The life-styles of some dinosaurs
Less than a century ago, we had an extremely limited, and highly distorted
view of dinosaurs, both in terms of their physiologies, and in terms of how they lived
and behaved.
Until the early 1930s, for example, the opinions of palaeontologists like Oliver Hay,
Gustuv Tornier, and Lawrence Lambe (to mention just three) held the field. These people
believed, implicitly at any rate, that the dinosaurs were all dim-witted, slow-moving, clumsy,
bumbling, accidents of nature: Evolutionary dead-ends, which were doomed to extinction almost
from the outset. For a sociologist of science, the genesis and ontology of this idea could well be a
fruitful area of study. It reflects a rather peculiar world-view in any case, one which is species-,
and biological-class-centric: as mammals, we have an inclination to see ourselves as the bee’s
knees of evolution, and our view of dinosaurs has always been rather condescending – the very
noun, dinosaur, has become synonymous with outmoded, old-fashioned, or cumbersome.
To give you some examples of these odd ideas about the dinosauria:
1. When stegosaurus was first discovered in the 19th century, palaeontologists
were so surprised at it’s small skull, and brain-case that Othaniel C. Marsh
broached the idea of it having a second brain in the rump;
Source: http://www.stupiddinosaurlies.org/the-stegosaurus-carving-that-isn-t
2. Brachiosaurus, which has its nostrils on the top of its head, was once thought
to live underwater, using its 40-foot neck and top-mounted nostrils as a sort of
snorkel. However, simple calculations would have shown that due to the high
water pressure at such depths, it would been unable to breathe;
Source: http://www.dinosaurjungle.com/gsp_brachiosaurus2.png
3. When it was established that caterpillars first evolved shortly before dinosaurs
went extinct, it was thought that they were the cause of the dinosaurs demise,
that they literally ate the dinosaurs to extinction by eating too many leaves;
A Hercules-moth caterpillar. This species was not around during the time of
the dinosaurs btw.
Source:
http://newsdesk.si.edu/images_full/images/museums/zoo/Rainforest_Caterpilla
r/large%20caterpillar.jpg
4. Some people thought that large dinosaurs were so slow, and unresponsive that
smarter mammals (our ancestors) could feed on them, starting perhaps with
their tails, even though they were alive and moving around;
5. When the first partial femur of a megalosaurus was unearthed in England in
1676, people thought it was the remains of a giant human being. It took 160
years before this error was corrected. This is an understandable error though,
since these were bipedal dinosaurs, and people had no clue at all at that time
that there were things called dinosaurs.
Source:
http://www.copyrightexpired.com/earlyimage/bones/display_hutchinson_mega
losaurus.jpg
6. Early fossils of iguanodon, one of the first dinosaurs to be studied, was
reconstructed with it’s horn-like ‘thumbs’ located in a rather unlikely position
on the top of its head.
If you look closely, you can see the horn on the nose of these rather
inaccurately reconstructed iguanodons. The photo on the right shows the
‘horn’ where it should actually be located, on the ‘hand’ it’s in fact a thumb.
Source: http://scienceray.com/earth-sciences/paleontology/130-million-yearold-mistake/
For more on mistaken ideas about dinosaurs, see:
http://dinosaurs.about.com/od/dinosaurdiscovery/tp/dinoblunders.htm the site
http://www.stupiddinosaurlies.org/ also has interesting information on dinosaur
misrepresentations on it.
The above-going is just a brief sample of some of the more outlandish ideas which people
have, in the past, held about dinosaurs. I suppose it’s hardly surprising though, as they are such
outlandish beasts compared to our contemporary fauna, and people generally have a tendency to
try and relate odd things they discover to what they think they already know about the world
already.
This whole paradigm however has undergone substantial revision over the past sixty years
or so, and along with this revision has come new, more accurate knowledge of how dinosaurs
might have lived, and this is the subject of today’s column.
Considering that they have been around for 160 million years or so, from about 225
million years ago, to about 65 million years ago, it is hard to see how anyone could have possibly
considered them to be evolutionary dead-ends, but a hundred and fifty years ago, humans, and
particularly, Victorian gentlemen from Europe, were a lot more certain of their absolute
superiority over all other species and skin colours.
Source: http://www.mbmg.mtech.edu/graphics/time-line.gif
If you look at the above time-line, you will see that the dinosaurs were around for the entire
Mesozoic, but humans have been around for so brief a period on this scale, that even the thin
black line which borders the yellow and orange square at the top of the graphic slightly
exaggerates how long humans have been on the scene.
