The Continuum

Subj: The Continuum

Date: 01/18/2001 6:37:17 PM US Mountain Standard Time

From: fca25@yahoo.com (Fred Allebach)

To:  (Chris Baisan)

1/18/01

Fred's notes and thoughts from:

Vertebrate History: Problems in Evolution

Barbara J. Stahl 1985

This questioning of how life unfolded has many chapters. It starts with how the universe was created, how life got started and then, how particular plants and animals came to be as they are now. Why is another question that is equally interesting yet much harder to answer.

When you look for exact links between species that led to vertebrates it is not clear, lots of theories, but no series of fossils that show unequivocally the lineage. Scientists use stuff like embryology to reconstruct links and similarities, but they don't have anything like a lock on how it happened, how there came to be back bones, jaws, paired appendages, those things emerged in the distant past and led to vertebrate life as we know it now, but they can't say exactly how, or which species were the links and the ancestors. Was it some echinoderm or an arthropod? You can never tell. When you look for the exact fish that were ancestral to Amphibians, there isn’t one. There is a good guess, but no prima facie evidence. (1)

For comparison’s sake, look at current theories of human origin, you can see how much scientists argue about the ancestors and the links, did one small group of anatomically moderns come out of Africa or did the local Homo erectus populations all arrive at the modern condition independently? And, as a corollary, did modern lions all come from one lineage or are they the result of local populations getting modern on their own? Did wolves arise as one group that displaced all the former wolf-like canids? The answers to these questions are not in any way clear, yet the events are much more recent than with fish to amphibians. If scientists can't get it for the near past, it becomes sketchy that they could for the distant past too. The arguments seem to be pretty much the same, just with more or less evidence.

The whole endeavor gets complex fast. How do you draw the line between species in the past? When do you say a bear is modern or a cave bear? There is a continuum over time and it is really impossible to say when the ancestor stopped being the ancestor and took another form. It is a grade, a cline. In this view, of constant change happening to a lineage, there never is a modern or an ancestor, it is just a continuum. Scientists get fooled into seeing particular species because that is all that the fossils show. Fossils only show a snapshot. This leads into problems in classification between lumpers and splitters.

For example, the American lion, of Pleistocene vintage, is called Panthera atrox. It was bigger than extant lions, but a lion nevertheless. Was it a really different species? Humans are currently understood to not be made up of different races, we are all the same species; our naive idea of race is the same as what the cline of human variation is. Wolves look different as they range around the world, but they are still wolves, Canis lupus. The splitters take these clinal differences and want to make new species. The lumpers see it as all one big cline, they like big categories. A splitter sees P. atrox, a lumper sees Leo leo, a splitter sees races, a lumper sees the whole species. This can then get translated through time. When is it us and when is it the predecessor? With fossils the temptation is to split, to see a species with every new bone. 

However, in spite of splitter’s preferences, that there is a unity of life is unquestionable; all life has DNA, the same type of cells, is made out of the same star dust and it only makes sense that modern life rests upon the life that came before it. Entirely new kinds of life just don’t fly in from Mars. There is genetic unity among all life; there is chemical unity of all matter. People, flat worms, microbes, algae, trees, insects, jellyfish are all made of the same chemical and physical stuff. We all have the same type of DNA and cellular structures; we have the same chemical components. There can be no argument about that. All of life and matter, as we know it, is related by being made of the same stuff, the same stuff that is spread across the whole universe. It is absolutely fascinating, but kind of like a stick diagram of a Rembrandt painting, you know the richness and detail is there, but all you have is a few lines.

Here is an excerpt from one of my Olympic beach journals: “Life crawls up the rocks as far as it can and still be nourished by the splash and spray of seawater. Then there is a zone of about 10 yards where nothing but anonymous slime grows, a transition zone where the boundary of sea and land life merge and above, the land plants start. Sitting here now, as a member of the human species, a young species as far as species go, our whole distinct line only around 2.5 million years old, reflecting on how my distant ancestors in the family of life somehow crossed that barrier of salt to fresh water, sea to land, crawled out and started the history that eventually led to me sitting here, is just a thought beyond comprehension. How vast the time! How many the steps and days through the millennia, and yet there is the connection. I came from that life out there in the inter-tidal area.” This brings me back to how amphibians came from fish.

