| Urumaco Formation | |
|---|---|
| Stratigraphic range:Late Miocene | |
| Type | Geological formation |
| Location | |
| Country | Venezuela |
TheUrumaco Formation is aformation inVenezuela that includes deposits from theLate Miocene. It is the site of several "giant forms": theturtles,crocodiles,sloths androdents of Urumaco are among the largest of their groups.
The Urumaco formation is located in theUrumaco region in theCaribbean coastalFalcón state. The deposits date from 10 to 5.3 million years ago and the Urumaco formation was deposited in an area with largerivers,swamps,estuaries,lagoons and shallow coastalseas. These conditions in the Late Miocene contrast strongly with the current dry environment in the area today.
There are 21 known species ofcartilaginous fishes from the Urumaco Formation, belonging to the ordersLamniformes,Carcharhiniformes,Myliobatiformes andRajiformes.[1]Carcharhinus caquetius is anendemic species ofpredator shark from Urumaco. A large number of well-preservedfossils of thesawfishPristis rostra have been found in the deposits. Themegalodon is also known from the Urumaco Formation. The coastal seas of Urumaco were further inhabited by species that still live in theCaribbean Sea today, such as thespotted eagle ray,smooth hammerhead shark,tiger shark andbull shark.
Thebony fishes from the Urumaco Formation includegroupers,piranha-like fish such aspacas,cuttlefish,thorny catfish andred-tailed catfish.[2]
The Urumaco Formation has a great diversity of crocodilians with twelve known species.[3] Seven species ofcaimans have been described:Caiman brevirostris,C. latirostris,Globidentosuchus brachyrostris,Melanosuchus fisheri,Mourasuchus arendsi,M. nativus andPurussaurus mirandai,Gryposuchus croizati,G. jessei,Hesperogavialis cruxenti andIkanogavialis gameroi are thegavials of Urumaco, a group that is no longer found inSouth America today. The kinship ofCharactosuchus mendesi with the other crocodilians is considered unclear. Multiple species of crocodilians were able to live together because they focused on specificniches, limiting infraspecific competition. For example, the 4.3–5.5 metres (14–18 ft)Mourasuchus arendsi[4] had aduck-like beak with which it caughtcrustaceans, the fish-eatingGryposuchus croizati, 10 metres (33 ft) in length,[5] lived particularly in estuaries, andPurussaurus mirandai, 10 metres (33 ft) in length,[6] hunted a wide range of prey animals.
Stupendemys geographicus is the best-known turtle species from the Urumaco formation. This animal from theAmerican necked turtles family was one of the largest turtles ever with a shell 2.4–3 metres (7.9–9.8 ft) long.[7] Other turtles from Urumaco include several species ofBairdemys,[8]themata mata Chelus lewisi andsoftshell turtles.
In addition to the multiple crocodilians and turtles, vertebra of aboa have also been found in the Urumaco Formation.[9]
Phoberomys pattersoni is one of the largest known rodents ever.[10] This three-meter-long relative of today'spacarana had a lifestyle similar to that of thecapybara. Several species ofxenarthrans are known from the Urumaco Formation.Urumaquia robusta was aground sloth from theMegatheriidae weighing four tons. Others ground sloths from Urumaco areBolivartherium urumaquensis,Urumacotherium garciai,Eionaletherium tanycnemius, andPseudoprepotherium venezuelanum belonging to theMylodontidae.[11]Urumacocnus urbani andPattersonocnus diazgameroi are ground sloths from theMegalonychidae.[12]Boreostemma pliocena is aglyptodont.Bounodus enigmaticus (Proterotheriidae,Litopterna) andGyrinodon (Toxodontidae,Notoungulata) are the South American ungulates of the Urumaco formation.[13] In the waters of Urumaco lived thefreshwater dolphinsIschyrorhynchus vanbenedeni andSaurodelphis and thedugongsNanosiren sanchezi and possiblyMetaxytherium.[14][15]