Figure 5. Hypothesized phylogenetic position of Notocolossus gonzalezparejasi and pedal evolution of Sauropoda.

(a) Time-calibrated hypothesis of phylogenetic relationships of Notocolossus with relevant clades labelled. Depicted topology is that of the single most parsimonious tree of 720 steps in length (Consistency Index = 0.52; Retention Index = 0.65). Stratigraphic ranges (indicated by coloured bars) for most taxa follow Lacovara et al.⁴: fig. 3 and references therein. Additional age sources are as follows: Apatosaurus⁵⁵, Cedarosaurus⁵⁸, Diamantinasaurus⁵⁹, Diplodocus³⁵, Europasaurus³⁵, Ligabuesaurus³⁵, Neuquensaurus⁶⁰, Omeisaurus⁵⁵, Saltasaurus⁶⁰, Shunosaurus⁵⁵, Trigonosaurus³⁵, Venenosaurus⁵⁸, Wintonotitan⁵⁹. Stratigraphic ranges are colour-coded to also indicate geographic provenance of each taxon: Africa (excluding Madagascar), light blue; Asia (excluding India), red; Australia, purple; Europe, light green; India, dark green; Madagascar, dark blue; North America, yellow; South America, orange. (b–h) Drawings of articulated or closely associated sauropod right pedes in dorsal (=anterior) view, with respective pedal phalangeal formulae and total number of phalanges per pes provided (the latter in parentheses). (b) Shunosaurus (ZDM T5402, reversed and redrawn from Zhang⁴⁵); (c) Apatosaurus (CM 89); (d) Camarasaurus (USNM 13786); (e) Cedarosaurus (FMNH PR 977, reversed from D’Emic³²); (f) Epachthosaurus (UNPSJB-PV 920, redrawn and modified from Martínez et al.²²); (g) Notocolossus; (h) Opisthocoelicaudia (ZPAL MgD-I-48). Note near-progressive decrease in total number of pedal phalanges and trend toward phalangeal reduction on pedal digits II–V throughout sauropod evolutionary history (culminating in phalangeal formula of 2-2-2-1-0 [seven total phalanges per pes] in the latest Cretaceous derived titanosaur Opisthocoelicaudia). Abbreviation: Mya, million years ago. Institutional abbreviations see Supplementary Information.