Glanosuchus
Encyclopedia
Glanosuchus is an genus
of scylacosaurid
therocephalia
n from the Late Permian of South Africa
. The type species
G. macrops was named by Robert Broom
in 1904. Glanosuchus had a middle ear
structure that was intermediate between that of early therapsids and mammals. Ridges in the nasal cavity
of Glanosuchus suggest it had an at least partially endothermic
metabolism similar to modern mammals.
skull. The skull has been distorted during fossilization and the bone is indistinguishable from the surrounding matrix
in some parts. In illustrating the holotype, Broom chose to reconstruct the skull of the species rather than draw the actual specimen.
The skull of Glanosuchus is about 12 inches (30.5 cm) long. In life, Glanosuchus probably grew to around 6 feet (1.8 m) in length. Like other early therocephalians, Glanosuchus had a long, deep snout and large canine
teeth. The incisor teeth at the front of the upper jaw are also large and blade-like. There are six incisors on either side of the upper jaw, the furthest one being noticeably smaller than the rest. Five small pointed teeth are located behind each canine. The snout is wider in the front than it is behind, an usual feature among therapsids but present in several other related therocephalians. The nostrils are positioned at the tip of the snout and directed forward.
. Modern mammals have three bones in the middle ear (the malleus
, incus
, and stapes) that transfer sound energy from the eardrum
to the fluid of the inner ear
. The malleus, incus, and stapes of mammals developed from the articular
, quadrate
, and angular bones of early therapsids. Studies of the bones of Glanosuchus show that it had a very thin plate of bone that acted as an ear drum, receiving sounds and transferring them to a small air-filled cavity. The stapes and vestibular foramen (the hole that connects the middle and inner ears) are preserved in one specimen of Glanosuchus that was examined by grinding away cross sections of the skull. The anular ligament, a ring-like structure that forms a seal between the end of the stapes and the rim of the vestibular foramen, was probably held in place by cartilage. The transfer of sound
between the thin bony plate and the vestibular foramen in Glanosuchus was not as effective as it is in mammals, meaning that the animal had a less acute sense of hearing.
s, the closest living relatives of mammals, are cold-blooded ectotherm
s with lower metabolic rates. Endothermic animals likely evolved from more primitive ectothermic synapsid
s sometime in the Permian or Triassic
.
While fur, commonly accepted as a clear indication of endothermy, has not been found in non-mammalian therapsids, some skeletal features preserved in therapsid remains may be an indication of the metabolic rates of these animals. Modern mammals possess maxilloturbinates
, which are a type of concha (shelf of bone) in the nasal cavity
that collect moisture from inhaled air. As endotherms, mammals must breath rapidly in order to supply enough oxygen for their high metabolisms. As oxygen passes into and out of the nasal cavity, it dries out the surrounding tissue. Water from inhaled air condenses on the maxilloturbinates, preventing the drying out of the nasal cavity and allowing mammals to inhale enough oxygen to support their high metabolisms.
Reptiles and more primitive synapsids have conchae, but these plates of bone are involved in sensing smell rather than preventing desiccation. While the maxilloturbinates of mammals are located in the path of airflow to collect moisture, sensory cochae in both mammals and reptiles are positioned farther back and above the nasal passage, away from the flow of air. Glanosuchus has ridges positioned low in the nasal cavity, indicating that it had maxilloturbinates that were in the direct path of airflow. The maxilloturbinates may not have been preserved because they were either very thin or cartilaginous. The possibility has also been raised that these ridges are associated with an olfactory epithelium
rather than turbinates. Nonetheless, the possible presence of maxilloturbinates suggests that Glanosuchus may have been able to rapidly breath air without the nasal passage drying out, and therefore could have been an endotherm.
Glanosuchus is the earliest known therapsid to possess maxilloturbinates, but it shares features with reptiles that suggest it was not fully endothermic. Choana
e, two holes in the palate that connect the nasal cavity to the mouth, are positioned far forward in reptiles, early synapsids, and Glanosuchus. This shortens the nasal cavity, thereby reducing the ability to humidify incoming air. The choanae migrated farther back in the palate later in therocephalian evolution, suggesting that advanced forms like Bauria had high metabolic rates similar to those of mammals. As the choanae moved farther back, a secondary palate
expanded in front of it. This expansion occurred in both therocephalians and the related cynodont
s, indicating that the two groups were convergently acquiring mammalian characteristics in the Permian and Triassic. Although therocephalians died out by the Middle Triassic
, cynodonts continued to diversify, giving rise to fully endothermic mammals in the Late Triassic
.
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 scylacosaurid
Scylacosauridae
Scylacosauridae is a family of therocephalian therapsids. Scylacosaurids lived during the Permian period and were among the most basal therocephalians. The family was named by South African paleontologist Robert Broom in 1903. Scylacosaurids have long snouts and unusual saber-like canine...
therocephalia
Therocephalia
Therocephalians are an extinct suborder of carnivorous eutheriodont therapsids that lived from the middle and late Permian into the Triassic 265.0—245.0 Ma existing for approximately ....
n from the Late Permian 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...
