Stunning Strata

Stunning Strata #1 Candeleros Formation

Time for a new series! Let’s get started!! In this series, I will talk about various formations, continents, and geological structures and the prehistoric ecosystems they help us to reconstruct. I hope you enjoy!

Hello everyone, welcome to Stunning Strata #1. This time around we have the Candeleros Formation, a formation I have actually been studying as a pet project for a while now:

The Candeleros Formation is part of the Neuquen group and outcrops in the Rio Negro, Mendoza, and Neuquen provinces of Argentina. It dates to around 99-92 million years ago. This formation was made famous among the paleontological community, at least, by the discovery of Giganotosaurus carolinni. 

The Candeleros Formation dates to the Cenomanian stage of the Cretaceous, a time when the carcharodontosauroids were the top predators on land and titanosaurs were the most diverse sauropod group. The Candeleros Formation played host to many of these animals. From the formation we have the sauropod Andesaurus, a medium sized basal titanosaur.  Predatory dinosaurs found in the Candeleros Formation include the giganotosaurine carcharodontosaurid Giganotosaurus carolinni, the medium-sized abelisaurid Ekrixinatosaurus novasi, the small unenlagiine Buitreraptor gonzalezorum, and the large basal coelurosaurian (and possible tyrannosauroid) Bicentenaria argentina. The alvarezsaurid theropod Alnashetri cerropoliciensis is also known from the Candeleros.

Buitreraptor gonzalezorum by the author.  Pencils on paper, 2015.

Buitreraptor gonzalezorum by the author. Pencils on paper, 2015.

Based on the remains of theropod lineages found in other areas of South America (i.e. Oxalaia quiliombensis from the Cenomanian of Brazil) and by comparing the Candeleros Formation to other formations of the same time period which contain similar floras and faunas, we can infer that taxa representing theropod lineages like the spinosaurids co-existed with the animals found in the Candeleros Formation. Therefore, the Candeleros Formation represents an ecosystem with fauna similar to the Bahariya Formation of Egypt and the Kem Kem beds of Morocco. This hypothesis is also supported by the fact that the environment represented by the Candeleros Formation was similar to that of the Bahariya Formation and the Kem Kem Beds. The habitat which the Candeleros Formation represents was a braided river system which a menagerie of fish, turtle, amphibian, mammal, arthropod, and dinosaur species called home. Buitreraptor may have even had adaptations specially suited for exploiting the bountiful fish of these ancient streams.

The primitive snake Najash rionegrina may also have been a predator of the wetlands, slithering through the water as it searched for prey. I should also note that there is ample evidence that suggests N. rionegrina assumed a subterranean lifestyle. Other animals, it seems, were more at home surviving off the land then off the wetlands…

Piney Lake in Vail, Colorado. The Candeleros Ecosystem was probably similar to that of Piney Lake's.  Photo by the author, 2014.

Piney Lake in Vail, Colorado. The Candeleros Ecosystem was probably similar to that of Piney Lake’s.
Photo by the author, 2014.

The Candeleros Formation played host to a number of terrestrial animals, namely dinosaurs. The first I want to mention is Bicentenaria argentina, a possible basal tyrannosauroid. I hypothesize this animal was a predator of small game, taking up a niche which would allow little if any competition with the megapredators of the area. B. argentina was probably the leopard to G. carolinni’s African lion. Giganotosaurus itself is a pretty interesting animal. This highly derived carcharodontosaurid was the largest predatory animal found in the Candeleros ecosystem. Well for right now, anyway. It is proposed that large carcharodontosauroid theropods were specialist hunters of sauropods. If so, G. carolinni lived in the carcharodontosaur version of paradise. So far, three medium-sized sauropods have been formally described from the Candeleros Formation. These are the basal titanosaurid Andesaurus delgadoi and the rebbechisaurids Limaysaurus tessonei and Nopcsaspondylus alarconensis. The rebbechisaurids are famous for their rake-like jaws, which may have been adaptations for a grazing lifestyle. Titanosaurs had needle-like teeth, which were probably used to rip leaves off trees. Indeterminate iguanodont tracks have also been found from the formation. I’ve heard of partial, undescribed iguanodont skeletons from the Candeleros gaining dust in collections, but I haven’t been able to find anything in the literature on the subject. Nevertheless, the track makers may have also constituted a food source for the massive carcharodontosaurids present in their ecosystem.

G. carolinni wasn’t always killing. It must have co-existed peacefully with sauropods at times, just like lion prides and zebra herds do in the modern African Savannah.

Giganotosaurus (foreground) rests in the antediluvian plains of the Candeleros Formation while Andesaurus browses in the background.  Illustration by the author.  Colored pencils on paper, 2015.

Giganotosaurus (foreground) rests in the plains of the Candeleros Formation while Andesaurus browses in the background.
Illustration by the author.
Colored pencils on paper, 2015.

The abelisaurid Ekrixinatosaurus novasi was also a resident of the Candeleros Formation ecosystem. E. novasi may have competed with Giganotosaurus for prey, but was way smaller compared to its giant carcharodontosaurid contemporary.  At an estimated 26 feet long, a fully-grown Ekrixinatosaurus would have been easily overpowered by an adult 42 foot long, 8 ton G. carolinni. 

We should also look at the smaller animals which make up the prehistoric fauna of the Candeleros Formation. These include reptiles, turtles, fish, and amphibians (specifically frogs). Two species of the turtle Prochelidella have been collected from Candeleros Formation sites. The running crocodylomorph Araripesuchus patagonicus is known from the Candeleros as well. Araripesuchus was a small predator, preying on the various animals which called the Candeleros wetlands home. Alnashetri was a small alvarezsaurid that most likely led an omnivorous lifestyle. Unfortunately, this dinosaur is only known from hindlimb material.

References

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2. Baez, Ana M. , Muzzopappa, Paula, and Nicoli, Laura. 2007. “Anurans from the Candeleros Formation (?Cenomanian-Turonian) of west-central Argentina: new evidence for pipoid evolution.” Cretaceous Research 28 (2007): 1005-1016.

3. Sánchez, Maria Lidia; Heredia, Susana & Calvo, Jorge O. 2006. “Paleoambientes sedimentarios del Cretácico Superior de la Formación Plottier (Grupo Neuquén), Departamento Confluencia, Neuquén.” Revista de la Asociación Geológica Argentina 61(1): 3-18.

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