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I am a politically-progressive, ethically-herbivorous anthropoid pursuing a paleontology education in the Los Angeles Basin. I am largely nocturnal, have rarely been photographed, and cannot thrive in captivity.

25 July 2010

Creationism Watch: The Old Beast Is Grumbling In LA

The Livingston Parish School Board in Louisiana is considering the re-introduction of creationism into the public school system:
During the board’s meeting Thursday, several board members expressed an interest in the teaching of creationism, an alternative to the study of the theory of evolution, in Livingston Parish public school classrooms.
 There is no "alternative" to the theory of evolution. No critic of the model has ever presented a viable, testable alternative. Evolution by natural selection is the only theory that fits all of the observed facts.

If there's an alternative, I'd sure like to see it.

This all stems, in part, from the general public's misunderstanding of the meaning of the word "theory." Most people confuse the colloquial definition -- meaning something akin to "speculation" or "unproven idea" -- with the scientific one -- meaning "a model with such a highly likelihood of being true that questioning it is simply foolish, absent overwhelming contrary evidence."

It will be interesting, however, to see the Livingston School Board try to get around the Supreme Court and lower court decisions banning the teaching of intelligent design.

Bears watching.

24 July 2010

Synapsid Song: The History Of Your Teeth, Part III

I'd like you to meet your cousin, several-million-times-removed, Archaeothyris florensis:

Image courtesy of Palaeos.com

She may look like a lizard, but she's not. In fact, she's more closely related to you -- and you to her -- than either of you are to any living reptile, bird or other non-mammal.

A. florensis is the earliest known pelycosaur in the fossil record, dating to Pennsylvanian time, about 307 million years ago. She is the first of a taxon of animals once known as "mammal-like reptiles" because of the several mammalian characters their fossils displayed. But that name has begun to fall out of favor in recent years, since it has become clear that the "mammal-like reptiles" never were reptiles to begin with.

You'll recall from my last post that the lines of the Synapsids and Sauropsids diverged from their common Amniote (animals capable of laying eggs outside the water) ancestor between 320 to 315 million years ago. While the earliest animals of each taxa have several superficial similarities, it is still inappropriate to class them together, because they each possess unique skeletal characters that profoundly affected the evolution of their descendants. As noted, the Sauropsids became reptiles, dinosaurs and birds. The Synapsids became mammals, but before that they were... something else. There's still a debate about what to call them, other than "mammal-like reptiles"; several terms have been suggested, such as "Permian synapsids," "stem-mammals," and -- the one that I prefer and will thenceforth use on this blog -- "proto-mammals."

The thing that separated the synapsids from other amniotes was -- and still is -- the number of temporal fenestrae in their skull. Synapsids possess only one on each side of their skull, and A. florensis was no different.

At top left, you can see a rendering of the generic synapsid skull, with the temporal fenestra in orange. This is the place where the protomammalian and mammalian jaw muscles are anchored. Contrast it with the distinct skull of the diapsids at bottom left. All synapsids, including you and your dog and your cousin A. florensis, display this pattern. All diapsids, including the dinosaurs and birds, have (or at one time had) two temporal fenestrae on each side.

A. florensis' fossils were found near Florence, Nova Scotia, in Carboniferous rocks indicating a humid, tropical, warm climate characterized by undergrowth of ferns and club mosses beneath a canopy of conifers. The lowland swamps of this time and place were full of masses of decaying vegetation, the origin of our modern-day coal beds. And like any swamp, it was full of insects, who in turn attracted your distant cousin.

She measured about 20 in./50cm. long, was very likely an insectivore, and possibly a predator of smaller insectivorous reptiles, like Hylonomous (the earliest known true reptile). In addition to her unique skull adaptations, A. florensis had several characters that peg her as an ancestor of mammals, and the first of the true proto-mammals; the most relevant of which (for our purposes here) were her teeth.

In A. florensis, we see the beginnings of mammalian heterodontism. Though her teeth were all the same shape, they were of varying sizes, including a pair of enlarged canines. The fact that clearly-differentiated teeth appeared so early in our evolution is important in understanding the context of the debate about anatomy and "ideal" or "evolutionary" diets for humans. It is often argued that because humans have canine teeth and sharp incisors, we are therefore natural carnivores. But, gazing back into deep time to our cousin A. florensis, we can see that distinct canines have been a part of our lineage for hundreds of millions of years.

In short, the reason humans have canine teeth is that our ancestors had them. It's that basic. Natural selection is conservative, and rarely produces entirely new designs. It works with what it has, and traits that aren't detrimental to a species' survival will be reproduced even if they serve no direct purpose for that species. Hence, we end up in modern times with deer fangs and primate canines. Various mammal species put their canines to various uses, but that doesn't mean the canines were "meant" for those uses. They weren't really "meant" for anything. They're just hand-me-downs from distant ancestors.

