Yecua Formation

The Yecua Formation is a geological Formation in what is now Bolivia. Studies suggest that the Yecua Formation preserves a coastal setting with humid to semiarid floodplains, shorelines and tidal as well as shallow marine environments including marshes, streams, lakes and brackish bodies of water. There may have been a connection to the Amazon Basin or the Paranaense Sea.^[2]

Yecua Formation
Stratigraphic range: Late Langhian-Early Messinian (Colloncuran-Huayquerian) ~14–7 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Underlies	Tariquia Formation
Overlies	Petaca Formation
Thickness	~50–300 m (160–980 ft)
Lithology
Primary	Mudstone, Sandstone[1]
Other	Gypsum
Location
Region	Chaco Basin
Country	Bolivia

Bivalves

Name	Species	Member	Material	Notes
Tellina[1]	T. sp
cf. Cyrena[1]	cf. C. sp
cf. Astarte[1]	cf. A. sp
cf. Lucina[1]	cf. L. sp
Senis[1]	S. cf. elongatus
cf. Corbula or Cymbophora sp.[1]	cf. C. sp
cf. Nucula[1]	cf. N. sp

Gastropods

Name	Species	Member	Material	Notes
cf. Gyrodes or Natica sp.[1]
cf. Turritella[1]	cf. T. sp

Crustaceans

Name	Species	Member	Material	Notes
Bythocypris[1]	B. sp
Cyprideis[1]	C. sp
cf. Balanus[1]	cf. B. sp
indetermined crabs [1]

Vertebrates

Name	Species	Member	Material	Notes	Image
cf. Theosodon[1]	cf. T. sp		distal limb bone	a litoptern
Rodentia indet.[1]			tooth
Mourasuchus[3]	M. sp.		skull fragments, partial vertebrae & ribs
Pleurodira[3]			shell elements
Humboldtichthys[4]	Humboldtichthys kirschbaumi		incompletely preserved anterior portion of the body and posterior head	a Glass Knifefish
Siluriformes indet.[1]				possibly Ariidae
Characiformes or Clupeiformes[1]			a scale