question: Are The Gaslight Anthem and Dinosaur Jr. both bands formed in the 20th century?
answer: no
context: Title: National anthem of Norway
  Passage: Norway does not have an official national anthem, but over the last 200 years, a number of anthems have been commonly regarded as "de facto" national anthems.  At times, multiple anthems have enjoyed this status simultaneously.  Today, the anthem "Ja, vi elsker dette landet" is the most recognised national anthem, but until the early 20th century, "Sønner av Norge" occupied this position.
  Title: Palaeoscincus
  Passage: Palaeoscincus (meaning "ancient skink" from the Greek παλαιός and σκίγγος) is a dubious genus of ankylosaurian dinosaur based on teeth from the mid-late Campanian-age Upper Cretaceous Judith River Formation of Montana.  Like several other dinosaur genera named by Joseph Leidy ("Deinodon", "Thespesius", and "Trachodon"), it is an historically important genus with a convoluted taxonomy that has been all but abandoned by modern dinosaur paleontologists. Because of its wide use in the early 20th century, it was somewhat well-known to the general public, often through illustrations of an animal with the armor of "Edmontonia" and the tail club of an ankylosaurid.
  Title: Bulgarian Legion
  Passage: The Bulgarian Legion (Bulgarian: Българска легия , "Balgarska legiya") was the name of two military bands formed by Bulgarian volunteers in the Serbian capital of Belgrade in the second part of the 19th century.  Their ultimate goal was the liberation of the Bulgarian people from Ottoman rule through coordinated actions with the neighbouring Balkan countries.
  Title: Himno de Yucatán
  Passage: The Anthem of Yucatán (Spanish: "Himno de Yucatán" ) was officially adopted on September 15, 1867.  The lyrics of the state anthem were composed by Manuel Palomeque and the music composed by Jacinto Cuevas.  The Anthem of Yucatán was the first state anthem in Mexico (the second was the state of Veracruz).  During almost all the 20th century, the anthem was sung in schools.
  Title: Sønner av Norge
  Passage: Sønner av Norge (originally "Sønner af Norge", literally "Sons of Norway") is the common title of the anthem Norsk Nationalsang (literally, "Norwegian National Anthem"), which was the "de facto" national anthem of Norway from 1820 until the early 20th century.  From the mid-1860s, "Ja, vi elsker dette landet" gradually came to occupy the unofficial position as national anthem, but was used alongside "Sønner af Norge" until the early 20th century, with "Sønner af Norge" being preferred in official situations.
  Title: Alexandre LeRoi
  Passage: Alexandre LeRoi appears as the main villain of the DC graphic novel "Batman: Master of the Future", the sequel to "Gotham by Gaslight", as an air pirate who intends to stop Gotham City's 20th Century celebrations, and to keep the looming century's polluting technology from becoming a reality.  He keeps a mobile base in a zeppelin-esque airship powered by gas, and controlled by a robot LeRoi calls Antonio.
  Title: Cultural impact of the Beach Boys
  Passage: The Beach Boys are an American rock band, formed in Hawthorne, California in 1961.  The group is considered to be one of the most critically acclaimed, commercially successful, and widely influential bands of all time.  Their co-founder and principal composer, Brian Wilson, is widely considered one of the most innovative and significant songwriters of the late 20th century.  With record sales estimated at over 100 million, they were one of the few American bands formed prior to the 1964 British Invasion to continue their success, and among artists of the 1960s, they are one of few central figures in the histories of rock.
  Title: Dinosaur Jr.
  Passage: Dinosaur Jr. is an American rock band formed in Amherst, Massachusetts, in 1984, originally simply called Dinosaur until legal issues forced a change in name.
  Title: Onamo, 'namo!
  Passage: "Onamo, 'namo!"  (Serbian Cyrillic: Онамо, 'намо! ; English: There, over there! )  also known as the Serbian Marseillaise (Српска марсељеза) was a popular anthem in Montenegro in the late 19th to early 20th century.  The royal state anthem of Montenegro at the time was To Our Beautiful Montenegro, while the education anthem was the Hymn to Saint Sava.
  Title: The Gaslight Anthem
  Passage: The Gaslight Anthem is an American rock band from New Brunswick, New Jersey, formed in 2006.  The band consists of Brian Fallon (lead vocals, rhythm guitar), Alex Rosamilia (lead guitar, backing vocals), Alex Levine (bass guitar, backing vocals), and Benny Horowitz (drums, percussion, backing vocals).
citations: The Gaslight Anthem Dinosaur Jr.