Skeletal pneumaticity

Skeletal pneumaticity is the presence of air spaces within bones. It is generally produced during development by excavation of bone by pneumatic diverticula (air sacs) from an air-filled space, such as the lungs or nasal cavity. Pneumatization is highly variable between individuals, and bones not normally pneumatized can become pneumatized in pathological development.

Paranasal sinuses numbers
The paranasal sinuses in a human, an example of skeletal pneumatization

Cranial pneumaticity

Pneumatization occurs in the skulls of mammals, crocodilians and birds among extant tetrapods. Pneumatization has been documented in extinct archosaurs including dinosaurs and pterosaurs. Pneumatic spaces include the paranasal sinuses and some of the mastoid cells.

Postcranial pneumaticity

Postcranial pneumaticity is found largely in certain archosaur groups, namely dinosaurs,[1] pterosaurs, and birds. Vertebral pneumatization is widespread among saurischian dinosaurs, and some theropods have quite widespread pneumatization, for example Aerosteon riocoloradensis has pneumatization of the ilium, furcula, and gastralia.[2] Many modern birds are extensively pneumatized. The air pockets of the bones are connected to the pulmonary air sacs:[3]

Air sacs Skeleton portion pneumatized by their divercula
cervical air sacs cervical and anterior thoracic vertebrae
abdominal air sacs posterior thoracic vertebrae, synsacrum and hindlimb
interclavicular air sac sternum, sternal ribs, coracoid, clavicle, scapula, and forelimb
anterior and posterior thoracic air sacs - (lack diverticula)

However the extent of pneumaticity depends on species. For example it is slight in diving birds, loons lack pneumatic bones at all.[3][4]

Postcranial pneumatization is rarer outside of Archosauria. Examples include the hyoid in howler monkeys Alouatta, and the dorsal vertebrae in the osteoglossiform fish Pantodon.[5] Slight pneumatization of the centra and rib heads by dorsal diverticula in the lungs of land tortoises has also been documented.[5] In addition, pathological pneumatization has been known to occur in the human atlas vertebra.[6]

Function of skeletal pneumaticity

The exact function of skeletal pneumaticity is not definitively known, but there are several working hypotheses concerning the role of skeletal pneumaticity in an organism.

Reduce body mass

By invading the bones, the pneumatic diverticula would replace marrow with air, reducing the overall body mass. Reducing the body mass would make it easier for pterosaurs and birds to fly as there is less mass to keep aloft with the same amount of muscle powering the flight strokes.[7] Pneumatizing the vertebral column of sauropods would reduce the weight of these organisms, and make it easier to support and move the massive neck.[1]

Alter skeletal mass distribution

Skeletal pneumaticity allows animals to redistribute the skeletal mass within their body. The skeletal mass of a bird (pneumatized) and a mammal (not pneumatized) with similar body size is roughly the same, yet the bones of birds were found to be denser than the bones of mammals. This suggests that pneumatization of bird bones does not affect the overall mass but allows for a better balance of weight within the body to allow for greater balance, agility and ease of flight.[8]

Balance

In theropods, the head and neck are greatly pneumatized, and the forearms are reduced. This would help reduce the mass further away from the center of balance. This adjustment to the center of mass would allow the animal to reduce its rotational inertia, thereby increasing its agility. The sacral pneumaticity would lower its center of mass to a more ventral position, allowing it more stabilization.[5]

Adaptation for high altitude

Screamers are highly pneumatized birds with pneumatic diverticula traveling throughout the bones and into the skin. As screamers fly at high altitudes, it is hypothesized that the extreme pneumaticity in these birds is indicative of an adaptation for flying in high altitudes.[9]

