Transitions: The Evolution of Life

The Eocene saw the rise of the euprimates (a term coined by Elwyn Simons). An alternative term is “primates of modern aspect”. Going back to R. D. Martin’s definition of fossil primates the euprimates share claws replaced by nails, opposable hallux (big toe) and postorbital closure (among other things) in common with all modern primates.The euprimates are divided into two families, the adapidae and omomyidae. The adapidae are composed of two subfamilies: nothartinae (5 genera) and adapinae (14 genera). The omomyidae are divided into three subfamilies: anaptomorphinae (15 genera), omomyinae (12 genera) and microchoerinae (4 genera) Plus two species (Arapahovius and Loveina) of uncertain affinities (for those who know something of taxonomy they are Omomyidae incerta sedis).

In general, Omomyids are tarsierlike in their morphology. For example, the dental formula (which gives the number of each type of tooth) is often similar (in particular the lower dental formula is sometimes 1 incisor, 1 canine, 3 premolars and 3 molars - as seen in tarsiers). The crania have tapered snouts and the ectotympanic bone is tubular - as in tarsiers. The nasal and olfactory regions are diminished in size and the eye orbits are expanded.

The adapids, on the other hand, are generally considered to be related to lemurs. They have a divergent hallux, flattened nails on the digits. Some (such as notharctus)have a postorbital bar and a petrosal bulla. Encephalization quotients (a ration of brain and body weight) have been calculated ad are withing the range of other Eocene mammals and are slightly lower than say, the Oligocene anthropoid Aegyptopithecus. In the middle ear region they bear some resemblance to lemurs. The ectotympanic bone (which supports the tympanic membrane) is variable in adapids ranging from a free ringlike structure (as in lemurs) to one that is expanded to form part of the lateral bull wall (as in lorises and Aegyptopithecus).

The morphology of both leads to several interesting problems. First, what are the phylogenetic relationships? There are three competing theories.

1) Omomyids share some characteristics with plesiadapiformes and at one time the plesiadapiformes were thought to have given rise to omoyids. In this theory the adapids were considered ancestral to anthropoids and the prosimians (other than tarsiers).

2) Since no shared derived characters link tarsiers and anthropoids to the other prosimians it has been suggested that plesiadapiformes gave rise to the euprimates which split into two branches. One branch was composed of adapids, lemurs and lorises, the other was composed of omomyids, tarsiers and anthropoids. In this theory, tarsiers are more closely related to omomyids than to anthropoids.

3)A variant of number 2, except tarsiers are more closely related to anthropoids than they are to omomyids.

There is a further complication. In both 2 and 3 above tarsiers are grouped with anthropoids and adapids are grouped with lemurs and lorises. The problem is adapids share quite a few traits with anthropoids, tarsiers share some traits with anthropoids but not lemurs and lorises. Paleontological data supported a linking of adapids and anthropoids. Comparitive anatomy (hemochorial placenta, presence of a retinal fovea, for example) and biochemical data supported a relationship between tarsiers (and consequently omomyids) and anthropoids. This led to something of a stalemate. If tarsiers (and hence omomyidae) were more closely related to the anthropoids (as the anatomical and biochemical data suggested) then adapids (as the paleontological data suggested) couldn’t be. Which was right. A very intersting solution to this problem was presented by Gingerich and Schoeninger in 1977. The suggestion wasn’t paid much attention to until 1986, when Rasmussen (in his 1986 paper “Anthropoid Origins: A Possible Solution to the Adapidae-Omomyidae Paradox”) revived it. Grant the paleontological evidence that relates the omomyidae to tarsiers and adapidae to anthropoids. Lemurs and lorises would then form a sister group to both the omomyidae-tarsier group and the adapidae-anthropoid group. Consequently, tarsiers would be more closely related to anthropoids than to lemurs and lorises - which satifies the anatomical and biochemical evidence and the omomyid-tarsier and adapid-anthropoid groups could still be kept - satisfying the paleontological evidence. It’s a good theory, unfortunately, one small fact stands in the way. This is the traits which seem to relate adapids to lemurs and lorises. In this theory, the traits relating adapids to lemurs and lorises are due to parallel evolution. Which has raised some objections since parsimony requires little or no parallel evolution.
It’s been my experience that these kinds of situations come up a lot in primate - and human - evolution. No matter what phylogenies you create parallel evolution always comes into play. Personally, I consider a certain amount of parallel evolution to be a fact of life in primate evolution.

I examined several definitions of the order primates in a previous post and looked at how any definition of primates has to be constricted when applied to the fossil record. In particular, the closer one gets to the common ancestor between primates and other mammals (insectivores for example) the harder it becomes to tell what is a primate and what is not.

