Several living and fossil organisms, vertebrates and invertebrates, share the use of bioapatite in building hard tissues for sheltering, structural supporting and processing food. They are formed by organic (cells and fibers) and mineralized (bioapatite) parts; the chemical composition of the latter usually presents ion substitutions. Bioapatite can incorporate trace elements during the mineral growth reflecting the environmental characteristics of the genetic environment and is generally assumed to be a reliable archive of the living environment. Conodonts have been using bioapatite through their full stratigraphic range (late Cambrian to Late Triassic) and they have been used for paleo-environmental investigations. But concrete hypotheses began to be advanced in which the concentration of trace elements in bioapatite could have been affected by chemical and mineralogical composition of the diagenetic environment. In this research, all major taxa who had processed bioapatite are investigated to verify if and how diagenesis imprints fossil bioapatite. We investigate samples from living, dead and fossilized organisms. Data were analyzed adopting a multi-methodological approach. The first constrain was to find proper reference standards and analytical conditions for LA-ICP-MS measurements. We propose a home-made external standard that reproduces as faithfully as possible the composition and physical-chemical characteristics of the matrix of the fossil samples. We tested this approach on two shark teeth (Malferrari et al., 2019). As we found this approach successful, after it was apply also to the characterization of fireworms chaetae with the goal of proposing, for the first time with the support of experimental data, their “crystal-chemical” composition which drive to relevant biological conclusion concerning the storing of toxin inside the organism (Righi et al., 2020). The first samples to be analyzed were conodonts (paraconodonts and euconodonts) from different taxa and covering the entire biostratigraphic range. We investigate conodont element crystal structure. Results clearly indicated two distinct distribution plots of cell parameters: one for euconodonts and one for paraconodonts. Taxonomy, provenience, age or other characteristics seem do not affect the dimensions of crystal cells (Medici et al., 2020a). Than we detected the uptake of HFSE in conodont elements recovered from a single stratigraphic horizon. We found that all conodont elements are characterized by a clear diagenetic signature, with minor but significant differences among taxa. These distinctions are evidenced also by the crystallinity index values (Medici et al., 2020b). We also investigated the mineralogical and chemical signatures of enigmatic microspherules: “conodont pearls”. Comparison between pearls, associated conodonts and other phosphatic elements present in the same stratigraphic level was run to reveal possible relations. We find that conodonts have a different bioapatite crystallographic lattice configuration and cell volume. And microspherules crystallographic parameters are similar to the brachiopods ones (Ferretti et al., 2020). We assembled all processed material to find a correlation between and taxonomy, aimed at understanding when diagenetic imprint starts on crystal chemistry and structure. We show that dead, fossil and alive organisms keep a distinct geometric signature in terms of apatite lattice cell parameters reflecting possible chemical re-positioning. We demonstrate that these changes start at the death of the organism, and reach a final stability only in mature fossils. If reliable and accepted, the model could assume a general valence and be further integrated with data from other researchers.
Diversi organismi viventi e fossili, sia vertebrati che invertebrati, usano la bioapatite per costruire tessuti rigidi di protezione, di sostegno e per nutrirsi. Questi sono formati da una parte organica (cellule e fibre) e da una mineralizzata (la bioapatite), la cui composizione chimica presenta sostituzioni ioniche. Vari elementi in traccia possono essere incorporati durante la crescita dei cristalli riflettendo le caratteristiche dell’ambiente di formazione. Per questo, la bioapatite è considerata un archivio affidabile di informazioni dell’ambiente di vita. I conodonti hanno utilizzato la bioapatite per tutto il loro range stratigrafico (dal Cambriano Superiore al Triassico Superiore) e sono stati usati per indagini paleo-ambientali. Emersero però ipotesi concrete secondo cui la concentrazione degli elementi in traccia nel reticolo cristallino della bioapatite poteva essere influenzata da composizione chimica e mineralogica dell’ambiente diagenetico. In questa ricerca, sono stati considerati tutti i maggiori taxa che utilizzano bioapatite per verificare se e come la diagenesi la influenzi. Abbiamo analizzato campioni da organismi fossili, morti e vivi. I dati sono stati ricavati con un approccio multi-metodologico. Il primo obbiettivo era identificare appropriati standard di riferimento e condizioni analitiche per le misure tramite LA-ICP-MS. Abbiamo proposto uno standard esterno fatto in casa che riproducesse la composizione e le caratteristiche chimico fisiche della matrice dei campioni fossili. Questo approccio è stato testato su due denti di squalo (Malferrari et al., 2019). Il test ha dato esito positivo, ed è stato quindi utilizzato per caratterizzare chete di vermocani con l’obbiettivo di proporre, per la prima volta col supporto di dati sperimentali, la loro composizione cristallochimica correlata a conclusioni biologiche (Righi et al., 2020). I primi campioni analizzati sono stati conodonti (paraconodonti ed euconodonti) di diversi taxa, coprendo l’intero range biostratigrafico. I risultati