Hans C. Bjerring
Encyclopedia
Hans Christian Bjerring (born May 30, 1931) is a Danish
-Swedish
vertebrate
paleontologist and comparative anatomist. He has spent his career at the Swedish Museum of Natural History
in Stockholm
, Sweden
, as curator
at the Department of Palaeozoology.
Bjerring's research is mainly about the fundamental structure of the head
in vertebrate evolution
. His studies are based on detailed analyses of models of the crania of the sarcopterygian fishes Eusthenopteron foordi
and Glyptolepis groenlandica from the Devonian
as well as serially-sectioned embryos of fishes and urodeles. He belongs to the Stockholm school of paleontology together with, among others, Erik Stensiö
, Erik Jarvik
, Gunnar Säve-Söderbergh
, and Tor Ørvig
.
A recurrent theme in Bjerring’s research is that much of the vertebrate head is formed by a complex intertwining of serially homologous
anatomical segments. According to Bjerring, this holds both for the distribution and composition of cranial nerves
, the pharyngeal arches
and their contributions to the braincase organs and structures derived from the pharyngeal clefts as well as muscle
s and cartilages at the base of the skull
.
Bjerring has also discussed a number of classical problems in comparative anatomy
. Like Erik Jarvik
, he has argued that the three ear ossicles of mammals can be derived from components of the hyoid branchial arch
of osteolepiforms rather than from both the mandibular and hyoid arches as claimed by the Reichert–Gaupp theory. Another classical problem is which one of two pairs of large dermal bone
s in the skull roof
of sarcopterygian fishes that is homologous to the parietal bone
of tetrapods. Here, Bjerring has proposed that neither alternative is correct; rather, the confusion may stem from the fact that, owing to the enormous expansion of the telencephalon
in theria
ns, one of the bone pairs has been displaced and forms the tentorium cerebelli
below the skull roof. He has also analysed the basic structure of the paired limbs by comparing the pectoral and pelvic fins of the Eusthenopteron
with the hindleg of the Devonian tetrapod Ichthyostega
and embryonic humans.
Bichir
s are a small group of aberrant bony fish whose anatomy has been explored by Bjerring. He identified a pair of intracranial ligament
s that hold their brains in place, variations in the structure of the vomer, the structure of the olfactory organ in bichir embryos, and reported a spinobulbar cistern resembling the cerebellomedullar cistern of mammals. Bjerring has disputed the common view that bichirs are actinopterygians, mainly because some alleged homologies between the cranial bones of bichirs and actinopterygians are dubious.
Bjerring has named the temnospondyls Selenocara and Aquiloniferus from the Lower Triassic
of East Greenland
. His papers are richly illustrated and characterized by a pregnant, sometimes polemic style. He has also written popular scientific articles.
Denmark
Denmark is a Scandinavian country in Northern Europe. The countries of Denmark and Greenland, as well as the Faroe Islands, constitute the Kingdom of Denmark . It is the southernmost of the Nordic countries, southwest of Sweden and south of Norway, and bordered to the south by Germany. Denmark...
-Swedish
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
paleontologist and comparative anatomist. He has spent his career at the Swedish Museum of Natural History
Swedish Museum of Natural History
The Swedish Museum of Natural History , in Stockholm, is one of two major museums of natural history in Sweden, the other one being located in Gothenburg....
in Stockholm
Stockholm
Stockholm is the capital and the largest city of Sweden and constitutes the most populated urban area in Scandinavia. Stockholm is the most populous city in Sweden, with a population of 851,155 in the municipality , 1.37 million in the urban area , and around 2.1 million in the metropolitan area...
, Sweden
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
, as curator
Curator
A curator is a manager or overseer. Traditionally, a curator or keeper of a cultural heritage institution is a content specialist responsible for an institution's collections and involved with the interpretation of heritage material...
at the Department of Palaeozoology.
