Placoderm Trip

[izak_]

A few weeks ago some friends and I visited a site near Braidwood in southern NSW (3 hours south of Sydney) for middle-late Devonian fish. The site was first published in Ritchie (1984) with the description of Placolepis budawangensis, a phyllolepid known only from this locality. This species is one of the two most common here, with the other being Bothriolepis longi (see Johanson 1999). So far, only these two species have been described from this locality but acanthodian spines and sarcopterygian scales are also known. All fish fossils from this locality occur in within a 75cm band of red siltsone and are mostly just disarticulated plates, but the P. budawangensis holotype is still fairly well articulated. The plates of both species are very recognisable, the Placolepis usually have lovely parallel ridges whereas the Bothriolepis are covered in tiny bumps.

 

Some photos of the siltsone band with some fish plates exposed on top. Peter did a great job on this hole, it's not easy work!

 

The specimens from this locality are quite weathered, so the bone is usually quite poor and doesn't split well. They still look nice, but I chose to dissolve away the bone in hydrochloric acid to latex the cavity for photography. Here are some as found:

 

Placolepis:

 

Bothriolepis:

 

Some bone in cross section (the horizontal black dotted lines):

 

Here are some latex casts of specimens after acid preparation. The latex is blackened with ink, then whitened with ammonium chloride for high contrast photos. Much easier to make out features in these than the unprepared specimens!

 

Bothriolepis longi plates and pectoral fins (compare with figures in Johanson 1999):

 

Placolepis budawangensis:

 

Sarcopterygian scale(?):

 

No idea on this one!

 

After the fish site, we quickly stopped in at a road cutting which yields occasional Devonian plant fossils. Nothing too exciting, but still nice to find some Devonian plants!

 

 

That's all for now, I might post more ammonium chloride photos when I take the next batch. Hope you enjoyed!

[Lone Hunter]

Wow. Just wow. Those latex casts are amazing!

[doushantuo]

good journalism!!

[izak_]

2 hours ago, izak_ said:

Sarcopterygian scale(?):

 

An update on this one, it is a scale belonging to the coelocanth Gavinia (thanks to Gavin Young for the ID!)

Edited February 25 by izak_

[Fossildude19]

Great report and finds, Izak!

Thanks for sharing them.

I find myself quite looking forward to your reports these days. 

 

[rocket]

thanks for the great report, nice finds!

[izak_]

Thank you all!

 

Here is a combined view of both sides of one of the Bothriolepis longi pectoral fins, as well as how the specimen looks before latex.

[Tidgy's Dad]

Wonderful report and finds!