This is not to say that teeth are irrelevant. Far from it. A. florensis most likely used her teeth and flexible jaws to snatch and eat insect prey. But as we will see, this did not consign her ancestors to perpetual insectivory. She was already quite advanced, and her differentiated teeth were themselves inherited from as-yet undiscovered ancestors. We thus cannot know for certain what, if any, selection pressures produced heterodontism in the Synapsids. But we do know that such versatile teeth were part of the key to mammalian flexibility, and thus to our success.

As the earliest pelycosaur, A. florensis has many fascinating relatives later in the fossil record, who will be the focus of the next post in this series. She may be our distant cousin, but her descendents are very likely our direct ancestors. And they, too, have interesting teeth.

17 July 2010

Deer Fangs & Deep Time: The History Of Your Teeth, Part II

So, why do some deer have fangs? Why do humans have canines and incisors? Why, for that matter, do lions, elephants, rats, monkeys, whales and walruses (to name only a few) have the teeth they have? Why do all us mammals have such a wide variety of teeth?

To really answer those questions, we first have to answer a more fundamental question: what, precisely, are mammals, and where do they come from?

(Okay, technically, that's two questions, but you grammar drones can sue me later.)

You'll recall from my previous post that one of the things that's distinctive about mammals is our heterodontism; that is, we have a mouth full of differently-shaped teeth.Yet, our teeth are not completely random. They're variations on a theme: four kinds of teeth, each serving a different purpose -- incisors, canines, premolars and molars. Different mammal species have these teeth in different combinations, yet there is little variation within a given species. All mammals possess some combination of these four types of teeth.

Despite this, though, it's not just teeth that make the mammal. Or even primarily the teeth. Mammal dentition is distinctive, but the defining characters of a mammal are
  • possession of mammary glands by the female of the species
  • possession of hair
  • the lower jaw is made of a single bone, rather than a collection of bones
  • the middle ear contains three bones -- the incus, the stapes and the malleus
  • possession of a leftward-curving artery leaving the heart
  • possession of a diaphragm
  • a single temporal opening on either side of the skull (the temporal fenestrae)
  • a bony secondary palate separating the respiratory passage from the mouth, allowing us to eat and breath at the same time
Like your teeth, these traits have a long evolutionary history, and understanding that history will help all of us put the incessant squabbling about veganism and teeth in its proper context. I, for one, wish more people knew this history and didn't focus so much on dinosaurs; as cool as dinos are, they're not really part of our story, the story of mammals, except as evolutionary adversaries (more about that later).

That's one of my main motives with this series. The story of mammals is fascinating in its own right, and just as ancient as that of the dinos and their kin. Your teeth have a glorious 300-million-year pedigree, and you have a right to know it all. We do our ancestors honor by keeping their memory alive.

Where do mammals come from?

Most people -- and I used to be one of them -- have a vague chronology in their heads that runs something like this: "single-celled organisms came first, then algae, then fish maybe, then, I don't know, amphibians, then reptiles (dinosaurs are reptiles, right?), then birds and mammals (aren't birds dinosaurs or something? and mammals came from reptiles, too, didn't they?). Insects and spiders and other creepy-crawlies fit in there somewhere, as do plants, but I'm not too sure about that."

In broad strokes, that notion is close to the truth, but it leaves a lot out, and creates some misconceptions. For our purposes, it specifically gives the impression that there weren't any mammals until the dinosaurs died out; or perhaps, that mammals evolved from a dinosaur like the birds did.

But it turns out, mammals and reptiles have divergent evolutionary paths, and didn't give rise to each other; at least, not the way many folks seem to think.

Mammal evolution really begins when our ancestral line diverged from that of the reptiles about 320 to 315 Ma. This shouldn't be taken to mean that mammals are descended from reptiles, though many people have this mistaken idea. More accurately, it means that reptiles and mammals shared a common ancestor, and each line split from that ancestor to follow a distinct, and thenceforth unrelated, path. The reptilian line became the Sauropsids (who included, ultimately, the reptiles, dinosaurs, plesiosaurs, icthyosaurs, pterosaurs, and the birds). The mammalian line became the Synapsids, which once included many taxa of animals, but whose only surviving kin are we lovely mammals.

And it is here, with the Synapsids, that we'll begin the story of your teeth in the next post. Take notes!

12 July 2010

Deer Fangs & Deep Time: The History Of Your Teeth, Part I

You're not seeing things, and it hasn't been photoshopped. That really is a picture of a deer with fangs. It's a musk deer, and a photo of its skull gives you an even more ominous view of its frightening dentition:
Musk deer aren't considered "true" deer, however. They belong to the family Moschidae, and true deer to the family Cervidae.

