ENCYCLOPEDIA

The following is a thorough encyclopedia of all the animals identified in the Life of a Prehistoric Animal stories:

ANIMALIA

Origins: 701 million years ago (Cryogenian period)

Extinction: Still extant

Animals are multicellular eukaryotic organisms that comprise the biological kingdom Animalia. Over 7.7 million species of animals are alive in the Holocene epoch, and a lot more existed before that. The most derived and abundant group of animals are the bilaterians, known for typically having bilateral symmetry (with some exceptions), including the echinoderms (such as crinoids), the protostomes (which include arthropods, mollusks and others) and the chordates, the latter of which is mostly comprised of the very successful vertebrates. Animals originated in the Precambrian, with many complex animal forms already appearing in the later Ediacarian, but ancestors of animals are present in the form of sponge-like fossils dating back to the much earlier Tonian period.

The word "animal" comes from the Latin animalis, meaning "having breath or soul". A synonym of Animalia is the clade Metazoa, deriving from the ancient Greek meta, meaning "later", and zōia, meaning "animal".

All animals, at some stage in their lives, are motile, with many, such as, for example, many bivalves, becoming sessile during the later stages of their life cycle. During development, the extracellular matrix of animal cells, being made of collagen and elastic glycoproteins, is a relatively flexible framework, allowing the cells to move and be reorganised, permitting the creating of complex cellular structures. Most animals have an internal digestive chamber, sometimes with just one opening, but, in the case of bilaterians, mostly two openings. Most animals make use of some form of sexual reproduction. They produce haploid gametes that fuse to form zygotes, which develop via mitosis into a blastula. The blastula undergoes extensive rearrangements, in derived animal groups, forming invaginations for the digestive chamber, and separate germ layers for the internal endoderm, the external ectoderm and often a middle layer called the mesoderm.

Animals can characterize themselves in relation to their eccological relationships, with trophic levels designated for the way each animal consumes its own organic material. Because often animals find food by eating other animals, selective pressures have evolved over millions of years in the form of an evolutionary arms race between predators and prey, creating complex arrays of competitive co-evolution, leading to the dramatic diversity of animals we know from more recent time periods. Many animals rely on the biomass and bioenergy produced by autotrophs, such as phytoplankton or macroscopic plants. This is mostly possible in areas with abundant sunlight, though in the depths of the ocean, animals that live close to hydrothermal vents and cold seeps will consume organic matter produced via chemosynthesis by archaea and bacteria. Animals can survive in most conditions planet Earth has to offer, except extreme temperatures such as very hot or very cold ones.

The early origins and evolution of animals are shrouded in mystery, specially given the earliest fossil records of these organisms are fragmentary, with sudden burst of diversity being recorded in the fossil record, such as the iconic Cambrian explosion, which might just be a result of a sudden appearance of favourable preservational conditions for fossils to form, instead of a literal diversification episode from that point in time. Fossils from the Precambrian seem to corroborate that hidden diversification periods were occurying before the Cambrian period, including the generation of the very first predatory animals. Although crown animals likely evolved around the early Cryogenian period, a period when Earth was in an intense icehouse episode, Tonian fossils suggest animal-like forms may have been present before, including trace fossils indicating advanced worm-like burrowing forms (though those could have just been produced by "protists", instead).

The closest extant relatives of animals are the "protist" choanoflagellates, likely splitting from them some 782 million years ago, during the Tonian. Their common ancestor would be a unicellular eukaryote that would eventually develop into a multicellular lineage as it evolved into animals. The exact phylogeny of modern animals is somewhat debated, specially in bilaterians, as deuterostomes (the group that includes chordates and echinoderms) may actually be paraphyletic in respect to protostomes, with echinoderms being part of a more basal group named Xenambulacraria, with chordates being the closest relatives to protostomes. Outside of Bilateria, however, debates surround which deserves the title of the most basal animal, with a few studies being against the traditional view that sponges are the most basal animals, instead giving that title to the comb jellies (or ctenophores). Regardless, sponges likely unite the plesiomorphic characteristics of the first animals, as simple cellular structures, draining water from pores and filtering out food and nutrients from their aqueous surroundings. Animal evolution culminates in the most diverse clade, the Bilateria, which tend to have a bilateral symmetry, and contain nearly 30 extant phylla and over a million described extant species. The bilaterians are triploblastic, meaning they have three well developed germ layers, and tissues that form different and varied organs. Bilaterians also tendentially form a front and back end, as their shape tends to be rather worm-like, and a front end implies a greater array of stimuli, such as the interaction with food, favouring the evolution of a head with sensory organs and a mouth. Although that's the standard condition for bilaterians, there are ones that have evolved away from these trends, such as echinoderms, which have a typically radial symmetry. Although deuterostomes might be paraphyletic, they differ from the certainly monophyletic protostomes in the formation of the mesoderm, where cells fill the interior of the gastrula to form it, in a proccess called schizocoelous development. Deuterostomes instead develop the mesoderm via entercoelic pouching, which consists of invagination of the endoderm. Echinoderms are an example of a deuterostome clade, including several animals, such as the crinoids, with chordates being another, this one including the vertebrates. Inside the protostomes, there are two groups, the Spiralia and the Ecdysozoa, with the ecdysozoans typically having ecdysis (i.e. growth by moulting) and also having a body with repeating segments, often with paired appendages. The Spiralia has a more complicated internal phylogeny, but it traditionally contains the Lophotrochozoa, and smaller groups such as the Rouphozoa. Lophotrochozoans include, among others, the mollusks, the second largest animal phyllum that includes the snails, bivalves and cephalopods, and the annelids, which are mostly segmented worms of varied eccologies.

Humans tried to classify animals since the antiquity, but the origins of the modern classification methods came in 1758, with Carl Linnaeus' first hierarchical classification in his Systema Naturae. Jean-Baptiste de Lamarck also made his own take in classifying animals, for his Philosophie Zoologique, in 1809, designating four phylla for vertebrates (mammals, birds, reptiles and fish), and another nine phylla for other creatures: mollusks, annelids, crustaceans, arachnids, insects, worms, radiates, polyps and infusorians.

Eventually our understanding of animals has evolved a lot since, and so did our relationship with other animals themselves, with our impact in the biomass being so severe that even our livestock comprises over 90% of that of all living mammals in the planet, and almost as much as that of all living insects. Humans have gone a long way since our early search to hunt other animals for their fur and skin to make clothing. Now we monopolize the animal world with the species that most favour our survival and comfort (never before has the dog, cat or rabbit become such a ubiquitous animal in this planet). Our intelligence goes now way beyond our understanding of other animals as merely things, as we now consider ourselves as part of them and perhaps also deserving of the same rights. They have long inspired our understanding of the world and the way we express ourselves, even artistically, to make sure we can appreciate their lives in the most spectacular fashion.

main source: Wikipedia

List of animals in The Life of a Prehistoric Animal