Anyone who thinks that the lion is king of the beasts obviously hasn’t taken a good luck at a Tyrannosaurus rex lately. However, since the T. rex has been extinct for a pretty long time, and Jurassic Park is unlikely to become reality, today you can only see models or skeletons of the great dinosaur. 3D printing technology has been used to recreate T. rex bones, study its smaller cousin, and determine its level of intelligence, and now a team of forensic dentists has 3D scanned the T. rex skull at the Field Museum of Natural History in Chicago.
The dentists scanned the skull of the dinosaur, dubbed Sue, in hopes of determining the cause of some strange holes in its jawbone. Sue was discovered in 1990, and is the largest, most complete T. rex skeleton found yet. For a long time, researchers assumed that the holes were teeth marks, likely caused by another attacking Tyrannosaurus. A group of University of Wisconsin paleontologists posited in 2009, though, that the holes could have been caused by a protozoal infection that penetrated the dinosaur’s jaw after eating infected prey.
To get a closer look at these holes, forensic dentists received permission to scan the skull; however, they realized that their high-resolution dental scanners couldn’t handle Sue’s enormous jaw. So they contacted the MIT Media Lab’s Camera Culture group, which is focused on developing a new class of imaging platforms. In 2015, the group created a prototype system for producing high-resolution 3D scans: by exploiting the polarization of light, the system was able to increase the depth resolution of conventional 3D imaging devices by as much as 1,000 times.
Once again, the size of Sue’s skull caused problems, and the prototype wasn’t able to take on the big job. But instead of giving up, the group pieced together a new system, using free software and $150 in hardware, that was able to produce a viable 3D scan of the five-foot-long skull. They published their results in a paper entitled “A method for rapid 3D scanning and replication of large paleontological specimens” in PLOS One; co-authors include Anshuman Das, a research scientist at the Camera Culture group; forensic dentists Kenneth Cohrn and Denise Murmann; and Ramesh Raskar, professor of media arts and science at MIT.
Das, the first author on the paper, said of the system, “A lot of people will be able to start using this. That’s the message I want to send out to people who would generally be cut off from using technology — for example, paleontologists or museums that are on a very tight budget. There are so many other fields that could benefit from this.”
If you’ve taken a look at 3DPrint.com’s 3D Scanner Buying Guide 2017, you know that there are all kinds of 3D scanners available, from inexpensive and portable to high-cost and high-resolution. A high-end commercial 3D scanner could set you back tens of thousands of dollars, but offer a depth resolution of 50 to 100 micrometers. MIT’s system uses a Microsoft Kinect, which features a resolution of only 500 micrometers but cost just $100. Its built-in software features a point cloud, which is a 3D map of points in a visual scene, where short infrared light bursts are reflected back to a sensor. Free MeshLab software analyzes the point cloud, and then infers the shape.
“A Microsoft Kinect v2 module was utilized as the 3D scanner. It is a module typically used for gesture recognition in gaming and can be modified to capture raw 3D scan data. The Kinect has a 1080p camera operating at 30 Hz that can also capture a regular 2D image that can be used to overlay the color image on the 3D reconstruction. The depth sensor operates at 30 Hz and has a 512×424 sensor. The minimum and maximum depth distances are 0.5 m and 4.5 m, respectively. The horizontal field of view is 70 degrees and the vertical field of view is 60 degrees. These features make the Kinect ideal for scanning large specimens,” the researchers state in their paper.
To capture the whole thing in as much detail as possible, while making a high-tech fashion statement, Das mounted the Kinect in a modified camera harness on his chest to scan Sue’s skull.
A team of researchers, which includes anthropologists, dentists, paleontologists, and veterinarians, is now using the Camera Culture’s 3D scan of Sue’s skull to analyze the mysterious jawbone holes. The scan disproves the hypotheses both that the holes were caused by an attacking T. rex and that they were caused by infection: according to MIT News, the holes taper from the outside in, which means no infection; additionally, “the angles at which the holes bore through the jaw are inconsistent enough that they almost certainly weren’t caused by a single bite.”
“Three-dimensional scanning has really revolutionized paleontology. We’re able to ask and answer a lot of quantitative questions. But in general we are a pretty underfunded field, and for a lot of folks, off-the-shelf scanning systems are still out of the usual reach of a research budget,” explained Peter Mackovicky, associate chair of paleontology at the Field Museum. “Having something that is very cheap, versatile, and relatively fast is certainly useful. And one nice thing about [the new] system is that your results are immediate. You can see in real-time whether you’re capturing the data you need, which is a great benefit.”
Das believes that Kinect scans could help in fields like archaeology and anthropology as well, so researchers and scientists who uncover large, fragile artifacts in remote areas of the world can scan them, and then share the scans with others. Additionally, some facilities, like the Field Museum, limit the amount of time researchers can spend with artifacts like Sue’s skull, so having 3D scans readily available is helpful.
Additionally, if researchers want to examine a certain feature of a 3D scan in detail, a replica can be 3D printed; the Camera Culture group demonstrated this by 3D printing a few models of Sue’s skull, at one-eighth the size. The high accuracy of the resulting 3D prints validated the 3D scanning method, the researchers reported, “indicating an accurate reconstruction.”
“It’s that critical size. If it’s something really small, you can use a 3-D scanner. But if you have something stationary that’s difficult to move, you just put on the [Kinect] rig and walk around,” said Das.
The Camera Culture group and a team of collaborators, including the Wisconsin paleontologists, are working together to determine what exactly caused the holes in Sue’s jawbone.
Mackovicky said, “For me, one of the challenges is working in other countries. I worked with local paleontologists in Argentina, and we have some material that’s been dug up, and we have a nice new species of very large meat-eating dinosaur. I tried some years ago to do some scanning with an entry-level tabletop laser-scanner system, and it was fairly good for some parts but extremely time consuming — literally hours for a single bone. [This] system is much, much faster. For a project like that, for me to have copies of these bones — which are far too large to ship here for study and also would require a very extensive permit application process to leave their country of origin — this is a really useful tool.”
Discuss in the T Rex forum at 3DPB.com.[Source: MIT News / All images: Anshuman Das, Kenneth Cohrn, Denise Murmann, and Ramesh Raskar via PLOS One/MIT News]