. 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...
G. macrops was named by Robert Broom
Robert Broom
Professor Robert Broom was a Scottish South African doctor and paleontologist. He qualified as a medical practitioner in 1895 and received his DSc in 1905 from the University of Glasgow...
in 1904. Glanosuchus had a middle ear
Middle ear
The middle ear is the portion of the ear internal to the eardrum, and external to the oval window of the cochlea. The mammalian middle ear contains three ossicles, which couple vibration of the eardrum into waves in the fluid and membranes of the inner ear. The hollow space of the middle ear has...
structure that was intermediate between that of early therapsids and mammals. Ridges in the nasal cavity
Nasal cavity
The nasal cavity is a large air filled space above and behind the nose in the middle of the face.- Function :The nasal cavity conditions the air to be received by the other areas of the respiratory tract...
of Glanosuchus suggest it had an at least partially endothermic
Endothermic
In thermodynamics, the word endothermic describes a process or reaction in which the system absorbs energy from the surroundings in the form of heat. Its etymology stems from the prefix endo- and the Greek word thermasi,...
metabolism similar to modern mammals.
Description
Glanosuchus macrops was first described in 1904 by South African paleontologist Robert Broom. He named the genus and species on the basis of a nearly complete holotypeHolotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
skull. The skull has been distorted during fossilization and the bone is indistinguishable from the surrounding matrix
Matrix (geology)
The matrix or groundmass of rock is the finer grained mass of material in which larger grains, crystals or clasts are embedded.The matrix of an igneous rock consists of finer grained, often microscopic, crystals in which larger crystals are embedded. This porphyritic texture is indicative of...
in some parts. In illustrating the holotype, Broom chose to reconstruct the skull of the species rather than draw the actual specimen.
The skull of Glanosuchus is about 12 inches (30.5 cm) long. In life, Glanosuchus probably grew to around 6 feet (1.8 m) in length. Like other early therocephalians, Glanosuchus had a long, deep snout and large canine
Canine
Canine may refer to:* Domestic dog* Animals belonging to the family Canidae, or the sub-family Caninae* Canine tooth* Ralph Canine, American soldier and government administrator* A character in Glenn Martin, DDS...
teeth. The incisor teeth at the front of the upper jaw are also large and blade-like. There are six incisors on either side of the upper jaw, the furthest one being noticeably smaller than the rest. Five small pointed teeth are located behind each canine. The snout is wider in the front than it is behind, an usual feature among therapsids but present in several other related therocephalians. The nostrils are positioned at the tip of the snout and directed forward.
Hearing
Glanosuchus represents an early stage in the development of the mammalian middle earMiddle ear
The middle ear is the portion of the ear internal to the eardrum, and external to the oval window of the cochlea. The mammalian middle ear contains three ossicles, which couple vibration of the eardrum into waves in the fluid and membranes of the inner ear. The hollow space of the middle ear has...
. Modern mammals have three bones in the middle ear (the malleus
Malleus
The malleus or hammer is a hammer-shaped small bone or ossicle of the middle ear which connects with the incus and is attached to the inner surface of the eardrum...
, incus
Incus
The incus or anvil is the anvil-shaped small bone or ossicle in themiddle ear. It connects the malleus to the stapes. It was first described by Alessandro Achillini of Bologna.The incus transmits sound vibrations from the malleus to the stapes....
, and stapes) that transfer sound energy from the eardrum
Eardrum
The eardrum, or tympanic membrane, is a thin membrane that separates the external ear from the middle ear in humans and other tetrapods. Its function is to transmit sound from the air to the ossicles inside the middle ear. The malleus bone bridges the gap between the eardrum and the other ossicles...
to the fluid of the inner ear
Inner ear
The inner ear is the innermost part of the vertebrate ear. In mammals, it consists of the bony labyrinth, a hollow cavity in the temporal bone of the skull with a system of passages comprising two main functional parts:...
. The malleus, incus, and stapes of mammals developed from the articular
Articular
The articular bone is part of the lower jaw of most tetrapods, including amphibians, sauropsids and early synapsids. In these animals it is connected to two other lower jaw bones, the suprangular and the angular...
, quadrate
Quadrate bone
The quadrate bone is part of a skull in most tetrapods, including amphibians, sauropsids , and early synapsids. In these animals it connects to the quadratojugal and squamosal in the skull, and forms part of the jaw joint .- Evolutionary variation :In snakes, the quadrate bone has become elongated...
, and angular bones of early therapsids. Studies of the bones of Glanosuchus show that it had a very thin plate of bone that acted as an ear drum, receiving sounds and transferring them to a small air-filled cavity. The stapes and vestibular foramen (the hole that connects the middle and inner ears) are preserved in one specimen of Glanosuchus that was examined by grinding away cross sections of the skull. The anular ligament, a ring-like structure that forms a seal between the end of the stapes and the rim of the vestibular foramen, was probably held in place by cartilage. The transfer of sound
Impedance matching
In electronics, impedance matching is the practice of designing the input impedance of an electrical load to maximize the power transfer and/or minimize reflections from the load....
between the thin bony plate and the vestibular foramen in Glanosuchus was not as effective as it is in mammals, meaning that the animal had a less acute sense of hearing.
