Mineralogical, Elemental and Chemical Composition of Dinosaur

P R O ME T H E US P R E S S / P A L A E O N T O L O G I C A L N E T W O R K F O UN D A T I O N
Journal of Taphonomy
(TERUEL)
2009
Available online at www.journaltaphonomy.com
Luque et al.
VOLUME 7 (ISSUE 2-3)
Mineralogical, Elemental and Chemical
Composition of Dinosaur Bones from
Teruel (Spain)
Luis Luque*, Luis Alcalá, Luis Mampel, Mª Dolores Pesquero,
Rafael Royo-Torres, Alberto Cobos, Eduardo Espílez,
Ana González, Daniel Ayala
Fundación Conjunto Paleontológico de Teruel-Dinópolis
Avda. Sagunto s/n. 44002 Teruel, Spain
Ainara Aberasturi
Escuela Taller de Restauración Paleontológica, Gobierno de Aragón
Avda. Sagunto s/n. 44002 Teruel, Spain
Paz Marzo, Ramiro Alloza
Laboratorio de Análisis e Investigación de Bienes Culturales
Castillo de Capua, 10, nave 31. 50197 Zaragoza, Spain
Journal of Taphonomy 7 (2-3) (2009), 151-178.
Manuscript received 17 December 2008, revised manuscript accepted 7 July 2009.
A detailed study has been carried out on 25 samples of dinosaur bone fragments which come
from 8 sites belonging to six stratigraphic units that span from the Tithonian (Upper Jurassic)
to Albian (Lower Cretaceous) in the province of Teruel, Spain. The aim of the study is to
further understand the mineralogical, elemental and chemical composition of the bones which
come from different depositional environments and try to determine the processes which
created this composition starting from the initial biogenic phosphate. A diversity of chemical
compositions within the same sedimentary environment, within the same site and even within
the same fossil is documented. This supports the idea that fossilization and postmortem
diagenesis is not a homogeneous process. The compositions of bones varied widely in their
Article JTa086. All rights reserved.
*E-mail: [email protected]
151
Composition of Dinosaur Bones
proportions of francolite, dahllite and hydroxyapatite phosphates. The most common cement is
calcite but the presence of unidentified iron oxides is also very frequent. Haematite or barite
cements are found more rarely. The association between the authigenic minerals kaolinite and
palygorskite provides information about the geochemical processes occurring in the microenvironment of fossilization, and the presence of iron oxides, pyrite or barite is informative of
microbial activity. Furthermore, different sources for fossils from a same site can potentially be
differentiated. In sum, a direct relationship between the mineralogy of the bone and cement
composition and the sedimentary environment cannot be inferred.
Keywords: BONE, DIAGENESIS, AUTHIGENIC MINERAL, DINOSAUR, ARAGÓN
Introduction
Two of the processes that affect fossils during
early and late diagenesis are 1) the chemical
transformation of the organic matter and
biominerals, such as carbonate hydroxyapatite
(dahllite), which form the bone, into new
minerals, mainly by replacing the earlier
phosphates in the interior of the structure
(Hedges, 2002), and 2) the precipitation of
authigenic minerals influenced by direct
environmental factors like geochemical
composition of the sediment and the ground
water during the burial, level of oxidation or
reduction of the environment, its alkalinity
and bacterial activity. Other indirect factors
that may affect the mineralization are climate,
local vegetation and the state of preservation
of the bone. Therefore, theoretically, mineralogical
composition, texture and structure of fossil
bones are sources of information about
biostratinomy (sensu Fernández-López &
Fernández-Jalvo, 2002) and early and late
diagenetic processes occurring to the bone
in its burial-depositional environment.
The diagenetic alteration of bioapatite
in bones and teeth has been widely studied
in archaeological remains and mammal fossils,
but studies in the mineralogy of dinosaur
bones are less frequent (e.g. Elorza et al., 1999;
Martill, 2001; Sung Paik et al., 2001; Wings,
2004; Chinsamy-Turan, A., 2005, or Goodwin
et al., 2007). Even if similar early diagenetic
processes occur in most continental vertebrate
sites, it is known that alterations of bone also
depend on the microscopic bone structure
(Nemliher et al., 2004; Goodwin et al., 2007).
Late diagenesis differs necessarily among
different sites due to the length of burial and
the exposure to a variety of conditions of
pressure and temperature, as in the case of
dinosaur sites.
From a geochemical point of view,
bones are an open system interacting with
biological, atmospheric and sedimentary
environments, from the moment that the loss
of organic matter begins. Once death occurs,
the apatite is no longer in thermodynamic
equilibrium with the atmosphere and reacts
with its environment. This produces changes
in its chemical composition, crystallographic
parameters, crystallite size, and lattice strains
(Nemliher et al., 2004). Diagenesis typically
causes modification of its composition with
substitutions of (PO4)3 for (CO3F)3, giving
rise to isomorphous crystals of carbonatefluorapatite (francolite) (Kolodny et al., 1996).
The substitution and the re-precipitation of
the original carbonate hydroxyapatite occur
early in diagenesis (Dauphin, 1998). In this first
biostratinomical phase and in early diagenesis
the bone micro-environment (specially pH
152
Luque et al.
values) is mainly conditioned by collagen decay,
while in later phases it is more influenced
by external environmental factors (Trueman
et al., 2003; Pfretzschner, 2004). Bone porosity
is also affected and it determines some of
the physical properties of the fossil (Hedges
et al., 1995).
The apatite can integrate calcite in
its structure, which alters its solubility
(Berna et al., 2004), as well as pyrite and
iron oxides (Pfretzschner, 2001 a and b) and
substitution of Ca for Sr, Na, K, U, Ba, Pb
and other metals, as well as substitutions of
P for As, V, Cr or Si. During diagenesis, the
bone structure also becomes enriched in
authigenic elements such as Al, Si, Mn, Fe
(Dauphin, 1998; Elorza et al., 1999; Goodwin
et al., 2007) and rare earth elements, which
may reflect the original depositional
environment (Trueman, 1999; Lécuyer et al.,
2003; Trueman et al., 2003). These chemical
modifications vary within the same deposit
(Reiche et al., 1999) and within the bone
(Dauphin, 1998). The alteration of the
apatite in the bone depends, not only on
environmental factors, but also on structural
factors such as the density and relative
porosity of bones and teeth (Nemliher et al.,
2004; Goodwin et al., 2007).
Other authigenic minerals cement the
structure of the bone by filling the voids. These
constitute a variety of neoformed minerals
(Hubert, et al., 1996; Wings, 2004) related to
the chemical conditions of the surrounding
water and sediment, which in turn depend
originally of the environment of sedimentation
The objective of this study is to
characterize the mineralogy and chemistry
of the dinosaur bones in an area spanning a
range of ages, depositional environments and
lithologies in the Iberian Range partially
located in the province of Teruel, Spain.
Fossil bones are located in different stratigraphic
units, ranging from Late Jurassic to Early
Cretaceous (Figure 1). The samples exhibit
a great variety of degrees of hardness, colors,
mineral crusts and cements as well as apatite
replacements. All the internal structural and
mineralogical modifications should reflect
their biostratinomic and diagenetic history.
Methods
The mineralogy of twenty five dinosaur bone
fragments from eight sites (Figure 1)
belonging to six stratigraphic units and four
depositional environments has been analyzed
through X-Ray diffraction (XRD) (Table 1)
in Gabinete Minero TEY Laboratory. Other
complementary techniques have been used,
such as petrographic and microscopic analyses,
given that it is known that these variations
can occur in very small distances in the bone
(Goodwin et al., 2007). These techniques
include thin sections, scanning electron
microscope (SEM) and energy dispersive
spectrometer/electron probe micro-analyses
(EDS).
Furthermore, a visual study of the
external characteristics of the fossils has been
carried out using some magnification (lenses)
with the aim of spotting features such as
weathering, transport and pre and post burial
bone breakage.
