Overall dossier about Premollidian biota

Every story has a beginning

This is the first chapter in Tahdora's life and therefore can't be discarded like some junk in a history.

Probably I should begin with the definition of Premollidian supereon ("before-soft") period. Briefly speaking it is a pretty big time interval. Everything that was before the beginning of Mollidian period ("soft period") is called premollidian. The boundary between them is the appearance of the first macroscopic predator. Premollidian is divided into shorter time intervals, which correspond to Hadean, Archean and Proterozoic eons of Earth, but it isn't as interesting for us as for Tahdorean's geologists.

Premollidian biota is the very first biota of the planet. The very basal clades appeared during this period of time, whose representatives or descendants are still alive. If we compare history of Earth and Tahdora, we'll find that the time of appearance of first macroscopic living organisms on Tahdora roughly corresponds to Ediacaran period on Earth.

One of the very basal clades is Greenbodied (Viridicorpusae). They are similar to our plants, as they are photosynthetic organisms too, but emerged independently on the planet. Their bulk was represented by unicellular organsisms on the whole surface of ocean until the Late Premollidian. Then multicellular forms have emerged and immediately divided into three groups. Membranous (Membranocorpusae) were not attached to anything and were just green membranes several cells thick floating on the ocean's surface. One-leafed (Unifolia) were attached fungi-like organisms that have chosen the shallow waters' seabed near shores and river mouths to be their main habitat. Also there was one group of purely planktonic multicellular Greenbodied - Dipetals (Dipetalae). As follows from their name, their body consists of two petal-like leaves and a small bridge between them. They are extremely spread everywhere where plankton can exist. They are usually the base of most food chains and marine ecosystems.

Water filter niche could not always be empty, too. The main representative groups were One-pharyngeal (Unifaucea) and Tentacle-leafed (Tentaculofolia). One-pharyngeal have found their place both in upper layer of the water column and on the seabed (attached forms). Their bodyplan is relatively simple: a capsule with the only one mouth opening, covered in cilia and sometimes having a bunch of flagellas on the bottom side. They create water currents for their needs with cilia in their only cavity. Attached forms do not have flagellas in adulthood, and there are external glands in their place which help organism to cling to the substrate.

Tentacle-leafed are rather simple organisms, radially symmetrical or asymmetrical. Their main body looks like flapjack burrowed into the substrate. They filtrate water with their long tentacles, which are often flattened, covered with ciiia and "leaf"-ended. Their "leaves" are usually even more flattened and wide.

There were also animals eating microbial mats accumulated over long millions of years - Libozoans. They were strongly similar to ediacaran organisms, such as Dickinsonia. Later representatives are also segmented, have simple eyes and a tendency to cephalization.

Clades mentioned above are main members of all premollidian ecosystems until the beginning of Mollidian period. In general, the situation in ocean in this time period can be characterized as "peaceful". Complete absence of macroscopic predators contributed to flourishing of filter-feeding and microbial mats-devouring species. There was no need in defense mechanisms.

But this situation could not last forever. Shortly before the beginning of Mollidian a new group takes almost all possible zooplankton niches - Branchopods (Branchopodae). These small "worms" with gills on their legs were only a few millimeters long, nevertheless soon they occupied all possible habitats. A very diverse group included planktonic forms, both herbivorous and carnivorous types, and bottom microorganisms. Their emergence incredibly affected all underwater life, especially in Mollidian, but we will talk about it in a next chapter.