Sturgeon backbone tests show early tetrapod necks were stiff
Dana Korneisel's Nature study applied sturgeon backbone stiffness to fossil tetrapods and found their necks allowed little movement. Surrounding tissue would cut that further, so the neck-mobility explanation for the body-plan change loses ground.
The Scientist · Science desk
What happened
- Shoulders detached from the skull sometime in the Devonian, leaving a new region of neck vertebrae between them, and for decades that separation was assumed to have freed the head.
- The team bent and twisted sturgeon backbones and notochord sections on a universal testing machine over three days, in batches of three or four, to measure stiffness.
- Head elevation in the animals was no more than would be expected in fish and sometimes even less, according to Korneisel.
Why it matters
- capability Notochordal columns were common through life's history, so a stiffness-scaling method built on sturgeon has a large pool of fossil candidates to test.
- precedent The date for a real gain in neck mobility moves later in the tetrapod family tree, so researchers dating it will be looking at younger lineages.
- constraint Explanations for the shoulder-skull separation can no longer lean on greater head mobility in the earliest tetrapods.
Early tetrapod backbones are unusual next to most vertebrates today. The animals kept a notochord all their lives, with small vertebrae arranged around a large tube of soft tissue [5]. That tissue behaves differently from the joints between vertebrae that are typical now, and until this work scientists had not been able to test the neck mobility hypothesis [6]. Sturgeon, a distantly related fish, have the same kind of backbone [7].
The team calculated the material stiffness of the sturgeon tissues and applied it to extinct animals [10]. The scaling is plain. "If you can measure the size and shape of both the thing you are testing and the part of the animal you want to model mobility of, it all comes down to dividing out the sturgeon number and multiplying by the fossil number," Korneisel said [11].
The design is lopsided in a useful way. Korneisel stressed that every estimate rests on the backbone alone, so actual mobility will have been less than the estimates, because muscles, skin and, for many of these animals, bones embedded in the skin would restrict movement further [12]. The model can exclude high mobility. The thing this doesn't tell you is how far any one animal actually moved its head.
The phys.org report says the results disprove the long-standing hypothesis [2]. That verdict is as strong as the premise that sturgeon notochord tissue behaves like the extinct animals' tissue, since the model applies sturgeon properties to the fossils [8]. On head movement, Korneisel said: "We found that the kind of head twisting that we can do when we shake our heads was not feasible in any of these animals." [14]
Korneisel said that while handling sturgeon spines she "felt that the tissue wasn't terribly stiff", and that "after doing the math, the lack of significant head mobility for almost all of these animals was a huge surprise" [15]. The article does not say how many sturgeon were tested in all, or which animals fall outside "almost all".
She does not argue that neck mobility never mattered. Of the early tetrapods, she said, "it was not an advantage available to these early tetrapods yet because of the limitations of their anatomy" [16]. Notochordal vertebral columns are rare today but were very common throughout life's history [17].
What to watch
- Whether other groups apply the sturgeon stiffness scaling to further notochordal fossils and check it against an independent measure.
- Which later tetrapod lineages get dated as the first with real neck mobility, now that the gain sits higher in the tree.
Clarity's read
What the record supports and how the coverage leans. The claims behind it follow.
Reality
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- Adoption
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- Hype gap+15
- Incentives
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- [1]
Researchers built a model using sturgeon as a material analog to estimate how the backbones of some of the first animals on land could and could not move.
- [2]
According to the phys.org report, the results disprove a long-standing hypothesis that changes in early tetrapod anatomy as they moved onto land gave them improved neck mobility.
- [3]
The study, led by a researcher at Uppsala University, formerly of Carleton University in Canada, was published in the journal Nature.
- [4]
In fish the shoulder blades are attached to the skull; in early tetrapods the shoulders became detached sometime in the Devonian and a new region of neck vertebrae separated shoulders and skull, and for decades it was assumed this allowed the head to move more freely.
- [5]
Early tetrapods kept a notochord for their whole lives, running through the vertebral column, so their vertebrae are small and arranged around a large tube of soft tissue.
- [6]
The soft tissue behaves differently from the joints between vertebrae that are typical today, and scientists had not been able to test the neck mobility hypothesis.
- [7]
The researchers modeled early tetrapod neck mobility using the sturgeon, a distantly related fish that has the same kind of backbone.
- [8]
Applying the material properties of sturgeon notochordal backbones to fossil animals, the researchers found early tetrapod necks were surprisingly stiff and, even free of surrounding bones, would not have allowed much mobility.
- [9]
The researchers dissected sturgeon backbones and bent and twisted them on a universal testing machine, testing batches of three or four at a time over three days, first the whole backbone and then sections of notochord.
- [10]
From the test data the researchers calculated the material stiffness of the sturgeon tissues and applied it to extinct animals.
- [11]
"If you can measure the size and shape of both the thing you are testing and the part of the animal you want to model mobility of, it all comes down to dividing out the sturgeon number and multiplying by the fossil number," said lead author Dana Korneisel.
- [12]
Korneisel stressed that all the estimates are based on the backbone alone, so actual mobility will have been less than the estimates because of surrounding tissues such as muscles, skin and, for many of these animals, bones embedded in the skin.
- [13]
Korneisel said head elevation in these animals was no more than would be expected in fish, and sometimes even less.
- [14]
"We found that the kind of head twisting that we can do when we shake our heads was not feasible in any of these animals," said Korneisel.
- [15]
Korneisel said that while handling sturgeon vertebral columns she felt that the tissue wasn't terribly stiff, and that "after doing the math, the lack of significant head mobility for almost all of these animals was a huge surprise."
- [16]
Korneisel said of the early tetrapods that higher neck mobility "was not an advantage available to these early tetrapods yet because of the limitations of their anatomy," and that the results push the gain of that function forward in time and up the evolutionary tree from where it was previously thought to occur.
- [17]
Notochordal vertebral columns are rare today but were very common throughout life's history on Earth.
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Sources
1 independent publisher whose own reporting we read for this story.
- phys.orgModeling study shows early tetrapods had surprisingly little ability to move their necks
1 article · October 14, 2026
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