Fossils Aren't Real Bones/teeth?

[M.Vignesh]

There are lots of different forms of fossilization, all with different levels of organic material still left in the fossil. Before, I said that your spinosaurus tooth is completely fossilized, and that is true, but as people have been saying the term fossil has a different meaning to many people...

Your spinosaurus tooth does have original enamel still left in it. Most fossilized dinosaur/shark teeth from formations that formed under saltwater undergo a process called permineralization. For example. Your Spinosaurus was running around eating things when suddenly a small meteor came out of nowhere and killed him, where he then fell into the river he was next to, floated off to the bottom, broke up into pieces, lost his teeth, and was buried by sediment. One of those teeth got buried, and over time, mineral rich water started seeping underground and around the fossil. The soft inner parts of the tooth have decayed by this time, and begin to fill with sediment and minerals. The enamel however - being an extremely corrosion resistant ceramic does not decay, rather, the mineral-rich water over time begins to deposit minerals (maybe calcite) into pores and holes in the enamel, which re not visible under the naked eye, but under a microscope. There minerals begin to crystalize and eventually completely fill the holes and pores in the enamel.

So yes, your tooth is completely fossilized in the sense that it is really old, and is completely permineralized, however enamel does not undergo any chemical change throughout the process, but basically becomes impregnated by other minerals. The minerals that impregnate the enamel determine the color of the fossil. For example, I am assuming your spinosaurus tooth is impregnated with calcite and some iron-oxide laden minerals.

In conclusion: there is still enamel. Permineralization almost always leaves the holes it fills intact, with the original material. Further, leaves and other soft organics - under special conditions - undergo per mineralization wherein the cellulitic walls of the cell membranes are still intact, but the cells are filled with minerals.

Hope this helps.

For more information, you can try to get access to this paper: Loren E. Babcock, "Permineralization", AccessScience McGraw-Hill.

It really helps alot! Thank you very much for your kind help buddy

I really appreciate your help on this.

[TNCollector]

It really helps alot! Thank you very much for your kind help buddy

I really appreciate your help on this.

I am glad to help!

I recommend reading about "permineralization" and "replacement", which are the two major processes that compose the process of petrification. "Permineralization" leaves original material, and "replacement" does not. Enamel almost always survives the replacement process (meaning it does not get replaced).

[Eocenecarnage]

Yes original enamel does exist on the teeth, but It has been partially mineralized

[Troodon]

1 hour ago, PetrosTrilobite said:

 

There are formations that original matterial stay on the teeth at least partially?

Fossilization typically happens over a long time through a process called permineralization.  That's where water seeps down through the sediment and over the teeth.  The different minerals are carried by the water into the open pores in the teeth.  These minerals affect the color you see.   So to address your question of dinosaur teeth the answer is no.   All the organic material decays away and the space it occupied is filled with minerals.  The thin outer enamel layer is less altered but still changes at the microscopic level why it's a different color.

[Troodon]

27 minutes ago, PetrosTrilobite said:

@Troodon do you believe that this is sad fact? 

Sad?. It's a fossil that's good

[FranzBernhard]

One thing is, that pores in enamel are filled with minerals during diagenesis.

 

Other thing is, has the enamel still the same crystalline structure / fabric as during lifetime of the animal? Or has the enamel undergone recrystallization during diagenesis? But its still "apatite".

 

Franz Bernhard

[Troodon]

37 minutes ago, FranzBernhard said:

One thing is, that pores in enamel are filled with minerals during diagenesis.

 

Other thing is, has the enamel still the same crystalline structure / fabric as during lifetime of the animal? Or has the enamel undergone recrystallization during diagenesis? But its still "apatite".

 

Franz Bernhard

Not a scientist so I looked up comments by the Florida Museum on shark teeth and they said that over hundreds to a few thousand years the original arrangement of the atoms in the crystals changes into a more stable pattern, and during this phase, some replacement of calcium atoms by those of iron, manganese and other elements occur.  These metallic elements cause the color change.  Because the thin outer layer of enamel on the crown starts out as nearly 100% mineral is less affected than the root and dentin.  But it still has changed mostly at the submicroscopic, or atomic level.

