Placing juvenile specimens in phylogenies: An ontogenetically sensitive phylogenetic assessment of a new genus of iguanodontian dinosaur from the Early Cretaceous Kirkwood Formation, South Africa

Abstract

The phylogenetic relationships of the new dryosaurid genus Iyuku are explored using parsimony analysis. As all known specimens are juvenile, each character of the data matrix was examined across all included taxa for morphological changes through ontogeny in the phylogenetic characters. Any character that changed in any taxon was considered an ontogenetically sensitive character (OSC) and coded as unknown for juvenile specimens, including all specimens of Iyuku. This method was tested with three other genera in the data set that are known from juvenile and adult specimens: Orodromeus, Dryosaurus, and Hypacrosaurus. Four separate analyses were performed: (1) standard phylogenetic coding, (2) coding OSCs as unknown for juveniles, with both juvenile and adult OTUs present, (3) removal of adult specimens from second analysis, (4) adult specimens where known, taxa known only from juveniles coded as unknown for OSCs. In all taxa, congeneric juvenile and adult specimens were recovered as sister taxa (analysis 2), and juveniles in analysis 3 were found at a congruent node to the congeneric adult in analyses 1 and 4, though with a loss of resolution in the tree. Consideration of the changes in morphology through ontogeny across a given set of taxa can allow some confidence in the phylogenetic affinities of juvenile specimens. In all analyses, Iyuku is recovered as the sister taxon to Dysalotosaurus within Dryosauridae.

Palaeoecological deductions from osteohistology

“…Embryonic and hatchlings typically have highly porous or spongy bone tissue, indicative of their rapid rate of bone deposition (e.g. [72][73][74]). In young juveniles, often one can identify a hatchling line (e.g.…”

The dentary of hadrosauroid dinosaurs: evolution through heterochrony

“…2011; Campione et al . 2013; Prieto‐Márquez 2014; Poole 2022). Combined with the significant morphological divergence between both known Edmontosaurus species (see Campione & Evans 2011), subsequent studies have favoured the more conservative return to Edmontosaurus sp.…”

Introduction to Dinosaurs: New Ideas from Old Bones papers honoring Peter Dodson

“…The recognition of Corythosaurus in the Judith River Formation extends the biogeographic range of this genus and establishes a framework for future biostratigraphic work within the Late Cretaceous dinosaur faunas of western North America (Takasaki et al, 2023). Poole (2023) examined phylogenetic relationships of the new dryosaurid genus Iyuku using specimens attributable to juveniles. As the only material available for her study was fossils attributable to juveniles, to compensate, characters were examined across all included taxa as a test for morphological changes through ontogeny (Poole, 2023).…”

“…As the only material available for her study was fossils attributable to juveniles, to compensate, characters were examined across all included taxa as a test for morphological changes through ontogeny (Poole, 2023). Her study strongly suggests that some confidence can be placed in the phylogenetic affinities of juvenile specimens (Poole, 2023). Nabavizadeh (2023) provides an updated review of the functional morphology of one of the most unusual skulls in evolutionary history, of one of the most iconic groups of dinosaurs, the ceratopsians.…”

“…Poole (2023) examined phylogenetic relationships of the new dryosaurid genus Iyuku using specimens attributable to juveniles. As the only material available for her study was fossils attributable to juveniles, to compensate, characters were examined across all included taxa as a test for morphological changes through ontogeny (Poole, 2023). Her study strongly suggests that some confidence can be placed in the phylogenetic affinities of juvenile specimens (Poole, 2023).…”