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.

Get dirty doing real paleontology during Fossil Wash Day in Sugar Land

If you want to be a paleontologist, you’ve got to get your hands dirty… and sometimes wet.

Now you can learn just what it takes to get down to the nitty-gritty of separating fossils from soil and get a little messy yourself! Just come to the Houston Museum of Natural Science at Sugar Land for Fossil Wash Day this Saturday from 9 a.m. to noon. You’ll be able to help our staff and other volunteers spray down samples dug from our very own exclusive fossil site near Seymour, Texas, the home of the famous fin-backed prehistoric reptile Dimetrodon. While you’re washing, you can chat with our experts about your favorite dinosaurs. Who knows? You may be the first to lay hands on a bone that hasn’t seen the sunlight in hundreds of millions of years.


Fossil Wash Day is a community gathering perfect for dinosaur fans and families interested in real science.

Fossil Wash Day is a four-year tradition at HMNS Sugar Land, the perfect location for splashing around and playing with mud. The “big back yard” has a nearby water source and is perfect for the process. Large clumps of Baylor County clay will be placed in five-gallon buckets of water with a bit of hydrogen peroxide to help deflocculate, or break up, the sample. Then the clay will be taken from the buckets of water and plopped onto a screen which will catch small fossil fragments.


Searching for fossils is a job for both children and adults, and is a big help to our museum paleontologists.

“We’re looking for the things we missed. The things we didn’t know were there,” said David Temple, Associate Curator of Paleontology, who usually hosts the event. A scheduled visit to a fossil site in Germany will prevent him from joining the fun.


HMNS Associate Curator of Paleontology David Temple teaches two children how to bag fossils at Fossil Wash Day. While Temple usually appears at the event, he will be out of the country this year.

“Once we run the samples through the screens, we empty the screens out and find bits of bone and things, and we catalog the bits,” Temple said. “It’s citizen science. A way for the public to get involved. It’s a chance to do real science and you’ll never know what you’ll find. And you do find things.”


At Fossil Wash Day, small bones such as this phalange discovered by a volunteer help the Houston Museum of Natural Science collect data about Permian-era reptiles and amphibians.

Most finds from these samples contain fossilized teeth from prehistoric sharks, Dimetrodon and others. Fossils discovered at the event go into our collection, where they are valued for the information they share about the distant past. From teeth, depending on the details on the fossil, paleontologists can tell how Permian-era creatures fed and fought with one another. Broken Dimetrodon teeth, for example, show that the animal chewed its food instead of swallowing it whole.

“If you’ve got shed teeth, you can tell something fed there, even if you don’t find bones there,” Temple said. “As opposed to finding a socketed tooth where the carcass has rotted. Sometimes we find crushed bone. From these fossils, we learn what they’re chewing on and how the teeth wear.”


The clay matrix from Seymour, Texas is transported in clumps back to Houston. In the clumps, you never know what you’ll find.

If you’ve got fossils at home, bring those along, too, and have them identified. With the paleontologists and volunteers working alongside the public, it’s a great opportunity to spark up a one-on-one Q&A. There will be more volunteers inside the museum preparing Eocene-era fossils from another dig site near Bryan-College Station. Plus, you’ll get a look at other specimens in our fossil touch carts.


Rinsing red mud from a screen.

“Fossil Wash Day is a super hands-on kind of thing. You get filthy,” Temple said. “Wear something you don’t mind getting wet.”

Back to Seymour, Back in Time: Part Two — Bringing back a city

The visit to our active digs at the Craddock Ranch red beds exhausted Kelly and I, but it was fascinating to learn how the Houston Museum of Natural Science discovers, jackets and moves its Permian fossils to our lab. The second day, we lent a hand at the Whiteside Museum of Natural History in Seymour for their one-year anniversary celebration. I conducted interviews with Museum Director Chris Flis, our associate paleo curator David Temple, and a handful of Seymour residents, while Kelly shot photos, posted Tweets and produced Periscope videos.


The Whiteside Museum of Natural History in Seymour, Texas has the potential to breathe new life in to the city through historic ecotourism. Jason Schaefer.

The Whiteside has the potential to bolster Seymour’s dwindling economy through historic ecotourism. Locals want to keep Baylor County fossils at home, housed in a single facility, in hopes that visitors will spend a weekend and their money in the shops, restaurants and hotels of the dusty Texas town. Dimetrodon has the potential to attract paleo-fans and academics alike from far and wide and give Seymour a new brand as the home of the richest Permian fossil accumulations in the world. It has been known as such unofficially for nearly 100 years.

