Scientific name:

Pronunciation:

Etymology:

Classification:

Geology:

Age:

Length:

Height:

Weight:

Discovered:

Custodian:

Minmi paravertebra (Molnar 1980)

min-mee  par-ah-ver-te-bra

From Minmi Crossing, having paravertebrae

Thyreophora, ?Ankylosauridae

Bungil and Toolebuc Formations (Allaru Mudstone) central eastern Queensland

Approximately 3 m

Approximately 1 m

Unknown

1964 by Dr Alan Bartholomai of Queensland Museum

Queensland Museum
Hughenden display specimen can be seen at Kronosaurus Korner, Richmond

 Minmi head reconstruction by artist Paul Stumkat 

Articulated fossil remains of the Minmi Roma specimen.
Image modified from Long 1994.

Minmi paravertebra is tentatively classified as an ankylosaur, a quadrupedal (four legged) dinosaur with body armour. Discovered in 1964, Minmi was the first ankylosaur known from the Southern Hemisphere. 

Ankylosaurs belong to a group of dinosaurs called the thyreophorans, which varied greatly in size and morphology (body form). Threyophorans include the ankylosaurs, nodosaurs, ceratopsians, stegosaurs and scelidosaurs.

Thyreophorans are called "shield bearers" because they usually have a well-developed body armor of bony plates (called "scutes" or "osteoderms") in their skin as well as more extreme defenses such as huge projecting spines and tail clubs. Ankylosaurs are amoungst the most well-armored of the group and could grow to massive size (Ankylosaurus being over nine metres long).

Both the Roma and Hughenden Minmi
specimens have been referred to as "mummified" because bones and other body elements were fossilised together and still attached, as in life. Mummified dinosaurs are rare and particularly valuable for research as they can tell us much more than bones alone. For example, the Hughenden Minmi fossil has preserved stomach contents, study of which found that Minmi ate seeds, ferns and other soft plant material.

Also preserved in Minmi are belly osteoderms, which show that even the underside was protected by small embedded bony scutes, each about 5 mm in diameter. Most thyreophorans lack bely armor, but their bodies were typically covered in rows of medium-sized scutes with polygonal masses of small scutes in between.

Minmi had bony body armor, on its head, back, abdomen, legs, and along the tail. Several types of armor are known and articulated in Minmi sp., including small ossicles, small keeled scutes on the body, large scutes without keels on the snout, large keeled scutes on the neck, shoulders, and possibly tail, spike-like scutes on the hips, and a combination of ridged and keeled scutes and triangular plates on the tail. One ring of scutes is preserved around the neck. The arrangement of armor is unclear on the tail, although the triangular plates may have run along the sides of the tail, with long scutes forming a row along the top. We do not know if Minmi had a tail club as this was not preserved in specimens to date, however it was a feature common to Ankylosaurs.

Just speculating...
Minmi's unusual defensive features are evolutionary adaptations to contend mainly with predators. On the other side of the arms race, Australovenator, a likley contemporary predator of Minmi, may have evolved its characteristic killing claw to attack animals like Minmi as its claw might have been quite effective in penetrating thick armored skin. It could conceivably have a greater penetrating ability than a row of teeth, since with a bite the force is distributed across several tooth points rather than at a single focused claw point.

Spikes along Minmi's hips and tail could also have discouraged attack from above as well as make it difficult for a predator to leap onto its hind quarters from behind to slow it down.

PARAVERTEBRAE

Minmi's is unique, even among ankylosaurs, in possessing paravertebrae; horizontal bony projections that lie alongside the neural spines of the dorsal vertebrae. These long thin bony rods, first identified by Molnar and Frey (1987), are thought to be ossified (turned to bone) tendons for muscle attachment. The paravertebrae resemble in both form and relationship to the ribs and vertebral column, the tendons and tendinous sheets (aponeuroses) of crocodiles. In crocodiles, these tendons strengthen and support the back and provide additional attachment areas for back muscle, allowing young crocodiles to gallop. The tendons and aponeuroses of crocodiles attach to dorsal armour and are not ossified.

Paravertebrae may exist in other ankylosaurs but have not been preserved, possibly because they were not ossified as they are in Minmi.

One theory concerning the function of the paravertebrae suggests that they reinforce the back to help it run. Most ankylosaurs would have been too large and heavily armoured to run with any speed, but given Minmi's small size (around 3 metres long) and its relatively long legs (for an ankylosaur), this theory has merit.

Paravertebrae of Minmi compared with tendons of the back musculature of crocodiles. A, C Minmi dorsals with one paravertebrae shown on the right; B, D crocodilian dorsals (and scutes at left) with a tendon of the dorsal trunk musculature (in black) on the right. The general similarity in form may be seen. A, B, dorsl views; C, D, lateral views. (From Molnar & Frey 1987).

Typical of many Australian dinosaurs, Minmi differs from similar animals in other parts of the world by being either an ancestral or divergent type.

Minmi has very characteristic vertebrae. In addition to paravertebral elements, dorsal vertebrae have short neural spines, are amphiplatan without notochordal knobs, transverse processes are slender and triangular (not T-shaped), the neural canal is broad, and the posterior intervertebral notch is shallow.

Teeth have seven to nine well-pronounced denticles, furrowed on one side and mostly smooth on the other.

The relationship between Minmi and other armored dinosaurs remains uncertain as it shares some ankylosaur features yet retains many primitive features expected from an ancestral thyreophoran. For example, the skull is longer than wide and the pattern of the bones that make up the skull are more similar to scelidosaurs than either ankylosaurs or nodosaurs, the snout region arches higher than the base of the skull, a feature of nodosaurs. The femur of most ankylosaurs it is flattened fore and aft, whereas Minmi's is rounded in cross section similar to ancestral thyreophorans. The acetabular and postacetabular regions of the ilium are long like that of scelidosaurs, whereas in ankylosaurs and stegosaurs it is much shorter. Minmi may turn out to be closer to ankylosaurs than to nodosaurs, although if so it seems to have split off early in its evolution. 

Restored Minmi vertebra (from Long 1998 after Molnar 1996).
Left; Side view. Right; front view.

Minmi skull (after Molnar 1996).
Left; side view or restored skull. Right; top view as preserved.