AND
YOU
THOUGHT
'JAWS'
WAS
BIG!
There is reliable
information that on a few occasions back before the really big GWs
were fished out at the height of 'Jaws' hysteria, some fisherman or
another managed to pluck a 21-ft or so GW out of the water. This grand
fish would be
admired hanging from a crane back on the docks - that is, until its jaws were
sliced out and the rest of the carcass was used as dogfood or such -
but I digress. Let's
represent this monster shark with the following 210-pixel line.
Tough to see just how big this is? Here is a six-foot
man either lying down next to that same shark.
Starting to see how big a
really large GW can grow? Pretty incredible to consider, huh? Well,
about 50 million years or go - give or take a couple of millenia, mind
you - there was a shark that swam the ocean blue that was twice as big
with much the same features as our friend old C. carcharias. Want
to see the comparison?
Humbling, isn't it? We'd be
like popcorn shrimp! This predator is truly one of
nature's most awesome creations ever, a fish that conceivably weighed more
than 20 tons and had a head the size of my car. In a sense, it could be
called the Great Great White Shark - although it is more accurate to
call it by the name scientists have given it - Megalodon.
YOU
SAY
'CARCHARODON',
I SAY
'CARCHAROCLES'
For most of my youth, I knew
of
the megalodon as Carcharodon megalodon, indicating a
relationship to contemporary Carcharodon carcharias, which we
already know as the GW. Scientists
didn't actually go so far as to say that the GW had directly descended
from C. megalodon but they did believe they were "proximate
twigs of the same evolutionary bramble bush" to quote Mr. Ellis
& Dr. McCosker's 'Great White Shark'. My youthful imagination was
likewise captured by the Guinness
Book of World Records when it printed the famous photo of six men
clustered together within a set of reconstructed jaws and said the shark
that went with them grew to be more than 100 feet long. Of course, at
the time, I also believed in the Tooth Fairy . . . go figure.
However,
upon researching further and digging into the depths of material on
Megalodon at my local university library, I came upon a controversy that
apparently has been raging between paleontologists
(scientists who study fossils to learn about animals of the past) and marine
biologists for a few years. It seems that several prominent paleontologists
believe that Megalodon should really be classified as Carcharocles
megalodon and not Carcharodon megalodon.
Big
deal, right? Who cares what we call a long-dead shark? Plenty of folks, it turns
out. As Jim Bourdon points out at his excellent website, Megalodon is a "poster child" for those who study
sharks much like Tyrannosaurus rex is for
those who study dinosaurs. Imagine the uproar if paleontologists came forward and wanted to
change its name from T. rex to T.somethingelseus and you
start to understand the emotional nature of the controversy.
As
for the factual basis of controversy, this can be found in studying the ancestry of the GW.
GWs are part of a grouping known as mackerel sharks, a grouping which
includes the salmon, porbeagle, and mako sharks. One of the mako's
ancestors is an extinct shark known as Isurus hastalis. Comparisons
of the teeth of I. hastalis and C. carcharias reveals that
they are remarkably similar, the only difference being that I.
hastalis teeth are smooth, lacking serrations. In the mid-80s, a
5-million year old shark specimen was found that some scientists
have concluded links I. hastalis with C. carcharias as it
had "weakly" serrated teeth. If true, this could indicate that
the GW is a likely descendent of I. hastalis.
 |
| These teeth from
the modern GW (left) are quite similar to the teeth
of the extinct I. hastalis (right) but notice the lack of
serrations in I. hastalis. |
Here's
where it gets fun. Let's say that the GW is a descendent of this ancient
mako-like shark. Megalodon does not share this immediate ancestry and thus,
belongs in a different genus entirely. Carcharocles had been put
forth as a genus for a few other species (C. angustidens, C.
auriculatus, & C. sulcidens for those who are curious)
and it is in this genus that some say Megalodon belongs. Bill Heim sums
up this argument by charting the lineage of the two sharks. (Note the
highlighting is my own.)
In support of the Carcharodon camp are three main
points as given by Dr. Samuel Gruber - again, by way of Jim Bourdon's
website.
-
There is a unifying tooth structure that
connects all the great tooth sharks to the living C.
carcharias i.e. tooth shape & the arrangement and
placement of these teeth in the jaw
-
Fossil teeth assigned to C. carcharias
have been found in deposits that are much older than the
teeth from the 5-million year old specimen I referred to
above that supposedly links Isurus hastalis and C.
carcharias meaning that the GW has been swimming around
since before this "intermediate" species
appeared.
-
Biochemical (DNA) evidence presented by
Andy Martin strongly suggests that Isurus hastalis
and Carcharodon
diverged 40 my ago well before the age of the
"intermediate tooth."
What does it all mean? It depends on your viewpoint -
how badly do you want C. megalodon to be related to C.
carcharias? Judging from the heated exchanges I've read on the
Internet, plenty of experts are on either side of the debate with
most paleontologists firmly on the side of Carcharocles and
most marine biologists showing their love for Carcharodon.
THE
HUMBLE
OPINION
OF
AN
IDIOT
Me?
I have to say that the Carcharocles camp seems to hold the most
weight in my mind. I've got tooth specimens from Otodus obliqus, C.
auriculatus, I. hastalis, and I. escheri in my collection and
I can see the progression that Bill Heim and others have argued - but
hey, who am I?? Just a guy from Arizona. I will say that the compelling
piece of evidence for me is the tooth shape from these two progressions
- the teeth that lead to C. carcharias all share a certain degree
of "flatness" while the teeth that lead to C. megalodon
have a more cone-like shape. Here's what I mean.
|
Carcharodon
carcharias Line |
|
Isurus
hastalis |
|
|
Isurus
escheri |
|
|
Carcharodon
carcharias |
 |
|
Carcharocles
megalodon Line |
|
Otodus
obliquus |
|
|
Carcharocles auriculatus |
 |
You can see how
"flat" the top grouping is. I don't have a megalodon specimen
to complete my demonstration but I have seen pictures of the teeth. When
you apply the scale of the tooth, it follows more closely the bottom
group than the top. Keep in mind again that this is just the rantings of
an uneducated shark guy . . . but you can see where the excitement is in
trying to piece together the puzzle?
MORE
MEGALODON
