Christine Marie Janis | |
|---|---|
 | |
| Alma mater | University of Cambridge 1973 Harvard University 1979 |
| Awards | George Gaylord Simpson Prize (1985) |
| Scientific career | |
| Institutions | University of Bristol current Brown University current Oregon State University University of Cambridge The Field Museum of Natural History The University of Chicago |
Christine Marie Janis is a British palaeontologist who specialises in mammals. She is currently based at the University of Bristol. [1]
Janis earned a bachelor's degree in Natural Sciences and Zoology from the University of Cambridge, and a PhD in Vertebrate Paleontology from Harvard University. [2] She has held positions as a researcher and lecturer at Oregon State University, Cambridge, the Field Museum of Natural History in the University of Chicago, the University of Bristol, and Brown University.
In 1985 Janis was awarded the George Gaylord Simpson Prize for Paleontology (Yale University, USA) and was elected Fellow of the Paleontological Society in 2007.
Janis attributes her interest in palaeontology to seeing Fantasia as a child. [2] She was married to fellow palaeontologist Jack Sepkoski (1948-1999).
Janis is best known for her contributions to the study of ungulates (hoofed mammals). As well as a large scientific publication list, Janis has contributed widely to textbooks and popular articles. [3]
Her earlier publications examine mammal teeth. For example, ungulate teeth changed from low crowned teeth to high crowned hypsodont teeth, as they evolved to adapt to a grassland diet, and this is correlated with changes in their digestion and can be used in their taxonomy. [4] [5] [6] She created the Hipsodonty Index, broadly used in mammal paleontology. [7] Her work on the evolution of horns in ungulates won her the Simpson Prize in 1985. [8]
In the 1990s, Janis switched focus from teeth to the biomechanics of locomotion. She has produced seminal works on the relationships between the lengths of limb bones in running mammals and their locomotion. [9] Latterly Janis has worked closely with her students and close colleagues to explore locomotion in various mammal groups, including camels, [10] various carnivores, [11] [12] and marsupials. [13] [14]
Among Janis's publications are the co-authored textbooks Evolution of Tertiary Mammals of North America. Vol. 2: Small Mammals, Edentates, and Marine Mammals and Vertebrate Life.
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Society of Vertebrate Paleontology (USA)
The Paleontological Society (USA)
The Palaeontological Association (UK)
GRIPS (Greater Rhode Island Paleontological Society) charter member.
Society for the Study of Mammalian Evolution (president)
Society for Integrative and Comparative Biology
National Center for Science Education
Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia and the Americas. A distinctive characteristic common to most of these species is that the young are carried in a pouch. Well-known marsupials include kangaroos, wallabies, koalas, opossums, wombats, Tasmanian devils, and the extinct thylacine. Some lesser-known marsupials are the dunnarts, potoroos, and the cuscus.
Ungulates are members of a diverse clade of primarily large mammals with hooves. These include odd-toed ungulates such as horses, rhinoceroses and tapirs, and even-toed ungulates such as cattle, pigs, giraffes, camels, sheep, deer, and hippopotamuses. Cetaceans are also even-toed ungulates, although they do not have hooves. Most terrestrial ungulates use the tips of their toes, usually hoofed, to sustain their whole body weight while moving.
Marsupial moles, the Notoryctidae, are highly specialized marsupial mammals, known from two species found at the Australian interior.
The order Peramelemorphia includes the bandicoots and bilbies; it equates approximately to the mainstream of marsupial omnivores. All members of the order are endemic to the twin land masses of Australia-New Guinea and most have the characteristic bandicoot shape: a plump, arch-backed body with a long, delicately tapering snout, very large upright ears, relatively long, thin legs, and a thin tail. Their size varies from about 140 grams up to 4 kilograms, but most species are about one kilogram, or the weight of a half-grown kitten.
Amphicyonidae is an extinct family of terrestrial carnivorans belonging to the suborder Caniformia. They first appeared in North America in the middle Eocene, spread to Europe by the late Eocene, and appear in Asia, and Africa by the early Miocene. They had largely disappeared worldwide by the late Miocene, with the latest recorded species at the end of the Miocene in Pakistan. They were among the first carnivorans to evolve large body size. Later in their history, they came into competition with hesperocyonine and borophagine canids. As dogs evolved similar body sizes and cranial and dental adaptations, the rise of these groups may have led to their extinction. Amphicyonids are often colloquially referred to as "bear-dogs".
Creodonta is an extinct, possibly polyphyletic order of carnivorous mammals that lived from the Paleocene to the Miocene epochs. Because they both possess carnassial teeth, creodonts and carnivorans were once thought to have shared a common ancestor, but given that different teeth are involved in making up the carnassials, this appears to be a case of evolutionary convergence. Carnassials are also known in other mammal clades, such as in the extinct bat Necromantis.
Condylarthra is an informal group – previously considered an order – of extinct placental mammals, known primarily from the Paleocene and Eocene epochs. They are considered early, primitive ungulates. It is now largely considered to be a wastebasket taxon, having served as a dumping ground for classifying ungulates which had not been clearly established as part of either Perissodactyla or Cetartiodactyla, being composed thus of several unrelated lineages.
Hypsodont is a pattern of dentition with high-crowned teeth and enamel extending past the gum line, providing extra material for wear and tear. Some examples of animals with hypsodont dentition are cows and horses; all animals that feed on gritty, fibrous material. The opposite condition is called brachydont.
