Brain size & scaling – virtual lab activity

Each year in my intro bio-anthro class, we start the course by asking how our brains contribute to making us humans such quirky animals. Our first lab assignment in the class uses 3D models of brain endocasts, to ask whether modern human and fossil hominin brains are merely primate brains scaled up to a larger size. In the Before Times, students downloaded 3D meshes that I had made, and study and measure them with the open-source software Meshlab. But since the pandemic has forced everyone onto their own personal computers, I made the activity all online, to minimize issues arising from unequal access to computing resources. And since it’s all online, I may as well make it available to everyone in case it’s useful for other people’s teaching.

The lab involves taking measurements on 3D models on Sketchfab using their handy measurement tool, and entering the data into a Google Sheets table, which then automatically creates graphs, examines the scaling relationship between brain size (endocranial volume, ECV) and endocast measurements, and makes predictions about humans and fossil hominins based off the primate scaling relationship. Here’s the quick walk-through:

Go to the “Data sources” tab in the Google Sheet, follow the link to the Sketchfab Measurement Tool, and copy the link to the endocast you want to study (3D models can only be accessed with the specific links).

Following the endocast Sketchfab link (column D) will bring you to a page with the 3D endocast, as well as some information about how the endocast was created and includes its overall brain size (ECV in cubic cm). Pasting the link when prompted in the Measurement Tool page will allow you to load, view, and take linear measurements on the endocast.

Hylobates lar endocast, measuring cerebral hemisphere length between the green and red dots.

Sketchfab makes it quite easy to take simple linear measurements, by simply clicking where you want to place the start and end points. The 3D models of the endocasts are all properly scaled, and so all measurements that appear in the window are in millimeters.

The assignment specifies three simple measurements for students to take on each endocast (length, width, and height). In addition, students get to propose a measurement for the size of the prefrontal cortex, since our accompanying reading (Schoenemann, 2006) explains that it is debated whether the human prefrontal is disproportionately enlarged. All measurements are then entered into the Google Sheet — I wanted students to manually enter the ECV for each endocast, to help them appreciate the overall brain size differences in this virtual dataset (size and scale are often lost when you have to look at everything on the same-sized 2D screen).

Feel free to use or adapt this assignment for your own classes. The assignment instructions can be found here, and the data recording sheet (with links to endocast 3D models) can be found here — these are Google documents that are visible, but you can save and edit them by either downloading them or making a copy to open in Docs or Sheets.

Ah, teaching in the pandemic 🙃

Osteology Everywhere: Aerial Ossicles

Last month I was flying down to New Orleans for the AAPA conference. I was excited to try authentic beignets & sazeracs, present new research, and catch up with colleagues. Midway through the flight I glanced out the window, not expecting to see much. But lo!


Thankfully there wasn’t something on the wing. But there was something strange out there in the sparkle of sprawling city lights:


What’s that I spy outside the city center?

A bit outside of the main jumble of street lamps appears to be a concentration of light superficially similar to an incus, one of the three auditory ossicles of the middle ear:


Left: An osteologist’s nightmare at 20,000 feet. Right: Ear ossicles from White et al. (2012).

As a good mammal, there are three small bones inside your middle ear. These are fully formed at birth, and help transfer and amplify sound vibrations from your eardrum to your inner ear. It’s nuts. What’s even more nuts is that paleontologists and anatomists have figured out that the tiny, internal incus and malleus of mammals evolved from larger, external pieces of the jaws of our pre-mammalian ancestors. INSANITY!


Cross section of a right ear, viewed from the front. Image credit.

Being so tiny, it’s not surprising that auditory ossicles are not often recovered from skeletal remains, and are pretty rare in the human fossil record. Nevertheless, some are known and their comparison with humans’ ossicles is pretty interesting. The oldest inci I know of are from SK 848 and SKW 18Australopithecus robustus fossils from Swartkrans in South Africa (Rak and Clarke, 1979; Quam et al., 2013). SK 848 is on the left in the set of images below:


Incus bones in three different views of SK 848, human chimpanzee, gorilla, sock puppet (left to right). Modified from Rak and Clarke, 1979.

SK 848 to differs from humans and African apes in looking more like a screaming sock puppet with a horn on the back of its head. Additional ossicles are known from South African australopithecines, including the older A. africanus from Sterkfontein (Quam et al., 2013). Interestingly, malleus of these hominins is very similar to that of humans, and Quam et al. (2013) think this ossicle may be one of the first bones in the entire skeleton to take on a human-like configuration during hominin evolution. Functionally, this may mean that the frequency range to which human ears are adapted may have appeared pretty early in our lineage as well (Quam et al., 2015).

Who’d’ve thunk we’d learn so much just from looking out an airplane window?

ResearchBlogging.orgRead more!

Quam, R., de Ruiter, D., Masali, M., Arsuaga, J., Martinez, I., & Moggi-Cecchi, J. (2013). Early hominin auditory ossicles from South Africa Proceedings of the National Academy of Sciences, 110 (22), 8847-8851 DOI: 10.1073/pnas.1303375110

Quam, R., Martinez, I., Rosa, M., Bonmati, A., Lorenzo, C., de Ruiter, D., Moggi-Cecchi, J., Conde Valverde, M., Jarabo, P., Menter, C., Thackeray, J., & Arsuaga, J. (2015). Early hominin auditory capacities Science Advances, 1 (8) DOI: 10.1126/sciadv.1500355

Rak Y, & Clarke RJ (1979). Ear ossicle of australopithecus robustus. Nature, 279 (5708), 62-3 PMID: 377094

Bioanthro lab activity: Hominin brain size

Last week in my Human Evolution class we looked at whether we could estimate hominin brain sizes, or endocranial volumes (ECV), based on just the length and width of the bony brain case. Students took these measurements on 3D surface scans…

Maximum cranial length in Australopithecus boisei specimen KNM-ER 406.

