The San Diego Alligator Lizard…two males vying for same female. The male grabs the female by the neck with his jaws and mounts her. They will stay like this for a whole day, sometimes, reminding me of a story you will never hear. Anyway, if only my pal Jeff had stayed and observed for several hours to see who succeeded, taking notes and talking like David Attenborough. I imagine both males did eventually. Hot lizardesses swing. The fact that both gnarly lizard dudes are fighting for the same female makes me wonder if their sperm contains spermicide that will attempt to destroy the previous lover’s sperm. I suppose there’s no reason you couldn’t have multiple fathers as there will be several eggs. This is getting way too complicated.
Our zebra danios have gotten scary. Where once they’d dash about madly at the top of the tank waiting for the flakes of food, now they wake slowly from sleep, huddled together, then in a three fish column begin moving slowly (not their usual frantic dash) into the plants, moving around them, seeking meat. The flakes of fish food float down all around them but they pay no attention. They keep prowling, methodically, maybe an inch or two from the bottom of the tank. I’ve come to suspect that this was how they killed the other fish, by catching them before they were completely awake there amid the plants. I can only imagine that all three would rush in, striking, chomping, killing. In the wild they eat insects and crustaceans and worms, so they are hunters, yet in the thirty some years we’ve been stocking our aquariums with them I have never witnessed them do anything more than grab flakes of fish food drifting by. I have certainly never seen this sort of apparently coordinated behavior. It seems that almost every vertebrate has within it the predatory behavior. We are all hunters. Hell, it was predation that drove evolution itself, the whole Cambrian Explosion with all its crazy speciation was the result of the ever evolving contest between predator and prey. And here, somehow, in our little aquarium, something turned these little inch and half long fish from eaters of fish food to eaters of fish, eaters of even their own kind (as there were five of them just two weeks ago). All was peaceful until the clown loach died. That loach, though never deliberately bothering any of the other fish, was at seven inches long to them like a whale shark is to us. It ruled the floor, digging up snails. The danios stayed up several inches in the tank, away from its sudden movements. But then the loach, one day two or three weeks ago, was dead. Old age. I noticed the next morning that the danios were down zipping around at the bottom of the tank. The neon tetras calmly minded their own business, the two glass catfish scooted about. Everyone, danios included, got very excited at feeding time, like they always did. Everyone swam around excitedly, grabbing bits of tetra min flakes floating by.
I’m not sure when exactly the danios turned into killers. Within two weeks I realized that all the fish were gone but these three zebra danios. Alone in the tank, they chased each other madly about, zipping one way, then another. I was mystified. Where had all the other fish gone? I did some research, and found desperate pleas on aquarium websites. “Help, my zebra danios are eating each other!!!!” or “My zebra danios are killing my other fish!!!” I read in shock just how murderous the little beasts can be. No one seemed to know why, but there was usually a dominant fish that sets it off. A handy bit of evolution, that, where some members of the species will suddenly go rogue, turn alpha, and eat everything piscene in sight. Obviously there is a genetic advantage in there somehow. Perhaps a surge in zebra danio testosterone. But I have no idea. Looking at the tank again, one of the danios is swimming like a lunatic now, frenzied. The other two have ducked behind the leaves. Perhaps there is murder afoot.
Nice bit of convergent evolution on display here when you compare this shark with the fish that evolved into all us four-limbed landlubbing tetrapods. Our own fish ancestors, though, were lobed finned with bone skeletons (like coelacanths, or an even better example, lungfish). Mudskippers, a walking ray-finned fish, are another bony fish though unlike either early tetrapods or this epaulette shark, it uses only its pectoral fins and not the pectoral and pelvic fins. Mudskippers pull themselves around by their front limbs. Tetrapods and epaulette sharks walk. Or proto-walk. They use all four limbs. Watching this little epaulette shark is eerily like watching a monitor lizard. It’s hard to think of anything strictly terrestrial that moves like a mudskipper. Yet it is conjectured that most early tetrapods like Tiktaalik lived much like mudskippers, and not much like this epaulette shark. Go further back a few million years into tetrapod evolutionary history and you can find lobed fish, such as Panderichthys, that probably lived lives much like our walking shark. Unlike mudskippers and we tetrapods, however, sharks are famously boneless. They leave lousy fossils, mostly teeth. Some really terrifying teeth, too. Megalodon has left its thirteen inch incisors scattered in fossil beds world wide.