Statistical analyses consists of
multiple regressions to determine the
relationships between independent and
dependent variables, such as different mineral
types in bones and sediments. This method
has been previously employed by Goodwin
et al. (2007) to compare element composition
of dinosaur bones. Results have been
represented in two dimensional scatter plots and
regression lines. The software used to perform
the statistical analyses is STATISTICA 7.1.
153
Composition of Dinosaur Bones
AGE
ALBIAN
Forcall
FORMATION
ESCUCHA
El Castellar
LOCALITY
UTRILLAS
TYPE
Cancellous
Cancellous
Cortex
Cortex+Cancellous
Cortex+Cancellous
Cortex+Cancellous
Cancellous
Cortex
Cortex+Cancellous
Cortex+Cancellous
Cortex+Cancellous
Cortex+Cancellous
Cancellous
Cancellous
Cancellous
Cortex
Cortex+Cancellous
Cortex+Cancellous
Cancellous
Cortex+Cancellous
Cortex
Cortex+Cancellous
Cortex+Cancellous
Cortex+Cancellous
Cortex+Cancellous
Cortex+Cancellous
XRD
x5
x3
x2
x2
SECTION SEM
THIN
EDS
Table 1. Analythical techniques employed with dinosaur bones from Teruel (Spain), and which samples were analysed (in grey): XRD, X-Ray diffraction;
SEM, Scanning electron microscope; EDS, energy dispersive spectrometer/electron probe micro-analyses; x2, two thin sections analysed; x3, three
thin sections analysed; x5, five thin sections analysed.
Aptian
Peñarroya de Tastavins
Riodeva
El Castellar
El Castellar
Gúdar
Aliaga
Xert
Villar del
Arzobispo
Castellar
Camarillas
Lower Aptian
Barremian
Late HauterivianLow Barremian
TithonianBerriasian
SITE
SAMPLE
UT-2 CPT-2022
CPT-831 A
CT-19 CPT-831 B
CT-19 H
Arsis ARS-90
CPT-2073
CPT-2071 A
DS
CPT-2071 B
GUD-13 CPT-2007
GUD-14 CPT-2008
CPT-1995 A
GUD-1
CPT-1995 B
CPT-908 A
CT-21
CPT-908 B
CPT-10-12 B
CT-10
CPT-10-12 A
CPT-1179
CPT-1142
CPT-1121
RD-10
CPT-1132
CPT-1228
CPT-1137
CPT-973
CPT-1012
CPT-1091
RD-11-3
RD-1
RD-3
RD-6
RD-11
154
Luque et al.
Analythical methodologies
XRD: Twenty five dinosaur bone samples and
twenty four sediment samples from the sites
were analyzed by X-ray diffraction (powder
method) to characterize the semi-quantitative
ratio of the sample mineralogical phases.
The XRD analyses were carried out using a
Philips diffractometer PW 1830, Cu cathode
with wavelength Ka = 1.54051. The angular
scan was recorded from 3º to 65º 2θ with a
digital register Philips PW 1710. The
diffractogram of samples was studied with
the XPowder software (version 2008) both
for the qualitative and quantitative analyses.
Petrographical and histological analyses
have been carried out on twenty six thin sections
of dinosaur bones. Thin sections were
impregnated with red alizarine to determine
calcite in the sample and observed under a
the petrographic microscope Nikon Eclipse
E-4000 POL with lenses from 4x to 100x
magnifications. Binocular lenses from 10x to
40x were also used as well as 10x hand lenses.
Six selected samples have been
examined using an environmental scanning
Figure 1. Location of the dinosaur sites studied in the province of Teruel (Spain) and their position
within a stratigraphic scheme and general chronology.
155
Composition of Dinosaur Bones
electron microscope (SEM) model QUANTA
200, housed at the Museo Nacional de
Ciencias Naturales (CSIC), at backscattered
and secondary electron mode, and a SEM of
the Laboratorio de Análisis e Investigación de
Bienes Culturales. Chemical analyses of these
samples have been carried out with coupled
Oxford-EDS/WDS detectors. EDS (EnergyDispersive X-ray Spectroscopy) analyses have
provided element chemical composition of
any specific area of interest within selected
specimens.
siliclastic (sandstone with conglomerates
and red clay mud). Generally, fossil bones are
found as clasts in a sandy channel fill or
interbedded with red and grey mudstones of
the floodplain.
Fossils studied were collected from
five sites: RD-1, RD-3, RD-6, RD-10 and RD-11
and present different characteristics according
to the site where they were found. This is
explained by the changes in the sedimentary
environments within each one of the various
sequences, spanning from tidal-marine to
alluvial influence.
Results
RD-1: The findings on the surface consist of
fragments of big bones and ribs of a
sauropod dinosaur (Royo-Torres et al., in
press). The cortical surface is intact,
although some of the outer lamellae layers
are missing.
Localities, lithologies and external characteristics
of fossils
The main characteristics identified by
macroscopic observations (Figure 2) and the
mineralogical composition of the formations
are presented in Table 2 and Table 3. In the
case where multiple samples come from the
same sediment of the same formation, the
percentage values of each mineral is obtained
by averaging the values of the samples from
that formation. The standardized color chart
has not been used due to the large variety of
small color spots composing the general
surface.
- Limestone, sandstone and mudstone of the
Villar del Arzobispo Formation in Riodeva.
The paleoenvironment of this formation is a
tidal flat (Mas et al., 1984) and its age
corresponds to Tithonian-Berriasian (Bádenas
et al., in press). In Riodeva, a variety of
environments are represented within various
sequences which are cyclical, spanning from
an environment with coastal influence to a more
continental one (Luque et al., 2005). In this
area, Villar del Arzobispo Fm. is dominantly
RD-3: The site contains remains of the
stegosaurid Dacentrurus and undetermined
fragments of vertebrates found on the
surface (Cobos et al., 2008). This site shows
possibly a mix of faunal elements, given
that the external appearance of the bones is
very different.
RD-6: A group of fragments of vertebrae and
ribs from an undetermined dinosaur found in
sandstone. It most likely was transported since
it shows signs of abrasion. The trabecular
tissue is often directly exposed (Figure 2A).
RD-10: The site is situated at the top of a
channel fill deposit between gray clays and
quartzitic sandstones. It yielded a large
concentration of bones including the holotype
of Turiasurus riodevensis (Royo-Torres et al.,
2006) as well as remains of stegosaurids (Cobos
et al., 2008). Some of the remains are found
articulated and very well preserved (Figure 2B).
156
Luque et al.
Figure 2. Some surface characteristics of the dinosaur bones studied: A. Rounded vertebra from the RD-6 site
(Villar del Arzobispo Fm., Riodeva); B. Vertebra showing well-preserved thin laminae from the RD-10 site (Villar
del Arzobispo Fm., Riodeva); C. Thin calcite crust on the CT-21 site (Villar del Arzobispo Fm., El Castellar); D.
Diagenetical micro-fissures in CT-21 fossils; E. Different mineralogical composition of cements in voids of bones
from the CT-10 site (Castellar Fm., El Castellar); F. Bone alteration on the edges of ribs from the Dehesillas site
(Camarillas Fm., Aliaga); G. Iron oxide crust on iron rich bones from the Gúdar site (Camarillas Fm.), and; H,
cortical bone lost and possible teeth marks in a vertebra from the Utrillas site (Escucha Fm.).
157
Composition of Dinosaur Bones
Dark
brown-gray
COLOR
No
No
TRANSPORT
TRACES
(Rounding and/or
abrassion)
Poorly preserved
cortex
Cortex well preserved
Cortex well preserved
WEATHERING
TRACES (Cortex
preservation)
Iron oxide
and calcite
Gypsum
No
Table 2. Characteristics identified by macroscopic observations of fossil bone material.
