Aardonyx
Encyclopedia
Aardonyx is a genus
of prosauropod dinosaur
. It is known from the type species
Aardonyx celestae found from the Lower Jurassic Elliot Formation
of South Africa
. A. celestae was named after Celeste Yates, who prepared much of the first known fossil material of the species. It has arm features that are intermediate between prosauropods and sauropods.
Based on the structure of the hind limbs and pelvic girdle of Aardonyx, the dinosaur normally moved bipedally but could drop to quadrupedal movement similar to Iguanodon
. It shares some attributes with giant quadrupedal sauropods like Apatosaurus
. Australian paleontologist Adam Yates and his team's discovery of the genus was published online before print in Proceedings of the Royal Society B
in November 2009, and is scheduled to appear in the March 2010 issue. British paleontologist Paul Barrett of the Natural History Museum
, London, who was not involved in the research, commented that the discovery of Aardonyx "helps to fill a marked gap in our knowledge of sauropod evolution, showing how a primarily two-legged animal could start to acquire the specific features necessary for a life spent on all-fours".
According to Dr. Matthew Bonnan
, a co-author on the study, "We already knew that the earliest sauropods and near-sauropods would be bipeds. What Aardonyx shows us, however, is that walking quadrupedally and bearing weight on the inside of the foot is a trend that started very early in these dinosaurs, much earlier than previously hypothesized." Bonnan adds, "On a scientific level, it's really fulfilling to have a hypothesis on how you think dinosaurs got large, then to test that in the field and get back these kind of data — a new dinosaur — that really does start to fill in some of those anatomical gaps."
s, gastralia, chevron
s, elements of the pectoral and pelvic girdles, and bones of the fore and hind limbs, manus
, and pes
. The presence of these bones in a single dense accumulation in a localized channel fill suggests that they came from relatively complete carcasses. Both individuals are thought to have been less than 10 years old at the time of their death because of the lack of peripheral rest lines in the cortices
of sampled bones. Additional evidence for immaturity at the time of death includes calcified cartilage at the articular end of the scapula
.
Aardonyx is thought to be the sister taxon of a sauropodomorph clade containing Melanorosaurus
and sauropods, which are all obligatory quadrupeds, based on a phylogenetic analysis conducted along with the first description of the genus. Many features of the skeleton support this relationship. These include derived traits seen in the vertebrae (such as hyposphenes that are as deep as the neural canal and mid-cervical neural spines that are less than twice as long as high) as well as the appendicular skeleton (such as the position of the fourth trochanter
over the midlength of the femur
and an adult femur length exceeding 600 mm).
of Aardonyx are smaller than those of other basal sauropodomorphs, and indicate that there was a reduction in blood supply to the buccal tissues and thus a loss of fleshy cheeks. The development of lateral plates along the alveolar margins of some bones of the skull would have helped brace the lingual
sides of the teeth against bucco-lingual forces during foliage stripping.
The presence of plesiomorphic V-shaped jaws along with the absence of fleshy cheeks is an unusual characteristic of Aardonyx. Previously, it was thought that broader jaws evolved prior to the reduction and loss in fleshy cheeks as an adaptation toward bulk-browsing in sauropods. The sauropod Chinshakiangosaurus
possessed jaws that were U-shaped, while still retaining fleshy cheeks, the opposite of the condition seen in Aardonyx. Because Chinshakiangosaurus is a more derived sauropodomorph, this suggests that a wide, cheekless gape may have evolved twice in Sauropodomorpha: once with Aardonyx and again with sauropods more advanced than Chinshakiangosaurus.
could be pronated
, and the length of the humerus is only 72 percent that of the femur. However, characteristics found in both the fore and hind limbs of Aardonyx show a trend toward more habitual quadrupedalism that would eventually lead to the obligatory quadrupedalism seen in sauropods. The proximal end of the ulna possesses an incipient craniolateral process that gives the bone a y-shape similar to, although more subtle than, those of obligatory quadrupedal sauropodomorphs. The radius is shifted cranially, and a radial fossa allows for the ulna to cradle the radius craniolaterally. These characteristics suggest that there was a development towards greater quadrupedalism in Aardonyx. Although the hindlimbs of Aardonyx clearly show evidence for bipedalism (such as the retention of a convex proximal lateral profile of the femur and the position of the cranial trochanter far from the lateral margin of the femur), there is also evidence that indicates a shift toward quadrupedalism. Features of the femur suggests that the gait of Aardonyx was slower than that of more basal sauropodomorphs. The shaft of the femur is straighter and the fourth trochanter is more distally placed. The repositioning of the fourth trochanter to a more distal position causes the M. caudofemoralis longus muscle, the main femoral retractor muscle, to have greater leverage (more mechanical advantage) but conversely a decrease in the velocity of femoral retraction; consequently, Aardonyx was a powerful but slower walker than typical prosauropods.
