The Silveirinha Formation is an

Early Eocene In the geologic timescale the Ypresian is the oldest age (geology), age or lowest stage (stratigraphy), stratigraphic stage of the Eocene. It spans the time between , is preceded by the Thanetian Age (part of the Paleocene) and is followed by th ...

(

Ypresian In the geologic timescale the Ypresian is the oldest age or lowest stratigraphic stage of the Eocene. It spans the time between , is preceded by the Thanetian Age (part of the Paleocene) and is followed by the Eocene Lutetian Age. The Ypresian i ...

, or MP7 or

Neustrian Neustria was the western part of the Kingdom of the Franks. Neustria included the land between the Loire and the Silva Carbonaria, approximately the north of present-day France, with Paris, Orléans, Tours, Soissons as its main cities. It later ...

in the ELMA classification)

geologic formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

of the

Mondego Basin Mondego may refer to: * Mondego River, Portugal * Rio Mondego, another name for the Miranda River (Brazil) * Baixo Mondego, a subregion of Portugal * Cabo Mondego, natural monument in Portugal * Metro Mondego, light rail network in Coimbra, Portug ...

in the Região Centro of central-western Portugal. The

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, ...

s and conglomerates were deposited in an

alluvial Alluvium (from Latin ''alluvius'', from ''alluere'' 'to wash against') is loose clay, silt, sand, or gravel that has been deposited by running water in a stream bed, on a floodplain, in an alluvial fan or beach, or in similar settings. Al ...

environment Environment most often refers to: __NOTOC__ * Natural environment, all living and non-living things occurring naturally * Biophysical environment, the physical and biological factors along with their chemical interactions that affect an organism or ...

.Silveirinha Formation
at

Fossilworks Fossilworks is a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database, a large relational database assembled by hundreds of paleontologists from around the world. History Fossilworks was cre ...

.org The formation has provided fossils of many mammals,

bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...

s, amphibians and reptiles, as well as

mollusk Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is es ...

s and

ostracod Ostracods, or ostracodes, are a class of the Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 70,000 species (only 13,000 of which are extant) have been identified, grouped into several orders. They are small crustaceans, typic ...

s, and is considered one of the richest Early Eocene faunal assemblages of Europe. The

taeniodont Taeniodonta ("banded teeth") is an extinct early group of cimolestid mammals known from the Maastrichtian to the Eocene. Taeniodonts evolved quickly into highly specialized digging animals, and varied greatly in size, from rat-sized to species ...

, typically known as a North American order; '' Eurodon silveirinhensis'' and the

'' Cypris silveirinhaensis'' have been named after the formation.

Description

The Silveirinha Formation, named after the Silveirinha clay pit, crops out in the western part of the

in the Região Centro of central-western Portugal.De la Peña, 1995, p.30 The formation comprises fossiliferous lenticular calcitic conglomerates as well as laminated and cross bedded sands and brownish-red silts. The conglomerates are interpreted as crevasse-splay deposit in a

alluvial plain An alluvial plain is a largely flat landform created by the deposition of sediment over a long period of time by one or more rivers coming from highland regions, from which alluvial soil forms. A floodplain is part of the process, being the s ...

, which eventually flooded and where bogs and possibly oxbows developed, crossed by channels depending on a river system that drained higher areas more north or eastwards.Antunes, 2003, p.20

Climate

The climate in the Early Eocene was substantially warmer than today.

Paleontological significance

The Silveirinha clay pit after which the formation is named was first discovered in 1977 by Rui Pena dos Reis of

Coimbra University The University of Coimbra (UC; pt, Universidade de Coimbra, ) is a Public university, public research university in Coimbra, Portugal. First established in Lisbon in 1290, it went through a number of relocations until moving permanently to Coi ...

. The unit is one of few earliest Eocene fossiliferous formations that provided a rich amphibian and reptile fauna.Rage & Augé, 2003, p.103 Most fossils were deposited in the channels after short transportation. Vegetation should have been rich in nearby areas, supporting a rich fauna.

Ostracod Ostracods, or ostracodes, are a class of the Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 70,000 species (only 13,000 of which are extant) have been identified, grouped into several orders. They are small crustaceans, typic ...

s, gastropods, amphibians and pelomedusid chelonians indicate fresh waters, although rare bivalves show that salt or at least brackish waters were not very far away. It is hypothesized that the species ''D. antunesi'' in the genus ''

Diacodexis ''Diacodexis'' is an extinct genus of small herbivore mammals belonging to the family Dichobunidae which lived in North America, Europe and Pakistan from 55.4 mya to 46.2 mya and existing for approximately . Description ''Diacodexis'' is th ...

'' was more primitive than the earliest

Wasatchian The Wasatchian North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 55,400,000 to 50,300,000 years BP lasting . It is usually c ...

