New old bony fish

[Oolon Colluphid]

Nature 458, 413-414 (26 March 2009) News and Views

Palaeontology: Beyond the Age of Fishes

Michael Coates

Discovery of an unusually intact and ancient fossil fish provides further evidence that the search for modern vertebrate origins requires breaking out of the Devonian and into the preceding period.

As a rule, the earliest fossils of living groups tend to be scrappy, and such fragments lend themselves to contentious interpretations. For 'bony fishes', Osteichthyes — the division of vertebrates that includes everything from humans to halibut — the record of articulated fossils peters out within the Lower Devonian1, some 400 million years ago. Earlier stretches of osteichthyan history are littered with fossil detritus, such as isolated teeth and scales. In certain instances, bits and pieces have been reassembled into conjectural species, some of which have surprising combinations of anatomical features. On page 469 of this issue, Zhu et al. introduce a fresh — albeit long-dead — fish into this poorly resolved patch of vertebrate evolution. Crucially, this piscine offshoot of our own distant past is both unusually intact and exceptionally old.
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.

FIGURE 2: Guiyu oneiros gen. et sp. nov., holotype V15541.

http://www.nature.com/nature/journal/v458/n7237/images/nature07855-f2.2.jpg

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.

FIGURE 3. Guiyu oneiros gen. et sp. nov.

http://www.nature.com/nature/journal/v458/n7237/images/nature07855-f3.2.jpg

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.

[Puck]

Oolon, you find the most interesting stuff, I only regret that I don't understand most of the technical stuff. But what little I do glean from such articles, always fascinates me.

[Oolon Colluphid]

Oolon, you find the most interesting stuff, I only regret that I don't understand most of the technical stuff. But what little I do glean from such articles, always fascinates me.
Puck, I only understand about a tenth of most of it myself... but as you say, just that little is fascinating :)