Currently, there are four theories as to which group primates arose from (although, there is general agreement that thier orgins lie in the Order Insectivora):

1) Erinoaceomorpha (hedgehogs)
2) The suborder Lipotyphla - which contains shrews, moles, tenrecs and selenodons.
3)Tree shrews
4) Archaic taxa such as Leptictidae or Apatemyidae - which may or may not be insectivores.
The earliest identifiable primates are the plesiadapiformes. The plesiadapiformes occur from the mid Paleocene to the Eocene (from about 65 mya to about 53 mya). They inhabited both North America and Europe. The plesiadapiformes are an infraorder composed of six families and almost forty genera. The families are:

1) Plesiadapidae (five genera)
2) Carpolostidae (three genera)
3) Saxonellidae (one genus)
4) Microsyopidae (24 genera)
5) Paromomyidae (three genera)
6) Picrodontidae (two genera)

The phylogeny of most of these groups has been worked out in greater or lesser detail. Consider the Plesiadapidae. The earliest genus was Pronothodectes. In North America the earliest member of this genus was Pro. matthewi. Pro. matthewi gave rise to Pro. jepi. From here it gets complicated. Pro. jepi gave rise to two different groups, Nanodectes and Plesiadapis. The Nanodectes lineage goes as follows: N. intermedius, N. gazini, N. simpsoni, and N. gidleyi. The Plesiadapid branch goes as follows: Ples. praecursor, Ples anceps. Ples anceps gave rise to two lineages. The first goes: Chiromyoides minor, C. caesor, C. potior, C. major. The second lineage of Ples. anceps goes as follows: Ples. res, Ples. churchilli. Ples. churchilli also split into two lineages. The first goes: Ples. fodinatus, Ples. dubius. The second lineage is Ples. simonsi, Ples. cookei. The phylogeny of the other families is equally complicated.

Comparitive work on modern primate dentitions has allowed us to come up with some general guidelines on determining things like diet. Based on this we say that the plesiadapiformes were primarily insectivorous with diets resembling modern prosimmians such as lemurs and galagos. However by the late Paleocene - Early Eocene some plesiadapiformes were adopting diets of fruit or leaves.

How are plesiadapifomes related to later primates? There are actually three different views on this question. One view is that plesiadapiformes are not primates because they are distinct from later primates. A second view places them in a suborder with tarsiiformes (because both groups share some traits in common - enlarged, protruding incisors, similar configurations of inner ear anatomy among others). A third view is that they are the earliest primate radiation (because they have primatelike teeth that make them important for understanding primate origins).

For Further Reading:

Primate-like mammals:
A stunning diversity in the tree tops

Archonta (primates, bats, tree shrews and flying lemurs)

The pictures below are all of primates.

The jury is still out as to whether the tree shrew (pictured below) is a primate, or is related to the primates.

Primates come in all shapes and sizes, so the question “how do anthropologists and paleontologists” is a natural one. The question necessarily involves a great deal of comparitive anatomy but I have tried to keep it to a minimum. Readers who need an overview can read this article on the anatomy of the skull. I have written this post in the form of a question and answer session.

What is a primate?
That is actually a good question and the answer is quite complicated.

What do you mean? Aren’t monkeys monkeys?
Well yes, but it’s more complicated than that. It is easier to define modern living primates. Primates as a group do share some unique, universal (among primates) features not shared by other mammals. Unfortunately, the also share features in common with other mammals.

Could you give an example of a unique (or diagnostic) feature that separates one mammal group from another?
Sure! The double pulley configuration of the astralgus (a bone in the hind limb) is diagnostic of artiodactyls.

But, what about primates?
That is a good question. Mivart first defined the order primates. His defination was:

Unguiculate, claviculate placental mammals, with orbits encircled by bone, three kinds of teeth, at least at one time of life; brain always with a posterior lobe and calcerine fissure; the innermost digit of at least one pair of extremities opposable; hallux with a flat nail or none; a well developed caecum; penis pendulous; testes scrotal; always two pectoral mammae.

Wow, that’s a lot!
Actually there is more. Mivart gave his definition in 1873. In 1959 Le Gros Clark added to it:

Preservation of generalised limb structure with primitive pentadactyly (five fingers). Enhancement of free mobility of the digits, especially of the pollex and hallux (both used for grasping). Replacement of sharp, compressed claws by flat nails; development of verysensitive tactile pads on the digits. Progressive shortening of the snout. Elaboration of the visual apparatus, with development of varying degrees of binocular vision. Reduction of the olfactory apparatus. Loss of certain elements of the primitive mammalian dentition. Preservation of a simple molar cusp pattern. Progressive expansion and elaboration of the brain especially of the cerebral cortex. Progressive and increasingly efficient development of gestational processes.

That seems pretty thorough. Is there more?
Yes, there is.

I was afraid of that.
Please don’t interupt. In 1967 Napier added two more:

Prolongation of postnatal life periods. Progressive development of truncal uprightness leading to a facultative bipedalism.

That’s a lot of information, where did you get it?
Mainly from R. D. Martin’s paper “Primates: A Definition”

So what’s the problem with the above definition of primates?
There are two problems. First, some of the above are actually trends, some of which are not features. Instead they refer to developments found only in some members of the group (remember, we are not trying to trace ancestor-descendent relationships at this point. We are trying to provide a definition of an order of mammals). Second, some of these are either traits that are probably primitive features of placental mammals or have arisen by convergence.

So, then how do we define primates?
Martin choose to examine living primates with an eye to creating a new definition, which I won’t bore you with since it is rather long.

You said the definition applies to living primates, what about fossils?
For fossils the definition has to be modified somewhat, but first we have to talk about tree-shrews.

?Tree-shrews?
Yes, you see Le Gros Clark argued that the Tupaiidae are more closely related to primates than to any other placental mammal and should be included in the order primates. This has been argued about ever since. Martin used tree-shrews as a test case for his definition of primates and decided (correctly, I think) that they were not primates.

That’s a pretty scientific approach!
Yes, it is. Paleoanthropology has a well developed scientific methodology and a rich body of theory to draw on.

