Ferromirum oukherbouchi
Age
Devonian（Famennian）
370 Ma
Taxonomy
Kingdom：Animalia
Phylum：Chordata
Class：Chondrichthyes
Order：Symmoriiformes
Genus：Ferromirum
Species：Ferromirum oukherbouchi
Morphological description
Ferromirum oukherbouchi was a small chondrichthyan that lived during the Late Devonian, with an estimated body length of approximately 33 cm.
It possessed a slender body, a short pointed snout, and exceptionally large orbits, which accounted for roughly 30% of the total neurocranial length. Its jaws contained approximately nine tooth rows composed of small cladodont teeth, each bearing a prominent central cusp flanked by smaller lateral cusps. The first dorsal fin spine was smooth and curved posteriorly toward its tip.
One of the most remarkable features of Ferromirum was its highly specialized jaw joint. During jaw opening, the paired Meckel's cartilages rotated outward, and during jaw closure they rotated back inward. This unique mechanism exposed more teeth to the prey during the strike, allowing a greater number of teeth to participate in prey capture and thereby improving feeding efficiency.
Etymology
The generic name Ferromirum combines the Latin words ferrum ("iron") and mirus ("wonder" or "marvel"). The former refers to the iron-rich red nodule in which the holotype was preserved, whereas the latter commemorates the remarkable discovery that the specimen—initially mistaken for the appendage of a crustacean—turned out, after preparation, to be an exceptionally well-preserved ancient cartilaginous fish.
The specific epithet oukherbouchi honors the fossil collector Said Oukherbouch, who discovered the specimen.
Biological interpretation
Only a single holotype specimen of Ferromirum oukherbouchi is currently known. Designated PIMUZ A/I 4806, it was recovered from the Ibâouane Formation in the Anti-Atlas Mountains of southeastern Morocco.
The specimen is extraordinarily well preserved, retaining not only the neurocranium, upper and lower jaws, hyoid arch, and gill arches, but also soft-tissue remains including the liver, spiral intestine, and possible stomach contents, making it one of the best-preserved Paleozoic cartilaginous fishes known.
Using computed tomography (CT), researchers reconstructed a complete three-dimensional model of the skull and analyzed its feeding mechanism, revealing a previously unknown mode of jaw function in ancient chondrichthyans. Unlike modern sharks, whose jaws primarily move up and down, Ferromirum rotated both Meckel's cartilages outward during jaw opening and inward during jaw closure. This movement exposed more teeth toward the prey, while jaw closure allowed the younger teeth to pierce and secure the prey before pushing it deeper into the oral cavity.
Researchers suggested that this specialized feeding mechanism was particularly effective for capturing small marine invertebrates such as crustaceans.
Phylogenetic analyses recovered Ferromirum within the Symmoriiformes, occupying a basal position within the Holocephali lineage.
The morphology of its skull, lower jaw, and hyoid apparatus further indicates that these structures changed very little throughout approximately 75 million years of symmoriiform evolution. This remarkable anatomical conservatism is consistent with genomic evidence suggesting that the holocephalan lineage evolved at a considerably slower rate than other major vertebrate groups.
（Author: Bai Leng）
Reference
Frey, L., Coates, M. I., Tietjen, K., Rücklin, M., Klug, C. (2020). A symmoriiform from the Late Devonian of Morocco demonstrates a derived jaw function in ancient chondrichthyans. Communications Biology.
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