Arsis
Dark brown
Abrassion
Abrassion
Strong loss of cortex
Strong loss of cortex
No
Iron oxide
No
Cortical preseved
Cortical preseved, few
losses
Gypsum
Iron oxide
Microfissures
longitudinal and
perpendicular
Longitudinal and
perpendicular
Large filled by
calcite
Longitudinal and
perpendicular
Multiple directions
Microfissures to
120º and 60º from
the main axis
Few fractures
filled by calcite
and iron oxide
Presure deformation
Perpendicular
filled by calcite
Longitudinal
Fissures filled by
sediments, bites
Oblique and
perpendicular
MINERAL FRACTURES
CRUSTS AND FISSURES
Xert
CT-19
Cream to
red oxide
SITE
Peñarroya de Tastavins
Forcall
Utrillas
FORMATION
El Castellar
Escucha
SITE LOCALITY
Utrillas
Abrassion
A lot of cortex lost
No
No
Cream to
white
Red to
purple
Abrassion
Cortex well preserved
No
Partial loss of cortex,
rootmarks
RD-3
Reddish
No
Strongly eroded cortex
and cancellous tissue
No
RD-6
Cream
Strong abrassion
Cream to
gray
RD-10
Reddish to
deep red
RD-1
CT-10
Villar del Arzobispo
Villar del Arzobispo
Riodeva
El Castellar
Rounded
CT-21
No
No
Strongly eroded cortex
Iron oxide
and cancellous tissue
Castellar
Camarillas
Dehesillas
Black
Red to deep
red
Gúdar
El Castellar
Aliaga
Camarillas
Black to
deep red
Gúdar
158
Luque et al.
RD-11: This site consists of two diplodocid
vertebrae and a number of unidentified
dinosaur bone fragments found in a gray
sandy mudstone deposit.
- Villar del Arzobispo Formation in El Castellar.
It is characterized by the presence, in the
base of each sequence, of layers of micritic
limestone deposited in a tidal environment
that sometimes include dinosaur footprints.
The fossils are found concentrated in small
channels of sandstone and conglomerate in
the middle part of the sequence, such as on
the red and gray silty mudstones.
The CT-10 site contains a stegosaurid
vertebra and fragments of undetermined
bones. Sometimes the fossils have an intense
oxidation and a fine calcitic crust (Figure 2C).
They have a characteristic micro-fissuration
with angles of 60º and 120º with respect to
the longitudinal axis (Figure 2D).
- Lacustrine limestones and marls of Castellar
Formation in El Castellar. This formation is
from the Late Hauterivian to Lower Barremian
age and is found discordant over the Villar
del Arzobispo Fm. (Soria, 1997; Martín-Closas,
2000). The formation is divided into two
sections -Soria et al. (2001)- which consist
of muddy clays and distal alluvial sands in the
base and marls and grey limestone of lacustrine
origin above. The base of the formation
consists of purple clays with siliceous
nodules, enriched with clinochlore (resulting
from alteration of minerals like amphibol,
pyroxene or biotite) and clays, with
embedded channel fills of very compact
siliceous sands. The dinosaur remains are
found in this lower section as well as
between the limestones, and the studied site
(CT-21) is found in an environment of
siliciclastic alluvial plain. Some bivalves
found within the sandy levels could be related
to specific moments of marine influence
(Soria, 1997).
The CT-21 site produced fragments
of ornithopod long bones as well as
undetermined fragments found on the surface.
There are not many diagenetic fractures but the
bones are filled with calcite and iron oxides
in their interior. There is a local variation of
the cement with the presence of a pink fringe
in the interior of the bone, parallel to the
bone surface, formed of barite.
- Red clays and sandstones of the Camarillas
Formation in Aliaga (included in the European
Geoparks Network). This formation has a
Barremian age and is a generally light to dark
red-colored alluvial plain grading to a clays
representing a shallow ephemeral fresh water
pond interbedded with white to reddish channel
fill sandstones of fluvial origin (Simón,
1998). The site of the dinosaur remains that
have been studied (called Dehesillas: DS) is
situated in gray clays under a layer of
laminated sandstone with bioturbation.
The DS site yielded vertebrae and
articulated ribs of an iguanodontid (Alcalá et
al., 2007). The cement infill of the bones is white
to oxide color and there are some shiny areas
associated with pyrite. Fractures are diagenetic
in origin and some of the bones have been
deformed by being pressed together. Mineral
regrowth affecting the bone can only be found
on the edges of some of the ribs (Figure 2F).
- Camarillas Formation in Gúdar. This site
shows fluvial white and reddish laminated
sandstones and red floodplain mudstones. It
is situated in the middle part of the
formation and the fossil remains have been
found both in situ and on the surface. The
first ones were included in lighter red and
darker red mudstones with a micaceous and
kaolinitic composition.
159
Composition of Dinosaur Bones
Utrillas
Peñarroya de Tastavins
El Castellar
SITE LOCALITY
Castellar
Villar del Arzobispo
Escucha
Xert
Forcall
FORMATION
Fluvial
Alluvial to lacustrine
Tidal flat to Alluvial
Tidal flat
Shallow marine
Shallow marine
PALAEOENVIRONMENT
Barremian
HauterivianBarremian
TithonianBerriasian
Albian
Lower Aptian
Aptian
AGE
Silt/clay
Silt/Clay
Silt/Clay
Sandstone
Sandstone
Silt/Clay
Limestone
Silt/clay
Sandstone/
conglomerate
Limestone
Silt/Clay
Sandstone
Silt/Clay
Sandstone
Silt/Clay
LITHOLOGY
44.6
25.1
7.3
7.2
15.1
5.7
14
20.5
52.5
99
34.9
68.2
46.3
34.3
17.5
53.7
41
33.4
8.9
30.3
25
36.2
11
7.7
86.4
13.5
39.7
99
2.2
1
2.5
8.5
14.2
9.2
4.9
6.2
5.8
9.1
5.1
7
1.7
<7
17.3
1
4.6
26.5
29
3.5
29
18.1
36.3
24.9
17.4
32.8
10.2
30.3
52.2
7.4
5.8
9
8.2
1.8
1
13
10.2
4.2
8.3
8.1
3.5
6.7
4.3
CALCITE QUARTZ FELDSPAR MICROCLINE ALBITE BIOTITE ILLITE CLORITE CLINOCLORE GYPSUM DOLOMITE KAOLINITE PYROXENE
Gúdar
Aliaga
El Castellar
Riodeva
Camarillas
Table 3. Paleoenvironments and lithologies of the dinosaur sites, and mineralogical composition (percentage) of the sediments where the studied dinosaur bones were found,
SITE
LOCALITY
Peñarroya de T.
El Castellar
Utrillas
Riodeva
El Castellar
Aliaga
Gúdar
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Luque et al.
The bones of the site in Gúdar
consist of undetermined fragments, vertebrae
and dinosaur ribs that show a light red to
intense dark red color in the interior, and a
fine iron crust on the surface (Figure 2G).
- Limestones and marls of the Xert Formation
in Peñarroya de Tastavins. This formation,
of lower Aptian age, is characterized by
sandstones and sandy limestones at the base
and calcarenite and bioclastic limestones with
abundant marine fauna on the top. It was
deposited in a coastal environment, with
continental sediment supply, which progressively
graded into subtidal conditions (Simón, 1998).
The site consists of siltstones and mudstones
of greenish color with oxidation on top
containing remains of carbonaceous vegetation,
rootcasts and marine invertebrates that have
colonized part of the dinosaur skeleton
(Royo-Torres, 2006).
The remains belong to the holotype
of the sauropod Tastavinsaurus sanzi (Canudo
et al., 2008) found articulated in shallow
marine deposits, which indicates little or no
transport postmortem. It has been suggested
that either the body was transported by
flotation (Canudo et al., 2008) or flooded by
a transgressive sea level rise after partial
unburial (Royo-Torres, 2006).
- Marls of the Forcall Formation in El
Castellar. This formation is of Aptian age and
lies conformably over the Xert Fm. It is made
up of grey marl which intercalates bioclastic
and nodulous limestones with orbitolines,
planktonic foraminifera, echinoderms and
ostreids, indicating a marine environment
due to a trangressive trend (Simón, 1998).
