Petrocardium is an extinct genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 of monocot

Monocotyledon

Monocotyledons, also known as monocots, are one of two major groups of flowering plants that are traditionally recognized, the other being dicotyledons, or dicots. Monocot seedlings typically have one cotyledon , in contrast to the two cotyledons typical of dicots...

 plant

Plant

Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...

 in the family Araceae

Araceae

Araceae are a family of monocotyledonous flowering plants in which flowers are borne on a type of inflorescence called a spadix. The spadix is usually accompanied by, and sometimes partially enclosed in, a spathe or leaf-like bract. Also known as the Arum family, members are often colloquially...

. At present it contains only two species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 Petrocardium cerrejonense and Petrocardium wayuuorum, the type species. The genus is solely known from the Middle to late Paleocene

Paleocene

The Paleocene or Palaeocene, the "early recent", is a geologic epoch that lasted from about . It is the first epoch of the Palaeogene Period in the modern Cenozoic Era...

 (about 60 to 58 Ma), Cerrejón Formation

Cerrejón Formation

The Cerrejón Formation is a geologic formation in Colombia dating back to the Middle-Late Paleocene. It is found in the El Cerrejón subbasin of the Racheria basin of La Guajira. The formation consists of bituminous coal fields that are an important economic resource. Coal from the Cerrejón...

 deposits in Colombia

Colombia

Colombia, officially the Republic of Colombia , is a unitary constitutional republic comprising thirty-two departments. The country is located in northwestern South America, bordered to the east by Venezuela and Brazil; to the south by Ecuador and Peru; to the north by the Caribbean Sea; to the...

.

History and classification

The genus is known only from the two holotype

Holotype

A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...

 specimens, number ING-0902, type specimen for Petrocardium wayuuorum, and ING-0804, type specimen for Petrocardium cerrejonense. The leaves

Leaves

-History:Vocalist Arnar Gudjonsson was formerly the guitarist with Mower, and he was joined by Hallur Hallsson , Arnar Ólafsson , Bjarni Grímsson , and Andri Ásgrímsson . Late in 2001 they played with Emiliana Torrini and drew early praise from the New York Times...

 are currently residing in the collections housed by the Colombian Geological Institute in Bogotá, Colombia. Both ING-0902 and ING-0804 were collected from Cerrejón Formation

Cerrejón Formation

The Cerrejón Formation is a geologic formation in Colombia dating back to the Middle-Late Paleocene. It is found in the El Cerrejón subbasin of the Racheria basin of La Guajira. The formation consists of bituminous coal fields that are an important economic resource. Coal from the Cerrejón...

 exposures in the Cerrejón coal mine, located in the Rancheria Basin, Colombia. They were first studied by a group of researchers from Florida Museum of Natural History

Florida Museum of Natural History

The Florida Museum of Natural History is the State of Florida's official state-sponsored and chartered natural history museum. Its main facilities are located on the campus of the University of Florida in Gainesville, Florida....

, the Smithsonian Museum of Natural History and led by Fabiany Herrera from the Smithsonian Tropical Research Institute

Smithsonian Tropical Research Institute

The Smithsonian Tropical Research Institute in Panama, the only bureau of the Smithsonian Institution based outside of the United States, is dedicated to understanding biological diversity. What began in 1923 as small field station on Barro Colorado Island in the Panama Canal Zone has developed...

. Herrera and associates published their 2008 type description in the American Journal of Botany

American Journal of Botany

The American Journal of Botany is a peer-reviewed scientific journal which includes research papers on all aspects of plant biology. It is published by the Botanical Society of America on a monthly basis since 1914....

.

The generic epithet Petrocardium is Greek

Greek language

Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

 in derivation and is a combination of the words petro meaning "rock" and cardium which means "heart" and references the heart shaped nature of the leaf fossils in the rocks. The specific epithet "wayuuorum" was chosen by the authors to honor the Wayuu

Wayuu

Wayuu is an Amerindian ethnic group of the La Guajira Peninsula in northern Colombia and northwest Venezuela. They are part of the Maipurean language family.- Geography :...