References

  1. ^ a b Wedel, Matthew J. (2005). "Postcranial skeletal pneumaticity in sauropods and its implications for mass estimates". In Curry Rogers, Kristina A.; Wilson, Jeffrey A. The Sauropods: evolution and paleobiology (PDF). Berkeley: University of California Press. pp. 201–228. ISBN 9780520246232.
  2. ^ Sereno, PC; Martinez, RN; Wilson, JA; Varricchio, DJ; Alcober, OA; Larsson, HC (30 September 2008). "Evidence for avian intrathoracic air sacs in a new predatory dinosaur from Argentina". PLOS One. 3 (9): e3303. doi:10.1371/journal.pone.0003303. PMC 2553519. PMID 18825273.
  3. ^ a b Wedel, Mathew J. (2003). "Vertebral pneumaticity, air sacs, and the physiology of sauropod dinosaurs" (PDF). Paleobiology. Paleontological Society. 29 (2): 243–255. doi:10.1666/0094-8373(2003)029<0243:vpasat>2.0.co;2. Retrieved 2014-01-21.
  4. ^ Schorger, A. W. (September 1947). "The deep diving of the loon and old-squaw and its mechanism" (PDF). The Wilson Bulletin. The Wilson Ornithological Society. 59 (3): 151–159. Retrieved 2014-01-21.
  5. ^ a b c Farmer, CG (November 2006). "On the origin of avian air sacs". Respiratory Physiology & Neurobiology. 154 (1–2): 89–106. doi:10.1016/j.resp.2006.04.014. PMID 16787763.
  6. ^ Moreira, Bruno; Som, Peter M. (July 2010). "Unexplained extensive skull base and atlas pneumatization: computed tomographic findings". JAMA Otolaryngology–Head & Neck Surgery. 136 (7): 731–3. doi:10.1001/archoto.2010.108. PMID 20644073.
  7. ^ Bennett, Christopher (2001). "The Osteology and Functional Morphology of the Late Cretaceous Pterosaur Pteranodon". Palaeontographica Abteilung A: 1–153.
  8. ^ Dumont, Elizabeth R. (2010-07-22). "Bone density and the lightweight skeletons of birds". Proceedings of the Royal Society of London B: Biological Sciences. 277 (1691): 2193–2198. doi:10.1098/rspb.2010.0117. ISSN 0962-8452. PMC 2880151. PMID 20236981.
  9. ^ Picasso, Mariana BJ; Mosto, Maria Clelia; Tozzi, Romina; Degrange, Federico J; Barbeito, Claudio G (2014). "A peculiar association: the skin and the subcutaneus diverticula of the Southern Screamer (Chauna torquata, Anseriformes)". Vertebrate Zoology. 64 (2): 245–249.
2012 in archosaur paleontology

The year 2012 in Archosaur paleontology was eventful. Archosaurs include the only living dinosaur group — birds — and the reptile crocodilians, plus all extinct dinosaurs, extinct crocodilian relatives, and pterosaurs. Archosaur palaeontology is the scientific study of those animals, especially as they existed before the Holocene Epoch began about 11,700 years ago. The year 2012 in paleontology included various significant developments regarding archosaurs.

This article records new taxa of fossil archosaurs of every kind that have been described during the year 2012, as well as other significant discoveries and events related to paleontology of archosaurs that occurred in the year 2012.

2017 in archosaur paleontology

The year 2017 in archosaur paleontology was eventful. Archosaurs include the only living dinosaur group — birds — and the reptile crocodilians, plus all extinct dinosaurs, extinct crocodilian relatives, and pterosaurs. Archosaur palaeontology is the scientific study of those animals, especially as they existed before the Holocene Epoch began about 11,700 years ago. The year 2017 in paleontology included various significant developments regarding archosaurs.

This article records new taxa of fossil archosaurs of every kind that have been described during the year 2017, as well as other significant discoveries and events related to paleontology of archosaurs that occurred in the year 2017.