The site is found at the base of the Forcall
Formation (Alcalá et al., 2007), in gray
mudstones lying on a sandstone bed probably
deposited in a marginal area of the basin. It
indicates a coastal influence and shows signs
of edaphization, which could indicate sub-aerial
exposure.
CT-19 yielded articulated and
associated bones of the same sauropod
dinosaur some of them orientated by water
current or waves. Smaller bones (such as
phalanges and tarsal bones) are poorly
preserved and are partially crumbling but the
larger ones show a well preserved cortex.
- Limestones, sandstones and clays of the Escucha
Formation in Utrillas. This formation of
Lower-Middle Albian age mainly consists
of gray to beige clay with redder levels that
intercalate fine to coarse quartz sandstones
rich in ostreids and other marine fauna. It is
defined as the transition from a shallow platform
to a tidal plain, a marshy environment and
finally an alluvial plain (Pardo & Villena,
1979). The site is found in the Middle Member
(Canudo et al., 2005), with facies of flood
plain with tidal influence (Pardo & Villena,
1979). Bones are surface collected, but some
of them show encrusted sandstone fragments
which suggest their stratigraphic origin.
Remains of vertebrae and undetermined
dinosaur bone fragments have been found
on the surface. The remains are very poorly
preserved. Some bones are rounded and the
surface exposes the trabeculae, sometimes
showing marks that could be due to possible
bites (Figure 2H).
Mineralogical composition of dinosaur
bones
For the mineralogical study via XRD, samples
of cortex as well as of cancellous tissue of
the dinosaur fossils were selected. In this
process we selected typical bone fragments.
The total proportions between minerals of
161
Composition of Dinosaur Bones
the cement and the quantity of phosphates
varies considerably according to the quantity
of voids in the bone. The results of the
mineralogy of the fossils are shown in Table 4.
- Forcall Fm. in El Castellar: The apatite is
francolite and the cements are calcite and
gypsum. Unlike other sites, biotite is found
in abundance.
- Villar del Arzobispo Fm. in Riodeva:
There is a diversity in composition given
the variety of environments in which the
sites have been formed. RD-10 includes
both dahllite and francolite suggesting two
families of bones within the same site and
two possible diagenetic histories. RD-1,
RD-3 and RD-6 show a quite homogenous
composition richer in dahllite with calcitic
cement.
- Escucha Fm. in Utrillas: There are no traces
of phosphates. The bone remains analyzed
in Utrillas show total original phosphate
mineral replacement and calcite has replaced
it by recrystallization.
- Villar del Arzobispo Fm. in El Castellar:
The apatite composition is 100% dahllite
and the cement is dominantly calcitic.
- Castellar Fm. in El Castellar: The apatite
composition of the bone is 100% francolite
showing calcite in its structure. The cements
are mainly both calcite and barite with a
rarer component palygorskite and kaolinite.
- Camarillas Fm. in Aliaga: Two of the three
samples taken come from the same bone
(cortex and cancellous tissue). The apatite
composition is 100% francolite and the
cements are both calcite and gypsum.
- Camarillas Fm. in Gúdar: Although the fossils
are intensely red-colored their mineralogical
composition greatly differs according to the
fossil. A group of fossils show hydroxyapatite
and barite while the other shows francolite
and haematite.
- Xert Fm. in Peñarroya de Tastavins. The
sample shows a low mineralogical diversity,
with dahllite and calcite as apatite and
cement, with quartz as a detritic.
Bone microstructure preservation and mineral
cements
Thin sections and SEM images analyses
show that the bone micron-scale structures,
such as Haversian canals and osteocyte
lacunae in the compact bone or lamellae
tissue, have been preserved in almost all the
studied cases. In some few cases collapse of
the internal cancellous structure exists
(Figure 3A). These ruptures favor the transport
of ions within the bone and its mineralization.
The degree of breakage could be also
related to bacterial activity, given that bone
is weakened during biostratinomy and in the
initial phases of diagenesis and, hence, it
may collapse more easily. Furthermore, it
could be related to the presence or lack of
cements before the stresses which caused
the breakage (Martill, 2001). Most of the
fissures are filled with calcite, but iron
oxide infill is also found relatively in
abundance.
Apatite and textural preservation
The fibrous structure of the bone has been
preserved in most cases although through
the alizarine red tinting it looks that there is
an incorporation of the calcite following the
162
Luque et al.
Table 4. Mineralogical composition (percentage) of the samples of the dinosaur bones from Teruel.
SITE LOCALITY FORMATION
Utrillas
Canaleta
Peñarroya de T.
Aliaga
Utrillas
Forcall
Xert
Camarillas
SAMPLE
CPT-2022
CPT-831 A
CPT-831 B
Camarillas
El Castellar
Castellar
El Castellar
Villar del
Arzobispo
DOLOMITE
K-FELDSPAR
BIOTITE
ILLITE
CLINOCLORE
PALIGORSKITE
0
1
0
0
0
1
0
KAOLINITE
0
5.9
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
CT-19 H
1.8
0
0
21.4
0
3.6
0
0
ARS-90
CPT-2073
5.38
0
0
0
0
0
0
0
4.6
0
0
3.2
0
0
0
0
CPT-2071 A
9
0
0
0
0
0
0
0
CPT-2071 B
4.8
0
0
0
0
0
0
0
13.98
12.01
4
0
0
4
0
0
0
CPT-2007
Gúdar
QUARTZ
CPT-2008
0
0
0
0
0
1
0
CPT-1995 A
5.05
0
0
0
0
1
0
0
CPT-1995 B
0
0
3
0
0
1
0
0
CPT-908 A
6.8
0
0
0
0
0
12.4
4.9
CPT-908 B
6.8
0
0
0
0
0
5.1
0.9
CPT-1012 B
6.51
0
0
0
0
1
0
0
CPT-1012 A
2
0
0
0
0
1
0
0
0
0
0
3
0
0
0
1
0
0
0
0
0
0
Riodeva
Riodeva
Villar del A. CPT-973
Villar del A. RD-3-8-R
2
1
Riodeva
Villar del A. CPT-1091
CPT-1179
0
0
4
0
1
0
0
0
4
0
3
0
1
0
0
0
CPT-1142
1
0
3
0
1
0
0
0
CPT-1121
1
0
1
0
1
0
0
0
CPT-1132
1
0
0
0
0
0
0
0
CPT-1228
4
0
0
0
0
0
0
0
CPT-1137
1
0
0
0
0
0
0
0
Riodeva
SITE LOCALITY
Villar del
Arzobispo
FORMATION
Utrillas
Utrillas
Canaleta
Forcall
Peñarroya de T.
Xert
Aliaga
Camarillas
Gúdar
Camarillas
El Castellar
Castellar
El Castellar
Villar del
Arzobispo
Riodeva
Riodeva
Riodeva
Riodeva
SAMPLE
CPT-2022
CPT-831 A
CPT-831 B
CT-19 H
ARS-90
CPT-2073
CPT-2071 A
CPT-2071 B
CPT-2007
CPT-2008
CPT-1995 A
CPT-1995 B
CPT-908 A
CPT-908 B
CPT-1012 B
CPT-1012 A
Villar del A. CPT-973
Villar del A. RD-3-8-R
Villar del A. CPT-1091
CPT-1179
CPT-1142
Villar del CPT-1121
Arzobispo CPT-1132
CPT-1228
CPT-1137
FRANCOLITE
HYDROXYAPATITE
DAHLLITE
CALCITE
HAEMATITE
BARITE
GYPSUM
0
27.9
88
69.8
0
45.8
16.2
61.2
0
0
48.09
45.72
37.1
54.2
0
0
16.98
18.16
20.49
0
0
0
17.64
20.02
17.53
0
0
0
0
0
0
0
0
27.11
30.33
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
25.28
0
0
0
0
0
0
0
0
0
10.29
69.81
63.41
56.38
59.75
40.91
32.97
21.43
53.42
51.81
36.47
97.9
66.2
8.1
3.5
69.33
30.6
18.1
25.7
0
0
0
0
28.3
33
81.19
28.06
16.81
20.53
14.04
49.72
59.82
75.01
28.94
23.23
46.01
0
0
0
0
0
0
0
0
0
0
46.87
41.31
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
40.87
69.64
0
9.37
10.4
40.87
0
0
0
0
0
0
0
0
0
0
0
0
0
3.9
0
0
15.9
56.7
8.3
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
163
Composition of Dinosaur Bones
structure and orientation of the crystallites
of the Haversian system and the lamellae in
many samples (Figure 3B). The iron oxide growth
follows weak areas in the bone structure in
relation to the Haversian systems (Figure
3B). Only in remains from the Arsis site the
iron oxides grow independent of the bone
microstructure. In other cases, the substitution
of the phosphate by calcite looks total,
retaining the bone structure, as happens in
the samples from the Escucha Fm. (Figure 3C).