Another characteristic that suggests a slower gait in Aardonyx is the robustness of metatarsal I in comparison with those of other basal sauropodomorphs. This is evidence of a more medial, or entaxonic
, position of the weight bearing axis of the foot, as opposed to a more mesaxonic
position where the weight bearing axis runs through digit III. The development of entaxony in Aardonyx provides further evidence for its reduced cursorial ability and wider gauge-gait, which is thought to have preceded obligatory quadrupedalism in sauropodomorphs. Previously, it was thought that entaxony developed after the divergence of Vulcanodon
due to the presence of mesaxony in the genus. However, the presence of mesaxony in Vulcanodon can be now considered an evolutionary reversal given the clear presence of entaxony in Aardonyx.
, "Digging up the Past", where it is described by paleontologist Paul Barrett as a transitional form between bipedal prosauropods and the giant quadrupedal sauropods.
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 prosauropod dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
. It is known from 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...
Aardonyx celestae found from the Lower Jurassic Elliot Formation
Elliot Formation
The Elliot Formation is a geological formation dating to roughly 210 to 190 million years ago and covering the Norian to Sinemurian stages. The Elliot Formation is found in South Africa and Lesotho and is a member of the Stormberg Group. It consists mainly of limestone, sandstone, and mudstone...
of South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
. A. celestae was named after Celeste Yates, who prepared much of the first known fossil material of the species. It has arm features that are intermediate between prosauropods and sauropods.
Based on the structure of the hind limbs and pelvic girdle of Aardonyx, the dinosaur normally moved bipedally but could drop to quadrupedal movement similar to Iguanodon
Iguanodon
Iguanodon is a genus of ornithopod dinosaur that lived roughly halfway between the first of the swift bipedal hypsilophodontids and the ornithopods' culmination in the duck-billed dinosaurs...
. It shares some attributes with giant quadrupedal sauropods like Apatosaurus
Apatosaurus
Apatosaurus , also known by the popular but scientifically deprecated synonym Brontosaurus, is a genus of sauropod dinosaur that lived from about 154 to 150 million years ago, during the Jurassic Period . It was one of the largest land animals that ever existed, with an average length of and a...
. Australian paleontologist Adam Yates and his team's discovery of the genus was published online before print in Proceedings of the Royal Society B
Proceedings of the Royal Society
Proceedings of the Royal Society is the parent title of two scientific journals published by the Royal Society, whereas its initial journal, Philosophical Transactions, is now devoted to special thematic issues...
in November 2009, and is scheduled to appear in the March 2010 issue. British paleontologist Paul Barrett of the Natural History Museum
Natural History Museum
The Natural History Museum is one of three large museums on Exhibition Road, South Kensington, London, England . Its main frontage is on Cromwell Road...
, London, who was not involved in the research, commented that the discovery of Aardonyx "helps to fill a marked gap in our knowledge of sauropod evolution, showing how a primarily two-legged animal could start to acquire the specific features necessary for a life spent on all-fours".
According to Dr. Matthew Bonnan
Matthew Bonnan
Matthew Bonnan is an American paleobiologist and an associate professor of biological sciences at Western Illinois University. His research combines traditional descriptive and anatomical study with computer-aided morphometric analysis and modeling of vertebrate skeletons. Dr...
, a co-author on the study, "We already knew that the earliest sauropods and near-sauropods would be bipeds. What Aardonyx shows us, however, is that walking quadrupedally and bearing weight on the inside of the foot is a trend that started very early in these dinosaurs, much earlier than previously hypothesized." Bonnan adds, "On a scientific level, it's really fulfilling to have a hypothesis on how you think dinosaurs got large, then to test that in the field and get back these kind of data — a new dinosaur — that really does start to fill in some of those anatomical gaps."
Description
The genus is known from disarticulated bones belonging to two immature individuals. The material consists of cranial elements, vertebrae, dorsal and cervical ribRib
In vertebrate anatomy, ribs are the long curved bones which form the rib cage. In most vertebrates, ribs surround the chest, enabling the lungs to expand and thus facilitate breathing by expanding the chest cavity. They serve to protect the lungs, heart, and other internal organs of the thorax...
s, gastralia, chevron
Chevron (anatomy)
A chevron is one of a series of bones on the ventral side of the tail in many reptiles, dinosaurs , and some mammals such as kangaroos and manatees....
s, elements of the pectoral and pelvic girdles, and bones of the fore and hind limbs, manus
Manus (zoology)
The manus is the zoological term for the distal portion of the fore limb of an animal. In tetrapods, it is the part of the pentadactyl limb that includes the metacarpals and digits . During evolution, it has taken many forms and served a variety of functions...
