Chanaresuchus bonapartei, Romer, 1971, Romer, 1971

Marsà, Jordi Alexis Garcia, Ponce, Denis A., Agnolín, Federico Lisandro & Novas, Fernando E., 2023, Histovariability and lifestyle in Proterochampsidae Romer, 1966 (Archosauriformes) from the Chañares Formation (Late Triassic), northwestern Argentina, Comptes Rendus Palevol 22 (30), pp. 605-622 : 610-611

FEMUR ( PULR-V 116 )

The cross section of the bone has been affected by diagenetic processes, with a collapse of the cortical surface that partially infilled into the medullary cavity. The diagenetic alterations do not affect the main features of bone microstructure.

The cortex is sparsely vascularized, in contrast to the femur of others specimens ( Marsà et al. 2020; Ponce et al. 2021). The vascular canals are configured as longitudinally oriented primary osteons. The cortex is conformed by PFB and is interrupted by one LAG ( Fig. 2A). Vascularization is very sparse, even null, in the subperiosteal area.

The medullary cavity is separated from the cortex by a resorption line, and it is infilled by a dense trabecular bone tissue, conformed by lamellar bone tissue.

The density of osteocyte lacunae across the cortex is low ( Fig. 2B), contrasting with the high density of osteocyte lacunae present throughout the femoral cortex of other specimens ( Marsà et al. 2020; Ponce et al. 2021). Their morphology ranges from circular to subcircular in both cortex and trabecular bone. The distribution between the osteocyte lacunae is equidistant.

TIBIA ( PULR-V 116 )

The cross section of the bone has been affected by diagenetic processes, being fractured in several areas and collapsing towards the medullary cavity. However, these diagenetic alterations do not affect the main features of bone microstructure.

The cortex is almost avascular, with a few longitudinal canals, few secondary osteons, and interrupted by three LAGs ( Fig. 3A). The cortex is constituted of LB and shows cyclical growth, with the presence of three LAGs. Some areas of the cortex present Sharpey’s fibers.

The medullary cavity is infilled by a dense network of trabecular cancellous bone, tissue that is separated from the compact cortex by an ATZ ( Fig. 3A, B), and conformed by lamellar bone tissue.Trabeculae are thicker than those described in the femur PULR-V 116.

The density of osteocyte lacunae is high ( Fig. 3B), contrasting with the low density of osteocyte lacunae present along the cortex of the femur PULR-V 116. These osteocyte lacunae are mostly circular in morphology, and orderly distributed. The osteocyte lacunae of the innermost cortex, adjacent to the CCCB, have a more elongated morphology.

FIBULA ( PULR-V 116 )

The cross section of the fibula has been affected by diagenesis, with the medullary cavity partially infilled by fragments of the cortex. But these diagenetic alterations do not affect the main features of bone microstructure.

The cortex is highly vascularized, in contrast to the femur and tibia of the same specimen ( Fig. 4), resembling the femur of specimen PULR-V 125 ( Marsà et al. 2020). The vascular canals are formed of primary osteons mostly longitudinally oriented, but some osteons exhibit a reticular pattern. A laminar arrangement of the primary osteons is also visible, but to a much lesser extent. In the inner cortex there are numerous secondary osteons. The half of the outer cortex closest to the subperiosteum consists of FLB and shows cyclical growth, with the presence of three LAGs ( Fig. 4). Regarding the LAGs and their location in the FLB cortex: the first is a double LAG located at the middle of the FLB, and the last is located close to the subperiosteum. A thin layer of PFB forms around the LAGs.

The medullary cavity is reduced in comparison to the thickness of the cortex and infilled by trabecular bone tissue ( Fig. 4).

A high density of osteocyte lacunae with oval morphology and irregular distribution are present throughout the cortex.