Updated human evolution video now extends back to Cambrian chordates

A human evolution video
listing and describing the ancestors of humans going back to Devonian tetrapods has been removed and updated to include recently added fish and chordates in our lineage going back to the Cambrian. Click to view this new 12:40 video on YouTube:

Gone are the more famous ‘transitional tetrapods’
Acanthostega and Ichthyostega. In their place are more direct transitional tetrapods, like Koilops and Trypanognathus. These taxa share more traits with their flat, small-lobed ancestors, Panderichthys and flat, small-limbed descendants, like Trimerorhachis, leading to frogs and reptiles… and ultimately mammals and humans.

Gone is the more famous ‘basal reptile’,
Hylonomus. In its place are the amphibian-like reptiles, Gephyrostegus and Silvanerpeton. The latter nests as the last common ancestors of all amniotes in the large reptile tree (LRT, 1691 taxa), the data source for the current list of human ancestors in the video.

Figure 1. From the Beginning - The Story of Human Evolution was published by Little Brown in 1991 and is now available as a FREE online PDF from DavidPetersStudio.com

Figure 1. From the Beginning – The Story of Human Evolution available as a FREE online PDF from DavidPetersStudio.com. Click here to view.

All of this interest
in evolution and human ancestry stems from research during the production of the book From the Beginning (Peters 1991). Back then it took 36 discrete steps from DNA to Homo to tell our story. While unprecedented for its time, that story can now be told more accurately with the addition of 50 more taxa based on knowledge gained in the last nine years while working on and constantly  improving ReptileEvolution.com.

Proviso: This nearly 30-year-old book includes both Ichthyostega and Hylonomus, so it is no longer up-to-date. That’s how science works, falsifying and building upon past hypotheses.

 

Evolution of consciousness in the human lineage

The following statements include several guesses
because no one has a talent for reading the ‘mind’ of a flatworm or any other animal. Levels of consciousness are surmised and estimated from sensory organs present and recorded behavior.

Bear in mind
that at the genesis of flatworms and roundworms there were no more advanced or dangerous predators present.

However, thereafter and until the present day,
a series of both vertebrate and invertebrate predators became important factors.

1 Flatworms (basal bilaterals ~ Ediacaran)
have a need and ability to get from ‘here’ to ‘there’, driven by desire (e.g. hunger) and thereafter finding shelter after satisfied. Flatworms have a ‘front’ in which primitive eyes capable of seeing blurry light vs dark are present. Nerve tissues are also concentrated toward the front. The ‘mouth’ is also the ‘anus’ and this opening is located ventrally and centrally in primitive flatworms. Flatworms sense pain (measured by a reflex response) of various sorts (physical, thermal, chemical). Flatworms seek the chemtrails of potential mates and avoid those of predators.

2 Ribbonworms and Roundworms (Cambrian)
The nervous system is concentrated in a single, central nerve chord and the skin is tough, but sprinkled with nerve endings. The mouth has migrated to the front while the anus has migrated to the rear. Roundworms dig to avoid predators and seek food using whole body all-axis undulation, rather than the cilia found beneath primitive flatworms. Fertilization is internal with genders separated into male and female, so not all conspecific individuals are potential mates. Pheromones are likely produced (and sensed) to indicate gender with sexual excitement present prior to fertilization.

Figure 1. Extant lancelet (genus: Amphioxus) in cross section and lateral view. The gill basket nearly fills an atrium, which intakes water + food, sends the food into the intestine and expels the rest of the water.

3 Lancelets (basal chordates ~ Cambrian)
Coordinated swimming (restricted to lateral undulations), in a 3D environment.  Lancelets collect in colonies, half-buried in sand. Drifting plankton are snared by mucous strands inside the oral cavity. Males expel sperm and females expel eggs for external fertilization on a mutual chemical stimulus (taste + olfaction) released into water.

4 Fish (basal vertebrates, craniates ~ Ordovician, Silurian)
Reversing back to flat and round worms (in contrast to living lancelets), basal fish pursue their prey which, consist of tiny defenseless organisms primitively (e.g. whale sharks, manta rays), building slowly to larger prey. More sensitive sensory organs (eyes with a lens and cornea + nostrils) and a brain appear, along with balancing organs (semi-circular canals) and lateral lines, increasing the sensory input. The tail pushes the head where it wants to go (e.g. toward prey), like a rocket engine on a guided missile. Sharks see in shades of gray. Bony fish see in color. Some fish migrate during ontogeny (from spawning, to feeding and nursery zones). Thus migration is driven by a subconscious (instinctual) sense of time.