Metabolism
Glanosuchus may have been one of the first therapsids to achieve endothermy, or warm-bloodedness. Endothermy is seen today in mammals, the only living group of therapsids. ReptileReptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
s, the closest living relatives of mammals, are cold-blooded ectotherm
Ectotherm
An ectotherm, from the Greek εκτός "outside" and θερμός "hot", refers to organisms that control body temperature through external means. As a result, organisms are dependent on environmental heat sources and have relatively low metabolic rates. For example, many reptiles regulate their body...
s with lower metabolic rates. Endothermic animals likely evolved from more primitive ectothermic synapsid
Synapsid
Synapsids are a group of animals that includes mammals and everything more closely related to mammals than to other living amniotes. They are easily separated from other amniotes by having an opening low in the skull roof behind each eye, leaving a bony arch beneath each, accounting for their name...
s sometime in the Permian or Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
.
While fur, commonly accepted as a clear indication of endothermy, has not been found in non-mammalian therapsids, some skeletal features preserved in therapsid remains may be an indication of the metabolic rates of these animals. Modern mammals possess maxilloturbinates
Turbinate
In anatomy, a nasal concha is a long, narrow and curled bone shelf that protrudes into the breathing passage of the nose...
, which are a type of concha (shelf of bone) in the nasal cavity
Nasal cavity
The nasal cavity is a large air filled space above and behind the nose in the middle of the face.- Function :The nasal cavity conditions the air to be received by the other areas of the respiratory tract...
that collect moisture from inhaled air. As endotherms, mammals must breath rapidly in order to supply enough oxygen for their high metabolisms. As oxygen passes into and out of the nasal cavity, it dries out the surrounding tissue. Water from inhaled air condenses on the maxilloturbinates, preventing the drying out of the nasal cavity and allowing mammals to inhale enough oxygen to support their high metabolisms.
Reptiles and more primitive synapsids have conchae, but these plates of bone are involved in sensing smell rather than preventing desiccation. While the maxilloturbinates of mammals are located in the path of airflow to collect moisture, sensory cochae in both mammals and reptiles are positioned farther back and above the nasal passage, away from the flow of air. Glanosuchus has ridges positioned low in the nasal cavity, indicating that it had maxilloturbinates that were in the direct path of airflow. The maxilloturbinates may not have been preserved because they were either very thin or cartilaginous. The possibility has also been raised that these ridges are associated with an olfactory epithelium
Epithelium
Epithelium is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. Epithelial tissues line the cavities and surfaces of structures throughout the body, and also form many glands. Functions of epithelial cells include secretion, selective...
rather than turbinates. Nonetheless, the possible presence of maxilloturbinates suggests that Glanosuchus may have been able to rapidly breath air without the nasal passage drying out, and therefore could have been an endotherm.
Glanosuchus is the earliest known therapsid to possess maxilloturbinates, but it shares features with reptiles that suggest it was not fully endothermic. Choana
Choana
Choana is the posterior nasal aperture.The choanae are separated by the vomer.- Boundaries :It is the opening between the nasal cavity and the nasopharynx....
e, two holes in the palate that connect the nasal cavity to the mouth, are positioned far forward in reptiles, early synapsids, and Glanosuchus. This shortens the nasal cavity, thereby reducing the ability to humidify incoming air. The choanae migrated farther back in the palate later in therocephalian evolution, suggesting that advanced forms like Bauria had high metabolic rates similar to those of mammals. As the choanae moved farther back, a secondary palate
Secondary palate
The secondary palate is an anatomical structure that divides the nasal cavity from the oral cavity in many vertebrates.In human embryology, it refers to that portion of the hard palate that is formed by the growth of the two palatine shelves medially and their mutual fusion in the midline...
expanded in front of it. This expansion occurred in both therocephalians and the related cynodont
Cynodont
Cynodontia or cynodonts are a taxon of therapsids which first appeared in the Late Permian and were eventually distributed throughout all seven continents by the Early Triassic . This clade includes modern mammals and their extinct close relatives. They were one of the most diverse groups of...
s, indicating that the two groups were convergently acquiring mammalian characteristics in the Permian and Triassic. Although therocephalians died out by the Middle Triassic
Middle Triassic
In the geologic timescale, the Middle Triassic is the second of three epochs of the Triassic period or the middle of three series in which the Triassic system is divided. It spans the time between 245 ± 1.5 Ma and 228 ± 2 Ma...
, cynodonts continued to diversify, giving rise to fully endothermic mammals in the Late Triassic
Late Triassic
The Late Triassic is in the geologic timescale the third and final of three epochs of the Triassic period. The corresponding series is known as the Upper Triassic. In the past it was sometimes called the Keuper, after a German lithostratigraphic group that has a roughly corresponding age...
.