# Cal Orck'o

19°00′18″S 65°14′08″W﻿ / ﻿19.004884781743645°S 65.23566559723122°W﻿ / -19.004884781743645; -65.23566559723122
Cal Orck’o is a fossil bed in Bolivia. It is located in a quarry approximately 4.4 km northwest of Sucre (Chuquisaca Department, Bolivia) in the Altiplano/Cordillera Oriental, within the El Molino Formation (Middle Maastrichtian).
The bed is composed of oolitic fossiliferous limestone, associated with large, freshwater stromatolites. It documents an open lacustrine environment and contains nine levels of dinosaur tracks (trace fossils).
The main track-bearing level is almost vertical with a surface area of approximately 65,000 m$^2$. High-resolution mapping of the site from 1998 to 2015 revealed a total of 12,092 individual dinosaur tracks in 465 trackways. Nine different morphotypes of dinosaur tracks have been documented, including several trackways of theropods, ornithopods, ankylosaurs, and sauropods, with the latter group accounting for 26% of the trackways.

## Etymology

The name "Cal Orck'o" derives from the Quechua words q'al meaning "lime" and urqu meaning "hill," referring to the limestone composition of the hill where the tracks are found.

## Geological Formation and Environmental Context

Cal Orck’o is situated within the El Molino Formation, dating to the Middle Maastrichtian stage of the Late Cretaceous period, approximately 68 million years ago. The formation consists of oolitic fossiliferous limestone, indicative of a lake environment with periods of subaerial exposure. The presence of freshwater stromatolites suggests that the area was once a shallow lake with abundant microbial activity.

## Discovery and Mapping

The Cal Orck’o tracks were discovered in 1994 during limestone quarrying by FANCESA (Fábrica Nacional de Cemento S.A.). Detailed mapping from 1998 to 2015 documented over 12,000 individual tracks across 465 trackways, confirming its status as the world’s largest dinosaur tracksite. Tectonic activity over millions of years has since tilted the lakebed to nearly vertical, now visible on a 300-foot-high limestone wall.

## Paleontological Significance

Cal Orck'o hosts a diverse array of dinosaur tracks, representing at least nine distinct morphotypes:
* Theropods: These tridactyl footprints belong to bipedal carnivorous dinosaurs.
* Ornithopods: Herbivorous dinosaurs, indicated by blunt-toed footprints.
* Sauropods: Tracks show large oval pes (foot) and smaller manus (hand) impressions. Two morphotypes, E and F, are documented: Morphotype E is linked to narrow-gauge trackways attributed to titanosaurids, while Morphotype F, named Calorckosauripus lazari, likely belonged to a basal titanosaur.
* Ankylosaurs: Some trackways feature the distinctive tetradactyl pattern associated with armored dinosaurs.

## Unique Features and Social Behavior

Notably, the presence of parallel trackways of juvenile ankylosaurs offers evidence of possible social behavior, indicating that some species may have moved in groups.

## Formation of the Track Wall

Originally, the area was a flat shoreline of a lake that attracted both herbivorous and carnivorous dinosaurs. The soft, humid ground caused their feet to sink, leaving deep impressions. Alternating wet and dry weather patterns preserved these footprints by creating sediment layers. Tectonic movements eventually tilted the flat ground, creating the nearly vertical 300-foot-high limestone wall observed today.

## Conservation Efforts and Visitor Information

Declared a National Monument in 1998, Cal Orck’o is part of the protected FANCESA Paleontological Reserve. Conservation efforts include limited public access via Parque Cretácico, a dedicated museum offering guided tours, educational exhibits, and close-up views of track segments. While a large section of the wall collapsed in 2010, extensive photographic documentation allows continued study and preservation.