DIY Ice Age Fossil Replicas

In this project we'll be making 3D-printed replicas of fossilized animal bones, based on 3D scans of real fossils. They make excellent educational tools and/or decor. Most of the animals we'll be focusing on in this guide died out around 10,000 years ago, near the end of the last ice age, when the warming climate and human activity likely contributed to their demise, but these techniques could be used to replicate fossilized remains of other creatures as well. The replicas I've made are part of an educational exhibit I designed to display in local libraries in my area. It includes the woolly mammoth, American mastodon, prehistoric giant beaver, extant North American beaver, giant ground sloth, giant short-faced bear, and dire wolf. By studying the fossils of now-extinct animals, we can learn about how they lived, what they ate, and why they are no longer with us. Imagine the short-faced bear, the largest land predator in North America during its time, standing 12 feet (3.7 meters) tall on its hind legs. With long legs and forward-facing feet (most modern bears are a bit pigeon-toed) it could have ran up to 40mph while using it's large short snout to smell for prey from far away. Terrifying, right? Now imagine the day that the last short-faced bear died and the species was lost to time forever. It was surely a sad day, and there are so many other amazing creatures that we lost along the way. By making 3D printed replicas of the remains of these animals, we remember them, learn more about them, and in some small way bring them back to life, if only in our imagination. Let's get started!

1. A 3D printer (I use a large format FDM, specifically the Elegoo Neptune 3 Plus which is in the 300mm size class)
2. A computer w/ internet connection for downloading and slicing .stl files
3. 3D printing filament; PLA works fine (ideally white or off-white/bone colored)
4. Sandpaper
5. White paint (preferably water-based paint-and-primer, or primer)
6. Matte clear spray paint (I prefer Krylon)
7. Wood stain(s) (color depending on desired finish)
8. Brushes for applying paint and stains
9. Rags or paper towels for wiping off excess stain

Optional equipment for hiding seams of models printed in multiple pieces:

1. 3D pen
2. a piece of filament in a dremel
3. super glue and baking soda
4. soldering iron

Optional equipment for mounting the finished replicas to stone bases:

1. Thin flat stones (limestone makes for easy drilling)
2. Masonry drill bits
3. Hollow-wall anchors w/ screws
4. e6000 adhesive
5. Drill, preferably with a hammer-drill setting.

Sketchfab, Morphosource, and Smithsonian 3D Digitization are just a few of the sites I use to find good 3D scan data. Because I'm an informal educator, I'm going for maximum accuracy with my models, so I've only printed models that were based on 3D scan data of real fossils, but there are a lot of good ones out there that are sculpted by artists too, and you can find those on sites like Cults3d. Here are the models I have printed:

You can find the 1/10 scale Woolly Mammoth here. The woolly mammoth mammuthus primigenius is a member of the elephant family that mostly died out around 10,000 years ago, although a small population was able to survive on an island off the coast of Siberia (northern Russia) until about 4,000 years ago, around the time the pyramids were being built in Egypt. Their thick coats of multi-layered fur made them well adapted to cold climates. Humans used ivory from their tusks, their hides for shelters, and meat for food.

Here's the saber-toothed cat, smildon fatalis. The most well-known and second largest of the saber-toothed cats, smilodon fatalis ("fatal scalpel tooth") had long upper canine teeth that could reach 7 inches in length. While similar in size to a modern African lion, they were more muscular and had shorter limbs. They likely preyed on bison, horses, and other large herbivores.

Here's the giant short-faced bear, arctodus simus. The short-faced bear was the largest and most powerful land predator in North America during its time. Taller than modern bears, with longer limbs and forward facing toes, it is believed this bear was built to chase its prey to exhaustion, running up to 40mph. Reared up onto its hind legs, it stood up to 12 feet tall and likely preyed on large herbivores like ground sloths, horses, and bison.

Here's the prehistoric giant beaver, castoroides ohioensis. These massive rodents, the largest beavers ever, could grow to the size of modern-day black bears. They were very similar in appearance to modern beavers, although with much larger hind feet, relatively shorter legs, and extraordinary teeth. It is assumed they lived a semi-aquatic lifestyle, munching on aquatic plants similar to the way the modern-day African hippopotamus does. It is also believed that they did not build dams, but may have lived in burrows the way that muskrats do.

