Geoscience Reference
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(e.g. Sanchez et al. 2008), biomechanics (e.g. Mar-
gerie et al. 2005), environments (e.g. Steyer et al.
2004) and development (e.g. Ricql
`
s 1983) can be
obtained from the study of the microstructural
organization of bone. The current study is focused on
the bone histology of a very well-preserved bran-
chiosaurid material. This represents different taxa of
Apateon, found in four different localities of three
different stratigraphical horizons within the Saar-
Nahe Basin. The objectives of these histological
and skeletochronological analyses are: (1) analyse
bone microstructure with respect to life-history
traits of Apateon, and (2) elucidate the palaeoecol-
ogy of this genus.
1993; Castanet et al. 1993). When some inner corti-
cal regions of the bone shafts were resorbed in oldest
individuals, the somatic age was assessed by retro-
calculation that is, taking into account the position
of the LAGs deposited during the early life in the
innermost region of the periosteal cortex and obser-
vable in juveniles (e.g. Leclair & Castanet 1987;
Castanet et al. 2003).
Mid-shaft palaeohistology and bone
deposition in the stylopods of Apateon taxa
Stylopod diaphyseal histology
Apateon pedestris from Odernheim. Humerus
(Fig. 2a): The diameter of the forelimb-stylopod at
mid-shaft ranges from 280 to 650 mm (Table 1).
The cortex is relatively thick (up to 300 mm thick
in the largest individual SMNS 54988, Table 1).
However, the marrow cavity is distinct and free of
any bone trabeculae. The periosteal cortical tissue,
made of primary bone, is rather compact. It is only
involved by a primary sparse vascularization, essen-
tially longitudinally oriented. The vascular canals
are mostly distributed in the innermost half of the
periosteal cortex. Numerous relatively large and
flattened osteocytic lacunae, with canaliculi, are
associated with lamellar tissues. These bone-cell
lacunae become rounder toward the periphery. Some
remodelling processes occur at the periphery of the
medullary cavity: the residual line left by the endo-
steal resorption irregularly delimits the small endo-
steal deposition from the rest of the cortex. This
endosteal deposition comprises fine lamellar bone.
The Katschenko's line, which constitutes some
remains of the former cartilaginous shaft (Castanet
et al. 2003), is still present in large individuals
such as SMNS 54981.
Femur: The diameter of the femoral diaphysis
varies from 435 to 720 mm (Table 1). The cortex
is thick (up to 320 mm thick in the largest individual
SMNS 54980, Table 1). The marrow cavity remains
empty. The periosteal bone is made of a primary
bone matrix. It is crossed by a poor vascularization,
essentially constituted of large longitudinal vascular
canals homogeneously distributed in the thickness
of the compacta. The density of osteocytic lacunae
is relatively high. They are mostly flattened. A cen-
tripetal bone deposition forms a thin endosteal layer
made of lamellar bone, which is separated from the
periosteal bone by the Katschenko's line.
Materials and methods
The material consists of growth series based on 21
specimens of Apateon from lacustrine environments
of the Lower Permian of SW Germany (Sch¨fer &
Sneh 1983; Boy & Sues 2000). The studied
samples represent two species: Apateon caducus
(n ¼ 6) and Apateon pedestris (n ¼ 15) (Table 1).
They come from four localities of the Saar-Nahe
Basin: Niederkirchen, n ¼ 7; Erdesbach, n ¼ 7;
Odernheim, n ¼ 6; and Rehborn, n ¼ 1 (Table 1,
Fig. 1). The four localities represent three different
horizons within the Lower Permian section of the
Lower Rotliegend (Autunian), falling within the
Meisenheim Formation (Fig. 1). They range from
the L-O-6-horizon (Niederkirchen) through L-O-7
(Erdesbach) to L-O-8 (Odernheim, Rehborn) (L-O:
Lauterecken-Odernheim). L-O-6 and L-O-7 rep-
resented small lakes (5 - 10 km in diameter), while
L-O-8 formed a large lake in the 70 - 80 km range
(Boy et al. 1990; Boy & Sues 2000). The specimens
are housed in the collections of the Staatliches
Museum f ¨r Naturkunde, Stuttgart (identified as
SMNS or GPIM-N) and the Museum f ¨r Natur-
kunde, Berlin (identified as MB.Am.).
Stylopods of the hind- and forelimbs were
extracted from three-dimensionally preserved speci-
mens. Limb bones were embedded in a polyester
resin. Thin sections were made, using an annular
diamond-powder saw, and were observed under
ordinary and polarized light through an optical
microscope (Nikon Eclipse 80i). Diaphyseal his-
tology of 12 humeri and 9 femora was observed
and analysed in the three sets of Apateon. Life
history traits were advanced according to the
interpretation of bone microstructural organization.
A skeletochronological analysis was carried out to
assess
Apateon caducus from Erdesbach. Humerus
(Fig. 2b): The bone diameter of humeral mid-shafts
varies from 375 to 570 mm (Table 1). The diaphy-
seal cortex is thick (up to 260 mm thick in the
largest individual GPIM-N 1572, Table 1), not
allowing
the
individual
ages
and
determine
the
longevity.
This analysis was rigorously compared to the
skeletochronological data obtained on extant tetra-
pods (Caetano et al. 1985; Caetano & Castanet
an
expanded
medullary
cavity
which