So what about the fossils?
Since we have only skeletons to examine the definition has to be contracted somewhat. This is what is left:

Well developed, divergent hallux with flat terminal phalanx in the foot. Elongated distal segment of the calcaneus. Relatively large, convergent orbits with restricted interorbital distance. Postorbital bar present; ethmoid exposure in the orbit possible (depending in interorbital distance relative to skull size). Petrosal bulla. Relativly large braincase. Sylvian sulcus on endocast. Dental formula maximally 2.1.3.3/2.1.3.3. Premaxilla short; upper incisors arranged more trnsversly than longitudally. Molars with low, rounded cusps. Lower molars with raised, enlarged talonids.

So, does it identify fossil primates?
Yes, it does. According to this definition omomyids and adapids, for example, are primates.

What about plesiadapids?
The jury is still out on this issue. But see the next post.

For Further Reading:

Primate Adaptation and Evolution”

Primate Evolution: An Introduction to Mans Place in Nature

Primate Evolution

The Evolution of Primate Behavior

Major Topics in Primate and Human Evolution

Additionally, if you have access to a good (University) library:

The American Journal of Physical Anthropology
The Journal of Human Evolution
Folia Primatologica

… if variations useful to any organic being do occur, assuredly individuals thus characterised will have the best chance of being preserved in the struggle for life; and from the strong principle of inheritance they will tend to produce offspring similarly characterised. This principle of preservation, I have called, for the sake of brevity, Natural Selection.
Charles Darwin, On the origin of Species, 1859¹

Another way to express what Darwin meant is that individuals with characteristics that are useful to them in their struggle to survive are more likely to produce offspring with the same characteristics. One straightforward consequence of Darwin’s idea is that animals that are sick or injured will be less successful to defend themselves against predators or to escape from them. Therefore, such individuals are more likely to be killed by predators before they have a chance to reproduce. This is so obvious that it should hardly need to be proven. Nevertheless, it has been demonstrated to take place in the wild many times. One example involving African wild dogs (Lycaon pictus) and their prey impala (Aepycerus melampus) in Zimbabwe was published recently².

African wild dogs
African wild dogs (also called African hunting dogs) hunt in packs and share their kill. One large animal that wild dogs prefer to hunt is impala. Once a pack finds an impala, or any other prey, they begin to chase it until the prey gets tired and they catch up with it. Such chases can apparently last for several kilometers at high speeds. Obviously, this hunting method is energetically very costly. Imagine yourself having to run, say, 2 kilometers (about 1.3 miles) as fast as you can before your every meal. Just to obtain enough energy to be able to run 3x2 fast kilometers a day, you would probably have to eat an extra meal every day, but that would make it necessary to run 2 additional kilometers!

This being the case, which impalas would a pack of wild dogs rather go after to minimize their energy expenditure during a hunt? Undoubtedly, the weak and the sick ones, because they will be slower than the healthier animals, and by chasing the slower impalas the wild dogs will spend less energy.

Impalas in Africa

To determine if this was indeed what was happening in the wild, British scientists² collected bone marrow from one group of impalas that had been killed by wild dogs and another group that had been killed non-selectively by humans. They knew from previous studies that impalas in poor condition had very little fat in their bone marrows. Therefore, as a measure of the physical condition of each impala they calculated the amount of fat it had in its bone marrow at the time of its death. The graph below shows their results.

The impalas that had been killed by wild dogs (bottom curve) had significantly less marrow fat than the impalas that had been killed by humans (top curve). Therefore, the authors of the study concluded that wild dogs selectively prey on impalas that are in poorer condition.

A more general result that we can derive is that the weaker impalas are less likely to live long enough to reproduce, while the stronger ones are more likely to escape from wild dogs (and other predators) and live long enough to reproduce. What does this mean in terms of evolution? It means that the healthier and stronger impalas are more likely to pass the genes that contribute to their good health and physical strength onto their offspring. In turn, their offspring will be more likely to be healthy and so on. This is basically how natural selection works.

Dinner is being served

For more information follow these links.

Natural selection 1
Natural selection 2
African wild dog 1
African wild dog 2
Impala 1
Impala 2

1. Charles Darwin, On the Origin of Species, 1859. full text
2. Alistair Pole, Iain J. Gordon and Martyn L. Gorman. African wild dogs test the ’survival of the fittest’ paradigm. Proc. R. Soc. Lond. B (Suppl.) Biology Letters 270, S57 (2003).

Wild dog and impala pictures were downloaded from the University of Michigan Museum of Zoology Animal Diversity Web

Cross-posted at Snail’s Tales

This is the second post DarkSyd has been kind enogh to allow me to post here. Please pay his site a visit and thank him. While you are there you should check out his series on human evolution - they are masterpieces!

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They serve as Icons for sports teams and multinational corporations, they live in lands of snow and ice, on mountain tops, and deep in lush, steamy, jungles. They can see in the dark, their ears are sensitive to a range of frequency fully three times broader than ours and sounds ten times as faint. They can run at 70 miles per hour across uneven ground and turn on a dime. They possess the strength, balance, and raw power any human athlete/gymnast would kill for. And, if they happen to lock in on you while you’re unarmed, helplessly alone in the twilight wilderness, their preternatural eyes gleaming, their toothy maws yawning in ghoulish anticipation of easy prey, you might as well cut your throat; before they do it for you.
More recently one version has ensconced themselves firmly into our domiciles, ensuring their evolutionary success for the next eon or two, whilst retaining more than any other domestic creature their feral, independent nature, enlisting humans not as owners, but as staff.

