Stephen Blair Hedges (known as S. Blair Hedges) is Laura H. Carnell Professor of Science and director of the Center for Biodiversity at Temple University where he researches the tree of life and leads conservation efforts in Haiti and elsewhere. He co-founded Haiti National Trust.
Hedges has a Bachelor of Science undergraduate degree from George Mason University, and a Masters and PhD in Zoology from the University of Maryland, supervised by Richard Highton. [1] Before he joined Temple University in 2014, he was a professor at Penn State. [1] [2] He is also a founding member of the NASA Astrobiology Center. He has published over 300 peer-reviewed works including 10 books and monographs. [3] He was elected as a fellow of the American Association for the Advancement of Science in 2009 for "revealing connections between biological evolution and Earth history in diverse groups of organisms", [4] and was awarded the 2011 Penn State Faculty Scholar Medal for Outstanding Achievement in the Life and Health Sciences. [5] A Cuban butterfly ( Leptodes hedgesi Schwartz & Johnson 1992), Cuban frog ( Eleutherodactylus blairhedgesi Estrada, Diaz, & Rodriguez 1997), and Cuban millipede ( Amphelictogon blairi Perez-Asso 1998) have been named in his honor.
Hedges has studied the relationships and timing of major groups in the tree of life using genomic data. [1] This research has led to a number of discoveries including an early origin for the orders of placental mammals and modern birds, [6] [7] estimates of when prokaryotes and eukaryotes first colonized land and its relevance for the planet, [8] [9] and the phylogenetic relationships of reptiles and insectivorous mammals. [10] [11] [12] [13] He has coined the word timetree for a phylogenetic tree scaled to time, co-founded the TimeTree database for exploring the time-scale of the tree of life, and co-edited the book Timetree of Life. [14] Hedges and his team produced a spiral tree of life in 2015 to visualize the relationships over time of 50,000 species, and discovered that diversification and speciation are both relatively constant through time and among groups. [15]
Hedges also has a field program in the Caribbean where he has studied the evolution and biogeography of amphibians and reptiles with genetic data and maintained a database of information on these species, Caribherp. He discovered many new species in his work and has so far named 135 species of reptiles, amphibians, and butterflies. He also described three of the smallest species of reptiles and amphibians, including the Monte Iberia dwarf frog (Eleutherodactylus iberia), [16] Jaragua gecko ( Sphaerodactylus ariasae ), and the Barbados threadsnake (Tetracheilostoma carlae). Twelve articles in the New York Times have described his research. [17]
Work by Hedges and his team in Haiti has defined hot spots of biodiversity leading to the establishment of three national parks in Haiti. He also initiated a captive breeding program to conserve ten endangered species of frog at the Philadelphia Zoo. [18] Together with Haitian CEO Philippe Bayard, he founded Haiti National Trust, an environmental protection NGO.
Hedges is interested in Renaissance art, which led him to conduct several scientific studies of early artwork, including the development of a method for dating old prints [19] and a study on the historical biogeography of beetles based on the holes they bored in old books. [20]
Amniotes are tetrapod vertebrate animals belonging to the clade Amniota, a large group that comprises the vast majority of living terrestrial and semiaquatic vertebrates. Amniotes evolved from amphibian ancestors during the Carboniferous period and further diverged into two groups, namely the sauropsids and synapsids, an event that marks the appearance of Amniota, according to the definition established under the PhyloCode. This basal divergence within Amniota has been dated by molecular studies at 310–329 Ma or 312–330 Ma, but the presence of Hylonomus at Joggins implies a minimal age of about 317 Ma. A fossilized birth-death process study of early amniotes suggested an age of 322–340 Ma. Amniotes are distinguished from the other living tetrapod clade — the non-amniote lissamphibians — by the development of three extraembryonic membranes, thicker and keratinized skin, and costal respiration. Additional unique features are the presence of adrenocortical and chromaffin tissues as a discrete pair of glands near their kidneys, which are more complex, the presence of an astragalus for better extremity range of motion, the diminished role of skin breathing, and the complete loss of metamorphosis, gills, and lateral lines.
The Lepidosauria is a subclass or superorder of reptiles, containing the orders Squamata and Rhynchocephalia. Squamata includes lizards and snakes. Squamata contains over 9,000 species, making it by far the most species-rich and diverse order of non-avian reptiles in the present day. Rhynchocephalia was a formerly widespread and diverse group of reptiles in the Mesozoic Era. However, it is represented by only one living species: the tuatara, a superficially lizard-like reptile native to New Zealand.
Afrotheria is a superorder of mammals, the living members of which belong to groups that are either currently living in Africa or of African origin: golden moles, elephant shrews, otter shrews, tenrecs, aardvarks, hyraxes, elephants, sea cows, and several extinct clades. Most groups of afrotheres share little or no superficial resemblance, and their similarities have only become known in recent times because of genetics and molecular studies. Many afrothere groups are found mostly or exclusively in Africa, reflecting the fact that Africa was an island continent from the Cretaceous until the early Miocene around 20 million years ago, when Afro-Arabia collided with Eurasia.
Sauropsida is a clade of amniotes, broadly equivalent to the class Reptilia, though typically used in a broader sense to also include extinct stem-group relatives of modern reptiles and birds. The most popular definition states that Sauropsida is the sibling taxon to Synapsida, the other clade of amniotes which includes mammals as its only modern representatives. Although early synapsids have historically been referred to as "mammal-like reptiles", all synapsids are more closely related to mammals than to any modern reptile. Sauropsids, on the other hand, include all amniotes more closely related to modern reptiles than to mammals. This includes Aves (birds), which are recognized as a subgroup of archosaurian reptiles despite originally being named as a separate class in Linnaean taxonomy.