Pore-infill mineral cements and crusts
The cements that fill voids of the bone
structures or bone fractures show the largest
mineral diversity of the samples (Table 4).
Depending on the site, different bone
cements have been found, which indicate a
differential exchange depending on the
surrounding lithology and the ground table
composition. The total proportion of the cement
in relation to the apatite described in Table
3 is only related to the porosity of the bone.
- Villar del Arzobispo Fm. in Riodeva:
Samples from RD-10 show different phases
of cementation, intercalating sparitic calcite
and iron oxides which are undeterminable
with XRD. The iron oxides are principally
between the Haversian systems and between
the voids of the cancellous tissue (Figure 3B)
growing after calcite precipitation. RD-3
samples are very similar to RD-1, but microfissures are somewhat orthogonal (70-90º).
These micro-fractures act as a path for
dissolved iron penetration and iron oxide
precipitation and calcite replacement. At RD-6,
the gap infill is mainly calcitic with sparitic
cement (Figure 3D). Bone EDS analyses in
SEM does not show a clear tendency or
distribution of the calcite replacement within
the bone (Figure 3E). The iron oxides are
not as widely distributed as in other sites
and coating calcite microcrystals growth.
Iron oxide is also found as nodules inside
the calcitic cement as well as on the bone
surface, conditioned by the fissures and the
histological structures. The concentration of
iron oxide in the bone is often diffuse and is
associated with an increase of the porosity
of the tissue (Figures 4A and 4B).
- Villar del Arzobispo Fm. in El Castellar:
The initial fissures, perpendicular to the
bone structure, are filled with iron oxides and
the later ones, parallel and perpendicular,
are filled with calcite. The cortex shows iron
oxides only in small fissures perpendicular
to the structure and the conducts in contact
with them. The cancellous tissue shows an
increase of the iron oxides between the
Haversian systems and towards the exterior.
Tunnels surrounding the Haversian canals
show also bacteria tunneling.
- In the Castellar Fm. of El Castellar there
are calcite crystals, which grew radially from
the bone. In some of the bone gaps of the
cancellous tissue, sedimentation of micrite
formed in two phases of cementation
separated by a small accumulation of iron,
which was later covered again by iron oxide
nodules. Finally, large crystals of barite are
growing in the interior of the cancellous bone
following the fringe parallel to the cortical
surface with a thickness of 5-7 mm (Figure 2E).
- Camarillas Fm. in Aliaga: SEM has shown
that in some areas of the ribs there is
formation of pyrite fringes covering the interior
of the voids and in the hole left over calcite
crystals that were partially dissolved afterwards
(Figure 4C). The most common cement,
however, is calcite rich in iron oxides.
164
Luque et al.
Figure 3. Bone microstructure, cementation and element distribution of dinosaur bones from the Riodeva and Utrillas
sites: A, Trabecular collapse in RD-10 bones; B, Cementation and mineral growth following apatite and Haversian
system microstructure; C, Total replacement of apatite by calcite (right side tinted with alizarine red) in the
Utrillas site; D, Sparitic calcite infill of voids in the RD-6 site remains, and; E, SEM EDS analysis of the same
sample showing element distribution from surface (on the left) to the mid bone (right) from the RD-6 site.
165
Composition of Dinosaur Bones
- Camarillas Fm. in Gúdar: the bones show
voids filled with iron oxides opaque to the
polarized light, consisting of haematites, in
the Haversian canals and cancellous tissue
and in the fractures formed by the collapse
caused by pressure, indicating a possible late
diagenetic origin. In some bone voids, within
the oxide a barite infill can be observed which
grows following the mentioned fractures and,
which reaffirms this late post compression
cementation (Figure 4D). The GUD-14
sample has two phases of barite crystal
growth separated by a precipitation of iron
oxides (haematite following XRD) (Figure
4E). The first generation of barite crystals is
radial-fibrous and is only formed in the
bigger voids. Also aluminosilicates have been
found which could correspond to chlorite in
the interior of some of the holes of the structure
(Figure 4F). There are small tetrahedric
phosphate crystals individualized on the
internal surface of the bones (Figure 4F).
- Xert Fm. in Arsis: The bone microstructure
is well preserved showing iron oxide growth
more intense in areas near the surface of the
sample. There are at least four stages of
cementation: the former consist of a partial
gravitational sediment infill from the exterior.
It consists both of very fine dark micrite and
fine sands in a micrite matrix showing marine
shell bioclasts. Secondly, a thin fringe of
radial sparite growth is followed by a thin
coat of sedimentary micrite. Finally there is a
growth of mosaic sparite crystals that fill
the voids.
- The Forcall Fm. in El Castellar: As in
many of the previous cases, we have noted a
complex cementation that intercalates the
formation of sparitic calcite crystals with
iron oxides. The calcite is somewhat altered
through dissolution and shows a possible
re-precipitation. In general, the structure is
in a much collapsed state. The larger fissures
and bone surface show a fine gypsum crust.
- In the fossils of the Escucha Fm. in Utrillas,
the cement is dominantly calcitic with sparite
crystals showing various phases of cementation.
After a bone breackage partially filled with
sparitic calcite a fine iron oxide layer is
produced and a micritic gravitational infill
occupies around 15% of the cancellous bone.
Afterwards new calcite radial cement, which
intercalates iron oxide masses, infilled the
rest of the hole. The occurrence of micrite
after a previous cementation may be related
to processes of reworking or, at least, with
significant re-sedimentation.
Discussion
Ionic exchange between the sediment, the
water table composition and the bone is always
occurring during fossilization. Due to their
high porosity, which favors migration of
fluids, bones are a suitable matter for the
formation of secondary diagenetic minerals.
Therefore, the authigenic minerals formed
in the bone as substitution of the original
mineral (dahllite) or as cements or crusts,
should have a direct chemical relationship
with the surrounding sediment and the fluids
that circulate throughout the sediment. The
type of sediment (lithology, structure, texture)
is conditioned in turn by the environment of
sedimentation and the matter of the source
area. However, the correlation between these
authigenic minerals and the environment of
sedimentation is not as clearly defined as
would be expected (Dauphin, 1998; Lécuyer
et al., 2003; Wings, 2004). The same occurs
in more recent archaeological burials (Hedges
et al., 1995) or has been observed experimentally
166
Luque et al.
Figure 4. A, Iron oxide concentration in the bone surface from the RD-10 site; B, Tunneling in iron
enriched areas of the RD-10 site fossil bone; C, Pyrite and calcite infill of voids in dinosaur ribs from the
Aliaga site; D, Void mineral infill in bone from the Gúdar site showing probable biogenic iron lamination
and barite growth; E, Two barite precipitation stages separated by an iron thin crust in trabecular tissue from
the Gúdar site, and; F, Authigenic apatite regrowth on the bone surface from the Gúdar site surrounded
by haematite and an aluminosillicated mineral (clinochlore?).
167
Composition of Dinosaur Bones
during bone decay (Nicholson, 1996; NielsenMarsh, et al., 2007). The taphonomic history
in this way shows itself to be very complex
and difficult to decipher (Nicholson, 1996).
