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.

 

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

Why do human males develop facial hair?

Distinct from other apes,
human males develop facial hair at puberty that creates a beard and mustache. Then many men shave it off. If you’ve ever wanted to know why, here are some recent hypotheses.

According to the BBC online, “beards probably evolved at least partly to help men boost their standing among other men.” because women are not more interested in men with beards. “To reproduce, it’s often not enough to simply be attractive. You also have to compete with the same sex for mating opportunities.”

“A man’s ability to grow a fulsome beard isn’t actually neatly linkedto his testosterone levels. “

“Both men and women perceive men with beards as olderstronger and more aggressive than others. And dominant men can get more mating opportunities by intimidating rivals to stand aside.”

Figure 1. Percent of body hair on males worldwide appease here in darker tones. Both equatorial and polar humans have less hair. Mediterranean and Scandinavian men have more hair covering their bodies.

Figure 1. Percent of body hair on males worldwide appease here in darker tones. Both equatorial and extreme polar humans have less hair. Mediterranean and Scandinavian men have more hair.

“Men on average also think their body should be more muscular than women report that they want, while women on average believe they need to be thinner and wear more make-up than men report that they want.”

“Make-up use, average body composition, and even the very ability to grow facial hair all differ enormously across the world – meaning we could get different results elsewhere.”

This BBC article originally appeared on The Conversation (links below).


References
Dixson A DSc, Dixson B and Anderson M 2005. Sexual Selection and the Evolution of Visually Conspicuous Sexually Dimorphic Traits in Male Monkeys, Apes, and Human Beings, Annual Review of Sex Research, 16:1, 1-19, DOI: 10.1080/10532528.2005.10559826

http://www.bbc.com
https://theconversation.com

(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).

Gorilla skull compared

Today’s blog is essentially a silent movie.
Just sit back and compare these two skulls: Gorilla gorilla vs. Homo sapiens. Note the differences AND the similarities.

Figure 1. Gorilla skull with DGS colors applied to distinguish the bones. Compare to Homo sapiens in figure 2.

Figure 1. Gorilla skull with DGS colors applied to distinguish the bones. Compare to Homo sapiens in figure 2.

Figure 2. Labeled skull bones in Homo sapiens.

Figure 2. Labeled skull bones in Homo sapiens.

Some subtle points you may have missed:

  1. Human upper canines are not behind the lower canines
  2. Human incisors are larger than the canines
  3. The pterygoid is visible through the orbit
  4. The rims and ridges around the temporal opening in Gorilla are anchors for jaw muscles, all reduced in Homo.
  5. The bridge of the nose in Homo is lacking in Gorilla
  6. Perhaps I missed a few you’ll notice…

Taxa closest to the human lineage in the LRT

The large reptile tree is capable of providing a list of taxa closest to the lineage of any included taxon. And it is updated all the time…

For instance,
in the lineage of humans (Homo sapiens) the following taxa are closest to that main line. Read this list with the understanding that taxa closest to the main line have often evolved traits that we infer (from phylogenetic bracketing) were not present in the actual hypothetical ancestor. The chance of finding the actual ancestors in the fossil record are vanishingly small, so we do the best we can with what specimens we have. Also note that the rare appearance of key fossils may be tens to hundreds of millions of years after their likely first appearance in this lineage. Thus the the chronological order may not match the phylogenetic order, but it does provide a ‘window’ to that first appearance.

