Iyuku

Did You Know?

• Other animals from the Kirkwood Formation include the sauropod Algoasaurus, the stegosaur Paranthodon, and the ornithomimosaur Nqwebasaurus.
• Sedimentological analysis of the holotype assemblage suggests it came from a horizon transitioning into a drier climate.

Discovery and naming

The dinosaur Iyuku is known from a single bonebed that preserved at least 27 juveniles and hatchlings, a count based on matching left thigh bones. This site was dug up over three field seasons from 1995 to 1999. For years, the fossils were called the "Kirkwood taxon" until 2022, when they were named Iyuku raathi. The name Iyuku comes from the Xhosa word for "hatchling," reflecting the young age of the specimens. The holotype, AM 6067, is a partial, partly connected skeleton that includes a skull, vertebrae, shoulder blades, hips, both legs, and ribs. The species name honors paleontologist Mike Raath.

Paleobiology

Fossil material from Iyuku represents at least four size classes: three juvenile growth phases, with the smallest likely representing the post-hatching stage, and a fourth, larger stage interpreted as a subadult. Two estimates of total length were provided for an incomplete tibia of a subadult specimen from an unknown location in the Kirkwood cliffs: either 35 cm or at least 42 cm long, four or five times the length of the largest juvenile tibia from the quarry site. The quarry site yielded mostly isolated bones of hatchling to juvenile individuals in a 20–30 cm thick horizon, with no preferred orientation of long bones and only five instances of articulation. The preservation resembles that of juvenile remains of Orodromeus, Maiasaura, and Hypacrosaurus, possibly representing mortality near nesting sites. Although no nests or eggshells were found, the concentration of young individuals may reflect seasonal attrition at or near a nesting site, with bone scattering likely caused by trampling or bioturbation. Bone histology shows rest lines indicating temporary arrests in bone deposition, hypothesized to result from repeated environmental stress such as drought or extreme heat during early ontogeny.