Guinyu: another of your Silurian ancestors

Guiyu oneiros
(Fig. 1) is considered ‘the world’s oldest articulated osteichthyan’.

Guiyu oneiros (Zhu et al. 2009; Silurian; V17914) is the basalmost crossopterygian in the LRT, yet the lobes are barely developed and large, placoderm-like cleithra precede them. The revised restoration differs somewhat from the original in having a smaller orbit, a tall jugal, a convex maxilla, a concave dentary and no teeth in the dentary. A flatter oblate cross-section is envisioned for the crushed torso.

Those presumed (not preserved) tiny eyes
in the revised reconstruction were inherited from an ancestor, the placoderm, Entelognathus (Fig. 2).

… and were passed down
to another of our ancestors, the flat-head crossopterygian, Tiniau (Fig. 3), a taxon close to Panderichthys.

The more typical crossopterygians,
Osteolepis and Eusthenopteron, nested in a clade in the large reptile tree (LRT, 1451 taxa, subset Fig. 4) that did not give rise to tetrapods, but to certain ray-fin fish, like Cheirolepis and Xiphactinus.

Worried about that internal naris?
I am, too. The working hypothesis is: it disappeared in Cheirolepis, Amia (Fig. 5) and Xiphactinus. Even so, Amia continues today to be able to breathe above or below the surface. Guinyu has twin nares (in and out) on the surface in front of the orbit, as seen in traditional ray-fins like Cheirolepis, Xiphactinus and Amia (Fig. 6).

And finally,
a nice side-by-side (not to scale) representation of the tested taxa we’re talking about today (Fig. 6).

References
Zhu M, Zhao WJ, Jia LT, Lu J, Qiao T, et al. 2009. The oldest articulated
osteichthyan reveals mosaic gnathostome characters. Nature 458: 469–474.

wiki/Guiyu_oneiros