New fossil record of Lactoridaceae in the Paleogene of southern Patagonia ( South America )

The new record of the family Lactoridaceae (Rosannia manika Srivastava) in Tierra del Fuego, Austral Basin corresponds to a sedimentary succession located at the south of the Irigoyen River, nearby the Cerro Malvinera. The palynology (principally dinoflagellates cysts) of different Paleogene formations (La Barca, Punta Torcida and Puesto José) in the Austral Basin was analyzed to calibrate the age of this outcrop. This result was compared with large datasets of organic dinoflagellate cyst (dinocyst) assemblages from Southern Pacific Ocean shelf sediments and other sections of the world. The majority of the palynomorph taxa from the Cerro Malvinera succession are present in the upper member LB2 of the La Barca Formation and both shared the presence of Lactoridaceae (Rosannia manika Srivastava) and the age-diagnostic dinocysts Pentadinium laticinctum (First Occurrences 51.95 Ma). An age not older than early Eocene is proposed for the LB2 member of the La Barca Formation and the Cerro Malvinera strata. This data expands the known fossil range of the Lactoridaceae in Patagonia and contributes to elucidate the probably migration routes of this family. A migration via Antarctica is postulated in this paper due to the record of this family in the Maastrichtian (López de Bertodano Formation). Depending on new records, due to the presence of this family in the Colorado Basin in the Danian, a migration route from the north of Patagonia to the south (Austral Basin) it is not discarded.


INTRODUCTION
In this paper we report a new fossil finding of Lactoridaceae tetrads form the Paleogene of southern Patagonia (Austral Basin), southern South America.Lactoridaceae are a monotypic family of shrubby angiosperms represented by a lone species: Lactoris fernandeziana Phil., now endemic to the cloud forests of Masatierra Island (= Robinson Crusoe) located at an altitude of 500 m and above (Crawford et al., 1991(Crawford et al., , 1994;;Stuessy et al., 1997Stuessy et al., , 1998)).The island belongs to the Juan Fernandez Group, located 667 km off the west coast of Chile in the Pacific Ocean.This species possesses both primitive and highly specialised/reduced characters (Carlquist, 1964).The Lactoridaceae are considerer to form part of an early-branching of angiosperms pertaining to the "paleoherbs" (according to Donoghue & Doyle, 1989), and to understanding of the early angiosperm evolution.It has being assigned to the Order Piperales based on exine structure and wood anatomy, the LauraIes, and the Magnoliales based on cladistic, and chemotaxonomic studies (from Macphail et al., 1997 and bibliography cited in this paper).Endress (1994) has summarized features of Lactoris which he considers implies a relationship with the Aristolochiales (Aristolochia).This is supported by phylogenetic analysis based on nucleotide sequences in the plastid gene rbcL (Chase et al., 1993).
Little is known of its reproductive biology.Lactoris is anemophilous, a syndrome perhaps reflected by the P/O (pollen/ovule) ratio.Low genetic diversity (isozymes and DNA) supports selfing and implies limited distance wind pollen dispersal.If the primitive angiosperms to which Lactoridaceae is related (Piperales, Magnoliales, Aristolochiales, Laurales; Stuessy et al., 1998) are presumed to be insect pollinated the anemophily is derived (Bernardello et al., 1999).
The discovery of fossil pollen of Lactoridaceae in the Upper Cretaceous (lower Turonian-Campanian) of the south-west coast (Orange Basin offshore Namaqualand), South Africa suggests that this family may have been a common element in the Cretaceous Gondwana flora (Zavada & Benson, 1987).The Turonian age for the Lactoridaceae should be cautiously accepted since the type material come from cutting samples (Srivastava & Braman, 2010).
The new register of the family in the area of Cerro Malvinera (Lat.54°34'55.9''S,Long.66°37´22.8"W,Austral Basin) corresponds to a sample in a succession of c. 180 m of black mudstones with minor intercalated sandstone beds, which was correlated to the Paleogene La Barca Formation (Torres Carbonell et al., 2008).The outcrops are located to the south of Irigoyen River where the mudstone-dominated succession is adjacent to Upper Cretaceous strata of the Policarpo Formation, but the stratigraphic contacts cannot be observed.
To evaluate the age of the succession at Cerro Malvinera its palynology (principally dinoflagellates cysts) was compared to that of different Paleogene formations (La Barca, Punta Torcida and Puesto José) at its type locality, exposed in the Austral Basin.The results were compared with large datasets of organic dinoflagellate cyst (dinocyst) assemblages from Southern Ocean shelf sediments and from other sections in the World ( Bijl et al., 2013, William et al., 1998, 1999, 2003).
It was also compared with a high-resolution Southern Pacific Ocean dinocyst zonation for the late Palaeocene to late Eocene (58-36 million years ago; Ma).The zonation consists of thirteen dinocyst zones, calibrated to the Geomagnetic Polarity Time Scale (GPTS) of Vandenberghe et al. (2012), which can likely be applied, to the entire Southern Ocean (Bijl et al., 2013).
The present results expanded the known fossil record of the Lactoridaceae in Patagonia and it is a contribution to elucidate the probably migration routes of this family.

