A study of the fossilised remains of an as yet unnamed species of ankylosaurid suggests that these dinosaurs were adapted for digging. Whilst it seems unlikely that these large herbivores could have lived in burrows, they may have been able to dig for roots and tubers, excavate wells in dried up rivers to reach subsurface water and dig into sediments to obtain supplementary minerals in a similar way that extant elephants do today.

The compact and low-slung Pinacosaurus could have been adapted for digging.
A compact and low-slung body shape with powerful limbs could be adaptations for digging. The low profile of the PNSO Pinacosaurus ankylosaurid model. A newly published scientific paper suggests that these types of dinosaurs may have dug shallow pits in which they could protect themselves from attack. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

Digging Pits to Protect Their Undersides

Furthermore, many palaeontologists have postulated that these armoured herbivores might have been able to hunker down to defend their limbs and undersides from theropod predators. If these animals dug shallow pits they might have been able to protect themselves from attack and make it difficult for carnivorous dinosaurs to spot them when they were partially buried. Horned lizards (Phrynosoma) have a similar flat body and lateral fringe scales as seen in some types of ankylosaurid, these extant reptiles adopt these types of defensive strategies.

Discovered in the Early 1970s

Remains of an armoured dinosaur was first reported by a joint Soviet-Mongolian expedition to the southern Gobi Desert of Mongolia in the early 1970s. The skeleton consisting of dorsal vertebrae, elements from the limbs, ribs parts of the pelvis and the pectoral girdle along with several armoured scutes, was partially prepared for removal, but the excavation was not completed. The fossil specimen remained uncollected but crated up until 2008 when it was taken away for preparation by members of a Korean/Mongolian research team.

The crate containing (MPC-D 100/1359)
A close view of the crate containing the postcranial remains in a dorsal orientation. The fossil specimen was partially crated up but not removed from the site at Hermiin Tsav in the southern Gobi Desert (Mongolia). Abbreviations sc = scapula, dr = dorsal ribs, il = ilium.

Probably a New Species of Armoured Dinosaur

The sandstone sediments of the Upper Cretaceous (Middle to Late Campanian stage), Baruungoyot Formation have yielded the remains of three ankylosaurid taxa, namely Saichania chulsanensis, Tarchia kielanae and Zaraapelta nomadis. Writing in the journal “Scientific Reports” the researchers which include such luminaries as Phil Currie and Eva Koppelhus (University of Alberta), Michael Ryan (Canadian Museum of Nature) and corresponding author Yuong-Nam Lee (Seoul National University, South Korea), state the unnamed ankylosaurid has some similarities to S. chulsanensis, but there are anatomical differences. Unfortunately, very little postcranial fossils of Tarchia kielanae and Zaraapelta nomadis have been found making it impossible to undertake a direct comparison with this specimen (MPC-D 100/1359).

Photograph (a) and line drawing (b) of ankylosaurid fossil material.
The new ankylosaurid postcranial specimen (MPC-D 100/1359). Photograph (a) and line drawing (b) of the specimen in ventral view. Note scale bar equals 1 metre.

Adapted for Digging

The scientists speculate that several anatomical features identified in MPC-D 100/1359 could indicate that this ankylosaurid was adapted for digging. The bones in its front feet are arranged in a shallow arc, which could have enabled it to dig soft earth. The fused vertebrae and the reduced number of bones in its hind feet, compared to other dinosaurs, may have helped anchor the ankylosaurid when digging or moving its tail. The body shape of MPC-D 100/1359, which is wider in the middle and narrower at the front and rear, may have helped its body to remain straight when digging. These traits such as the narrow-wide-narrow body shape and the manus (hand) and pes (foot) bone configuration are also known in other ankylosaurids.

Dig Those Ankylosaurs

Digging for resources out of reach from other animals and excavating shallow pits as part of a defensive strategy might have been prevalent amongst these armoured dinosaurs.

Ankylosaurid skeletal drawing.
Line drawing of the ankylosaurid skeleton, known elements in white (c) dorsal view, (d) left lateral view with armour shown, (e) left lateral view with armour removed. Note scale bar = 1 metre.

To read Everything Dinosaur’s article from 2014 about the discovery of Zaraapelta nomadis: New Species of ankylosaurid in Praise of Victoria Arbour.

The scientific paper: “A new ankylosaurid skeleton from the Upper Cretaceous Baruungoyot Formation of Mongolia: its implications for ankylosaurid postcranial evolution” by Jin-Young Park, Yuong-Nam Lee, Philip J. Currie, Michael J. Ryan, Phil Bell, Robin Sissons, Eva B. Koppelhus, Rinchen Barsbold, Sungjin Lee and Su-Hwan Kim published in Scientific Reports.

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