Because monkeys typically live in lush forests where sediment is rarely deposited, they rarely fossilise.
|
|
The preservation of these fossils is one of their great fascinations to science. As soft-bodied organisms, they would normally not fossilise. Unlike later soft-bodied fossil biota (such as the Burgess Shale, or Solnhofen Limestone) the Ediacara biota is not found in a restricted environment subject to unusual local conditions: they were a global phenomenon. The processes that were operating must have been systemic and worldwide.
|
|
Taphonomic bias is caused by the difference in how organisms decay and fossilise. It is another challenge faced by paleontologists as the fossil records are often incomplete. Moreover, some localities have better-preserved record due to their geological history than the others, leading to misinterpretations in biogeography. This is especially true for dinosaurian fossil records since localities in North America and China had a much higher abundance of fossils preserved in sedimentary rocks.
|
|
Further details are available at Fossil embryos. This may reflect a genuine absence of bilateria, but caution is due -- it could be that bilateria didn't lay eggs in sediment, where they would be likely to fossilise. Molecular techniques can generate expected dates of the divergence between the bilaterian clades, and thus an assessment of when the urbilaterian lived. These dates have huge margins of error, though they are becoming more accurate with time.
|
|
The first of these is the appearance of wood tissue and bark-bearing trees. The evolution of the wood fiber lignin and the bark-sealing, waxy substance suberin variously opposed decay organisms so effectively that dead materials accumulated long enough to fossilise on a large scale. The second factor was the lower sea levels that occurred during the Carboniferous as compared to the preceding Devonian period. This promoted the development of extensive lowland swamps and forests in North America and Europe.
|
|
There was something very different about the Ediacaran Period that permitted these delicate creatures to be left behind. It is thought that the fossils were preserved by virtue of rapid covering by ash or sand, trapping them against the mud or microbial mats on which they lived. However, it is more common to find Ediacaran fossils under sandy beds deposited by storms or high-energy, bottom-scraping ocean currents known as turbidites. Soft-bodied organisms today almost never fossilise during such events.
|
|
The archaeological record shows Neanderthals commonly used animal hide and birch bark, and it is possible they used them to make cooking containers, though this is based largely on circumstantial evidence as neither fossilise well. It is possible the Neanderthals at Kebara Cave, Israel, used the shells of the spur-thighed tortoise as containers. At the Italian Poggetti Vecchi site, there is evidence they used fire to process boxwood branches to make digging sticks, a common implement in hunter-gatherer societies.
|
|
Only teeth and 4 mandibles are known currently, and other skeletal elements were likely consumed by porcupines before they could fossilise. Gigantopithecus was once argued to be a hominin, a member of the human line, but it is now thought to be closely allied with orangutans, classified in the subfamily Ponginae. Gigantopithecus has traditionally been restored as a massive, gorilla-like ape, potentially when alive, but the paucity of remains make total size estimates highly speculative. The species may have been sexually dimorphic, with males much bigger than females.
|
|
The delicate skeletons of bats do not fossilise well; it is estimated that only 12% of bat genera that lived have been found in the fossil record. Most of the oldest known bat fossils were already very similar to modern microbats, such as Archaeopteropus (32 million years ago). The extinct bats Palaeochiropteryx tupaiodon (48 million years ago) and Hassianycteris kumari (55 million years ago) are the first fossil mammals whose colouration has been discovered: both were reddish-brown. Bats were formerly grouped in the superorder Archonta, along with the treeshrews (Scandentia), colugos (Dermoptera), and primates.
|
|
When it comes to the fossil record, soft-bodied and minuscule invertebrates—such as hydras, jellies, flatworms, hairworms, nematodes, ribbon worms, rotifers and roundworms—are infrequently fossilized. As a result, paleontologists and other fossil hunters must often rely on trace fossils, microfossils, or chemofossil residue when scouting for these prehistoric creatures. Hard-bodied and large invertebrates are much more commonly preserved; typically as sizeable macrofossils. These invertebrates are more frequently preserved because their hard parts fossilise more readily—for example, shell, armor, plates, tests, exoskeleton, jaws or teeth.
|
|
The evolutionary embryologist Gavin de Beer anticipated evolutionary developmental biology in his 1930 book Embryos and Ancestors, by showing that evolution could occur by heterochrony, such as in the retention of juvenile features in the adult. This, de Beer argued, could cause apparently sudden changes in the fossil record, since embryos fossilise poorly. As the gaps in the fossil record had been used as an argument against Darwin's gradualist evolution, de Beer's explanation supported the Darwinian position. However, despite de Beer, the modern synthesis largely ignored embryonic development to explain the form of organisms, since population genetics appeared to be an adequate explanation of how forms evolved.
|
|
Fossil of a possible leech from the Silurian of Wisconsin The most ancient annelid group consists of the free- living polychaetes that evolved in the Cambrian period, being plentiful in the Burgess Shale about 500;million years ago. Oligochaetes evolved from polychaetes and the leeches branched off from the oligochaetes. Both the oligochaetes and the leeches, having no hard parts, do not fossilise well. The oldest leech fossils are from the Jurassic period around 150;million years ago, but a fossil with external ring markings found in Wisconsin in the 1980s, with what appears to be a large sucker, seems to extend the group's evolutionary history back to the Silurian, some 437;million years ago.
|
|
The traditional view is that developmental biology played little part in the modern synthesis, but in his 1930 book Embryos and Ancestors, the evolutionary embryologist Gavin de Beer anticipated evolutionary developmental biology by showing that evolution could occur by heterochrony, such as in the retention of juvenile features in the adult. This, de Beer argued, could cause apparently sudden changes in the fossil record, since embryos fossilise poorly. As the gaps in the fossil record had been used as an argument against Darwin's gradualist evolution, de Beer's explanation supported the Darwinian position. However, despite de Beer, the modern synthesis largely ignored embryonic development to explain the form of organisms, since population genetics appeared to be an adequate explanation of how forms evolved.
|
|
EEMH also created bone whistles out of deer phalanges. Such sophisticated music technology could potentially speak to a much longer musical tradition than the archaeological record indicates, as modern hunter-gatherers have been documented to create instruments out of: more biodegradable materials (less likely to fossilise) such as reeds, gourds, skins, and bark; more or less unmodified items such as horns, conch shells, logs, and stones; and their weapons, including spear thrower shafts or boomerangs as clapsticks, or a hunting bow. Potential EEMH instruments: bone flute (left), whistle (centre), idiophone (bottom), and bullroarer (top) It is speculated that a few EEMH artefacts represent bullroarers or percussion instruments such as rasps, but these are harder to prove. One probable bullroarer is identified at Lalinde, France, dating to 14 to 12 thousand years ago, measuring long and decorated with geometric incisions.
|
|