STUDIED LOCALITY AND COMPARED PALEOGENE FORMATIONS
The mountain front of the Fuegian Andes is formed by the Fuegian Thrust-Fold Belt, which constitutes a thin-skinned wedge that involves Upper Cretaceous to Miocene sequences (Klepeis & Austin, 1997;Ghiglione et al., 2002;Torres Carbonell et al., 2008).The stratigraphic successions involved in the thrust-fold belt correspond to the Magallanes/Austral foreland basin, and the successions have been divided into several unconformity bounded sequences (Olivero & Malumián, 2008) that records the kinematic evolution of the Fuegian Thrust-Fold Belt.During the Paleogene, the foreland successions cropping out at the Atlantic shore include two main tectonically controlled depocenters: a foredeep depocenter with early Eocene deep marine turbidites of the Punta Torcida Formation, and a wedge-top depocenter filled with several Eocene to Oligocene formations (Torres Carbonell et al., 2009;Torres Carbonell & Olivero, 2011), of which the mudstones of the Puesto José Formation are of interest for this study.The interpretation of the La Barca Formation is presently not clear, and it was tentatively considered either as part of relatively shallow fandeltaic systems flanking the northern mountain front or as part of a Paleogene-Eocene foredeep system (Olivero et al., 2002;Torres Carbonell et al., 2009).

La Barca Formation (Olivero et al., 2002)
The La Barca Formation, only recognized at the type locality (Fig. 1), c. 220 m, includes a lower member LB1, of tuffaceous sandstones and intercalated carbonaceous siltstones; and an upper member LB2 of black mudstones (Olivero & Malumián, 2008).In the La Barca Formation a restricted horizon of the lower member LB1 (100 m) bears a mostly cosmopolitan Midway Type assemblage dominated by buliminids; the assemblage includes the dominant Bulimina karpatica, and exceptional endemic species such as Buliminella isabelleana and Antarcticella sp., both known from Antarctica and very common and widespread in Patagonia.LB2 (120 m) contains only scarce agglutinated foraminifera, dominated by Spiroplectammina spectabilis (Malumián & Caramés, 2002;Olivero & Malumián, 2008).
There has not been register diagnostic megafauna in the La Barca Formation.The associations of dinocysts (Palaeocystodinium golzowense and Glaphyrocysta sp.) of the member LB1 are poor preserved.In LB2 member only Palaeocystodinium golzowense was recognized (Olivero et al., 2002).A Late Paleocene age was proposed for LB2 member (Olivero et al., 2002).
The studied samples in this paper correspond to LB2 member: 80 m (372-19) and 180 m (372-25) above the sample with Paleocene forams of the LB1 member.
The formation contains abundant ostracods (Jannou, 2009) foraminifera and radiolarians.Most of the benthic foraminifera were described from the Agua Fresca Formation in the pioneer work in Austral Basin of Todd & Kniker (1952) and include common endemic species such as Antarcticella ceccioni.Planktonic foraminifera indicate an early Eocene age and the benthonic ones are mostly dominated by agglutinated forms typical of turbiditic settings (Olivero & Malumián, 1999).The radiolarians are correlated with the RP 10 Zone of the South Pacific calibrated between 51 to 47 Ma (Hollis, 1997) by Jannou (2014).
In the type section the last occurrence datum of S. angiporoides restrict the age of the strata below this level to the early Oligocene (30 Ma) Torres Carbonell et al., 2009.

MATERIAL AND METHODS
The palynomorphs were recovered from outcrop samples corresponding to different Paleogene formations of the Austral Basin (Table 1).Age control was provided principally by foraminifera, dinoflagellates and spore and pollen species whose time distributions are significant.
Due to the characteristics of the analyzed for-Quattrocchio: New fossil record of Lactoridaceae in the Paleogene of Patagonia mations, with common reworked material during different phases of the episodic evolution of the thrust-fold belt only the palynomorphs in a good state of preservation were considered.
The material physically or chemically altered was considered reworked from older deposits.
Physical and chemical extraction was carried out using standard palynological processing techniques (Volkheimer & Melendi, 1976), which involve treatment with hydrochloric and hydrofluoric acids.A brief oxidation (two minutes or less) in nitric acid was realized.The residue was sieved through a 10 μm mesh to concentrate the palynomorphs.All figured specimens are lodged in the collections of the Palynological Laboratory, Universidad Nacional del Sur, Bahía Blanca, Argentina.In the citation of specimens referred to or illustrated, the sample and slide number is given first and the position on the slide indicated by an England Finder reference (e.g.G36/4).