Fish are the most successful vertebrate line, established in the Devonian period, long before the appearance of land vertebrate forms. Fish have maintained supremacy in their environment for 400 million years. The Age of Fish is still going. Vertebrates descended from fish are called tetrapod vertebrates and these include amphibians, reptiles, birds and mammals. The oldest tetrapod vertebrates, amphibians, have derivative features from rhipidistian fish. The skeleton and skull show similarities. The rhipidistian-amphibian transition is interesting, looking at the skull and fin structure of the ancestral fishes and how they changed into 5 toed feet, how the eyes and ears needed to change to adapt to life on land, how fins turned into legs, how gills became lungs, etc.

One question that keeps cropping up is whether amphibians, reptiles, mammals and birds were monophyletic or polyphyletic. Did they all come from one common ancestor or did different kinds evolve from multiple, different ancestors? Same deal with human ancestors. The question is a common monkey wrench to throw in, because you can never get a good answer. It stokes the fires of debate. With human evolution the argument has taken on deep personal animosities the main mono and polyphyletic protagonists

The then there came the reptiles, with tough skin, eggs with shells, a more advanced heart and able to transcend the need to always be near water. Reptiles may be descended from only one group of amphibians; those that had "land eggs". Then again maybe not, you can’t say for sure. In turn mammals evolved out of therapsid reptiles. Birds came from the pseudosuchian reptiles. Birds developed feathers out of scales, wings, and a warm-blooded metabolism. Mammals were warm blooded as well, got hair from scales and more specialized teeth for chewing. Mammals got rid of external eggs and developed mammary glands to feed the young; they became more invested in raising the young. Birds conquered the sky. Mammals conquered the night.

In mammals, there are 3 extant groups, monotremes, marsupials and placentals, the first 2 presumably a reflection of primitive mammalian stages, monotremes being more like reptiles and marsupials bridging the gap with placentals. Placental mammals make up the bulk of modern mammals.

A special interest of mine is the order Carnivora. Carnivora evolved from a group of mammals called miacids, in the late Eocene. Carnivores are split between two basic types, the dog-like and the cat-like, canoid and feloid. Another division in Carnivora is between pinniped and fissiped, or between the seals, sea lions and walruses and land Carnivores. Since the pinnipeds have fused wrist bones, a character that is post-miacid and shared by all of Carnivora, it fixes their evolution as part of the Carnivore line. By the Miocene, the three modern pinniped groups were present. Pinniped tooth specialization includes loss of shearing carnassial cheek teeth, towards a more conical tooth for grasping fish. They retain large canine teeth and with their whiskers and facial profile, look similar to land Carnivora.

Whales, Cetaceae, do not have the fused wrist bones, no unique structures to link them to animals of a particular order. Whales are so specialized; they may be as ancient as from the late Cretaceous or early Paleocene. The whale’s ancestors remain a mystery. Then there are also the manatees and dugongs. Where did those guys come from? These are the crux of my interest; how did these curious and interesting animals come to be?

In the end, it is a great and fantastic story but when you press for the details, the fossils and the links aren't all there; you get a lot of theories and hypothesizing. You've never seen so many disclaimers and perhaps this and perhaps that as in this book. The truth is behind the veil of time and we can't part it to see exactly what happened, to see the events that gave rise to particular lines and types of animals. It's like we get to know the outcome of a Sherlock Holmes mystery but with practically none of the characters we most want to know about. Wouldn't it be great to know exactly how amphibians got to be amphibians, how birds got to be birds, how fins turned into legs and then into wings? What we get instead is a lot of educated meandering that is inevitably contested by other educated meandering and it's just supremely unsatisfying for the interested layman to run up against. It’s a fait accompli with little actual proof for the transitions in evolution.

There is a distinct political twist to scientific discovery and for a theory to really gain dominance, there has to be a preponderance of evidence for years and years, or until all the antagonists die. I want to know the actual transitional animals and there are hardly any.

