August 2025 Natural Mystery Answered

We received three correct answers to last month’s Natural Mystery. Congratulations to Ronnie Hartman, Greg Schayes, and Kirsten Welge for correctly identifying the original owner of this skull. All three used Mark Elbroch’s Animal Skulls as their reference. Their process ranged from simple visual comparisons to detailed analysis of specific features.

This is the skull of a plains pocket gopher (Geomys bursarius).

Ronnie will kick us off with her straight-forward and totally effective analysis:

"The skull size appears to fall within the right parameters, and the skull features seem to match what I'm seeing in Elbroch's Animal Skulls, while nothing else looks close, as far as I can tell.” 

Ronnie notes that she isn’t conversant with skull terminology—but she clearly still knows what to look for when comparing skulls. I don’t know how many people unfamiliar with skulls morphology would say that nothing else among the 275 skulls illustrated in Elbrock’s 727 page tome “even looks close” to the skull in our photo. The technical language used for describing skulls can help us talk about the difference we see, but seeing the differences is the important part.

Greg tells us a bit more about the difference he sees. He began by noting the color of the incisors and considering the habitat before consulting his references:

“The first obvious characteristics of this skull I noticed were the long yellowish incisors which pointed me to the rodent order. Thinking about the habitat (large sandy area) I put pocket gophers on the top of my list. Referencing Mark Elbroch’s Animal Skulls book I check the overall length, which I estimated to be 55mm putting it in the middle of the range for the Plains Pocket Gopher (40.5mm-60.0mm). Other notable features that are diagnostic of Pocket Gophers are the relatively flat top of the skull and the large gap (diastema) between the incisors and the other teeth.”

Kirsten offers detailed descriptions of the skull, using fairly technical language. This technical language is quite helpful for discussing skull features—but it takes some time to get familiar with it. I’ve included definitions and descriptions for several of the terms she uses.

"Overall skull shape is very flat along the dorsal [top] line. Dentition [teeth] shows orange incisors; a large diastema [gap between teeth—in this case, the gap between incisors and cheek teeth]; and cheek teeth that appear “swept back.” The zygomatic arches [cheekbones] are missing. Auditory bullae [smooth, rounded projections on the bottom of the skull near the back which enclose parts of the inner ear] are large. The skull measures 5.3 cm L, 2 cm H.

Overall mandible [jawbone] shape is deep and very curved from incisor to the coronoid process [uppermost projection at the rear of the jawbone], with rather shallow scoops dividing the processes [bony projections] at the back.  L 3.7 cm, H 2.5 cm

Developing a Candidate List: When I see a large diastema on a small skull, I go straight to rodents and lagomorphs as my top candidates."

Kirsten then ruled out cottontails and other lagomorphs due to the size; the flat top and curving mandible; and the “lack of fenestrae [literally ‘windows’] (lace-like bone structure) in the jaw.” This left her with a short list of four rodents:

"Eastern gray squirrel skulls show a gentle arc from rostrum to the top of the cranium [the complete skull, excluding the mandible or jawbone] behind the eye sockets, then a drop to the occipital crest [the side-to-side ridge at rear of the cranium, just above where it attaches to the neck]. Their cheek teeth also appear more like human molars, showing cusps. The skull length range is reasonable, though from 5.3-6.6 cm.

Muskrat overall skull shape is similar but has a subtle peak to the dorsal line. Muskrat skulls would typically be larger (5.8 cm-7.2 cm length). Their mandible is a pretty good match for the radical curve, but shows much larger scoops between the processes than what's seen here.

Woodchuck: the overall skull shape is a reasonable match, but is much larger than our specimen (lengths of 7.3-10.2 cm). Woodchuck mandibles are also much flatter than the mandible in the photo.

Pocket Gopher: the range of skull lengths spans our example (4-6 cm), and all observed features from our sample are present."

As Ronnie, Greg, and Kirsten all demonstrate, skull identification basically boils down to comparing the size and shape of the skull as a whole and of specific features on the skull. Congratulations to all three for sorting out last month's Natural Mystery and sharing some details of their process with the rest of us. And thanks as always to everyone who submitted an answer.