Tony De La Rosa, 72, a Tejano musician who helped bring conjunto music from the isolated ranchlands of the South Texas brush country to loud and lively urban dance halls throughout the Southwest, died June 2 during heart surgery at Christus Spohn Hospital-Memorial in Corpus Christi, Tex.

"There are three or four individuals who really define the conjunto sound, and Tony's one of them," said Pat Jasper of Austin, where she is a curator of the International Accordion Festival and one of the organizers of the Texas Music Hall of Fame. "In a sense, with his death, it's the end of an era. Valerio Longoria, Don Santiago Jimenez, Narciso Martinez and Tony De La Rosa are really the people who created the music. They're the founding figures."

Conjunto is the outgrowth of a musical menage a trois: Spanish and Mexican folk tunes and accordion-flavored music brought to Texas by 19th-century German immigrants and combined with Anglo American country music.

Mr. De La Rosa, who was known for his lively, improvisational accordion style and his popular dance pieces, took the music of the rural Mexican American working class -- the ranch hands and migrant farmworkers of the Texas-Mexico borderlands -- and, during the 1950s and 1960s, brought it into the modern era. He added drums and saxophones and electronically amplified the bass and the bajo sexto, a 12-string guitar. He also made radio appearances and recordings part of the conjunto movement.

"More than anyone else, he was responsible for launching the classic era of conjunto in the 1950s," said Manuel H. Pena, a professor of music history at California State University at Fresno and author of "The Texas-Mexican Conjunto: History of a Working-Class Music" (1985).

"El Conde (The Count)," as he was known during his glory days in the '50s and '60s, also was known as the father of a dance style associated with conjunto: El tacuachito, or "the little possum."

"The possum style itself was different from polka European-style, where the dancers mainly bounce up and down," Pena said. "El tacuachito is danced in a gliding style, like a possum ambling across a field. If you've ever seen a possum, you know that it never seems to be in a rush. It's slow, very cool, . . . which means that the music has to be slow. Instead of, say, 130 beats per minute, Tony would play it 110 beats a minute."

Antonio De La Rosa was born in Sarita, Tex., a tiny community near the famed King Ranch, where most of Sarita's residents worked. He was one of 12 children in a family of fieldworkers. At age 6, he learned to play the harmonica, and at 14 he bought an accordion, a simple model with one row of buttons he spotted in a Sears, Roebuck catalogue, which he paid for with money he had saved working as a shoeshine boy.

According to Linda Escobar, Mr. De La Rosa's goddaughter, shoeshine customers also were treated to an accordion serenade from the budding musician. Soon he was playing with country music groups -- until he heard the sounds of Martinez, a famed accordionist who is considered the father of conjunto music, and realized what he was born to play.

Mr. De La Rosa recorded his first pieces of music in 1949. They were the polkas "Sarita" and "Tres Rios" (Three Rivers), both named for Texas towns. By the late 1950s, he had recorded more than a dozen hits, including an old Mexican instrumental called "Atotonilco" (a town in Mexico) and "El Circo" ("The Circus"), a conjunto version of country musician Red Foley's "Alabama Jubilee." Both became classics. Other hits included "Los Frijoles Bailan" ("The Dancing Beans") and "La Periodista" ("The Journalist"). He named many of his pieces for towns or women.

In the 1990s, Mr. De La Rosa recorded two albums for Rounder Records -- "Asi Se Baila en Tejas" ("This Is the Way They Dance in Texas") and "Es Mi Derecho" ("It's My Right"). In 2001, he recorded his last album, "Mi Ultimo Beso" ("My Last Kiss").

"He had a very distinctive singing voice," recalled Juan Tejeda, leader of the San Antonio-based group Conjunto Aztlan and founder of the annual Tejano Music Festival. "It was slightly raspy, with distinctive inflections. It would almost break up on certain notes. The voice, plus his style of play on the accordion, with his runs, his riffs -- anyone who heard it knew it was Tony."

Tejeda recalled him as a humble man who remained true to his working-class roots. "He was all heart, puro corazon, a man who had a great love for the music and the people he played it for. He was a big man, but I've seen him on stage playing, singing, talking to the people who had come to hear him, and he would just start crying, it meant so much to him."

Mr. De La Rosa, a member of the Tejano Conjunto Hall of Fame, was awarded a National Heritage Fellowship in 1998 by the National Endowment for the Arts.

Survivors include his wife, Lucia De La Rosa; three sons; a daughter; two stepsons; three brothers; five sisters; nine grandchildren; and two great-grandchildren.