A dentin-based 87 Sr / 86 A method for accurately identifying Yangtze finless porpoises and East Asian finless porpoises using the Sr ratio.

Abstract

The application discloses a method for accurately identifying Yangtze finless porpoises and East Asian finless porpoises based on dentin 87 Sr / 86 The method comprises the following steps: collecting a tooth sample of the finless porpoise, pretreating the tooth, measuring the growth layer group of the dentin 87 Sr / 86 Analyzing the Sr / Ca ratio, measuring the growth layer group of the tooth, reconstructing 87 Sr / 86 The average value of the Sr / Ca ratio change stage is compared with the Sr / Ca ratio of the Yangtze River mainstream and the ocean 87 Sr / 86 The average value of the Sr / Ca ratio change stage is compared with the Sr / Ca ratio of the Yangtze River mainstream and the ocean 87 Sr / 86 The habitat type of the finless porpoise during the formation period is judged, so that the finless porpoise is judged to be the Yangtze finless porpoise or the East Asian finless porpoise according to the habitat type, and important evidence is provided for judging the species of the dead finless porpoise individual in the Yangtze River estuary.

Description

Technical Field

[0001] This invention belongs to the field of ecological technology, specifically relating to a method based on dentin. 87 Sr / 86 A method for accurately identifying Yangtze finless porpoises and East Asian finless porpoises using the Sr ratio. Background Technology

[0002] In recent years, based on the whole genome sequencing and population genomics analysis of the Yangtze finless porpoise, it has been found that the Yangtze finless porpoise and the East Asian finless porpoise have significant and stable genetic differentiation, and that the genetic differentiation has reached the interspecific level.

[0003] The Yangtze finless porpoise is a freshwater cetacean endemic to China, inhabiting the middle and lower reaches of the Yangtze River and two major lakes connected to the river (Dongting Lake and Poyang Lake).

[0004] The Yangtze River Estuary, located at the confluence of the Yangtze River, the East China Sea, and the Yellow Sea, possesses extremely rich food resources and is one of the hotspots for the Yangtze finless porpoise. The distribution areas of the East Asian finless porpoise and the Yangtze finless porpoise are similar in this area. However, the estuary region is greatly affected by factors such as tides and salinity variations; therefore, the distribution ranges of the Yangtze finless porpoise and the East Asian finless porpoise in the Yangtze River Estuary may overlap spatially. In recent years, with the deepening of conservation efforts, dead finless porpoises in the Yangtze River Estuary have been promptly discovered and reported. Accurately identifying dead individuals as either Yangtze finless porpoises or East Asian finless porpoises has become a prerequisite for conservation management and scientific research. While the habitats of the Yangtze finless porpoise and the East Asian finless porpoise differ significantly, their distribution boundaries are not clear in the brackish water confluence area of ​​the Yangtze River Estuary. Furthermore, dead finless porpoises may drift downstream, making species identification of dead finless porpoises found in this area challenging. The Yangtze finless porpoise and the East Asian finless porpoise are morphologically similar, and currently, they are mainly distinguished by differences in morphological features such as dorsal spine height, width of the wart area, and number of wart rows. However, since both the Yangtze and East Asian finless porpoises are nationally protected wild animals, the number of samples that can be collected to establish morphological differentiation parameters is very small. Furthermore, these morphological characteristics are affected by the individual's growth and development stage, thus lacking mature standards for morphological differentiation, and the identification results are highly subjective. In addition, dead finless porpoises are usually found with varying degrees of decomposition, which severely affects the identification of their body surface morphology. Moreover, although current high-throughput molecular sequencing technologies such as resequencing indicate significant genetic differentiation between the East Asian and Yangtze finless porpoises, there is currently a lack of molecular markers that can accurately and cost-effectively distinguish between the two.