Air sac

Air sacs are spaces within an organism where there is the constant presence of air. Among modern animals, birds possess the most air sacs (9–11), with their extinct dinosaurian relatives showing a great increase in the pneumatization (presence of air) in their bones. Theropods, like Aerosteon, have many air sacs in the body that are not just in bones, and they can be identified as the more primitive form of modern bird airways. Sauropods are well known for the amount of air pockets in their bones (especially vertebra), although one theropod, Deinocheirus, shows a rivalling amount of air pockets.

Baryonyx

Baryonyx () is a genus of theropod dinosaur which lived in the Barremian stage of the Early Cretaceous Period, about 130–125 million years ago. The first skeleton was discovered in 1983 in the Weald Clay Formation of Surrey, England, and became the holotype specimen of B. walkeri, named by palaeontologists Alan J. Charig and Angela C. Milner in 1986. The generic name, Baryonyx, means "heavy claw" and alludes to the animal's very large claw on the first finger; the specific name, walkeri, refers to its discoverer, amateur fossil collector William J. Walker. The holotype specimen is one of the most complete theropod skeletons from the UK (and remains the most complete spinosaurid), and its discovery attracted media attention. Specimens later discovered in other parts of the United Kingdom and Iberia have also been assigned to the genus.

The holotype specimen, which may not have been fully grown, was estimated to have been between 7.5 and 10 m (25 and 33 ft) long and to have weighed between 1.2 and 1.7 t (1.3 and 1.9 short tons). Baryonyx had a long, low, and narrow snout, which has been compared to that of a gharial. The tip of the snout expanded to the sides in the shape of a rosette. Behind this, the upper jaw had a notch which fitted into the lower jaw (which curved upwards in the same area). It had a triangular crest on the top of its nasal bones. Baryonyx had a large number of finely serrated, conical teeth, with the largest teeth in front. The neck formed an S-shape, and the neural spines of its dorsal vertebrae increased in height from front to back. One elongated neural spine indicates it may have had a hump or ridge along the centre of its back. It had robust forelimbs, with the eponymous first-finger claw measuring about 31 cm (12 in) long.

Now recognised as a member of the family Spinosauridae, Baryonyx's affinities were obscure when it was discovered. Some researchers have suggested that Suchosaurus cultridens is a senior synonym (being an older name), and that Suchomimus tenerensis belongs in the same genus; subsequent authors have kept them separate. Baryonyx was the first theropod dinosaur demonstrated to have been piscivorous (fish-eating), as evidenced by fish scales in the stomach region of the holotype specimen. It may also have been an active predator of larger prey and a scavenger, since it also contained bones of a juvenile Iguanodon. The creature would have caught and processed its prey primarily with its forelimbs and large claws. Baryonyx may have had semiaquatic habits, and coexisted with other theropod, ornithopod, and sauropod dinosaurs, as well as pterosaurs, crocodiles, turtles and fishes, in a fluvial environment.

Bird anatomy

Bird anatomy, or the physiological structure of birds' bodies, shows many unique adaptations, mostly aiding flight. Birds have a light skeletal system and light but powerful musculature which, along with circulatory and respiratory systems capable of very high metabolic rates and oxygen supply, permit the bird to fly. The development of a beak has led to evolution of a specially adapted digestive system. These anatomical specializations have earned birds their own class in the vertebrate phylum.

Common loon

The common loon or great northern diver (Gavia immer) is a large member of the loon, or diver, family of birds. Breeding adults have a plumage that includes a broad black head and neck with a greenish, purplish, or bluish sheen, blackish or blackish-grey upperparts, and pure white underparts except some black on the undertail coverts and vent. Non-breeding adults are brownish with a dark neck and head marked with dark grey-brown. Their upperparts are dark brownish-grey with an unclear pattern of squares on the shoulders, and the underparts, lower face, chin, and throat are whitish. The sexes look alike, though males are significantly heavier than females. During the breeding season, loons live on lakes and other waterways in Canada; the northern United States (including Alaska); and southern parts of Greenland and Iceland. Small numbers breed on Svalbard and sporadically elsewhere in Arctic Eurasia. Common loons winter on both coasts of the US as far south as Mexico, and on the Atlantic coast of Europe.