Figure 1. Loganellia, from the Silurian, had a large, wide gill chamber inside a low skull.

Figure 2. Loganellia, from the Silurian, had a large, wide gill chamber inside a low skull.

5 Amphibians (basal tetrapods ~ Devonian)
At their genesis amphibians clamber through muddy waters, then soft and very wet muddy and sandy banks, then more substantial substrates above the surface of the water. Amphibians are instinctively driven back to water for sex and egg-laying. As in primitive fish, hundreds of eggs are laid and no care is offered to hatchlings of basal amphibians. Terrestrial amphibians can get thirsty, so they absorb water through the permeable skin of their belly and inner thighs when needed. Frogs have eardrums for hearing social frog songs and croaks. Amphibans have a nictating membrane and tear glands to moisten the eyeball. A fleshy tongue is not only more sensitive to irritants and poisons, but muscular and capable of manipulating food. Amphibians retreat underwater when disturbance is detected by others nearby. Amphibians lose sensory organ sensitive to aquatic vibrations: the lateral line system and porous bony scales,

6 Reptiles (basal amniotes – Early Carboniferous)
Typically silent, reptile mates are encountered by following scent trails. The nostrils are at the tip of the snout facilitating the detection of chemtrails. Internal fertilization requires cloaca to cloaca contact. Gravid females have greatly expanded abdomens prior to laying eggs. So they are heavy and awkward when the eggs are at their largest. With a slender stapes, reptiles are capable of hearing higher pitched sounds. Basal reptiles remain cold-blooded so they present themselves to warm sunlight and seek shadows when overheated.

Figure 2. Silvanerpeton from the Upper Viséan (331 mya) is the outgroup taxon for Gephyrostegus and the Amniota.

Figure 3. Silvanerpeton from the Upper Viséan (331 mya) is the outgroup taxon for Gephyrostegus and the Amniota.

7 Basal synapsids (Early Permian)
Early in this lineage saber-toothed Biarmosuchus was an apex predator. In smaller, more derived taxa, families and colonies gathered in dens that are purposefully and instinctively dug anticipating a future need to avoid weather, enemies, etc. and to raise tiny young out of danger.

Biarmosuchus, the most basal therapsid.

Figure 4. Biarmosuchus, a basal therapsid.

8 Basal mammals (Late Triassic)
Larger brains increase visualization (creating a mental map) during nocturnal activities in which hearing and olfaction came to dominate sight (with loss of color vision). Lactation and nursing increased hormonal releases that helped bond mothers to infants, which were tiny and helpless upon hatching.

9 Basal therians (Early Jurassic)
A prehensile ability was added to the tail (e.g. Didelphis, the opossum) as a sensory and locomotory organ. This was lost in many derived marsupials. Young were no longer raised in a den, but were carried about by the mother until large enough to survive on their own. This time period permitted learning for the young and extended the sense of a mother’s love and responsibility for her juveniles.

Figure 1. The marsupial, Monodelphis domestica, nests as a sister to Eomaia, the oldest known placental.

Figure 5. The marsupial, Monodelphis domestica, nests as a sister to Eomaia, the oldest known placental.

10 Basal arboreal placentals (Middle Jurassic)
Increased metabolism and brain size led to faster locomotion in a 3D arboreal environment that included leaping, often with young attached. Nests were built for some young to permit the mother to roam seeking more food. This was required (3x their own weight every day) by faster growing juveniles. Rapid-eye-movement dreaming first appears. Basal placentals can be aggressive to their own kind.  Patrol areas are marked off with scent glands and body waste.

Figure 2. Human evolution back to the cynodonts, some 230 mya.

Figure 2. Human evolution back to the cynodonts, some 230 mya.

