Palaeozoology or paleozoology (Greek: παλαιόν, palaeon "old" and ζῷον, zoon "animal") is the branch of paleontology and evolutionary biology that specifically deal with the study of prehistoric organisms from the kingdom Animalia and the recovery and identification of their fossil remains from geological (or even archeological) contexts. The field also extends to the use of these fossil records for reconstructive phylogeny (via comparative anatomy and phylogenetics) and paleoecology, i.e. the study of ancient natural environments and ecosystems. While speculative fossils of earliest animals (in the form of primitive sponges such as Otavia) can trace back to the late Tonian period of the mid-Neoproterozoic era, definitive macroscopic metazoan remains are mainly found in the fossil record from the Ediacaran period onwards, although they do not become common until after the Cambrian Explosion, and vertebrate fossils do not become common until the Late Devonian period in the latter half of the Paleozoic era. Perhaps the best known macrofossils group is the dinosaurs. Other popularly known animal-derived macrofossils include trilobites, crustaceans, echinoderms, brachiopods, mollusks, bony fishes, sharks, Vertebrate teeth, and shells of numerous invertebrate groups. This is because hard organic parts, such as bones, teeth, and shells resist decay, and are the most commonly preserved and found animal fossils. Exclusively soft-bodied animals — such as jellyfish, flatworms, nematodes, and annelids — are consequently rarely fossilized, as these groups have few mineralized tissues that can survive geological processes, although trace fossils of their existence and activities can be preserved.
Vertebrate paleozoology Vertebrate paleozoology refers to the use of morphological, temporal, and stratigraphic data to map vertebrate history in evolutionary theory. Vertebrates are classified as a subphylum of Chordata, a phylum used to classify species adhering to a rod-shaped, flexible body type called a notochord. They differ from other phyla in that other phyla may have cartilage or cartilage-like tissues forming a sort of skeleton, but only vertebrates possess what we define as bone. Classes of vertebrates listed in chronological order from oldest to most recent include heterostracans, osteostracans, coelolepid agnathans, acanthodians, osteichthyan fishes, chondrichthyan fishes, amphibians, reptiles, mammals, and birds. All vertebrates are studied under standard evolutionary generalizations of behavior and life process, although there is controversy over whether population can be accurately estimated from limited fossil resources. Evolutionary origins of vertebrates as well as the phylum Chordata have not been scientifically determined. Many believe vertebrates diverged from a common ancestor of chordates and echinoderms. This belief is well supported by the prehistoric marine creature Amphioxus. Amphioxus does not possess bone, making it an invertebrate, but it has common features with vertebrates including a segmented body and a notochord. This could imply that Amphioxus is a transitional form between an early chordate, echinoderm or common ancestor, and vertebrates.
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