January 2, 2005
CENOTES & THE CHICXULUB CRATER
One of the most striking features of the Yucatan's geology is that there are lots of cenotes -- easily seen when you fly over the land. A cenote is a natural hole in limestone bedrock -- a sinkhole -- with water at the bottom of it. Some cenotes are small and shallow but others are very large and deep. A wonderful map showing northwestern Yucatan's identified cenotes is at www.lpl.arizona.edu/SIC/impact_cratering/Chicxulub/gpcenotes.jpg.
The above map not only shows a lot of cenotes but also a very conspicuous and strange feature that at first glance seems inexplicable: A dense ring of cenotes surrounds the capital city of Merida, and inside the ring few cenotes exist. Well, this feature constitutes important evidence for one of the most important discoveries ever made relating to the evolution of life on Earth. And I am writing to you from inside this ring.
About 65 million years ago a worldwide extinction of many plant and animal species took place. One feature of the extinction was that reptiles, particularly dinosaurs, were largely wiped out. Mammals, which at that time were fairly small, simple, unimportant, rat- like animals, then were able to evolve into niches formerly occupied by reptiles. In other words, if it hadn't been for the extinction disaster, a scaly reptile might be writing these words, not a hairy mammal.
It's now believed that that extinction was caused by an asteroid or comet hitting Earth. The object's impact center is thought to be near where today stands the Yucatec town of Chicxulub, so today science refers to the Chicxulub Crater.
From here inside the impact zone you see no evidence of a crater. That's because when the comet hit, the Yucatan Peninsula lay deep beneath the Gulf of Mexico's waters. Now what remains of the crater is buried beneath thick layers of limestone deposited later.
I'm not clear on how the object's impact came to produce the ring of cenotes around Merida, and why within the zone cenotes are so rare, but I do know that here at Komchén we have two small cenotes. The one I visited was about 15 feet deep and the size of a bathroom. You could climb down into it and float in the cool, clean water. Farther inland where cenotes are deeper, the ancient Maya often regarded them as mystical places and sometimes people were sacrificed to the gods by being thrown into them.
You can read a lot more about the Chicxulub Crater, see an animation of how the crater was formed, read about regional and global affects of the impact, and find more links at a NASA/University of Arizona site at www.lpl.arizona.edu/SIC/impact_cratering/Chicxulub/Discovering_crater.html.
We have lots of bird-kinds here that many North American birders have never heard of. For example, there are becards, tityras, saltators, trogons and motmots. One of the latter, the Turquoise-browed Motmot, I hear every day, and get a glimpse of maybe every other day. It's such a pretty, curious bird that it's Komchén's logo. You can see one at http://ontfin.com/Fav/TBMO2.htm.
In general size and shape motmots are like long-tailed mockingbirds but in terms of color they're more like the rainbow. Our Turquoise-browed species has a rich chestnut belly, blue tail, green crown, black throat and eye-stripe, and that day-glow-turquoise eyebrow.
The thing about motmots, though, is their tails. The tails consist of two long central feathers that are stripped of their webbing for an inch or two, an inch or so above the tips. The adult birds remove the webbing themselves and I'm not at all sure why. Moreover, the birds tend to perch slowly swinging their tails from side to side like clock pendulums.
A good guess is that the strange-looking swinging tails cause predators such as hawks to attack the wrong end of the bird. One problem with that theory, however, is that often you would overlook the bird entirely were it not for that slow-swinging tail. The dark greens and blues of most motmot species help them blend marvelously into their forest-canopy background.
Motmots feed on flying insects and small fruits. They are found only in the Americas from Mexico to Argentina, and most of the species occur in Mexico.
One of the nicest features about Komchén is that fishponds and troughs of water are scattered all about, not only for the benefit of fish and thirsty wildlife but also because in this dry area fishponds are just great to see and sit beside. Some fishponds are covered with aquatic vegetation -- waterhyacinth, duckweed and an interesting aquatic fern.
Of course ferns are supposed to be frilly fronds arising from the ground, so it surprises some folks to learn that ferns can grow atop water. We've already seen when I was writing from Mississippi that fern species of the genus Lygodium can be vines. I can also tell you that a couple of states south of here you can see tree ferns. Therefore, the world of ferns may be more varied than you think.
I'm guessing that the aquatic fern in our fishponds is the Common Salvinia, SALVINIA MINIMA. I identified it using a USGS page comparing three Salvinia species at http://salvinia.er.usgs.gov/html/comparison.html.