Bjerring's research is mainly about the fundamental structure of the head
Head
In anatomy, the head of an animal is the rostral part that usually comprises the brain, eyes, ears, nose and mouth . Some very simple animals may not have a head, but many bilaterally symmetric forms do....
in vertebrate evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
. His studies are based on detailed analyses of models of the crania of the sarcopterygian fishes Eusthenopteron foordi
Eusthenopteron
Eusthenopteron is a genus of prehistoric lobe-finned fish which has attained an iconic status from its close relationships to tetrapods. Early depictions of this animal show it emerging onto land, however paleontologists now widely agree that it was a strictly aquatic animal...
and Glyptolepis groenlandica from the Devonian
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
as well as serially-sectioned embryos of fishes and urodeles. He belongs to the Stockholm school of paleontology together with, among others, Erik Stensiö
Erik Stensiö
Erik Helge Osvald Stensiö was a Swedish paleozoologist.Erik Andersson, as his original name was, was born in the village of Stensjö in Döderhult parish in Kalmar County; he later took his new surname from his place of origin and is occasionally referred to with both names...
, Erik Jarvik
Erik Jarvik
Anders Erik Vilhelm Jarvik was a Swedish palaeozoologist who worked extensively on the sarcopterygian fish Eusthenopteron...
, Gunnar Säve-Söderbergh
Gunnar Säve-Söderbergh
Gunnar Säve-Söderbergh was a Swedish palaeontologist and geologist. Säve-Söderbergh was born at Falun, the son of the neurologist Gotthard Söderbergh and Inga Säve. He passed his G.C.E. at Gothenburg in 1928 and took bachelor's and licentiate's degrees at Uppsala University in 1931 and 1933,...
, and Tor Ørvig
Tor Ørvig
Tor Ørvig was a Norwegian-born Swedish paleontologist who explored the histology of early vertebrates. He was professor at the Swedish Museum of Natural History in Stockholm and member of the Royal Swedish Academy of Sciences.- References:...
.
A recurrent theme in Bjerring’s research is that much of the vertebrate head is formed by a complex intertwining of serially homologous
Homology (biology)
Homology forms the basis of organization for comparative biology. In 1843, Richard Owen defined homology as "the same organ in different animals under every variety of form and function". Organs as different as a bat's wing, a seal's flipper, a cat's paw and a human hand have a common underlying...
anatomical segments. According to Bjerring, this holds both for the distribution and composition of cranial nerves
Cranial nerves
Cranial nerves are nerves that emerge directly from the brain, in contrast to spinal nerves, which emerge from segments of the spinal cord. In humans, there are traditionally twelve pairs of cranial nerves...
, the pharyngeal arches
Branchial arch
In the development of vertebrate animals, the pharyngeal arches are anlage for a multitude of structures. In humans, they develop during the fourth week in utero as a series of mesodermal outpouchings on the left and right sides of the developing pharynx...
and their contributions to the braincase organs and structures derived from the pharyngeal clefts as well as muscle
Muscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...
s and cartilages at the base of the skull
Skull
The skull is a bony structure in the head of many animals that supports the structures of the face and forms a cavity for the brain.The skull is composed of two parts: the cranium and the mandible. A skull without a mandible is only a cranium. Animals that have skulls are called craniates...
.
Bjerring has also discussed a number of classical problems in comparative anatomy
Comparative anatomy
Comparative anatomy is the study of similarities and differences in the anatomy of organisms. It is closely related to evolutionary biology and phylogeny .-Description:...
. Like Erik Jarvik
Erik Jarvik
Anders Erik Vilhelm Jarvik was a Swedish palaeozoologist who worked extensively on the sarcopterygian fish Eusthenopteron...
