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Defining the Beak
Defining the beak...
One of the most important aspects in the debate over whether or not certain
theropods did or did not possess a beak, is that many people in the debate may
be using varied definitions for the term "beak". I do not know if anyone has
tried to straighten this problem out, but I think if no one has, people should
There are many problems that arise when one tries to define a beak in an
evolutionary context... I don't believe that there is any real way around that.
But, looking at how we define what a mammal is can do a good job at
illustrating many of the problems we could encounter when trying to define a
Though mammals are defined by a multitude of traits, milk production seems to
be the universally accepted trait that ends the debate on what is and what is
not a mammal. If an animal produces milk, it is a mammal. Simple as that. Since
we cannot know for absolute certainty whether or not some fossil animal in the
known record produced milk (at best we can infer), we need to utilize other
methods for defining what type of animal it was. So, what has been done to help
us spot a mammal in the fossil record? Well, in many cases, the way the lower
jaws articulates with the upper jaw can be used to shed some light on the
issue. According to many a person, mammals are supposed to have only one bone
for their lower jaw. If they have more, then they are not actually considered
mammals. However, there are quite a few problems with using this method as a
defining characteristic. The old fashioned articular-quadrate type of joint is
not totally lost in many animals that are considered t!
be mammals in the fossil record. Also, some marsupials today are born with this
joint still in place, but lose it as they develop. Therefore, they technically
have more than one bone as part of their lower jaw. Does this mean that
marsupials that possess this trait are not mammals until they become adults,
even though they are feeding on milk produced by their mother?
The point is that we are once again drawing lines, even though most aspects of
evolutionary change seems to fade from one to another in a more mosaic pattern
(This mosaic pattern may sometimes be repeated during development as just
So where am I going with this?... How should problems with identifying mammals
influence our opinions on how to define a beak? For one, it is highly likely
that the modern beak was not just there in one generation. There was most
definitely several steps involved, and many people seem to already have
opinions about what these steps were. How do we refer to these steps, in either
a hypothetical sense or an actual sense, if one is found in place on a fossil?
One problem with this issue is that beaks are supposed to be toothless by at
least some definitions. Therefore, if there were teeth, then there can be no
beak. If beak always means toothless, well then fine... When it came to the
beak, evolution took only one step. So by definition, a beak wasn't in place
until the final tooth was lost, regardless if some regions or the total region
was covered in a single keratinous covering.
The issue is how we define a beak in a stepwise evolutionary context.
People like to throw around the term rhamphotheca, but by definition a
rhamphothca is just the keratinous covering of a region already called a beak
by the defining aspect that it "has no teeth". Would it be legitimate to call
an upper and lower jaw that was covered with a complete and singular keratinous
covering a beak if those jaws also possessed teeth which were used as the
biting surface? To restate this question another way... Does one require a
tomial crest before one can call the region a beak?
If we accept that the presence of teeth does not stop one from calling the
region a beak, other questions logically come about... Do teeth need to
protrude through the keratinous region where the tomia is present, or can they
protrude through true fleshy gums medial to a keratinous covering yet still
qualify the lateral region as a beak? Does the entire region need to be
covered, or can we settle with just singular bones in those regions? A popular
example could be that the premaxilla and nasal bones were covered with one
continuous cornified covering, while the true maxilla was left uncovered. If
this, or something similar to it, is found to be the case, can we call such an
arrangement a beak? A partial beak? A prerhamphotheca? A pseudorhamphotheca?
Much of what was just said here is semantics for sure... I admit that... But,
since there is so little in the way of a universal set of definitions,
semantics are going to be abundant.
And that's my 2 cents worth.