In fact, the interrelationship of the majority
of the variables presented in this work:
weathering, transport, cracking, color, lithology
and sediment mineralogy, bone apatite
replacement, bone cement composition,
cementation phases or microbial activity traces
in general do not show a direct relationship
with the environment of sedimentation and
seem to show that each site follows an
independent taphonomic history. This variability
is extended to the elements within the same
site and even, in some cases, within each bone
itself. Some of the more indirect parameters,
such as color or abrasion, seem to have a
correlation that is more direct with the
environment than the bone mineralogy or
chemistry.
Apatite preservation and replacement
General bone structure is well preserved in
almost all the studied dinosaur samples in
the region of Teruel. Chemically, the most
common process in the bone structure has
been the replacement of dahllite with
francolite, although it is likely that fossil
dahllite does not contain the original crystals
but these have rather been replaced. These
partial or total substitutions of carbonatehydroxiapatite during the diagenesis for
carbonate-fluorapatite is common in many
other dinosaur sites (Hubert et al., 1996;
Elorza et al., 1999; Pereda-Suberbiola et al.,
2000; González & Astini, 2007). In our results
it seems that there is a divergent relationship
between the quantity of calcite of the sample
and the proportion of dahllite/francolite. In
the case of many of the sites, when the bone
shows more than 40% of calcite, almost all the
apatite is exclusively dahllite, and francolite
is not present (Figure 5). While in Riodeva, low
calcite content implies a higher dahllite
percentage, but in the last case, the linear
trend of dahllite reduction when calcite increase
is also related with porosity and calcite cement
infill inside the bone. This may be related to
what has been previously described as
transformation from carbonate-hydroxyapatite
into fluorapatite occurring with very low
carbonate-ion content (Nemliher et al., 2004).
The tendency during fossilization is to
precipitate a variety of apatite with lower
OH-ion content and a higher F content, which
is related to the intensity of the diagenetic
processes more than with the age itself
(Nemliher et al., 2004). Perhaps the presence
of early carbonated cement influences the
capacity of transport and reaction of the fluids
rich in fluorine and locks or delays the
formation of francolite.
The incorporation of calcite between
lattice apatite suggested by thin sections
has been described in Mesozoic reptiles
(Holz & Schultz, 1998) but not in other
cases with dinosaurs (e.g. Wings, 2004). This
calcium carbonate may precipitate very early
associated with shifts in pH in response to
the decay process (Briggs et al., 1993). Iron
oxides have also been observed in thin
sections in the lattice apatite and it could be
both the result of the iron oxide precipitation
during the early diagenesis due to penetration
of iron-rich water into collagen (Pfretzschner,
2000, 2001b; Wings, 2004) or the result of
oxidization of biogenic pyrite previously
precipitated under anoxic conditions
(Pfretzschner, 2001a, 2001b).
Successive EDS analyses from the
core to the surface show divergent results of
F and CO3 distribution into the bone. There is
an increase of calcite both on the surface and
168
Luque et al.
Figure 5. Relationship between francolite and dahllite versus calcite content. Note the linear
trend of Villar del Arzobispo Fm. remains mainly related with porosity and cement content.
in the inner part of the bones depending on the
sample from the same site (RD-10 in this
case). The distribution is not homogenous but
apatite preservation does not seem to follow
any trend in the selected bones. This fact has
also been recorded by Hubert et al. (1996)
who found no trends in the distribution of
C, F, and P in the Morrison Fm. bones.
The Gúdar site is the only place where
a third phosphatic mineral phase has been
found, the hydroxyapatite (Ca5(PO4)3OH).
In this case the OH- ion has not been
replaced by fluoride, chloride or carbonate.
Biogenic hydroxyapatite has been found in
caves and is associated with the reaction
between the acids of bat dung and the
calcite and clay minerals of the cave (Fiore
& Laviano, 1991; Dumitras et al., 2003).
Experimentally, with evaporation of complex
aqueous solutions, it has been observed that
an increase of the acidity of the environment
(through acids in the solution or through
increase of pCO2) increases the precipitation
of the hydroxyapatite together with the
dolomite (also appearing in one of these
samples) while the calcite content decreases
(Kochetkova et al., 2008). This all suggests
that an acidic micro-environment has been
established, perhaps organic or microbial in
origin, in the reprecipitation of the original
phosphate in the Gúdar site.
Therefore, the type of apatite present
in the dinosaur bones does not seem to have
a direct relationship with the environment. Not
even is there a trend of the maintenance of
dahllite in more coastal environments than
continental environments. This could be due to
the precipitation of the calcite as cement
more rapidly due to being inside the water
during biostratinomy and early diagenesis.
Contrarily, it has been observed that in coastal
environments the chemical transformation
of the hydroxyapatite increases the quantity of
fluor, as if the environment has oxidizing
conditions where the accumulation of iron
and manganese hydroxides is very high
(Nemliher, et al., 2004). Thus, the sites of La
Canaleta (CT-19) and Utrillas are two
exceptions of environments of coastal
influence. In the case of El Castellar, in the
169
Composition of Dinosaur Bones
CT-10 site, where bone is rich in fluorine,
the alluvial facies are very siliciclastics and
different from the carbonated ones overlying
it, and it is possible that a burial may have
been delayed in a similar way both in the
shallow marine and the alluvial flood plain.
In the case of Riodeva or the Villar del
Arzobispo Fm. in El Castellar, there is no
correlation between marine influence and an
increase of fluor. In fact, there is a lack of
francolite or this one is less than 25%.
Therefore the data seem contradictory.
As has been mentioned, the metabolic
bacterial activity can create biogenic secondary
minerals and alter the bone structure making
it become more porous and delicate and
conditioning geochemical reactions. As a
consequence, the porosity of the bone is
increased and may collapse with the
subsequent change of form and shape (Holz
& Schulz, 1998) and the diffusion of the
solutes (Hedges & Millard, 1995). This
influences precipitation and reprecipitation
of cements inside. Microbial attack has been
observed both in the Barremian bones of
Gúdar and in the Titonian-Berriasian bones
of Riodeva, coming from different sites,
which correspond as much to a continental
sedimentary environment as to coastal
influence (mainly tidal). Microbial tunneling
may be one of the earliest types of alteration
during the biostratinomy phase, as much as
in early diagenesis. In some cases like
Utrillas or Gúdar, the cancellous bone collapse
may be of bacterial origin but usually the
structure preservation is high. This is the
most typical level of alteration (Hedges et
al., 1995; Trueman & Martill, 2002) given
that possibly a higher level would mean the
total destruction of the bone, as occurs with
modern bones (Hedges et al., 1995). An
alternative to bone preservation is to make
mineral cements grow rapidly, which in turn
fills the holes (Trueman et al., 2004). On the
other hand, the frequent different infills in areas
close within the bone itself, like iron oxides
or barite, may be due to modifications of pH
and other conditions possibly as a result of
microbial activity, as has been seen in certain
areas of vertebrae bones of the Upper Triassic
and the Lower Cretaceous of the British
Isles (Trueman et al., 2003).
In the case of Gúdar, some small
tetragonal phosphate crystals (EDS) occur on
the edge of the bone surface inside the voids
and surrounded by iron oxide (haematites).
We do not dismiss the bacterial role in the
precipitation of this phosphate, which constitutes
quite a rare case of authigenic apatite
formation outside the bone structure (Elorza
et al., 1999). The usual absence of authigenic
phosphate in the bones, in spite of the
richness in phosphate and, the geochemical
processes that give rise to other stable
minerals in similar conditions, such as
calcite or pyrite, can be due to the fact that
the former needs an anoxic and acidic
environment for precipitation, while the
latter may develop in voids under anoxic yet
alkaline settings (Briggs et al., 1993).