[0005] Teeth are of significant value in studies of age, habitat reconstruction, and dietary shifts in many marine and terrestrial mammals. Dental tissue is highly mineralized, with dentin forming the main body of the tooth, covered by enamel, and the vascularized pulp surrounded by dentin. Approximately 72% of dentin mass is composed of inorganic minerals (primarily hydroxyapatite), 10% water, and various organic components make up about 20%. Dentin begins to form during the fetal stage and gradually grows towards the pulp cavity, reflecting changes in the individual's growth rate during its accumulation, thus forming discernible growth rings. During growth, dentin records information about the elements and isotopes of its habitats. Due to the metabolic inertia of highly mineralized tissue, trace elements and isotopes in teeth remain unchanged once deposited, allowing teeth to record elemental and isotopic information about their habitats throughout their lives. Current research explores the use of tooth elemental analysis to distinguish between the Yangtze finless porpoise, which mainly lives in freshwater, and the East Asian finless porpoise, which mainly lives in the ocean.

[0006] However, due to the multiple biofilm barriers through which elements are deposited in dentin, the relationship between dentin elemental content and environmental elemental content is difficult to quantify, making it impossible to establish elemental content standards corresponding to freshwater or marine habitats for finless porpoises. Furthermore, existing research has shown that physiological factors during animal growth and development can also lead to changes in the content of elements such as Sr and Zn in mammalian teeth. This significantly interferes with the interpretation of habitat changes inferred from elemental variations, limiting the objectivity of using tooth elemental content in studies of animal habitat transition. Therefore, there is an urgent need to develop accurate methods for distinguishing between the Yangtze finless porpoise and the East Asian finless porpoise. Summary of the Invention

[0007] Technical Problem Solved: To address the above-mentioned technical problem, this invention provides a dentin-based... 87 Sr / 86 The method of accurately identifying Yangtze finless porpoises and East Asian finless porpoises based on Sr ratios differs from the Sr element content; during the formation of biological materials, Sr isotopes (… 87 Sr / 86 Sr hardly undergoes fractionation and is unaffected by physiological factors such as growth and development, directly reflecting its origin. 87 Sr / 86 Sr, therefore dentin 87 Sr / 86 Sr can represent the habitat experienced by an animal. 87 Sr / 86 A direct and complete record of Sr. Furthermore, different habitats, such as marine and freshwater, have... 87 Sr / 86 Significant differences in Sr ratios in the ocean 87 Sr / 86 The Sr ratio is relatively uniform, in the ocean 87 Sr / 86 The Sr ratio is approximately 0.7092, while in the main stream of the middle and lower reaches of the Yangtze River in China, 87 Sr / 86 The Sr ratio is between 0.7100 and 0.7110. 87 Sr / 86 The Sr ratio is mainly influenced by watershed geological factors and remains stable across different years. In summary, it can be determined based on the dentin... 87 Sr / 86 Sr ratio is used to determine the habitat of individual finless porpoises. 87 Sr / 86 A Sr ratio of 0.7092 corresponds to a marine habitat life history. 87 Sr / 86 A Sr ratio of 0.7100-0.7110 corresponds to the freshwater life history of the Yangtze River, which can be used to determine whether it is a Yangtze finless porpoise or an East Asian finless porpoise.

[0008] Technical solution: A dentin-based 87 Sr / 86 A method for accurately identifying the Yangtze finless porpoise and the East Asian finless porpoise using the Sr ratio includes the following steps:

[0009] Step 1) Collect teeth samples from finless porpoises: Collect the straight teeth from the middle left side of the lower jaw of dead finless porpoises in the wild. If the individual is severely decomposed, take the teeth from the nearest location if possible. If too many teeth are missing, select the teeth that are not severely worn.

[0010] Step 2) Tooth Pretreatment: After extracting the tooth, soak it in trypsin solution for 24 hours. Then, use ultrasound to vibrate the tooth in the trypsin solution to remove the soft tissue attached to the tooth surface and pulp cavity. Afterward, use deionized water to repeatedly vibrate and clean the outer surface of the tooth and the inside of the pulp cavity. Use cold-mounting resin to embed the cleaned and dried tooth. Use a diamond saw blade of a small cutting machine to cut along the longest axis of the coronal plane of the tooth to cut the tooth into two parts. Use sandpaper to finely grind the cut coronal plane, and then polish it with polishing cloth and silica suspension. After polishing, clean the tooth slice with deionized water and dry it.

