Osborne, Mary Pope

Dinosaurs before dark by Mary Pope Osborne ( Book )
67 editions published between 1992 and 2012 in 12 languages and held by 3,207 libraries worldwide
Eight-year-old Jack and his younger sister Annie find a magic treehouse, which whisks them back to an ancient time zone where they see live dinosaurs.

The knight at dawn by Mary Pope Osborne ( Book )
59 editions published between 1992 and 2010 in 9 languages and held by 3,006 libraries worldwide
Eight-year-old Jack and his younger sister Annie use the magic treehouse to travel back to the Middle Ages, where they explore a castle and are helped by a mysterious knight.

Mummies in the morning by Mary Pope Osborne ( Book )
41 editions published between 1983 and 2009 in 10 languages and held by 2,979 libraries worldwide
Jack and his younger sister take a trip in their tree house back to ancient Egypt, where they help a queen's mummy continue her voyage to the Next Life.

Dolphins at daybreak by Mary Pope Osborne ( Book )
53 editions published between 1997 and 2010 in 12 languages and held by 2,935 libraries worldwide
Their magic tree house takes Jack and Annie deep into the sea, where they meet up with dolphins, sharks, and octopi as they search for the answer to an ancient riddle. Morgan le Fay will make Jack and Annie masters of the tree house if only they can solve four riddles -- which will take four books, of course! Dolphins at Daybreak begins the third set of four books in this magical (and increasingly popular) series! Jack and Annie are off in the Magic Tree House again, this time to a whole new world under the ocean. Complete with a giant octopus, a hungry shark, and dolphins to the rescue, this Magic Tree House book delivers an underwater adventure kids can dream about.

Sunset of the sabertooth by Mary Pope Osborne ( Book )
49 editions published between 1996 and 2010 in 11 languages and held by 2,905 libraries worldwide
The magic tree house transports Jack and Annie on a mission to the Ice Age where they encounter Cro-Magnons, cave bears, sabertooth tigers, and woolly mammoths.

Afternoon on the Amazon by Mary Pope Osborne ( Book )
35 editions published between 1995 and 2009 in 8 languages and held by 2,848 libraries worldwide
Eight-year-old Jack, his seven-year-old sister, Annie, and Peanut the mouse ride in a tree house to the Amazon rain forests, where they encounter giant ants, flesh-eating piranhas, hungry crocodiles, and wild jaguars.

Polar bears past bedtime by Mary Pope Osborne ( Book )
35 editions published between 1997 and 2009 in 8 languages and held by 2,822 libraries worldwide
Their magic tree house takes Jack and Annie to the Arctic, where a polar bear leads them onto very thin ice.

Pirates past noon by Mary Pope Osborne ( Book )
36 editions published between 1994 and 2008 in 9 languages and held by 2,815 libraries worldwide
The magic treehouse whisks Jack and Annie back to the days of deserted islands, secret maps, hidden gold, and nasty pirates.

Night of the Ninjas by Mary Pope Osborne ( Book )
47 editions published between 1994 and 2009 in 9 languages and held by 2,787 libraries worldwide
The magic tree house takes Jack and Annie back in time to feudal Japan where the siblings learn about the ways of the Ninja.

Vacation under the volcano by Mary Pope Osborne ( Book )
34 editions published between 1998 and 2008 in 10 languages and held by 2,783 libraries worldwide
Their magic tree house takes Annie and Jack to Pompeii just as Vesuvius is about to erupt, and they must find a Roman scroll before everything is covered with burning ash.