Evolutionary implications of the divergent long bone histologies of Nothosaurus and Pistosaurus(Sauropterygia, Triassic)

Table 1 Results of the histological examination of eosauropterygian taxa

Taxon	Collection number	Bone type	Type of section	Bone tissue type	Number of growth cycles	Ontogenetic stage	Medullary Index (%)	Histological specialization
N. marchicus/ N. winterswijkensis	MfN R 174-2	Humerus	ts of proximal shaft	lzb	7	Adult	42.5	Some osteosclerosis
N. mirabilis	SIPB R 54/2	Humerus	dts, lts of proximal head, 9 ps	lzb	10	Adult	63.8	Much reduced cortex
N. mirabilis	SIPB R 50/2	Femur	dts	lzb	9	Subadult	63.0	None
N. mirabilis	SIPB R 54/1	Femur	dts, lts of proximal head, 8 ps	lzb	8	Adult	42.5	Some osteosclerosis
N. mirabilis	SIPB R 50/1	Femur	dts	lzb	9	Subadult	32.9	Osteosclerosis
N. giganteus	SIPB R 45	Humerus	dts	lzb	EFS	Fully grown	58.8	Much reduced cortex
N. giganteus	SIPB R 53	Humerus	dts	lzb	EFS	Fully grown	77.4	Much reduced cortex
N. giganteus	SIPB R 40	Humerus	ts of proximal shaft	lzb	/	Adult	74.7	Much reduced cortex
N. giganteus	MHI 1903	Humerus	2 mts	lzb	8	/	/	/
N. giganteus	SIPB R 49	Femur	dts	lzb	7	Subadult	75.8	Much reduced cortex
Nothosaurus sp. indet.	MHI 1906	Humerus	dts	lzb	3	Juvenile	35.0	Osteosclerosis
Nothosaurus sp. indet.	MHI 633	Humerus	dts	flb	3	Juvenile	26.9	Thick cortex of flb
Nothosaurus sp. indet.	SMNS 84856	Femur	dts	lzb	10	Adult	27.8	Osteosclerosis
Pistosaurus longaevus	SIPB R 46	Humerus	dts	flb	5	Adult	6.7	Thick cortex of flb
Pistosaurus longaevus	SMNS 84825	Humerus	dts	flb	7	Adult	5.0	Thick cortex of flb
Pistosaurus longaevus	SIPB R 74	Femur	dts	lzb	8	Subadult or adult	65.8	Some osteosclerosis
Plesiosaurus dolichodeirus	SIPB R 90	Femur	dts	flb	EFS	Fully grown	35.0	Haversian remodeling

Overview of the sampled taxa, long bones, and histological observations. A low MI means a small medullary region. Abbreviations: dts diaphyseal thin section, EFS external fundamental system, flb fibrolamellar bone, lts longitudinal thin section, lzb lamellar zonal bone, mts metaphyseal thin section, ps polished sections, ts thin section, / absent or growth marks not identifiable.