[FranzBernhard]

18 minutes ago, Troodon said:

But it still has changed mostly at the submicroscopic, or atomic level.

Thank you!

This sounds like recrystallization. An important aspect that has also to be considered on calcitic shell fossils. I don´t mention aragonitic shell fossils, thats a different thing what happens there.

Franz Bernhard

[JBkansas]

Has anyone demonstrated that the fluorapatite in fossil teeth developed post mortem rather than dino/cretaceous reptiles having teeth more similar to sharks?  This article argues the second POV. 

 

https://pubs.rsc.org/en/content/articlehtml/2015/ra/c5ra11560d

 

From the linked article: "Another, albeit less probable reason for the presence of fluoroapatite in the dentin of all investigated teeth could be a hitherto undescribed chemical pathway where hydroxyapatite recrystallized to fluoroapatite during the millions of years of diagenesis. Given the fact that the measured fluoride content was high and similar on all extinct species despite their different age, excavation sites and diagenetic history, this appears very unlikely. Therefore, we rule out artefacts, e.g. of an intake of fluoride during fossilization, as the teeth were preserved in completely different environments and as this would not explain the pathway of fluoride inside all these fossilized teeth samples without changing the crystal morphology. In this respect, compact teeth are certainly different than porous dinosaur bones where a fluoride intake was reported by Elorza et al. Kohn et al. reported some chemical changes in fossil teeth, including some fluoride uptake. However, this was much less pronounced in enamel than in dentin. Therefore, unlike Bauluz et al. who studied the diagenesis of a tooth of an iguanodontian dinosaur to aluminium phosphate phases and proposed fluoroapatite as diagenetic phase, we are convinced that fluoroapatite was present in the teeth of the extinct species when they were still alive. These considerations are supported by EDX line scans across the teeth (see ESI)."

Edited January 18, 2023 by JBkansas

[ThePhysicist]

19 hours ago, FranzBernhard said:

Other thing is, has the enamel still the same crystalline structure / fabric as during lifetime of the animal? Or has the enamel undergone recrystallization during diagenesis? But its still "apatite".

 

 

14 hours ago, JBkansas said:

Has anyone demonstrated that the fluorapatite in fossil teeth developed post mortem rather than dino/cretaceous reptiles having teeth more similar to sharks?  This article argues the second POV. 

 

https://pubs.rsc.org/en/content/articlehtml/2015/ra/c5ra11560d

 

From the linked article: "Another, albeit less probable reason for the presence of fluoroapatite in the dentin of all investigated teeth could be a hitherto undescribed chemical pathway where hydroxyapatite recrystallized to fluoroapatite during the millions of years of diagenesis. Given the fact that the measured fluoride content was high and similar on all extinct species despite their different age, excavation sites and diagenetic history, this appears very unlikely. Therefore, we rule out artefacts, e.g. of an intake of fluoride during fossilization, as the teeth were preserved in completely different environments and as this would not explain the pathway of fluoride inside all these fossilized teeth samples without changing the crystal morphology. In this respect, compact teeth are certainly different than porous dinosaur bones where a fluoride intake was reported by Elorza et al. Kohn et al. reported some chemical changes in fossil teeth, including some fluoride uptake. However, this was much less pronounced in enamel than in dentin. Therefore, unlike Bauluz et al. who studied the diagenesis of a tooth of an iguanodontian dinosaur to aluminium phosphate phases and proposed fluoroapatite as diagenetic phase, we are convinced that fluoroapatite was present in the teeth of the extinct species when they were still alive. These considerations are supported by EDX line scans across the teeth (see ESI)."

To add on to @JBkansas, there have been many papers in recent years studying original isotopic signals in dinosaur enamel from which many things may be inferred from climate to trophic position(!). The best self-contained discussion on the "originality" of the signal(s) and the extent of diagenetic modification I've seen so far is in Owocki et al. (2019), which investigates Tarbosaurus tooth enamel. I'll paste part of the discussion in case people don't have access:

 

"Evaluating the possibility of diagenetic alteration

The record of palaeoenviromental proxies in the stable isotope geochemistry of biological apatite has been repeatedly challenged on the grounds that the process of fossilisation involves diagenetic alteration (Kolodny et al., 1996) as well as potential overprinting of the primary isotopic signal by secondary precipitation of apatite and isotopic exchange during microbially mediated reactions (Blake et al., 1997; Zazzo et al., 2004).