Here's the regular sized beaver castor canadensis to go with the giant beaver (for scale). The modern North American beaver is a semi-aquatic rodent that lives in dams and lodges it builds from trees and branches. It cuts down trees and cuts them apart using its powerful bite and sharp incisors. Their front teeth are orange because they have iron in their enamel, which makes the teeth stronger. They can swim at speeds of up to 5 miles per hour, and can stay underwater for up to 15 minutes. They lived alongside the Giant Beaver during the last ice age.

Here's the dire wolf, aenocyon dirus. Slightly larger and more robust than modern grey wolves, the dire wolf was a canid carnivore that once roamed much of the contiguous United States, as well as further south into Central and South America.

Here's the 1/10 scale American mastodon to go with the 1/10 scale mammoth. The American mastodon, mammut americanum, is a member of the elephant family that mostly died out around 10,000 years ago. Generally shorter, stockier, and less hairy than the woolly mammoth, they had straighter tusks than mammoths and also lacked the domed skull. While mammoths have flat teeth with ridges like a washboard that helped them chew food they found in grasslands, mastodons have cone-like cusps on their molars that helped them chew tough food that they found in their forest habitat.

Here's the giant ground sloth, megalonyx jeffersonii, named in honor of United States founding father and statesman Thomas Jefferson, who, upon seeing the giant claw bones of an unknown animal that had been found in a cave in Kentucky in the early 1800s, mistook them for the claws of a giant lion. Thus, megalonyx ("great claw"). The bones were later discovered to be from giant ground sloths, large herbivores the size of cows that could stand on their hind legs to eat from trees. Its large claws are adapted for digging.

3D printing is a hobby unto itself and explaining how to go about it in detail is beyond the scope of this instructable; However, I'll go over the specifics that pertain to printing fossil models.

Since I'm usually going for non-structural replicas that aren't meant to be handled, I've often opted to use 3 walls and lightning infill. This results in a finished print that is very conservative on filament, and I haven't had any trouble with having flimsy prints because the natural shapes of the bones are pretty good at being light and strong to begin with. Using z-hop when retracted is a good idea because even though it will slow down some already long prints, it can prevent the nozzle from catching on parts of the print that warp slightly if you are using thin walls and lightning infill.

Optionally, if you knew the mass of the skull or other bone you are trying to replicate, you could set the infill density percentage to result in a finished print with the same mass. This would probably only be meaningful for a classroom setting where the finished fossil replica will be picked up, as the correct mass would add to the realism. I usually print mine in way that's so conservative on filament that it feels like a blow-molded plastic skull you'd get at a dollar store to use as Halloween decor, but mine aren't meant to be picked up anyways so it doesn't matter if they feel fake when hefted.

I usually print my models in white but there are bone colored filaments you can use as well. As long as you print the model in one piece, it will look pretty good. Seems are harder to hide if you don't go through the finishing steps of painting and coloring with wood stains that I usually do.

I use an Elegoo Neptune 3 Plus for my printing, because it's in the 300mm bed size class, and it has fit most of the models I've printed fairly well with some creative positioning. I usually end up splitting models because they don't have any flat surfaces to rest on the build plate and cutting the model apart will create some while also if done properly reduce the need for supports. However, since switching from Cura slicer to Orca (or Elegoo slicer, which is a fork of Orca) I've notice improved results with supports and that's how I was able to print the American mastodon model with impressive results, so that's probably something to consider if you are still using Cura.

Once you've printed a model, you'll have to remove it from the print bed and remove all brims, supports, and other extraneous bits of plastic that aren't part of the model itself. This is all pretty straightforward but removing supports can be pretty tedious on some of the more detailed models like the American mastodon. Just be patient and imagine yourself as a paleontologist carefully extricating a fossil from the surrounding stone. You may have to do a bit of sanding afterwards in the areas where the supports attached to the model.

Obviously it's better if you can get away with printing the model in one piece but if you don't, there's a few different ways you can go about trying to hide the seam. I've tried all of these methods, and didn't really like any of them:

1. 3D pen
2. a piece of filament in a dremel
3. super glue and baking soda
4. soldering iron

Automotive body filler is another possible choice for trying to hide the seams, but I haven't tried it on fossil models. The problem is that the seam is usually pretty small, so it can be hard to get materials to actually go into the crack. The 3D pen method works okay, but depending on how fancy your pen is it may not have the fine controls to precisely vary the extrusion speed which is pretty critical. You may still end up coming back over the seam with a soldering iron (preferably temperature controlled) to smooth things out. The piece of filament in a Dremel method is supposed to spin the filament so fast that when it rubs on the model it melts a bit, and this can be a bit like stir welding the seam together. It works okay but not when the crack is large because it doesn't lay down much material.