Dinosaur bone mineralogy and cementation
The mineralogical composition of the
dinosaur bones from the sites of Teruel
show that, apart from the presence of the
different polymorphs of the apatite, there is
a great variety in minerals forming the
cement of the bone structure. The most
abundant cement is calcite, which is
generally present in various phases of the
growth of sparitic crystals. The different
phases in growth are usually separated by
fine coatings or spots of iron oxide
nodules, which are more abundant in
170
Luque et al.
fissures and in weak areas within the bone
histological structure. Barite and haematite
are rare. There are also other cements like
palygorskite, kaolinite or mica-chlorite
which are also rare. Furthermore, detritic
minerals are found incorporated to the
bone structure, such as quartz, feldspar,
illite, biotite or chlorites.
Once again, the mineralogical analyses
of the sediments from sites shows little
relationship with the depositional environment
(Tables 3 and 4): this could be due to very
diverse factors: variations within the depositional
environment itself, different source areas,
different rates of sedimentation/burial, different
edaphic processes, different evolution processes
during diagenesis (hydrothermal conditions,
tectonic stresses, etc.). This fact is important
because if trying to correlate bone composition
with environments of sedimentation, the
divergence between the sediment and the
depositional environment prevents a direct
correlation between the fossil and its
environment of fossilization.
Bone cements contain the most
abundant authigenic minerals and play a
predominant role in the rest of the fossil
history by conditioning the porosity, the
permeability of the solutes, the physical
resistance and as source of elements for
later chemical reactions. Calcite is common
in the dinosaur bone voids and fissures studied
occurring with a variety of crystal sizes and
shapes. This calcite cement has frequently
been observed in other dinosaur sites or
Mesozoic reptiles and it is considered one
of the first minerals to have been formed
(Hubert et al., 1996; Dauphin, 1998; Holz &
Schultz, 1998; Martill, 2001; Sung Paik et
al., 2001; Wings, 2004; Pyzalla et al., 2006;
González & Astini, 2007). Generally, the calcite
in bone samples is sparitic and intercalates
visible opaque iron oxides in thin sections.
Except in Gúdar (Camarillas Fm.), the latter
is also the most typical cement in the dinosaur
bones of Teruel. As the sites shows a very
different lithology and depositional origin
(tidal, fluvial to shallow coastal deposits),
this suggests that the calcite precipitates
easily and depends on the carbonated fluids
that circulate inside the voids where it
crystallizes. Therefore, the calcite does not
bear any environmental indication: solutions
rich in CO3Ca invade the vadose zone and
precipitates almost independently of the
environment of sedimentation.
The other cement that is most
abundant, especially in the Villar del Arzobispo
Fm., is iron oxide that is not detected in
XRD except as haematite in some samples
from Gúdar. Iron oxide occurs in fissures and
it is specially developed among Haversian
systems in the compact bone. Occasionally it
is the first precipitated mineral, but oxidation is
also produced after the fractures and the infill
of calcitic or other type cement, as occurs in
the site of Laño (Pereda-Suberbiola et al.,
2000). Those remains which show iron oxide
distributed on the surface making nodules
related to increased porosity of the apatite
suggest bacterial origin during early diagenesis
(Pfretzschner, 2001a). These iron oxides could
be a consequence of the oxidation of pyrite or
the microbial activity that rises the pH in the
bone and favours its precipitation (Pfretzschner,
2001a, 2001b). Calcite and fissures coating by
iron oxides can be explained by non biogenic
changes of the pH or the redox condition
into the voids during late diagenesis. Ironrich fluids reach holes or pores and an
amorphous iron oxide mass can be formed
(Pfretzschner, 2001b). These iron oxides are
common and visible to the naked eye, but
few crystalline remains have been detected
by XRD as mentioned by Pfretzschner
(2001b) in pyrite-derived iron oxides.
171
Composition of Dinosaur Bones
The iron oxide in mineral phase
(haematite) recognizable in XRD can be seen
in the Gúdar site as a significant part of the
volume of the bone. It can also result from
pyrite oxidation and have a bacterial origin but
haematites and other iron oxides can be formed
easily by the water table in continental
environments. During the wet season, close to
the surface, reducing atmosphere soils retain
cations as Fe2+ and during the dry season
evapotranspiration and oxygenation generates
the precipitation of goethite or haematite
(Pereda-Suberbiola et al., 2000; González &
Astini, 2007). This seasonal variation could
characterize the fluvial atmosphere where
the Gúdar site was formed.
Barite is found in alluvial facies of the
Castellar Fm. and in the fluvial facies of
Gúdar sites. In this latter site, it is only found
abundantly where there is no haematite, yet
there is hydroxyapatite. Thus, francolite and/or
haematite seem to inhibit the barite precipitation
in some way. In the Gúdar samples, the whole
voids and channels have been filled with iron
oxides, and if there was a space in the former
iron crust, barite crystals grow inside. This
mineral has been found associated with
cements of bone fossils from Triassic reptiles
(Holz & Schultz, 1998), dinosaurs (Martill,
2001; Wings, 2004) and even in very early
mammal diagenesis (Trueman et al., 2004).
In bones from the Isle of Wight it usually
occurs in discrete patches or aggregates
inside bones (Martill, 2001). In our samples,
barite is more evident in the thin sections than
in XRD, as also described by Wings (2004).
Having an inorganic origin, Martill (2001)
associates it with later phases of diagenesis
and subsequent to the precipitation of the
calcite, but the barite itself does not allow us
to determine specific geochemical formational
conditions, given that it is considered a
mineral of wide distribution (Wings, 2004).
The bones from Castellar Fm.
(alluvial and lacustrine environment) show an
association between kaolinite and palygorskite.
These clays may come from detrital processes
or occur as typical secondary products during
diagenesis. The palygorskite, which is more
abundant, is associated with soils of arid or
semi-arid nature, given that if rainfall rises
lightly (only by 300 mm/year) it is transformed
into montmorillonite (e. g. Paquet & Millot,
1972; Watts, 1976). In lacustrine conditions,
it is associated with alkaline lakes and with
high activity of Si and Mg and low Al
activity (Singer, 1979). It is also associated
with sepiolite, forming in lacustrine margins
where silicate meteoric waters mix with
lacustrine water with low pH. As it is found in
the inside of the bone and not in the sediment,
we can consider that it is not an hereditary
but a secondary authigenic mineral.
Kaolinite is a classical product of
neoformation in soils under contrasting
conditions (Wilson, 1999). As an authigenic
mineral, it is typical of freely drained, acid and
base-depleted tropical environments (warm
and humid no lower than 15º C) in the presence
of organic matter and is derived from Kfeldspars (like microcline) and muscovite in
early diagenesis. It is also associated with fluvial
facies low in pH and ionic concentration of
meteoric waters (Hurst & Irwin, 1982). Kaolinite
is frequent in the sediments of the Villar del
Arzobispo Fm., both in Riodeva and El Castellar,
given that it comes from the alteration of the
frequent microcline. It is also found in the
mudstones of Camarillas in Gúdar and above
all in the Escucha Fm., but not in any of the
fossils of these formations. It is only found
in the fossils from Castellar Fm., where it is
not in the sediments, which means that we can
rule out that it is hereditary.
Palygorskite and kaolinite are so
opposite with regard to their conditions of
172
Luque et al.
formation that they have been used to define
periods that swing from a warm and humid
environment with high rainfall to an environment
with a progressive development of arid climatic
conditions (Bolle & Adatte, 2001). So it is
contradictory to find both minerals in the
same fossil. However, the kaolinitization of
the palygorskite has been observed as a
result of root activity and organic matter
decomposition as well as clay destabilization
caused by Mg uptake by plants (Khademi &
Arocena, 2008), which could explain the
connection. This could indicate a semi-arid
environment during the formation of the
Castellar sites in El Castellar. The decay of
the organic matter of the bones and the
associated activity of plants could iniciate the
kaolinite transformation from the palygorskite
in an arid or semi-arid environment of the
lacustrine-alluvial facies of the Castellar Fm.