But that doesn't let us out of this strange world of fanged deers. For among the Cervidae, there are three species of deer with fangs; the muntjac, the tufted deer and the Chinese water deer. And as many hunters can attest, sometimes even white-tailed deer sport a set of nasty canines.

So, what is going on here, and what the heck does it have to do with veganism? Well, if you're like me, you've been confronted with the argument that "humans have canines, therefore we must be meat-eaters"; or, more broadly, that "humans have meat-eating teeth." Our teeth are used as a defense of human carnivory, yet another piece of evidence that our critics insist means we must eat meat. It's part of our evolution, after all. Teeth don't lie.

What, I wonder, would such critics make of this argument if confronted by a fanged deer? Would they imagine that these deer eat meat? Or would they recognize that deer fangs are a primitive characteristic put to a new use, inherited from the deer's distant ancestors, many of whom were not highly-specialized herbivores? And if they can acknowledge this about deer, why can't they do the same for humans?

It's true that humans have canines, and teeth that are generally described as "omnivorous." Like other primates, we are equipped with a set of primitive characteristics that make us successful dietary generalists. But as I've noted before, that is only the beginning of a discussion, not the end of one. It tells us something about our capabilities, but nothing about our obligations, particularly to nonhuman animals.

Why, then, the big deal about teeth? Vegans and carnists both argue about them incessantly, apparently convinced that teeth are the key to proving our "ideal" (and therefore, it's often implied, our obligatory) diet. I used to do the same, insisting that because we don't have specialized carnivore teeth, we must therefore be natural herbivores. But since I started studying evolution and paleontology, I've come to understand that both "sides" are right. Or perhaps, that neither of them is. Human teeth are generalist, specialized neither for herbivory (like deer) nor for carnivory (like lions).

In short, they're not nearly as profound to either sides' ethics as they both like to think. I no longer argue that our teeth prove we aren't meat-eaters by nature. I now simply point out that our teeth really aren't useful in figuring out what our "ideal" diet should be. Vegans and carnists both make the same mistake in marshaling tooth evidence for their side.

To help put this debate point in its proper context, I'll spend the next few posts discussing the history of human teeth, going all the way back to our pre-mammalian ancestors in the Permian, before dinosaurs walked the earth. It's a history few people know, and one that I have come to find eminently fascinating.

To start, we should understand that teeth are one of the defnining characteristics of mammals. Mammals are heterodonts, meaning that we have teeth of many different shapes. Other kinds of animals aren't like this; reptiles and fish, for instance, have teeth of different sizes in each individual, but all of them are basically the same shape. The University of Michigan's Animal Diversity Web has an excellent primer on mammalian teeth, and I won't reproduce its work here. Instead, I'll focus on how mammal teeth got to be this way, and show that human teeth are just a variation on the generalist pattern most mammals possess. And thus, that they can't really be used to define the ethical debate over veganism, one way or the other.

10 July 2010

Dino Mojo Rising

A new ceratopsian dinosaur gets a whimsical name -- Mojoceratops.

The general public is often unknowing about the role of whimsy in science, and that's a shame. Though it appeals to many, I think its appeal would be broadened if more layfolks were allowed a peek into scientists' often-salacious senses of humor.

05 July 2010

More Evidence Of Pleistocene Overkill

A new study backs up the Pleistocene overkill hypothesis. The authors editorialize a bit about the relevance of paleontology to modern animal and eco issues:
Trophic cascades initiated by humans are broadly demonstrated, the researchers report. In North America, it may have started with the arrival of the first humans, but continues today with the extirpation of wolves, cougars and other predators around the world. The hunting of whales in the last century may have led to predatory killer whales turning their attention to other prey, such as seals and sea otters — and the declines in sea otter populations has led to an explosion of sea urchins and the collapse of kelp forest ecosystems.
The tragic cascade of species declines due to human harvesting of marine megafauna happening now may be a repeat of the cascade that occurred with the onset of human harvesting of terrestrial megafauna more than 10,000 years ago. This is a sobering thought, but it is not too late to alter our course this time around in the interest of sustaining Earth's ecosystems.
A word of caution, however: it's important never to read too much into a single study. Though I favor the overkill hypothesis because I think it has the strongest evidence on its side (especially in Australia and the Americas), the evidence is still inconclusive.

Humane Hypothesizing About Ostriches & Dinos

One of the main reasons paleontology appeals me -- and why I chose it as my academic pursuit -- is that it allows me to study animals without exploiting them. So, it's refreshing to see scientists take the same philosophy when trying to gain insights about past life through the lens of modern species:
Dr Schaller hand-raised the ostriches for her research to ensure they could be studied in a natural, controlled environment which allowed them free space to perform without constraint.
"Ostriches can be very dangerous and can react with violent (even lethal) kicks and so it was crucial that we shared a deep level of mutual trust," she explained.
This is, one hopes, the way of the future.