Flis, Temple, and paleo curator Dr. Robert Bakker, who arrived in Seymour the previous night, regard the Craddock bone bed as crucial in the understanding of some of the most important enigmas of modern paleontology. In the past century, the information unearthed from the caked deposits of these ancient rivers has answered many questions about Permian ecosystems. However, with each layer removed, new riddles emerge. How many species of Dimetrodon were there? Why did they live so far away from the swamp, where the herbivorous Edaphosaurus lived? Shouldn’t Dimetrodon have preyed on Edaphosaurus? Should Dimetrodon be considered a mammal ancestor? And, perhaps the most fascinating, why are there more carnivores than herbivores buried here? Paleontologists are certain the story is in the bones, and for this era, there’s no better place to find them.


At the Whiteside Museum of Natural History, Dr. Robert Bakker puzzles over the broken shin bone of a Diadectes, a rare Permian herbivore. Kelly Russo.

The exposed Permian landscape from north Texas into southern Oklahoma dates back about 290 million years. To the southeast of Seymour, the rocks get a little older, providing samples from the Pennsylvanian era, about 310 million years ago. The landscape grows younger as you travel west out of Baylor County, then ages again in eastern New Mexico about 100 miles away. Here, paleontologists have found other Permian-era sites that extend as far as Arizona, Flis explained.

“Those sites are well-known for trackways, but they’re not well-known for bones,” Flis said. “For bones, Texas is the best.”


Jacketed lumps of earth lining the wall of the Whiteside Museum of Natural History contain not only fossil specimens, but valuable information about Permian ecosystems. Jason Schaefer.

The soil is rich with exposed Permian fossils. Visitors can walk across the landscape and happen upon excellent specimens of vertebrae, joints, and bits of Dimetrodon’s famous fin spines right at their feet. The bones are preserved so well in the clay soil, they still carry their indigo luminescence when turned in the sunlight. These aren’t mineralized bones, but the real thing. They are the actual mummified parts of animals that human hands have never moved, that haven’t been exposed to light or air since their deaths.


The Craddock red beds are rich with outstanding bone fossils, nearly half of them crushed, broken or bearing tooth marks from Permian-era violence. This fragment of Dimetrodon rib could tell paleontologists more about how the reptile lived than a complete skeleton. Kelly Russo.

It’s not just the bones or their ubiquity in the red beds that makes the Craddock so valuable. It’s the story the bones tell in pieces. A perfect skeleton is great for anatomy, but for information about ancient ecosystems, the pulverized fragments are pay dirt. Paleontologists learn much more about the interaction between extinct species from bones damaged by chewing or some other trauma than from bones unscathed. There’s no story in a complete skeleton.

“You don’t know how it died. You don’t know who chewed it,” Bakker said. “It tells you nothing.”

When Bakker and HMNS teams first began digging at the Craddock about 11 years ago, he was looking for shed Dimetrodon teeth, he said, knowing that losing teeth was common for the reptile. He didn’t expect as many as he found.

“There were shed teeth everywhere,” Bakker said. “It was like a Civil War battlefield that souvenir hunters hadn’t gone over.”


The Whiteside Museum of Natural History is outfitted to prepare its own fossils with its own lab. Volunteer Dr. Mitch Fruitstone removes sedimentary rock from a fossilized jaw specimen. Jason Schaefer.

The team estimated less than five percent of the specimens would be chewed and have tooth marks. After all, T. rex swallowed his prey in chunks, tearing flesh from their bodies without much mastication. From what he’d learned from his predecessors, Bakker expected the same of Dimetrodon. However, the bones were marked in high frequency, about 45 percent, and some were chewed to pieces.

“This means Dimetrodon wasn’t chewing like a dinosaur. It was chewing like a wolf or a hyena,” Bakker said. “That’s the most surprising thing. That’s a way primitive guy, but it’s chewing like an advanced mammal predator. … Our group is the first to document that.”

Through observations made at the Craddock, these discoveries broke open new possibilities for the life of Dimetrodon and the Permian world in which it lived. It could be an ancient relative of mammals instead of reptiles. As a cross-section of the development of life on Earth, the Permian represents the dawn of land-dwellers, when amphibians first began to crawl out of the water. The link between amphibians and reptiles was discovered in the Craddock in 1904, putting Seymour on the paleontological map. Named Seymouria baylorensis to pay homage to its home town, it contended with gravity better than its amphibious predecessors 20 million years earlier, and had other adaptations that allowed the species to succeed in the dry Permian landscape.


Volunteer Dr. Mitch Fruitstone demonstrates precision fossil preparation as a child looks on during the Whiteside Museum of Natural History’s first anniversary celebration. Jason Schaefer.

Now, a model of the animal occupies a hallowed space in the Whiteside, a shining example of the value of this area to the study of the Permian. As Baylor County digs continue, paleontologists layer details about the past with each layer of soil removed: microfossils, traces of flesh-eating arthropods and fossilized pollen grains, and what appears to be different species of Dimetrodon or perhaps just male and female aspects. Bite marks and stab wounds from Xenocanth suggest the ancient shark preyed on Dimetrodon from the water while it hunted the shark from land. With each shovel of soil and swing of the pickaxe, more comes to light about Eryops, Diplocaulus, Trimerorachus and Edaphosaurus.