11 Basal primates (Cretaceous)
Increasingly arboreal, primates have better hand-eye coordination. Objects are brought to the nose and mouth by the hands. The hallux and pollex (thumb and medial toe) become better at grasping and manipulating objects. Social vocalization reappears (from the days of amphibians). Colonies appear, some with leaders and followers, facilitated by dominance and submission. Aggression and mutual grooming may keep the group in order. Individuals are identified by variations in the face and hair. Facial expressions originate here, at first by drawing back the lips to expose the canines. Binocular vision appears. Color vision and dreaming returns with a switch to a diurnal (daylight) existence. Rather than nervously cocking their heads to estimate leaping distance, primates maintain a steady gaze, like that of a cat. Nictating membranes disappear. Primates have a longer pregnancy with fewer young, down to one at a time, rarely twins. Vegetation added to the diet. The lifespan becomes longer (e.g. 18 years for lemurs) facilitating multi-generational help in raising young.

12 Basal anthropoids (apes ~ Eocene)
Delight, humor and sympathy appear. A sense of self is apparent. Sitting on haunches takes more time. The loss of the tail includes loss of the use of this appendage for sensory, signaling and locomotory functions. In its place a new form of locomotion: brachiation (hanging and swinging from one branch to another). Apes are more adaptable and teachable. They hide food for later use. Sexual union is used for more than just reproduction (e.g. dispute settlement).

13 Humans (recent)
This is when the behavioral growth curve of consciousness ascends exponentially. With increased brain size and larger social groups comes object trading, cooperation and coordination with strangers, music, art, dance, speech, invention and respect for the dead (e.g. ceremonial burial). Bipedal locomotion frees the hands to carry things (e.g. possessions, children, food and weapons). Pair-bonding replaces harem collecting due to greater interdependence on tribe members. Tribes are formed for mutual defense and offense. Walking and sharing food evolves into nomadic tribal culture. The ability to throw rocks and spears enables humans to kill without the risk of hand-to-hand, tooth and claw killing.

Instinct reduced, learning enhanced
The brain increases in size as cooperation during the hunt, muscular coordination for the hurling of stones, and the mental ability to detect deception become more and more important. The nose opens ventrally, permitting dives underwater.

Visual signals for sexual receptivity
become hidden when females assume a bipedal configuration, so the frenzy of a mating season is reduced. A courtship period (e.g. dating) aids to establish mutual trust. The rate of reproduction rises to about 5x that of apes due to being able to carry infants in various ways and by the aid given by neighbors and older tribe members.

Dreams
are the brain’s way of ‘keeping the motor running’ while asleep, helping to store memories. Dreams work in the subconscious with images generated without sensory input, often with strangers, strange places and strange goals that go beyond an individual’s ability to decode them.

Other taxa
(e.g. parrots, dogs, elephants, dolphins) had their own evolution of consciousness at appropriate nodes after shared ancestors. Aside from humans, there are only a handful of animals able to recognize themselves in mirrors: elephants, gorillas, Rhesus monkeys, magpies, dolphins, orcas, pigs.

Some YouTube videos
(below) may prove helpful for additional information on this topic.


References
Peters D 1991. From the beginning – the story of human evolution. Little Brown. PDF

wiki/Mirror_test
wiki/Pain_in_invertebrates

https://www.youtube.com/results?search_query=human+consciousness

Why did humans evolve ever-growing cranial hair?

How humans evolved to have head / beard hair
“that continues to grow longer than other animals, while losing hair elsewhere, is a topic that many anthropologists & biologists are still not sure about and there is no general consensus as to “why” yet.”

The following hypotheses are copied from the online references below.
They do not represent my original thoughts or anything to do with the LRT. Academic citations follow and can be accessed via the reference links.

The three main views are:

1) Evolution of the “Aquatic Ape.” (Ingram, 2000: Morgan 1997; 1982)

  • Infants, in order to hold onto their mothers in the water, would latch onto her hair. Limiting separation from the mother & increasing chances of survivability
  • Longer hair meant that infants / small children would need to swim less in order to get to their mother
  • Believed to be supported even further when you consider that aquatic mammals are almost always hairless, indicating that at one point, humans were highly “aquatic” mammals.