How did this diverse group of profoundly graceful predators arise and what makes them so successful?

Warning: Large Graphics Below

Felus Catus is your taxonomic nomenclature.
An endothermic quadruped, carnivorous by nature.
Your visual, olfactory, and auditory senses
Contribute to your hunting skills and natural defenses.

I find myself intrigued by your sub vocal oscillations.
A singular development of cat communications.
That obviates your basic hedonistic predilection
For a rhythmic stroking of your fur to demonstrate affection.

A tail is quite essential for your acrobatic talents.
You would not be so agile if you lacked its counterbalance.
And when not being utilized to aid in locomotion,
It often serves to illustrate the state of your emotions.

Oh Spot, the complex levels of behavior you display
Connote a fairly well developed cognitive array.
And though you are not sentient, Spot, and do not comprehend,
I none the less consider you a true and valued friend.

Ode to Spot by Lt. Commander Data

Cats are mammals of course and members of the family Felidea. Cat species make up one of nine groups in the order Carnivora, which includes canids (Dogs, wolves, foxes), raccoons, and bears, as well as weasels, otters, skunks, and pinnepeds (Walruses, sea lions, seals). Carnivora arose from the hardy stock of critters such as basal Cynodonts, reptile-like mammals which predate the first dinosaur and have been around for a whopping 250 million years.

 

           Cynodont

Genetic analysis of cat DNA indicates the order carnivora split from the precursors of primates like ourselves about 80-100 million years ago in the middle Cretaceous Period, and both primates and carnivora split from insectivores; something like Cimolestes although the details are murky, perhaps as early as 150 MYA in the late Jurrassic Period. Long before the dinosaurs were exterminated, the ancestors of cats and people lived side by side in a strange evolutionary parallel of today. Both types of early mammals probably shared many a meal and competed for prey with one another in the nocturnal undergrowth of the ancient rain forests and woodlands dominated by ferns and pines, furtively scanning for raptorial predators of both the avian and terrestrial kind.

But like all mammals, the Day of the Cat would not begin to dawn until after the saurian overlords of a now bygone world had left the evolutionary scene in the hands of their more adaptive mammalian underlings.

In the late Paleocene, about 55 million years ago, the first recognizable candidate for a cat (And dog) ancestor appears: The Miacids. These sleek carnivores, most about the size of a bobcat, radiated into an array of predatory eco-niches left by the vanquished giants in a few million years. Miacids likely hunted smaller prey in the rain forest canopies and dim floors of the Eocene jungles roughly 50 MYA.

       Artist’s rendition of an early Miacid

Over the next twenty million years, the miacids diverged into the forerunners of modern cats and dogs, and by twenty million years ago the first true cats appear in the fossil record such as this Proailurus.

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Without a doubt the most famous prehistoric cat is the Saber toothed “Tiger”; which is not a tiger at all in the formal sense and describes a huge array of cats and protocats rather than a single species. The most commonly portrayed genus, known as Smilodon, boasts a South American species, S. populator, that is among the largest and undoubtedly one of the most dangerous felines to ever silently pad across the earth.

                         
Enlarge Saber tooth next to a quarter                                 The Saber Toothed Smilodon

Cats appear capable of evolving quickly. Most extant Great Cats are relatively new, reflecting the pace of feline plasticity. Tigers and Lions emerged so recently form a common ancestor that they’re still able to mate and occasionally even produce fertile offspring called Tigons or Ligers. Cheetahs apparently went through a genetic bottle neck at the end of the last ice age so severe only a few families survived. The animals are now all so closely related that tissue grafts from one to another take as though they’re identical twins.

The reason cats are so successful today and thus so widespread, is the same reason they’re so much fun to watch: They’re amazingly agile creatures, endowed with a big, socially adept, brain, and well-armed with an array of weaponry, which possess an astonishing repertoire of evolutionary plasticity allowing them to occupy and dominate virtually every predatory niche on land. They come in large and small sizes, live everywhere from jungle floors and canopies to alpine mountain tops, and they can get along in large packs, small harems and family groups, and as lone ambush hunters.

Cats have spines in which the vertebrae articulate in such a manner as to provide an enormous range of motion compared to most vertebrates and these back bones are sandwiched between fat, intervetebral disks able to withstand substantial violent force. Each padded foot is a springy ‘fourpod’ of toes, the end point of a complex, triple jointed shock absorbing system which can take falls and g-forces that leave a human broken and mangled. The feet, legs, and trunk may be riddled with what are essentially tiny three-dimensional accelerometers which act like a host of fully independent inner ears, sending dozens if not hundreds of separate signals to a brain which processes the data like a super computer and solves horridly complex, partial differential equations, routing that solution to all parts of the body and spine. The result is the cat can execute a flawless double-twisting, double-flip, contorting and even corkscrewing its spine almost forty-five degrees in any plane and controlling the angular momenta with its tail, feet, and head, all in less than a second, and land on its feet … to bat its tail in anger and race away unhurt, even it was thrown head-over-heels into the air for ten feet or more.

They can pad silently over dead leaves, freeze motionless for long periods of time, stare unblinkingly, barely breathing, and then flash out in a burst of blinding speed to strike without, so far as we can tell, being out of breath.

