A New Branch: How anthropologists added Homo naledi to our family tree

In a well-deserved world-wide wave of publicity, the existence of a new hominid species was announced recently. Fossil hominins were first recognized in the Dinaledi Chamber in the Rising Star Cave system in October 2013. Now, some two years later, and after exhaustive analysis of more than 1,500 bone fragments, the team decided to go public with this first milestone: the identification of a new human ancestor.

A selection of these bones have been scanned and uploaded to the internet. They also wrote up their findings and published them in an open-access source, eLife, rather than more established channels such as Nature or Science. (A brief side note: as can be seen in this video, one of the thirty specialists involved in the initial evaluation of these remains was Viktor Deak, who was part of the Houston Museum of Natural Science’s team putting together the Lucy’s Legacy exhibit as well as the section on human evolution in the museum’s Morian Hall of Paleontology.)


Fossilized bones discovered in Rising Star Cave in South Africa belong to a new species of hominid.

While social media are currently lit up with all kinds of references to this new species, it might be interesting to address this fundamental question: how does one define a new
hominid species? In other words: “Why is naledi called naledi?“

A starting point in this process is to identify a type specimen. Such a specimen is described in great detail, listing the similarities to and differences from closely related species. There is no central authority that decides on the validity of a species. Rather, this depends on the acceptance of such a designation within the scientific world. New discoveries and more information have given impetus to revisit previous species designations and change them.

As a result, “[i]f two type specimens are later determined to belong to the same species, then the first one named takes priority. For example, when it was decided that the 2nd known australopithecine fossil, assigned to Plesianthropus transvaalensis, actually belonged to the same species as the first that name became invalid and all Plesianthropus fossils were reassigned to Australopithecus africanus.


Skull fragments from the holotype specimen show Homo naledi had a brain about the size of an orange.

If it is decided that the fossils previously assigned to a species actually belong to two different species, then the type specimen and any other specimens belonging to the same species as it keep the old name. The other fossils will take the name of whichever specimen among them is first used as a type specimen for a new species definition. An example is Homo habilis (type specimen OH 7); the species Homo rudolfensis, with type specimen ER 1470, consists of fossils formerly assigned to habilis.”

This new species belongs to the genus Homo. Traditionally, one is a member of that genus if the following criteria are met (Since these are set by human researchers, they are subject to periodic re-evaluation):

  • Brain size: at least 600 cubic cm.
  • Possession of language
  • Opposable thumbs and precision grip
  • Ability to manufacture (stone) tools

We all belong to the genus Homo, species sapiens and subspecies sapiens. We are “Humans, wise, wise” or “very smart humans.” (Since we are the humans investigating ourselves and our ancestors, it should not come as a surprise that we have kept the most honorific label for ourselves.)

If we translate Homo naledi into plain English, we can start with naledi. The species was named Homo naledi; ‘naledi’ means ‘star’ in Sotho (also called Sesotho), one of the languages spoken in South Africa.

According to the research team, the definition of the new species was not “based on a single jaw or skull because the entire body of material has informed our understanding of its biology.”

Interestingly, Homo naledi’s brain size is in the 400 to 600 cubic cm range, yet they are considered to be members of the genus Homo. Here is why: “The shared derived features that connect H. naledi with other members of Homo occupy most regions of the H. naledi skeleton and represent distinct functional systems, including locomotion, manipulation, and mastication.”

Homo naledi - brain size - range

Brain size and tooth size in hominins. (Lee R. Berger et al. eLife Sciences 2015; 4:e09560)

Fossil Dating

One aspect currently left unanswered is when Homo naledi lived; the scientists offer what-if scenarios for dates ranging between one and two million years ago, some even more recent. These are just that: scenarios. They do not provide a date, as none exists at this point.

That brings up the question: how does one date a fossil? Knowing when a human ancestor lived helps us understand the affiliations of different species and who might have evolved from whom. Scientists have access to a wide array of dating techniques.


Homo naledi had human-like hands, though smaller than our own.

Radiometric Dating

Several techniques measure the amount of radioactive decay of chemical elements. Known as radiometric dating techniques, these include potassium-argon dating, argon-argon dating, carbon-14 (or radiocarbon), and uranium series. This radioactive decay occurs in a consistent manner over long periods of time. A benchmark concept in using this approach is that of a “half life,” defined as “the time it takes for one-half of the atoms of a radioactive material to disintegrate.” Early hominid sites in Eastern Africa have stratigraphic affiliations with volcanic layers. These layers can be dated with the radiometric dating techniques just described. As we will see below, the situation in Southern Africa is different.

Measuring Stored Electrons

Thermoluminescence, optically stimulated luminescence and electron spin resonance measure the amount of electrons that get absorbed and trapped inside a rock or tooth over time. The application of these techniques to date fossils highlights how the study of human origins truly is a multi-disciplinary effort.

