Giles et al. 2015 looked at
the tiny (1cm wide) fossil skull roof of Janusiscus schultzei (Fig. 1) and nested it between placoderms and bony fish + spiny sharks + sharks. This represents yet another example of taxon exclusion in a traditional family tree of fossil fish.
From the abstract:
“The phylogeny of Silurian and Devonian (443–358 million years (Myr) ago) fishes remains the foremost problem in the study of the origin of modern gnathostomes (jawed vertebrates). A central question concerns the morphology of the last common ancestor of living jawed vertebrates, with competing hypotheses advancing either a chondrichthyan-or osteichthyan-like model. Here we present Janusiscus schultzei gen. et sp. nov., an Early Devonian (approximately 415 Myr ago) gnathostome from Siberia previously interpreted as a ray-finned fish, which provides important new information about cranial anatomy near the last common ancestor of chondrichthyans and osteichthyans.”
Five years ago, when Giles et al. 2015 was published,the LRT included few to no fish. Today that problem has been rectified (subset Fig. x).
The large reptile tree (LRT, 1733+ taxa; subset Fig. x) employs a much wider gamut of taxa than traditional fish cladograms, like those used by Giles et al. 2015. Here tiny Janusiscus nests with the much larger and coeval Uranolophus, known since 1968.
Given the tiny size of Janusiscus,
one wonders if it is a hatchling or juvenile of a larger genus, like Uranolophus?
Giles S, Friedman M and Brazeau MD 2015. Osteichthyan-like conditions in an Early Devonian stem gnathostome. Nature 520(7545):82–85.