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Animals - Kingdom: Animalia
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Photo by E.Beringen
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“The wild things of this earth are not ours to do with as we please. They have been given to us in trust, and we must account for them to the generation which will come after us and audit our accounts.” - William Temple Hornaday, founder of the American conservation movement, 1854-1937.
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The word 'animal' is derived from the Latin 'animalis' meaning 'to have breath' or 'to have soul' and members of the Kingdom: Animalia are all multi-cellular, eukaryotic organisms that can be distinguished from other lifeforms by a number of features. Nearly all animals breathe (of those that do, most breathe oxygen), and all have the ability to move of their own accord at some stage of their life (with some becoming sessile in later stages). Animals are heterotrophic, they eat and digest other organic material. Most tellingly though, all animals go through an embryonic stage called the 'blastula'. This is the first stage in a sequence that eventually allows embryonic cells to differentiate into specialized cells that form tissues and organs.
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Image 1. After fertilization of the egg, the cells multiply to form a clump of cells first (1) which later develops into the hollow balll that is the blastula. (2)
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Despite the similarities in embryonic development and the fact that all animals currently living share well over 6,000 groups of genes - which possibly came from a single, common ancestor - the Kingdom: Animalia shows enormous variety both in size and form. From the smallest, the Cnidarian Myxobolus shekel, which measures a mere 8.5 micrometres (or 0.0085 millimetres) to the largest ever, the Blue Whale Balaenoptera musculus, which, at as much as 33 metres in length may tip the scales at up to 190 metric tonnes.
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The earliest animals appeared in the Earth's seas and started moving onto land at some time around 530 Myo. Arthropods were among the first of these colonists and it took about 130 My for the vertebrates to follow. Near complete penetration of our world's habitats was accomplished relatively soon after the first land animals appeared and yet there will always be pockets where animal life cannot be sustained. These pockets - as temporary as they often are - usually have high prevailing temperatures. (Most animals perish in constant 50plus degrees heat.)
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Estimates of the number of animals and other species on Earth have varied wildly over the years with numbers ranging from 3 to 100 million. Studies from the year 2011 however, appear to have pinned the numbers a bit more accurately and yielded the following outcomes. (Numbers are from 2011 and rounded the nearest 1000 where suitable) About 7.77 million species of animals with nearly 1 million described and catalogued. By comparison, the remaining four Kingdoms contained, as of 2011, just under 1 million species, combined. Fungi came in at ~611,000 (~43,000 described), Plants at ~298,000 (~216,000 described), Protozoa at ~36,400 (8,000+ described) and Chromista at ~27,500 species (~13,000 described). As you can see animal species outnumber all other species by nearly 8 to 1. Marine species are a minority as well with about 25 % of all species in the five Kingdoms being confined to the world's seas. At the time of the study only about 1 in 7 species was known to science, i.e. described and catalogued, since the introduction of the binominal system of Linnaeus in 1758. To be fair, the pace at which additional species are added to the scientific database has quickened substantially since new techniques using DNA became more commonplace.
Continued below.
Currently the Kingdom: Animalia is divided into 33 phyla although this may soon be only 32 once the Acanthocaphala and the Rotifera are merged. Even though members of most phyla are likely to be found in the Northern Rivers, not all are covered here in detail. Some phyla contain species too small or too scarce to be encountered.
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There is no clear answer as to when animals started to evolve. During an era known as the Cambrian Explosion a large variety of animals representing various phyla, started to appear in the fossil record. All this from about 539 My ago and onwards. The absence of animal fossils from earlier periods does not mean there were no animals though. Fossils found in the Trezona Formation in South Australia have been identified but not confirmed, as 'sponge-grade metazoans' and are dated as 610Myo. Older trace fossils have been found, some as old as 1.7 Gya but, their interpretation is not agreed upon by all.
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Image 2. Fossil Spriggina of the Ediacara biota
from the Houston Museum of Natural History, Houston, Texas. Photo by Daderot
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The oldest identified and confirmed animal fossils date from the Ediacaran era, 578-538 My ago. They were first discovered by the South Australian geologist and conservationist, Reginald Sprigg in 1946. The areas where the fossils were - and continue to be - found have become so significant to our understanding of Pre-Cambrian life that they are now heritage protected. Since the original discovery in South Australia, Ediacaran fossils have also been found in Ukraine, Russia, India and China.
