Data for: A phylogeny for Heterostraci (stem-gnathostomes)

The armoured jawless fishes (“ostracoderms”) are major and widespread components of middle Palaeozoic ecosystems. As successive branches on the gnathostome stem lineage, they reveal the early sequences of vertebrate evolution, including the assembly of the vertebrate skeleton. This is predicated however, on understanding of their diversity and interrelationships. The largest ostracoderm clade, the Pteraspidomorphi, is often reconstructed as sister taxon to other boney vertebrates yet they lack a cladistic phylogenetic framework, in particular the heterostracans. Problematic heterostracans with a tessellate headshield (‘tessellate-basal’ model) are often regarded as the plesiomorphic condition for the clade but no phylogenetic analysis has included these taxa. Here we review the Heterostraci and present their first comprehensive phylogenetic analysis (131 heterostracan taxa and 55 outgroup taxa). Heterostraci are recovered as monophyletic, and forming a clade together with the Ordovician..., , , # Data for: A phylogeny for Heterostraci (stem-gnathostomes)

[https://doi.org/10.5061/dryad.cfxpnvxhh](https://doi.org/10.5061/dryad.cfxpnvxhh)

## Description of the data and file structure

Morphological Matrices in

1. Nexus format with character names and character settings (new_het3.nex)
2. TNT format with discretised continuous characters and TNT search commands and settings (new_het3.tnt)
3. TNT format with raw continuous characters and TNT search commands and settings (new_het3cont)
4. Nexus format with Mr Bayes search commands (new_het3 MrBayes.nex)
5. Character list with supplementary figures (Supplementary_Information._Randle_et_al_2025_v2.pdf)
6. Stratigraphic age range data used for construction of figure 6 (Thesis_Heterostraci_Strat3.txt)

Note: Taxon name *Helaspis* was used in early earlier versions of this manuscript but has been superceded by *Clavulaspis* (Elliott D. et al. 2020 The last pteraspids (Vertebrata, Heterostraci): new material from the Middle Devonian of ...,