, he has argued that the three ear ossicles of mammals can be derived from components of the hyoid branchial arch
Branchial arch
In the development of vertebrate animals, the pharyngeal arches are anlage for a multitude of structures. In humans, they develop during the fourth week in utero as a series of mesodermal outpouchings on the left and right sides of the developing pharynx...
of osteolepiforms rather than from both the mandibular and hyoid arches as claimed by the Reichert–Gaupp theory. Another classical problem is which one of two pairs of large dermal bone
Dermal bone
A dermal bone - bony structures derived from intramembranous ossification that form components of the vertebrate skeleton including the skull, jaws, gills, fins and exoskeleton. In contrast to endochondral bone, dermal bone does not form from cartilage first and then calcify...
s in the skull roof
Skull roof
The skull roof , or the roofing bones of the skull are a set of bones covering the brain, eyes and nostrils in bony fishes and all land living vertebrates. The bones are derived from dermal bone, hence the alternative name dermatocranium...
of sarcopterygian fishes that is homologous to the parietal bone
Parietal bone
The parietal bones are bones in the human skull which, when joined together, form the sides and roof of the cranium. Each bone is roughly quadrilateral in form, and has two surfaces, four borders, and four angles. It is named from the Latin pariet-, wall....
of tetrapods. Here, Bjerring has proposed that neither alternative is correct; rather, the confusion may stem from the fact that, owing to the enormous expansion of the telencephalon
Telencephalon
The cerebrum or telencephalon, together with the diencephalon, constitutes the forebrain. The cerebrum is the most anterior region of the vertebrate central nervous system. Telencephalon refers to the embryonic structure, from which the mature cerebrum develops...
in theria
Theria
Theria is a subclass of mammals that give birth to live young without using a shelled egg, including both eutherians and metatherians . The only omitted extant mammal group is the egg-laying monotremes....
ns, one of the bone pairs has been displaced and forms the tentorium cerebelli
Tentorium cerebelli
The tentorium cerebelli or cerebellar tentorium is an extension of the dura mater that separates the cerebellum from the inferior portion of the occipital lobes.-Anatomy:...
below the skull roof. He has also analysed the basic structure of the paired limbs by comparing the pectoral and pelvic fins of the Eusthenopteron
Eusthenopteron
Eusthenopteron is a genus of prehistoric lobe-finned fish which has attained an iconic status from its close relationships to tetrapods. Early depictions of this animal show it emerging onto land, however paleontologists now widely agree that it was a strictly aquatic animal...
with the hindleg of the Devonian tetrapod Ichthyostega
Ichthyostega
Ichthyostega is an early tetrapod genus that lived at the end of the Upper Devonian period . It was a labyrinthodont, one of the first fossil record of tetrapods. Ichthyostega possessed lungs and limbs that helped it navigate through shallow water in swamps...
and embryonic humans.
Bichir
Bichir
The bichirs are a family, Polypteridae, of archaic-looking ray-finned fishes, the sole family in the order Polypteriformes.All species occur in freshwater habitats in tropical Africa and the Nile River system, mainly swampy, shallow floodplains and estuaries.-Anatomy and appearance:Bichirs are...
s are a small group of aberrant bony fish whose anatomy has been explored by Bjerring. He identified a pair of intracranial ligament
Ligament
In anatomy, the term ligament is used to denote any of three types of structures. Most commonly, it refers to fibrous tissue that connects bones to other bones and is also known as articular ligament, articular larua, fibrous ligament, or true ligament.Ligament can also refer to:* Peritoneal...
s that hold their brains in place, variations in the structure of the vomer, the structure of the olfactory organ in bichir embryos, and reported a spinobulbar cistern resembling the cerebellomedullar cistern of mammals. Bjerring has disputed the common view that bichirs are actinopterygians, mainly because some alleged homologies between the cranial bones of bichirs and actinopterygians are dubious.
Bjerring has named the temnospondyls Selenocara and Aquiloniferus from the Lower 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...
of East Greenland
Greenland
Greenland is an autonomous country within the Kingdom of Denmark, located between the Arctic and Atlantic Oceans, east of the Canadian Arctic Archipelago. Though physiographically a part of the continent of North America, Greenland has been politically and culturally associated with Europe for...
. His papers are richly illustrated and characterized by a pregnant, sometimes polemic style. He has also written popular scientific articles.