2) No real benefit, but used as a tool for “mate selection.” (Darwin, 1871; Cooper 1971)

  • The view held by many of the Darwin school of thought is that at first, “hairiness” was sexually attractive, but eventually “hairlessness” became more sexually attractive in most places (i.e. the face to see facial expressions & socialize better; Wong & Simmons 2001)
  • A sign of “virility” & “health” as can be seen in the mate-selection behavior of lions. Which is true even today as human diagnostic material for health (Klevay, 1972).

3) Practical evolutionary benefits for the human species specifically

  • A lot of body heat escapes from the head, probably the most important part of your body. Hair is a good insulator that can keep in heat. This increases survivability in colder climates. (Wong & Simmons 2001; Bubenick 2003). (Disputed but considered credible reason, especially when you compare hair length and types across different regions throughout history)
  • Protection against damaging UV rays (while still permitting adequate Vitamin D3 to come through) & some protection from free-radicals or other harmful particles. Because we became bi-pedal, the head was the main area exposed to the sun (as well as some of our back). Extending hair’s usefulness to even hot environments, while other body hair became less important with the development of sweat glands (Wheeler 1985).
  • Heightened “Situational Awareness” through “Touch sense.” A concept that may seem silly at first but has some evidence to support the theory. Though the hair is not “alive,” it is connected to the follicles & your nerves. In a nutshell, it may help to increase “sensory awareness” & “data gathering” of your environment, which would favor longer hair. This would be an asset in survivability (Kardong 2002; keratin.com 2010; Sabah 1974)
  • Though not a collegiate journal article, if reasonably credible, this small article is an interesting case for supporting hair & “Touch sense” in “recent history” & in combat-survival : http://www.sott.net/article/234783-The-Truth-About-Hair-and-Why-Indians-Would-Keep-Their-Hair-Long.

Other thoughts…

“Evolution selected for intelligence – and for hair. The person who radically shapes his hair, exploiting its continuous growth to demonstrate his on-going Neanderthal chic, is more likely to attract partners than the person whose hair is dull, lifeless and matted.”

“Darwin, noting that every human society, however primitive, invariably paints, tattoos, pierces and otherwise decorates its bodies, argued that, in the remorseless competition for sexual partners, we humans, during the evolutionary past, shed our hair to create a canvas on which to flaunt our creativity, flair and beauty.”


In a tweet:
“The reason we (mostly) still have head hair is mostly because it serves as a sun-screen – and the reason we still have pubic hair is because it traps pheromones.”


On the other hand…
“Left alone, our hair produces a three-foot, smelly, matted, greasy, bug-infested mass that will snag on trees and provide predators with a claw-hold.”


Personally
I prefer this one: “diagnostic material for health (Klevay, 1972).” 


References

https://biology.stackexchange.com/questions/5676/why-does-human-facial-and-head-hair-continue-to-grow

https://www.quora.com/Why-have-humans-evolved-to-have-more-hair-on-their-head

https://www.telegraph.co.uk/comment/4263009/Why-does-the-hair-on-our-heads-keep-growing.html

(Human vs chimp) vs (Humans vs chimps)

What makes humans special
and distinct from chimps is our ability to cooperate and remain flexible while cooperating, according to Yuval Harari in his new book, “Sapiens: A brief history of humankind” (YouTube video below, click to play, it’s about an hour long).

Chimps could never work together like this.
From building ships to crossing the ocean to sending men to the moon (Fig. 2) humans work together for a common goal, believing in a common story. Ants and bees work together, but they are inflexible, as are the individual siphonophores working together in the Portuguese man o’war.

Figure 2. Mission control, Houston, Texas. These humans were only a small part of a huge cooperative effort that sent men to the moon and back.

Figure 2. Mission control, Houston, Texas. These humans were only a small part of a huge cooperative effort that sent men to the moon and back. Chimps can’t even imagine doing that.

Stanley Kubrik (2001: A Space Odyssey) got it wrong in this regard.
Not violence (Fig. 3), but cooperation marked the genesis of humankind. Chimps (not bonobos) are all about violence. Most of the time, humans find it more profitable and mutually beneficial to trade and work towards common goals. Ironically, and largely overlooked, in the rest of the Kubrick movie there is little to no conflict between humans. Rather the many products of cooperation (space ships, clothing,computers, polite conversation, sharing sandwiches, etc.) fill the screen, not to mention the speakers (choirs, symphonies, etc.)

