18 Fossil News – Summer 2017

he best-known Cuban fossils (Oxfordian ammo-nites and giant marine reptiles) come from a place

180 kilometers to the west of the city of Havana, in theViñales Valley, the most famous karstic valley in Cubaand one of the most beautiful landscapes in the world.In the eastern portion of Mayabeque Province, onCuba’s northwest coast, however, very interesting fos-sils have also been found near the town of Madruga.Although the Madruga area yields fossils preserved inLate Cretaceous, Paleocene, Miocene, and Pleistocenerocks, only a few papers have been dedicated to theirstudy and investigation over the last few decades.

How Old Are Madruga Formation Fossils?According to Manuel Iturralde-Vinent, past presidentof the Cuban Geological Society:

The oldest rocks known in Madruga are theserpentinites, greenish-blue rocks that commonlyform small hills and which originated more than100 kilometers deep in the upper mantle of theEarth. Rocks of the Cretaceous Period are also ex-posed around Madruga, formed when reptiles, es-pecially the dinosaurs, dominated our planet. Theseancient rocks constitute the remains of volcanic is-lands that existed more than seventy million years

Cuba’s Madruga FormationMogotes and Cenozoic Secrets

T ago in the Pacific Ocean. Continental drift broughtthem here, to what is now Cuba.

The fossils from the Late Cretaceous that have beenfound in Madruga are rudists (Durania, Biradiolites,and Praebarretia), a strange group of extinct mollusksthat attached their shells to the ocean floor;spatangoid echinoids (Cardiaster palmeri, Hemiastermadrugaensis, and Hemiaster siboneyensis);scaphopods (Hamulus); brachiopods (Orthothyris ra-diata, Terebratulina spp., Cruralina cubensis, andDyscritothyris cubensis); and fairly common foramin-ifera (Bulimina madrugaensis, Operculina bermudezi,and Vaughanina cubensis).

The rocks on which most of the town of Madrugaitself was founded are classified by geologists as be-longing to the Madruga Formation. They represent apiece of Tertiary (Paleocene) history. Iturralde-Vinent,who directed the geological investigation of the areaat the end of the 1970s, explains:

The type locality of the Madruga Formation waslocated in a roadcut on both sides of the centralhighway under the railroad bridge of the cen-tral Boris Luis Santa Coloma at the entrance ofthe town of Madruga. Studies indicate that

19Fossil News – Summer 2017

those rocks have about sixtyto sixty-four million years oldand were formed at the bot-tom of the primitive Carib-bean Sea, when Cuba did notyet exist, at a depth of than300 meters.

The Madruga Formation is a se-quence of shales, sandy shales, andfine radiolarian sandstones that ir-regularly conserve calcareous ce-ment. The formation is difficult toobserve in places today because theoriginal roadcut (already deterio-rated) is covered with vegetation.

In Iturralde-Vinent’s view, whenthe brown earth of the cut is washedand filtered, it yields a fossiliferousresidue that today still manifests arich and varied small marine faunaof Late Paleocene exotic foramin-ifera (Eponides vanbelleni,Cibicides madrugaensis, Boldia

madrugaensis, B. cubensis, Ano-malina madrugaensis, Valvulineriamadrugaensis, and Gyroidinamadrugaensis); radiolarians, bra-chiopods, mollusks, and echino-derms from little more than sixtymillion years ago. Using foramini-fers (Marginulina tuberculata,Dentalina gardnerae, Bulloporachapmani, Siphogenerinoideseleganta), paleontologists corre-lated this Paleocene assemblagewith similar fauna from Alabama,Texas, Arkansas, Illinois, and Mis-sissippi.

A Complex Geologic HistoryBetween fifteen and twenty-five mil-lion years ago, Madruga lay beneaththe sea, though the waters betweenMayabeque Province and Isla de laJuventud (the modern-day Gulf ofBatabona) were shallower than theyare today. During that time, remains

Life-restoration of Cenozoic vertebrates from Madruga. A) Giant ground megalonychid sloth B) Ancient wood-pecker C) Cuban red macaw, Ara tricolor D) The Cuban giant owl, Ornimegalonyx. Art ©Dmitry Bogdanov. Usedby permission.

of corals, mollusks, algae, and cal-careous microorganisms becamefossilized, later forming the rocks ofthe Sierra del Grillo mountains.Those seas were also infested by thegiant extinct shark Carcharodonmegalodon, whose enormous teethsometimes appear among the redsoils of the plain. This occurrence isprobably related to the existence ofa Lower-Middle Miocene waterchannel across western Cuba thatconnected the Atlantic Ocean withthe Caribbean Sea.

Throughout its geologic history,this territory also experienced greatcataclysms that brought rocks to thesurface that had lain many kilome-ters deep. These forces elevated theserpentinites, formed the island ofCuba, and shaped the Sierra delGrillo mountains as well as thelandscape that today surrounds thearea where the town of Madruga is

20 Fossil News – Summer 2017

situated. Long before Europeancolonizers arrived, aboriginalnatives lived in these lands, andlong before humans occupiedCuba, plant-eating mammalsas large as bears had arrivedfrom South America. These an-cient mammals included the gi-ant Caribbean ground slothsMegalocnus, Parocnus, andmany others, which disap-peared as recently as 4,200years ago. At the beginning ofthe twentieth century, the fa-mous Cuban naturalist Carlosde la Torre y Huerta, who tookhis vacations in Madruga,found fossil remains of theseanimals in the Sierra del Grillo.

After the hills of the Sierradel Grillo formed, acidic rain-water penetrated into the poresand cracks of these rocks andopened caverns of differentmagnitudes under the surface.Water accumulated under-ground in those caverns, andtoday those waters are ex-tracted by means of wells. Inprehistoric times, near the cav-erns in the mogotes (steep-sided residual hills of limestoneor marble) small rodents thatlived there were hunted by largepredatory owls such asOrnimegalonyx, the Cuban gi-ant owl. Also present in thatearly Eden were beautiful birdssuch as Ara tricolor (Cuban redmacaw), and ancient wood-peckers.

The area near the Sierra delGrillo has produced water aswell as petroleum, and itssprings of sulfurous water arealso known for their medicinalproperties. Madruga’s complex pre-history has left a legacy of fossil andgeologic treasures that have trans-formed the area into an excellentsite for scientific tourism.

— Yasmani Ceballos Izquierdo &Tracy Lee Ford

Marine fossils from Madruga: A-C) Late Cretaceous foraminifers, Buliminamadrugaensis; D-E) Eponides vanbelleni, in peripheral and dorsal view; F)Valvulineria madrugaensis in dorsal view; G-H) Gyroidina madrugaensisin ventral and peripheral view; I) Coleites reticulosus in dorsal view; J)Vaughanina cubensis; K) Late Cretaceous Operculina bermudezi, earlychambers of a megalospheric specimen; and L-N) the Late Cretaceous rudistbivalves, Biradiolites, a few centimeters in length. Art ©Tracy Lee Ford.Used by permission.