Maximum cranial length in Australopithecus boisei specimen KNM-ER 406.

… and then plugged their data into equations relating these measurements to brain size in chimpanzees (Neubauer et al., 2012) and humans (Coqueugniot and Hublin, 2012).

The relationship between cranial length (x axis) and ECV (y axis).

The relationship between cranial length (x axis) and ECV (y axis). Left shows the chimpanzee regression (modified from Fig. 2 in Neubauer et al., 2012), while the right plot is humans (from the Supplementary Materials of Coqueugniot and Hublin, 2012).

So in addition to spending time with fossils, students also learned about osteometric landmarks with fun names like “glabella” and “opisthocranion.” More importantly, students compared their estimates with published endocranial volumes for these specimens, based on endocast measurements:

Human and chimpanzee regression equations don't do great at estimating hominin brain sizes.

Human and chimpanzee regression equations don’t do great at predicting hominin brain sizes. Each point is a hominin fossil, the x value depicting its directly-measured endocranial volume and the y value its estimated volume based on different regression equations. Black and red points are estimates based on chimpanzee cranial width and length, respectively, while green and blue points are based on human width and length, respectively. The dashed line shows y=x, or a correct estimate.

This comparison highlights the point that regression equations might not be appropriate outside of the samples on which they are developed. Here, estimates based on the relationship between cranial dimensions and brain size in chimpanzees tend to underestimate fossils’ actual values (black and red in the plot above), while the human regressions tend to overestimate hominins’ brain sizes. Students must think about why these equations perform poorly on fossil hominins.

Most of the fossil scans come from, but a few are from Artec’s sample gallery. One of the cool, fairly recent humans at African Fossils (KNM ER 5306) will give students something else to think about:

"Why doesn't this look like the rest of the human crania we've seen this semester?"

“Why doesn’t this look like the rest of the human crania we’ve seen this semester?”

Here are the lab materials so you can use and adapt this for your own class:

Lab 4-Brain size (Instructions & questions)

Lab 4 data table (with equations)

Coqueugniot, H., & Hublin, J. (2012). Age-related changes of digital endocranial volume during human ontogeny: Results from an osteological reference collection American Journal of Physical Anthropology, 147 (2), 312-318 DOI: 10.1002/ajpa.21655

Neubauer, S., Gunz, P., Schwarz, U., Hublin, J., & Boesch, C. (2012). Brief communication: Endocranial volumes in an ontogenetic sample of chimpanzees from the taï forest national park, ivory coast American Journal of Physical Anthropology, 147 (2), 319-325 DOI: 10.1002/ajpa.21641

Osteology Everywhere: Ilium Nublar

Jurassic Park is objectively the greatest film ever made, so I don’t need to explain why I recently watched it for the bajillionth time. Despite having seen this empirically excellent movie countless times, I finally noticed something I’d never seen before.

Hold on to your butts. What's that on the screen in front of Ray Arnold?

Hold on to your butts – what’s that on the screen in front of John Arnold? (image credit)

The film takes place on the fictitious island “Isla Nublar,” a map of which features prominently in the computer control room when s**t starts to go down. Here’s a clearer screenshot of one of Dennis Nedry‘s monitors:

Isla Nublar from the JP control room. Quiet, all of you! They’re approaching the tyrannosaur paddock…. (image credit)

It dawned on me that the inspiration for this island is none other than MLD 7, a juvenile Australopithecus africanus ilium from the Makapansgat site in South Africa:

Figure 1 from Dart, 1958. Left side is MLD 7 and right is MLD 25. Top row is the lateral view (from the side) and bottom row is the medial view (from the inside).

Figure 1 from Dart, 1958. Left side is MLD 7 and right is MLD 25. Top row is the lateral view (from the side) and bottom row is the medial view (from the inside). These two hip bones are from the left side of the body (see the pelvis figure in this post). Note the prominent anterior inferior iliac spine on MLD 7, a quintessential feature of bipeds.

Isla Nublar is basically MLD 7 viewed at an angle so that appears relatively narrower from side to side:

MLD at a slightly oblique view (or stretched top to bottom) magically transforms into Isla Nublar.

MLD 7 at a slightly oblique view (or stretched top to bottom) magically transforms into Isla Nublar.

It’s rather remarkable that some of the most complete pelvic remains we have for australopithecines are two juveniles of similar developmental ages and sizes from the same site. In both, the iliac crest is not fused, and joints of the acetabulum (hip socket) hadn’t fused together yet. The immaturity of these two fossils matches what is seen prior to puberty in humans and chimpanzees. Berge (1998) also noted that MLD 7, serving as an archetype for juvenile Australopithecus, is similar in shape to juvenile humans, whereas adult Australopithecus (represented by Sts 14 and AL 288) are much flatter and wider side to side. Berge took this pattern of ontogenetic variation to match an ape-like pattern of ilium shape growth. This suggests a role of heterochrony in the evolution of human pelvic shape, or as Berge (1998: 451) put it, “Parallel change in pelvic shape between human ontogeny and hominid phylogeny.” In layman’s terms, ‘similar changes in both pelvic growth and pelvis evolution.’