But this shark here is maybe three feet long and quite harmless, and I watch and rewatch him perambulating across the Coral Sea floor cartilaginously, a nifty trick, but severely limiting if one is thinking about evolving into a land animal. Without the buoyancy of water, one needs the support of a bony skeleton. Gravity is a bitch. But one also needs a bony skeleton to evolve fins into limbs that all of us tetrapods use for legs, arms, feet, hands, fingers, toes, and wings (and sometimes back into fins). The jointedness of bones seems to open up a wide range of mutation possibilities–and evolution is all about mutations–that cartilage just does not seem to have. Sharks and us have been on dramatically divergent evolutionary paths since we last shared a common ancestor well over four hundred million years ago. And shark evolution, though impressive enough in its sleekness, is vastly less varied than that of those of us who spring from the homelier lobed finned fishes (and less varied than the bony ray-finned fishes, which make up well over 99% of all fish species but never left the water). Aside from our perambulating friend here, all sharks (and their cousins, the rays) swim, while nearly all of the tetrapods (i.e., four limbed creatures who live on land) walk. But the same mutational capacity that enabled the first tetrapods’ pectoral and pelvic fins to evolve into a dizzying variety of limbs continues to enable tetrapods to evolve amazing adaptations with their limbs. Vertebrate flight has evolved three times (pterosaurs, birds, bats) while frogs and kangaroos hop and snakes and legless lizards slither limblessly. There are lizards and a number of mammals who glide. Pangolins go totally post-tetrapodal and curl up into an armored ball and hurl themselves down hillsides (the sort of thing that does not show up in cladistics.) A few tetrapods have even gone back to the ocean for good to swim again, the front limbs evolving again to pectoral fins, the backs legs disappearing entirely, as if four hundred million years of terrestrial evolution had all been some terrible mistake.
Yet the simple advantages of walking along rather than swimming over a shallow sea bottom (watch the video at about 25 seconds when the shark stops to peer into a cavity, looking or smelling for possible prey) apparently led this shark along a trail of mutation that eventually allows the thing to walk with ease. And it is extremely unusual for a shark. The range of design among sharks and rays is very minimal. Very few sharks don’t look very similar to other sharks. Rays look like rays. A Greenland shark is notorious for being so old and creepy and strange looking. But it looks very similar to almost all other sharks. An aquarium with nothing but sharks would be a pretty dull looking aquarium. They look a lot alike, they act a lot alike. Then we see a video of a epaulette shark walking along the ocean floor like it’s the most natural thing in the world.
A prowler of tidal zones, an epaulette shark can survive for hours in extremely low oxygen pools. It cannot breathe air, though, as mudskippers and lungfish do and our own water’s edge ancestors once did. Rather this shark has evolved a way to reduce blood flow in critical periods to all but the brain and heart. Handy, but a no go as a terrestrial adaptation. One needs to breathe air to make it on land. So this remarkable shark is no more like us than we are like it. It’s a marine animal who sometimes can stay on the edge of land for a couple hours, just as we are terrestrial animals who sometimes can swim with the fish for short periods.
But it was the combination of using fins to lift and carry across surfaces (i.e., walking) where swimming was difficult or impossible, with getting oxygen from the air via lungs (i.e., breathing) instead of taking oxygen from the water via gills, that made vertebrate land animals possible. (Insects were already there–doubtless tetrapods were eating them–but they had evolved from marine invertebrates, and our last common ancestor was somewhere deep in the Pre-Cambrian). There are over 30,000 species of tetrapods today–7,500 amphibian, 10,000 reptile, 10,000 bird and over 5,500 mammal species–and all remarkably seem to have come from one species of lobed finned fish that managed to combine both fin walking and air breathing, and had an unusual capacity for mutation in pectoral and pelvic fins. There was a wide range of these mutated fins at first–as many as eight digits on each fin–before the final five toes/fingers was arrived at. (Perhaps the occasional six toed kitten or baby are a mutational echo of that.) There seem to have been many species that could do so and apparently the lush and swampy Devonian shore line was rich enough in food and varied enough in niches a half billion years ago to allow evolution to run riot. But apparently only one of those species led to all the four footed or two footed and two armed or winged creatures breathing air today, including us. And while this beautiful little epaulette shark has nothing to do with any of our own evolution since the Devonian, as it is only very distantly related to any of us tetrapods, watching it trundle across the ocean floor does give a brief glimpse of what our own origins looked like nearly half a billion years ago.
Neighbor’s cat stuck up in our back yard tree for the third day now. So far all attempts at rescue have failed. All it has to do is climb down six more feet and it can be rescued. So of course, being an idiot cat, it climbs up another ten or twenty or thirty feet. From there it could also go another six feet and leap onto the roof. Nope. No one ever said cats were smart. Cute, OK, but not smart. Natural selection in house cats eliminated that sort of thinking in favor of snookumsness a long time ago. Hell, the dumb things can’t even conjugate a simple verb intelligently. I can haz cheeseburger, sheesh. And so there we are, three days of standing around the trunk of the tree and looking up as the stupid if adorable little beast looks down and cries at us like it’s our fault. Perhaps it is our fault. We domesticated them. Leopards don’t get stuck in trees. Then again leopards eat people. It’s important to keep things in perspective.
Tonite we will wind up picnicking around the tree, eating pork loin, mashed potatoes, corn on the cob and drinking wine, just to torment the little dope into coming down for a morsel. Not that it will work. Instead we will probably be attacked by raccoons. They, at least, are smart. And annoying. If cats were smart they’d be just as annoying, and we’d never have domesticated them. Problem solved.
Incidentally, here is a margay. A margay can climb down a tree, headfirst. Obviously we domesticated the wrong species. Of course, margays are from South America, and we are from Africa. One of us was on the wrong continent. Hence, there is a descendant of an African sand cat–native to deserts and Sahel, treeless all–stuck far up in the branches in our backyard, meowing its little sand cat heart out.