watching the dinosaurs

Over more than a century dinosaurs have become ingrained within our culture. Even if your acquittance with them is limited to Jurassic Park and reading to your children, you can name iconic dinosaurs: tyrannosaurus. velociraptor and … well you know, those long-necked herbiverous ones … I set out to sketch grazing geese in response to this post in  “Tetrapod Zoology” http://blogs.scientificamerican.com/tetrapod-zoology/2011/12/19/second-workshop-on-sauropod-biology-pt-i/. Sauropods were the really big dinosaurs, many tens of tons, held up on on four pillar-like legs.  They all had small heads on long necks.  Check out Mark Witton’s artwork on that post showing a herd of Diplodicus at a water hole.

What made the sauropods (diplodocus, brachiosaurus, apatosaurus and the rest) such successful dinosaurs over millions of years and how did they get so big? Some of their critical features are shared with their kin, the birds: highly efficient lungs incorporating air cavities in bones, a fast metabolism, warm bloodedness and egg laying.  They produced many small offspring and grew very fast.  Growth was obviously not limited to a single season and predator pressure must have advantaged gigantism (I think birds, by contrast, pretty much reach adult size  in a season and parental care plus flight are quite different ways to escape predators that largely do not drive size selection).

Why all sauropods had long necks is clearly controversial among scientists.  One hypothesis brought to my mind similarities with many birds.  Geese have small heads on long necks.  They do not chew their food.  Birds have a gastric mill, grinding food with swallowed stones.  Sauropods certainly did not chew but there’s not evidence for a gastric mill.  Their great bulk would have housed guts like vast fermentation tanks to release nutrients from the ingested vegetation.  It is common place to watch geese walk, stop, graze in an arc and walk on again.  A long neck allows harvesting from a wide area without moving the body’s bulk.  Perhaps a similar strategy in sauropods was a critical factor in enabling gigantism because for a very large animal it reduced the cost of accelerating and stopping to feed.

The geese here by the way are the common greylag, apparently the source stock of the farmyard animal.  They are dismissed even by the Royal Society for the Protection of Birds as being uninspiring.  I don’t think so.  I watched this group feed across a flooded gravel pit. My field sketches were limited but I took photographs.  These I later worked up into a charcoal drawing and finally added colour with chalk pastels.

    

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