Erick Morales

First evidence of Ecuadorian mosasaur (marine reptile) fossils

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First record of a mosasaurid (Squamata: Mosasauridae) from the Upper Cretaceous of Ecuador

By: D. N. Garzon, Paul Arellano, Jorge Toro-Álava, José Luis Román Carrión, Julián Escobar Ordoñez, Pamela Andrade, Carlos Mendoza-Ochoa, Paula Ayala, Mateo Oleas, Anthony Vizcaino, Nelson Mesías Jiménez-Orellana

Summarized by: Erick Morales, who lives in Bedford Hills, NY, and is a senior at Binghamton University studying biology on the pre-physical therapy track. He also plays for the Binghamton University Symphony Orchestra as a violist. In his spare time, Erick loves to spend time with his family and friends and go to the gym. 

What data were used? This whole study is based on one fossil, which is an incomplete upper right jawbone, called the maxilla bone. Scientists identified it as a mosasaurid jaw based on the shape of the maxilla and the seven preserved teeth (Fig. 1). Mosasaurs were large marine reptiles that lived during the Late Cretaceous. This maxilla contains seven preserved teeth that are conical, smooth, and robust, which are key features that help determine it belongs to a mosasaurid. These teeth provided important anatomical evidence, despite the fossil being a fragment. The fossil was discovered in a limestone cave by members of the Rikuna research expedition together with Carlos Cerda, an Indigenous leader from the Tamia Yura community. Scientists also examined the surrounding limestone, marine sediments, and small fossils within the cave’s stratigraphic layers. 

What is the point of this paper since there is no hypothesis? The point of this paper was to document the first ever known mosasaurid fossil in Ecuador and provide geological and evolutionary context to it.

Methods: After the fossil was first recovered, researchers used preparation techniques such as careful acid cleaning to remove the surrounding rock without damaging the specimen. Once the fossil was exposed, they used computed tomography (CT) scanning to create a high-resolution 3D digital model of the jaw. The CT scans allowed the scientists to examine internal structures, such as the tooth roots and ridges , and to confirm the fossil’s identity without physically altering it. To determine the age, the researchers analyzed the stratigraphic layer in which it was found. They used biostratigraphy (i.e. they used fossils with a known geologic time span)  to identify the surrounding limestone and sediments as part of the Middle Napo Formation in the Cretaceous.

Results: From what was gathered, the fossil found consists of an incomplete right maxilla of about 30 centimeters in length, which holds seven teeth. These teeth are conical, smooth, and robust, which are characteristics of teeth that match a mosasaurid. Although the fossil is incomplete, comparisons with a similar species found in Colombia allowed scientists to approximate the length of the skull at about 30 centimeters and the full skeleton at likely 608.7 centimeters (about 6 meters). The fossil was preserved in rocks formed in shallow marine waters, indicating that the region where the Amazon rainforest is today was once covered by warm and coastal waters.

A- Line drawing of a mosasaur skull in side view, showing the jaws and teeth. A shaded section near the middle of the upper jaw highlights the area represented by the fossil described in the study. B- Photograph of the incomplete right maxilla preserved in brown limestone. The fragment is about 30 centimeters long and shows smooth bone surfaces with several teeth. A white scale bar in the lower right corner represents 5 millimeters for size reference.
Figure 1: A. Line drawing of the found mosasaur skull in side view showing the position of the maxilla, with the shaded region indicating the portion preserved in the fossil; the unshaded region is the likely shape of the fossil based on other mosasaurid fossils. B. Photograph of the incomplete maxilla preserved in brown limestone inside the Uctu lji Changa cave in Ecuador. A white 5 mm scale bar is shown for reference. The size and tooth structure indicate it belonged to an average-sized mosasaurid that lived in shallow marine waters during the Late Cretaceous 

Why is this study important? This fossil is the first evidence of a mosasaur in Ecuador, which fills a major gap in South America’s fossil record. Many mosasaurid fossils were found in other parts of South America, but not Ecuador. Its discovery shows that these ancient marine reptiles ranged throughout much of the Cretaceous seas in South America. 

Broader implications beyond this study: Because the fossil was preserved in shallow-marine rocks, it provides direct evidence that the area now occupied by the Amazon rainforest was once part of a warm coastal seaway during the Late Cretaceous. By showing that mosasaurs lived in what is now inland Ecuador, the fossil expands the known range of Cretaceous marine environments in South America. This data helps paleontologists map where ancient coastlines and seaways once existed. Furthermore, it’s possible that the cave system containing the fossil still harbors other fossils, implying that this discovery is just the start.

Citation: Garzón, D. N., Arellano, P., Toro-Álava, J., Román-Carrión, J. L., Ordoñez, J. E., Andrade, P., Mendoza-Ochoa, C., Ayala, P., Oleas, M., Vizcaino, A., & Jiménez-Orellana, N. M. (2024). First record of a mosasaurid (Squamata: Mosasauridae) from the Upper Cretaceous of Ecuador. Spanish Journal of Palaeontology, 39, 1–12. https://doi.org/10.7203/sjp.29179