Thermoluminescence “(or TL) is a geochronometric technique used for sediment. The technique has an age range of 1,000 to 500,000 years. The technique is used on sediment grains with defects and impurities, which function as natural radiation dosimeters when buried. Part of the radioactive decay from K, U, Th, and Rb in the soil, as well as contributions from cosmic rays, are trapped over time in sediments. The longer the burial, the more absorbed dose is stored in sediment; the dose is proportional to a glow curve of light obtained in response when the sample is heated or exposed to light from LEDs. Greater light doses indicate an older age.”

Luminescence dating is “a form of geochronology that measures the energy of photons being released. In natural settings, ionizing radiation (U, Th, Rb, & K) is absorbed and stored by sediments in the crystal lattice. This stored radiation dose can be evicted with stimulation and released as luminescence. The calculated age is the time since the last exposure to sunlight or intense heat.”


Homo naledi’s feet appear nearly human.

Finally, “electron spin resonance (ESR) measures the number of trapped electrons accumulated, since the time of burial, in the flaws of dental enamel’s crystalline structure. At sites containing human and animal teeth, ESR can be used to determine how long the teeth have been in the ground, but finding teeth at an archaeological site is unusual, so this dating method is not as common as thermoluminescence or radiocarbon dating.”

Another dating technique altogether is paleomagnetism. It compares the direction of the magnetic particles in layers of sediment to the known worldwide shifts in Earth’s magnetic field, which have well-established dates using other dating methods.

Sites in Southern Africa cannot be dated with techniques outlined earlier. A lot of the fossil remains are found in a stone matrix, rather than on the surface. These fossils can be dated using biochronology. Most often – though not always – hominid remains are found in stratigraphic association with animal bones. Quite often, these animal remains belong to animal species that roamed elsewhere in Africa, where absolute dates are available. In this way, sites that do not have radioactive or other materials for dating can still be given a reliable age estimate.

Finally, one can estimate the time that elapsed since two species separated from a common ancestor. This is based on the concept of a molecular clock. This method compares the amount of genetic difference between living organisms and computes an age based on well-tested rates of genetic mutation over time.  Since genetic material (like DNA) decays rapidly, the molecular clock method cannot date very old fossils. The most ancient DNA that has been retrieved thus far dates back to 300,000 to 400,000 years ago.

There is no doubt that more information will be forthcoming from the Rising Star Cave system in South Africa. Over the last two years, the researchers have literally scratched the surface of what is in the cave. As mentioned earlier, the genus Homo is defined by a number of features. One of these used to be that we buried our dead. This appeared to have happened in this case as well. Once the remains are dated, we will know if this fundamentally human trait extended further back in time than we ever imagined. Or not.

Dipsy the Diplodocus is back at HMNS!

After a 2 year absence, “Dipsy” the Diplodocus is back at HMNS!  Making it’s debut back in 1975, Dipsy was the first dinosaur to call HMNS home. In 2013, our Diplodocus was de-installed from its original place in the Glassell Hall and sent off for a much needed spa retreat in Utah. While there, the bones were carefully cleaned and a new mounting frame designed. This week, she arrived back in Houston and was permanently installed in our Morian Hall of Paleontology.

Diplodocus installation, March 2015

Spine, tail and rib bones go up first. Followed by the legs.

Front leg installation.  Dipsy's stance has been modified from it's previous posture. Now, the skeleton assumes a tripod stance, as if rearing up to feed on leaves.

Front leg installation: Dipsy’s stance has been modified from it’s previous posture. Now, the skeleton assumes a tripod stance, as if rearing up to feed on leaves.

Associate Curator of Paleontology, David Temple, overseeing the installation process.

HMNS Associate Curator of Paleontology, David Temple, oversaw the installation process.

 Fun Facts about “Dipsy” the Diplodocus

  • This particular Diplodocus skeleton is a holotype for Diplodocus hayii. A holotype is a single physical example (or illustration) of an organism, known to have been used when the species was formally described. HMNS is the only place in the world where you can see a Diplodocus hayii on display.
  • Paleontologists don’t know for sure whether Dipsy is male or female.
  • Diplodocus hayii were herbivores. Their skulls, however, have many small, sharp teeth. These were used for stripping plants, not for chewing.
  • This skeleton is 72 feet long and about 25 feet high.
Dipsy's skull was the last piece  to be installed. Notice the small, sharp teeth present.

Dipsy’s skull was the last piece to be installed. Notice the small, sharp teeth present.

For more photos of the installation, visit out Instagram page.

Kathy Reichs of Bones (Temperance Brennan IRL) visits HMNS and talks scientific vs. script-writing, creating the “crimedy” & more

What better place for the creator of Bones to give a presentation than at the Houston Museum of Natural Science?

Dr. Kathy Reichs — forensic anthropologist, best-selling author and real-life inspiration for the popular television series (and original “crimedy“) Bones — spoke to students of HCC’s Northwest Audio Recording & Filmmaking Department on Sept. 7 — and we snuck in to share some tales from the real-life Temperance Brennan.

