Darwinopterus
Encyclopedia
Darwinopterus is a genus
of pterosaur
, discovered in China
and named after biologist Charles Darwin
. Between 30 and 40 fossil specimens have been identified, all collected from the Tiaojishan Formation
, which dates to the middle Jurassic
period. The type
species, D. modularis, was described in February of 2010
. D. modularis was the first known pterosaur to display features of both long-tailed ('rhamphorhynchoid
') and short-tailed (pterodactyloid
) pterosaurs, and was described as a transitional fossil
between the two groups. Two additional species, D. linglongtaensis and D. robustodens, were described from the same fossil beds in December of 2010 and June 2011, respectively.
pterosaurian features. While it had a long tail and other features characteristic of the 'rhamphorhynchoids', it also had distinct pterodactyloid features, such as long vertebrae in the neck and a single skull opening in front of the eyes, the nasoantorbital fenestra (in most 'rhamphorhynchoids', the antorbital fenestra and the nasal opening are separate).
Darwinopterus is distinguished from its close relatives by the greater relative length of the back portion of the skull compared to its jaws, thin nasal bone, and elongated hip bone (illium). The teeth in all species were spaced widely with the longest teeth at the jaw tips. The teeth were spike-like in form, and set into tooth sockets with raised margins. The hand bones were relatively short, even shorter than the femur. The tail was long, with over 20 vertebrae, and was partially stiffened by long, thin bony projections. Unlike other wukongopterids
, the head crest found in males was supported by a thin bony extension of the skull, with a serrated top edge. The serrations probably helped anchor an even larger keratin
extension.
Specimens of Darwinopterus have been divided into three distinct species, based largely on the size and shape of their teeth. The first, D. modularis, was named by Lü Junchang and colleagues in 2010. D. modularis had an especially elongated back end to the skull, and widely-spaced, "spike-like" teeth. D. linglongtaensis was named by Wang Xiaolin and colleagues in later in 2010. It was characterized by a shorter and taller skull and shorter, cone-shaped teeth. In 2011, Lü and another team of scientists described and named D. robustodens, for a new specimen with very robust teeth. Lü and colleagues (2011) suggested that these differences in tooth shape may indicate that each Darwinopterus species occupied a different ecological niche, with the teeth of each becoming specialized for different food sources. The robust teeth of D. robustodens, for example, may have been used to feed on hard-shelled beetle
s.
(variation that can separate specimens into two distinct categories) can be seen across the large number of known specimens. In one specimen category, individuals have small, narrow hips and often large crests on their skulls. The other specimen type has larger, broader hips and often have small crests or no crests at all. However, while these were thought to represent different sexes, no direct evidence was found at first to determine which was male and which was female. The first specimen in which sex could be confidently identified was specimen M8802 in the collections of the Zhejiang Museum of Natural History, nicknamed "Mrs T" (short for "Mrs Pterodactyl"), described by Lü Junchang and colleagues in January 2011. This specimen was preserved with the impression of an egg between its thighs in close association with its pelvis. This specimen had a broad pelvis (matching the diameter of the egg) and lacked any evidence of a crest. This link to an unhatched egg, which was probably expelled from the body during decomposition, allowed scientists to identify the second, crestless type of Darwinopterus as the females.
Pterosaur researcher Kevin Padian, however, questioned some of the conclusions drawn about this specimen by Lü and his colleagues. Padian suggested in a 2011 interview that in other animals with elaborate display crests (such as ceratopsia
n dinosaur
s), the size and shape of the crests change dramatically with age. He noted that the "Mrs T" specimen may simply have been a sub-adult which had not yet developed a crest (most animals are able to reproduce before they are fully grown).
, requiring little to no parental care. These results imply that reproduction in pterosaurs was more like that in modern reptiles and significantly differed from reproduction in birds.
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 pterosaur
Pterosaur
Pterosaurs were flying reptiles of the clade or order Pterosauria. They existed from the late Triassic to the end of the Cretaceous Period . Pterosaurs are the earliest vertebrates known to have evolved powered flight...
, discovered in China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
and named after biologist Charles Darwin
Charles Darwin
Charles Robert Darwin FRS was an English naturalist. He established that all species of life have descended over time from common ancestry, and proposed the scientific theory that this branching pattern of evolution resulted from a process that he called natural selection.He published his theory...
