Chondrichthyan and acanthodian origins: Morra 2026

From the Morra 2026 abstract
“The early evolutionary history of acanthodians, a paraphyletic group of Palaeozoic stem chondrichthyans, is reconstructed using a comprehensive and updated morphological phylogenetic dataset consisting of 429 characters scored for 87 articulated taxa. Results of a time-calibrated Bayesian analysis suggest a Middle Ordovician origin for total-group Chondrichthyes,“

From the Morra Introduction
“Acanthodii are a globally distributed and morphologically distinct grade of Palaeozoic cartilaginous fishes, with a fossil record ranging from the early Silurian to the Permian. Found in both marine and freshwater palaeoenvironments, their most distinctive and easily preserved features are the fin spines, located anteriorly to all fins except the caudal one, and the characteristic micromeric scales.”

“Moreover, new data about the early evolutionary history of the group, represented
by the recently described early Silurian taxa Shenacanthus (Zhu et al., 2022) and Fajingshania [= Fanjingshania known from disassociated bits and pieces] (Andreev et al., 2022b) have  never been incorporated in a tip-dating analysis and used to infer the timing of the early radiation of ‘Acanthodii’.”

The LRT added Shenacanthus to its taxon list here four years ago.

“The aim of this study is to construct a new comprehensive morphological dataset focused on early total-group chondrichthyans’ relationships, including all the informative characters available in the literature and most of the better known and reasonably complete acanthodian taxa.”

Unfortunately, once again, taxon exclusion marred this study.
The Morra cladogram recovered a single ‘Osteichthys’ clade arising from Entelognathus . It recovered Silurian Shenacanthus as a derived taxon. It recovered the shark-like flat placoderm, Gladbachus basal to sharks and rays.

In the LRT Shenacanthus gives rise to acanthodians on one branch and chondrichthys on the other branch.

PS
Let me congratulate student Lorenzo Morra (University of Modena and Reggio Emilia) for publishing a single author paper.

Those are rare nowadays.

References
Morra LE 2026 Tip dating supports a Middle Ordovician origin for total-group chondrichthyans and a rapid radiation of acanthodian-grade taxa. Open Palaeontology, 3(1), 1–9