SYSTEMATIC DESCRIPTION
The original diagnosis of the genus Rosannia as R. manika, were based on a misinterpretation of its morphological characteristics (Srivastava, 1968).The genus was erroneuously diagnosed as a monad.Rosannia would have priority over Lactoripollenites Zavada & Benson, 1987. Gamerro & Barreda (2008) found fossil tetrads of Lactoridaceae and informally named as 'Lactoris type' pending an emended diagnosis of Rosannia based on the type material.It was done in Srivastava & Braman (2010).Then this material is assigned here to the genus Rosannia.
Remarks: We compare and not assigned to R. manika due to in the present material the infratectal ornamentation microreticulate characteristic of the species is not observed.The sexine is thinner (1.0 µm) in the studied material in relation to the type species (1.5 µm).This material shows a close resemblance to Lactoris type of Gamerro & Barreda (2008) and Lactoripollenites africanus Zavada & Benson (1987), sharing a similar morphology.The distal aperture is clearly defined in one of the specimen of Pedro Luro Formation, characteristic not observed in Lactoris type (Gamerro & Barreda, 2008).Lactoripollenites from Australia (Macphail et al., 1999) differs in having a thick exine (1,5-2 µm) and larger size (40-56 µm) than the present material (28-37 µm).

DISCUSSION
The new register of the Lactoridaceae in the area of Cerro Malvinera expanded the known fossil range of this family in Patagonia.To evaluate the age of the succession at Cerro Malvinera its palynology was compared to that of different Paleogene formations (La Barca, Punta Torcida and Puesto José) at its type locality, exposed in the Austral Basin.Several dinocyst events were recognized in the compared Paleogene formations.The first occurrences (FO) and last occurrences (LO) of these events are documented in Table 2. Magnetostratigaphycally calibrated ages of key dinocysts species in the Southern Ocean (Bijl et al., 2013) and from other sections in the world recognized in these formations are given.
In comparing the palynomorphs of Cerro Malvinera with those recorded in La Barca, Punta Torcida and Puesto José formations (Table 3) it should be noted that the majority of taxa of this profile are present in La Barca Formation (7 species in common).Four species are shared with Punta Torcida Formation and only two with Puesto José Formation.
In Table 3 the list of palynomorphs recognized in the different formations is given.Taking into account the dinocysts species some stratigraphic considerations about the analyzed formations are given.
La Barca Formation is considered to be Late Paleocene in previous studies (Olivero et al., 2002) due to the presence of Paleocystodinium golzowense.According to Bijl et al., 2013 this species has its LO 51.50 Ma in the South Pacific Ocean and in other oceans FO 54.31 Ma (Table 2).Also this species is present in Austral Basin, Chile in the Chorrillo Chico Formation in the Late Paleocene associated with Palaeoperidinium pyrophorum (Late Campanian-Late Selandian) and in the lower part (early Eocene) of Agua Fresca Formation (Quattrocchio, 2009).The presence of Palaeocystodinium golzowense from PP18 sample upwards in the Agua Fresca Formation (early to middle Eocene) is considered reworking (Quattrocchio, 2009).Other species are Operculodinium azcaratei, Volkheimeridium lantern, which were cited for Chorrillo Chico and Agua Fresca formations, Paleocene-middle Eocene of Chile (Quattrocchio, 2009).
Due to the presence of Pentadinium laticinctum  Ma in other oceans) an age not older than early Eocene is proposed for La Barca Formation in the studied sample of LB2 member.
An age not older than middle Oligocene is proposed for the studied samples from Puesto José Formation due the presence of Phthanoperidinium coreoides, which it is associated with Leujenecysta fallax (middle Eocene to middle Miocene).