The fore claws are naturally retracted when not in use and are extended by a stout tendon actuated by a powerful muscle which runs the length of the ulna and anchors securely just below the elbow/knee. The claws themselves are made of bony protein, superhardened with mineral matrices almost to the point of a synthetic glass, which flakes off in natural conical layers leaving the claws with a permanent, needle sharp point and microscopic serrated cutting edge. With these weapons the cat first strikes and pierces the flesh, and then cuts a long laceration upon withdrawal. And larger cats such as a tiger or lion can do it with the force of a swinging sledgehammer, all focused on those tiny, sharp, edges, in the blink of an eye.

Guessing ebcuase I can’t quite make out the caption next to the exhibit … I think starting at the top right and going clockwise, it’s something like … the claw of a Siberian Tiger, African Lion, Cougar, Jaguar, Cheetah, another Cheetah, Leopard, Lynx, another Lynx(?) .. and a Bobcat?

 

The felid jaw is short and robust, giving all cats that characteristic cropped muzzle look. This architecture provides leverage and thus lends the animal a powerful bite akin to that of an english bulldog. If the cat wants to hang on, it can support several times its own weight with its entire dental arcade sunk firmly into flailing victims, crushing muscle and in some larger species even heavy bone, the long, upper and lower canines are usually quite slender and close in finely honed opposition like a pair of garden shears. They reach deep into the prey, reaching vulnerable blood vessels and arteries.  It can even reposition it’s bite with lightning speed, in mid-flail, searching for new vessels and organs with each attempt to deliver the knock out injury. They usually make straight for the neck or spine, all the while ripping into the hapless prey with all four clawed feet to gain a solid purchase and drive those killer teeth in deeper.

Between the teeth, jaw power, claws, brain, speed, eyes, ears, nose, stalking/ambushing skills, and agility, cats are probably the most precision made killing machines walking the earth today. Not since the days of velociraptor has such elegance, power, and coordination, all teamed up in one large animal. It’s no wonder warriors from Babylonian swordsmen to disciples of Shaolin kung-fu, have studied cats hoping to mimic just a portion of their gracefully lethal skills.

And, they have become our friends; among the best of our companions. The traditional story is that small Libyan Wild cats were first tamed in north Africa, enlisted as trusted domestic allies keeping down rodents and other pests in ancient horticultural civilizations on the banks of the Nile. But the reality today may be much less complimentary to our allegedly superior human management and negotiating skills: Sleeping where and when they wish, playing or hunting at their convenience, disappearing for days on end only to turn up demanding food, water, and love, we slave away in factories and offices while they loll around in abject leisure. It’s arguable cats have domesticated us more than vice-versa!

Watch the cat, even the fluff-ball of a kitten. Compared to a dog or a horse, he or she has given up almost nothing in terms of independence and feral abilities. Lurking just beneath the surface of that playful pussy is a serial killer. Their ancestral predatory intensity is easily seen with a ball of yarn standing in for a mouse, or the poor lizard who gets cornered and tormented to jazz up an otherwise boring day between naps; all in a day’s work for the common feline. When some asshole takes a kitten and throws him out of a car on the side of a rural road, odds are decent the poor thing will survive for months, maybe years, using its wits and prowess. Most dogs would be dead in a matter of days or weeks without the benefit of human resources (Hell my sheltie puppy is afraid of june bugs and cowers in fear from them on the other side of a window).

They are truly fascinating animals and I’m glad we have made an arrangement with at least some of them. And I’m hopeful we’ll preserve those magnificent great cats in the wild which are still left. Sadly for us and for them, many are barely managing to maintain viable population numbers as humans continue to encroach on their range, and they are dangerous to have roaming around your backyard. Let’s meet a few of those …

 

Felis ocreata or Libyan Wild Cat. Likely ancestor of the hundreds of modern breeds of housecat, first domesticated in ancient Egypt

Black leopard with cub. Contrary to popular belief, there is no single species of great cat called a Black Panther. Pictures of such are almost always unusually dark leopards or unusually dark Jaguars

Florida Panther; beautiful, powerful, and on the brink of extinction.

           
   Siberian Tiger Cubs                                     Lions, leopards, and tigers, oh my!

       

    A Cheetah blazing along at 50 MPH executes an abrupt, forty-five degree turn on rough, open savanna, without missing a beat. Extraordinary evolutionary adaptations such as a spine which virtually dislocates with each five meter stride and a small streamlined head allows Cheetahs to hold the land speed record at 70 plus MPH.

     

    A gorgeous Snow Leopard, now hunted for their skins, they now number only few thousand.

And what kind of Friday Cat Blogging would be replete without a goofy picture of our own cat? … But alas our cat Nikki, Absolute Lord and Life-time Ruler of DarkSyde Manor does not denigrate herself with goofiness. She regally declined an online interview or an invitation to be immortalized in film. However, in the interests of maintaining domestic non-human harmony in the Manor, and given this post has been almost exclusively about cats, I did allow our aforementioned, cowardly but lovable puppy-dog, “Darwin”, to ham it up for the digital camera instead, and have his say, below, which consisted of “Bacon?”.

Darwin adds, “Have a wonderful weekend!”

Now that you have read DarkSyd’s excellent post on the evolution of whales here is a website you can visit to explore whale evolution:

Whale Evolution Kiosk and have fun comparing whales, fish and cats.

DarkSyd has graciously allowed me to post this, in it’s entirety. Thanks!

