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
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