Cerrejón Formation

Fossil Zingiberales have been uncovered from the Cerrejón Formation

The floral record of the Cerrejón Formation is well known, with many identifiable and well preserved plant microfossils having been found from the Cerrejón mine. The fossils are well preserved, and in some cases their cell structure is intact.[15] In comparison to modern Neotropical rainforests, the diversity of plants is quite low. This may be an indication of the early stage of Neotropical diversification, or a delayed recovery period following the Cretaceous–Paleogene extinction event.[2]

Many plants from the Cerrejón Formation belong to families that are still common today in modern Neotropical rainforests. There is a diverse variety of palms and legumes in the formation. In addition to palms and legumes, much of the biomass of the Paleocene forest consisted of laurales, malvales, menisperms, aroids, and zingiberaleans.[2] Studies of fossil plants from Cretaceous-age sites indicate that the floral composition below the Cretaceous–Paleogene boundary (K–T boundary) was very different from that of the Paleocene. Legumes are absent from Cretaceous strata, and likely appeared or diversified during the Paleocene.[15]

The presence of these types of flora in Paleocene strata shows that plants characteristic of modern Neotropical rainforests have existed for geologically long periods of time, being able to withstand climatic and geographic changes in South America. It has been suggested that today's Neotropical rainforests are the result of environmental changes brought about by Quaternary glacial cycles (i.e. the recent ice age). These cycles would have caused fluctuation in the diversity and extent of rainforests. If this was the case, the current diversity of the Amazon rainforest would be a recent speciation in a changing environment.[16] However, the floral record from the Cerrejón Formation shows that the current diversity of the Amazon Rainforest can be traced back into the early Cenozoic.[2]

Reconstruction of the giant Carbonemys cofrinii

Feeding damage from insects is evident on some of the plant macrofossils from the Cerrejón Formation. One survey of plant macrofossils showed that around half of the studied specimens had been attacked by herbivorous insects.[2] The insects that damaged the leaves were predominantly generalist feeders, unlike modern Neotropical insects that are mainly specialist herbivores. There is no evidence of the elevated insect-feeding diversity or host-specialized feeding associations that are seen in later Neotropical forests. The insect diversity in the Cerrejón Formation is low in comparison to the diversity of insects in Neotropical rainforests today, and it is likely that leaf damage was made by relatively few species.[2]

Remains of the giant boid Titanoboa cerrejonensis have been found from a gray claystone layer underlying Coal Seam 90 in the Cerrejón mine. Titanoboa is the largest known snake to have ever existed, reaching an estimated length of 12.8 metres (42 ft). Eunectes, the anaconda, is likely to be a close living analogue of Titanoboa.[9]

A dyrosaurid crocodylomorph called Cerrejonisuchus improcerus was described in 2010 from the Cerrejón Formation in the same layer as Titanoboa. It was a small dyrosaurid, and had the shortest snout length relative to its skull length of any dyrosaurid. Most dyrosaurids were marine, with long snouts adapted for catching fish. The short snout of Cerrejonisuchus is likely to have been an adaptation for a more generalized diet in a transitional aquatic environment.[17] It is possible that Cerrejonisuchus was a food source for Titanoboa, as the two inhabited the same riverine environment.[18] The anaconda has been documented consuming caimans, a feeding habit that is similar to the inferred habit of Titanoboa. A second dyrosaurid, Acherontisuchus, was named in 2011 from the formation. With a large body and long snout, it resembles most other dyrosaurids.[19] A third dyrosaurid, Anthracosuchus, was named in 2014. Unlike other dyrosaurids, it had blunt teeth and a short skull. Anthracosuchus likely had massive jaw muscles allowing it to feed on large turtles, a behavior which is corroborated by predation marks found at the site.[20]

• Hastings, Alexander K.; Jonathan I. Bloch, and Carlos A. Jaramillo. 2011. A new longirostrine Dyrosaurid (Crocodylomorpha, Mesoeucrocodylia) from the Paleocene of north-eastern Colombia: Biogeographocal and behavioural implications for New-World Dyrosayridae. Palaeontology 54. 1095–1116. Accessed 2017-06-14.
• Head, J.J.; J.I. Bloch; A.K. Hastings; J.R. Bourque; E.A. Cadena; F.A. Herrera; P.D. Polly, and C.A. Jaramillo. 2009. Giant boid snake from the paleocene neotropics reveals hotter past equatorial temperatures. Nature 457. 715–718. Accessed 2017-06-14.
• Ojeda Marulanda, Carolina, and Carlos Alberto Sánchez Quiñónez. 2013. Petrografía, petrología y análisis de procedencia de unidades paleógenas en las cuencas Cesar - Ranchería y Catatumbo. Boletín de Geología, Universidad Industrial de Santander 35. 67–80. Accessed 2017-06-14.
• Rodríguez, Gabriel, and Ana Cristina Londoño. 2002. Mapa geológico del Departamento de La Guajira - 1:250,000, 1–259. INGEOMINAS. Accessed 2017-08-08.
• Wing, Scott L.; Fabiany Herrera; Carlos A. Jaramillo; Carolina Gómez Navarro; Peter Wilf, and Conrad C. Labandeira. 2009. Late Paleocene fossils from the Cerrejón Formation, Columbia ((sic)), are the earliest record of Neotropical rainforest. Proceedings of the National Academy of Sciences 106. 18627–18632. Accessed 2017-06-14.