[0011] Step 3) Dentin 87 Sr / 86 Sr ratio analysis: Linear scanning analysis of dentin from the cusp to the pulp chamber was performed using a laser ablation-connected multi-receiver inductively coupled plasma mass spectrometer to obtain dentin data. 87 Sr / 86 Sr ratio;

[0012] Step 4) Tooth growth layer measurement: Use a biological polarizing microscope to capture images of the teeth, identify the dentin growth layers, and use image measurement software along... 87 Sr / 86 The laser scanning line measurement of the growth layer width for Sr ratio analysis will... 87 Sr / 86 The change in the Sr ratio is related to the growth time;

[0013] Step 5) Reconstruct 87 Sr / 86 Sr ratio changes: Analysis of dentin from the enamel interface to the pulp cavity 87 Sr / 86 Sr ratio, analysis of dentin 87 Sr / 86 The changes in the Sr ratio and the location of these changes; the division of different dentin types. 87 Sr / 86 The average values ​​of the Sr ratio during the different stages of change are respectively compared with those of the Yangtze River main stream and the ocean. 87 Sr / 86 By comparing the Sr ratio, we can determine the habitat type of the finless porpoise during its formation period, and thus determine whether it is a Yangtze finless porpoise or an East Asian finless porpoise based on the habitat type.

[0014] Preferably, in step 3), a laser ablation-connected multi-receiver inductively coupled plasma mass spectrometer is used to examine dentin. 87 Sr / 86 Sr ratio analysis was performed in medium-resolution mode. The laser energy density in the laser ablation-connected multi-receiver inductively coupled plasma mass spectrometry experiment was 6.5 J / cm². 2 The ablation spot diameter was 64 μm, the frequency was 10 Hz, and the ablation rate was 5 μm / s. Before each laser ablation, the background intensity of each isotope was measured for 200 cycles, and the average value was used for blank background correction during sample analysis. The apatite standard (Durango) and modern marine shark teeth were measured at the beginning and end of each analysis and every 30 minutes during the analysis. 87 Sr / 86 Sr ratio was used to evaluate the dental samples of finless porpoises. 87 Sr / 86 The accuracy and repeatability of the Sr ratio.

[0015] Preferably, in step 3), by setting the Faraday cup configuration of the multi-receiver inductively coupled plasma mass spectrometer, signals at m / z values ​​of 82, 83, 83.5, 84, 85, 86, 86.5, 87, and 88 are received. During data analysis, the "peak-zero" method is used to correct Kr interference by subtracting the average signal of the blank background from each analysis cycle; the signal at m / z 82 is received to monitor...42 Ca 40 Ar / 42 Ca 40 Ca peak; through monitoring 85 The Rb signal is calculated based on the isotope ratio. 87 Rb, and on 87 Rb / 85 Rb underwent instrumental mass fractionation calibration. The calibration process assumes that Rb and Sr have the same mass fractionation factor, and firstly, the measured... 88 Sr and 86 Sr signal, according to 88 Sr / 86 The natural isotopic abundance ratio of Sr is 8.375209. The mass fractionation factor was calculated using the exponential law. Based on the mass fractionation factor and... 87 Rb / 85 The natural isotopic abundance ratio of Rb is 0.38567. The corrected ratio is calculated... 87 Rb / 85 Rb, thus obtaining the corrected Rb 87 Rb. Subtract the corrected value from m / z = 87. 87 Rb, according to the correction 87 Rb / 85 Rb's steps for deduction 87 Rb after 87 Sr / 86 The Sr ratio is used for instrument mass fractionation correction to obtain the measured value after mass fractionation correction and interference correction.

[0016] Preferably, in step 5), CHANGEPOINT in the programming statistical software R is used to analyze the data. 87 Sr / 86 The raw Sr ratio data were analyzed to obtain individual... 87 Sr / 86 The point where the Sr ratio changes significantly is obtained. 87 Sr / 86 The Sr ratio did not change significantly during the stationary phase, and the stationary phase was calculated. 87 Sr / 86 The average Sr ratio; the average value was compared with the Yangtze River main stream and the ocean respectively. 87 Sr / 86 By comparing the Sr ratio, we can determine the habitat type of the finless porpoise during its formation period, and thus infer the species of the finless porpoise based on the habitat type.