02 July 2010

Taxonomy vs. Diet

An anonymous commenter on my previous post feels I'm confusing taxonomic classification with dietary behaviors:
Humans can indeed live on an astoundingly wide variety of diets and it is remarkable.

However, this is a confusion between taxonomy and diet. Please educate yourself further.
My response:
Actually, anonymous, I'm not confused about the difference at all. On the contrary, the difference is what this post was all about. It is critics of veganism who are confused about the subject, when they tell me that humans are classified as omnivores and therefore MUST eat meat.

However, I will concede that, upon re-reading this post, I can see why you are confused about my meaning. So, thank you for your constructive criticism. I will edit the post for clarity, and put up an entirely new one to make sure there's no confusion.

Note to self: stop posting first drafts!
So first, I should apologize to any other readers confused about the difference because of my last post. Omnivora and Carnivora aren't about diet per se, but about anatomy. I was trying to keep this distinction in mind, because we vegans are often told that humans are omnivores by nature, and therefore must eat animals. That charge is based on the confusion of taxonomy and diet. However, because I didn't take time to read the post before uploading it, I can see where the reader's confusion crept in.

I'm trying to argue on this blog that, at least in the context of the debate over veganism, terms like "omnivore" and "herbivore" are fairly useless. Critics of the vegan way have endowed these colloquial descriptions with a "scientific" authority beyond their actual meaning, and need to have the difference between taxonomy and diet clarified for them. Humans are "omnivores," true; but that is merely the beginning of a discussion, not the end of one.

"Omnivore" and "herbivore" are not, as some vegan critics seem to think, taxonomic classifications. They are mere descriptions of an organism's diet. In the fossil record, it makes sense to call an animal a herbivore because though we know it ate plants, we can't usually tell what parts of the plant it ate. When dealing with extant species, the practice these days is to use more specific terms, like "folivore," "frugivore," or "graminivore." But even then, these are descriptions, not classifications.

This is not to say that there aren't animals with highly specialized diet strategies and anatomies, like the artiodactyls and perissodactyls. But while such "herbivore" animals do not normally eat meat, anyone who's spent time with them knows they're more than capable of it. I've met a horse who's fond of cheeseburgers and hot dogs. Goats are notorious for their omnivory, despite being highly-specialized "herbivores."

Conversely, "carnivores" (as opposed to Carnivorans) are also capable of eating and digesting plant matter. My cat (who's both a carnivore and a Carnivoran) loves mashed potatoes and brown rice, and is always trying to steal them from me. Wolves in the wild are known to eat generous amounts of grasses.

The bottom line is that mammals are highly versatile creatures, who've inherited dietary capabilities from their distant common ancestors. Despite specializations developed over millions of years of evolution, they still retain their basic ability (though not necessarily a desire or a need) to eat and digest a wide variety of foods.

The confusion here, among critics of veganism, lies in the definition of the word "omnivore." Many treat the word as a proscription of food choices, when it's actually quite the opposite. An "omnivore" -- or, as I prefer in the context of the vegan debate, a generalist -- has the fewest restrictions on its choices, and is thus the most flexible. Vegan critics who level the charge that "(h)umans are omnivores, which means that a vegan diet is not optimal for us," fundamentally misunderstand what the word omnivore means. They also misunderstand evolution, in arguing that there is such a thing as an "optimal" human diet to begin with.

A generalist animal -- that is, an omnivore -- can eat both plants and animals. That doesn't mean it has to eat either one, generally speaking, and most focus on one or the other. Primates are generalists capable of eating bugs and animals, but nonetheless eat mostly plants. They obtain some nutrients from insects and small game to differing extents based on primate species, but this doesn't mean they must do so, given other options.

Science marches on, and ethics often follows. There is no dispute that for most of our history, humans have been "omnivores." But, as ethical awareness expands to include nonhuman animals, many people mistake past practices with future or current obligations. Humans do not need meat and dairy; just because we have used them in the past does not mean we are stuck with them.

My previous post was meant to address this misunderstanding of diet and taxonomy. The Carnivora aren't necessarily all meat eaters, and the fact that an animal eats mostly other animals does not necessarily make it a member of Order Carnivora. Membership in that group is based on common possession of a suite of biological and morphological traits, not necessarily on diet (as noted, pandas are herbivorous Carnivorans).

Similarly, humans are not, and never have been, classified as Omnivora, despite our generalist habits. The brief history of Sub-order Omnivora in my last post was meant to highlight, in part, this distinction between taxonomy and diet.

Saying humans are omnivores isn't really telling us much about our evolution, since most mammals could reasonably be described in the same way. It tells us nothing about our dietary or ethical obligations. It is simply a banal observation, the beginning of a discussion, not the end of one.

So, no, Anonymous, I'm not confused at all. And after this, I hope none of my readers are, either.