  1. Ichthyostegabasal tetrapod  365 mya
  2. Pederpes 350 mya
  3. Proterogyrinus 322 mya
  4. Seymouria 275 mya
  5. Utegenia – also basal to frogs 300 mya
  6. Silvanerpetonproximal to the basalmost reptile 335 mya
  7. Gephyrostegus bohemicusbasalmost reptile/amniote 310 mya
  8. Eldeceeonbasalmost archosauromorph 335 mya
  9. Romeriscus 306 mya
  10. Solenodonsaurus also basal to chroniosuchids 290 mya
  11. Casineria – 335 mya
  12. Brouffia 310 mya
  13. Coelostegus  310 mya
  14. Protorothyris MCZ 1532 290 mya
  15. Protorothyris CM 8617 290 mya
  16. Protorothyris MCA 2149 290 mya
  17. Vaughnictis – last common ancestor of mammals and dinosaurs 290 mya
  18. Apsisaurus –  basalmost synapsid 295 mya
  19. Varanosaurus FMNH PR 1760 280 mya
  20. Varanosaurus BSPHM 1891 XV20 280 mya
  21. Archaeothyris 306 mya
  22. Ophiacodon 290 mya
  23. Haptodus – also basal to pelycosaurs 305 mya
  24. Stenocybus – also basal to anomodontids 295 mya
  25. Cutleria basalmost therapsid 295 mya
  26. Hipposaurusbasalmost kynodont 260 mya
  27. Ictidorhinus 260 mya
  28. Biarmosuchus 260 mya
  29. Eotitanosuchus 260 mya
  30. Lycosuchus 260 mya
  31. Procynosuchusbasalmost cynodont 250 mya
  32. Thrinaxodon 245 mya
  33. Probainognathus 230 mya
  34. Haldanodon 145 mya
  35. Pachygenelus 195 mya
  36. Sinoconodonbasalmost mammal, also basal to living monotremes 195 mya
  37. Megazostrodon 200 mya
  38. Juramaia 160 mya
  39. Cronopio 98 mya
  40. Didelphisbasalmost metatherian extant
  41. Thylacinus – basal to many living marsupials recently extinct
  42. Monodelphisbasalmost eutherian extant
  43. Eomaia 125 mya
  44. Nandinia – also basal to carnivores extant
  45. Ptilocercus – basalmost primate/dermpteran/bat extant
  46. Notharctus – also basal to lemurs 54 mya
  47. Aegyptopithecus* 33 mya
  48. Proconsulbasalmost anthropoid 18 mya
  49. Ardipithecus* basalmost hominid 5 mya
  50. Australopithecus* 3 mya
  51. Homo sapiens extant

* not yet listed in the LRT, but documented at ReptileEvolution.com

With the recent addition of certain stem mammals,
like Haldanodon and Liaconodon, this list expands upon and refines the list that first appeared in Peters 1991. Each of the names links to further information. There is also a video that includes most of these taxa here on YouTube.com.

References
Peters D 1991. From the Beginning, the Story of Human Evolution. online PDF.

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

You Must See: Your Inner Fish with host Neil Shubin

PBS presented part 1 of 3 last night of Your Inner Fish, a new TV series hosted by and based on Neil Shubin’s book of the same name. I recommend this highly. It’s wonderfully done and, it goes without saying, this subject is close to my heart. Shubin is an excellent host and his presentation is clear, true and entertaining.

Figure 1. Click to go to the website. Your Inner Fish is Neil Shubin's 3-part series based on his book of the same name. This the best presentation on human evolution I have seen on TV.

Figure 1. Click to go to the website. Your Inner Fish is Neil Shubin’s 3-part series based on his book of the same name. This the best presentation on human evolution I have seen on TV.

The book, Your Inner Fish, came out in 2008. Here’s the Amazon.com synopsis.
Why do we look the way we do? Neil Shubin, the paleontologist and professor of anatomy who co-discovered Tiktaalik, the “fish with hands,” tells the story of our bodies as you’ve never heard it before. By examining fossils and DNA, he shows us that our hands actually resemble fish fins, our heads are organized like long-extinct jawless fish, and major parts of our genomes look and function like those of worms and bacteria. Your Inner Fish makes us look at ourselves and our world in an illuminating new light. This is science writing at its finest—enlightening, accessible and told with irresistible enthusiasm.”

 

Author Neil Shubin along with this discovery, Tiktaalik.

Figure 2. Author Neil Shubin along with his discovery, Tiktaalik.

How the book came to be as told by author Neil Shubin
“This book grew out of an extraordinary circumstance in my life. On account of faculty departures, I ended up directing the human anatomy course at the University of Chicago medical school. Anatomy is the course during which nervous first-year medical students dissect human cadavers while learning the names and organization of most of the organs, holes, nerves, and vessels in the body. This is their grand entrance to the world of medicine, a formative experience on their path to becoming physicians. At first glance, you couldn’t have imagined a worse candidate for the job of training the next generation of doctors: I’m a fish paleontologist.