One unfortunate artefact of this Victorian view of things, according to Steven Jay Gould,
in The Book of Life, was that they left future generations a legacy, in the form of a terribly
inaccurate, but rather graphic collection of icons; a collection which was to have a subtle, but
profound impact on the way in which many future palaeontologists learnt, while they were still
children, to view dinosaurs. (For an interesting essay on the topic see Gould’s essay: Dinosaur
Deconstruction, first published in Discovery Magazine, October 1993 issue. The on-line version
may be found here: http://discovermagazine.com/1993/oct/dinosaurdeconstr284)
Given how powerfully “Jurassic Park” has influenced our views of dinosaurs, there can be
little doubt but that as Victorians viewed the imaginative, impressive, but unfortunately
oftentimes inaccurate exhibits, on display at places like the Crystal Palace, or the British
Museum, for instance, these displays must have given form to the outlines of a paradigm that, in a
parallel manner, influenced all their future thinking on the subject.
Some Crystal Palace reptiles. Not very convincing to us today, but highly influential 150 years ago.. Source:
http://www.biocrawler.com/w/images/3/3d/London_-_Crystal_Palace_-_Victorian_Dinosaurs.JPG
So, what do we now know about dinosaurs? From the extensive fossil record, we know
that they came in a tremendous variety of forms, ranging from gigantic, forty tonne, quadrupedal
herbivores, to minuscule, kilogram-weight, bipedal insectivores. Again, based on where these
fossils have been found, and what types of plant remains have been fossilised with them, we
know that these animals lived in a wide range of different habitats and climactic conditions.
Indeed, dinosaurs appear to have lived on every continent.
Source: http://en.wikipedia.org/wiki/File:Largestdinosaursbysuborder_scale.svg
Scale diagram of the largest known dinosaurs (length and mass) of four suborders:
Sauropodomorpha (Amphicoelias fragillimus in lilac, ca. 60 m long), Cerapoda (Lambeosaurus
laticaudus in rusty-red, ca 15 m long), Theropoda (Spinosaurus aegyptiacus in green, ca 17 m
long), and Thyreophora (Stegosaurus stenops in orange, ca 9 m long). Compared in size with a
human. Each grid section represents 1 square meter.
Source: http://en.wikipedia.org/wiki/List_of_dinosaur_classifications
This graphic may give you some sense of the vast range of dinosaur forms so far discovered. For
more detailed information, take a look for example at
http://en.wikipedia.org/wiki/List_of_dinosaur_classifications to get some idea of the diversity of
the dinosauria. Do keep in mind though that: i) our knowledge of dinosaurs is based solely on the
fossils we have found so far; and ii) there is still a lot of debate as to where exactly each dinosaur
discovered fits within the overall classificatory scheme of things.
Source: http://thisrecording.files.wordpress.com/2008/05/800px-london_-_crystal_palace__victorian_dinosaurs_1.jpg Compare this Victorian sculpture of megalosaurus to how we depict
dinosaurs (including megalosaurus – see above) today, and you’ll see that our ideas about them
have advanced significantly. Compare this interpretation megalosaurus to the velociraptor
shown at the end of this post, and you’ll see that the assumptions informing the artists has been
revolutionized.
Source: http://en.wikipedia.org/wiki/File:CeratopsiaI_BW.jpg
This is an illustration, to scale, of just 18 of the known basal ceratopsians for example. It serves
to illustrate the diversity of the dinosauria as a whole.
All of this however is not so very surprising a set of discoveries. What are interesting
however are two things. The first, is how sophisticated analysis of fossilised remains can yield all
manner of clues as to dinosaurian life-styles. The second, is what some of the more recent fossil
finds have been like.
As an aside, let me note that some fossils were lost through various mishaps: ships carrying
remains sinking for example, and that through ignorance, many early fossils were not excavated
properly, and so much useful information was lost as a result of this. For example, much
information about their life-styles can be extracted from studying the rocks in which the fossils
are found, and in the case of multiple fossil-finds, in analysing their relative positions with
respect to each other. We are however learning, and as it matures, palaeontology and its
practitioners are making fewer such mistakes, and learning better how to extract all the
information which it is possible to obtain from a fossil, and its surrounds.
By looking, for example at hadrosaurian nests, a whole colony of which were found in
Montana about twenty years ago, and by asking some novel questions, it has been possible to
reconstruct some tentative details about their how they lived their lives.
The nest itself, a shallow bowl-like indentation in the ground, which seems to have been
lined with vegetation, looks to have been deliberately constructed. Inside these nests, researchers
found the fossilised remains of egg shells that had been broken into small pieces. This is
consistent with the view that the young remained in the nest for a substantial amount of time after
hatching, at least long enough to trample the shells. In some nests, the researchers found the
fossilised remains of babies. These babies also had teeth which revealed evidence of wear. These
two facts together suggest a scenario in which baby hadrosaurs remain in the nest for a substantial
period of their infancy, either in the care of their parents, or fending for themselves and then
returning to a safe roost. Further studies on various dead hatchlings however showed that their leg
joints were too poorly developed to enable them to get about very much.
