Welcome to 2017! Let's start the year with a cautionary tale. I'll
leap straight to the moral, then give an example: it's very easy
to reach the wrong conclusion about fossils from photos. That's
because no single photo can give an accurate impression of distortion.
For that, you need at least a much bigger selection of photos; or better
still, a 3d model; or of course best of all, the fossil itself.
Here's the motivating example:
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width="480" height="227"
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Cervical vertebrae 8-16 of Barosaurus lentus AMNH 6341; and
BYU 9024 "Supersaurus" cervical ?9. All in left lateral view.
A correspondent — I will not divulge his or her name unless the
person in question chooses to reveal it — had looked over the
slides for our
2016 SVPCA talk on new Barosaurus specimens, which claims
that Jensen's
Dry Mesa "Supersaurus" cervical BYU 9024 actually belongs
to Barosaurus.
Matt and I felt, based largely on the degree of neural spine
bifurcation, that the BYU vertebra compares most similarly to C9 of the
AMNH specimen — the middle one in the top row of the composite
illustration above. But my correspondent put together the composite, and
wrote [lightly edited for clarity]:
I've already compared BYU 9024 with the AMNH cervicals, I attach a
photo, because for me it is also very similar to C14: the centrum is
much more similar to C14 than C9, I think. What do you think about
this?
Like I said: you always need to be careful about interpreting any one
view of a fossil. In this case, BYU 9024 is misleading in lateral view
because the CPOLs are folded upwards and inwards, and the ventrolateral
flanges are (to a lesser extent) folded downwards and inwards — making
the posterior part of the centrum look much taller (and rather narrower)
than it really is.
This is hard to see in photos, because the fossil is so smashed up
and the matrix is so visually similar to the bone, but take a look at
the posterior view (with dorsal to the right of the photo):
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large-file="https://svpow.wordpress.com/wp-content/uploads/2017/01/img_3516.jpg?w=1024"
width="480" height="360"
srcset="https://svpow.wordpress.com/wp-content/uploads/2017/01/img_3516.jpg?w=480&h=360
480w,
https://svpow.wordpress.com/wp-content/uploads/2017/01/img_3516.jpg?w=960&h=720
960w,
https://svpow.wordpress.com/wp-content/uploads/2017/01/img_3516.jpg?w=150&h=113
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Here are the key parts, annotated, as best I can make out. (And bear
in mind that even I am not sure, after having spent a whole day with the
fossil, and with literally hundreds of photos to consult.)
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image-title="img_3516-annotated" image-description="" image-caption=""
medium-file="https://svpow.wordpress.com/wp-content/uploads/2017/01/img_3516-annotated.jpeg?w=300"
large-file="https://svpow.wordpress.com/wp-content/uploads/2017/01/img_3516-annotated.jpeg?w=1024"
width="480" height="360"
srcset="https://svpow.wordpress.com/wp-content/uploads/2017/01/img_3516-annotated.jpeg?w=480&h=360
480w,
https://svpow.wordpress.com/wp-content/uploads/2017/01/img_3516-annotated.jpeg?w=960&h=720
960w,
https://svpow.wordpress.com/wp-content/uploads/2017/01/img_3516-annotated.jpeg?w=150&h=113
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https://svpow.wordpress.com/wp-content/uploads/2017/01/img_3516-annotated.jpeg?w=768&h=576
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As you can see, the centrum accounts for only a small proportion of
the apparent height of the posterior end of the vertebra — and even that
is probably exaggerated, as the eccentricity of the condyle indicates
that crushing has increased its height at the expense of its width.
Put it all together, and Jensen's much-derided sculpture of what the
vertebra should have looked like is actually pretty good:
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image-title="img_3399" image-description="" image-caption=""
medium-file="https://svpow.wordpress.com/wp-content/uploads/2017/01/img_3399.jpg?w=300"
large-file="https://svpow.wordpress.com/wp-content/uploads/2017/01/img_3399.jpg?w=1024"
width="480" height="360"
srcset="https://svpow.wordpress.com/wp-content/uploads/2017/01/img_3399.jpg?w=480&h=360
480w,
https://svpow.wordpress.com/wp-content/uploads/2017/01/img_3399.jpg?w=960&h=720
960w,
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150w,
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300w,
https://svpow.wordpress.com/wp-content/uploads/2017/01/img_3399.jpg?w=768&h=576
768w" sizes="(max-width: 480px) 100vw, 480px"}
The upshot of this anecdote is an obvious one, but it bears
repeating: you simply cannot do a meaningful description of a fossil
without seeing it yourself — or at the very least a
high-quality 3d model. Photos just won't cut it.