However, multiple studies have proven that tooth enamel is suitable for isotopic analyses because it is more resistant to diagenetic modification over geological time (Kohn and Cerling, 2002; Kirsanow et al., 2008) and can preserve ecologically meaningful carbon and oxygen isotope compositions, even over millions of years (e.g. Sponheimer and Lee-Thorp, 2006; Fricke et al., 2008). The low organic content and porosity of tooth enamel make crystallisation of diagenetic phosphate in the enamel highly unlikely (Kohn et al., 1999). The apatite crystals in enamel are large and densely packed in comparison to bone hydroxylapatite crystals; accordingly, it has been suggested that diagenetic microbial degradation might not reset the original isotopic signal (Kolodny et al., 1996; Amiot et al., 2011). Contrastingly, bone and dentine are prone to diagenetic alteration through an exchange of isotopes and trace elements with ambient pore fluids (Bocherens et al., 1994; Kolodny et al., 1996; Iacumin et al., 1996; Trueman et al., 2003; Herwartz et al., 2011) or microbial re-precipitation (Ayliffe et al., 1994; Kolodny et al., 1996; Blake et al., 1997). Evaluation of diagenesis in fossil bioapatites is best accomplished by utilising several types of analyses, each of which will independently provide evidence for or against alteration of the original isotope values, as no single test can conclusively indicate pristine preservation. There are several approaches to testing for diagenetic alteration. Five important empirical tests are:

 

1) Comparison of the isotope composition of skeletal tissues with various levels of preservation potential, such as enamel and dentine (e.g. Ayliffe et al., 1994; Sharp et al., 2000; Bocherens et al., 2011);

2) Analysis of the preservation of expected isotopic differences between sympatric taxa with known ecological or physiological differences (e.g. Lee-Thorp and Sponheimer, 2005; Fricke et al., 2008) and of seasonal cycles (Stanton Thomas and Carlson, 2004; Straight et al., 2004; Goedert et al., 2016; Bocherens et al., 2017);

3) Analysis of enamel crystalline microstructure and composition as prerequisites to preservation of original isotope values (Kolodny et al., 1996);

4) Precipitation of secondary minerals in bioapatite through water-fossil interactions can result in elemental enrichment of e.g. Fe and Mn and substitution of these elements in the apatite lattice, causing orange-brown luminescence in cathodoluminescence (Dauphin, 1991; Kohn et al., 1999; Sponheimer and Lee-Thorp, 1999; Goodwin and Bench, 2000);

5) Testing the linear correlation between the δ18O of the phosphate and carbonate components of bioapatite show a linear correlation, since in mammals phosphate and carbonate are mineralized in equilibrium from the same oxygen source (body water) at the same temperature (e.g. Iacumin et al., 1996)

 

Diagenesis tends to homogenise seasonal signals, as it resets the original isotope values to those of the surrounding sediment and pore fluids (Quade et al., 1992; Lécuyer et al., 2003). The preservation of significant intra-tooth variations in the enamel samples from Tarbosaurus (Fig. 3) suggests at least partial preservation of in vivo environmental isotopic signals. It is highly unlikely that the diagenetic imprint of δ18O signatures could result in the presence of complementary isotopic profiles from two different teeth from the lower jaw of specimen ZPAL MgD I/175. Moreover, enamel samples are characterised by isotopic values that vary significantly from the isotopic signatures obtained from corresponding dentine samples (Fig. 2A). In vivo dentine has a high organic component content (about 20 wt% in human dentine; Goldberg et al., 2011) and exhibits a high degree of porosity, is therefore very prone to diagenesis (e.g. Sharp et al., 2000). These features probably explain the overlap of isotopic signatures between dentine and surrounding sediment and diagenetic carbonate samples.

