The processions are the high point of Brazil's five-day pre-Lent celebrations, and the riot of color and music that began late Sunday and continued nearly to dawn was to be repeated Monday night, with other extravagant displays of costumes and carnality.
A life-size elephant, and a jaguar, a parrot and butterflies all resized to giant proportions, as well as a King Kong gorilla, were among the fauna featured on the elaborate floats that filed through Sunday night, under intermittent rain.
The other wildlife to grab the attention of the 50,000-strong crowd were the many nearly-nude women dancers, all with supernaturally white smiles and bodies trained into sensual yet powerful curves, and all cellulite-free.
Modesty having no place in the parades, many of the women wore very little, mostly glittering g-strings and long feathers.
Others wore even less, including two in the opening entry by the Sao Clemente samba school. Its two carnival queens danced their way along the 700-meter (-yard) parade runway in nothing more than a bottle-top-sized piece of shiny stick-on foil in a strategic spot.
Tourists in the audience were awestruck by the lavish floats and lascivious models.
Locals, though, gave their heartiest applause to a runway cleaner who briefly got distracted by the samba and put on his own impromptu show, using his broom as a prop.
"Each carnival, the parades just get better and better," enthused Glaucia Medici, a 37-year-old Brazilian bank manager in the stands.
"At this time of year, all everyone wants to do is samba and have fun," she said.
The parades are in fact a competition between Rio de Janeiro's top 12 samba schools.
Each was being judged on criteria including the lyrics of their songs, the allegories represented by their floats -- and their ability to get their 5,000 members over the finish line in less than 80 minutes.
One costumed participant, who gave her name as Edna, said after completing the parade that she felt "overjoyed" and "emotional" at the experience under the arc lights and cameras.
This year, one of the groups, Unidos do Viradouro, caused a storm of controversy for a planned float that would have depicted Hitler dancing alongside skeletal Holocaust victims, as a sort of warning against such atrocities being repeated.
A Jewish group successfully sued to have the display banned. But that triggered a debate in the media over censorship and bad taste in the parades, which have a social-political component.
The school changed the float to represent an ironic tribute to "freedom of expression." It was due to be unveiled for the first time early Monday.
Rain came and went for much of the first night of parades, but crowds did not shrink, and dancers said the showers were merely "refreshing".
Just 80 kilometers (50 miles) from Rio, though, the precipitation caused mudslides that hit houses in Itaipava, an inland town used by many Rio residents escaping the carnival madness, killing nine people.
Carnival tragedy also struck the neighboring state of Minas Gerais, when a carnival truck in the town of Sabara ran into 14 people dancing next to it, killing a six-year-old girl and her teenage cousin, police said.