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Minmi (dinosaur)
Encyclopedia
Minmi, named after Minmi Crossing, Australia
(where it was found), is a genus
of small ankylosauria
n dinosaur that lived during the early Cretaceous Period, about 119 to 113 million years ago. The type species
, M. paravertebra, was described by Ralph Molnar
in 1980. A new cladistic analysis performed by Thompson et al., 2011 suggests that Minmi is the basalmost
known ankylosaurid.
Previously holding the record for the shortest dinosaur genus name, the title now goes to Mei
, a carnivore from China that was named in 2004, and Kol
, a carnivore from Mongolia that was named in 2009. Two good specimens of Minmi have been described, including a mostly complete skeleton, and additional fragments may pertain to this genus.
Minmi was found near the Minmi Crossing, in the Bungil Formation, near Roma, Queensland
, Australia
. It was first described in 1980 by Ralph E. Molnar
, who also named the type
(and only known) species.
. The dinosaur grew to about 2 m (10 ft) long and was roughly 1 m (3 ft) tall to the top of the shoulder
. Minmi probably moved relatively slowly on four legs, based on its estimated mass and its leg length as determined by scientists from fossilized tracks.
dinosaur, classified in Ankylosauria
(too primitive to be included in either the Ankylosauridae
or Nodosauridae
), that was quadrupedal and had a long tail. As with other ankylosaurians, Minmi was herbivorous
. Unlike most herbivorous dinosaurs, there is direct evidence of the diet of Minmi: gut contents are known from the well-preserved nearly complete Minmi sp. specimen, found in the abdominal cavity in front of the left ilium
. The gut contents consist of fragments of fibrous or vascular
plant tissue, fruit
ing bodies, spherical seed
s, and vesicular
tissue (possibly from fern
sporangia
). The most common remains are the fibrous or vascular fragments, which are typically rather uniform in size at 0.6 to 2.7 millimetres (0.02 to 0.11 in) long and have clean cuts at their ends, perpendicular
to a given fragment's long axis. Because of the small size of the fragments, they have been interpreted as having been nibbled from plants or chopped in the mouth, evidence of some method of retaining food in the mouth. These small fragments may have come from twigs or stems, but their size is more suggestive of vascular bundles in leaves. The clean cuts and lack of gastrolith
s suggest that the animal relied on oral processing instead of gastroliths or grit to grind food. The seeds (0.3 mm [0.01 in] across) and fruiting bodies (4.5 mm [0.18 in] across) were apparently swallowed whole. Comparison to gut contents and scat from modern herbivorous lizard
, emu
, and goose
indicates that this Minmi individual had a more sophisticated process for cutting up plant material.
It had bony protrusions, also known as body armour
, on its head, back, abdomen, legs and along the tail. Several types of armour are known in place 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. There was one preserved ring of scutes around the neck. The arrangement of armour is unclear on the tail, although the triangular plates may have run on the sides of the tail, with long scutes forming a row along the top of the tail. However, unlike other ankylosaurians, Minmi had horizontal plates of bones that ran along the sides of its vertebrae (hence its species name, M. paravertebra).
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
(where it was found), is a genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of small ankylosauria
Ankylosauria
Ankylosauria is a group of herbivorous dinosaurs of the order Ornithischia. It includes the great majority of dinosaurs with armor in the form of bony osteoderms. Ankylosaurs were bulky quadrupeds, with short, powerful limbs. They are first known to have appeared in the early Jurassic Period of...
n dinosaur that lived during the early Cretaceous Period, about 119 to 113 million years ago. The type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
, M. paravertebra, was described by Ralph Molnar
Ralph Molnar
Ralph E. Molnar is a paleontologist who had been Curator of Mammals at the Queensland Museum and more recently associated with the Museum of Northern Arizona. He is also a research associate at the Texas natural Science Centre. He co-authored descriptions of the dinosaurs Muttaburrasaurus, Kakuru,...
in 1980. A new cladistic analysis performed by Thompson et al., 2011 suggests that Minmi is the basalmost
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
known ankylosaurid.
