Little Ligulalepis grabbed headlines in 2018 (due to taxon exclusion)

Academic and publicity headlines:
“The most primitive osteichthyan braincase?”
“Neurocranial anatomy of an enigmatic Early Devonian fish shed light on early osteichthyan evolution.”

No. Far from it. Living moray eels (genus: Gymnothorax) have a much more primitive osteichthyan braincase than Ligulalepis (Fig. 1). A proper phylogenetic context (Fig. 2) is essential, but was not present in prior studies of this tiny fish due to taxon exclusion.

What does the small size of Ligulalepis tell us?
Phylogenetic miniaturization usually retains juvenile traits (e.g. short rostrum, large eyes, small size) into adulthood. These changes can lead to novel clades. Presently no new clades arise from Ligulalepis. That can change. Presently Ligulalepis is tiny without descendants, just the opposite of what the headlines said back in 2018.

References
Basden AM et al. 2000. The most primitive osteichthyan braincase? Nature 403(6766): 185–188.
Burrow CJ 1994. “Form and function in scales of Ligulalepis toombsi Schultze, a palaeoniscoid from the Early Devonian of Australia”. Records of the South Australian Museum. 27 (2):175–185.
Chang M-M and Yu X-B 1981. A new crossopterygian Youngolepis praecursor gen. et sp. nove.form Lower Devonianof E. Yunna, China. Scientia Sinica 24:89–97.
Chang M and Zhu M 1993. A new Middle Devonian osteolepidid from Qujing, Yunnan. Mem. Assoc. Australas. Palaeontol. 15 183-198.
Clement AM et al. 2018. Neurocranial anatomy of an enigmatic Early Devonian fish shed light on early osteichthyan evolution. eLife 7. doi:10.7554/eLife.34349
Schultze H-P 1968. Palæoniscoidea-Schuppen aus dem Unterdevon Australiens und Kanadas und aus dem Mitteldevon Spitzbergens. Bulletin of the British Museum. 16: 343–368.
Zhu M and Ahlberg P 2004. The origin of the internal nostril of tetrapods. Nature 432:94-97.

wiki/Kenichthys
wiki/Youngolepis
wiki/Ligulalepis

Publicity

theconversation.com/its-less-than-2cm-long-but-this-400-million-year-old-fossil-fish-changes-our-view-of-vertebrate-evolution-96419

labonline.com.au/content/life-scientist/news/the-ancestor-of-all-bony-fish-has-a-surprising-link-to-humans-433759295