The earliest known vertebrates are the Armoured Fishes of the Silurian. They have had hard
skeletons and carapaces, and that is why they were capable of fossilization when they died in seawater-pools or lagoons,
under conditions favourable for their preservation.
Incomplete and fragmentary as it is, the geological record only gives indications about ancient faunae.
This does not represent the actual links in the evolutionary chain, nor does it demonstrate any evidence of chronological
order ( fish, then amphibians, reptiles, birds and mammals ) in which the series of the vertebrates should be listed.
Pisces, indeed, appear to be highly specialized water animals which proceeded from more
primitive vertebrates that preserved less evolved features, such as 4 legs and functional lung, that transformed
in fish into fins and natatory bladder... The remarkable thing about Crossoptérygians, and also Dipnoi ( lungfish ),
is that they preserved choanae or internal nostrils, and lungs for air-breathing [ gills being posteriorly added ].
According to a classical view, the land vertebrates which flourished in Carboniferan times were
clumsily built amphibians. However, even though fossil records have not been discovered as yet, there lived logically at the
same time with several more completely terrestrial lineages which sprung from some branch of the homonculian stem.
Fossilized mammals are known from early Triassic layers as small creatures said to have originated from
reptiles. However, only the mammalian level of structure should have reached such perfection and adaptability to produce
set-types which specialized in various ways and at different times during early geological periods. It means, we must believe the
contrary, i.e. that reptiles once evolved from mammalian creatures. We can call this process ( an adaptive
simplification of body structures ) : reptilization. This entails the fashioning of various reptilian
and reptile-like lineages form originel mammals ; and the evolution may develop further to amphibians
or to completely aquatic forms, such as the fish.
I’d like briefly to present here my individual concepts about the morphological appearance
of the first vertebrate that was intended to conquer the land.
In this article we will not evoke problems as to demonstrate whether a fish looking like a crossopterygian
could really have walked on its paired fins [in which the bones have remained comparable to those of the tetrapod fore
and hind limbs, or we will not discuss if such fins should necessarily disappear, as the fish was winding about
on land [ like a snake ] by undulating the whole body in a horizontal movement. Let me only stress here the fact that
such a creature entering land must have had a real motivation to move forward onto a new and hostile environment !
A small-brained, also physically unadapted, crossopterygian fish would be indeed
not capable to undertake such an adventure.
This biological fact seems to have been forgotten, perhaps because observers have adopted
the habit of imagining here something like a tadpole that leaves its native pool, before changing into a land-living and
air-breathing frog !
The first land vertebrate really had -without any assistance of heredity- to adapt itself to a strange
new world, to avoid the drying of its organism, to endure and support the daily changes in temperature, to carry a body that
became heavier on land... Food searching was also a problem ! It was necessary to improvise and to make
do with what was possible to find on land : algae, perhaps a few animals with shells, or arthropods.
During the Precambrian time, the archaic vertebrate already made the decisive step towards
land-conquest, leaving the ocean where its ancestor have lived. Our present human endeavour and trend to travel through
countries and to reach new unexplored places is still a continuation of this fundamental trend of archaic
The Homonculus in its archepagoge [ full aquatic ] stage has just
developed its brain, its osseous skull and its limbs. The spinal column, quite upright, was indeed ossified before
the pre-hominid left the water ! Dessication and thermic regulation of the whole body were the chief problems for a
creature that was trying to make the ’big step’ out of the ocean... On land, the differences in temperature are large and sudden.
It was very essential, too, to avoid the dessication of the body. The skin of the first land vertebrate
had to be kept supple, but also covered with an outer horny layer that would restrict the loss of water,
and owning an isolating hairy coat ! The sweat glands in the skin did intervene in case of too much heat,
producing sweat which evaporated and cooled the organism. The sebaceous glands served to lubricate the skin and the hairs.
This is a self-regulatory system, able to maintain a stable body temperature, despite external variations.
Such control permitted an adaptation to life on land after past life in the ocean.
The development of teeth which allow the Homonculus to chew and to digest its food more
quickly is connected with the acquisition of homeothermy, which also requires a great need of energy.
The apparition of isolating hairs is indeed connected with the demand for thermoregulation. All these characters
were present before the end of the aquatic stage !
The globular form of the human skull, also a primitive ( plesiomorphic ) feature,
represents the final evolution of the sea-living Homonculus’s floating and sustenance organ :
such a round configuration could only develop naturally in water !
This ocean-dwelling pre-hominid then started to evolve into the first land-living ’true’ vertebrate.
This is what I refer to as ’Homonculus in his phytophore stage’, or ’archaic man’. As we have also
emphasized, this creature had an inborn tendency to explore, and he possessed an effective nervous
system [ the big brain developed from the marine floating organ ]. The Homonculus already had the
required physical pre-adaptations, such as : bipedal gait and orthograde body-position, air-breathing,
thermoregulation, and digestive organs that allowed him to eat the terrestrial plants and the small animals that were living all around.
