Eosteus chongqingensis is the oldest spiny shark, not the oldest bony fish, in the LRT

Eosteus chongqingensis
(Zhu YA et al 2026, Early Silurian 436 mya, China) was promoted as the earliest articulated bony fish = osteichthyan. Here in the large reptile tree (LRT, 2340 taxa) Eosteus nests between Early Silurian Shenacanthus and the previously tested most primitive acanthodian = spiny shark, Diplacanthus.

Click the links to see the specimen graphics.

According to the authors,
“This tiny fish exhibits a fusiform, generalized osteichthyan body outline, with plesiomorphic osteichthyan characters, including the lack of lepidotrichia and the presence of serial median dorsal plates, pectoral and dorsal fin spines and an anal fin spine reported previously exclusively in stem chondrichthyans and one placoderm. It also displays features, such as a single dorsal fin and caudal fulcra, seen commonly in actinopterygians.”

In the LRT, the most primitive bony fish
following the spiny sharks is Middle Triassic Robustichthys followed by several sea robins. Notably, this is only one of several origins for bony fish in the LRT. A convergent origin of bony fish was not recovered by Zhu et al, likely due to taxon exclusion, even though they included several taxa not tested in the LRT, it was not as wide a gamut.

The authors assumed Osteostraci was the outgroup. In the LRT other bony fish clades evolved from placoderms, lampreys and conodonts, rather than osteostracans.

References
Zhu YA et al 2026. The oldest articulated bony fish from the early Silurian period. Nature 651:128–134. https://doi.org/10.1038/s41586-026-10125-2

From the publicity:
“BEIJING, March 5 (Xinhua) — Fossils of two fish from over 400 million years ago — one a tiny streamlined creature, the other a giant among vertebrates of its time with bizarre teeth — have been discovered in China, filling a critical gap in the evolutionary journey “from fish to human.”

“They found the world’s earliest known complete bony fish fossil, named Eosteus chongqingensis, in southwest China’s Chongqing Municipality. They also comprehensively analyzed the complete head structure and tooth morphology of Megamastax amblyodus, the largest known vertebrate of the Silurian Period, found in Qujing in southwest China’s Yunnan Province. These findings make China a “cradle” of early vertebrate evolution.“

“According to Zhu Min, an academician of CAS from the IVPP, bony fishes form the main trunk of the vertebrate tree of life. Their two surviving lineages, ray-finned fishes and lobe-finned fishes, have conquered a wide range of niches in aquatic and terrestrial ecosystems, respectively. Ray-finned fishes evolved into over 30,000 species, including the vast majority of fishes we see today. One lineage of lobe-finned fishes eventually ventured onto land during the Devonian Period, evolving into all tetrapods and humans.“

“Eosteus chongqingensis, which lived 436 million years ago, measured only about 3 cm in total length, but was preserved with its head and tail intact.

“Megamastax amblyodus, discovered in strata dating back approximately 423 million years, exceeded one meter in length, making it the largest vertebrate of the Silurian Period.“

“After nearly a decade of effort, the team used advanced imaging technology and computer-based 3D reconstruction to reveal its complete three-dimensional head structure and the deeply hidden internal features. The scientists found that Megamastax amblyodus had teeth arranged in two rows, inner and outer, with each tooth “cushion” in the inner row bearing many sharp “spines.”

“Phylogenetic analysis places both these ancient fishes within the bony fish stem group, representing primitive types that existed before the divergence of ray-finned and lobe-finned fishes, Zhu said.”