Figure 3. Scene from 2001: A Space Odyssey by director Stanley Kubrick. Not violence, but cooperation marked the genesis of humankind. Chimps are all about violence.

Figure 3. Scene from 2001: A Space Odyssey by director Stanley Kubrick. Not violence, but cooperation marked the genesis of humankind. Chimps are all about violence. Many humans (not all, of course) learned to accept the other for the mutual benefit of trade and alliances. After the movie, 2001, was released in 1968 paleontologists discovered that human ancestors stood upright (Fig. 4), rather than crouched as Kubrick and others guessed.

The large reptile tree (LRT, 1281 taxa) includes human ancestors going back to Devonian tetrapods and vertebrates. The last 200 million years or so are captured in the following illustration (Fig. 4). Starting with the trading of stone tools and who knows what else, the genus Homo (erectus + sapiens) slowly, then much more quickly, became the dominant organism on the planet.

Figure 2. Human evolution back to the cynodonts, some 230 mya.

Figure 4. Human evolution back to the cynodonts, some 230 mya. The human hand is compared to the lemur hand.

Communication.
Humans learn quickly from other humans, even dead and distant humans (in the form of writing and recently, YouTube videos). Take the invention of the airplane for example. The Wright brothers invent the steerable, heavier-than-air craft in its most basic form. Glenn Curtiss adds wheels and ailerons. Louis Bléirot puts the the control surfaces in the back and the propeller in the front. Junkers and Co. put aluminum on the skin. Others add jet engines. The point is, no one alone invents the modern jet from scratch. Even though only a few individuals are brilliant enough to innovate, others are smart enough to copy (adopt) a good idea.

Chimps learn from other chimps,
but only by direct contact. Humans learn from from mentors, cuneiform tablets, printed paper and computer monitors.

On that note, and not to be forgotten…
an uneducated human alone on an island can only do so much, not much more than a chimp alone can do given the same starting point (you can’t count education in this test).

European evolution

The attached video from YouTube
shows the changing boundaries and populations of various clades of Europeans and their invading neighbors evolving over a brief amount of time: only 2417 years. You’ll witness growth, death, aggression, expansion, division, union, stasis, invasion, decay and exploration.

In evolutionary terms, Europe is a petrie dish
and we who have ancestors that lived there with rising and falling fortunes. And there is no reason to suggest that things will never change in the future. Similar videos have appeared for Asia, the world, various words, etc. etc.

Things happen.
Weather changes. Volcanoes spew. Diseases decimate. People interbreed and emigrate. Languages change. So does DNA. Sometimes education is elevated. Sometimes religion is elevated. Sometimes slaves are imported. Sometimes slaves are freed. Sometimes autocrats run amok. Sometimes cooler heads prevail.

Somehow everyone living today
had an unbroken chain of ancestors going back to tetrapods in the Devonians, chordates in the Cambrian and worms in the Ediacaran and beyond. All of this is evolution at its finest, both short term (Fig. 1) and long.

Homo floresiensis compared

Brown et al. 2004
described this diminutive (1.1m tall) Indonesian “hobbit” (Fig. 1) from 190,000–50,000 years ago.

Figure 1. Homo floresiensis compared to Homo sapiens. Not much difference, other than the chin and cranium. Not to scale.

Figure 1. Homo floresiensis compared to Homo sapiens. Not much difference, other than the chin and cranium. Not to scale.

Is this a species distinct from Homo sapiens?
The consensus says “Yes.” But many workers identified the best skull as a severely pathological Homo sapiens. We’ve seen this in our branch of paleontology when workers describe things they desire to see rather than things that are present (or absent) and to disregard taxa and traits that don’t fit their world view. Better to let the software make the important decisions when bias has any chance of influencing results.

Identifying features of H. floresiensis include:

  1. smaller body
  2. smaller cranial capacity
  3. the form of the teeth
  4. lack of a chin
  5. smaller angle in the humerus head

That’s not a long list
because the hobbit is indeed very close to extant humans.

Figure 2. Homo floresiensis to scale compared to Homo sapiens

Figure 2. Homo floresiensis to scale compared to Homo sapiens The central portion of the H. floresiensis skull has been restored here.