Common loons eat a variety of animal prey including fish, crustaceans, insect larvae, molluscs, and occasionally aquatic plant life. They swallow most of their prey underwater, where it is caught, but some larger items are first brought to the surface. Loons are monogamous; that is, a single female and male often together defend a territory and may breed together for a decade or more. Both members of a pair build a large nest out of dead marsh grasses and other plants formed into a mound along the vegetated shores of lakes. A single brood is raised each year from a clutch of one or two olive-brown oval eggs with dark brown spots which are incubated for about 28 days by both parents. Fed by both parents, the chicks fledge in 70 to 77 days. The chicks are capable of diving underwater when just a few days old, and they fly to their wintering areas before ice forms in the fall.

The common loon is assessed as a species of least concern on the IUCN Red List of Endangered Species. It is one of the species to which the Agreement on the Conservation of African-Eurasian Migratory Waterbirds applies. The United States Forest Service has designated the common loon a species of special status because of threats from habitat loss and toxic metal poisoning in its US range.

The common loon is the provincial bird of Ontario, and it appears on Canadian currency, including the one-dollar "loonie" coin and a previous series of $20 bills. In 1961, it was designated the state bird of Minnesota, and appears on the Minnesota State Quarter.

Diverticulum

A diverticulum (plural: diverticula) is the medical or biological term for an outpouching of a hollow (or a fluid-filled) structure in the body. Depending upon which layers of the structure are involved, they are described as being either true or false.

In medicine, the term usually implies the structure is not normally present. However, in the embryonic stage, some normal structures begin development as a diverticulum arising from another structure.

Mastoid cells

A section of the mastoid process of the temporal bone of the cranium shows it to be hollowed out into a number of spaces, the mastoid cells, which exhibit great variety in their size and number.

At the upper and front part of the process they are large and irregular and contain air (a form of skeletal pneumaticity), but toward the lower part they diminish in size, while those at the apex of the process are frequently quite small and contain marrow; occasionally they are entirely absent, and the mastoid is then solid throughout.

At birth the mastoid is not pneumatized, but becomes aerated over the first year of life. Poor pneumatization is associated with eustachian tube dysfunction.

Nigersaurus

Nigersaurus is a genus of rebbachisaurid sauropod dinosaur that lived during the middle Cretaceous period, about 115 to 105 million years ago. It was discovered in the Elrhaz Formation in an area called Gadoufaoua, in the Republic of Niger. Fossils of this dinosaur were first described in 1976, but it was only named Nigersaurus taqueti in 1999, after further and more complete remains were found and described. The genus name means "Niger reptile", and the specific name honours the French palaeontologist Philippe Taquet, who discovered the first remains.

Small for a sauropod, Nigersaurus was about 9 metres (30 feet) long, and had a short neck. It weighed around four tonnes, comparable to a modern elephant. Its skeleton was highly pneumatised (filled with air spaces connected to air sacs), but the limbs were robustly built. Its skull was very specialised for feeding, with large fenestrae and thin bones. It had a wide muzzle filled with more than 500 teeth, which were replaced at a rapid rate: around every 14 days. The jaws may have borne a keratinous sheath. Unlike other tetrapods, the tooth-bearing bones of its jaws were rotated transversely relative to the rest of the skull, so that all of its teeth were located far to the front.

Nigersaurus and its closest relatives are grouped within the subfamily Rebbachisaurinae (formerly thought to be grouped in the eponymous Nigersaurinae) of the family Rebbachisauridae, which is part of the sauropod superfamily Diplodocoidea. Nigersaurus was probably a browser, and fed with its head close to the ground. The region of its brain that detected smell was underdeveloped, although its brain size was comparable to that of other dinosaurs. There has been debate on whether its head was habitually held downwards, or horizontally like other sauropods. It lived in a riparian habitat, and its diet probably consisted of soft plants, such as ferns, horsetails, and angiosperms. It is one of the most common fossil vertebrates found in the area, and shared its habitat with other dinosaurian megaherbivores, as well as large theropods and crocodylomorphs.

