How to make water into a tongue
This is one of the coolest bits of functional morphology work I've seen in a while. +Ed Yong
summarizes the new paper below. The new paper is entitled "A fish that uses its hydrodynamic tongue to feed on land" and it looks at mudskippers, which are among the coolest creatures ever, so that's already a good start.
What's really cool is how mudskippers feed on land. Fish typically do not have a tongue that they can protrude from the mouth or use to help them swallow (Basal fish do not have a true tongue at all. Sharks, for example, have a pad of thickened tissue at the floor of their mouth, but no real tongue. Teleost fish have a tongue, but it's a chewing structure, not something they can stick out of their mouth or use for swallowing). Instead, fish typically use suction to swallow, and many use suction to grab prey in the first place.
That's a potential problem for mudskippers, which scoot around on land to find much of their food. So, how does a fish with a suction-type mouth manage to eat on land? The answer turns out to be that mudskippers take a reservoir of water with them in their mouths, and shoot it out to act as a virtual tongue. That's right, mudskippers grab and swallow prey on land using what is basically a prosthetic tongue made of water
In any case, read the full Phenomena
article by Ed Yong to get the full scoop on the study, and what it says about the evolution of the vertebrate tongue, which is one of my favorite topics in evolutionary morphology (because it's complicated).
The original article is here: spb.royalsocietypublishing.org/content/282/1805/20150057
The authors have shared data here: http://datadryad.org/resource/doi:10.5061/dryad.0fg55
And this is the abstract:
To capture and swallow food on land, a sticky tongue supported by the hyoid and gill arch skeleton has evolved in land vertebrates from aquatic ancestors that used mouth-cavity-expanding actions of the hyoid to suck food into the mouth. However, the evolutionary pathway bridging this drastic shift in feeding mechanism and associated hyoid motions remains unknown. Modern fish that feed on land may help to unravel the physical constraints and biomechanical solutions that led to terrestrialization of fish-feeding systems. Here, we show that the mudskipper emerges onto land with its mouth cavity filled with water, which it uses as a protruding and retracting ‘hydrodynamic tongue’ during the initial capture and subsequent intra-oral transport of food. Our analyses link this hydrodynamic action of the intra-oral water to a sequence of compressive and expansive cranial motions that diverge from the general pattern known for suction feeding in fishes. However, the hyoid motion pattern showed a remarkable resemblance to newts during tongue prehension. Consequently, although alternative scenarios cannot be excluded, hydrodynamic tongue usage may be a transitional step onto which the evolution of adhesive mucosa and intrinsic lingual muscles can be added to gain further independence from water for terrestrial foraging.