References
Brown P et al. 2004. A new small-bodied hominin from the Late Pleistocene of Flores, Indonesia. Nature. 431 (7012): 1055–1061.

https://en.wikipedia.org/wiki/Homo_floresiensis
and other links therein

The human occiput and palate

We looked at the facial portion
of the human skull earlier. Today we’ll look at the occiput and palate (Fig. 1).

Figure 1. Human occiput and palate. On most tetrapods these two are usually set at right angles to each other, but an upright stance has rotated the occiput to a ventral orientation.

Figure 1. Human occiput and palate. On most tetrapods these two are usually set at right angles to each other, but an upright stance has rotated the occiput to a ventral orientation.

There’s nothing new here. 
This is just an opportunity to educate myself on the human palate and occiput. Only the endotympanic (En) is a novel ossification. The occiput is a single bone here, the product of the fusion of several occipital bones. Can you find the suborbital fenestra? It’s pretty small here.

The asymmetry is interesting here.
Sure, this is an old adult, missing some teeth, but you’ll see other examples elsewhere.

Let me know
if you see any errors and they will be corrected. As you already know, everything I present here was learned only 48 hours earlier — or less.

Basal hominid, fenestrasaur and archosaur analogies

When you look at the transition
from quadrupedal locomotion to bipedal locomotion in early hominids (Fig. 1), among many other details, you can’t help but be impressed by the increase in the relative length of the hind limbs.

Figure 1. When hominids became bipedal, their hind limbs became longer.

Figure 1. When hominids became bipedal, their hind limbs became much longer.

The same can be said
for the transition from semi-bipedal Cosesaurus (based on matching Rotodactylus tracks) to the fully bipedal Sharovipteryx (Fig. 2).

Figure 2. Cosesaurus was experimenting with a bipedal configuration according to matching Rotodactylus tracks and a coracoid shape similar to those of flapping tetrapods. Long-legged Sharovipteryx was fully committed to a bipedal configuration.

Figure 2. Cosesaurus was experimenting with a bipedal configuration according to matching Rotodactylus tracks and a coracoid shape similar to those of flapping tetrapods. Long-legged Sharovipteryx was fully committed to a bipedal configuration, analogous to hominids.

As in hominids,
freeing the fore limbs from terrestrial locomotion enabled fenestrasaurs to do something else, like flapping for secondary sexual displays, adding motion to their morphological ornaments. While the forelimbs were relatively smaller in Sharovipteryx, they were relatively larger in Bergamodactylus (Fig. 3) a long-legged basal pterosaur. There were no constraints on forelimb evolution in fenestrasaurs, analogous to theropod dinosaurs that ultimately became birds. Some theropods and birds grew larger forelimbs, while others reduced their forelimbs.

Figure 2. Updated reconstruction of Bergamodactylus to scale with an outgroup, Cosesaurus.

Figure 3. Updated reconstruction of Bergamodactylus to scale with an outgroup, Cosesaurus.

Lest we not forget
in the basal archosaurs (crocs + dinos) early attempts at bipedal locomotion (Fig. 3) also corresponded to a longer hind limb length in bipedal Scleromochlus and Pseudhesperosuchus as opposed to their common ancestor, a sister to short-legged Gracilisuchus.

Figure 3. Short-legged Gracilisuchus, along with sisters, long-legged bipedal Pseudhesperosuchus and Scleromochlus.

Figure 3. Short-legged Gracilisuchus, along with sisters, long-legged bipedal Pseudhesperosuchus and Scleromochlus.

Based on those tiny hands,
the forelimbs of Scleromochlus were becoming vestiges. Based on the long proximal carpals of Pseudhesperosuchus, the manus was occasionally lowered to the ground, perhaps while feeding. The origin of bipedal locomotion in basal crocs is the same as in pre-dinosaurs.

It took much longer and proceeded more indirectly
for bipedal archosaurs to start flapping their forelimbs, giving them a new use that ultimately produced thrust and lift as bird forelimbs continued to evolve and become larger.

See videos produced by ReptileEvolution.com
on the origin of dinosaurs here, on the origin of humans here, and on the origin of pterosaurs here.

A sign of beauty and/or Olympic potential
is a long-legged model or athlete.