Nyasasaurus

Nyasasaurus (meaning "Lake Nyasa lizard") is an extinct genus of dinosauriform reptile from the Middle Triassic Manda Formation of Tanzania that appears to be the earliest known dinosaur. The type species Nyasasaurus parringtoni was first described in 1956 in the doctoral thesis of English paleontologist Alan J. Charig, but it was not formally described until 2013. Previously, the oldest record of dinosaurs was from Argentina and dated back to the late Carnian stage, about 231.4 million years ago. Nyasasaurus comes from a deposit that dates back to the Anisian stage, meaning that it predates other early dinosaurs by about 12 million years.

Physiology of dinosaurs

Preliminary note: In this article "dinosaur" means "non-avian dinosaur," since birds are a monophyletic taxon within the clade Dinosauria and most experts regard birds as dinosaurs.The physiology of dinosaurs has historically been a controversial subject, particularly their thermoregulation. Recently, many new lines of evidence have been brought to bear on dinosaur physiology generally, including not only metabolic systems and thermoregulation, but on respiratory and cardiovascular systems as well.

During the early years of dinosaur paleontology, it was widely considered that they were sluggish, cumbersome, and sprawling cold-blooded lizards. However, with the discovery of much more complete skeletons in western United States, starting in the 1870s, scientists could make more informed interpretations of dinosaur biology and physiology. Edward Drinker Cope, opponent of Othniel Charles Marsh in the Bone Wars, propounded at least some dinosaurs as active and agile, as seen in the painting of two fighting "Laelaps" produced under his direction by Charles R. Knight.In parallel, the development of Darwinian evolution, and the discoveries of Archaeopteryx and Compsognathus, led Thomas Henry Huxley to propose that dinosaurs were closely related to birds. Despite these considerations, the image of dinosaurs as large reptiles had already taken root, and most aspects of their paleobiology were interpreted as being typically reptilian for the first half of the twentieth century. Beginning in the 1960s and with the advent of the Dinosaur Renaissance, views of dinosaurs and their physiology have changed dramatically, including the discovery of feathered dinosaurs in Early Cretaceous age deposits in China, indicating that birds evolved from highly agile maniraptoran dinosaurs.

Plateosaurus

Plateosaurus (probably meaning "broad lizard", often mistranslated as "flat lizard") is a genus of plateosaurid dinosaur that lived during the Late Triassic period, around 214 to 204 million years ago, in what is now Central and Northern Europe and Greenland, North America. Plateosaurus is a basal (early) sauropodomorph dinosaur, a so-called "prosauropod". As of 2011, two species are recognised: the type species P. engelhardti from the late Norian and Rhaetian, and the slightly earlier P. gracilis from the lower Norian. However, others have been assigned in the past, and there is no broad consensus on the species taxonomy of plateosaurid dinosaurs. Similarly, there are a plethora of synonyms (invalid duplicate names) at the genus level.

Discovered in 1834 by Johann Friedrich Engelhardt and described three years later by Hermann von Meyer, Plateosaurus was the fifth named dinosaur genus that is still considered valid. Although it had been described before Richard Owen formally named Dinosauria in 1842, it was not one of the three genera used by Owen to define the group, because at the time, it was poorly known and difficult to identify as a dinosaur. It is now among the dinosaurs best known to science: over 100 skeletons have been found, some of them nearly complete. The abundance of its fossils in Swabia, Germany, has led to the nickname Schwäbischer Lindwurm (Swabian lindworm).

