Friday - December 18, 2009

Is there a biologist in the house?

Kingdom, Phylum, (sub-phylum), Class, Order, Family, Genus, Species. Let’s put every kind of life in the proper category, nice and neat. And absolute.

Sharks:
Kingdom - Animalia
Phylum - Chordata
Sub-Phylum - Vertebrata
Class - Chondrichthyes (cartilaginous “fishes")
Order - Elasmobranchii

Halibut:
Kingdom - Animalia
Phylum - Chordata
Sub-Phylum - Vertebrata
Class - Osteichthyes (bony “fishes")
Order - Pleuronectiformes

People:
Kingdom - Animalia
Phylum - Chordata
Sub-Phylum - Vertebrata
Class - Mammalia
Order - Primates

Duck Billed Platypuses:
Kingdom - Animalia
Phylum - Chordata
Sub-Phylum - Vertebrata
Class - Mammalia
Order - Monotremata

Even though sharks and halibut appear to be related by the common word “fishes” at the Class level, you have to go up to the Sub-Phylum level to connect their clades (evolutionary branches). Human beings and duck billed platypussessesesii belong to the same Class, and differ at the lower Order level.

So is it fair to say that people are more closely related to platypii then sharks are to halibut?

There is another Class of “fishes”, called agnatha, which embraces the jawless fish like lampreys. Now, agnatha is also a superclass within the sub-phylum vertebrata, so as to exclude “things with gills that live in water and have jawbones” which are called gnathostomes. Ok, fine, I’m down with that. Super-Class fits in below Sub-Phylum and above Class, though using agnatha both as class and super-class seems to be bending the rules a bit.

So which taxonomic label does the “category” “fish” belong to? Is this a super-class? If so it doesn’t seem official (no Latin or Greek name for it) but it does seem like common sense. Wikipedia puts up a diagram which implies a super-class, and they give a broad definition of fish as

A fish is any aquatic vertebrate animal that is covered with scales, and equipped with two sets of paired fins and several unpaired fins.

Ok, do we have a big AH HA!!! moment here? Because sharks don’t have scales. They have skin. Or do they? While they don’t have the big obvious scales of regular fish (teleosts), they do have very tiny platelets on their skin called dermal denticles. Literally “teeth on the skin”. So, are these teeth, or scales? I don’t know.



Why am I asking this? Well, if you thought I was tenacious about the mount for that ADA bathroom sink I have to repair, you ain’t seen nothing yet.

I was a very bright child. Far too smart for my own good. Knew how to read before kindergarten, knew “big words” at such a young age that I was helping my 2nd grade teacher with her vocabulary when she couldn’t express herself satisfactorily. Did complex math in my head, had all the school books read and pretty much memorized by October. I was the kid who had his hand up to answer the question, every question, long before the teacher was finished asking it. In other words, I was probably a holy terror. A real challenge in a public school system geared to the low average student. I was also very high energy, very exacting, and impatient. Major recipe for loneliness there.

Anyway, in 2nd or 3rd grade we had this meaningless little assignment. Here’s a handout with several words on it, and pictures of some of those things. Draw a line between the word and the picture.
One word was “fish” and the picture was of a shark. I left it blank. I got that one wrong. I put up a fight. I went to the principal’s office. He was a decent guy, and already knowing about my abilities, he wondered why I didn’t draw that line. “Because a shark is not a fish”, I told him, “it’s an elasmobranch”. Second grade. Heck, I’d already been to sea. We’d taken a couple sailing vacations, out on the open ocean, and I’d seen a shark with my own eyes. And my parents both had huge amounts of undergraduate science. When I asked questions I got real answers. None of that “because I said so” nonsense. So yeah, I knew the difference. No swim bladder, no actual bones, no scales, no gill pump, no urea excretory system, etc.

Nearly 45 years later it still bothers me. No, not being sent to the principal’s. That happened all the time. What bothers me is the gray area in the taxonomic stratification. Because “fish” isn’t really a formal super-class. Shouldn’t it be? And there is no room for informal in there at all. So can it be ignored? Every beastie in its proper place. Absolute certainty. Taxonomy, like mathematics, is one of those few things that are dependably black and white. And whenever I see, hear, or read anything about sharks, I remember. And have that little nagging doubt. We’re talking about lifeforms that had fully diverged by the late Silurian period of the Paleozoic Era. 400 million years ago, maybe 370 at the very least. Twice as long ago as the dinosaurs. Is it fair to glom both with that same simplistic label?

Lest you think I’m wierd ... weirder ... I’m not the only person confused about the evolution and taxonomy of swimming critters. It’s all pretty fishy.

Posted by Drew458     on 12/18/2009 at 12:45 PM   
Filed Under: • Animals •  
• Comments (4) • Trackbacks(0)  Permalink •  

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