04 March 2014

Deeper Dive on the PhyloPic T-shirt

Just to review:
  •  PhyloPic is a website featuring freely-reusable silhouettes of organisms. Anybody may submit images under a Creative Commons license.
  • I am attempting to raise funds to host PhyloPic for the next two years by selling a PhyloPic T-shirt, depicting the past half-billion years of our evolutionary lineage with free silhouettes.
We've come a long way.
In this post I'll go into more detail about what, exactly, is on the shirt, starting with the final silhouette and going back in time. In each entry, the taxonomic name links to a page for the image, with artist and license information. Some terminology first: "concestor" means "most recent shared ancestor", and "stem-X" means "not X, but more closely related to X than to anything else alive".

The final silhouette is a modern human, Homo sapiens sapiens, specifically a Melanesian woman. Melanesians and other Oceanians represent one of the furthest migrations of humanity from our original geographical range.

Immediately behind her is another Homo sapiens sapiens, this one a Subsaharan African man. Subsaharan Africa is the wellspring of modern humanity. (This isn't meant to imply an ancestordescendant relationship between the two figures; they're just coexisting members of the same subspecies.)

Behind him is another Subsaharan African man, but a different subspecies: Homo sapiens idaltu. This subspecies is often considered to be the primary ancestral population for most living humans. We've now gone back in time about 160,000 years.

He is preceded by a Neandertal woman (Homo neanderthalensis or Homo sapiens neanderthalensis). Neandertals were once considered a side-branch to humanity, but now we know that a few of their genes persist in many people today, especially outside of Subsaharan Africa. (According to one genomic analysis, I myself am ~3.0% Neandertal.)
Behind her is a Homo ergaster man, modeled after "Turkana Boy". His brain is somewhat smaller than that of modern humans, but still quite large. At 1.5 million years old, he is one of the earliest stem-humans with long legs, like us.
Just behind him is a diminutive Homo habilis woman. Her species may be ancestral to us, although late Homo habilis persisted alongside early Homo ergaster.

She is preceded by a running Homo rudolfensis man. Homo habilis and rudolfensis are the two earliest species of our genus, Homo (and they are possibly synonymous). At this stage in our evolution, males were much larger, on average, than females (much moreso than today).

Behind him is a little Australopithecus sediba female. This species is considered by some to be the most human-like of the Australopithecus species. Being just shy of 2 million years old, she occurs too late to be one of our actual ancestors, but in profile she is a very good approximation. Her brain is roughly chimpanzee-size.

Behind her is an Australopithecus afarensis (or Praeanthropus afarensis) male, modeled after specimen AL 444. He is of the same species as the famous "Lucy" specimen, and he is over 3 million years old.
Last in line is "Ardi", a female Ardipithecus ramidus. She is the best-preserved stem-human specimen from her time period (about 4.4 million years ago), and only shows a handful of traits that mark her as being more human-like than any living great apes.
Above her, swinging from the trees, is a Sahelanthropus tchadensis male. This species, roughly 7 million years old, may be stem-human, or it may pre-date the chimpanzeehuman lineage split. Either way, it is very close to the humanchimpanzee concestor. It is known from only a skull, so the body is speculative. But the way its skull attached to its spine seems to indicate that it was primarily bipedal (at least arboreally, if not terrestrially).
Above him is a Proconsul africanus, a stem-ape roughly 1520 million years old. This species was an arboreal quadruped, like many living monkeys.
Behind the stem-ape is an Aegyptopithecus zeuxis, a precursor of the split between apes and Old World monkeys. It lived 3335 million years ago.
Beneath that is a squirrel monkey (Saimiri sciureus). Obviously this is not one of our ancestors, since it is alive today! But its general form (and hence its silhouette) has changed little since from the simian concestor, which is thought to have lived over 40 million years ago.
Beneath and behind the squirrel monkey is a tiny Archicebus achilles, a stem-tarsier from about 55 million years ago. It is not one of our ancestors, but in form it is a close approximation of the concestor of the dry-nosed primates (Haplorhini). That ancestor might have lived sometime around the CretaceousPaleogene extinction, famous for killing off the non-avian dinosaurs.
Behind that is a pen-tailed treeshrew (Ptilocercus lowii). Again, as a living animal, this is obviously not one of our actual ancestors, but its form has changed very little from the concestor of primates, treeshrews, and colugos (gliding mammals also known as "flying lemurs"). It has evolved in other ways, though. Notably, it has evolved a very high alcohol tolerance! (I am not making this up.) Just because the silhouette has barely changed doesn't mean the species has stopped evolving.
We return to the ground, and leave the Cenozoic (often called the "Age of Mammals"). This little Zalambdalestes lechi is a stem-placental that lived toward the end of the Mesozoic (the so-called "Age of Reptiles").