The clinochlore (an intermediary
term of a series of solid solutions within the
chlorites with the ripidolite rich in iron on one
extreme and the penninite rich in magnesium
on the other) appears in very small quantities
in fossils from the Forcall Fm. (shallow
coast), Villar del Arzobispo in El Castellar
(tidal to alluvial), Camarillas in Gúdar
(fluvial) and Escucha in Utrillas (tidal), which
dismisses it as an environmental indicator.
Frequently, mica is hereditary, given that the
primary chlorites are easily modified under
weathering, even though they may also be
authigenic from soil solutions, after weathering
of aluminous minerals such as feldspars, or
even from decomposition of organic matter
containing absorbed Al (Wilson, 1999).
Chlorite, together with illite, are considered as
common products of meteorization reactions in
environments of cool temperature and/or dry
climates (Li et al., 2000), as described for fluvial
(Hubert et al., 1996) and distal floodplain
(Sung Paik et al., 2001) environments. If we
are dealing with diagenetic chlorites, it could
mean environments with low organic matter
content, oxidizing conditions and frequent
wetting and drying cycles, as is typical in
highly weathered soils (Wilson, 1999). The
chlorites could, however, be products of
alteration of the illite (frequent in Villar del
Arzobispo and Castellar Fms.) or the biotite in
the case of the Forcall Fm., given that neither
amphiboles nor pyroxenes are found, which
is another source of alteration. The illite would
be inherited, given that it requires hydrothermal
conditions for its authigenic origin.
Another typical mineral in the bone
fossils is pyrite, although we only found this in
one sample from Aliaga. It can be explained
by the large number of above mentioned
samples enriched in iron oxides as a result
of later oxidization of original pyrite
(Pfretzschner, 2001a, 2001b). Pyrite appears
in SEM inside Haversian canals and
cancellous bone. Holes inside pyrite are
partially filled in by secondary calcite that has
been partially dissolved. The bone around
the pyrite is chemically enriched in sulphur.
This secondary product is very common in
different sites even during early diagenesis
and can be found both in the bones and in
the surrounding sediment (Wings, 2004).
Pyrite biomediated precipitation in the initial
stages of the diagenesis, as a consequence
of the decomposition of the organic matter,
is the most probable origin in such early
stages via bacteria colonization of the inner
void surfaces (Canfield & Raiswell, 1991). It
has been found in archaeological bones,
tertiary mammals or dinosaurs (Hubert et al.,
1996; Martill, 2001; Wings, 2004).
Gypsum has only been found as part
of the infill in the cancellous tissue in the
Camarillas Fm., in Aliaga Fm. and in the
Forcall Fm., where it forms a fine crust coating
bones. In sediments, it is also found in the
173
Composition of Dinosaur Bones
Forcall Fm., in Villar del Arzobispo Fm. and
in Castellar Fm. In Villar del Arzobispo Fm.
and in Castellar Fm. it is found as veins inside
major fractures of the bones and, therefore,
it is considered a product of late diagenesis
by water table loaded with sulfates.
All this data indicates that each
bone of the site tells a different taphonomic
story, depending on local factors. Therefore,
despite the abundant information about the
mineral composition of dinosaur bones at the
moment, there is not a general model that
correlates the composition of the fossil bones
with a concrete environment of sedimentation,
not even a determined composition of the
sediment that covers the fossils.
External characteristics of fossils which
influenced their mineralization
Collagen and apatite degradation due to
weathering, abrasion due to transport and the
presence of mineral crusts can deeply condition
bone mineral preservation and replacement
given their influence on the capacity of
penetration of fluids with solutes. The
degradation during the biostratinomic phase
occurs on the surface mainly due to changes
in temperature, humidity and the exposure
to UV rays (Behrensmeyer, 1978; Bromage,
1985; Tuross et al., 1989), but once the
remains have been buried, during diagenesis,
the main environmental factors that influence
the rate in which collagen degrades are the
pH and hydrology of the soil, oxygenation,
temperature, and changes introduced by
soil flora and fauna (Henderson, 1987;
Shiffer, 1987). Other conditioning factors
are the time of exposure and burial, the
anatomic element, the taxon bone microstructure
and the state of conservation of the bone
before its burial.
Once that superficial characteristics
and the natural fractures of the bones of the
studied sites have been observed, there does not
seem to be a direct application of these models
to adjust the grade of weathering to a standard
scale, given that neither longitudinal cracks
nor splinters or flakes have been found on the
fossil bones in a similar way to mammals.
The fractures seem to be all diagenetic or as
a result of transport. The flaking is limited to
the flat very thin section on the surface of the
cortical surface. It may end up disappearing
until it shows again in the cancellous bone,
and in the more advanced cases it is
associated with abrasion by transport, given
that the fractures also show roundness.
Differences in color are considered,
given that these have been attributed to
weather conditions and to early burial (Martill,
2001). Fossils brighter in color, white or
cream, are found in sites of tidal influence,
such as those of the Villar del Arzobispo
Fm. These colors are possibly a result of the
total oxidation of their organic component
swinging to atmospheric weathering while
the bones were lying on the floodplain
surface under alternating humid and semiarid seasons (Martill, 2001). However, these
same sites include light to dark-red fossils,
which could be related to different origins, as
has been documented in the dinosaur site of
Laño Quarry (Pereda-Suberbiola et al., 2000),
where differences in abrasion and weathering
were also noticed. The fossils that are clearly
red are fluvial or alluvial/lacustrine from the
Camarillas and Castellar Fms., which also
have black-colored fossils. Furthermore, the
black-colored fossils are found in two sites
formed in shallow coastal environments (Xert
and Forcall Fms.). It has been suggested that
black and brown color in fossils from the
Isle of Wight (Martill, 2001) may be due to
the abundance of organic matter and with
174
Luque et al.
rapid burial. This leads to sulfate reduction
and pyrite formation that eventually may be the
cause of the dark coloration. The black-colored
bones of the formations Camarillas in Aliaga,
Xert and Forcall are found articulated which
may mean a rapid burial that preserved the
organic matter too.
Conclusions
The dinosaur bones of Teruel show a diverse
mineralogical composition independent from
the surrounding lithology, the environment
of sedimentation and age. A certain diversity
of composition has also been found in the
site itself and occasionally in the same
sample. The original apatite has been replaced
and different proportions of dahllite, francolite
and hydroxyapatite are found with no direct
relationship with the environment of
sedimentation. The cements show a large
diversity of compositions. Calcite is the
most typical cement which seems to
maintain a relationship with the type of
phosphatic phase, given that an early
cementation with calcite could favor the
recrystallization of the dahllite as opposed
to the francolite, given the limitation of the
flow of fluorine within the bone. Iron oxide
not detected by XRD is also common and
could be due to microbial origin after
oxidizing of biogenic pyrite. Its distribution
into the bone is associated with increased
porosity of the tissues. Other secondary
minerals are haematite, barite, gypsum,
chlorite, mica, palygorskite and kaolinite.
Some of these contribute with environmental
information. On the other hand, mineralogical,
elemental and chemical analyses have been
useful to interpret the presence of groups of
remains with different sources prior to final
burial (bone transport and fossil reworking).
Acknowledgements
Dirección General de Patrimonio Cultural/
Gobierno de Aragón, Ministerio de Ciencia
e Innovación/Fondos Europeos de Desarrollo
Regional-FEDER (Project CGL2009-07792BTE;
El patrimonio paleontológico como recurso
para el desarrollo: los yacimientos de
dinosaurios de Aragón, Plan Nacional
I+D+i), Rafael González (MNCN-CSIC)
and Manuel Domínguez-Rodrigo (Universidad
Complutense, Madrid). This study is part of
the paleontological research projects subsidized
by: Departamento de Educación, Cultura y
Deporte and Dirección General de Investigación,
Innovación y Desarrollo (Research Group
E-62, FOCONTUR), Gobierno de Aragón.
This manuscript benefited considerably
from the useful comments of the referees
Dr. Mark B. Goodwin, Dr. Oliver Wings and
the special editor Dr. Julio Aguirre.
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