''D. ilicis'' of North America, strongly supporting a Europe to America dispersal of this genus.Godinot & De Lapparent, 2003, p.262

Fossil content

The formation has provided the following fossils:

Mammals

;Primates * '' Arcius zbyszewskii'' * '' Donrussellia lusitanica'' ;Acreodi * '' Mondegodon eutrigonus''Tabuce et al., 2011, p.146 ;Artiodactyls * '' Diacodexis antunesi''Estravís & Russell, 1989 ;Carnivora * '' cf. Miacis sp.'' * Miacidae indet. ;Cimolesta * '' Ilerdoryctes cf. sigei''Estravís, 2000, p.284 ;"Condylartha" * '' Microhyus reisi''Tabuce et al., 2006, p.41Antunes et al., 1987 ;Ferae * '' Dormaalocyon latouri'' * '' cf. Viverravus sp.'' ;Glires * '' Euromys cardosoi''Escarguel, 1999, p.142 * '' Corbarimys paisi''Escarguel, 1999, p.251Estravís, 1994 * '' Microparamys cf. nanus''Badiola et al., 2009, p.248 ;Hyaenodonta * '' Didelphodus sp.''Estravís, 2000, p.283 ;Insectivora * '' Russellmys denisae''Estravís, 1990 * '' Apatemys sp.''Estravís, 2000, p.282 * '' Heterohyus sp.'' ;Perissodactyls * '' Paschatherium marianae''Estravís & Russell, 1992b * '' Pliolophus vulpiceps'' * '' Teilhardimys reisi'' * '' cf. Lophiaspis maurettei'' ;Taeniodonta * '' Eurodon silveirinhensis''Estravís & Russell, 1992a, p.195 ;Theriiformes * ''

Archaeonycteris praecursor ''Archaeonycteris'' is an archaic bat genus whose fossilised remains have been found in Germany, France, England and India. The genus was established in 1917, when Pierre Revilliod described the material excavated at the Messel Pit as the fossil ...

''Tabuce et al., 2009 * '' Leptacodon nascimentoi''Estravís, 1996 * '' Peratherium cf. constans'' * '' cf. Leptacodon sp.'' * '' ?Talpavus sp.'' * Creodonta indet. * Nyctitheriidae indet.

Birds

Charadriiformes Charadriiformes (, from '' Charadrius'', the type genus of family Charadriidae) is a diverse order of small to medium-large birds. It includes about 390 species and has members in all parts of the world. Most charadriiform birds live near water ...

Recurvirostridae The Recurvirostridae are a family of birds in the wader suborder Charadrii. It contains two distinct groups of birds, the avocets (one genus) and the stilts (two genera). Description Avocets and stilts range in length from and in weight from ; ...

*** '' Fluviatilavis antunesi''Harrison, 1983 *

Ornithurae Ornithurae (meaning "bird tails" in Greek) is a natural group which includes the common ancestor of '' Ichthyornis'', '' Hesperornis'', and all modern birds as well as all other descendants of that common ancestor. Classification Ernst Haeckel c ...

** Neornithes indet.Antunes, 2003, p.7

Reptiles

;Crocodiles * '' Diplocynodon sp.''Antunes, 2003, p.10 ;Lizards * '' Geiseltaliellus sp.'' * '' cf. Melanosaurus sp.''Rage & Augé, 2003, p.107 * '' cf. Tinosaurus sp.'' * Amphisbaenidae indet.Rage & Augé, 2003, p.108 * Glyptosaurinae indet. * Glyptosaurini indet.Rage & Augé, 2003, p.106 * Gekkonidae indet. * Iguanidae indet. * Melanosaurini indet. * Scincomorpha indet. * ?Anguinae indet. * ?Varanidae indet. ;Snakes * '' Dunnophis matronensis''Rage & Augé, 2003, p.109 * Boidae indet. ;Turtles * '' Neochelys sp.''Lapparent de Broin, 2003, p.118

Amphibians

* Pelobatidae indet.Rage & Augé, 2003, p.105 * Salamandridae indet.Rage & Augé, 2003, p.104

Invertebrates

;Mollusks * '' Bithynia soaresi''Callapez, 2003, p.84 * '' Gyraulus antunesi''Callapez, 2003, p.85 * '' Chlamys sp.'' * Cardiacea indet. ;Ostracods * '' Cypris silveirinhaensis''Colin & Antunes, 2003, p.92 * '' Ilyocypris lusitanicus'' * '' ?Cyclocypris sp.''

References

Bibliography

* * * * * * * * * * * * * * * * * * * * {{citation , last=Harrison , first=C. J. O , year=1983 , title=A new wader, Recurvirostridae (Charadriiformes), from the Early Eocene of Portugal , journal= Ciencias da Terra , volume=7 , pages=9–16 Geologic formations of Portugal Eocene Series of Europe Paleogene Portugal Ypresian Stage Conglomerate formations Sandstone formations Siltstone formations Alluvial deposits Fossiliferous stratigraphic units of Europe Paleontology in Portugal Formations Formations