They are the grandest beasts we know of to ever roam our planet. They come in a wondrous variety of shapes and sizes, some larger than a double decker bus, others smaller than humans. Endowed with two forms of vision, one a sonar enhanced acoustical over lay of optical images giving them the ability to take an ulrasound image or deliver a stunning taser like blow of focused sound, and the largest brains in the animal kingdom, they communicate across hundreds of kilometers of ocean with eerie, soulful music. And for many years these magnificent creatures served as the unwilling prey of both hunters wielding harpoons, and Creationists wielding confabulations.

They are the Whales, the cetaceans, our fellow mammals. And they are magnificent manifestations of megafauna and evolutionary biology alike. If you’d like a short break from the intensity of politics, let us talk of the Whale’s Evolutionary Tale and Creationist lies …

Warning: Lot of Largish Graphics Below

From playful Porpoises to the majestic great Blue, they all arose from humble beginnings in a brilliant burst of Punctuated Equilibrium over a few scant million years from an animal the size of a Great Dane. Since that time these giants have served as one of the most sobering, astonishing, examples of megafauna sown from the fertile fields of evolutionary biology, growing to a state of resplendent majesty unparalleled on our ocean world. They have no formal language, as far as we can ascertain, although they may have the intelligence to rival a chimpanzee, but we can speak for them, and we must.

For years Creationists have attacked evolution. It continues to this day, sometimes with breathtaking ignorance and outright dishonesty as in Creationism for Dummies. And one of their many lines of assault has been the incessantly repeated claim that “There are no transitional fossils!” For years in the 1970s and 1980s Young Earth Creationists used whales as an angle with which to pursue their agenda. ‘Where are the transitional whales’ they would ask in mock surprise, and then go on to conclude that because there were none, yet, we never would have any, and therefore, somehow, Young Earth Creationism “wins”. They don’t say that any longer …

A word on what a transitional fossil specimen really is: A transitional is not necessarily directly ancestral to the later organism. It might be, but we really can’t know for certain if a given transitional is the direct forebear of a later species or not. Consider the paleontologist who finds the partial skeleton of a Dachshund, a red fox, and a wolf. Is one ancestral to the other? Which way does the lineage flow; from big to little or vice-versa? What if you have only a few leg bones and some pelvis for the red fox, a partial skull of the Dachshund, and the lower jaw and a scrap of spine for the wolf? And what if you’d never seen a living canid of any kind! That’s the dilemma paleontologists are in when they try to assign ancestry. It’s pretty amazing, a testament to the dedication and expertise of paleobiologists, that they’ve been as successful as they have. This uncertinaty becomes increasingly resolved when the fossil record is more complete. In the case of some arthoropods or mollusks for exmaple, in some places for certian periods of time, the fossil record is like the pages of a book. It was for this reason Eldridge and Gould chose snails in a specific location as a data source for Punctuated Equilibrium: The transitions of direct anceastors to descendants were unamibigeous and detailed.

A transitional fossil only means that the intermediate exemplar possesses morphological characteristics (Physical features) which are also present in both modified and/or unmodified versions in a later, likely descendent, species. In an egregiously very broad sense, every fish is a transitional tetrapod, because every fish has a spinal column and fins which are present in later modified (Fins to limbs) and relatively unmodified (Spinal column) versions in all in land vertebrates such as amphibians or mammals. This means that a transitional population can over lap descendent populations in time: wolves are transitional to Dachshunds and directly ancestral to them, but wolf populations didn’t magically disappear when Dachshunds came to be!
Likewise, in another broad sense, every reptile is a transitional bird, because birds have modified arms they use as wings and relatively unmodified spines both of which are present in reptiles. That doesn’t mean every fish is directly ancestral to every species of reptiles or rodent or that every reptile is ancestral to every species of bird; all fish and all reptiles are obviously not directly ancestral to those respective clades!

Whales are closely related to Mesonychids but not directly derived from them. Mesonychids are a diverse group of proto-hoofed predators which first arose in the late Paleocene Epoch, beginning about 65 million years ago, in the ashes of a world still reeling from the K-T Impact which may have escorted the dinosaurs off the evolutionary stage. They diversified into a number of species. Some of them, especially early on, were the size of a collie, others rank as the largest mammalian land predator to ever tip the scales, such as Andrewsarchus above.
Because of this semi-hoofed ancestry, DNA comparisons, and recent fossil evidence, Whales are now technically classified in the order of Artiodactyls, meaning ‘even toed’. This order includes hippos, giraffes, and pigs.

Illustration courtesy UTI commentator, contributor, and wildlife artist, O’George

The first notable transition in our tale of the whale is a kind of cute looking critter called Pakicetus, from over fifty-million years ago early in the Eocene Epoch. This fellow looks kind of like a big, bad, long snouted wolf in size, but probably occupied the eco-niche of a sort of beach combing Hyena. Eeking out a living on crabs, mussels, and sundry carcasses washed up from the ocean.

                Ambulocetus

The next stop in our whale’s tale is what looks for all the world like the mammalian version of a crocodile: Ambulocetus meaning “walking whale”, at about 49 million years ago. This is a bad boy, a mean looking customer, long, powerful, low slung, partially aquatic, and the jaws are outfitted to clamp down, hold on to, and crush prey. It probably made it’s living a lot like crocs do; snapping up fish from the water and unwary mammals from the beckoning shores of lakes and bays.

