Minimi paravertebra
An armoured ankylosaur from the Cretaceous of Australia Image: Anne Musser
Anne Musser

Fast Facts

  • Classification
    Species
    paravertebra
    Genus
    Minmi
    Family
    incertae sedis
    Suborder
    Cerapoda
    Infraorder
    Ankylosauria
    Order
    Ornithischia
    Superorder
    Dinosauria
    Subdivision
    Avemetatarsalia
    Division
    Archosauria
    Infraclass
    Archosauromorpha
    Subclass
    Diapsida
    Class
    Sauropsida
    Series
    Amniota
    Super Class
    Tetrapoda
    Subphylum
    Vertebrata
    Phylum
    Chordata
    Kingdom
    Animalia
  • Size Range
    3m long
  • View Fossil Record
    Fossil Record
    Cretaceous Period
    (141 million years ago - 65 million years ago)

Introduction

Minmi paravertebra was an ankylosaur, a quadrupedal dinosaur covered in bony armour. It was discovered in 1964 near Minmi Crossing, Queensland, and was the first ankylosaur known from the Southern Hemisphere. Minmi had thin bony rods (ossified tendons, or 'paravertabrae') along its spine that may have been for muscle attachment. This extra muscle power along with its comparatively long legs may have made Minmi a speedy runner. A study of gut contents found that Minmi ate seeds, ferns and other soft plant material.

Identification

Ankylosaurs were heavy-bodied, quadrupedal herbivores. They were armoured for protection against predators. Minmi was unique among ankylosaurs (and other dinosaurs) in having small, backwardly directed bony projections (paravertebrae, or ossified tendons) along the backbone to provide extra attachment for back muscles. These were similar to the bony structures found in crocodiles that strengthen and support the back during the 'high walk'. Along with its unusually long legs, these paravertebrae suggest that Minmi could have outrun at least some predators rather than relying solely on armour for protection.

Minmi had belly armour (absent in most ankylosaurs and related stegosaurs) along with armour (scutes, spikes and dermal ossicles) over the neck and trunk. Minmi did not have a clubbed tail and, unlike almost all other ankylosaurs, had no dermal armour on the skull.

Habitat

During the Early Cretaceous, part of Queensland formed a large island separate from the rest of Australia. The environment is interpreted as a mix of floodplains and woodlands. Although Minmi was found in marine sediments, it was undoubtedly washed out to sea from this nearby terrestrial environment.

Distribution

Minmi fossils have been found at two sites in central Queensland. The first specimen was found at Minmi Crossing near Roma on the western Darling Downs, southeast Queensland. A second specimen was later found at Marathon Station near Hughenden in north central Queensland. Although ankylosaur fossils have now been found in both New Zealand and Antarctica, these fossils do not appear to belong to Minmi.

Feeding and diet

A study of preserved gut contents (cololites) in Minmi shows that it ate the seeds and fruiting bodies of flowering plants as well as ferns and other soft-leaved plants. This is the first such study in either ankylosaurs or stegosaurs, and the best evidence yet for the diet of herbivorous dinosaurs. It suggests a mainly herbivorous diet for Minmi (one theory proposes that ankylosaurs may have been partly insectivorous). The plant material found in Minmi's abdominal region was finely diced, and Minmi may have cut its food with its serrated cheek teeth after nipping the vegetation off with its beak. The food would then be within the mouth (possibly helped by development of fleshy cheeks). Gastroliths were absent, suggesting that Minmi's teeth were quite efficient at processing food.

Fossils description

Between the Minmi Crossing and Marathon specimens, about 90 per cent of Minmi'sskeleton has been found, including parts of its armour. This makes it the most complete Australian dinosaur known. The Marathon specimen has much of the body armour, including dorsal neck and trunk armour, as well as smaller ossicles covering the body over the neck, and possibly the limbs, as well as the belly. A transverse band of scutes (plates) on the neck, and spines projecting from the hip, are also preserved. A third, partially articulated specimen has also been recovered in north central Queensland but has not yet been described.

Evolutionary relationships

Minmi is placed within the Ankylosauria as its most primitive member. It is neither nodosaurid nor ankylosaurid, despite having some features of both groups. In a recent analysis, Minmi was placed close to but outside of to Nodosauridae. Minmi lacks some typical ankylosaur features, either because of its primitiveness (the most likely explanation) or because it has lost these more advanced features. As a basal ankylosaur, Minmi's ancestors probably appeared around the Middle Jurassic, making Minmi a relict from an earlier period in the Early Cretaceous of Australia (a trend seen in many other Australian Cretaceous plants and animals).

References

  • Carpenter, K. 2001. Chapter 21: Phylogenetic analysis of the Ankylosauridae. pp. 455-480 in Carpenter, K. (ed.) The Armored Dinosaurs, Indiana University Press, Bloomington.
  • Molnar, R. E. 1980a. An ankylosaur (Ornithischia: Reptilia) from the Lower Cretaceous of southern Queensland. Memoirs of the Queensland Museum 20, 77-87.
  • Molnar, R. E. and Frey, E. 1987. The paravertebral elements of the Australian ankylosaur Minmi (Reptilia: Ornithischia, Cretaceous). Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen. 175, 19-37.
  • Molnar, R.E. 1996. Preliminary report on a new ankylosaur from the Early Cretaceous of Queensland, Australia. Memoirs of the Queensland Museum 39, 653-668.
  • Molnar, R. E. 2001. Chapter 16: Armor of the small ankylosaur, Minmi. pp. 341-362 in Carpenter, K. (ed.) The Armored Dinosaurs, Indiana University Press, Bloomington.
  • Molnar, R. E. and Clifford, H. T. 2001. Chapter 19: An ankylosaurian cololite from the Lower Cretaceous of Queensland, Australia. pp. 399-412 in Carpenter, K. (ed.) The Armored Dinosaurs, Indiana University Press, Bloomington.

Further reading

  • Carpenter, K. (ed.) The Armored Dinosaurs, Indiana University Press, Bloomington.
  • Long, J. A. et al. 2002. Dinosaurs of Australia and New Zealand and Other Animals of the Mesozoic Era. New South Wales University Press, Sydney; 188 pp.