Hypothetical reconstruction of the Homonculus
at his phytophore stage,
as the first vertebrate that ever entered land
Bipedalism certainly preadapted the early hominids to a life on land. The upright position was already
acquired before leaving the ocean lagoons. Further modifications of the post-cranial skeleton, such
as the configuration of the plantigrade foot, resulted from the constraints that were imposed by the environment,
and by an active awareness of these new terrestrial habits.
It was, indeed, in remote times, the completion of the human form, and the conception
of the original type of placentary mammals. The phytophore Homonculus presented the important new
characteristic of conceiving and bringing into world living young [ offsprings ]. Before the birth, the childs
grows and develops in his mother’s uterus. The placenta is the organ that feeds and discharges it from
wastage [ through the umbilical cord ], while the amnios is the cavity filled with water
where the ftus floats.
A derived feature is that of the mammals without placenta ( Marsupialia ),
and of other vertebrates ! There may be a ’more evolved’ feature in the egg-laying of birds, reptiles and also
of some mammals ( Monotremata )... where the embryo [ which still needs to develop in water ] is
surrounded with the same amnios. This organ then becomes superfluous when the level of organization of amphibian
and fish is reached ! They indeed constantly live in water, or use water for their larvae [ which exhibit
aquatic specialization : this allows the species to spread through lakes and rivers ! ]. The eggs
of fishes and of amphibians are consequently without calcarious shell, and don’t develop the amnios or allantois
of ’higher vertebrates’.
Now, thanks to his viviparity, the Homonculus on land should have assured a good rate
of reproduction. Above all, this disposition permitted a complete growth of the big brain in the uterus, and
preserved the globular form of the human ’primitive’ skull. Viviparity also allowed a definitive independence
of all aquatic contingencies.
Just after this hard step of leaving the water, the terrestrial Homonculus was ready to
colonize this new milieu that became open to it. By pursuing their structural evolution ( specialization )
beyond the achievement point of the human form, diverse mammalian creatures could arise...
a part of them became quadrupeds by adaptation, but all belonged originally to our own bipedal line
of ascent !
These animals established on dry land and in many other ( for exemple, semi-aquatic )
environments, or also reintroduced the ocean. In this way, fishes ( Pisces ) themselves have returned
secondarly to life in water, just like some reptiles or mammals did. In such a hypothesis, today ( and fossil )
groups of fishes evolved several times from different ’amphibian’ lineages, which developed themselves from reptiloid quadrupeds.
From his remote prehuman ancestors, man has inherited the ability to stand erect on his hind legs
( initial bipedalism ). The forelimbs, relieved from any locomotory function, were set free - since the
beginning - to serve the large brain in providing for its needs.
As a matter of fact, man has remained morphologically and anatomically the same through out the
course of geologic ages. Among living - and fossil - vertebrates, he is the least removed from the
ancient prototype !
Man preserved the original orthograde body position, a head resting
without musculature support on the vertebral column, a big brain and the round-shaped skull,
the hands in primitive form and the plantigrade foot.
Many features ( aptitude of perfect bipedal gait ! ) have been lost by today apes,
and already by australopithecines and other fossil-known hominoids. The chin, also, kept in man its original characteristics,
while it has disappeared in other primates [ included ’Homo erectus’ and similar forms ] because
of the strong development of the jaws, the lengthening of the skull, and the specialization of teeth. These various groups
of homin(o)ids have followed their own evolution parallel to Homo sapiens’ progression, and at the
same time branching out in different lineages. Such a process is called : dehumanization.
Another evolved feature in hominoids may be the development of animal hairs that
are added to original human hairy coat. It’s a relevant characteristic of dehumanized beings,
demonstrated for instance in Dr. Heuvelmans’ Homo pongoides [ see the illustration to the article
of Michel Raynal in the same issue of Bipedia ] and by living apes.
The unborn chimpanzee, indeed, has hair on his head like a human, but little hair on the body. Then,
the ape-baby develops his specific hairs. The apparent ’hairlessness’ of man is not due to an absence of hairs, but it is
due to the fact that these hairs remain normally small and thin. As a matter of fact, man is not a ’naked ape’...
and the apes’ hairs are the result of a more advanced evolution than man never followed !
The strong development of the teeth, jaws, chewing muscles, and mouth of non-human
mammals is indeed in inverse proportion to the brain development. At a certain point of its embryogenesis, the
animal embryo carries on developing after the point where the human embryo was complete...
and the formation of a large brain is countered as dentition and jaws become more powerful !
As a matter of fact, only the human lineage ( Homo sapiens ) preserved
a primordial brain disposition and a globular skull [ which were acquired before the passage from an
aquatic to a terrestrial existence ]. This indeed carries the problem of anthropogenesis back to
a very early stage in the evolution of the vertebrate line...