It turns out that being a paleontologist is a huge advantage in teaching human anatomy. Why? The best roadmaps to human bodies lie in the bodies of other animals. The simplest way to teach students the nerves in the human head is to show them the state of affairs in sharks. The easiest roadmap to their limbs lies in fish. Reptiles are a real help with the structure of the brain. The reason is that the bodies of these creatures are simpler versions of ours.

During the summer of my second year leading the course, working in the Arctic, my colleagues and I discovered fossil fish that gave us powerful new insights into the invasion of land by fish over 375 million years ago. That discovery and my foray into teaching human anatomy led me to a profound connection. That connection became this book.”

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 3. 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

If you are interested in human evolution and want to see more details on the development of human body parts and — when — they came to be, see “From the Beginning, the Story of Human Evolution” free online pdf here.

Only a few updates to this 1991 book are needed based on more recent discoveries. Updates can be found at reptileevolution.com where you can also read about the evolution of any reptile, from snakes to pterosaurs to whales, dinosaurs and bats, from their fishy genesis through all their transitional taxa.

Congratulations
to Neil Shubin for work well done!

 

 

Our Face, from Fish to Man (Gregory 1929) updated

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 was published by Little Brown in 1991 and is now available as a FREE online PDF from DavidPetersStudio.com

Ever since the advent of evolutionary thought and the quasi-religious and often racist origins for the hypothesis of the “Ascent of Man,” (see below) scientists have illustrated their take on the tree of life, from simple to human.

Knowing little to nothing
of this history, but filled with newbie zeal, back in the day (1991) I wrote and illustrated “From the Beginning – the Story of Human Evolution” which presented 36 steps from raw chemicals to cells, worms, fish, reptiles, mammals, primates and humans. Included, along with skeletons, descriptions and hundreds of figures, was a two-page spread that illustrated the evolution of the human face from a worm on up.

Here’s the Update
Here (Fig. 1), with more taxa (added in gray) the picture is more complete. And, no doubt, this list of images is already incomplete and will continue to grow. But it does provide a good map of the process.

Figure 1. Click to enlarge. The evolution of the human face. Many images come from Peters 1991, From the Beginning.

Figure 1. Click to enlarge. The evolution of the human face to scale from Peters 1991, From the Beginning. Gray images were added recently and modified from those.

Since 1991,
only Haptodus and the tree shrews, Tupaia and Ptilocercus, were dropped from the 1991 list. Ophiacodonts, rather than sphenacodonts, were found to be in the lineage of therapsids. Haptodus was replaced by the very similar StenocybusVulpavus, rather than tree shrews, were found to nest closer to basal lemurs like Notharctus.

It’s noteworthy
that size reduction and size increase is a large part of human evolution, especially at the origin of major clades (Reptilia, Therapsida, Mammalia). Likewise noteworthy are the rotation of the eyes to the front of the skull, the enlargement and reduction of the canines, the development of scales, hair and skin and the loss of gills, the appearance of the outer ear. Earlier we looked at the evolution of the mandible and ear ossicles here.

For anyone interested, a high-rez version is available by request.

Human evolution.

Figure 2. Human evolution back to the cynodonts — and beyond. Click to learn more.

Details also shown at reptileevolution.com

Figure 2. Our Face from Fish to Man by WK Gregory 1929.

Figure 2. Our Face from Fish to Man cover and spine by WK Gregory 1929.

A Long History of Prehistory
The origin of humans has a long history going back several hundred years. More recently, professor WK Gregory of the AMNH published a book in 1929, “Our Face From Fish to Man” (Fig. 2, online here) that was popularized in a magazine viewable here. Like several earlier attempts at ordering the descent of modern humans, it suffers from a certain amount of racial bigotry.

Later WK Gregory (1951) published “Evolution Emerging – A Survey of Changing Patterns from Primeval Life to Man – Two Volumes,” in which more details were added because more fossils had been found (Fig. 3) in the 20 years since his first book.

The “Brain Pickings” blog of Maria Popova has a review of Theodore W. Pietsch  about the history of evolutionary thought and family trees.

Figure 3. From Gregory 1951, pink arrows added. This is essentially the same evolutionary pathway shown in figure 1, with fewer details known more than 60 years ago.

Figure 3. From Gregory 1951, pink arrows added. This is essentially the same evolutionary pathway shown in figure 1, with fewer details known more than 60 years ago.