For the agricultural residents of Seymour, the science could spell success for a struggling community. A contract with the landowners ensures the fossils excavated from the Craddock will remain in Texas, and most of them at the Whiteside. According to Bakker, having a municipal museum is “a huge game-changer” for Seymour, for HMNS and for the state.



Dr. Robert Bakker uses his sketching skills to teach children about Dimetrodon. “Science should make you giggle,” he told the kids. Jason Schaefer.

“Our hope would be that the Whiteside would be a locus not for just digging local fossils but for teaching short courses, especially for teachers so they have hands-on experience digging fossils,” Bakker said. “We’ll take them out and they’ll go back to their classroom and show how fossils are dug.”

The building itself is not without its own history. A renovated Chevrolet dealership, it was handed down from former owner Gene Porter Robinson, who had sold cars out of the building since the 1950s. As Chevy went corporate, Robinson kept the business open, remaining active until 2001 as one of the last remaining independently-owned dealerships in the franchise.


Judge Clyde Whiteside of Baylor County, and the namesake of the Whiteside Museum of Natural History, sits beside models of Edaphosaurus and Dimetrodon during the museum’s first anniversary celebration. Jason Schaefer.

When Robinson died, Judge Clyde Whiteside recognized the value of the lot, and cherishing his friendship with Robinson, decided to purchase the half-block with the clear intent of turning it into a museum to re-invigorate the community.

“I bought my first car right here,” Whiteside said, seated in his wheelchair beside the first Dimetrodon model display. “Hopefully this will bring people back. … Now that we’ve got this interest in [the Craddock], we’ve got five active digs going, and we’re finding stuff you wouldn’t believe! I’m not a scientist, I’m a lawyer and a farmer. But it’s working, and I’m thrilled to death by it. It makes my life worth living.”

Author’s note: This is the second part in a series detailing the HMNS excursion to the Craddock Bone Bed.

Stego says HMNS makes field trips easier on teachers

by Kaylee Gund

Hi all,

Stego the Stegosaurus here, putting my best plate forward for the beginning of the school year!


Stego the Stegosaurus, team leader for the field trips department.

I was chatting with my Discovery Guide pals the other day and we’re all looking forward to the great school field trips we see every year. But surprisingly, a few local teachers they’ve spoken to are intimidated by the prospect of planning a field trip.

I have to admit, the idea of taking more than 500 students off campus and bringing them back in one piece does sound overwhelming, but here at HMNS, it’s our job to make field trips the best possible experience for everyone involved.

As the face of the Youth Education Sales team, I, Stego the Stegosaurus, feel duty-bound to dispel the myth that organizing a field trip is by nature stressful. In fact, I’d like to take this opportunity to introduce you to two wonderful ladies who can give you all sorts of great tips and ideas for students to put a spike in their learning curve (pun intended).

Karly - Paleo

Karly Hunt, Marketing Coordinator (khunt@hmns.org).

The newest member of our team, Karly Hunt, is the Marketing Coordinator for all districts west of Houston. She comes to us from Liberty Hill ISD, where she taught high school science. Karly, by the way, appreciates a good chemistry joke, but unfortunately all the good ones Argon… Get it?

This is Karly’s first year at HMNS, but she is already hard at work sharing her love of all things scientific with Houston educators. Her favorite part of the museum is the Morian Hall of Paleontology.

“We have such an amazing collection that really puts prehistory in perspective,” Karly said.

Needless to say, being a dinosaur myself, I like her already!

When she’s not traveling to schools, you’ll find Karly spending time outside, enjoying music of all genres, and playing with her dogs.

Cathy - Jurrasic Bark

Cathy Walton, Lead Marketing Coordinator (cwalton@hmns.org).

Cathy Walton, our Lead Marketing Coordinator, is the museum representative for schools in Houston ISD, districts centrally located in the metroplex, and districts to the East. Having originally taught World Geography in Tennessee, she began her career at HMNS three years ago. Cathy is a wizard at finding field trip packages that fit an individual teacher’s needs, and she loves being able to work with amazing educators to help them inspire their students. She encourages teachers to “be as creative as you can to get students excited about learning!”

Cathy enjoys hiking, cooking, and entertaining (when she’s not hanging out with us dinos, of course). Fun fact: she grew up in Shelbyville, Tenn., better known as “Pencil City,” home of the No. 2 pencil!

If you have any questions or would like to know what exciting new exhibits your students can learn from next, feel free to contact one of these representatives. Check out our free curriculum and our field trip preparation guide for more info, too. And you can fill out a booking request form online if you already have an idea of what you’d like to do at the museum.

Have fun, keep learning, and we’ll see you soon!




Editor’s Note: Kaylee Gund is in Youth Education Sales at the Houston Museum of Natural Science.