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Home / Science / Half of the species in a new Cambrian fossil area is completely new to us

Half of the species in a new Cambrian fossil area is completely new to us



  Very detailed impression of a segmented, multi-legged organism.
Enlarge / In some fossils, the level of detail is amazing.

Dongjing Fu et. al.

The first signs of complex animal life begin in the Ediacaran period, which began more than 600 million years ago. However, it is difficult to understand how these organisms relate to today's life. Part of this problem is that these fossils are rare, as many rocks of that time seem to have been wiped off the earth by global icing. But another problem is that the organisms we see from that time are not clearly related to what came afterwards.

With the arrival of the Cambrian period about 550 million years ago, all this changed. In fossilized camps, such as the famous Burgess Shale, we can see organisms that clearly show characteristics of the most important groups of life that continue to this day. As more fossil collections become available, we can even observe how groups diversify throughout the Cambrian. However, there is still considerable debate as to whether these changes represent a true "explosion" of several million years and what environmental changes might have led to this diversification.

Answering these questions may well be short of great help Scientists announce the discovery of a spectacular deposit of fossils from Kambria, southern China. The fossils include dozens of species, half of which we have never seen before, and appear to represent a previously overvalued ecological zone. Conservation is such that soft bodies such as jellyfish and the softer body parts of living things with shellfish can be easily recognized in the rocks. The researchers who discovered the samples are the most likely to suspect that rocks of the same formation are widespread in China.

Rescued Half a Billion Years

In order to preserve these fossils in the Changyang area, some elements had to come together from China. The animals found in the deposits, collectively referred to as Qingjiang biota, needed sufficient oxygen in the marine waters to thrive. However, oxygen also feeds organisms that would destroy the bodies of these living things once they die or dig through the sediments after the bodies have been buried in them. The researchers suspect that the organisms on the relatively shallow continental shelf flowered in the water, but were drawn after their passing from currents in deeper, oxygen-poor waters. The same currents also provided a steady stream of sediment that quickly buried the bodies of soft creatures while they were still intact.

After the material had been crushed into sedimentary rock, it had to be avoided to heat up or distort the rocks and everything that contained them, such as volcanic geological processes. The result of this combination of rare conditions is what is technically referred to as a deposit, a rich fossil sedimentary rock. In this case, the deposit is located in Hubei Province along the Qingjiang River, visibly as a series of alternating light and dark rock strata, with the entire arrangement up to 50 meters thick in some places.

This formation aroused the interest of Chinese explorers, as the rocks had been deposited at the same time as the fossil layers in Chengjiang, some 518 million years ago, or slightly earlier than the Burgess Shale. 19659006] Their interest was derived from the collection of an astonishing amount of Cambrian fossils, with more than 100 species of animals represented. Although they date from the same period as Chengjiang's fossil deposits, more than half of the species have not been previously described in Qingjiang, and only eight of them share the two sites. For the authors, this indicates that Qingjiang is a different ecosystem from a community in deeper waters.

Good condition

The preservation of these fossils is absolutely stunning. Soft bodies such as sponges, jellyfish and anemones have received details such as tentacles and mouth. In many cases, internal organs can also be identified. "Unexpectedly, on some bed surfaces of the Qingjiang assembly, there are submillimeter to millimeter-sized, delicate, larval or juvenile forms." The authors write. You can also see details of the algae with which they have shared their environment.

Even without formal descriptions of the new species, the fossils answer questions. Ctenophore, also called comb gels, are one of the earliest branches of the evolutionary animal tree. In their present form they have tentacles, but with these appendages there was no early fossil, leading to the assumption that they have evolved lately. But in Qingjiang, there is a full-bodied comb jelly, so the debate seems to be over.

All this suggests that much work can be expected from the four seasons of fieldwork that the team has already done in Qingjiang. But the revelations may begin first. In the beginning, the Qingjiang were neither heated nor weathered. This does not apply to the Burgess Shale or Chengjiang Formation. The preservation of soft fossil materials may be even better than at these sites.

The authors also refer to occurrences from the Cambrian era in Qingjiang, China as "widespread," and initial samples suggest that similar fossils can be found from other sites in the region. Depending on how far they are from them, there is a chance that these other sites will receive more ecosystems. If this turns out to be the case, these rocks could give a clearer picture of the diversity of ecosystems available to some of the earliest animals on earth, and show how the conditions in each species shaped the species there ,

Science 2019. DOI: 10.1126 / science.aau8800 (About DOIs).


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