The first thing I do is apply a white or off-white paint, usually a paint-in-primer or primer, to the print. This is to help hide the layer lines of the print, and give the subsequent finishes something to stick to rather than just the raw plastic. Primers often have blocking solids in them which makes gives them more substance than traditional paint, which is good in this application. I use brush paints because sprays will generally take too many coats to reach the desired thickness of coverage. It can be a bit tedious to reach all the nooks and crannies of a skull but it's worth it. We can also do multiple coats which will help to cover imperfections and layer lines, and seams if the model was glued/fused together from multiple peices. If we just skip this step and go to applying wood stains the stain will just pool in the layer lines and imperfections of the print and make it look bad. It's okay if the paint job gets a little blobby or is imperfect because fossils are natural artifacts and aren't perfect.

The next thing is applying the wood stains. Minwax Golden Oak is a good one, and is what I used on the saber-toothed cat skull. It usually gives a soft "found this fossil in a dry lake bed" finish, but you can try other stains with darker finishes, to achieve something more akin to "found this in a bog". Some finishes that are very dark will give more of a "found in a tar pit" finish like on the woolly mammoth skeleton I made. Wood stains are good for this application because they self-level, resist the formation of lapping marks, and are semi-transparent. This means that you can simply apply more coats if you want a darker finish, and you can also apply coats of a different stain color and the colors will blend a bit visually so you aren't likely to end up with hard transition lines. I usually apply the stain and let it dry for a bit (the time depends on what kind of stain it is and what its dry time is) and then take a rag and wipe off areas that I want to highlight, usually the teeth. On some of the skulls like the dire wolf or the giant short-faced bear, I used darker stains to darken the areas around the base of the teeth. I also generally allow the stain to naturally pool in the low areas of the model, and in places like the nasal passages, to allow them to dry darker. This helps to bring out the detail of the model and make it seem more realistic.

Since most wood stains are going to leave your fossils a bit shiny, and most fossils aren't shiny, or at least not that shiny, you probably want to dull that down to a matte finish. You also want to lock in your work and give it some protection from UV rays and things like that, and make it easier to dust. So, I usually apply a coat or two of Krylon matte clear spray. It's the best one that I've tried for this application, and leaves a nice soft matte coating similar to what you'd expect a bone to have. It also dries fast.

Many of the models look better with some kind of a base, and some kinda need a base (like the mammoth and mastodon) in order to stand up. The 3D print files for the mammoth include a 3D printable base, but the mastodon does not. I like to use stone, but wood or other materials would work as well as a base material. Stone, I think, looks best but it's also the hardest (literally) to work with. Glue can hold the models to a base, and in some cases like the giant short-face bear, I basically just glued the model to a flat rock with e6000. For other models, like the saber-toothed cat, I wanted them mounted with mouth open so that necessitated a metal rod to support the cranium at its base. The shiny stainless steel tubes that often comprise the stem of cheap solar stake lights are what I used, and in the case of the saber-tooth I used steel wires running through the tube with loops at the end that I could send screws through into the rock.

As for drilling into the rocks to set anchors, I used regular masonry drill bits that are usually meant for things like brick, cinder block, and concrete. I just used them in a regular drill, but a hammer-drill would probably be better. Most stones are actually harder than either brick, cinder block, or even concrete, so while I've had decent luck with drilling limestone, sandstone is much harder to drill and it's been a bit hit-or-miss in that area. More typical methods for drilling in stone involve things like diamond burrs that I don't have. Whatever you do, just make sure to wear eye protection and keep your bit lubricated with plenty of water. Once I have made a hole in the rock, I just insert a hollow-wall anchor like the kind you would use in drywall and then put a screw into it. Even with a screw, I usually add e6000 glue to the area to help stabilize everything.

In my case, I've decided to put all my fossil replicas together into a public display, to tour around to some of the different public libraries in the area and maybe even a bank. I also like to include freebies like free stickers and coloring sheets in my displays. Obviously I went big, but even one fossil replica is enough for an educational public display if paired with an info graphic or other kind of informative sign. Attached to this step are some PDF files that you can print out to make little 4"x6" signs detailing the size and estimated range of each animal, along with some interesting facts. They are designed to fit into the little 4"x6" vertical plexiglass frames (I got mine from Walmart). Anyways, thanks for reading and happy fossilizing!