Mesonychia is an extinct taxon of small to large-sized carnivorous ungulates related to the cetartiodactyls. Mesonychids first appeared in the early Paleocene, went into a sharp decline at the end of the Eocene, and died out entirely when the last genus, Mongolestes, became extinct in the early Oligocene. In Asia, the record of their history suggests they grew gradually larger and more predatory over time, then shifted to scavenging and bone-crushing lifestyles before the group became extinct.
Thylacosmilus is an extinct genus of saber-toothed metatherian mammals that inhabited South America from the Late Miocene to Pliocene epochs. Though Thylacosmilus looks similar to the "saber-toothed cats", it was not a felid, like the well-known North American Smilodon, but a sparassodont, a group closely related to marsupials, and only superficially resembled other saber-toothed mammals due to convergent evolution. A 2005 study found that the bite forces of Thylacosmilus and Smilodon were low, which indicates the killing-techniques of saber-toothed animals differed from those of extant species. Remains of Thylacosmilus have been found primarily in Catamarca, Entre Ríos, and La Pampa Provinces in northern Argentina.
Carnassials are paired upper and lower teeth modified in such a way as to allow enlarged and often self-sharpening edges to pass by each other in a shearing manner. The modification arose separately in several groups of carnivorous mammals. Different pairs of teeth were involved in the separate modifications. In modern Carnivora, the carnassials are the modified fourth upper premolar and the first lower molar. These teeth are also referred to as sectorial teeth. Humans lack carnassial teeth.
A cursorial organism is one that is adapted specifically to run. An animal can be considered cursorial if it has the ability to run fast or if it can keep a constant speed for a long distance. "Cursorial" is often used to categorize a certain locomotor mode, which is helpful for biologists who examine behaviors of different animals and the way they move in their environment. Cursorial adaptations can be identified by morphological characteristics, physiological characteristics, maximum speed, and how often running is used in life. There is much debate over how to define a cursorial animal specifically. The most accepted definitions include that a cursorial organism could be considered adapted to long-distance running at high speeds or has the ability to accelerate quickly over short distances. Among vertebrates, animals under 1 kg of mass are rarely considered cursorial, and cursorial behaviors and morphology is thought to only occur at relatively large body masses in mammals. There are a few mammals that have been termed "micro-cursors" that are less than 1 kg in mass and have the ability to run faster than other small animals of similar sizes.
The evolution of mammals has passed through many stages since the first appearance of their synapsid ancestors in the Pennsylvanian sub-period of the late Carboniferous period. By the mid-Triassic, there were many synapsid species that looked like mammals. The lineage leading to today's mammals split up in the Jurassic; synapsids from this period include Dryolestes, more closely related to extant placentals and marsupials than to monotremes, as well as Ambondro, more closely related to monotremes. Later on, the eutherian and metatherian lineages separated; the metatherians are the animals more closely related to the marsupials, while the eutherians are those more closely related to the placentals. Since Juramaia, the earliest known eutherian, lived 160 million years ago in the Jurassic, this divergence must have occurred in the same period.
Sinonyx is a genus of extinct, superficially wolf-like mesonychid mammals from the late Paleocene of China. It is within the family Mesonychidae, and cladistic analysis of a skull of Sinonyxjiashanensis identifies its closest relative as Ankalagon. S.jiashanensis was discovered in Anhui province, China, in the Tuijinshan formation.
Parictis is the earliest genus of bears known. It was a very small and graceful ursid with a skull only 7 cm long. Parictis first appeared in North America in the Late Eocene, but it did not arrive in Eurasia until the Miocene. Some suggest that Parictis may have emigrated from Asia into North America during the major sea level low about 37 mya, because of the continued evolution of the Amphicynodontinae into the Hemicyoninae in Asia. Although no Parictis fossils have been found in East Asia, Parictis does appear in Eurasia and Africa, but not until the Miocene.
Natalia Rybczynski is a Canadian paleobiologist, professor and researcher.
Phenacodontidae is an extinct family of large herbivorous mammals traditionally placed in the “wastebasket taxon” Condylarthra, which may instead represent early-stage perissodactyls. They lived between the Paleocene and Eocene epochs and their fossil remains have been found in North America and Europe.
Several mammals are known from the Mesozoic of Madagascar. The Bathonian Ambondro, known from a piece of jaw with three teeth, is the earliest known mammal with molars showing the modern, tribosphenic pattern that is characteristic of marsupial and placental mammals. Interpretations of its affinities have differed; one proposal places it in a group known as Australosphenida with other Mesozoic tribosphenic mammals from the southern continents (Gondwana) as well as the monotremes, while others favor closer affinities with northern (Laurasian) tribosphenic mammals or specifically with placentals. At least five species are known from the Maastrichtian, including a yet undescribed species known from a nearly complete skeleton that may represent a completely new group of mammals. The gondwanathere Lavanify, known from two teeth, is most closely related to other gondwanatheres found in India and Argentina. Two other teeth may represent another gondwanathere or a different kind of mammal. One molar fragment is one of the few known remains of a multituberculate mammal from Gondwana and another has been interpreted as either a marsupial or a placental.
The Grit, not grass hypothesis is an evolutionary hypothesis that explains the evolution of high-crowned teeth, particularly in New World mammals. The hypothesis is that the ingestion of gritty soil is the primary driver of hypsodont tooth development, not the silica-rich composition of grass, as was previously thought.
Etayoa is an ungulate of the family Carodniidae in the order Xenungulata that lived during the Early Eocene in northern South America.
