A fossil neck is a row of bones with much of its working machinery missing. Cartilage once separated the vertebrae, ligaments helped keep them together, and muscles moved them. Before asking how high a dinosaur could reach, a researcher must decide how those bones fitted together in the first place.
A growing giraffe makes that problem unusually clear. A newborn has a long neck, but its bones have not reached adult proportions or finished ossifying. If the spaces in its skeleton are reconstructed incorrectly, the resulting neck can look shorter and behave differently from the original animal.
In a 2020 study, Daniel Vidal and colleagues compared digital necks from a newborn and an adult giraffe with younger and older specimens of the sauropod Spinophorosaurus nigerensis. They found that the older skeletons allowed greater overall movement under the same modelling rules, even though their relative intervertebral gaps were smaller. The important change was the geometry of the entire joint, rather than gap width considered alone. Read the focal study.
A reconstruction that could be checked against an intact neck
The newborn giraffe provided a valuable starting point because it had been CT-scanned after death with the vertebrae still surrounded by tissue. Researchers could measure their separation before digitally taking the skeleton apart. They could then rebuild it and ask whether a rule based on bone shape recovered approximately the same spaces.
Vertebrae meet through more than the large ends of their central bodies. Small paired surfaces above them also articulate and slide against one another. These are the zygapophyseal joints. The team defined a standard starting configuration by bringing those small joint surfaces into full overlap.
That choice mattered. In the newborn, forcing the large vertebral ends into a different, tightly fitted alignment nearly eliminated the gaps. Aligning the smaller joint surfaces instead left substantial spaces between the central bodies, much closer to the intact CT scan.
Across the measured neck segment, intervertebral space occupied 27.27% of the length in the scanned specimen and 27.03% in the reconstruction. The close match was a useful check on the method in this particular animal. It did not establish that the same procedure would recover an exact cartilage thickness in every species, or that the starting alignment was the posture a giraffe habitually adopted.
An earlier dissection by Michael P. Taylor and Mathew J. Wedel showed the cost of omitting these spaces. A two-week-old giraffe’s neck measured 51 centimetres with its tissues intact. Once cleaned, the bones could be fitted closely into a row only 41 centimetres long. That experiment and the later CT comparison address the same practical problem: a plausible arrangement of clean bones can lose part of the original neck. Their percentages use different denominators, so the measured lengths are the clearer comparison. Read the cartilage study.
Smaller gaps, greater movement
The adult giraffe reconstruction had much smaller relative spaces: approximately 4.8% of its measured segment. Yet its neck allowed a greater total range of bending than the newborn model.
To estimate that range, the researchers rotated one vertebra at a time while holding its neighbour still. They continued until the sliding joint surfaces retained only minimal overlap, unless bone contact stopped movement earlier. This was an explicit modelling boundary, not a measurement of forces acting in a live neck.
Under those rules, the adult model could bend farther overall both upward and downward, and turn farther sideways. The result was not uniform at every joint. For example, the joint nearest the trunk in the reported giraffe comparison had a slightly greater up-and-down range in the newborn. Growth changed the distribution of movement as well as its total.
The geometric explanation involves where the sliding surfaces sit relative to the centre around which a joint rotates. A joint surface farther from that centre travels a greater distance for the same angular turn. If the available sliding distance stays limited, contact is lost sooner. As vertebrae elongate, the relative arrangement of these structures changes. The authors proposed that this helped account for the larger ranges in the older necks, rather than attributing flexibility simply to the amount of cartilage between bones.
The models could also fold each giraffe’s head back toward its body while retaining some joint overlap. That supported the usefulness of the chosen bone-contact rules for reproducing an extreme giraffe posture. It did not show how much muscle effort was required or measure the remaining safety margin in the joint capsule.
Why a giraffe helps interpret a dinosaur
The sauropod material offered a rare comparison: a small, probably juvenile neck and a much larger neck attributed to the same species. The larger specimen was treated as a subadult in the paper, although its precise maturity remained uncertain. Additional bones from another, more mature specimen helped complete the reconstruction.
The broad pattern resembled the giraffe comparison. The younger sauropod had proportionally larger spaces between vertebrae, while the larger animal’s reconstructed neck allowed more movement. A juvenile fossil neck therefore could not be treated as a reduced adult whose joint proportions and movement stayed unchanged.
There was also a revealing difference. The giraffe generally allowed more movement at an individual joint, whereas Spinophorosaurus accumulated movement across more neck vertebrae. Similar overall flexibility need not arise from identical anatomical arrangements.
Some parts of the dinosaur comparison were necessarily reconstructed. Several juvenile joints were damaged, and their movement was estimated from neighbouring joints. Much of its body was represented by a scaled version of the larger skeleton. These choices affect estimates such as maximum feeding height more directly than they affect an observation made on a well-preserved pair of neck bones.
Sauropods also had elongated, overlapping cervical ribs that giraffes lack. The study did not calculate their full effect on neck movement. A pose permitted by the model’s main joints might still have been restricted by those ribs or by soft tissues. The paper therefore supports a set of anatomical possibilities, rather than an observed dinosaur feeding or resting behaviour.
Growth belongs inside the reconstruction
Two giraffes cannot describe the full developmental range of the species. The comparison also separates bone geometry from a living neck’s active control and tissue resistance. Those limits define the next useful evidence: more ages, intact joints and measurements that connect skeletal movement to the tissues around it.
The advance is nevertheless concrete. An intact newborn neck supplied a check on how separated bones should be assembled, and the age comparison showed that decreasing relative gaps did not automatically mean decreasing mobility. For fossil reconstruction, maturity becomes part of the mechanical question. A skeleton’s capacity to move depends on how its joints grew together, not just on how long its neck became.
Sources
Daniel Vidal, Pedro Mocho, Adrián Páramo, José Luis Sanz and Francisco Ortega (2020). “Ontogenetic similarities between giraffe and sauropod neck osteological mobility.” PLOS ONE 15(1): e0227537. Full paper.
Michael P. Taylor and Mathew J. Wedel (2013). “The Effect of Intervertebral Cartilage on Neutral Posture and Range of Motion in the Necks of Sauropod Dinosaurs.” PLOS ONE 8(10): e78214. Full paper.