Previously holding the record for the shortest dinosaur genus name, the title now goes to Mei
Mei (dinosaur)
Mei is a genus of duck-sized troodontid dinosaur first unearthed by paleontologists in Liaoning, China in 2004. Mei lived during the Early Cretaceous Period. Its binomial name, Mei long means sleeping dragon...
, a carnivore from China that was named in 2004, and Kol
Kol (dinosaur)
Kol is a genus of alvarezsaurid theropod dinosaur from the Late Cretaceous of Mongolia. The type specimen was excavated from the Ukhaa Tolgod locality of the Djadochta Formation, dating to about 75 million years ago. It is believed to have been about twice the size of the contemporary Shuvuuia...
, a carnivore from Mongolia that was named in 2009. Two good specimens of Minmi have been described, including a mostly complete skeleton, and additional fragments may pertain to this genus.
Discovery and species
Roma, Queensland
Roma is a town in the western Darling Downs area of Queensland, Australia, by rail WNW of Brisbane. It is situated at the junction of the Warrego and Carnarvon highways...
, Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
. It was first described in 1980 by Ralph E. Molnar
Ralph Molnar
Ralph E. Molnar is a paleontologist who had been Curator of Mammals at the Queensland Museum and more recently associated with the Museum of Northern Arizona. He is also a research associate at the Texas natural Science Centre. He co-authored descriptions of the dinosaurs Muttaburrasaurus, Kakuru,...
, who also named the type
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
(and only known) species.
Description
Minmi had four long (for an ankylosaurian) legs, with hind legs that were larger than front legs, a short neck and a wide skull with a very small brainBrain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
. The dinosaur grew to about 2 m (10 ft) long and was roughly 1 m (3 ft) tall to the top of the shoulder
Shoulder
The human shoulder is made up of three bones: the clavicle , the scapula , and the humerus as well as associated muscles, ligaments and tendons. The articulations between the bones of the shoulder make up the shoulder joints. The major joint of the shoulder is the glenohumeral joint, which...
. Minmi probably moved relatively slowly on four legs, based on its estimated mass and its leg length as determined by scientists from fossilized tracks.
Paleobiology
Minmi was a small armouredArmour (zoology)
Armour in animals is external or superficial protection against attack by predators, formed as part of the body , usually through the hardening of body tissues, outgrowths or secretions. It has therefore mostly developed in 'prey' species...
dinosaur, classified in Ankylosauria
Ankylosauria
Ankylosauria is a group of herbivorous dinosaurs of the order Ornithischia. It includes the great majority of dinosaurs with armor in the form of bony osteoderms. Ankylosaurs were bulky quadrupeds, with short, powerful limbs. They are first known to have appeared in the early Jurassic Period of...
(too primitive to be included in either the Ankylosauridae
Ankylosauridae
An ankylosaurid is a member of the Ankylosauridae family of armored dinosaurs that evolved 125 million years ago and became extinct 65 million years ago during the Cretaceous-Tertiary extinction event...
or Nodosauridae
Nodosauridae
Nodosauridae is a family of ankylosaurian dinosaurs, from the Late Jurassic to the Late Cretaceous Period of what are now North America, Asia, Antarctica and Europe.-Characteristics:...
), that was quadrupedal and had a long tail. As with other ankylosaurians, Minmi was herbivorous
Herbivore
Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...
. Unlike most herbivorous dinosaurs, there is direct evidence of the diet of Minmi: gut contents are known from the well-preserved nearly complete Minmi sp. specimen, found in the abdominal cavity in front of the left ilium
Ilium (bone)
The ilium is the uppermost and largest bone of the pelvis, and appears in most vertebrates including mammals and birds, but not bony fish. All reptiles have an ilium except snakes, although some snake species have a tiny bone which is considered to be an ilium.The name comes from the Latin ,...
