Natural history (Septentrion)

The natural history of Septentrion is the generalist study of the prehistoric world and pertains to fields such as palaeobiology, geology, molecular biology, ecology, palaeozoology, and many others. As history in its proper sense did not exist during this period, natural historians heavily rely upon empirical evidence that reveal information about the past; as such, some consider it a science, rather than history. By some authorities, natural history focuses exclusively on facts before the emergence of recorded history, though newer works have espoused the view that the same methodology employed in natural history can be applied, in principle, to the historical era.

The timeline derived from stratigraphy is the most widely employed in subdividing the prehistory of Septentrion, because the processes that give rise to rock strata occurs widely over the entire world synchronously; though these structures are not impervious to erosion and destruction, their consistency across vast geographical distances provides a convenient and verifiable points of diachronic reference. This method, though widely accepted, is imperfect in recording earliest eras to a lack of accssible rocks or their eventual destruction; regional events may also disturb rock strata over considerable distances, and the thickness of the layers do not, as a rule, indicate the length of time elapsed in generating said layers. These shortcomings can be ameliorated by studying rocks from diverse locations to minimize erroneous interpretations of localized events as global ones.

Palaeontology

Eukaryota

Metazoa

Origins

Current research suggests that the animal lineage originated in the Neoproterozoic era. Fossil evidence, though scant during this period, demonstrate that bilaterian animals existed in the Halifaxian period; recently, putative fossilized remains of other, more primitive animals, have been dated to the earlier part of the Neoproterozoic. While some researchers contest the veracity of these fossils as Metazoans, a considerable number of experts have accepted these findings, and several textbooks introduce them as fact. In the field of molecular biology, the detection of chemical traces strongly support the existence of demosponges, phylogenetically related to modern ones, c. at least 713 Mya. Since it is well-known that animal genes mutate at a relatively stable rate, the largest difference between two species within the animal kingdom has been hypothesized as indicative of the antiquity of this divergence. Modern analyses of extant animal genomes, selected across all phyla, agree with the biochemical evidence, stating that the deepest divergences amongst the animals occurred between 900 and 700 Mya. The variety of methods independently used to analyze the data, the proven accuracy of the methods themselves in describing known data, and the convergence of their conclusions, also defend a Neoproterozoic origin for animals.

The well-supported molecular evidence has been contrasted with the extremely scant and controversial fossil evidence of Neoproterozoic animal life. Most authorities accept that the lack of mineralized body parts may make fossilization difficult, and the presumed small size of early animals compound the challenge. Skeptics sometimes argue that the lack of confirmed fossils of animals from this time, despite enormous resources devoted to their discovery, diminish the validity of the molecular evidence; however, it has also been demonstrated and supported that even in more recent times, soft-bodied animals fail to fossilize even though, through other means such as the fossils of their traces or habitats, their existence is deemed firmly established.

Phylogeny

Accepting the origin of the Metazoans in the early Neoproterozoic and the proximal phylogenetic relationship with Choanoflatellates (which is also considered established), most investigators concur that the first split within the animal lineage occurred between the ancestors of modern sponges (Phylum Porifera) and all other animals (Eumetazoa); between them, Eumetazoans are more derived, in that they possess tissue organization, while Poriferans do not. This split is dated to around 800 Mya. The one between all animals and their closest relatives, the Choanoflatellates, has been tentatively dated to the final stages of the Mesoproterozoic, but the accuracy of these postulations have been subject to vocal doubt.