Kingaspidoides spinirecurvatus: A new species of Trilobite from the Cambrian of the Anti‑Atlas, Morocco, with unexpectedly curved spines.
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The development of spines in Trilobites reflects an evolutionary arms race over most of the Palaeozoic. This is particularly signposted by a palpable bloom of spiny Trilobites from the late Silurian to the end of the Devonian. Spines are present among the earliest Trilobites at the base of Cambrian Stage 3, but these include genal spines and more or less pronounced pleural spines only (as in genera such as Eofallotaspis, Fallotaspis or Archaeaspis). All of these are best regarded as representing part of a beneficial cover by the dorsal exoskeleton in species that needed to perform a more or less distinct inclination of the body along the length axis to allow pronounced enrolment, in some species possibly combined with improved stability on a soft substrate. Early Cambrian Trilobites generally retained such a 'primordial' organisation and spinosity. However, small to medium-sized spines on the occipital ring, axial rings or the lateral and posterior margins of the pygidium developed progressively, apparently as a response to environmental factors, and all of them were nearly upright to more or less gently rearwardly directed. It is generally accepted that new selective pressures from predators prompted animals to craft innovative protective devices, which in several species included longer and more strongly curved spines.