Loganellia and Gladbachus

Loganellia scotica (Traquair 1898; Early Silurian) is a the most primitive soft placoderm, transitional to sharks and acanthodians. Note the pectoral fins, a heterocercal tail. The skin had a shark-like sandpaper appearance and texture. The mouth was terminal and transverse (in the lower taxon) to U-shaped (in the upper taxon).

According to the National History Museum in London, "Shark-like scales from the Late Ordovician have been found, but no teeth. If these were from sharks it would suggest that the earliest forms could have been toothless. Scientists are still debating if these were true sharks or shark-like animals."

Gladbachus adentatus (Heidtke & Krätschmer 2001; Burrow and Turner 2013; Coates et al. 2018; Middle Devonian, est. 54cm) was originally considered an 'unfamiliar' basal chondrichthyan close to acanthodians (spiny sharks). Here it nests with Doliodus near the base of the shark clade. This toothless or tiny-toothed taxon with a wide gape and flat skullwas apparently a filter feeder with enormous gill bars. The unique holotype preserves the pelvic area.

The tiny Early Devonian placoderm > shark transitional taxon, Doliodus, provides clues to the evolution of Gladbachus as applied colors here indicate.

Burrow C and Turner S 2013. Scale structure of putative chondrichthyan Gladbachus adentatus Heidtke & Krätschmer, 2001 from the Middle Devonian Rheinisches Schiefergebirge, Germany. Historical Biology 25(3):385–390.

Coates MI, et al (7 co-authors) 2018. An early chondrichthyan and the evolutionary assembly of a shark body plan. Proceedings of the Royal Society B 285(1870):20172418.

Heidtke UHJ and Krätschmer K 2001. Gladbachus adentatus nov. gen. et sp., ein primitiver Hai aus dem Oberen Givetium (Oberes Mitteldevon) der Bergisch Gladbach – Paffrath-Mulde (Rheinisches Schiefergebirge). Mainzer geowiss. Mitt. 30, 105–122.

St. John OH and Worthen AH 1883. Description of fossil fishes: a partial revision of the Cochliodonts and Pasmmodonts. Geological Survey of Illiniois 7:55–264.

Schultze H-P and Bardac D 1987. Diversity and size changes in Palaeonisciform fishes (Actinopterygii, Pisces) from the Pennsylvanian Mazon Creek Fauna, Illinois, U.S.A

Traquair RH 1898. Report on fossils fishes. Summary of Progress of the Geological Survey of the United Kingdom for 1897: 72-76.

Žigaite Ž and Goujet D 2012. New observations on the squamation patterns of articulated specimens of Loganellia scotica (Traquair, 1898) (Vertebrata: Thelodonti) from the Lower Silurian of Scotland. Geodiversitas 34 (2): 253-270.

wiki/Loganellia
wki/Gladbachus

Placodermi

Drepanaspis

Qilinyu

Manta

Loganellia