This clinched the case for the Maiasaura (good mother dinosaur) as they came to be
called. Here was a dinosaur that clearly had a family life at least as complex as that of a bird.
Source: http://www.nhm.ac.uk/about-us/news/2007/september/images/dino-nest370_12393_1.jpg Fossil of a maiasaura nest
Source: http://www.dinosaursociety.com/images/maiasaura.jpg
Artist’s interpretation of a Maiasaura caring for its young.
Next, came another set of remarkable discoveries about this group of animals. Exactly like
modern day penguins, the hadrosaurs nested in massive colonies to which they returned year after
year, as the layering of nesting remains seemed to indicate.
This of course raised the question where were they returning from? Work in other parts of
the world indicate that the hadrosaurs, like many herding animals today, migrated in vast droves.
Towards the poles in summer, and back towards the equator in winter. It was apparently an
organised move, to judge from the rare fossilised trackways that we have found, with the young
ringed by a protective band of strong healthy adults.
Again, as in the modern African savannah, wherever the herbivores went, the predators
followed, a behavioural pattern suggested by fossils of trackways, and by other finds. Not too far
from the hadrosaurian nesting ground, and at the same geological level, for example,
palaeontologists have found the nests of Troodon, an opportunistic predator, which probably fed
on untended young, and on infirm hadrosaurs.
Source: http://www.buscate.com.mx/educativo/dinosaurios/troodon.jpg
Source: http://www.howardism.org/Philosophy/Questions/Troodon.gif
Above are two different artists’ versions of what troodon may have looked like. Remember that it
is very difficult indeed to flesh-out a fossil. Below is an image of what a complete, but un-fleshedout troodon fossil, might have looked like. Looking at this, you can see how difficult it would be
to ‘clothe’ these bones.
Source: http://s3.images.com/huge.96.481131.JPG
Any one who has seen a hadrosaurian fossil cannot fail to remark their most singular
feature – the large, species-specific crests that, with rare exceptions, they all sported. Although
there is much debate about the function of this appendage, some palaeontologists have argued
most convincingly that it served two functions, as a resonator for mating and signalling calls, and
as a visual signalling and identification device. If this is true, then it lends further support to the
idea that hadrosaurs engaged in complex migratory behaviours, and had highly organised social
lives, as non-social animals don’t normally need to signal much.
Source: http://www.oucom.ohiou.edu/dbms-witmer/images/hadrosaur_heads.jpg
Some different hadrosaurs showing a few of the different types of head-gear they sported.
This set of findings about hadrosaurs however is not necessarily applicable to all
dinosaurs. Not far from the Maiasaura nests, researchers have found the nests of the
hypsilophodontid Orodromeus, which was about hip-high to a human-being The fossilised eggshell remains in these nests shows much less evidence of trampling. Furthermore, unlike the legjoints of the Maiasaura hatchlings, those of the Orodromeus were clearly well-formed from birth.
All of this is consistent with the view that baby Orodromeuses were born fully formed, and left
the nest – which itself may have been buried, or otherwise hidden, and then left largely untended
– as soon as they hatched.
Source: http://dinosaurs.about.com/od/dinosaurpictures/ig/OrnithopodPictures/Orodromeus.htm
Source: http://serc.carleton.edu/images/research_education/cretaceous/dinochase2.jpg
The two images above show an orodromeus (top), and the fossil of an orodromeus being pursued
by a fossil of a troodon. The little orodromeus (which was about the size of a very large dog), was
on the menu of troodon, which was more-or-less human-sized.
Similar studies have looked at predation patterns, and they indicate that while some
dinosaurs, the stegosaurs and the ankylosaurs for example, were no doubt not very clever, others,
like Velociraptor and perhaps Oviraptor for instance, were intelligent enough to engage in some
form of coordinated predation, much as wolves do today.
Source: http://www.acad.carleton.edu/curricular/BIOL/classes/bio302/pages/ankylosaurus.jpg
An ankylosaurus
Source: http://www.nzine.co.nz/images/velociraptor_big.jpg
A velociraptor, as imagined by an artist, in mid-attack.
So, were all dinosaurs slow, evolutionarily-retarded, primitive, lumbering brutes,
stumbling clumsily along whilst waiting for the mammals to supersede them, I
don’t
think so, but then again, I’m no Victorian gentleman – thank goodness.
Next
post, I’ll look at the emergence of birds.