. Between 30 and 40 fossil specimens have been identified, all collected from the Tiaojishan Formation
Tiaojishan Formation
The Tiaojishan Formation is a geological formation in Hebei and Liaoning, People's Republic of China, dating to the middle-late Jurassic period . It is known for its fossil plants, and is made up mainly of pyroclastic rock interspersed with basic volcanic and sedimentary rocks...
, which dates to the middle Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
period. 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...
species, D. modularis, was described in February of 2010
2010 in paleontology
-Anomalocaridids:-Newly named crustaceans:-Newly named insects:* A new family, Cascopleciidae, is published by Poinar Jr.* A new family of ceraphronoid Hymenopters, Radiophronidae, is published by Ortega-Blanco, Rasnitsyn, and Delclòs....
. D. modularis was the first known pterosaur to display features of both long-tailed ('rhamphorhynchoid
Rhamphorhynchoidea
The Rhamphorhynchoidea forms one of the two suborders of pterosaurs and represent an evolutionary grade of primitive members of this group of flying reptiles. This suborder is paraphyletic in relation to the Pterodactyloidea, which arose from within the Rhamphorhynchoidea, not from a more distant...
') and short-tailed (pterodactyloid
Pterodactyloidea
Pterodactyloidea forms one of the two suborders of pterosaurs , and contains the most derived members of this group of flying reptiles...
) pterosaurs, and was described as a transitional fossil
Transitional fossil
A transitional fossil is any fossilized remains of a lifeform that exhibits characteristics of two distinct taxonomic groups. A transitional fossil is the fossil of an organism near the branching point where major individual lineages diverge...
between the two groups. Two additional species, D. linglongtaensis and D. robustodens, were described from the same fossil beds in December of 2010 and June 2011, respectively.
Description
Darwinopterus, like its closest relatives, is characterized by its unique combination of basal and derivedDerived
In phylogenetics, a derived trait is a trait that is present in an organism, but was absent in the last common ancestor of the group being considered. This may also refer to structures that are not present in an organism, but were present in its ancestors, i.e. traits that have undergone secondary...
pterosaurian features. While it had a long tail and other features characteristic of the 'rhamphorhynchoids', it also had distinct pterodactyloid features, such as long vertebrae in the neck and a single skull opening in front of the eyes, the nasoantorbital fenestra (in most 'rhamphorhynchoids', the antorbital fenestra and the nasal opening are separate).
Darwinopterus is distinguished from its close relatives by the greater relative length of the back portion of the skull compared to its jaws, thin nasal bone, and elongated hip bone (illium). The teeth in all species were spaced widely with the longest teeth at the jaw tips. The teeth were spike-like in form, and set into tooth sockets with raised margins. The hand bones were relatively short, even shorter than the femur. The tail was long, with over 20 vertebrae, and was partially stiffened by long, thin bony projections. Unlike other wukongopterids
Wukongopteridae
The Wukongopteridae are a group of basal pterosaurs, found exclusively in China. It contained in 2010 five species in four genera, all collected from the Tiaojishan Formation and/or Daohugou Beds, which may date to the middle Jurassic period, though other studies have given a date of late Jurassic,...
, the head crest found in males was supported by a thin bony extension of the skull, with a serrated top edge. The serrations probably helped anchor an even larger keratin
Keratin
Keratin refers to a family of fibrous structural proteins. Keratin is the key of structural material making up the outer layer of human skin. It is also the key structural component of hair and nails...
extension.
Specimens of Darwinopterus have been divided into three distinct species, based largely on the size and shape of their teeth. The first, D. modularis, was named by Lü Junchang and colleagues in 2010. D. modularis had an especially elongated back end to the skull, and widely-spaced, "spike-like" teeth. D. linglongtaensis was named by Wang Xiaolin and colleagues in later in 2010. It was characterized by a shorter and taller skull and shorter, cone-shaped teeth. In 2011, Lü and another team of scientists described and named D. robustodens, for a new specimen with very robust teeth. Lü and colleagues (2011) suggested that these differences in tooth shape may indicate that each Darwinopterus species occupied a different ecological niche, with the teeth of each becoming specialized for different food sources. The robust teeth of D. robustodens, for example, may have been used to feed on hard-shelled beetle
Beetle
Coleoptera is an order of insects commonly called beetles. The word "coleoptera" is from the Greek , koleos, "sheath"; and , pteron, "wing", thus "sheathed wing". Coleoptera contains more species than any other order, constituting almost 25% of all known life-forms...
s.
