medusozoan jellyfish, which floated or swam near the surface, basking in the sun. Through internal symbiosis with certain algae, they were able to photosynthesize in order to feed. Antagonism from aquatic predators below ultimately forced some of these forms to take to the air. They evolved large balloon-like gas bags, filled with buoyant gases, which enabled them to float in the air up to several meters above the water. Soon after this, they evolved waxy secretions that prevented desiccation, now that they were out of the water. The Ctenophores eventually evolved a rear opening that would allow them to gulp air into their mouth and shunt it out the rear, enabling them to move about more vigorously.
Eventually, these floating green jellies formed an ecosystem contained in the air above the ocean’s surface, becoming as thick as 6 or 7 meters. The larvae of these forms produced a soup-like mist which encouraged the evolution of the first predatory airborne Ctenophores and Medusae. This thick cloud of larva was the first step towards the aeroplankton which would later evolve. Eventually, this opaque surface-hugging belt of floating animals drew other forms of invertebrate to take to the air, to pursue them as food. Dinocaridian and Chelicerate arthropods, as well as Polychaete worms and free-swimming molluscs, began to evolve wing-like organs and air pockets inside their bodies, to enable them to “swim” in the air”.
From these beginnings, the aerial fauna became steadily more advanced. Most kinds developed glands and organs that were ever better at producing buoyant gases to enable their flight, in some cases these are stored in large bladder-like sacs, and in other cases in air pockets throughout the body. Some (including the air jellies) evolved improved vision, and with this, eventually came the evolution of light-producing organs. Light emitting organs would serve to aid communication, to bluff predators, and to attract small prey within reach.
As the Ordovician waned, the aerial fauna evolved towards colonising the upper reaches of the troposphere, and eventually the stratosphere. This was facilitated by the evolution of the aeroplankton, a nutrient-rich medium formed from critter larvae as well as many kinds of tinier critters, much like the plankton of the earth’s oceans..
As the colonisation of the land began in the Devonian, most aerial fauna that still lived near the surface was eventually out-competed by the animals and plants. By the Triassic, the aerial fauna was restricted mostly to the uppermost troposphere and the stratosphere. Eventually however, some aerial fauna would re-colonise the surface, becoming certain elusive and sparsely populated forms.
It seems that the prevalence of aquatic predators in the Cambrian oceans forced some kinds of invertebrate to switch from a passive surface-swimming lifestyle, to that of an airborne floater. The first ancestral critters were various Ctenophore, Siphonophore, and Medusozoan jellyfish, which floated or swam near the surface, basking in the sun. Through internal symbiosis with certain algae, they were able to photosynthesize in order to feed. Antagonism from aquatic predators below ultimately forced some of these forms to take to the air. They evolved large balloon-like gas bags, filled with buoyant gases, which enabled them to float in the air up to several meters above the water. Soon after this, they evolved waxy secretions that prevented desiccation, now that they were out of the water. The Ctenophores eventually evolved a rear opening that would allow them to gulp air into their mouth and shunt it out the rear, enabling them to move about more vigorously.
Eventually, these floating green jellies formed an ecosystem contained in the air above the ocean’s surface, becoming as thick as 6 or 7 meters. The larvae of these forms produced a soup-like mist which encouraged the evolution of the first predatory airborne Ctenophores and Medusae. This thick cloud of larva was the first step towards the aeroplankton which would later evolve. Eventually, this opaque surface-hugging belt of floating animals drew other forms of invertebrate to take to the air, to pursue them as food. Dinocaridian and Chelicerate arthropods, as well as Polychaete worms and free-swimming molluscs, began to evolve wing-like organs and air pockets inside their bodies, to enable them to “swim” in the air”.
From these beginnings, the aerial fauna became steadily more advanced. Most kinds developed glands and organs that were ever better at producing buoyant gases to enable their flight, in some cases these are stored in large bladder-like sacs, and in other cases in air pockets throughout the body. Some (including the air jellies) evolved improved vision, and with this, eventually came the evolution of light-producing organs. Light emitting organs would serve to aid communication, to bluff predators, and to attract small prey within reach.
As the Ordovician waned, the aerial fauna evolved towards colonising the upper reaches of the troposphere, and eventually the stratosphere. This was facilitated by the evolution of the aeroplankton, a nutrient-rich medium formed from critter larvae as well as many kinds of tinier critters, much like the plankton of the earth’s oceans..
As the colonisation of the land began in the Devonian, most aerial fauna that still lived near the surface was eventually out-competed by the animals and plants. By the Triassic, the aerial fauna was restricted mostly to the uppermost troposphere and the stratosphere. Eventually however, some aerial fauna would re-colonise the surface, becoming certain elusive and sparsely populated forms.