Speaking of intermediates, how does Rodhocetus above look for a transitional whale candidate in both skeleton and artist’s rendition? This fellow was roaming the south Asian seas at 45-50 million years ago.

Then we get into Dalanistes at circa 45 MYA. Followed by Protcetidae some of which were the first fully aquatic whale ancestors, and then on into full blown early whales such as archaic Odontocetids (Early toothed whales), like Dorudons and Basilisaurids by about 40 million years ago-the latter incidentally still trailing tiny, but fully formed, rear legs

Basilosaurid skeleton. Note the vestigial rear leg bones. It possible Baslisaurus may have used these small limbs to lock together during mating

How do we know that these fossils, in some case just partial skulls, are really whales ancestors or early whales? Well, it happens that the Whale Ear, from the Pakicetus to modern whales, is highly distinctive and easily recognized if you know what to look for. The ear slowly turned into the receiver for cetacean sonar, preserving and modifying those distinguishable features during that transition. Since the ear cavity and inner structure is part of the skull and the crania in general is one of the most likely portions of the skeleton to be preserved as a fossil, the morphology of that ear cavity is a fantastically useful diagnostic trait for determining if you’re dealing with a whale and for discerning the particular stage of evolution of that specimen. Evolutionary biologist PZ Myers provides an outline:

Start with the top left diagram. This is the ear of a typical modern land mammal. The horn shaped structure angling down towards 8 o’clock is the external auditory meatus (EAM), your ear hole, which leads to the dark gray oval, the tympanic membrane (TyMe), better known as the ear drum. Sound in air travels down the EAM to the TyMe, which vibrates. The vibrations are amplified the the chain of inner ear bones, the malleus (Mal), incus (Inc), and stapes (Sta), or hammer, anvil, and stirrup (I know–the terminology gets a little dense). Finally, the amplified vibrations are transmitted to the cochlea, where they are transduced into localized deflections of hair cells that trigger pitch-specific nerve impulses.
That’s the path that works well in the air, but it doesn’t work so well in water. Try immersing your head in the bathtub or swimming pool, though, and sounds are immediately dampened; the EAM fills with water that puts pressure on the eardrum, reducing the amplitude. Instead, the vibrations are transmitted through the bones and tissues of the head, vibrating the tympanic bone (TyBo) and by that path the inner ear bones.

The next three diagrams show the progression of changes in the whale lineage. The top right picture (b) is a pakicetid from about 50 million years ago. It’s not much different from the generic land mammal, with an EAM, eardrum, etc., but note the one special feature: the tympanic bone isn’t connected to the periotic bone (Per), and it’s actually thickened into a structure called the involucrum. Basically, the bony structure of the ear is less tightly attached to the skull, and is more free to vibrate in response to sound transmitted through the tissue of the head.

The next step is seen in a group of whales called the remingtonocetid/protocetids, from 43-46 million years ago (c). The ear capsule is even less strongly attached to the skull, and the involucrum is more robust and even more remote from the skull–the whole thing is better at moving freely. The ear drum is reduced and conical in shape, and the malleus is fused to the bone, so although the pieces are all there, it’s not going to be particularly effective at capturing sound waves in air. Another feature is a deep groove in the mandible that indicates that these animals had a fat pad (FaPa) in the jaw that would better transmit vibrations from the jaw bone to the ear capsule.

Last (d) is the ear structure of a modern whale. All of the trends of the previous organisms are accentuated: the ear capsule is specialized to receive sounds transmitted through the fat pad, and has completely given up on sounds transmitted through air–the external auditory meatus is closed off and gone, and while the eardrum is present, it’s not connected to the external world.

In addition to the unique morphology of the ear canal and bones, whales also have a distinctive spine which was modified over time to provide motive force underwater. Most folks understand that whales move by swinging their large tail flukes up and down, rather than side to side as most fish. The modifications in the spine, especially around the pelvic girdle, is a dead giveaway if you have the requisite vertebrae.

Now that we’ve met a few of the actors in our Whale’s Tale, and armed with new found fossil specimens, ear analysis, and DNA comparisons, we can construct a rough, provisional evolutionary progression, showing a plausible series of whale transitionals, starting with a fully terrestrial animal and ending with modern cetaceans. Thanks again to O’George’s artistic skills here it is:

It’s not meant to be a perfect line of ascending cetaceans and the sporadic nature of the fossil record ensures it never will be. We don’t know for a fact who or what is directly ancestral to later specimens or any intermediate, or which ones are ancestral to which whales, or even if any of early lineage’s shown survived. Modern whales may be the descendants of a small offshoot of one of the earlier protocetids and never preserved, which we will therefore never know about in detail. But sequentially as a gross series, that’s all pretty damn reasonable. Each intermediate is definitely a whale or an indirect/direct precursor to a whale. Each is found in the correct chronological order in the geological record and exhibits the clear signs of a transitional form progressing from a four legged terrestrial mammal to a full blown, aquatic one.

Creationists claim we have No transitional fossils? Bullshit: Utterly fallacious! Here’s hundreds of vertebrate intermediates alone, whales are just the tip of the iceberg. For the most part Creationist claims that we have no intermediate candidates for whales have fallen silent. Now when they address the topic of whale evolution, they focus on disinformation regarding the rich series of transitionals whales we do have.

