Santa Marta Formation - Flora and Fauna

Flora and Fauna

A wide variety of microorganisms inhabited the coastal waters at the time of the deposition of the Santa Marta Formation. Microfossils include ostracods and dinoflagellates.

Invertebrates were also common. Fossils of ammonites can be found in the formation, often embedded vertically in the bedding plane. Originally it was thought that dead ammonites could only be oriented this way in sediment if they were in shallow waters below a certain pressure, but there is evidence to support that due to specific conditions during burial, it was possible for these ammonites to be vertically oriented at greater depths. Ammonite genera present in the formation include Anagaudryceras, Anapachydiscus, Eupachydiscus, Gaudryceras, Maorites, Natalites, Parasolenoceras, Yezoites, and the heteromorph ammonites Ainoceras, Eubostrychoceras, Ryugasella and Baculites. Many bivalve fossils have been found such as Cucullaea, Panopea, Pinna, and Pterotrigonia. Polychaete annelid worms such as Rotularia and gastropods such as the cerithiid sea snail Cerithium have also been discovered in beds within the formation.

Numerous ichnofossils provide evidence of benthic activity, along with the bioturbated sediments previously mentioned. Vertical spreite trace fossils have been found as part of fodinichnia dominated ichnocoenosis and were assigned to ichnogenre such as Paradictyodora. Trackways thought to belong to decapods have also been found.

Fish were present, including one of the first frilled sharks, Chlamydoselachus thomsoni. Other marine vertebrates included the small mosasaur Taniwhasaurus antarcticus, previously known as Lakumasaurus antarcticus. The close relation of T. antarcticus to other species of Taniwhasaurus found in New Zealand and Patagonia provides evidence for a Gondwanan endemism.

Antarctopelta oliveroi, an ankylosaur, was discovered in 1986 on the northern part of James Ross Island about 2 kilometers south of Santa Marta Cove in beds that were part of the Santa Marta Formation. It was the first dinosaur found in Antarctica. It may be a possible nodosaur but there has been no formal phylogenic analysis to prove its relationship with other ankylosaurs. Although the formation is made up of only marine deposits, the bodies of these animals along with other debris may have frequently been washed out to sea to later sink to the bottom and be buried by sediment.

Leaves and fragments of plants are commonly found as fossils throughout the formation as well as large tree trunks in the lower members. This is evidence of the forested environment that covered Antarctica during the Late Cretaceous due to the overall warmer global temperature and milder climate. At that time the river delta had much vegetation, and was able to support large herbivores such as Antarctopelta.