[0017] Preferred, the main stream of the Yangtze River 87 Sr / 86 The Sr ratio is 0.7100-0.7110, marine. 87 Sr / 86The Sr ratio is 0.7092.

[0018] Beneficial effects: This invention is based on animal biomineralized materials 87 Sr / 86 The Sr ratio can directly reflect the environment. 87 Sr / 86 The characteristics of the Sr ratio, and marine and freshwater habitats 87 Sr / 86 The Sr ratio showed significant differences, and the use of finless porpoise teeth as a habitat for finless porpoises was investigated. 87 Sr / 86 The Sr ratio indicator is used to reconstruct the habitat of finless porpoises, allowing for the inference of whether the porpoise is a Yangtze finless porpoise or an East Asian finless porpoise based on whether it lives in freshwater or ocean. This invention offers advantages such as accuracy, independence from physiological factors, and the ability to establish numerical discrimination standards. It can be used to reconstruct the habitats experienced by finless porpoises, thereby identifying Yangtze and East Asian finless porpoises. It overcomes the shortcomings of traditional morphological methods, which are difficult to use for identification and whose appearance is easily affected by factors such as injury and decay; it also overcomes the drawbacks of dentin elemental composition being easily affected by growth and development factors and the difficulty in establishing environmentally relevant content standards. This provides a basis for reconstructing the habitats of deceased finless porpoises, thereby differentiating between Yangtze and East Asian finless porpoises in the Yangtze Estuary. Attached Figure Description

[0019] Figure 1 It is a tooth in the lower left jaw of a Yangtze finless porpoise;

[0020] Figure 2 A section of a finless porpoise's tooth; the continuous shallow grooves from the cusp to the pulp cavity in the image are traces left by laser ablation of dentin.

[0021] Figure 3 Dentin of a dead East Asian finless porpoise found on the eastern coast 87 Sr / 86 Sr ratio, the black curve represents... 87 Sr / 86 Sr ratio, the gray horizontal line represents the value obtained from CHANGEPOINT analysis. 87 Sr / 86 Segments with significant changes in the Sr ratio are indicated by the position of the gray horizontal line on the Y-axis within the segment. 87 Sr / 86 Average Sr ratio;

[0022] Figure 4 Dentin of a dead Yangtze finless porpoise found in the lower reaches of the Yangtze River 87 Sr / 86 Sr ratio, the black curve represents... 87 Sr / 86 Sr ratio, not detected by CHANGEPOINT analysis. 87 Sr / 86Significant changes in the Sr ratio are indicated by the position of the gray horizontal line on the Y-axis within the segment. 87 Sr / 86 The average Sr ratio; where the black line represents the fitted value, the gray area represents the confidence interval, and the light blue background represents the main stream of the Yangtze River. 87 Sr / 86 Sr ratio range, light red background indicates ocean. 87 Sr / 86 The Sr ratio, with the x-axis representing the distance from the cusp to the pulp chamber along the dentin growth axis. Detailed Implementation

[0023] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments:

[0024] The dentin used in this invention is highly mineralized and metabolically inert, meaning it remains unchanged once formed. Furthermore, dentin begins to form during the fetal stage and gradually grows towards the pulp cavity, forming discernible growth rings based on individual growth rates. Additionally, the Sr isotopes of the habitats experienced during dentin growth are directly recorded during dentin growth. 87 Sr / 86 Sr ratio information. Due to the ocean 87 Sr / 86 The Sr ratio is relatively uniform, which is characteristic of contemporary oceans. 87 Sr / 86 The Sr ratio is 0.70918, while in the main stream of the middle and lower reaches of the Yangtze River in China, 87 Sr / 86 The Sr ratio is between 0.710 and 0.711. Therefore, the different habitats experienced by the Yangtze finless porpoise and the East Asian finless porpoise will be reflected in their dentin. 87 Sr / 86 Regarding the Sr ratio, dentin can be used. 87 Sr / 86 Sr ratio is used to determine species.