indicano due distribuzioni distinte dei parametri di cella: una per euconodonti e una per paraconodonti. Le dimensioni delle celle cristalline non sono invece influenzate da caratteristiche tassonomiche, età o provenienza (Medici et al., 2020a). Abbiamo quindi ricavato HFSE negli elementi a conodonti ricavati da un singolo orizzonte stratigrafico. È emerso che tutti sono caratterizzati da un chiaro segnale diagenetico, con differenze minori ma significative fra i taxa. Queste distinzioni sono evidenti anche dai valori dell’indice di cristallinità (Medici et al., 2020b). Abbiamo quindi analizzato la traccia mineralogica e chimica di microsfere enigmatiche: le “conodont pearls”. È stato effettuato un confronto fra perle, conodonti associati e altro materiale fosfatico presente nello stesso livello stratigrafico al fine di rivelare possibili affinità. Lo studio rivela che i conodonti hanno un reticolo cristallino diverso in termini di configurazione e volume di cella; le perle sono invece simili ai brachiopodi (Ferretti et al., 2020). Quindi, abbiamo considerato tutto il materiale raccolto per cercare di trovare una correlazione fra età e tassonomia, con l’obbiettivo di capire quando l’impronta diagenetica inizia a essere riconoscibile nella struttura e nella chimica dei cristalli. Abbiamo visto che organismi fossili, morti e vivi hanno un distinto segnale in termini di parametri di cella della bioapatite riflettendo possibili riorganizzazioni chimiche. Abbiamo dimostrato che questi cambiamenti hanno inizio al momento della morte dell’organismo, e raggiungono una stabilità finale solo nei fossili maturi. Se affidabile e accettato, il modello può assumere una valenza generale e può essere integrato coi dati degli altri ricercatori.
La bioapatite in organismi fossili e attuali / Martina Savioli , 2021 Apr 12. 33. ciclo, Anno Accademico 2019/2020.
La bioapatite in organismi fossili e attuali
SAVIOLI, MARTINA
2021
Abstract
Several living and fossil organisms, vertebrates and invertebrates, share the use of bioapatite in building hard tissues for sheltering, structural supporting and processing food. They are formed by organic (cells and fibers) and mineralized (bioapatite) parts; the chemical composition of the latter usually presents ion substitutions. Bioapatite can incorporate trace elements during the mineral growth reflecting the environmental characteristics of the genetic environment and is generally assumed to be a reliable archive of the living environment. Conodonts have been using bioapatite through their full stratigraphic range (late Cambrian to Late Triassic) and they have been used for paleo-environmental investigations. But concrete hypotheses began to be advanced in which the concentration of trace elements in bioapatite could have been affected by chemical and mineralogical composition of the diagenetic environment. In this research, all major taxa who had processed bioapatite are investigated to verify if and how diagenesis imprints fossil bioapatite. We investigate samples from living, dead and fossilized organisms. Data were analyzed adopting a multi-methodological approach. The first constrain was to find proper reference standards and analytical conditions for LA-ICP-MS measurements. We propose a home-made external standard that reproduces as faithfully as possible the composition and physical-chemical characteristics of the matrix of the fossil samples. We tested this approach on two shark teeth (Malferrari et al., 2019). As we found this approach successful, after it was apply also to the characterization of fireworms chaetae with the goal of proposing, for the first time with the support of experimental data, their “crystal-chemical” composition which drive to relevant biological conclusion concerning the storing of toxin inside the organism (Righi et al., 2020). The first samples to be analyzed were conodonts (paraconodonts and euconodonts) from different taxa and covering the entire biostratigraphic range. We investigate conodont element crystal structure. Results clearly indicated two distinct distribution plots of cell parameters: one for euconodonts and one for paraconodonts. Taxonomy, provenience, age or other characteristics seem do not affect the dimensions of crystal cells (Medici et al., 2020a). Than we detected the uptake of HFSE in conodont elements recovered from a single stratigraphic horizon. We found that all conodont elements are characterized by a clear diagenetic signature, with minor but significant differences among taxa. These distinctions are evidenced also by the crystallinity index values (Medici et al., 2020b). We also investigated the mineralogical and chemical signatures of enigmatic microspherules: “conodont pearls”. Comparison between pearls, associated conodonts and other phosphatic elements present in the same stratigraphic level was run to reveal possible relations. We find that conodonts have a different bioapatite crystallographic lattice configuration and cell volume. And microspherules crystallographic parameters are similar to the brachiopods ones (Ferretti et al., 2020). We assembled all processed material to find a correlation between and taxonomy, aimed at understanding when diagenetic imprint starts on crystal chemistry and structure. We show that dead, fossil and alive organisms keep a distinct geometric signature in terms of apatite lattice cell parameters reflecting possible chemical re-positioning. We demonstrate that these changes start at the death of the organism, and reach a final stability only in mature fossils. If reliable and accepted, the model could assume a general valence and be further integrated with data from other researchers.File | Dimensione | Formato | |
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