Migration routes
The discovery of fossil pollen of Lactoridaceae in the Late Cretaceous (early Turonian-Campanian) deposits of the south-west coast (Orange Basin offshore Namaqualand), South Africa suggests that this family may have been a common element in the Cretaceous Gondwana flora (Zavada & Benson, 1987).Due to the type material was documented from cutting samples; the Turonian age for the Lactoridaceae should be cautiously accepted (Srivastava & Braman, 2010).
Different explanations have been postulated about the migratory routes of the family now restricted to a volcanic island in the Pacific Ocean (Macphail et al., 1999;Gamerro & Barreda, 2008;Srivastava & Braman, 2010) ( Bijl et al., 2013, William et al., 1998, 1999, 2003) (Macphail et al., 1999).Macphail et al. (1999) considered that the Lactoridaceae could have entered Australia through the north from Africa during the middle-late Campanian.None of the Southeast Australian specimens of Lactoridace were an exact match for the South African and it could be presume that Lactoris fernandeziana is merley the sole survivor of a much larger clade (Mcphail com.pers.).
Lactoridaceae is also present in in the Danian and early Miocene of South America (Ruiz & Quattrocchio, 1997;Gamerro & Barreda, 2008, Barreda et al., 2012) and the Senonian of India (Prasad et al., 1995;Prasad & Pundeer, 2002), which was connected with Africa in the Senonian (Srivastava, 1988;Briggs, 2003).Africa and South America had land connections by the Río Grande Rise and the Walvis Ridge then the migrations of Lactoridaceae in the late Cretaceous throughout the Atlantic Ocean could be possible (Gamerro & Barreda, 2008).Gamerro and Barreda (2008) also postulated a migration via Antarctica due to the record of this family (Lactoridaceae s.l. A. Partridge, pers.comm. in Gamerro & Barreda 2008) in the Maastrichtian (López de Bertodano Formation).The southernmost extreme of South America (Patagonia) remained connected to the present Antarctic Peninsula at least up until about 30 Ma., that was part of the landscape up to the first part of the Paleogene, and quite probably also including part of the remaining Antarctic continent (Pascual & Ortiz-Jaureguizar, 2007) .Secular variation of neodymium isotope ratios at Agulhas Ridge (Southern Ocean, Atlantic sector) suggests an early middle Eocene (approximately 41 Ma) for the opening of the Drake Passage (Scher & Martin, 2006) The migration from North to South America is also possible (Gamerro & Barreda, 2008).By the beginning of the Late Cretaceous, the volcanic and diastrophic processes that finally led to the differentiation of the Caribbean region and Central America built up transient geographic connections that permitted the initiation of an overland inter-American exchange that included dinosaurian titanosaurs from South America and hadrosaurs from North America.Marsupials (polydolopimorphian marsupials) were assumed to have differentiated in South America prior to new discoveries from the North American Late Cretaceous (Pascual & Ortiz-Jaureguizar, 2007).But the lack of fossils of Lactoridaceae in north-ern and central South America indicates that this route (North American) could be less probably (Gamerro & Barrera, 2008).
The route followed by this family to its present distribution is explained in Gamerro & Barreda (2008, p. 48).The youngest record is in the early Miocene (Austral Basin) in Argentina.Gamerro & Barreda (2008) considered that Lactoris migrated to the west (Robinson Crusoe Island) before the Andean maximum uplift in the middle-late Miocene.
A migration via Antarctica is postulated in this paper due to the record of this family in the Maastrichtian (Lopez de Bertodano Formation).The southernmost extreme of South America (Patagonia) remained connected to the present Antarctic Peninsula at least up until about 41 Ma.Depending on new records due to the presence of this family in the Colorado Basin in the Danian, a migration route from the north of Patagonia to the south (Austral Basin) it is not discarded.

CONCLUSION
The majority of palynomorph taxa from the Cerro Malvinera succession are present in the upper member LB2 of the La Barca Formation and both shared the presence of Lactoridaceae (Rosannia manika Srivastava) and the age-diagnostic dinocysts Pentadinium laticinctum (First Occurrences 51.95 Ma).An age not older than early Eocene is proposed for the studied samples of LB2 member of the La Barca Formation and the Cerro Malvinera strata.
These data expands the known fossil record of the Lactoridaceae in Patagonia and contributes to elucidate the probably migration routes of this family.A migration via Antarctica is postulated in this paper due to the record of this family in the Maastrichtian (Lopez de Bertodano Formation).The southernmost extreme of South America (Patagonia) remained connected to the present Antarctic Peninsula at least up early middle Eocene (approximately 41 Ma).Depending on new records due to the presence of this family in the Colorado Basin in the Danian, a migration route from the north of Patagonia to the south (Austral Basin) it is not descarded.

Table 2 :
. In Australia, pollen grains of one or more closely related species of Lactoripollenites Zavada & Magnetostratigraphically calibrated ages of key dinocyst species in the Southern Ocean and from other sections in the World

Table 3 :
. Quattrocchio: New fossil record of Lactoridaceae in the Paleogene of Patagonia List of palynomorphs recognized in the analyzed formations.Benson, 1987 have been recorded since 1970 in marine and terrestrial sediments, which range in age from Campanian to early Oligocene