[0025] Example 1

[0026] A method based on accurate dentin measurement 87 Sr / 86 The method for identifying the Yangtze finless porpoise and the East Asian finless porpoise using the Sr ratio is as follows:

[0027] Step 1) Tooth collection: The second tooth on the left side of the lower jaw was extracted from the mouths of the dead finless porpoises found in Chongming, Lianyungang and Hangzhou Bay respectively. For individuals with severe decay and missing teeth, other available teeth were used for analysis.

[0028] Step 2) Tooth Pretreatment: The extracted tooth was soaked in trypsin solution (2000 BAEE U / mg) (Sigma-Aldrich, Seelze, Germany) for 24 hours, followed by ultrasonic agitation in the trypsin solution for 10 minutes to clean the soft tissue and attachments on the tooth root and remove any remaining nerve tissue from the pulp cavity; then, the tooth was ultrasonically cleaned three times with deionized water, and dried after cleaning (the cleaned tooth looks like...). Figure 1 (As shown); the tooth was embedded in cold-mounted resin; the tooth was cut into two parts along the longest axis of the coronal surface using a diamond saw blade from a small cutting machine (Struers, Copenhagen, Denmark); one half of the coronal surface was finely ground with sandpaper, and then polished with a polishing cloth and silica suspension; the tooth slice was rinsed with deionized water and air-dried.

[0029] Step 3) Dentin 87 Sr / 86 Sr ratio analysis: A laser ablation-connected multi-receiver inductively coupled plasma mass spectrometer (LA-MC-ICP-MS) was used to perform line scanning analysis from the enamel-dentin interface at the cusp to the pulp cavity to obtain dentin values. 87 Sr / 86 The Sr ratio was determined using an instrumentation system comprising a RESOlution SE 193nm laser ablation system (Australian Scientific Instruments, ACT, Australia) and a Neptune plus multi-receiver inductively coupled plasma mass spectrometer (Thermo Scientific, Dreieich, Germany); the laser energy density used in the analysis was 6.5 J / cm². 2 The ablation spot diameter was 64 μm, the frequency was 10 Hz, and the ablation velocity was 5 μm / s. Before analysis, the peak shape of the multi-receiver inductively coupled plasma mass spectrometer was calibrated using a NIST SRM610 glass standard via laser ablation to ensure acceptable peak shape. The instrument signal and stability were calibrated using the international apatite standard, Durango, via laser ablation to ensure acceptable sensitivity and stability. Before each laser ablation, the background intensity (V) of each isotope was measured for 200 cycles, and the average value was used for blank background correction during sample analysis. Measurements were taken at the beginning and end of each analysis, as well as every 30 minutes during the analysis, of the apatite standard (Durango) and modern marine shark teeth (collected in nearshore waters). 87 Sr / 86 Sr ratio was used to evaluate the dental samples of finless porpoises. 87 Sr / 86 The accuracy and repeatability of the Sr ratio.

[0030] By configuring a Faraday cup setup on a multi-receiver inductively coupled plasma mass spectrometer, signals at m / z values ​​of 82, 83, 83.5, 84, 85, 86, 86.5, 87, and 88 were received. During data analysis, the "peak-zero" method was used to correct for Kr interference by subtracting the average signal from the blank background from each analysis period; the signal at m / z 82 was received to monitor... 42 Ca 40 Ar / 42 Ca 40 Ca peak; through monitoring 85 The Rb signal is calculated based on the isotope ratio. 87 Rb, and on 87 Rb / 85 Rb underwent instrumental mass fractionation calibration. The calibration process assumes that Rb and Sr have the same mass fractionation factor, and first uses the measured... 88 Sr and 86 Sr signal, according to 88 Sr / 86 The natural isotopic abundance ratio of Sr is 8.375209. The mass fractionation factor was calculated using the exponential law. Based on the mass fractionation factor and... 87 Rb / 85 The natural isotopic abundance ratio of Rb is 0.38567. The corrected ratio is calculated... 87 Rb / 85 Rb, thus obtaining the corrected Rb 87 Rb. Subtract the corrected value from m / z = 87. 87 Rb, according to the correction 87 Rb / 85 Rb's steps for deduction 87 Rb after 87 Sr / 86 The Sr ratio was calibrated using instrument mass fractionation to obtain measured values ​​after mass fractionation and interference correction. Data processing and correction were performed using the open-source LA-MC-ICP-MS data fast offline reduction program "SrDR". The MC-ICP-MS analysis mode was medium-resolution static mode. The mass numbers and corresponding analytes measured by the mass spectrometer during the analysis are shown in Table 1.

