[dinosaur] Mesosaur microanatomy and growth: Stereosternum & Brazilosaurus (free pdf)

Ben Creisler
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A recent paper not yet mentioned, with free pdf:


Free pdf:


Nicole Klein, Antoine Verrière, Heitor Sartorelli, Tanja Wintrich, and Jörg
Fröbisch (2019)
Microanatomy and growth of the mesosaurs Stereosternum tumidum and
Brazilosaurus sanpauloensis (Reptilia, Parareptilia).
Fossil Record 22: 91–110
doi: https://urldefense.proofpoint.com/v2/url?u=https-3A__doi.org_10.5194_fr-2D22-2D91-2D2019&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=BleziE6ydHbLbNgTlxLVvOrCRtALxMw_nV7BzFgcuD4&s=5iCnZ5tk0on1h4VqjYf1q13p0MACNRWfHAZZ54JI1Ws&e= 
https://urldefense.proofpoint.com/v2/url?u=https-3A__www.foss-2Drec.net_22_91_2019_&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=BleziE6ydHbLbNgTlxLVvOrCRtALxMw_nV7BzFgcuD4&s=PLi95N3W1eblE4F9FZd2cJDZxpXijOsqV3PQ_4c5oJw&e= 

Free pdf:
https://urldefense.proofpoint.com/v2/url?u=https-3A__www.foss-2Drec.net_22_91_2019_fr-2D22-2D91-2D2019.pdf&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=BleziE6ydHbLbNgTlxLVvOrCRtALxMw_nV7BzFgcuD4&s=wrc7kLSjjvOyITeqMXfF9rkY3G4i9kn-JPkxWUy40pI&e= 

Histology and microanatomy of vertebrae, ribs, haemal arch, and humeri and
femora of 10 individuals of Stereosternum and two dorsal ribs of 1
individual of Brazilosaurus were studied. All individuals had achieved a
body length of 50 cm (equal to 65 % of the maximum known body length) or
larger. All sampled bones are highly osteosclerotic due to the reduction of
medullary cavities and the filling of medullary regions by endosteal bone.
Calcified cartilage occurs – if at all – only locally in small clusters in
the medullary regions of midshaft and in higher amounts only in
non-midshaft sections of long bones and towards the medio-distal rib shaft,
respectively. The primary bone tissue consists of highly organized
parallel-fibred tissue and/or lamellar tissue, which is in most samples
relatively lightly vascularized or even avascular. If present, vascular
canals are mainly longitudinally oriented; some show a radial orientation.
Simple vascular canals as well as primary osteons occur. Some of the latter
are secondarily altered, i.e. widened. Remodelling of the periosteal cortex
is only documented by few scattered erosion cavities and secondary osteons.
The tissue is regularly stratified by lines of arrested growth (LAGs),
which usually appear as double or multiple rest lines, indicating strong
dependence on exogenous and endogenous factors. Because of the inhibition
of periosteal remodelling the growth record is complete and no inner cycles
are lost. Individuals of Stereosternum show a poor correlation of body size
and number of growth marks, which might be the result of developmental
plasticity. Brazilosaurus shows a highly organized, avascular lamellar
tissue and a high number of regularly deposited rest lines throughout the
cortex of the ribs. The medullary region in the ribs of Brazilosaurus is
distinctly larger when compared to ribs of Stereosternum. However, strong
osteosclerosis is obvious in both taxa, pointing to a high degree of
aquatic adaption. Ribs of Stereosternum, Brazilosaurus, and Mesosaurus are
clearly distinguishable from each other by the distribution of the
periosteal and endosteal territory. Furthermore, Brazilosaurus differs in
its growth pattern (i.e. spacing of rest lines) when compared to
Stereosternum and Mesosaurus.



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