Panderichthys has fingers?

[Naraoia]

Has anyone else come across this?

The pectoral fin of Panderichthys and the origin of digits (Nature)

Apparently, these guys/gals found some missing bones of Panderichthys. And it turns out that these (at least in their arrangement) look more like fingers than anything any other known fish had.

The abstract (bolding mine):

One of the identifying characteristics of tetrapods (limbed vertebrates) is the presence of fingers and toes. Whereas the proximal part of the tetrapod limb skeleton can easily be homologized with the paired fin skeletons of sarcopterygian (lobe-finned) fish, there has been much debate about the origin of digits. Early hypotheses1 interpreted digits as derivatives of fin radials, but during the 1990s the idea gained acceptance that digits are evolutionary novelties without direct equivalents in fish fin skeletons. This was partly based on developmental genetic data2, but also substantially on the pectoral fin skeleton of the elpistostegid (transitional fish/tetrapod) Panderichthys, which appeared to lack distal digit-like radials3. Here we present a CT scan study of an undisturbed pectoral fin of Panderichthys demonstrating that the plate-like 'ulnare' of previous reconstructions is an artefact and that distal radials are in fact present. This distal portion is more tetrapod-like than that found in Tiktaalik4 and, in combination with new data about fin development in basal actinopterygians5, sharks6 and lungfish7, makes a strong case for fingers not being a novelty of tetrapods but derived from pre-existing distal radials present in all sarcopterygian fish.

It's a short paper but it has really nice pictures so even I can understand what the authors mean . The "more tetrapod-like than Tiktaalik" bit refers to this (from the paper itself):

In Tiktaalik4, like in 'osteolepiforms'17 and rhizodonts18 (more primitive fish members of the stem group), the ulna and ulnare are of similar size. The axis of the fin comprises two more elements distal to the ulnare, and the distal radials are arranged pinnately around this axis. In contrast, in Panderichthys and tetrapods, the ulna is much longer than the ulnare, the ulnare is the last axial element, and the distal radials/digits are arranged in a transverse fan shape11, 21

In layman's terms, at least as far as I can understand based on the pictures and my (very) limited knowledge of bones'n'stuff, this means that Tiktaalik's "hand" looks as if my fingers sprouted off the sides of my (long, jointed) wrist, while Panderichthys has a "wrist" and then fingers*.

Here has a nice computer model of the CTed fin/limb for free (don't read the accompanying article, it's rather sub-standard IMHO). Look at the brown bones at the bottom (these are the previously missing radials) and compare with the nice big Tiktaalik fin here.

Awesome, I say.

*Now I assume these aren't fingers proper yet, but given the developmental genetic evidence the authors mention, they are probably something that became fingers in our ancestors.

 

[Bombila]

That is very interesting.

I wonder how Panderichthys used that part of the fin; why fingerish bits and a primitive wrist turned out to be useful enough to be an advantage for that particular fish?

 

[Naraoia]

The idea seems to be that these limblike fins were good for living/moving around in shallow water. Which is a useful ability when you share your pond with giant predatory fish and/or face competition for food.

My all-time favourite Devonian Times has this (I wonder when/if DT will get updated with the new Panderichthys):

By the Late Devonian, a variety of new and promising aquatic habitats had developed. Extensive terrestrial vegetation and accelerated soil formation moderated flow regimes and stabilized banks and bottom sediments. This in turn generated a variety of microhabitats ranging from deeper channels to shallow zones to periodically inundated wetlands. Detrital inputs from terrestrial and wetlands vegetation provided a trophic base for increasingly complex food webs. Aquatic plants, which are less readily fossilized than their terrestrial counterparts, probably flourished in some of the shallow zones and would have also added substantially to the food supply of Late Devonian ecosystems.

The exploitation of these stable and productive shallows and wetlands probably provided the driving force behind the evolution of the tetrapods. Refinements and variations of the adaptations and features that enabled tetrapods to use these new shallow habitats would later enable them to expand onto the land.

Exploiting weedy shallows and wetlands would provide new food resources and possibly provide a relatively protected nursery for the young as well as an adult refuge from giant lobe-fin predators (e.g., Eusthenodon, Hyneria and rhizodonts).

 

[Naraoia]

That is very interesting.

I wonder how Panderichthys used that part of the fin; why fingerish bits and a primitive wrist turned out to be useful enough to be an advantage for that particular fish?

Hmm, in fact I'm not sure Panderichthys actually had a functional wrist joint. (IIRC Tiktaalik's "wrist" was analogous, rather than homologous to ours.) Having wrist bone homologues isn't the same as having a wrist. Perhaps I should have avoided calling it a wrist

 

[Bombila]

No prob. I wasn't assuming it functioned like a mammal wrist, anyway, just wondering about what such fins would look like in use.