New Evolution of Humans Video on YouTube

The origin of mammals from cynodonts is universally accepted.
The origin of humans from primates is universally accepted among paleontologists, not among religious conservatives. Perhaps this short video can help fact check a few misconceptions.

Figure 1. Human evolution video on YouTube. Cllick to view.

Figure 1. Human evolution video on YouTube. Cllick to view.

Here you’ll see the origin of humans,
and all their many body parts, in a new light. We start with fishy tetrapods, just hitting the beachheads 365 million years ago (mya). By 340 mya the first reptiles were already diversifying. Our lineage goes on from there in a stepwise progression with novel traits appearing with each successive taxon every few million years in the fossil record.

The record is becoming more and more complete.
Using the closest known sister taxa to the actual lineage we can document a gradual accumulation of human traits, both bones and soft tissues, as well as likely behaviors based on phylogenetic bracketing. Here the human lineage runs through the reptilomorphs and seymouriamorphs, the basal reptiles, the synapsids, the therapsids, the cynodonts, the mammals, primates, anthropoids and hominids, only some of which ultimately evolved to become human.

Feel free to pause the video
at any point if scenes change before you finish reading a frame.

Look for other YouTube videos
that document the origin of pterosaurs, dinosaurs and turtles in a similar fashion.

More details and reference materials
can be found at ReptileEvolution.com

Want more?
For the story of human evolution going back through raw chemicals, cells, worms and fish (along with all of the above taxa), read “From the Beginning, the Story of Human Evolution” by David Peters (Little Brown, 1991), a copy of which can be found as a pdf online at www.davidpetersstudio.com/books.htm

The origin of feathers and hair (part 2: hair)

Yesterday we looked at reptile skin and scales, alpha and beta-keratins and examined the fossil record of scales, naked skin and pterosaur extra dermal membranes. Today we’ll take on mammal hair.

Pre-mammals
Mammals, like Megazostrodon, evolved in the Jurassic from synapsid reptiles, like Archaeothyris, that first appeared in the Late Pennsylvanian.

Dhouailly 2009 reports: “The synapsid lineage, which separated from the amniote taxa in the Pennsylvanian about 310 million years ago, may have evolved a glandular rather than a scaled integument, with a thin alpha-keratinized layer adorned with alpha-keratinized bumps. Those bumps may have even presented some cysteine-rich alpha-keratins, precursors of the hair-type keratins. In addition, the first synapsids may have developed both a lipid barrier outside the epidermis, similar to current amphibians living in xeric habitats, and some lipid complex with the alpha-keratins of the stratum corneum as in current mammals as a means to strengthen the barrier against water loss of the integument.”

So reptilian scales were never part of the mammal legacy — just naked glandular skin.

Mammals
A dense coat of fur is found in all basal extant mammals, even those that lay eggs. Thus the origin of hair is to be found in the common ancestor of all living mammals, perhaps among therapsid-grade synapsids (Thrinaxodon Chiniquodon), or, more conservatively, perhaps right at the origin of early Jurassic mammals.

Dhouailly 2009 reports: “No intermediate form has ever been found between scales and hairs, resulting in only a few proposals of how mammalian hairs may have evolved from scales. These proposals were based on the development of sensory bristles in the hinge scale region of reptiles.”  Unfortunately basal reptiles and therapsids did not have scales (see below).

The traditional cynodont whisker hypothsis
Foramina (tiny holes) on the faces of basal gorgonopsians, therocephalians and cynodonts have been interpreted as providing passages for nerves and blood vessels supplying movable skin (subcutaneous muscles) and sensory vibrissae (whiskers). This would represent the first appearance of hair only to be followed by more and more hair spreading around the body. This essentially duplicates the new hypothesis on feather origin by Persons and Currie (2015, see that discussion tomorrow).

Unfortunately for this hypothesis,
the basal lizard, Tupinambis has similar rostral foramina, yet it lacks sensory vibrissae (Bennett and Ruben 1986).

An alternate mammal hair genesis hypothesis
Given that pelycosaurs and Estemmenosuchus were naked and had no hair, the origin of mammal-type hair must have occurred closer to mammals. On their way to evolving into mammals, taxa like Pachygenelus and Megazostrodon became progressively smaller in a rather common process known as phylogenetic miniaturization (the opposite of Cope’s Rule).

