FIRST PRELIMINARY PALEOHISTOLOGICAL AND HISTOTAPHONOMIC STUDY OF BONE REMAINS FROM RANCHO LA BREA (LATE PLEISTOCENE, USA)

1. FIRST PRELIMINARY PALEOHISTOLOGICAL AND
HISTOTAPHONOMIC STUDY OF BONE REMAINS FROM
RANCHO LA BREA (LATE PLEISTOCENE, USA)
M.C. Garrone1, M.D. Marin-Morfort1, R.L. Tomassini1, M.D. Pesquero2, I.A. Cerda3, J.L. Prado4,
C.I. Montalvo5, Y. Fernández-Jalvo2, M.T. Alberdi2
1INGEOSUR, Departamento de Geología Universidad Nacional del Sur (UNS)-CONICET, Bahía Blanca, Buenos Aires, Argentina
2Departamento de Paleobiología, Museo Nacional de Ciencias Naturales (CSIC), José Gutiérrez Abascal, Madrid, Spain
3CONICET-Instituto de Investigación en Paleobiología y Geología, Museo Carlos Ameghino, Universidad Nacional de Río
Negro, Cipolletti, Río Negro, Argentina
4INCUAPA-Departamento de Arqueología, Universidad Nacional del Centro, Olavarría, Buenos Aires, Argentina
5Facultad de Ciencias Exactas y Naturales, Universidad Nacional de La Pampa, Santa Rosa, La Pampa, Argentina

2. The asphalt deposits
of Rancho La Brea (California, USA)
are well known for the quantity and
quality of their Late Pleistocene vertebrate fossil
record. Paleobiological and paleoecological
knowledge of the different groups of mammals
from this site has increased notably in the last
decades. However, there is little information
regarding to the taphonomy, and particularly to
the histology of the bone remains.
INTRODUCTION
This work investigates for the first time the
osteohistological and histotaphonomic features in the
bone microstructure of Equus occidentalis (Equidae)
recovered from different tar pits of Rancho la Brea.

3. MATERIAL AND METHODS
Histology Histotaphonomy
• Distribution of primary and secondary tissues
• Vascular pattern
• Osteocytes lacunae (form and density)
• Growth marks
• Microscopic focal destructions (mfd)
• Fissures
• Microcracks
• Enlarged canaliculi
• Cavity infillings
Parameters considered:
The anatomical elements used in this study (all of them
incompletes) correspond to femur (n=1), humeri (n=2), radius
(n=1), metacarpals (n=2) and metatarsals (n=2). Thin sections
were prepared following the methodology described by
Garrone et al. (2020). Specimens are hosted in Natural History
Museum of Los Angeles (Los Angeles, California, USA).
The slides were assessed using petrographic and scanning
electron microscope to describe the osteohistological
features of the bone microstructure and the taphonomic
alterations. 5 cm
Thin section obtained
from the femur

4. All the samples are mainly constituted by fibrolamellar
tissue (FLB), with longitudinal, circumferential and some
radial vascular canals and lines of arrested growth in
some bones (LAG's - white arrows).
Also, an internal circumferential layer (ICL) of lamellar
bone (LB) is recognized almost completely surrounding
the medullary cavity (mc).
BONE HISTOLOGY
Metapodials also show:
a) parallel fibered bone (PFB) and
compacted coarse cancellous bone
(CCCB) in contact with the ICL;
b) external fundamental system (EFS) in
contact with the FLB.
External fundamental
system
Parallel fibered bone
Fibrolamellar bone Lamellar bone
fast rate of bone
deposition
(Description and interpretation follows Enlow, 1963; Francillon-Vieillot et al., 1990; Nacarino-Meneses et al., 2016)
cessation or decrease
of periosteal bone
growth.
Compact coarse
cancellous bone
linked to the
modeling processes

5. BONE HISTOLOGY
Secondary remodelling:
It is present with different intensity and location in all the skeletal elements. Even in a same sample, it
was noted areas with a high density of secondary osteons and areas where they were scarce and
dispersed. This process would be associated to changes occurred during ontogeny and to
biomechanical factors (e.g., Martínez-Maza et al., 2014; Zedda et al., 2008, 2020).
low density
of Secondary osteons
could be areas subjected
to tension deformation
high density
of Secondary osteons
could be areas subjected
to compression loads
Metatarsal
thin section

6. HISTOTAPHONOMY
In general, the bone histology show a good preservation (OHI=5 sensu Hedges et al., 1995).
However, diverse agents and processes slightly altered the microstructure. Modifications identified
comprise enlargement of canaliculi, microtunelling, microcracks on secondary osteons, and fissures.
Most fissures and cavities are filled with asphalt-impregnated clastic material. No evidence of
bacterial attack altering the original histology was recorded.
Microcracks Fissures Microtunelling
Enlarged canaliculi
soil corrosion
(e.g., Jans et al., 2004;
Fernández-Jalvo et al., 2010)
fungal attack
(Wedl tunneling)
(e.g., Hackett, 1981;
Fernández-Jalvo & Andrews, 2016)
dry conditions (a)
wet conditions (b)
(e.g., Pfretzschner, 2000, 2004;
Pfretzschner & Tütken, 2011)
lithostatic load
b
a
(e.g., Tomassini et al., 2015)

7. From a paleohistology viewpoint, the distribution and characterization of bone tissues and
remodelling in the different skeletal elements are, in general lines, similar to that described
for other extant and extinct equids.
From a histotaphonomic viewpoint, the variations in the pre- and post-burial alterations
recorded evidence different taphonomic histories and preservation conditions among
pits, which may be related to seasonal periods of accumulation.
The absence of bacterial attack evidence is possibly linked to this type of extreme
environmental context (asphalt deposits), which require specialized adaptations and,
therefore, limits the microbial development. This condition could explain the good
preservation of the bone microstructure.
FINAL REMARKS

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