Ophidia is a group of squamate reptiles including modern snakes and reptiles more closely related to snakes than to other living groups of lizards.
The Archonta are a now-abandoned group of mammals, considered a superorder in some classifications, which consists of these orders:
Hutias are moderately large cavy-like rodents of the subfamily Capromyinae that inhabit the Caribbean islands. Most species are restricted to Cuba, but species are known from all of the Greater Antilles, as well as The Bahamas and (formerly) Little Swan Island off of Honduras.
Toxicofera is a proposed clade of scaled reptiles (squamates) that includes the Serpentes (snakes), Anguimorpha and Iguania. Toxicofera contains about 4,600 species, of extant Squamata. It encompasses all venomous reptile species, as well as numerous related non-venomous species. There is little morphological evidence to support this grouping; however, it has been recovered by all molecular analyses as of 2012.
Neognathae is an infraclass of birds, called neognaths, within the class Aves of the clade Archosauria. Neognathae includes the majority of living birds; the exceptions being the tinamous and the flightless ratites, which belong instead to the sister taxon Palaeognathae. There are nearly 10,000 living species of neognaths.
The tree of life or universal tree of life is a metaphor, conceptual model, and research tool used to explore the evolution of life and describe the relationships between organisms, both living and extinct, as described in a famous passage in Charles Darwin's On the Origin of Species (1859).
The affinities of all the beings of the same class have sometimes been represented by a great tree. I believe this simile largely speaks the truth.
Eusporangiate ferns are vascular spore plants, whose sporangia arise from several epidermal cells and not from a single cell as in leptosporangiate ferns. Typically these ferns have reduced root systems and sporangia that produce large amounts of spores.
Monotremes are mammals of the order Monotremata. They are the only known group of living mammals that lay eggs, rather than bearing live young. The extant monotreme species are the platypus and the four species of echidnas. Monotremes are typified by structural differences in their brains, jaws, digestive tract, reproductive tract, and other body parts, compared to the more common mammalian types. Although they are different from almost all mammals in that they lay eggs, like all mammals, the female monotremes nurse their young with milk.
Terrabacteria is a taxon containing approximately two-thirds of prokaryote species, including those in the gram positive phyla as well as the phyla "Cyanobacteria", Chloroflexota, and Deinococcota.
TimeTree is a free public database developed by S. Blair Hedges and Sudhir Kumar, now at Temple University, for presenting times of divergence in the tree of life. The basic concept has been to produce and present a community consensus of the timetree of life from published studies, and allow easy access to that information on the web or mobile device. The database permits searching for average node times between two species or higher taxa, viewing a timeline from the perspective of a taxon, which shows all divergences back to the origin of life, and building a timetree of a chosen taxon or user-submitted group of taxa. TimeTree has been used in public education to conceptualize the evolution of life, such as in high school settings. David Attenborough's Emmy Award-winning film and television program Rise of Animals used Hedges and Kumar's circular timetree of life, generated from the TimeTree database, as a framework for the production. The timetree was brought to life using animated computer-generated imagery in scenes every 10 minutes during the 2-hour movie. The original development of TimeTree, by Hedges and Kumar, dates to the late 1990s, with initial support from NASA Astrobiology Institute. Since then, it has been supported by additional grants from NASA, and by NSF and NIH. The current version (v5) was released in 2022 and contains data from 4,075 studies and 137,306 species.
Hydrobacteria is a taxon containing approximately one-third of prokaryote species, mostly gram-negative bacteria and their relatives. It was found to be the closest relative of an even larger group of Bacteria, Terrabacteria, which are mostly gram-positive bacteria. The name Hydrobacteria refers to the moist environment inferred for the common ancestor of those species. In contrast, species of Terrabacteria possess adaptations for life on land.
Triumph of the Vertebrates is a 2013 British documentary film by David Attenborough. It is about the evolution of vertebrates. The first part is From the Seas to the Skies, while the second is Dawn of the Mammals. The film uses a circular timetree of life generated by scientists S. Blair Hedges and Sudhir Kumar, from their TimeTree database, as a temporal framework for the production. The timetree was created using animated computer-generated imagery in scenes every 10 minutes during the 2-hour movie. The circular timetree was published by Hedges and Kumar in 2009 and Hedges was consulted during the production of the film.
A timetree is a phylogenetic tree scaled to time. It shows the evolutionary relationships of a group of organisms in a temporal framework.
The Amerophidia, also known as amerophidian snakes, are a superfamily of snakes that contains two families: Aniliidae and the boa-like Tropidophiidae.
Neoanguimorpha is a clade of anguimorphs comprising Monstersauria and Diploglossa. Morphological studies in the past had classified helodermatids with the varanoids in the clade Platynota, while the Chinese crocodile lizard was classified as a xenosaurid. However molecular work found no support in these groupings and instead has found the helodermatids more related to Diploglossa, while the Chinese crocodile lizard and varanoids to form the clade Paleoanguimorpha.
Emma Caroline Teeling is an Irish zoologist, geneticist and genomicist, who specialises in the phylogenetics and genomics of bats. Her work includes understanding of the bat genome and study of how insights from other mammals such as bats might contribute to better understanding and management of ageing and a number of conditions, including deafness and blindness, in humans. She is the co-founder of the Bat1K project to map the genomes of all species of bat. She is also concerned with understanding of the places of bats in the environment and how to conserve their ecosystem.
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