Phoenix from the Flames: New FAQ

[Mike Taylor <mike@indexdata.com>]

Dear DMLers,

You may remember that a year or two ago, I was hard at work putting
together a FAQ for this mailing list, which was and is available at
        http://www.miketaylor.org.uk/dino/faq/
It answers such perennial questions as "What were the longest/heaviest
predatory dinosaurs?", "What is cladistics?", "How can I obtain
technical papers?" and "Why do mass estimates vary so much?"

The FAQ has been a tad moribund over the last year or so due to some
awkward personal circumstances (basically, the Internet start-up I was
working for got into such dire financial straits that they stopped
paying their employees, so that my spare time had to go into paying
work rather than the FAQ.)  But now that I am in a nice, regular job
again, I am all geared up to finish the FAQ.

Today I present a new question and answer, which you can find at
        http://www.miketaylor.org.uk/dino/faq/s-anatomy/vertebra/
but which I also reproduce below, knowing full well that no-one ever
follows the links from list messages.  I welcome any and all comments
on this answer.  You can send them either directly to me if they're
little issues (typos and the like), or to the dinofaq mailing list if
they're of more general interest.  The new, advert-free, dinofaq list
is hosted at
        http://www.indexdata.com/mailman/listinfo/dinofaq
and anyone who wishes to join it is welcome.

OK, people!  Let's make the FAQ into the best dinosaur-science
learning resource on the web!

 _/|_    _______________________________________________________________
/o ) \/  Mike Taylor  <mike@indexdata.com>  http://www.miketaylor.org.uk
)_v__/\  "It is only possible to live happily ever after on a day to
         day basis" -- Margaret Bonnano.

--

Old music-hall joke: I say, I say, I say! What's the difference
between a centroparapophyseal lamina and a spinoprezygopophyseal
lamina?

27th October 2003

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QUESTION

Basic dinosaur anatomy seems straightforward enough: what vetebrae
are, the difference between a femur and a tibia, where to find a
dentary, etc., But there seems to be a mass of specialised terminology
for vertebrae, most of pretty opaque. What do all those terms mean?

ANSWER

Actually, vertebral anatomy is nowhere near as complicated as it
looks. The sheer length of the names of the laminae shouldn't put you
off: they're that way because they describe exactly what the laminae
are.

Here's a description of vertebrae in six easy stages.

Stage 1: The Centrum

The main part of every vertebra is the centrum (plural centra), a mass
of bone that is roughly cylindrical (although this can change
dramatically in more derived animals). The centra within a spinal
column line up end to end, and are generally joined together by
ball-and-socket joints. Within the neck and torso in particular, these
tend to have the ball part (the condyle) at the front of the centrum,
and the socket part (the cotyle) at the back.

Some vertebrae really are this simple - just a a centrum. For example,
the vertebrae near the end of the tail in diplodocids are like
this. However, most vertebrae need to be more complex so there's
somewhere to anchor the muscles that move them.

Stage 2: The Neural Spine

Most vertebrae have a bony spike that sticks up from the top surface
of the centrum. This is the neural spine. It provides a place for
muscles and ligaments to attach, to hold the vertebral column in place
and move it, and also provides protection for the spinal cord, which
passes through a hole from the front to the back of the neural cspine
called the neural canal. The tip of the neural spine is called the
neurapophysis.

Stage 3: The Zygopophyses

For most vertebrae, the contacts between the centra alone do not
provide enough stability, so there are extra articular surfaces
between adjacent vertebrae. These are called the zygopophyses
(sometimes just called ``zygs'' for short).

There are two pairs of zygopophyses on each vertebra, all of them
located above the centrum. The prezygopophyses are in front on the
neural spine (one each on the left and right), and their articular
surfaces face forward, upward and inward (or craniodorsomedially, if
you like). The postzygopophyses are behind the neural spine, with
their articular surfaces facing backwards, downward and outward (or
caudoventrolaterally).

Each vertebra's prezygs articulate with the postzygs of the vertebra
in front. The zygs can slide across each other to some extent, being
enclosed in a synovial joint when the animal is alive, so there is
some flexibility to the neck.

Stage 4: The Ribs

Ribs, including cervical ribs on neck vertebra, do not articulate
directly with the centrum but with two more pairs of bony processes
that emerge from the sides of the centrum. The higher pair is called
the diapophyses, and the lower the parapophyses. Most ribs are forked
at the top, with the upper fork articulating with the diapophysis and
the lower with the parapophysis.

In some sauropods, the cervical ribs are very long (e.g. as long as
three vertebrae in Sauroposeidon), so they lie along the lower edge of
the neck in bundles three thick, stiffening and strengthening the
neck.

Stage 5: Excavation

Many vertebrae, particularly in saurischians, have various hollows in
the sides, broadly known as excavations. A shallow depression is
called a fossa (or pneumatic fossa), a deeper one a foramen. The Beach
Boys used a foramen to great effect on Good Vibrations.

These are most common in the centrum, but in some cases occur in the
neural spine as well. They are generally interpreted as an adaptation
to lighten the spinal column.

Stage 6: The Laminae

More complex vertebra, particularly in sauropods, have laminae with
long, potentially confusing names. Each lamina is a more or less flat
sheet of bone connecting two parts of the vertebra, and it is named
for the two parts that it connects. For example, the
centroparapophyseal laminae connect the centrum with the parapophyses,
forming a flattish sheet of bone at the bottom of the vertebra. And
the spinoprezygopophyseal laminae connect the neural spine with the
prezygopophyses.

And that's all there is to it!

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Any comments? Good! Please email them to dinofaq@indexdata.com
(See How can I help? for more details.)

-- END --