[0031] Table 1. Mass numbers and corresponding isotopes determined by MC-ICP-MS

[0032]

[0033] Step 4) Tooth growth layer measurement: Images of the teeth were taken using a biological polarizing microscope (Leica, Solms, Germany) (e.g., ...). Figure 2 As shown), the growth layers of dentin are distinguished using image measurement software along...87 Sr / 86 The laser scanning line measurement of the growth layer width for Sr ratio analysis will... 87 Sr / 86 The change in the Sr ratio is related to the growth time;

[0034] Step 5) Reconstruct 87 Sr / 86 Sr ratio change: Analysis of dentin from the enamel interface to the pulp cavity using Changepoint Statistics. 87 Sr / 86 Sr ratio, used to assess dentin 87 Sr / 86 Does the Sr ratio change significantly, and where does the change occur? What are the different dentin segments segmented by Changepoint Statistics analysis? 87 Sr / 86 The average values ​​of the Sr ratio during the different stages of change are respectively compared with those of the Yangtze River main stream. 87 Sr / 86 Sr ratio 0.7100-0.7110, marine 87 Sr / 86 By comparing the Sr ratio of 0.7092, we can determine the habitat type of the finless porpoise during its formation period, and thus infer the species of the finless porpoise based on the habitat type.

[0035] This embodiment includes tooth samples from a dead finless porpoise found along the coast and another dead finless porpoise found in the lower reaches of the Yangtze River. Sr isotope analysis results are as follows: Figures 3-4 As shown, the horizontal axis represents the distance from the cusp to the pulp chamber along the dentin growth axis; the vertical axis represents the distance during the tooth's life history. 87 Sr / 86 Changes in the Sr ratio are related to changes in the domestic aquatic environment.

[0036] like Figure 3 The image shows the dentin of a dead finless porpoise found along the coast. 87 Sr / 86 The Sr ratio fluctuated very little, remaining around 0.70918, a result consistent with contemporary marine measurements (0.70918), indicating that this finless porpoise lived in... 87 Sr / 86 In oceans with stable Sr ratios, this indicates that it is an East Asian finless porpoise. Figure 4 The image shows the teeth of a dead finless porpoise found in the lower reaches of the Yangtze River. 87 Sr / 86The variation in the Sr ratio was not significant, remaining within the range of 0.7100-0.7110. This result is close to the measured value of water samples from the main stream of the Yangtze River, indicating that these individuals lived in the freshwater environment of the Yangtze River and should be identified as Yangtze finless porpoises.