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William Temple Hornaday (see the quote at the top of the page) was an American hunter and taxidermist who worked for the Iowa State Agricultural College and Ward's Natural Science Establishment in Rochester, New York. In 1886, when it was generally accepted that the American Bison would soon be extinct, he was sent to Montana to collect specimens to be mounted and used in a display at the U.S. National Museum. This journey became the inspiration for Hornaday's book, "The Extermination of the American Bison." which itself was the catalyst that eventually led to a major conservation effort to save the American Bison as well as as other popular game animals. You can find the book HERE.
References and links:
> Image 1. Blastulation. image by Pidalka44 CCO, via Wikimedia Commons
> Image 2. <a href="https://commons.wikimedia.org/wiki/File:Spriggina,_Ediacaran_metazoan,_Vendian,_Ediacara_Hills,_south_Australia_-_Houston_Museum_of_Natural_Science_-_DSC01385.JPG">Daderot</a>, CC0, via Wikimedia Commons
> Bobrovskiy, I., Hope, J.M., Ivantsov, A., Nettersheim, B.J., Hallmann, C., Brocks, J.J., (2018). 'Ancient steroids establish the Ediacaran fossil Dickinsonia as one of the earliest animals.' Science. 361 (6408): 1246–1249.
> Census of Marine Life. 'How many species on Earth? About 8.7 million, new estimate says.' ScienceDaily. ScienceDaily, 24 August 2011. <www.sciencedaily.com/releases/2011/08/110823180459.htm>.
> Cohen, K.M., Harper, D.A.T., Gibbard, P.L., (2022). ICS International Chronostratigraphic Chart 2022/10. International Commission on Stratigraphy, IUGS. www.stratigraphy.org (visited: 2022/12/08)
> Hornaday, W.T., (1889). 'The Extermination of the American Bison.' Government Printing Office, Washington.
> Linnaei, C., Sveci, Doctoris Medicinae, (1735). 'Systema Naturae, sive, Regna tria naturae systematice proposita per classes, ordines, genera, & species.'
Apud Theodorum Haak :Ex Typographia Joannis Wilhelmi de Groot, Lugduni Batavorum (= Leiden, the Netherlands).
> Maloof, A., Rose, C., Beach, R. et al. (2010). 'Possible animal-body fossils in pre-Marinoan limestones from South Australia.' Nature Geosci 3, 653–659 (2010). https://doi.org/10.1038/ngeo934
> Mora, C., Tittensor, D.P., Adl, S., Simpson, Alastair G.B., Worm, B., (2011). Mace, Georgina M. (ed.). 'How Many Species Are There on Earth and in the Ocean?' PLOS Biology. Version 9 (8): e1001127.
https://inaturalist.ala.org.au/taxa/1-Animalia
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3160336/
https://stratigraphy.org/
https://upload.wikimedia.org/wikipedia/commons/2/2c/Spriggina%2C_Ediacaran_metazoan%2C_Vendian%2C_Ediacara_Hills%2C_south_Australia_-_Houston_Museum_of_Natural_Science_-_DSC01385.JPG
https://en.wikipedia.org/wiki/Cambrian_explosion
https://en.wikipedia.org/wiki/Cellular_differentiation
https://en.wikipedia.org/wiki/Ediacara_Hills
https://en.wikipedia.org/wiki/Heterotroph
https://en.wikipedia.org/wiki/Reg_Sprigg
https://en.wikipedia.org/wiki/Sessility_(motility)
https://en.wikipedia.org/wiki/Smallest_organisms#Eukaryotes_(Eukaryota)
https://en.wikipedia.org/wiki/Trace_fossil
https://en.wikipedia.org/wiki/William_Temple_Hornaday
https://www.gutenberg.org/files/17748/17748-h/17748-h.htm
Header photo:
Erik Beringen.
Erik Beringen.