You can find all sorts of transitional animals, which display intermediate characters between reptiles and birds, between reptiles and mammals, between fish and amphibians; you can see how it might have been, how it might have unfolded, and based on past climate reconstructions, past geography and geology, why it might have happened. If you are going to crawl out of the ocean and do OK on land, you need better eyes and ears, some limbs to do the job of locomotion, lungs to breath air. And why would animals do this? Were they crawling from one pool to another to escape drought? Were they responding to lack of oxygen in shallow, warm water? Were they enticed by a bounty of arthropods that had already colonized the land? Did hunger and a free lunch drive them to get up there and pick off some bugs for dinner?

Once amphibians came onto the land and established a foothold, the adaptive radiation was incredible. The hands I type with now were made by the efforts of ancient slimy salamanders slithering through the muck, grasping, walking, on legs, which I use to go make my living. I could have had wings and been outside now singing a song to the sunset, my lineage could have perished like the dinosaurs or the Dire wolves, only to be part of the molecules now which make up cardboard boxes or the curtains on the window. Yet I am still on the continuum, the whole lineage of all life standing behind me. That's some real family history! The continuum, that was the kind of insight I was hoping to generate, a feeling of being connected with all of life.

(1)

CLASSIFICATION Taxonomy, Phylogeny, Cladistics, Systematics:

Classification shows the relations and similarities between all of life. I thought I would have one big key to understanding the world if I could name all of life. In classification there is plenty of argument between lumpers and splitters as to what category goes where. This is par for the course in science. Looking into classification eventually led me to notions of the continuum. Below I’ll classify people and garlic.

Kingdom Animalia, Plantae

Phylum (Division) Chordata, Angiospermophyta

Subphylum* Vertebrata

Class Mammalia, Monocotyledoneae

Order Primates, Liliales

Family Hominoidea, Liliaceae

Genus Homo, Alium

Species Homo sapiens, Alium sativum

*intermediate levels can be added w/prefixes sub- and super-

FIVE KINGDOMS model

Monera- bacteria, cyanobacteria (blue-green algae/stromatolites), prokaryotes

Protista- single celled eukaryotes, individual protozoans and some types of algae

Fungi- molds, mushrooms

Plantae- multicellular algae and land plants

Animalia- multicellular animals

Prokaryotes: mostly small cells, all are microbes, many are strictly anaerobes (which are killed by oxygen) much simpler than....

Eukaryotes: mostly large cells, some are microbes, most are large organisms, almost all are aerobic

Viruses - non-cellular molecular parasites, line between organic and inorganic, living/not living, they are not cells, they are particles of genetic material and protein, can invade cells and take over metabolic processes and reproduce, have natural selection just as with "life", can be crystalline and inert, "as crystals they were clearly not living cells but some sort of inert entity." -see "the crystalline entity" on

Star Trek: The Next Generation

Human viruses: Measles, Rubella, Atypical pneumonia, common cold

(Coryza viruses, Rhinoviruses) influenza, Hepatitis, Mononucleosis,

Poliomyelitis, Mumps, Smallpox, Rabies, Dengue fever, Yellow fever, HIV

Phyla of Kingdom Animalia: all the major types of animals

Protista, (Protozoa), includes certain plant-like organisms

Porifera: sponges

Placozoa: "scale-ozoa"

Cnidaria: (Coelenterata), hydras, jellyfish, sea anemones, corals, the cnidae or nematocysts are used to ensnare or poison prey

Ctenophora: sea gooseberries or comb jellies, similar to Cnidaria

Platyhelminthes: flat worms

Nemertea: littoral and marine worms, a few terrestrial genera

Rotifera: small, minute animals distinguished by a complex feeding apparatus

Nematomorpha: horse hair worms Order: Gordioidea, appears as long horse hair or violin string up to a meter long, in springs, streams and stagnant water, especially in the mountains (I saw one in Romero Canyon)

Nematoda: eel worms

Mollusca: bivalves, cephalopods, gastropods, brachiopods

Annelida: earth worms, tongue worms, segemented, worm-like animals

Onychophora: some features of annelids and arthropods

Arthropoda: insects, spiders, crustaceans (barnacles)

Echinodermata: spiny skinned: sea urchins, sea stars, sand dollars, sea cucumber, feather star, crinoids/ sea lilies

