Published on October 8th, 2023 | by David Marshall


Episode 156: Bird necks

Whilst the evolution of feathers and flight might be seen as the greatest evolutionary innovation of the birds, the development of their wings precluded their forearms from holding many functions outside of flight. It is widely recognised that beaks are utilised as a ‘surrogate hand’, but if so, then surely the avian neck must function as a ‘surrogate arm’.

In this interview, we speak to University College London’s resident “neckspert™” Dr Ryan Marek. Ryan introduces us to bird necks detailing their anatomy, how they’re used, and what constrains their form and function. We end by craning our necks back to look up the vertebrate family tree to see when such specialised structures evolved.

This interview is based on Ryan’s recently published review article, freely available here: Marek 2023.

It’s not hard to understand why many palaeontologists would be interested in studying the necks of dinosaurs such as Diplodocus. However, before that’s done, there’s an awful lot we don’t know about the necks of modern dinosaurs that must first be explored.
Birds use their necks for a range of functions, from pecking and preening (pictured), to stabilisation in flight and even tearing flesh from prey. If the beak is a ‘surrogate hand’, then the neck is the ‘surrogate arm’.

Parrots have even been demonstrated to possess ‘tripedal’ locomotion in specific circumstances. The force to move in such a way is generated by the neck. Courtesy and copyright of Young et. al. 2022.

Neck morphology in birds varies between species in terms of the number of cervical (neck) vertebrae (A), the overall shape and posture of the neck (B-E) as well as the shape of individual vertebrae (B-E).
Image: A) Evolutionary tree of birds that displays the variation in the number of vertebrae between species (red = more cervical vertebrae, blue = fewer). B-E) Variation in the morphology of individual vertebrae (blue = vertebrae near the head, pink = middle neck vertebrae, gold = vertebrae at the base of the neck) and overall neck posture between 4 species of birds (B parrot, C eagle, D darter bird, E goose).
Complicating this is that there is a huge amount of variation between the soft tissues of the neck, as can also be seen from the next image. Here, the M. biventer cervicis muscles (bc) are incredibly large in the Humboldt penguin (A,B), as compared to the North American barn owl (C). This demonstrates that understanding bird necks is far more complicated than just looking their bones.
The function of the neck and the morphology of the muscles that contribute to these movements varies greatly across different species of birds. Neck movements can vary between waterfowl (a) and chickens (b) due to many factors such as feeding in water. C-G shows a diagrammatic representation of the variation in muscle attachment schemes across the neck of 5 birds (C seriema, D red throated loon, E Galapagos penguin, F ring-necked pheasant, G tawny owl). Numbered boxes represent the head and cervical vertebrae. Coloured lines are representations of muscles. Dorsal musculature: M. complexus (red), M. biventer cervicis (black), M. splenius capitis (purple), M. longus colli dorsalis pars caudalis (pink), M. longus dorsalis pars cranialis (gold), M. longus colli dorsalis pars profunda (green). Ventral musculature: M. rectus capitis ventralis (red, M. rectus capitis lateralis (Yellow), M. rectus capitis dorsalis (blue), M. longus colli ventralis (black). Dashed lines for M. longus colli dorsalis pars caudalis represent discrete origination slips.

Ryan demonstrates the flexibility of a gannet’s neck as controlled by just the ligaments on the dorsal side.

Only when we better understand modern necks, will we be able to make informed inferences about similar necks in the past. Here, an ornithomimid displays the classic avian ‘death pose’, with its head thrown backwards by a curvature of its long bird-like neck.
The exact causes of this ‘opisthotonic position’ is still unclear, but contraction of the musculature and/ligaments of the neck is through to be a contributing factor. Regardless, the similarities between birds and dinosaurs are self-evident.
Having laid strong foundations in understanding the necks of birds, Ryan is now beginning to look at the necks of dinosaurs, including this, the holotype of Tyrannosaurus rex.
Given the importance of necks to birds, such work has the potential to be highly informative to our understanding of the functional anatomy and potential behaviours of dinosaurs. Image: the therizinosaur Falcarius.

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