[0037] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A dentin-based 87 Sr / 86 A method for accurately identifying the Yangtze finless porpoise and the East Asian finless porpoise using the Sr ratio, characterized by: Includes the following steps: Step 1) Collect teeth samples from finless porpoises: Collect the middle straight tooth on the left side of the lower jaw of a dead finless porpoise in the wild. If the individual is severely decomposed, take the tooth from the nearest position if possible. If too many teeth are missing, choose the tooth that is not severely worn. Step 2) Tooth Pretreatment: After extracting the tooth, soak it in trypsin solution for 24 hours. Then, use ultrasound to vibrate the tooth in the trypsin solution to remove the soft tissue attached to the tooth surface and pulp cavity. Afterward, use deionized water to repeatedly vibrate and clean the outer surface of the tooth and the inside of the pulp cavity. Use cold-mounting resin to embed the cleaned and dried tooth. Use a diamond saw blade of a small cutting machine to cut along the longest axis of the coronal plane of the tooth to cut the tooth into two parts. Use sandpaper to finely grind the cut coronal plane, and then polish it with polishing cloth and silica suspension. After polishing, clean the tooth slice with deionized water and dry it. Step 3) Dentin 87 Sr / 86 Sr ratio analysis: Linear scanning analysis of dentin from the cusp to the pulp chamber was performed using a laser ablation-connected multi-receiver inductively coupled plasma mass spectrometer to obtain dentin data. 87 Sr / 86 Sr ratio; dentin analysis using laser ablation coupled with a multi-receiver inductively coupled plasma mass spectrometer. 87 Sr / 86 Sr ratio analysis was performed using medium-resolution mode; the laser energy density in the laser ablation-connected multi-receiver inductively coupled plasma mass spectrometry experiment was 6.5 J / cm². 2 The ablation spot diameter was 64 μm, the frequency was 10 Hz, and the ablation rate was 5 μm / s. Before each laser ablation, the background intensity of each isotope was measured for 200 cycles, and the average value was used for blank background correction during sample analysis. The apatite standard and modern marine shark teeth were measured at the beginning and end of each analysis, as well as every 30 minutes during the analysis. 87 Sr / 86 Sr ratio was used to evaluate the dental samples of finless porpoises. 87 Sr / 86 The accuracy and repeatability of the Sr ratio were assessed; signals at m / z 82, 83, 83.5, 84, 85, 86, 86.5, 87, and 88 were received using a Faraday cup configuration on a multi-receiver inductively coupled plasma mass spectrometer; during data analysis, the "peak-zero" method was used to correct for Kr interference by subtracting the average signal from the blank background from each analysis period; the signal at m / z 82 was received to monitor... 42 Ca 40 Ar / 42 Ca 40 Ca peak; through monitoring 85 The Rb signal is calculated based on the isotope ratio. 87 Rb, and on 87 Rb / 85 Rb underwent instrumental mass fractionation calibration; the calibration process assumed that Rb and Sr had the same mass fractionation factor, and firstly, the measured... 88 Sr and 86 Sr signal, according to 88 Sr / 86 The natural isotopic abundance ratio of Sr is 8.375209. The mass fractionation factor was calculated using the exponential law. Based on the mass fractionation factor and... 87 Rb / 85 The natural isotopic abundance ratio of Rb is 0.38567. The corrected ratio is calculated... 87 Rb / 85 Rb, thus obtaining the corrected Rb 87 Rb; after subtracting the correction from m / z = 87 87 Rb, according to the correction 87 Rb / 85 Rb's steps for deduction 87 Rb after 87 Sr / 86 The Sr ratio is used for instrument mass fractionation correction to obtain the measured value after mass fractionation correction and interference correction; Step 4) Tooth growth layer measurement: Use a biological polarizing microscope to take images of the teeth, distinguish the growth layers of dentin, and use image measurement software along... 87 Sr / 86 The laser scanning line measurement of the growth layer width for Sr ratio analysis will... 87 Sr / 86 The change in the Sr ratio is related to the growth time; Step 5) Reconstruct 87 Sr / 86 Sr ratio changes: Analysis of dentin from the enamel interface to the pulp cavity 87 Sr / 86 Sr ratio, analysis of dentin 87 Sr / 86 The changes in the Sr ratio and the location of these changes; the division of different dentin types. 87 Sr / 86 The average values ​​of the Sr ratio during the different stages of change are respectively compared with those of the Yangtze River main stream and the ocean. 87 Sr / 86 By comparing the Sr ratio, the habitat type of the finless porpoise during its formation was determined, and thus, based on the habitat type, it was identified as either the Yangtze finless porpoise or the East Asian finless porpoise; the CHANGEPOINT function in the programming statistical software R was used to analyze the data. 87 Sr / 86 The raw Sr ratio data were analyzed to obtain individual... 87 Sr / 86 The point where the Sr ratio changes significantly is obtained. 87 Sr / 86 The Sr ratio did not change significantly during the stationary phase, and the stationary phase was calculated. 87 Sr / 86 The average Sr ratio; the average value was compared with the Yangtze River main stream and the ocean respectively. 87 Sr / 86 By comparing the Sr ratio, we can determine the habitat type of the finless porpoise during its formation, and thus infer the species of the finless porpoise based on the habitat type. Yangtze River Mainstream 87 Sr / 86 The Sr ratio is 0.7100-0.7110, marine. 87 Sr / 86 The Sr ratio is 0.7092.

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