Dr. Kathy Reich

For those of you who don’t know, Dr. Kathy Reichs has spun her real-life experiences into more than a dozen best-selling fiction novels since 1997. Then in 2005, FOX adapted her novels into a comedic crime series (called the “crimedy”), based around Reichs’ semi-autobiographical heroine, Temperance Brennan. And in a quirky TV twist, TV’s Temperance Brennan also writes crime novels in her spare time — about a fictional forensic anthropologist named Kathy Reichs.

With her latest book, Bones are Forever, out now, with Bones entering its eighth season and with a new series of young adult novels written with her son Brendan, Reichs took the time out to talk process, crack some (OK, a lot of) jokes and chat about how she sold her first novel on the first try — and won an award for it.

Dr. Kathy Reich

Here are the highlights:

Reichs found success via the old adage “write what you know.” Although the crimes featured in her novels draw from real-life experience, she changes names, places and dates. “I take a case and then ask myself, ‘What if?’ and spin off from there,” she says.

To say that Reichs has had an adventurous career would be an understatement. She has been hired by the Catholic church to exhume the body of a 1700s woman being considered for sainthood. She did disaster recovery work after Hurricane Katrina and the Sept. 11 attacks. She has also worked on human rights cases in Guatemala and Rwanda.

Reichs is extremely involved in the writing room on the set of Bones, keeping the science honest and even penning an episode — “The Witch in the Wardrobe” — herself! She says the lab featured in the show is realistic — nothing exists in the lab that doesn’t exist in the real world — but she’s never been in a lab that nice.

The Tempe on TV is not the Tempe of Reichs’ books, but she’s OK with that. “I think of the TV show as a prequel,” Reichs says. “It’s early Tempe; she hasn’t come into herself yet.”

Reichs says being a good anthropologist aided her writing. “If you’re a good observer, you can’t help but be a good writer.”

Dr. Reichs donated her honorarium to raise awareness for Houston Community College Northwest’s Audio Recording and Filmmaking Department. To learn more about Reichs’ work, her latest novel and her young adult series, “Virals,” click here.

The Seymour Blob: Putting something in your head from the ground beneath your feet

As you may already know, the Houston Museum of Natural Science has long been digging up wonderful Permian fossils in Seymour, Texas. Curator of Paleontology Dr. Robert T. Bakker and his team of hot, tired and pink (from the dirt) volunteers have made major finds, but sometimes it’s the little things that count — like finding little amphibians, such as the boomerang-headed Diplocaulus and the snake-like Lysorophus, too.

lysorophus 2

The rock stars of the Seymour dig are people like Chris Flis, who finds bones everywhere. There are also geologists on the team, like Gretchen Sparks, who are interested in sedimentology (how the dirt got there) and who pick up interesting bits and wonder what they are.

This is a warty blob (that’s a technical term) that she found. It sort of looks like a bone or a burrow dug by something. I tested it and found that it is made of calcium carbonate.


To see more, I ground and polished the end. Now we can see that this is not a bone because it does not have a marrow cavity or bone lamellae. Warty surfaces like this are frequently found on the outsides of arthropod burrows because the animal lines the burrow with spit and sediments balls — but the warty parts of these structures are inside and on the exterior, so this is not a shrimp burrow.

The flowery appearance of the growth indicates that this is caliche, one of those sedimentary features that often get little attention.

Caliche is a hard-water deposit on steroids. Caliche forms in dry areas like North Texas when more water evaporates from the surface of the ground than falls as rain. Ground water dissolves minerals like calcium carbonate and gypsum from the soil and rock. When the water evaporates from the surface, these minerals are deposited in flowery growths called “efflorescences”.

The climate in Seymour is so dry that caliche is growing right now. During the Permian (about 250 million years ago), the climate must have been even dryer, because we find bands of caliche in the soil. Each band represents an ancient soil layer.

CalichiCloseupc Annotated

We can even tell the history of the caliche deposition. The interpretation is based on what covers what:

A.    White layer was deposited in a nearly flat crack in the dirt. Note the white flowers.
B.    The pink layer covers the white and has the same shape of flowers but contains more iron.
C.    Layer B was partially covered by darker pink laminations. The laminations indicate that crystal growth was much slower.
D.    The blob fractured and the dark red layer of sediment was deposited along with fragments of Layers A and B. This is a mini sedimentary dike.
E.    Since Layer D is made of sediment and not hard caliche, it shrank and cracked in the process of drying. This crack was filled with a quickly-deposited rind of fine grained white material followed by very slow growing clear crystals, making the darker band inside the white. This looks like an agate filling but is still carbonate.

Were all these layers deposited 250 million years ago? That actually would be easy to tell, because young carbonate has a carbon delta C13 signature well within the 50,000 year sensitivity range for the method. It just costs money to have the analysis done, and there are probably better uses for the resources right now – like having more specimens mounted!

I conclude that the warty bone-looking thing is really an inorganic crystallization of carbonate and possibly gypsum. Did you know you could learn so much from gravel?