(continued) Chapter 3. Long Evolution: Life Emerging
Modern reptiles come in four main groups: turtles and tortoises; snakes and lizards; alligators, caimans, gavials and crocodiles; and a small nondescript creature from isolated New Zealand called a tuatara. Reptiles are found in habitats of every nature throughout the earth other than arctic tundra and polar ice, with special concentrations in Amazonia, southern US/Mexico/central America, west Africa and south Asia. Following is as much as you need to know about them unless you make your living as a reptile expert.
Tortoises and turtles are both reptiles, the only major distinction being that tortoises live on land whereas turtles spend their lives in water some or most of the time. Both live inside a moderately hard shell to which internal body structure is integrally attached. The upper shell (“carapace”) and lower (“plastron”) are attached by a bridge, an arrangement which allows head and legs to be either extended or, when danger threatens, tucked tightly inside the defensive shell. Tortoise shells are highdomed, turtle shells tend to be flatter and more streamlined for movement in water. Both reptiles are generally shy and reclusive. Most tortoises are herbivores, turtles are omnivores. Tortoises are alleged to live up to three centuries, turtles live less than one century.
Snakes and lizards have in common only that they both are cold-blooded reptiles with scales; their differences are fundamental. Most lizards, for example, have four legs, external ear openings that hear as ours do, and two movable eyelids that blink. In contrast, snakes’ long, sinuous bodies move by undulating and are legless (excepting vestigial internal legs on their skeletons), they only “hear” ground vibrations through their skull bones, and cannot close their eyes. Lizards have tails which they can detach when fleeing danger – then the tail grows back! Snakes shed and re-grow their outer skin once annually. Lizards are omnivorous, consuming a variety of insects and plants. Snakes are carnivorous and have unusual flexible jaws which they can unhinge to swallow prey larger than their own diameter. Lizards come with two lungs, while snakes have only one functioning lung plus, in most snakes, a vestigial lung.
Some lizards can change color. And since they can be observed to do this at will, obviously by their own choice in responding to conditions in their environment – such as blending in to evade a predator’s hungry eye – this practical use of their lizardy little brains in deciding to change color says something important about conscious free will and power of thoughtful decision in creatures less complex than us. Be careful what you presumptuously assign to “instinct” – whatever that is – and remember this paragraph when we come to a later chapter in this book-length exploration of human mindsets.
Alligators, caimans, gavials and crocodiles are all “crocodilians” though they are not all crocodiles. The word “crocodile” refers only to what are deemed “true crocodiles.”
True crocodiles can always be noticed a by their long pointy snouts with an especially noticeable fang protruding on each side. Indeed it is this elongated jaw section of the skull – the part that classically opens wide to snap shut on prey – which distinguishes crocks from “Alligatoridae” (alligators and caimans) and Gavialidae (gavials, also inexplicably called “gharials” with needlessly different spelling). The skull and jaws of all crocodilians have the same group of bones and work the same way, but come in different shapes to help us tell these aggressive flesh eaters apart and keep a discerning eye when strolling close by an Everglades shoreline with our beloved puppydogs. While we’re on the subject, Australian crocodiles, especially the males, can famously grow to more than twenty feet in length and weigh well over a ton. Quite fleet of foot, these behemoths tend to ambush and eat large prey such as cattle, horses, wallabies, pigs, other crocodiles, and the occasional tourist who didn’t believe the warning signs.
Alligators and caimans have broad snouts, sometimes called shovel-shaped, with no fangs showing on the outside. There are seven distinct species of them, the most popular among Americans being the so-called Alligator mississippiensis found all over humid American southlands and, every once in a while most alarmingly, up the Mississippi and Ohio rivers as far as domestic backyards along Beargrass Creek.in Louisville, Kentucky. Caimans dwell in Central and South America and differ from their close alligator relatives by having more slender teeth, overlapping bony plates for their body armor, and an absence of the alligator’s bony septum between the nostrils.
Gavial/Gharials have a smallish head at the back end of a truly odd-looking prominent and elongated very narrow snout. The snout has a lump resembling a doorknob at the front end but contains 110 unwelcoming sharp teeth. An unusually long crocodilian, gavial/gharials can grow to as much as twenty feet in length. Native to riverine habitats in hungry overcrowded northern India, this drastically declining species eats mainly fish and is critically endangered.
The Bottom Line: all these thousands of reptile species can be genetically traced back, and back – back through the twigs and branches and limbs of countless thousands of generations over the millennia of long evolution, a many-braided stream – to a single reptile-like creature, the ancestor common to them all.
The fourth class of vertebrates, officially known as “Aves” (from Latin fare well) is what the rest of us unofficially call “birds.” In habitats of every nature all over the globe, there are today between nine and ten thousand known species of this extremely diverse and successful group of vertebrates.
Of considerable interest, only within the past twenty years or so have birds been widely recognized as the only living direct descendants of dinosaurs. Right down to the tiniest, delicate and brilliantly-colored hummingbird, birds are the only dinosaurs that survived extinction when a large asteroid struck Yucatan some 65 million years ago, triggering massive volcanic eruptions and chaos in the earth’s environments. Though some modern reptiles may “look and seem” dinosaur-like, they are but distant relatives – descended from ancient reptiles that were related to dinosaurs but were not themselves dinosaurs (meaning they all had a common ancestor). The dozens of ancient creatures we today think of as dinosaurs – large and scary to small and meek – were but one among the several broad categories of reptile groups living at the time of the worldwide disaster. For authenticity as real dinosaurs which somehow managed to not go extinct at that time, modern birds have it.
