TABLE 1.

Potential correlates for the avascular zone (AVZ) in the femoral bone histology of Greererpeton

Life history event	Cessation of growth?	Post‐ossification juvenile event?	Single event?	Supporting evidence	Opposing evidence
Seasonal stress	Yes	Yes	No	Known to be recorded in bone microstructure 1	AVZ is histologically distinct from a repetitive seasonal LAG or annuli
Metamorphosis	Yes	Yes	Yes	Causes metabolic stress and occurs early in ontogeny 2	No anatomical evidence of metamorphosis in Greererpeton 3
Extended juvenile phase	Yes	Yes	Yes	Common in modern amphibians that are also tied to aquatic settings 4	Greererpeton was not polymorphic 3 and this event occurred well before skeletal maturity 4
Juvenile environmental stress	Yes	Yes	Yes	Resource availability can pause juvenile growth 5	Occurs on a population level 6 ; the AVZ is found at a taxon level
				Juveniles may not be able to escape poor living conditions	Late‐stage juveniles typically leave environmentally stressed conditions 7
Migration	Yes	Yes	No	Common in aquatically bound modern tetrapods 8 ; can be recorded by bone histology 9	Occurs multiple times during the lifetime of an animal 8
Dispersal	Yes	Yes	Yes	Common in aquatically bound modern tetrapods 8 ; occurs once in late‐stage juveniles 8	Tetrapod dispersal commonly involves terrestrial excursions 8 ; Greererpeton was primarily aquatic in habit 3

¹ Esteban et al. (1996); Köhler et al. (2012); Sinsch (2015).

² Kirschman et al. (2017).

³ Godfrey (1989a, 1989b).

⁴ Denoël et al. (2005).

⁵ Klein, Scheyer and Tütken (2009).

⁶ Conover and Schultz (1995).

⁷ Hutton (1989); Semlitsch (2008).

⁸ Semlitsch (2008).

⁹ Köhler et al. (2012).