 Amerindian tribe which lives in the Rancheria Basin area of Colombia. The specific epithet "cerrejonense" is a derivation of Cerrejón and reflects the type locality, the Cerrejón Formation.

Description

Although several angiosperm families, such as Alismataceae

Alismataceae

The water-plantains are a family of flowering plants, comprising 11 genera and between 85-95 species. The family has a cosmopolitan distribution, with the greatest number of species in temperate regions of the Northern Hemisphere...

, and Potamogetonaceae

Potamogetonaceae

The Potamogetonaceae, commonly referred to as the pondweed family, is an aquatic family of monocotyledonous flowering plants. There are roughly 120 species spread across six genera in the Potamagetonaceae...

 have leaf morphologies similar to Petrocardium, its lack of the primary vein structure found in those families excludes them as relatives. Petrocardium is placed as incertae sedis

Incertae sedis

, is a term used to define a taxonomic group where its broader relationships are unknown or undefined. Uncertainty at specific taxonomic levels is attributed by , , and similar terms.-Examples:*The fossil plant Paradinandra suecica could not be assigned to any...

within the Araceae due to the unique combination of leaf morphology characteristics present in both species. Of the modern Araceae genera, Petrocardium is most similar to the modern tropical genus Anthurium

Anthurium

Anthurium , is a large genus of about 600–800 species, belonging to the arum family . Anthurium can also be called "Flamingo Flower" or "Boy Flower", both referring to the structure of the spathe and spadix....

in tribe Pothoeae. However it is not close in structure to the other three genera in the tribe, Pedicellarum

Pedicellarum

Pedicellarum is a monotypic genus of flowering plants in the Araceae family. The single species that comprises the genus is Pedicellarum paiei. This species is endemic to Indomalaysia.-References:...

, Pothoidium

Pothoidium

Pothoidium is a monotypic genus of flowering plants in the Araceae family. The single species that comprises the genus is Pothoidium lobbianum. This species is endemic to the Moluccas, Sulawesi, the Philippines, and Taiwan.-References:...

, and Pothos

Pothos

Pothos may refer to:* Pothos , a character in Greek mythology* Pothos , a group of plants* Epipremnum aureum, a plant often grown indoors* A statue by Scopas...

. This disparity lead the research team to leave the genus unplaced as to subfamily and tribe. Overall the genus possesses entire margined leaves with a generally ovate shape. The leaf apex is long and tapers to a point, while the base is heart to arrowhead shaped. The overall depositional environment was that of sedimentation associated with a fluvial channel area formed within a Neotropical rainforest

Rainforest

Rainforests are forests characterized by high rainfall, with definitions based on a minimum normal annual rainfall of 1750-2000 mm...

basin.

Petrocardium wayuuorum

The single known specimen of P. wayuuorum, ING-0902, was recovered from locality 0315, a 6 metres (19.7 ft) by 50 centimetres (19.7 in) lens of fine grained sandstone in the Cerrejón Formation. The specimen is missing the basal portion of the leaf but shows a smooth margin in the preserved regions of the leaf blade and was either cordate or sagittate. The overall size of the leaf was 6.2 by, and has a vein structure similar to that of Anthurium species that form secondary veins which group in single cluster of veins parallel to the outer margin of the leaf. This secondary vein structure is used to distinguish P. wayuuorum from P. cerrejonense.

Petrocardium cerrejonense

As with P. wayuuorum, P. cerrejonense is known from only one partial leaf and specimen ING-0804, is also from locality 0315. The specimen is incomplete with only portions of the tip and middle area of the leaf blade known. The overall size of the leaf was over 9.5 by, with an acuminate tip and smooth margin. P. cerrejonense has a vein structure similar to that of Anthurium species which form secondary veins which group into two clusters of veins parallel to the outer margin of the leaf and the secondary vein structure is used to distinguish P. cerrejonense from P. wayuuorum.