Plateosaurus was a bipedal herbivore with a small skull on a long, flexible neck, sharp but plump plant-crushing teeth, powerful hind limbs, short but muscular arms and grasping hands with large claws on three fingers, possibly used for defence and feeding. Unusually for a dinosaur, Plateosaurus showed strong developmental plasticity: instead of having a fairly uniform adult size, fully grown individuals were between 4.8 and 10 metres (16 and 33 ft) long and weighed between 600 and 4,000 kilograms (1,300 and 8,800 lb). Commonly, the animals lived for at least 12 to 20 years, but the maximum life span is not known.

Despite the great quantity and excellent quality of the fossil material, Plateosaurus was for a long time one of the most misunderstood dinosaurs. Some researchers proposed theories that were later shown to conflict with geological and palaeontological evidence, but have become the paradigm of public opinion. Since 1980 the taxonomy (relationships), taphonomy (how the animals became embedded and fossilised), biomechanics (how their skeletons worked), and palaeobiology (life circumstances) of Plateosaurus have been re-studied in detail, altering the interpretation of the animal's biology, posture and behaviour.

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 common ancestor. Because it is not a completely natural grouping, Rhamphorhynchoidea is not used as a formal group in most scientific literature, though some pterosaur scientists continue to use it as an informal grouping in popular works, such as The Pterosaurs: From Deep Time by David Unwin, and in some formal studies. Rhamphorhynchoids were the first pterosaurs to have appeared, in the late Triassic Period (Norian age, about 210 million years ago). Unlike their descendants the pterodactyloids, most rhamphorhynchoids had teeth and long tails, and most species lacked a bony crest, though several are known to have crests formed from soft tissue like keratin. They were generally small, with wingspans rarely exceeding 2.5 meters, though one species alluded to by Alexander Stoyanow might be among the largest pterosaurs of all time with a wingspan of 10 meters, comparable to the largest azhdarchids. Nearly all had become extinct by the end of the Jurassic Period, though least one anurognathid genus, Dendrorhynchoides, persisted to the early Cretaceous. The family Wukongopteridae, which shows a mix of rhamphorhynchoid and pterodactyloid features, is known from the Daohugou Beds which are most commonly dated to the Jurassic, but a few studies give a Cretaceous date. Further more, remains of a non-pterodactyloid from the Candeleros Formation extend the presence of basal pterosaurs into the at least early Late Cretaceous.

Trabecula

A trabecula (plural trabeculae, from Latin for "small beam") is a small, often microscopic, tissue element in the form of a small beam, strut or rod that supports or anchors a framework of parts within a body or organ. A trabecula generally has a mechanical function, and is usually composed of dense collagenous tissue (such as the trabecula of the spleen). They can be composed of other materials such as muscle and bone. In the heart, muscles form trabeculae carneae and septomarginal trabecula. Cancellous bone is formed from groupings of trabeculated bone tissue.

In cross sections, trabeculae of a cancellous bone can look like septa, but in three dimensions they are topologically distinct, with trabeculae being roughly rod or pillar-shaped and septa being sheet-like.

When crossing fluid-filled spaces, trabeculae may have the function of resisting tension (as in the penis, see for example trabeculae of corpora cavernosa and trabeculae of corpus spongiosum) or providing a cell filter (as in the trabecular meshwork of the eye).

Multiple perforations in a septum may reduce it to a collection of trabeculae, as happens to the walls of some of the pulmonary alveoli in emphysema.

Vjushkovisaurus

Vjushkovisaurus is an extinct genus of Middle Triassic archosauriform. It is known from the Anisian-aged Donguz Gorizont in Sol-Iletsk, Orenburg Oblast, Russia. The genus was named in 1982, with the type species being V. berdjanensis. Material has been collected in the Berdyanka II locality from a fossil assemblage called the Eryosuchus Fauna along the Berdyanka River, specifically in a sand-carbonate concretion in the upper part of the main river channel. Vjushkovisaurus is known only from the holotype PIN 2865/62 (formerly SGU 104/3871), a partial postcranial skeleton which consists of 12 presacral vertebrae, left humerus, ribs, a fragment of the coracoid and a fragment of the fibula.

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