It seems as if
I have taken up WK Gregory’s mantle, taking it to the next level based on the new taxa discovered between now and then. Unfortunately, at present, this goes unrecognized because publishing online or for a children’s book and without a PhD is not taken as seriously as publishing in an academic journal without a PhD or publishing in an academic journal with a PhD. I’m working on that, but it’s going to take a PhD to recognize the value of the large reptile tree. I don’t see that happening any time soon. So, we’ll keep running alongside the mainstream.

References
Gregory WK 1929. Our Face from Fish to Man, G. P. Pntman’s Sens, New. York.
Gregory WK 1951. Evolution Emerging – A Survey of Changing Patterns from Primeval Life to Man – Two Volumes. Macmillan Company.
Peters D 1991. From the Beginning – The Story of Human Evolution, Little Brown. pdf
Theodore W. Pietsch 2012. Trees of Life – A Visual History of Evolution. Johns Hopkins University Press. online with preview at Amazon

Variation in Homo sapiens – reptile evolution continues

Similarities and differences in the face of humans
Each one of us has eyes, ears, a nose and forehead, but a variety of subtle differences in their shape and placement helps define and distinguish us as individuals. Even twins can be identified given enough familiarity with them. Our similarity binds us together. Our differences make us unique. Variation is very basic to evolution. Over time, enough variation produces new species and larger clades. 

Evolution works in very basic ways.
Overall and in their various body parts, progeny can be distinct from their parents in these several ways (among others unlisted):

  1. larger or smaller
  2. wider or narrower
  3. longer or shorter
  4. more robust or more gracile
  5. more permeable or more durable (skin/scales/osteoderms)
  6. adding protrusions (from horns and hair to feathers to fins to feet and toes) or eliminating them
  7. migrating body parts (more anteriorly, more posteriorly, etc.)
  8. more juvenile or more adult
  9. faster maturation, or slower
  10. colors, shades, transparencies
  11. faster or slower speed capabilities
  12. nocturnal, diurnal
  13. urges to swim, urges to dig, urges to climb

Nearly all of the variation between taxa in the large reptile tree can be attributed to these variations overall or in certain body parts.

Two human males. One has deeper eyes, a protruding chin and less distance from the ear to the back of the head than the other.

Figure 1. Two human males. One has deeper eyes, a protruding chin and less distance from the ear to the back of the head than the other.

Here we’ll show some of the basic elements in the human face.

Chin size
In most humans the chin more or less protrudes. This trait separates us from other species within our genus, like Homo neanderthalensis, as well as archaic members of our own species. No other vertebrates have a chin. It is unique to our species. Lacking a prominent chin nowadays does not make anyone less human. That is just in our gene heritage.

Ear location
The anterior rim of the ear flap is found at the apex of the mandible, in keeping with the origin of the ear bones as former jaw bones. The location of this point can be near to the back of the skull or far (Fig. 1).

Eye location
The eyes can be large and close to the profile (Fig. 1) or deep set and further back from the profile. The further back location provides more shade for the eyeballs.

Wide vs. narrow face.

Figure 2. Wide vs. narrow face.

Face width
Here (Fig. 2) we see two faces scaled to match eyes, nostrils and mouths vertically. However, they do not share the same face width (horizontal bar below faces).

Vertical variation in two faces. What appears to be a low forehead is actually a high face and vice versa.

Figure 3. Vertical variation in two faces. What appears to be a low forehead is actually a high face and vice versa. A large forehead and small chin are childlike features retained in the adult, or not.

Face Height
In some people the face is set higher on the skull, reducing the forehead height and raising the location of the eyes, mouth and nose (Fig. 3). These subtle differences, can be the basis for major changes over eons of time.

Wider skulls in Reptiles
One of the major differences between basal crocs and basal dinosaurs is skull width, with crocs trending toward a wider skull posteriorly. The same can be said about the basal reptiles. The plant-eating lepidosauromorphs trend toward a wider skull, while the insect-eating archosaurmorphs do not. Dimorphodon had a tall skull. The flat-head anurognathid had a wide one.

The migration of the nostrils posteriorly on parasuchians is enhanced by the elongation of the premaxilla. Conversely, in the related champsosaurs, the nostril migrates back to the snout tip… all a matter of facial proportions (Fig. 3).

This is just a primer, a jumping off point. You can find many more examples of convergence for nearly every character trait you may wish to list.