A line drawing showing our fern's biology resides at http://salvinia.er.usgs.gov/html/s_minima_biology.html.
In the southern US there's fear that introduced water fern will damage some of our aquatic ecosystems. The Giant Salvinia, SALVINIA MOLESTA, already is established in many areas as far north as northern Virginia. You can see a map of its US distribution at http://salvinia.er.usgs.gov/html/distribution_map.html.
Our species is pretty tough. Our waterhyacinths tend to be runty and die, and the fish and birds eat our duckweed, but these Salvinias just keep multiplying until you can hardly see the water's surface.
Komchén's bougainvilleas are putting on a real show now, sprawling and rambling over trellises, along fences and into trees, with gorgeous flower clusters ranging from traditional bright red through pinks and salmon into creams and white. A page about pruning bougainvilleas and showing a picture of one is at www.heirloomgardenexperts.com/info-sheets/bougainvillea.htm.
Botanically bougainvilleas are known as Bougainvillea glabra, Bougainvillea peruviana, or Bougainvillea x Buttiana (which is a hybrid of the previous two.)
A very nice close-up of some bougainvillea flowers at www.oasinweb.com/il%20giardino/bouganvillea.JPG shows something interesting: Each thing most people think of as a flower is actually a cluster of three flowers. In the picture, each roundish, whitish object is the spreading mouth of a real bougainvillea flower, which is shaped somewhat like a slender bottle. Below each real flower arises a flaring, flat, red bract, and each flower cluster consists of three flowers and three bracts held together to look like a flower.
Last week we ran into brightly colored bracts when I described the ancestor of the Christmas Poinsettia encountered on weedy sand dunes north of here. These kinds of bracts are leaves modified to attract attention to the much smaller flowers they subtend. That picture is worth studying.
I've been surprised to learn that getting starts of bougainvillea is pretty easy. As if it were a willow stem you wanted to root, just whack off a stem and push it into moist earth. I like to remove green leaves to cut down on water-loss stress to the cutting and its buds.
Right after I arrived at Komchén a few weeks ago someone went to the saltflats just north of here and shot flamingos. Several were killed outright but most - - over 30 mostly young birds -- died when they flew blindly into high-voltage lines. Well, no one guards the birds, and there's not even a sign up saying that birds shouldn't be shot.
I can't think of that incident without recalling something from my childhood. Back on our isolated farm in Kentucky, each spring for several years in a row it seemed that a certain Great Blue Heron landed at least once in the top of one of our Lombardy Poplars. My father and I were always anticipating the visit because we wanted to see who could shoot it down. After several attempts by both of us over several years we never succeeded, but I fear the bird or birds were often wounded, because we were pretty good shots.
When I got into my teens something happened inside me, almost overnight, that suddenly caused me to fill with shame just thinking about shooting at those beautiful birds. I wish I knew what the thing was that caused me to suddenly shift my perspective so drastically, not only with regard to shooting herons but also to my feelings about civil rights for Black people (these were the 60s), vegetarianism, and a whole bag of other concerns that ultimately brought about my isolation from the culture in which I was embedded.
I've never understood what caused those changes, but just because I've thought so much about the subject of how humans come to decide what is right and wrong, I think I've attained a certain insight. That is, human civilization is a very thin, fragile, maybe temporary veneer of learned civility enveloping humanity like the shimmering surface of a very fragile bubble -- ready to shatter at any moment.
Moreover, humanity, from what I can see, still runs mainly on dumb, uncritical instinct, not rationality (viz the last US election). The unfortunate thing is that humanity's instinctual urges have been programmed in our genes over millions of years of primate evolution, and it overwhelmingly expresses itself in primal urges for sex, territory and status, and not much else. Niceties such as not shooting herons and letting people unlike ourselves live in dignity is purely cerebral stuff that can be and will be forgotten as soon as conditions get rough for us.
Whatever the case, with regard to humanity's thin veneer of civility, my opinion is that it's something worth protecting and expanding.
If violent, consumption-focused commercial TV continues to program our children, the good will of our teachers continues to be abused, and our politics and religiosity continue to grow ever more extreme, we're all going to end up shooting flamingoes and herons.
The problem with that is that it's not only hard on the flamingos and herons, but also an ugly, damnable way to be.
Best wishes to all Newsletter subscribers,
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