, and pes
Pes (zoology)
The pes is the zoological term for the distal portion of the hind limb of tetrapod animals. It is the part of the pentadactyl limb that includes the metatarsals and digits . During evolution, it has taken many forms and served a variety of functions...
. The presence of these bones in a single dense accumulation in a localized channel fill suggests that they came from relatively complete carcasses. Both individuals are thought to have been less than 10 years old at the time of their death because of the lack of peripheral rest lines in the cortices
Cortical bone
Cortical bone, synonymous with compact bone, is one of the two types of osseous tissue that form bones. Cortical bone facilitates bone's main functions: to support the whole body, protect organs, provide levers for movement, and store and release chemical elements, mainly calcium. As its name...
of sampled bones. Additional evidence for immaturity at the time of death includes calcified cartilage at the articular end of the scapula
Scapula
In anatomy, the scapula , omo, or shoulder blade, is the bone that connects the humerus with the clavicle ....
.
Classification
| {clade|style=font-size:75%;line-height:75% | label1=Sauropodomorpha Sauropodomorpha Sauropodomorpha is an extinct clade of long-necked, herbivorous, saurischian dinosaurs which includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had long necks and tails, were quadrupedal, and became the largest animals to ever walk the Earth. The... |
1= }} Cladogram A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational... showing the position of Aardonyx within Sauropodomorpha after Yates et al., in print. |
Aardonyx is thought to be the sister taxon of a sauropodomorph clade containing Melanorosaurus
Melanorosaurus
Melanorosaurus , is a genus of basal sauropodomorph dinosaur that lived during the Late Triassic period. A herbivore from South Africa, it had a large body and sturdy limbs, suggesting it moved about on all fours...
and sauropods, which are all obligatory quadrupeds, based on a phylogenetic analysis conducted along with the first description of the genus. Many features of the skeleton support this relationship. These include derived traits seen in the vertebrae (such as hyposphenes that are as deep as the neural canal and mid-cervical neural spines that are less than twice as long as high) as well as the appendicular skeleton (such as the position of the fourth trochanter
Fourth trochanter
The fourth trochanter is a shared characteristic common to archosaurs. It is a knob-like feature on the medial side of the femur that serves as a muscle attachment....
over the midlength of the femur
Femur
The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...
and an adult femur length exceeding 600 mm).
Feeding
Aardonyx shows a transition toward the bulk-browsing form of feeding characteristic of sauropods. The jaws of Aardonyx are narrow and V-shaped with a pointed symphysis, a plesiomorphic characteristic shared with other basal sauropodomorphs. In sauropods, the jaws are broad and U-shaped to allow for a wider bite. The absence of a lateral ridge at the caudal end of the dentary is indicative of a loss of fleshy cheeks. This is seen as an adaptation for a wider gape to facilitate in bulk browsing, and is observed in nearly all sauropods. The lateral neurovascular foramina of the maxillaMaxilla
The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...
of Aardonyx are smaller than those of other basal sauropodomorphs, and indicate that there was a reduction in blood supply to the buccal tissues and thus a loss of fleshy cheeks. The development of lateral plates along the alveolar margins of some bones of the skull would have helped brace the lingual
Commonly used terms of relationship and comparison in dentistry
There are numerous commonly used terms of relationship and comparison that refer to different aspects of teeth and are frequently utilized in articles about dentistry...
sides of the teeth against bucco-lingual forces during foliage stripping.
The presence of plesiomorphic V-shaped jaws along with the absence of fleshy cheeks is an unusual characteristic of Aardonyx. Previously, it was thought that broader jaws evolved prior to the reduction and loss in fleshy cheeks as an adaptation toward bulk-browsing in sauropods. The sauropod Chinshakiangosaurus
Chinshakiangosaurus
Chinshakiangosaurus was a genus of dinosaur from the Early Jurassic Period. It lived in what is now present-day China. It is classified as a sauropod, but is not well known. The type species, Chinshakiangosaurus chuhghoensis, was first named by Ye, but described by Dong Zhiming in 1992...
possessed jaws that were U-shaped, while still retaining fleshy cheeks, the opposite of the condition seen in Aardonyx. Because Chinshakiangosaurus is a more derived sauropodomorph, this suggests that a wide, cheekless gape may have evolved twice in Sauropodomorpha: once with Aardonyx and again with sauropods more advanced than Chinshakiangosaurus.
