The Oldest Articulated Osteichthyan Reveals Mosaic Gnathostome Characters

[Guest solius symbiosus]

A new fossil shows that the divergence of the sarcopterygians(lobe finned) and actinopterygians(ray finned) in the Osteichthyes Superclass occurred, at least, before 419mybp. Further, the fish exhibits sarcopterygian, actinopterygian, and rhipidistian characteristics.

a, b, A near-complete fish in part and counterpart. c, Close-up view of the anterior portion of the trunk shield in dorsal view, showing MD1 and MD2 flanked by rhomboid scales. d, Close-up view of the dorsal fin spine. MD1, first median dorsal plate; MD2, second median dorsal plate. Scale bar, 1 cm.

a, Restoration of the entire fish in lateral view. b, Interpretive drawing of the holotype V15541. Areas shaded in grey are unknown, and are reconstructed from other early osteichthyans. ano, anterior nostril; br, branchiostegal ray; cla, clavicle; cle, cleithrum; drs, dorsal ridge scale; dsp, dorsal fin spine; et, extratemporal; eta, accessory extratemporal; f.add, adductor fossa; f.gl, glenoid fossa; gu, gular; ju, jugal; l.ext, lateral extrascapular; lj, lower jaw; m.ext, median extrascapular; mx, maxillary; n.sp., spiracular notch; op, opercular; pa, parietal shield; pcl, postcleithrum; pop, preopercular; ppa, postparietal shield; psc, presupracleithrum; pt, post-temporal; scl, supracleithrum; sop, subopercular; sp., pectoral spine; tr, lepidotrichia; vrs, ventral ridge scale.

The abstract:

Nature 458, 469-474 (26 March 2009)

The oldest articulated osteichthyan reveals mosaic gnathostome characters

Min Zhu1, Wenjin Zhao1, Liantao Jia1, Jing Lu1,2, Tuo Qiao1,2 & Qingming Qu1,2

The evolutionary history of osteichthyans (bony fishes plus tetrapods) extends back to the Ludlow epoch of the Silurian period. However, these Silurian forms have been documented exclusively by fragmentary fossils. Here we report the discovery of an exceptionally preserved primitive fish from the Ludlow of Yunnan, China, that represents the oldest near-complete gnathostome (jawed vertebrate). The postcranial skeleton of this fish includes a primitive pectoral girdle and median fin spine as in non-osteichthyan gnathostomes, but a derived macromeric squamation as in crown osteichthyans, and substantiates the unexpected mix of postcranial features in basal sarcopterygians, previously restored from the disarticulated remains of Psarolepis. As the oldest articulated sarcopterygian, the new taxon offers insights into the origin and early divergence of osteichthyans, and indicates that the minimum date for the actinopterygian–sarcopterygian split was no later than 419 million years ago.

http://www.nature.com/nature/journal/v458/...ature07855.html

[Auspex]

Took me a minute, but I finally realized how significant this fossil is!

[Frank Menser]

I am looking at that (for want of a better term) mess and I have to give one big hat tip to the scientists who sorted it out and figured what it likely looked like.

Very Interesting!