Q: All over the earth, that ancient mega-disaster wiped out not only the non-avian dinosaurs, but huge numbers of avians, insects, mammals and plants as well. Given the catastrophe’s massive worldwide impact, why didn’t it wipe out every complex creature living at the time? A: The fossil record indicates that eighty to ninety percent of fish species survived, probably because they were aquatic omnivores able to adapt to other foods when the disaster disrupted their regular food supply. Half of North American plant species disappeared, but another other half did not, and southern hemisphere plants were not as drastically affected as in the north. While a few amphibians went extinct, most had very little decline. Of six turtle species then alive, all six are still represented by their descendants today. In fact, so many creatures (complex; far above the level of bacteria) survived the great dinosaur extinction that listing them would fill a whole book. In this context, the reason so many birds survived most probably is simply because they could fly away from damaged habitats to more survivable habitats. It’s not always clear why some species go extinct and others do not, but in this case the big picture is quite clear even if some details are not. Very shortly we’ll also address why mammals survived.
During their 65 million years of evolution from that time to this, dinosaur-birds have undergone some remarkably specialized bodily modifications which undeniably establish them as the world’s natural experts in flight. Through those millions of generations, for example, their bones have become hollow and light but still very strong – unlike T. rex whose whopping leg bones can be seen in museums. In fact, many of the bones their ancestors had have become fused or disappeared altogether. Their muscles have turned into powerful drivers of flapping wings able to lift heavier-than-air bodies into graceful soaring flight, able to remain aloft for many hours and carry their bodies thousands of miles in annual migrations. Perhaps birds can do this so well because they have evolved a specialized one-way type of breathing in which air flows in only one direction through pressure changes in a respiratory system of tube-like air sacs. In consequence of this, birds lack the expanding-contracting diaphragm we mammals think normal – i.e., you won’t visibly notice them “breathing.”
Perhaps most important of all, birds – and only birds – have feathers. They are the most prominent features of bird anatomy and they perform several invaluable functions, the most significant being enabling birds to fly. The size and shape of individual feathers in the wings and tail play important roles in controlling flight, but feathers have other vital roles as well. They insulate birds’ bodies, protecting them from water and cold weather, maintaining body temperature at around 102 degrees Fahrenheit. Feathers provide camouflage from predators and can be handy sexual displays for impressing a potential mating partner, just ask any peacock. Feathers also may be plucked for lining nests to help insulate eggs and newborn chicks.
The number of breeding North American birds has plummeted by approximately 1.5 billion over the past 40 years, according to a new report. Forty-six species have lost at least half their populations – primarily through urbanization and habitat degradation.
Scientific American, December 2016
Ostriches, hummingbirds, blackbirds and wrens, parrots and pigeons and herons and hens, penguins and pewees and eagles and crows – how many kinds are there, sure no one knows. Properly classified according to their DNA genetics, they come in some thirty different classes arrayed in 227 bird families of every imaginable shape, color and size. Therefore, though it may bring bird geneticists to apoplexy, we’re going to scan through them a bit faster than the menagerie might warrant if we didn’t have so much other evolved life yet to examine. Thus from our abbreviated angle of approach, paying attention to only nine “types” of birds will get us by with the few essentials we really ought to know anyway. They certainly are easier to remember this way.
1) Songbirds. For quality of music, splendid examples include meadowlarks, thrushes, warblers and mockingbirds. Roughly half of all bird species (four to five thousand) “sing” what we humans call “songs,” many of which may sound quite complex and beautiful to the human ear. Their intent in so singing cannot be certainly known to us, and, though they certainly project their melodies to the community at large when courting or warning others away from their territory, not a few experienced birders swear that many often sing for the sheer joy of it quite as we do. Observed and carefully listened to on a warm spring morning when the woods are alive with birdsongs, this is hard to refute. Also called perching birds, common songbirds have grasping feet with three toes pointing forward and a larger fourth toe pointing backwards. Song birds seem nearly infinite in their variety of habitat, size, color and behavior. The alleged top ten sweetest-sounding songbirds are nightingales, the Asian koel (a cuckoo), male canaries, whistling cockatiels, the Malabar whistling thrush, veerys, mockingbirds, rose-breasted grosbeaks, orange-winged green parrots and common loons.
But beautiful sound is a subjective thing. I personally am enchanted by the sound of two whippoorwills calling to each other soon after sunset on a spring evening from points a half-mile mile apart in the forest beyond my window. And crows, not usually considered songbirds, employ a vocabulary of highly nuanced caws, croaks and muttered chatterings that sound for all the world like gossip, making them a special case in the little understood arena of bird languages. My crow claims may be verified by anyone who bothers to listen to a murder of intelligent crows engaged in their daily assemblies in the high branches of tall forests at mid-morning on warm summer days.
2) Birds of prey. This diverse group of fierce predators includes some of the world’s largest birds – eagles, owls, hawks, falcons, ospreys, kestrels, kites, harriers and secretary birds. Collectively known as “raptors” (from Latin repere – to seize or take by force), “birds of prey” has more descriptive ornithological meaning: i.e., large eyes with extraordinarily sharp vision for spotting prey while soaring high, muscular legs bearing long, sharp talons for holding prey, and strong hooked beaks for tearing flesh. They generally prey on vertebrates that are relatively large in proportion to the bird’s own body size. Vultures and condors are included in the group, though they normally scavenge for their food. The ornithological meaning excludes other large carnivorous birds such as penguins, storks, gulls, kookaburras and skuas because they lack the leg-talon weaponry and rely mainly on their beaks to catch and kill prey such as fish, small birds and animals.
* © *
…to be continued in one week…
SHARE THE BLOG: If you’re enjoying MINDSET please invite your friends to view
The Fixy Populist …at… fixypopulist.com