a) Schematic of the FGF/ERK signaling pathway. b) Distribution of pERK levels in TBXT+ cells versus ISL1+ and other cells based on data and thresholds in Supp. Fig. 2b. c) Expression of key markers in PHATE39 projection of scRNA-seq data for 42h colony. d) Cell type annotation. PS-LC: primitive streak-like cells, NasMe: nascent mesoderm, AE-LC: amniotic ectoderm-like cells: PGC-LC: primordial germ cell-like cells, endo: definitive endoderm. e) Expression of canonical FGF ligands (log transformed and smoothened). f) Comparison of FGF ligand expression in 2D human gastruloids to human, monkey, and mouse embryo, normalized within each type of sample. g-i) Expression of several genes involved in FGF signaling with strong differential expression between PS-like cells or nascent mesoderm and pluripotent cells, split by gene category.