Behind it, barely visible, is a wee mammalian concestor. It is based on Hadrocodium wui, a very close mammal relative that lived in the Early Jurassic, nearly 200 million years ago.  Mammals are thought to have originated in the Jurassic.

Now we come to the stem-mammals. Behind that speck is an Oligokyphus lufengensis, a species which spanned the TriassicJurassic boundary. It was likely furry and warm-blooded, like mammals, but its skeleton was somewhat more primitive (notably the ear bones).

Larger still is Cynognathus crateronotus, a predatory stem-mammal. This creature hunted small prey in the EarlyMiddle Triassic.
Now we go back before the Mesozoic, into the Paleozoic. Parabradysaurus silantevi was a rather large stem-mammal that lived around 275 million years ago. It was not one of our ancestors, but part of a plant-eating offshoot lineage (Dinocephalia, the "terrible heads"). But it may be similar to our earliest warm-blooded ancestors.

Body size shrinks again. Nearly 300 million years old, Tetraceratops insignis may be the earliest known member of Therapsida, a group which includes us mammals and our closest stem-mammal kin.

Haptodus garnettensis is one of the earliest stem-mammals to have differentiated tooth types, as in living mammals. It is over 300 million years old.
Below that is a tiny Archaeovenator hamiltonensis. It is similar in age to Haptodus garnettensis, but a more primitive relic in its time. It is one of the most primitive stem-mammals. (In silhouette form, it looks rather like a lizard, although it is not closely related to them.)
Now we go back before the concestor of mammals and reptiles (including birds). Solenodonsaurus janenschi, which may be a stem-amniote, is nearly 320 million years old.
The next "lizardy-looking" thing is Westlothiana lizziae. At 335 million years old, it is one of the first tetrapods.

Gephyrostegus bohemicus, about 310 million years old, is younger than Westlothiana lizziae. But it probably branched off before the amphibianamniote split, and may be close in general form to the forerunners of tetrapods.
Roughly 340 million years old, Eucritta melanolimnetes is also close in general form to the forerunners of tetrapods. Its name means "True Creature from the Black Lagoon".

Getting bigger again. Hynerpeton bassetti is a possibly amphibious stem-tetrapod about 360 million years old.
Below that is an Acanthostega gunnari, one of the first stem-tetrapods with digits (although it had eight instead of five). It lived 365 million years ago.

Now we reach something that is about human size! Tiktaalik roseae, about 375 million years old, did not have digits, but it was one of the first stem-tetrapods with wrists. It is sometimes called a "fishapod".

Panderichthys rhombolepis is one of the stem-tetrapod fish most closely related to limbed vertebrates. It lived 380 million years ago.

About 390 million years old, Tinirau clackae is only slightly less tetrapod-like than Panderichthys rhombolepis.
Above that is the much smaller Gogonasus andrewsae. It lived after Tinirau clackae, around the same time as Pandericthys rhombolepis. But its form is more primitive, like that of the earliest stem-tetrapod fish.

Behind that is Quebecius quebecensis, a stem-lungfish. It is not one of our ancestors, but its form is probably close to that of the lungfishtetrapod concestor.
Now we come to one of the earliest lobe-finned fishes, Guiyu oneiros. It lived nearly 420 million years ago.

The vaguely shark-like Cheirolepis canadensis is actually part of the ray-finned fish stem group. (Most living fishes are ray-finned.) As such, it is not one of our ancestors, although it is probably close in form to the concestor of ray-finned and lobe-finned fishes. (We tetrapods are basically terrestrial lobe-fins.)

Acanthodes bronni is very close in form to the concestor of living cartilaginous fishes (sharks, rays, ratfishes, etc.) and bony fishes (ray-finnned and lobe-finned fishes), although it lived much too late to be one of our actual ancestors (about 290 million years ago).

Bothriolepis also occurs too late to be one of our actual ancestors (about 375 million years ago), but it is probably similar in form to the earliest fishes with jaws.

Hemicyclaspis was a jawless fish (but a close relative of jawed fishes) that lived over 420 million years ago.

The tiny Haikouichthys ercaicunensis is one of the very earliest vertebrates (or possibly a stem-vertebrate). It dates from the "Cambrian explosion", around 530 million years ago, a time when many of the modern animal "phyla" first appear in the fossil record.

We leave the Paleozoic and finally come to Kimberella quadrata, an Ediacaran animal about 555 million years old. Its exact affinities are uncertain, but it probably resembled the very earliest animals with bilateral symmetry and a coelom (body cavity).
At this point I could have gone further, but most of the silhouettes would not be visible at this scale. You can still see them on the human lineage page on PhyloPic. The very earliest one, a hammerhead ribozyme, appears on the back of the shirt. Ribozymes can behave both as genetic material and as catalytic enzymes, so they may provide clues about the molecular precursors of extant life.

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