Chordata

CHORDATA

Superphyla: Craniata (Vertebrata) with cranium, visceral arches, vertebrae and brain,

Phylum: Chordata

Subphylum: Gnathostomata: with jaws and usually paired appendages

Superclass: Pisces: paired fins, gills and skin w/scales

Class: Placodermi: ancient fishes

Chondrichthyes: sharks and rays, skeleton cartilage

Osteichthyes: bony fishes

Superclass: Tetrapoda: paired limbs, lungs, cornified skin and bony skeleton

Class: Amphibia, Reptilia, Aves, Mammalia

Class Amphibia

Order Salientia frogs and toads

Caudata salamanders

Meanres sirens (small front legs no tail)

Gymnophiona no limbs, tropics

Class Reptilia

Subclass Anapsida

Order Cotylosauria primitive ancestors

Order Testudines turtles

Subclass Euryapsida ancient marine reptiles

Subclass Ichthyopterygia ancient fish-like reptiles

Subclass Lepidosauria diapsids

Order Rhynchocephalia primitive lizard-like

Order Squamata advanced lepidosaurians: lizards, snakes, amphisbaenids

Subclass Archosauria four extinct orders including dinosaurs and pterosaurs

Order Crocodilia alligators (el legarto) and crocodiles

Subclass Synapsida

Order Pelycosauria early mammal-like reptiles

Order Therapsida advanced mammal-like reptiles

Class Mammalia

Order

Monotremata echidna, platypus

Marsupiala kangaroos, opossums

Insectivora tenrecs, shrews, moles, hedgehog

Edentata sloths, anteaters, armadillos

Pholidota pangolin

Tubilidentata aardvark

Chiroptera bats

Dermoptera flying lemur

Primates monkeys, apes, humans

Carnivora:

-Canids, Mustelids, Ursids, Viverrids, Procyonids, Felids, Hyaenids, Phocids, Otarids

Proboscidea elephants

Sirenia manatee, sea cow

Hyracoidea conies

Perissodactyla odd-toes ungulates: tapirs, rhinos, horses

Artiodactyla even-toed ungulates: pigs, camels, deer, sheep, goats, giraffes, antelope, cattle

Cetaceae whales

Rodentia rodents, gnawing mammals

Lagomorpha rabbits, hares

Class Aves

Order Struthioniformes ostriches

Rheiformes rheas

Casuariiformes cassowaries

Aepyornithiformes elephant birds: turkey to ostrich sized flightless birds of Africa and Madagascar: EXTINCT historically

Dinorthiformes moas, EXTINCT w/in last 300 years

Apterygiformes kiwis

Tinamiformes tinamous: Mexico to S.America

Gaviformes loons

Sphenisciformes penguins

Podicipediformes grebes

Procellariiformes albatrosses, shearwaters, fulmars, petrels, tropic birds

Pelecaniformes pelicans, gannets, cormorants, aningha, frigate bird

Ciconiiformes herons, bitterns, storks, ibises

Subphyla: Agnatha: no true jaws or paired appendages

Class: Ostracodermi: ancient armored fishes

Cyclostomata: lampreys and hagfish

Superphyla Acrania: no cranium or brain

Phylum Chordata

Subphyla: Hemichordata: notochord short, anterior, nerve tissues in epidermis

Class: Enteropneusta: tongue worms (annelids?)

Pterobranchia:

Graptozoa: graptolites: colonial, branched, w/ chitinous covering

Subphyla: Tunicata:

Class: Larvacea: tadpole-like

Ascidiacea: ascidians, tunic w/ scattered muscles, many gill slits

Thaliacea: chain tunicates, tunic w/ circular muscle bands

Subphyla: Cephalochordata: notochord and nerve chord along entire body

Class: Leptocardii: Lancelets, slender, fish-like, no scales, many gill slits

Qui respiciunt ad pauca de facili pronunciat.

"They who take few points into account find it easy to pronounce judgement." (Latin saying)

"It is the theory that decides what we can observe." Albert Einstein

"The effectiveness of a doctrine does not come from it's meaning, but from it's certitude." Eric Hoffer