Biology
Because Darwinopterus is known from numerous well-preserved specimens including an egg, scientists have been able to deduce various aspects of its biology, including growth patterns and life history, reproduction, and possible variation between sexes.Sexual variation
Darwinopterus specimens have been reported to show several differences between males and females. Distinct dimorphismSexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
(variation that can separate specimens into two distinct categories) can be seen across the large number of known specimens. In one specimen category, individuals have small, narrow hips and often large crests on their skulls. The other specimen type has larger, broader hips and often have small crests or no crests at all. However, while these were thought to represent different sexes, no direct evidence was found at first to determine which was male and which was female. The first specimen in which sex could be confidently identified was specimen M8802 in the collections of the Zhejiang Museum of Natural History, nicknamed "Mrs T" (short for "Mrs Pterodactyl"), described by Lü Junchang and colleagues in January 2011. This specimen was preserved with the impression of an egg between its thighs in close association with its pelvis. This specimen had a broad pelvis (matching the diameter of the egg) and lacked any evidence of a crest. This link to an unhatched egg, which was probably expelled from the body during decomposition, allowed scientists to identify the second, crestless type of Darwinopterus as the females.
Pterosaur researcher Kevin Padian, however, questioned some of the conclusions drawn about this specimen by Lü and his colleagues. Padian suggested in a 2011 interview that in other animals with elaborate display crests (such as ceratopsia
Ceratopsia
Ceratopsia or Ceratopia is a group of herbivorous, beaked dinosaurs which thrived in what are now North America, Europe, and Asia, during the Cretaceous Period, although ancestral forms lived earlier, in the Jurassic. The earliest known ceratopsian, Yinlong downsi, lived between 161.2 and 155.7...
n 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...
s), the size and shape of the crests change dramatically with age. He noted that the "Mrs T" specimen may simply have been a sub-adult which had not yet developed a crest (most animals are able to reproduce before they are fully grown).
Reproduction
The specimen preserved along with an egg (nicknamed "Mrs T"), described by Lü and colleagues in 2011, offers insight into the reproductive strategies of Darwinopterus and pterosaurs in general. Like the eggs of later pterosaurs and modern reptiles, the eggs of Darwinopterus had a parchment-like, soft shell. In modern birds, the eggshell is hardened with calcium, completely shielding the embryo from the outside environment. Soft-shelled eggs are permeable, and allow significant amounts of water to be absorbed into the egg during development. Eggs of this type are more vulnerable to the elements and are typically buried in soil. The eggs of Darwinopterus would have weighed about 6 gram (0.211643772630672 oz) when they were laid, but due to moisture intake, they may have doubled in weight by the time of hatching. The eggs were small compared to the size of the mother (the "Mrs T" specimen weighed between 110 grams (3.9 oz) and 220 grams (7.8 oz)), also more like modern reptiles than birds. David Unwin, a co-author of the paper, suggested that Darwinopterus probably laid many small eggs at a time and buried them, and that juveniles could fly upon hatchingSuperprecocial
The term superprecocial refers to a level of physical maturity and capability in young animals that is most extreme. Examples are the Megapode birds, which have full flight feathers and which, in some species, can fly on the same day they hatch from their eggs...
, requiring little to no parental care. These results imply that reproduction in pterosaurs was more like that in modern reptiles and significantly differed from reproduction in birds.
Implications
As the name Darwinopterus modularis implies, the researchers who first described this genus saw it as evidence that pterodactyloid pterosaurs evolved from the more primitive 'rhamphorhynchoids' via modular evolution. In other words, rather than a gradual change from one body type to the other, various major aspects of pterodactyloid anatomy arose piecemeal, producing species with distinct combinations of both primitive and advanced features.See also
- WukongopterusWukongopterusWukongopterus is a genus of basal pterosaur, found in Liaoning, China, from the Daohugou Beds, of the Late Jurassic or Early Cretaceous. It was unusual for having both an elongate neck and a long tail....
- 2010 in paleontology2010 in paleontology-Anomalocaridids:-Newly named crustaceans:-Newly named insects:* A new family, Cascopleciidae, is published by Poinar Jr.* A new family of ceraphronoid Hymenopters, Radiophronidae, is published by Ortega-Blanco, Rasnitsyn, and Delclòs....
- List of pterosaurs