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Simulation experimental taphonomy of modern fish embryos—Enlightenment for the early fossil embryos
AbstractPhosphate fossil embryos were found in the Ediacaran D o u s h a n t u o F o r m a t i o n a n d E a r l y C a m b r i a n Kuanchuanpu Formation in the Guizhou and Shaanxi provinces of South China respectively. The structure of the fossils is delicate and artistic. Although there has been some work done to date to identify the nature of these fossil embryos, their identification and characterization still are controversial. Therefore, we used experimental taphonomy approach to provide insight into the origin of these structures. Previous studies confirmed that delicate, perishable structures could be re ta ined by minera l iza t ion , but the experiments about the early morphological changes are few. Research about the sequencing of embryonic structure during the mineralization process is an important direction.
Instruction The experimental taphonomy in this study simulated the chemical conditions (pH and Eh) of the sediment environment to observe the morphological changes of Bluntnose black bream embryos (Megalobrama amblycephala). We assume that silicate mineralization is similar to phosphate mineralization, and that silicified fossil embryos are comparable to fossil embryos preserved by phosphate. In the experiment, a silicate solution was used instead of a phosphate solution. The result shows that the preservation of the embryos is affected by the environment. Silicification is a very rapid process, taking place over 15 days. Different forms and part of embryos are preserved entirely. The results also show that the substitution reaction occurs within the structure of embryo rather than just as a coating. Experimental taphonomy provides a good way to explore the origin and preservation of Early Cambrian fossil embryos.
Method1.Putting the bluntnose black bream embryos in jars which are aseptic condition.2. Pouring Na SiO solution into jars. 2 3
3.Dropping hydrochloric acid(HCl) solution into jars to regulate pH.4.Then, jars are sealed and removed to shade place.5.15 days later, taking out samples, solidifying embryos in biochemistry method.6 . T e s t i n g s a m p l e s b y e n e r g y d i s p e r s e spect roscopy(EDS) and observing samples by scanning electron microscopy(SEM).
Results
62 bottles embryos
78 boxes solidified embryos
0
2
4
6
8
10
12
14
1 2 3 4 5 6 7 8 9 10 11 12 13
Microenvironment pH changes
original 15 days later
-50
0
50
100
150
1 2 3 4 5 6 7 8 9 10 11 12 13
Microenvironment Eh changes
original 15 days later
10
10.5
11
11.5
12
12.5
13
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
pH blank test ( no embryos )
open environment sealed
-50
0
50
100
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Eh blank test ( no embryos)
open environment sealed
Reflected-light microscope
1
4145
17
<0.3 0.3-0.4 0.4-0.5 >0.5
Individual difference
number
0.5㎜
( a )
0.5㎜
( b )
0.5㎜
( c )
0.5㎜
( d )
0.5㎜
( e )
0.5㎜
( f )
Fossils and embryos
SEM figures
e
ca b
d f
g h I
j k l
m n o
p q r
EDS figures
Minerals on embryo surface
Surface analysis by SEM
Conclusion1.During buried stage, some physical and chemical reactions occur between biological and microenvironment.2.Acidic medium and reducing environment are requirements for fossil preservation.3.Embryo oolemma and ovokaryon can be saved in a short time. Some time they are saved differentiate.4.Different shapes and sizes can be saved at same time.5.Embryo is mineralized in two ways, one is metasomatism, the other one is coating
Reference1.Kear A J, Briggs D E G, Donovan D T., 1995, Decay and fossilization of non-mineralised tissue in coleoid cephalopods: Palaeontology, v.38,p.105-131.2.Xiao S H, Zhang Y, Knoll A H.,1998, Three-dimensional preservation of algae and animal embryos in a Neo-proterozoic phosporite: Nature, v.391,p. 553-558.3.Martill D M.,1990, Macromolecular resolution of fossilized muscle tissues from an elopomorph fish: Nature,v.346,p.171-172.4.Wilby P R, Martill D M.,1992, Fossil fish stomachs: A microenvironment for exceptional preservation: Hist Biol,v.6,p.25-36.5.Jones B, Konhauser K O, Renaut R, Wheeler R S,2004, Microbial silicification in Iodine Pool, Waimangu geothermal area, North Island, New Zealand: Implications for recognition and identification of ancient silified microbes: Journal of the Geological Society,v.161,p.983-993
JinJie Ren, Department of Geology, CCSU & Department of Geology, Northwest University, ChinaE-mail: [email protected] & [email protected]
Hong Hua, Department of Geology, Northwest University Email: [email protected]