Of course the everyday Creationist victim you’re likely to encounter at work, church, or school, will sometimes pipe up with “Why aren’t dogs evolving into whales now, right now, before my very eyes?” Well obviously the question is loaded: Dogs did not evolve into whales in the first place and any future evolution is not going to produce a creature exactly like whales. Nor would the scope of human life permit such an observation. But we certainly have all kinds of examples of clearly terrestrial creatures which appear to be caught in mid evolution in various states of marine adaptivity, changing forms from land dwellers to water dwellers. Seals, walruses, sea otters, beavers, and Penguins, just to name a few, come to mind. Brown bears and Polar bears are still technically the same species as they can interbreeed and produce viable, fertile offspring. But a couple of hundred thousand years ago they went their separate evolutionary ways, and now the Polar Bear is so often found in water and so at home there, it’s taxonimic nomenclature is Ursus Maritimus or Sea Bear. Given the opportunity and time, any one of those groups could go on to become fully aquatic and get as big as a diesel rig, just like the descendants of ambulocetus did.

Top left: Blue Whale   Top Right: Sperm Whale   Bottom Left: A small pod of Narwhales (Note single tusk in males. It’s actually an elongated tooth)   Bottom Right: Bowhead Whale with Beluga Whale escort

A few whales and other creatures by size

Enlarge (Hi-res image warning)

Most nations are curbing whaling as an industry. Even the Blue-whale is making something of a comeback. But pollution and over fishing are just as much of a threat to the delicate balance of the marine ecosystem whales depend on as a Japanese Trawler with an explosive tipped harpoon gun.

Whales and their four-limbed ancestors were here long before humans or hominids or even the great apes and monkeys. They rose from the tableau of a shattered world, the smoldering remains of the long lost planet of the dinosaurs. In a little over ten million years they grew from the size of antelope to the most massive animals known, and now dominate the ocean in both intelligence and size. They have survived ice ages, continental drift, super-volcanic eruptions, and greenhouse gases. Now they face their biggest threat yet: The fleets of whalers both past and present, and pollution led by the United States headed by a cabal of neo-cons and their swindled right-wing Christian followers who enable them in the belief that God put whales and everything else on this planet to be plundered until the approaching glorious rapture (Any day now). Regardless of where they came from and how they evolved, looking forward, our world without whales would be a tragedy; a world poorer, a loss of riches, their extinction at our hands unacceptable.

But we must bear in mind these are wild creatures, born free in an alien three-dimensional realm of deep ocean; they are neither the Demons which tomented Captain Ahab or the tame, gentle giants of Seaworld. They can and have attacked humans, at times for no apparent reason, albeit rarely. And they have saved drowning people, again we have no idea why. They do not exist for crass amusement, but they surely provide us with wonder if observed with respect.

They are mysterious, mostly just curious, and generally, but not always, harmless. But after their recent experiences with the walking ape, I’d guess what they would really like, if they could speak for themselves, is simply to be left alone.

The ocean is vast, surely big enough for both whales, and ourselves, to co-exist. Maybe that’s what this guy is trying to tell us … If only we could decipher his song.

Darksyd at Unscrewing the Inscrutable has an excellent post on the evolution of the felidae. Check it out.

What could be more fun than an elephant on the road?

Two elephants on the road - of course.
The above is a picture of african elephants (scientific name Loxodonta africanus). Below is a picture of an asian elephant (Elephas maximus). They are the only surviving members of a widespread and diverse group of animals.

The earliest known member of the elephant family (elephants are placed in the order Proboscidea) was an animal called moeritherium which lived approximately 50-60 million years ago. Moeritheres were small animals about the size of pigs. Bekow is a picture of a moeritherium skull. Note the large incisors.

Around 40 million years ago a group called the palaeomastadons split off from the moeritheriums. The palaeomastodons were to give rise to a diverse number of other species. Among them are Deinotheres,

mastadons,

stegodons, mammoths, and modern elephants. Here are two charts to help you keep them all straight. The first gives an outline of the main branches of the evolutionary history of elephants. It also gives a timeframe. keep in mind, when looking at it that that most of the groups contain more than one species. Stegodon, for example, is a genus (a group that contains one or more related species) that contains six species.

The next chart shows the more recent (about the last five million years) evolutionary history of the elephant family in more detail. There are a couple of interesting details in the chart. Notice that there are three species of Loxodonta (african elephant) and at least ten species of Elephas (asian elephant).

One other, interesting, fact that did not make it in the chart is that there is some evidence that asian elephants are more closely related to mammoths than to african elephants.

Other interesting facts:
Elephants are related to manatees and hyraxs
Elephants have specific sounds they use as greetings

Other interesting links:

Elephant Multimedia (movies and sounds)

Elephant Information Repository

All Elephants

Mammals of Southern Africa

Absolut Elephant

More Multimedia at Elephant Nature Park

From Elephant-Shrews

Many biologists currently include the elephant-shrews in a new superorder, the Afrotheria, which encompasses several other distinctive African orders. These include elephants, sea cows, and hyraxes (the Paenungulata); and the aardvark, elephant-shrews, golden-moles, and tenrecs …

Interesting Facts:
1) Shrews range in size from the pygmy shrew-the smallest mammal in the world, it can pass through a worm hole-to the giant elephant shrews of East Africa.
2) This shrew is a swift runner and with its long hind legs can make leaps of almost 3 feet. Its keen senses of sight, hearing and smell alert it quickly to danger.

Interesting Links:

African Wildlife Foundation

Elephant -Shrew Movies

BBC - Science and Nature