Did Long-Necked Dinosaurs Hold their Heads Up High?

The debate over the posture of the sauropodomorphs has been opened up again with a new research paper published by a team from the University of Portsmouth, England.  The research findings based on close examination of the cervical vertebrae of a number of sauropods plus comparisons with extant mammals and birds indicate that some of these long-necked dinosaurs may have been able to lift their heads high into trees to feed.

This work is in contrast to an earlier Australian study (published in April 2009), postulating that the hearts of these massive animal’s were not able to sustain enough blood pressure to permit blood circulation if their heads were held in a more vertical position.

By examining the skeletons of living animals, animals which share the dinosaur’s unique upright stance (mammals and birds), the University of Portsmouth team have concluded that the long-necked dinosaurs may have held their heads higher for much of the time.

The research, led by Dr Mike Taylor could re-shape the way museums pose their sauropod exhibits.  The classic interpretation of the stance of sauropods (the swan-like neck), was first put forward in the late 19th century when almost complete skeletons of dinosaurs such as Diplodocus, Apatosaurus and Brontosaurus were excavated from the Morrison Formation in the Western United States.  Such large animals became the central attraction at many museums when they were put on display and the papers written about them did depict them with their heads held high.  Often in conjunction with this stance, they were depicted in water, as it was thought that these animals were to heavy to walk around on land comfortably.

A Replica of a Sauropod Skeleton (Diplodocid) on Display at the Naturmuseum Senckenberg

A sauropod (diplodocid) skeleton exhibit on display at the Frankfurt Natural History Museum (Naturmuseum Senckenberg). Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

In the picture (above), a replica of a sauropod skeleton (diplodocid) is shown on display at the Frankfurt Natural History Museum, Germany.

However, there is more than one way in which to articulate the vertebrae of a long-necked dinosaur and a different interpretation has taken hold over the last few years, one that shows these dinosaurs with their heads held in a more horizontal position.  Indeed, the range of movement of the necks of sauropods is believed to be very limited according to some scientists.  Sauropods such as Nigersaurus (Nigersaurus taqueti), which was named and formerly described in 1999, may have been specialist feeders on low growing vegetation and had no need to lift their heads high to feed.  In fact the structure of the vertebrae of this strange dinosaur from Africa is so bizarre that some scientists have marvelled at how it could have lifted its head at all.

The Bizarre Sauropodomorph Nigersaurus – A Specialist Low Browser?

The “Lawn Mower” Sauropod

Picture credit: Everything Dinosaur.

To view a models of various sauropods including brachiosaurids, titanosaurs and diplodocids: Dinosaur and Prehistoric Animal Models.

However, acknowledging the number of conflicting theories regarding the stance and posture of these large dinosaurs, Dr Mike Taylor and his team are not suggesting that museums reassemble their sauropod exhibits.

He went onto comment:

“The Diplodocus in the main hall vestibule of the Natural History Museum [London] is in a perfectly good posture.  It is one within a whole range of movement that would have been entirely possible”.

The University of Portsmouth researchers used X-rays and other sophisticated techniques to plot the range of movement and structure of the necks of several sauropods and then compared them to the movement shown in living animals.  Based on this study, the team have concluded that sauropods could have held their heads high (natural resting position).

Dr Taylor and his colleagues concluded that the necks of mammals and birds (who share an upright stance with dinosaurs), have necks that are “strongly vertically inclined”.  Based on these comparisons they team have suggested that sauropods too, could hold their heads high.  Explaining that fossil bones could only provide part of the story and it was important to consider muscle structure; the team have concluded that these huge necks could have been more flexible than the bones themselves suggest.

The problem is soft-tissue in dinosaurs is very rarely preserved and with sauropods even finding an articulated neck in association with skull material is an extremely rare event in itself.

Dr Taylor added, that based on this new study:

“We can be confident that they [sauropods] held their heads upright”.

This theory is in direct contrast to work published by an Australian team of scientists led by Dr Roger Seymour, who proposed that the elevation of the skull above the heart would have caused enormous problems with blood pressure, raising it to perhaps lethal levels as the dinosaurs tried to pump blood to their elevated brains.

To read more about the Australian team’s work: Dinosaurs with their Heads Held High – the Debate Continues.

Dr Taylor is not convinced by the argument put forward by the Australian team.

“There are some [living animals] where the heart is able to exert much greater pressure than Seymour’s equations predict [is possible].  We don’t see why that couldn’t also be true in sauropods.”

Dr Paul Barrett, a palaeontologist from London’s Natural History Museum, the person responsible for designing the Diplodocus in the museum’s model series, thinks the sauropods were likely to have been able to lift their heads high, but he remains unconvinced that would have been their “resting posture”.

Dr Barret stated:

“It would require lots of muscular activity, and put a lot of strain on their hearts”.

Dr Barrett explained that, since it is impossible to know how thick the pads of connective tissue between the dinosaurs’ vertebrae were, it is difficult to estimate how much of a role this tissue, along with muscles and tendons, played in the animals’ range of movement.

He went onto add:

“Finding a model in biology to explain the stance and posture of these creatures is not easy”.

To view Dr Paul Barrett’s model interpretation of Diplodocus and other prehistoric animals in the Natural History Museum’s range of prehistoric animal models: Natural History Museum Dinosaur Models.

This debate is liable to run and run as further fossil evidence is uncovered.  Perhaps scientists will be fortunate to find a more complete fossil of a sauropod, perhaps a juvenile with some soft tissue preserved so we can gain a better understanding of the range of movement of these amazing prehistoric animals.

The changing scientific opinion regarding Sauropodomorpha: The Changing Views on Sauropods.