Due to their increased surface/volume ratio, smaller animals find it more difficult to internally thermoregulate because their insides are closer to their outsides. Having insulating fur when tiny would be helpful. That’s the traditional hypothesis for mammal hair genesis in tiny taxa, like Megazostrodon. Unfortunately the insulation hypothesis gives no reason for the first appearance of tiny sprigs of precursor hair, not yet plentiful enough to trap air (for insulation). Nor does it take into account that the smallest of all basal mammals, their newborns, are hairless.

Dhouailly 2009 reports: “Hairs [may have] evolved from sebaceous glands, with the hairshaft serving as a wick to draw the product of the gland to the skin surface, strengthening the barrier against water loss.”

Figure 2. An automobile driver can sense the presence of the curb on approach when a curb feeler is in place. This saves wear and tear on tires, just like individual hairs would touch the inside of burrows before the skin comes into contact.

Figure 2. An automobile driver can sense the presence of a curb on approach when a “curb feeler” is in place. This saves wear and tear on tires. Similarly individual hairs would touch the inside of burrows before the skin comes into contact.

The curb-feeler hypothesis
As others have noted, individual hairs provide tactile feedback. Those are especially useful to nocturnal and burrowing animals.

Naked mole rats provide a good analogy. Like therapsids, naked mole rats burrow, adjust their internal temperature to ambient temperatures, AND they have only a few whisker-like hairs that crisscross the body to form a sensitive array that helps them navigate in the dark. We know that certain small cynodonts were  also burrowers. That’s where we find them. We don’t know if they had whisker-like hairs that crisscrossed their body. Only the bones are preserved.

In this way,
individual hairs would have been like curb-feelers (Fig. 2), small wires that make a noise whenever a 1950s era automobile approaches a curb. Thus provided, basal mammals could have avoided multiple abrasions while running through their tunnels using their own curb feelers.

Nevertheless,
if that’s how hair started, once provided with the ability to grow hair, simply growing more hair would have provided incremental opportunities to spend more and more time outside of the burrow. Hair insulated mammals not only from ambient temperature, but from the environment at large, including the approach of winged insects like flies and mosquitoes. Note that those insects that finally developed the ability to burrow past the hair barrier, fleas, lost their wings in order to do so.

Navigation skills
learned in dark tunnels could be readily transferred to leaf litter in the open air at night (all the while avoiding the predatory gaze of hungry Jurassic dinosaurs).

Opossum tail showing rectangular eupelycosaurian scales

Figure 2. Opossum tail showing false scales. A couple of ‘curb feelers’ appear on the proximal tail.

The “scaly tail” of mammals,
like the opossum (Fig. 2), is actually, a criss-cross series of epidermal folds interspersed with hairs, not homologous with the scale of any other animal (Dhouailly 2009).

Figure 3. Naked mouse babies surround the furry mother mouse.

Figure 3. Naked mouse babies surround the furry mother mouse. The babies may be recapitulating evolution as they are naked and unable to maintain their own body temperature without a little help from mom.

The surprising origin of mammary glands
Dhouailly 2009 reports: “The mammary gland apparently derives from an ancestral sweat or sebaceous gland that was associated with hair follicles, an association which is retained in living monotremes, and transiently in living marsupials. The original function of the mammary gland precursor may not have been feeding the young, but as a means to provide moisture to the eggs.”

Tomorrow: dinosaur feathers.

References
Bennett AF and Ruben JA 1986. The metabolic thermoregulartory status of therapsids. In The Ecology and Biology of Mammal-like reptiles (Hottom, Roth and Roth eds) 207-218. Smithsonian Institution Press, Washington DC
Chudinov PK 1970. Skin covering of therapsids [in Russian] In: Data on the evolution of terrestrial vertebrates (Flerov ed.) pp.45-50 Moscow: Nauka.
Dhouailly D 2009. A new scenario for the evolutionary origin of hair, feather, and avian scales. Journal of Anatomy 214:587-606.
Persons WC4 and Currie PF 2015. Bristles before down: A new perspective on the functional origin of feathers.Evolution (advance online publication) DOI: 10.1111/evo.12634