Allaeochelys delheidi was a highly aquatic carettochelyid, an extinct relative of the living pig-nosed turtle. Its shell followed an unusual evolutionary route towards a soft, skin-covered exterior: the usual keratinous scute sulci were lost, yet the bony peripheral rim of the carapace was retained. This combination produced a flexible-looking but still structurally reinforced shell well suited to an aquatic animal.

Carettochelyids were strong swimmers and were primarily associated with freshwater systems, although some members could tolerate brackish conditions. The London Clay occurrence therefore most plausibly represents an animal using estuaries or a carcass transported from nearby rivers rather than proof of a fully oceanic lifestyle. Its diet is not directly known; generalist omnivory or predation on aquatic invertebrates and small vertebrates is a reasonable inference from related carettochelyids. The species is known from shell material and, outside Britain, cranial remains.