#balaenopterids

What is the tongue like within rorquals (at least the lunge feeding ones)? In pictures of fetal tongues they are shown as filling the mouth much like the tongues of humans or dolphin. Image1 Image2 However in other images show the tongue as particularly far back in the mouth as this tiny lump in the back of the mouth not covering the sling at all. Image 1 Image 2 (tumblr seems to be inconsistantly linking them so I hope some of these images actually work). Do the tongues change shape (besides losing the papillae) as the whales become adults, or are rorqual tongues particularly motile they seem to just disappear in certain images, or is something else happening?

Kindly, Kala

Hi there! What an interesting question. Thanks for casting me down the proverbial whale gullet of rorqual tongues (and cetacean tongues in general). Tumblr did bug out a bit and only linked the second image for both examples but it gave me a good starting point. I want to begin with linking this awesome review paper covering everything ceta-tongue related you ever wanted to know: https://onlinelibrary.wiley.com/doi/10.1111/joa.13876 It's free to read online with lots of great images!

And this paper: https://link.springer.com/article/10.1007/s12562-024-01806-w Your first linked image is from there, not sure if you caught the whole article. Also free to read! It specifically looks at the neonatal tongue in Minke whales, but also offers some comparisons with adults and other species.

With that out of the way; the answer to your question is that cetacean tongues are weird. And none weirder than those of the rorquals. Many of the functions we associate with tongue-having, like suckling, noise production or tasting, are absent in cetaceans. Their morphology is instead highly catered to their assistance (or not) in feeding methods. Suction-feeding species like Beaked whales need a tongue that can move back enough to create suction. In bowhead and right whales, the tongue should be movable enough to change shape, so that it can both direct water flow through the baleen, as well as clean those baleen. Dolphins need it to expel water from their mouth after they've caught a fish and close their gullet when not feeding (I've seen a dolphin do this underwater; it looks bizarre as their lips flare open when the water rushes out, and for a moment they have this very localised toothy grin).

Many tongues, many feeding strategies. But when cetaceans are young, they all have one and the same feeding strategy: drinking milk from mom. Unlike land-based mammals who actively suckle, cetacean mothers expel their milk into the water. The milk is so fatty and thick the consistency is more like that of toothpaste, so it does not dissipate instantly. It is up to the calves to channel this into their mouths. And so, as young calves, they have these marginal papillae, fringes at the edges of the tongue, which can create a seal when the tongue is curled up. Kind of like a biological straw.

Rorquals of course need to nurse too. So as calves, they have a tongue that is quite similar to that of other cetaceans: thick, muscular, mobile and with the mentioned marginal papillae. However, as they mature their feeding strategy becomes quite different. And as such, their tongues undergo a transformation too. In adults the tongue is floppy, more like a water bed. It is far less shapely, highly flexible and can't extend past the tip of the mandibles. It is probably impossible for the adult rorqual to move their tongue much. However, when feeding the tongue does something incredible. Because, along with the throat pouch, it too stretches and inflates as water comes rushing it. The tongue forms part of the lining inside the whale's incredible distended throat when eating. Now you see why it simply can't retain the fleshy, muscular tongue of its calf days.

Here's a schematic illustration from the first paper I linked. Looking at this it's clear what an incredible and unique structure the rorqual's tongue truly is.

This also explains why in many photos of wild whales lunging underwater it's hard to locate: once a rorqual opens their mouth, water automatically flows into the oral cavity, pushing the tongue back. On stranded whales the tongue may be in a more natural position and seem larger.