Maiasaura Milk?

Vernal's Dinah the dinosaur invites visitors for a swim. Photo by Brian Switek.

On the road to Dinosaur National Monument, along Vernal, Utah’s main drag, there stands a dinosaur wearing a bikini. The cartoon Diplodocus has always unsettled me a little. Dinosaurs did not have mammary glands, much less breasts – that’s only a feature of some placental mammals, such as primates, elephants, and sea cows – so I’m not entirely sure why Dinah had to be covered up. The top implies the existence of something that could not have existed. Yet, even though we can be certain that dinosaurs did not have monstrous mammaries, a new Journal of Experimental Biology paper proposes that the archosaurs might have been capable of nurturing their young with an alternative to mammalian milk.

Simply titled “Dinosaur lactation?”, the commentary by University of Wollongong health scientist Paul Else speculates that a peculiar form of nurturing seen among modern birds might have originated among non-avian dinosaurs. Birds such as doves, flamingos, penguins, and petrels can produce a milky substance in their crops or other parts of their upper digestive system. The fluid contains antibodies, fat, protein, and other nourishing elements. Perhaps, Else speculates, non-avian dinosaurs fed their young a similar substance.

There is no direct evidence that dinosaurs produced “crop milk.” Else makes his case based upon the evolutionary connection between birds and dinosaurs, as well as the hypothesis that the substance would have been one way for adult dinosaurs to feed their newly-hatched young.

Of all dinosaurs, Else suggests that hadrosaurs such as Maiasaura were the most likely to produce milk because their babies may not have been able to effectively break down plant food until they developed teeth and the proper gut flora. Else hypothesizes that the fluid could have been a starter substitute until the infants were able to consume and digest fibrous vegetation. Such a fortified liquid boost, Else also supposes, might account for why young dinosaurs grew incredibly rapidly.

I doubt that proud parental Parasaurolophus slobbered milk into the mouths of nestlings, though. As evocative as Else’s foray into speculative zoology is, his hypothesis is undermined by the relationships of birds that produce milk-like products.

All of the birds Else mentions in his study belong to a group called Neoaves, and each of the mentioned avian species produce the milk-like substance in different ways. Pigeons generate the fluid in their crop, for example, whereas emperor penguins secrete the liquid from the lining of their esophagus. This hints that the ability to produce such substances evolved multiple times within Neoaves, rather than being a shared feature that goes back to non-avian dinosaurs.

If alligators and crocodiles engaged in “secretory feeding”, as well as birds throughout the avian family tree, then we could build a case that dinosaurs might have done the same. This principle, known as the extant phylogenetic bracket, is quite simple. Birds are dinosaurs, and crocodylians are the closet living relatives to the Dinosauria as a whole. If both birds and crocodylians share a particular feature, then there’s a chance that the trait was present in non-avian dinosaurs, too. It’s the same logic behind the hypothesis that male dinosaurs had an “intromittent organ.” Male crocodylians do, and various species among the basal branches of the bird family tree do, as well, and so it’s reasonable to hypothesize that any given male dinosaur had a phallus even though fossil evidence of the organ has never been found. In the case of bird pseudo-milk, by contrast, the presence of the ability in some derived birds and the lack of the trait in crocodylians indicates that there’s no good reason to think that dinosaurs lactated in any sense of the word. Maiasaura milk only exists in the realm of imagination.


Else, P. 2013. Dinosaur lactation? Journal of Experimental Biology. 216: 347-351

7 thoughts on “Maiasaura Milk?

  1. More than once I saw little duckchicks feeding on insects and grownups slobbering vegetation. Could it be that not “milk” but comparable differences in feeding between youngsters and adults, made possible the quick growing of babysaurs?
    Thereabove I wonder, how the – so cute! – baby Maiasaura in the nice restauration of the nest, managed to get out of their eggs? I’ve seen how chickenchicks do it, a hell of a job by the way: with a kind of little chisel on their upperbill they loose soon after. But though perhaps their scales were different, HOW by the hell did this kind of saurs – pictured without such a “chisel” and on the contrary of wet and exhausted – got out???

  2. I think they went through the same thing (at least, not much different)… Weren’t hadrosaurs born with teeth though? They aren’t edentulous, right?

  3. Discus fish feed their babies a sort of milk. If fish and mammals can do it, why not others? Fish even use the same hormone as humans. What is possible for fish and us, is possible for other creatures. Don’t count it out.
    “Studies of the expression of the prolactin receptor in the discus fish skin reveal that it’s expressed in significantly increased numbers during the parental phase, as you can see in the figure above, indicating that it’s prolactin that stimulates mucus production!”

  4. Switek: “In the case of bird pseudo-milk, by contrast, the presence of the ability in some derived birds and the lack of the trait in crocodylians indicates that there’s no good reason to think that dinosaurs lactated in any sense of the word.”

    Actually, there is good reason. W/all due respect, you’re forgetting something important: When it comes to extrapolating non-avian dino behavior, EPB is only 1/2 the story; “Analogy with ecologically similar species” is the other 1/2 (–-picking-the-right-analogue/ ). In this case, like neoavians & unlike crocs, hadrosaurs had altricial young & crops.

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