Sauropod Nostrils – Where do they belong?

Dinosaurs are so ubiquitous these days sometimes it is worthwhile reminding ourselves just how little we actually know about them.  Certainly, our knowledge is improving all the time and many commentators have claimed that we are presently in another “golden age of dinosaur discoveries”.  With all the new techniques available, more work can be done on the existing fossil record and with more parts of the world being opened up to exploration the number of dinosaur fossils is increasing rapidly.  However, despite huge advances we still know relatively little about many of these creatures.  As the Walking with Dinosaurs – Live experience tours Canada we could all be mistaken for thinking that there is no more to learn, but this is far from the reality.

For example, where on a long-necked dinosaur was its nose?

The long-necked dinosaurs (sauropoda) have been known for a very long time, Apatosaurus (formerly known as Brontosaurus) was named and described by Othniel Charles Marsh 130 years ago, Brachiosaurus was named and described by Riggs in 1903 and thanks to the philanthropist Andrew Carnegie fully mounted skeletons of Diplodocus (albeit in the wrong posture) have adorned the main halls of many Natural History museums all over the world for nearly a Century.

When fossils of these huge animals first came to light, scientists could not imagine them as purely terrestrial creatures, surely such huge reptiles, many estimated to have weighed 50 Tonnes or more would be much more comfortable living in water, where their huge bulk could have been supported by the water.  Certain skeletal features supported this view, such as the arrangements of claws on the feet, supposedly to stop these sauropods slipping on the muddy lake floors, the arrangement of the their weak peg like teeth – surely only suited to cropping soft vegetation found in lakes and on their margins.

Scientists assumptions about these dinosaurs and their aquatic lifestyles were reinforced in 1884 with the discovery of an almost intact skull of a Diplodocus.  This showed a large hole at the top of the head, which scientists interpreted as the entire nasal cavity.  After all, if  you spent all  your time under water, a blow-hole type structure at the top of the head would make a lot of sense.   It was argued that these animals were as big as whales and whales lived in water with a nostril arrangement at the top of their heads so the dinosaurs had evolved a similar structure to assist them with their underwater lifestyle.

A Snorkeling Brachiosaur

Picture courtesy of Lindahall.org

The picture above was drawn by Zdenck Burian in 1941, the idea of aquatic sauropods was first postulated in the late 19th Century, most famously by the American palaeontologist Edward Drinker Cope.  This type of illustration featured in numerous books, magazines and publications right up to the 1980s.  However, the modern interpretation of sauropod fossils depict them as largely terrestrial creatures, but despite this seismic shift in our perception, the nostrils of these animals are still placed at the top of head.  This can be clearly seen in many drawings and artistic impressions as well as in many scale models.

Lawrence M. Witmer famously challenged this view and placed the nostrils of Diplodocus in a much more anterior position on the skull.  Working as an associate professor of biomedical sciences at the University of Ohio, Witmer had access to a number of late Jurassic sauropod specimens and conducted an analysis of sauropod skulls with an emphasis on the Duplicates.  Soft tissue scars found on skull bones were studied, along with 62 animals from 45 species of crocodile, birds and schemata, which were x-rayed and dissected, the soft tissue making up the nasal cavities and naris were mapped and the extant species were compared to the fossil evidence.

From this work, Witmer re-modelled the skull of Diplodocus putting the nose much closer to the mouth at the front of the beast.  What’s more the conclusions from this work led palaeontologists to acknowledge the existence of quite sophisticated and highly vascular, taking up to 50% of the space available in an Diplodocus skull.

An Artist’s Impression showing the Evolution of the Diplodocus Nose

Artists impression drawn by Michael Skrepnick

The pink skull at the top of the diagram clearly shows the large naris opening at the top of the head (now believed to only part of this animal’s complicated nasal system), using Witmer’s work as a guide the nostrils have no been placed at the front of the skull.

The position of the nostrils has considerable implications for a number of biological and physical processes in Diplodocoid physiology.  If the nostrils were placed at the front then they alter our perceptions of the role of sense of smell for this animal.  Did sense of smell help these huge animals find a mate, avoid danger or to find food?  The close proximity of these sensory organs (mouth and nose) in Witmer’s model does make sense from a morphology and physiological standpoint.  With a better understanding of the structure of the nasal passages palaeontologists can speculate on how these passages may have helped humidify and filter air on the way to and from the lungs.  With a head exposed to the sun could these nasal passages play an important role in cooling the brain and regulating body temperature.  Losing heat for an animal of such volume would not necessarily have been an issue but thermal regulation of the brain could have been a problem as these beasts wandered the hot Jurassic landscape.

Witmer and his team have more work to do, especially on the role of these complicated nasal airwaves on body and brain temperature regulation.  Although the naris at the top of the skull in sauropods is seen as part of the nasal system it seems that the passages were much more complicated than first thought.  However, the scientific community remains divided on some of the more controversial findings from Witmer’s work.  Some scientists still place a greater emphasis on the naris at the top of the skull and if the work of Witmer is to be accepted it has implications for other types of dinosaurs, the ornithischia, for example.  If these concepts are developed this could lead to a whole new interpretation of the crests on Hadrosaurs.

Modellers still depict sauropods with nostrils in a more posterior position.  Although more modern interpretations are coming to the fore.  We recently worked on the Brachiosaurus for the dinosaur collection preferring to opt for a more posterior position for placement of the nostrils.  As a member of the “macronarians”, the big nostril sauropods we thought this was appropriate.

Dinosaur Collection Brachiosaurus (the Collecta Brachiosaurus and the Collecta rearing Diplodocus model): Dinosaur Toys for Boys and Girls

The lack of sauropod skull material still continues to frustrate palaeontologists, perhaps the recent discoveries of new well preserved diplodocoid skulls in Western North America well shed further light on this anatomical puzzle.

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