University of Michigan · ANTHRBIO 474 Hominid Origins · 2015

Endocasts in 3D

An endocast is a cast of the inside of a skull: the closest thing to a fossil brain. For Milford Wolpoff's Hominid Origins course I laser-scanned five endocast casts from his lab, then measured the casts, the scans, and 3D prints of the scans to see whether the copies are faithful enough for real measurements. Mostly, they are. The scans are below. Turn them, and take them.

By Caleb C. Vogt · page built with Claude Opus 5.5

5endocasts scanned

33D-printed

< 1.3%length, width, height
(scanned + printed casts)

< 4%volume

The scans

Drag to turn, scroll or pinch to zoom. These are lightened copies for the browser (70,000 triangles); the downloads are the full scans.

The five endocasts side by side at the same scale — All five at the same scale: the unknown primate, the Taung Child, STS 60, Jebel Irhoud 2, and La Quina 5.

How it was done

1 · Measure the casts

Maximum length, width, and height of each cast with digital calipers, three times each, averaged. Volume of the three smaller casts by how much brown rice each displaced in a graduated cylinder.

2 · Scan

Each cast was scanned with a handheld Creaform HandyScan 3D REVscan at the University of Michigan 3D Lab, and the passes stitched and cleaned up in Materialise 3-matic.

3 · Measure the scans

The same length, width, and height, taken on screen with 3D-Tool's measuring tool; volume straight from the closed surface.

4 · Print and measure again

The Taung Child, STS 60, and the unknown primate were printed on a Dimension Elite (0.254 mm layers), measured with calipers, and their volume taken by water displacement.

Endocast casts laid out on a table at the UM 3D Lab

The HandyScan 3D REVscan handheld laser scanner on its stand

Holding the scanner, with a scan building up on the laptop behind

The UM 3D Lab, spring 2015: casts waiting their turn, and the handheld laser scanner.

Jebel Irhoud 2 length measured on the scan

Unknown primate height measured on the scan

Unknown primate width measured on the scan

Measuring the scans in 3D-Tool. Each labelled line is one of the three repeats.

Did the copies measure like the casts?

Difference from the cast, in percent: (copy − cast) / cast. The casts' own values are the caliper averages; their volumes, rice displacement. The two large Homo casts were scanned but not printed, and their volume was not measured by displacement.

For the three casts that were both scanned and printed, every length, width, and height agreed within 1.3%, and the prints were about as close as the scans. Volume came out within 4%, the loosest of the measures, which says as much about rice and water in a graduated cylinder as about the scans. The biggest gap overall was Jebel Irhoud 2's height, 4.7% taller on the scan than by calipers: on a large, irregular cast, "maximum height" is easy to take from two slightly different places. So, for linear measurements and with student-accessible equipment, a scan or a printed copy can stand in for a cast, which matters because casts of these fossils are scarce, fragile, and expensive. Whether the scans are fine enough to compare individual sulci on the brain's surface was left for another day.

The poster

Poster: Validation of a Novel Method in Paleoneurology: Endocast 3D Scanning and Printing

Presented at the end of the course in 2015. Download the PDF. One correction: the poster says every measurement fell within 1% error, but its own error chart is in fractions, not percent. The table above has the actual figures.

Download the scans

Full-resolution STL files, in millimetres, free to use under CC BY 4.0: print them, measure them, teach with them. Please credit "Caleb C. Vogt (2015), endocast 3D scans". Each is a scan of a cast, not of the original fossil, and is only as good as the cast.