Pyramid of the Lost World was an solar viewing platform for equinox and solstices
The Lost World Pyramid began as a small astronomical viewing platform which faced three structures to its east which marked, in turn, the position of the rising sun at the spring solstice (north building), the equinox (center building), and the winter solstice (south building).
"The location of the Lost World Pyramid was first occupied in the earliest times of Tikal's settlement. A pyramid with four stairs, one to each side, is called a radial pyramid, and the first version was built by 500 BC.
The astronomical concept was formalized with new constructions between 500 and 250 BC in the Late Preclassic including a new radial platform and a new eastern platform, both much larger than the prototype from the Middle Preclassic.
The importance of the east-west axis was established at this time by the placing of burials and caches along it. There is a contrast between this formal and ritual complex with that of the other major contemporary complex, the North Acropolis in which the ritual axis of importance to burials was north-south."
Peter Harrison, The Lords of Tikal, p. 56
This is a portion of a model of Tikal which stands at the entrance to the site
This model shows the Pyramid of the Lost World in relation to the three small sighting temples to the east used to view the rising sun at the spring solstice (north building), the equinox (center building), and the winter solstice (south building). This configuration is called an E-Group, and was first identified and named after such a structure at the neighboring site of Uaxactun.
From this model, it is possible to see all the platforms and stages available for elaborate performances celebrating the yearly progression of the sun at this latitude. These rituals presumably took place at dawn, marking the first rising of the sun.
"This configuration grew in size over the years, with the small western platform finally becoming the Lost World Pyramid itself, a giant pyramid some 32 m high, square in plan with stairways on the four sides.
Part way up the stairs are giant stone and sculptured stucco masks, now in a state of severe disintegration.
Enough detail remained in one or two cases to indicate that these were jaguar masks not unlike those on E-7-Sub, the central structure at Uaxactun that gave its name to this architectural configuration.
At Uaxactun the masks were paired vertically, with the one below displaying Night Jaguar and the one above displaying Day Jaguar, the two manifestations of the sun god Kinich Ahau in his night and day appearances."
Peter Harrison, The Lords of Tikal, p. 56
"The line between these paired masks was a platform marking the horizon to the east, the point at which an observer needed to stand to view the solar phenomena as they related to the eastern structure.
Peter Harrison, The Lords of Tikal, p. 56
Commemorating and ritualizing solar or planetary cycles in architecture was a common practice among the ancient Maya, and the sun god, Kinich Ahau, was prominent everywhere. We can only imagine the pagents and dance rituals that were staged upon this platform to celebrate the yearly cycles of Kinich Ahau, the sun-faced one.
Rising over a main viewing platform, this jaguar probably represented Night Jaguar, the "Sun at Night". I can almost imagine that a snout and perhaps a fang are still visible...
The Lost World Pyramid was constructed as a solar observatory in relation to these three small sighting temples to the east.
The Lost World group gets its name from Sir Author Conan Doyle's classic 1912 novel, "The Lost World", about a fictional scientific expedition into the Amazon jungles.
Early explorers & mappers of this area felt it evoked the atmosphere of that novel.
E–Complexes like the Pyramid of the Lost World had quite different functions from the Twin Pyramid Complexes at Tikal, even though they both involved what has been called Radial Pyramids, or pyramids without a temple at the top and with stairways facing all four directions.
The Pyramid of the Lost World celebrated the yearly agricultural cycle of the sun, while Twin Pyramid Complexes were built to celebrate k'atun–ending dates, which in the Maya Long Count calendar represented ritually significant twenty–year time period endings.
Nonetheless, the square form of these structures, with each side facing a cardinal direction and a bare platform at the top, all represented aspects of time: the daily east to west movement of the sun as well as the sideways progression of sunrises during the equinox and the solstices.