Bioapatite is characterised by in vivo ionic substitutions of carbonate ions, 4–6 wt% (Vennemann et al., 2001; Rink and Schwarcz, 1995). Carbonate content in the enamel of Tarbosaurus (Fig. 2B) is characterised by an average value of 5.68 wt% (min-max 5.1–6.0 wt%), dentine by an average value of 4.28 wt% (min-max 3.8–4.3 wt%). Bones are characterised by values close to those of enamel, with an average carbonate content of 5.15 wt% (min–max 4.8–5.5 wt%). Sampled herbivores from Nemegt formation are characterised by a range of enamel structural carbonate content of 5.1–5.3 wt% and while bone samples varies between 5.7 and 10.2 wt% (Fig. 2D). Enamel and bone samples seem to retain ‘unaltered’ biological concentrations of structural carbonate, whereas dentine appears at least partially altered by diagenesis. Enamel tend to have lower content of carbonate than bone (Pasteris et al., 2008) and bone has a wide range of structural carbonate proportion, depending on the type of bone and its maturity (e.g. Legros et al., 1987). Theropod dentine has taken up some carbonate during recrystallization that shows similar isotopic composition to the diagenetic carbonate/sediment and herbivore bones have values of carbonate content within in vivo range of 5–13 wt% (Pasteris et al., 2008; Wang et al., 2016, Goedert et al., 2018)

Diagenesis results in the substitution of ions in the bioapatite structure and precipitation of secondary minerals through pore water-fossil interactions, resulting in elemental enrichments such as Mn, Fe, Al, Si, Ba, and REEs (rare earth elements) (Bocherens et al., 1994; Dauphin and Williams, 2007). Cathodoluminescence microphotographs of a polished thin section (Fig. 4A–C) show the outer hypermineralised enamel and tooth dentine. The outer layer (enamel) shows the dark violet luminescence of apatite, suggesting the original chemical composition with minute REE content (Habermann et al., 1999; Ségalen et al., 2008). In contrast, the CL colour of the dentine appears brown to orange, as caused by the presence of manganese and possibly of ions of REEs present as substitutions in the dentine apatite lattice, as well as by the presence of diagenetic oxides in dentinal tubules (Gaft et al., 1996; Ségalen et al., 2008).

The enamel of the sampled Tarbosaurus teeth is characterised by the excellent preservation of the original crystallite structure, in which columnar enamel consists of uniform units (with a width of ca 10–15 μm) with central lines of crystallite divergence (Fig. 4D). Some authors consider the presence of such a fine microstructure as an indicator of the preservation of original isotope values (e.g. Kolodny et al., 1996).

The preservation of the ‘expected’ relationships of isotopic values among the herbivores and carnivores discussed in the paragraphs below also supports the negligible influence of diagenesis on the examined dinosaur enamel samples (Lee-Thorp and van der Merwe, 1987)."

 

Also, from Suarez et al. (2017)

"The isotopic composition of tooth phosphate is the more robust of the two main components of teeth; phosphate and carbonate. The O-isotopic composition of both molecules can be compared to determine if diagenetic overprinting has taken place. If δ18OCO3 values are the same as δ18Op values it may suggest overprinting. This is not the case (see electronic supplemental material). Deviation from theoretical equilibrium would also suggest alteration to one or both O-isotope values. Relative to bone, tooth enamel crystallites are much larger and contain much less organic matter, restricting alteration to the phosphate molecule. Thus, tooth δ18Op values likely represent primary biogenic values. Additionally, if diagenesis had reset δ18Op, there would be no trend in the data, rather it would converge on a single value or have a wide scatter with no trend at all. Finally, the sinusoidal trend could only represent seasonality or seasonal migration, since an ontogenetic trend such as a change in metabolism would result in a directional trend rather than a cyclic trend."

 

Here are a couple of additional recent papers that may be of interest,

Cullen, T.M., et al., 2020, Large-scale stable isotope characterization of a Late Cretaceous dinosaur-dominated ecosystem: Geology, v. 48, p. 546–551, https://doi.org/10.1130/G47399.1

Cullen, T.M., Zhang, S., Spencer, J. and Cousens, B. (2022), Sr-O-C isotope signatures reveal herbivore niche-partitioning in a Cretaceous ecosystem. Palaeontology, 65: e12591. https://doi.org/10.1111/pala.12591

 

In sum, there appears to be consensus that much of the enamel both in structure and composition is unaltered in well-preserved teeth (no significant "recrystallization"), or at least sufficiently original to perform these sorts of neat analyses.