Locomotion
Characteristics of the limbs of Aardonyx suggest that it was habitually bipedal. Evidence for bipedalism can be seen in the forelimbs; the structure of the radius and ulna limited the degree to which the manusManus (zoology)
The manus is the zoological term for the distal portion of the fore limb of an animal. In tetrapods, it is the part of the pentadactyl limb that includes the metacarpals and digits . During evolution, it has taken many forms and served a variety of functions...
could be pronated
Pronation
In anatomy, pronation is a rotational movement of the forearm at the radioulnar joint, or of the foot at the subtalar and talocalcaneonavicular joints. For the forearm, when standing in the anatomical position, pronation will move the palm of the hand from an anterior-facing position to a...
, and the length of the humerus is only 72 percent that of the femur. However, characteristics found in both the fore and hind limbs of Aardonyx show a trend toward more habitual quadrupedalism that would eventually lead to the obligatory quadrupedalism seen in sauropods. The proximal end of the ulna possesses an incipient craniolateral process that gives the bone a y-shape similar to, although more subtle than, those of obligatory quadrupedal sauropodomorphs. The radius is shifted cranially, and a radial fossa allows for the ulna to cradle the radius craniolaterally. These characteristics suggest that there was a development towards greater quadrupedalism in Aardonyx. Although the hindlimbs of Aardonyx clearly show evidence for bipedalism (such as the retention of a convex proximal lateral profile of the femur and the position of the cranial trochanter far from the lateral margin of the femur), there is also evidence that indicates a shift toward quadrupedalism. Features of the femur suggests that the gait of Aardonyx was slower than that of more basal sauropodomorphs. The shaft of the femur is straighter and the fourth trochanter is more distally placed. The repositioning of the fourth trochanter to a more distal position causes the M. caudofemoralis longus muscle, the main femoral retractor muscle, to have greater leverage (more mechanical advantage) but conversely a decrease in the velocity of femoral retraction; consequently, Aardonyx was a powerful but slower walker than typical prosauropods.
Another characteristic that suggests a slower gait in Aardonyx is the robustness of metatarsal I in comparison with those of other basal sauropodomorphs. This is evidence of a more medial, or entaxonic
Entaxonic
Entaxonic is a term used to describe an animal whose inner digits of the hand or foot are more strongly developed than the outer ones, such as humans and sauropod dinosaurs....
, position of the weight bearing axis of the foot, as opposed to a more mesaxonic
Mesaxonic
Mesaxonic is a term used to describe animals whose middle digits of the hand or foot are more strongly developed than the inner or outer ones, such as birds....
position where the weight bearing axis runs through digit III. The development of entaxony in Aardonyx provides further evidence for its reduced cursorial ability and wider gauge-gait, which is thought to have preceded obligatory quadrupedalism in sauropodomorphs. Previously, it was thought that entaxony developed after the divergence of Vulcanodon
Vulcanodon
Vulcanodon was a relatively small early sauropod dinosaur genus from the Early Jurassic of southern Africa. About 6.5 metres long, Vulcanodon was herbivorous and had unusually long bones of the first toe and large claws on the inside toes. The type species, V. karibaensis, was formally...
due to the presence of mesaxony in the genus. However, the presence of mesaxony in Vulcanodon can be now considered an evolutionary reversal given the clear presence of entaxony in Aardonyx.
Popular reception
The discovery of Aardonyx is presented in the second episode of the 2010 BBC documentary Museum of LifeMuseum of Life (documentary)
Museum of Life is a 2010 BBC2 documentary, that takes a look behind the scenes at the British Museum of Natural History. It is introduced and co-presented by Jimmy Doherty, who was a volunteer at the Natural History Museum ten years previously...
, "Digging up the Past", where it is described by paleontologist Paul Barrett as a transitional form between bipedal prosauropods and the giant quadrupedal sauropods.
External links
- Western Illinois University: Earth Claw
- Fleshed-out restoration of an Aardonyx celestae. by paleoartist Julius T. CsotonyiJulius T. CsotonyiJulius Thomas Csotonyi is a Canadian paleoartist and natural history illustrator living in Winnipeg, Canada. He specialises in photo-realistic restorations of dinosaurs, paleo-environments and extant animals. His techniques encompass both traditional and digital media...
- Dr. Bonnan's blog, Jurassic Journeys, where Aardonyx is discussed.
- Dracovenator, Dr. Adam Yates's blog site where Aardonyx is discussed.