. The gut contents consist of fragments of fibrous or vascular
Vascular tissue
Vascular tissue is a complex conducting tissue, formed of more than one cell type, found in vascular plants. The primary components of vascular tissue are the xylem and phloem. These two tissues transport fluid and nutrients internally. There are also two meristems associated with vascular tissue:...
plant tissue, fruit
Fruit
In broad terms, a fruit is a structure of a plant that contains its seeds.The term has different meanings dependent on context. In non-technical usage, such as food preparation, fruit normally means the fleshy seed-associated structures of certain plants that are sweet and edible in the raw state,...
ing bodies, spherical seed
Seed
A seed is a small embryonic plant enclosed in a covering called the seed coat, usually with some stored food. It is the product of the ripened ovule of gymnosperm and angiosperm plants which occurs after fertilization and some growth within the mother plant...
s, and vesicular
Vesicle (biology)
A vesicle is a bubble of liquid within another liquid, a supramolecular assembly made up of many different molecules. More technically, a vesicle is a small membrane-enclosed sack that can store or transport substances. Vesicles can form naturally because of the properties of lipid membranes , or...
tissue (possibly from fern
Fern
A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...
sporangia
Sporangium
A sporangium is an enclosure in which spores are formed. It can be composed of a single cell or can be multicellular. All plants, fungi, and many other lineages form sporangia at some point in their life cycle...
). The most common remains are the fibrous or vascular fragments, which are typically rather uniform in size at 0.6 to 2.7 millimetres (0.02 to 0.11 in) long and have clean cuts at their ends, perpendicular
Perpendicular
In geometry, two lines or planes are considered perpendicular to each other if they form congruent adjacent angles . The term may be used as a noun or adjective...
to a given fragment's long axis. Because of the small size of the fragments, they have been interpreted as having been nibbled from plants or chopped in the mouth, evidence of some method of retaining food in the mouth. These small fragments may have come from twigs or stems, but their size is more suggestive of vascular bundles in leaves. The clean cuts and lack of gastrolith
Gastrolith
A gastrolith, also called a stomach stone or gizzard stones, is a rock held inside a gastrointestinal tract. Gastroliths are retained in the muscular gizzard and used to grind food in animals lacking suitable grinding teeth. The grain size depends upon the size of the animal and the gastrolith's...
s suggest that the animal relied on oral processing instead of gastroliths or grit to grind food. The seeds (0.3 mm [0.01 in] across) and fruiting bodies (4.5 mm [0.18 in] across) were apparently swallowed whole. Comparison to gut contents and scat from modern herbivorous lizard
Lizard
Lizards are a widespread group of squamate reptiles, with nearly 3800 species, ranging across all continents except Antarctica as well as most oceanic island chains...
, emu
Emu
The Emu Dromaius novaehollandiae) is the largest bird native to Australia and the only extant member of the genus Dromaius. It is the second-largest extant bird in the world by height, after its ratite relative, the ostrich. There are three subspecies of Emus in Australia...
, and goose
Goose
The word goose is the English name for a group of waterfowl, belonging to the family Anatidae. This family also includes swans, most of which are larger than true geese, and ducks, which are smaller....
indicates that this Minmi individual had a more sophisticated process for cutting up plant material.
It had bony protrusions, also known as body armour
Armour (zoology)
Armour in animals is external or superficial protection against attack by predators, formed as part of the body , usually through the hardening of body tissues, outgrowths or secretions. It has therefore mostly developed in 'prey' species...
, on its head, back, abdomen, legs and along the tail. Several types of armour are known in place 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. There was one preserved ring of scutes around the neck. The arrangement of armour is unclear on the tail, although the triangular plates may have run on the sides of the tail, with long scutes forming a row along the top of the tail. However, unlike other ankylosaurians, Minmi had horizontal plates of bones that ran along the sides of its vertebrae (hence its species name, M. paravertebra).