The presence of crushing tooth plates in the form of flat, noded infragnathals and superagnathals suggest that the species' diet may have included prey with hard external shells such as molluscs, crustaceans or arthropods.

[10] Groenlandaspis is unusual among placoderms in that it is known what color it was; preserved pigment cells in its fossils indicate that its posterior was red and its anterior was silvery-white in a countershaded pattern, camouflaging it in the murky, silty waters of the rivers in which it dwelled.

[11] Groenlandaspis riniensis is one of two arthrodire placoderms described in 1999 from the Waterloo Farm lagerstätte in South Africa,[12][13] with a third species having been subsequently described.

G. riniensis appears to have spent its entire life cycle within the Waterloo Farm estuary as it is represented by a full ontogenetic series.

[9] Evidence from other Late Devonian localities with similar placoderm taxa which suggest that while many larvae or small juveniles stayed in the littoral zone close to adult habitats, others may have moved upriver to avoid predation.