New chondrichthyans from Bartonian-Priabonian levels of Río de Las Minas and Sierra Dorotea, Magallanes Basin, Chilean Patagonia

Here we studied new fossil chondrichthyans from two localities, Río de Las Minas, and Sierra Dorotea, both in the Magallanes Region, southernmost Chile. In Río de Las Minas, the upper section of the Priabonian Loreto Formation have yielded material referable to the taxa Megascyliorhinus sp., Pristiophorus sp., Rhinoptera sp., and Callorhinchus sp. In Sierra Dorotea, middle-to-late Eocene levels of the Río Turbio Formation have provided teeth referable to the taxa Striatolamia macrota (Agassiz), Palaeohypotodus rutoti (Winkler), Squalus aff. weltoni Long, Carcharias sp., Paraorthacodus sp., Rhinoptera sp., and indeterminate Myliobatids. These new records show the presence of common chondrichtyan diversity along most of the Magallanes Basin. The new record of Paraorthacodus sp. and P. rutoti, support the extension of their respective biochrons in the Magallanes Basin and likely in the southeastern Pacific.


Introduction
The research of fossil vertebrates carried out in the last years along the Magallanes Region and supported by two Antarctic Ring projects (Anillos de Ciencia Antártica, Conicyt-Chile; ARTG-04 2007ARTG-04 -2009; ACT-105 2010ACT-105 -2013) ) have recovered a diversity of chondrichthyans ranging a time span between the Maastrichtian and the late Eocene.Two main localities have yielded abundant remains of the group.The upper section of the Loreto Formation exposed at Río de Las Minas near Punta Arenas includes so far at least 13 different taxa from a single level of Priabonian age (Otero et al., 2012).The second and richest locality is Sierra Baguales in the northern part of the Magallanes Region, which has provided remains of five typically Maastrichtian taxa and at least eighteen Paleogene taxa (Otero et al., 2013a).
We present new finds of fossil sharks (Chondrichthyes, Elasmobranchi, Neoselachii) and chimaeroid fishes (Holocephali, Chimaeriformes) recovered from two localities of the Magallanes Region in southernmost Chile.The first is Río de Las Minas, west of Punta Arenas.From the upper section of the Loreto Formation the first local records of Megascyliorhinus cooperi Cappetta and Ward, 1977, Pristiophorus sp., Callorhinchus sp., and Rhinoptera sp. are here described.The second studied locality is Sierra Dorotea, northeast of Puerto Natales.In the latter, upper levels of the Río Turbio Formation (Bartonian-Priabonian) have yielded specimens referable to the taxa Striatolamia macrota (Agassiz), Carcharias 'hopei' (Agassiz), Palaeohypotodus rutoti (Winkler), Paraorthacodus sp., Rhinoptera sp., as well as indeterminate miliobatoids and indeterminate callorhynchids.

Sierra Dorotea, Puerto Natales
The f irst locality studied is Sierra Dorotea (51°35"S; 72°21"W), settled 20 km NE from Puerto Natales, near the international border with Argentina (Fig. 1).In this locality, the base of the section is better exposed on the cliffs facing to Puerto Natales.The latter are part of the Dorotea Formation (Katz, 1963) originally assigned to the Maastrichtian-Danian based on biostratigraphic correlations, and later constrained to the late Maastrichtian based on U-Pb shrimp radioisotopic dates (Hervé et al., 2004).The eastern part of the Sierra have unequivocally Cenozoic levels, these being distinguished by the presence of Glycimeris cf.ibari (Philippi, 1887), Panopea cf.clausa (Wilckens, 1910) and Venericardia (Venericor) carrerensis Griffin, 1991.This fauna was recognized by Griffin (1991) in outcrops of the Río Turbio Formation (Feruglio, 1938) exposed in Argentina.The unit extends beyond the northern margin of the international border, and follows a general N-S strike as it happens with most of the sedimentary units in the studied area.It is easily observed that the levels of the Río Turbio Formation are continous over the Chilean side.Following the scheme of Hünicken (1955), the studied levels are part of the upper section originally assigned to the Paleocene-Eocene, based on stratigraphic correlations and fossil marine invertebrates.The age of this section was later constrained to the middle-late Eocene by Malumián and Caramés (1997) based on stratigraphic correlations and microfossils.
The chondrichthyan-bearing level studied here comprises brown-to-greenish sandstones with coarse-to-fine grain.Fossils are abundant and mostly represented by marine invertebrates of the genera Cucullaea, Glycimeris, Pholadomya, Panopea, as well as ostreids.Vertebrates include the presence of the penguin genus Palaeeudyptes (Sallaberry et al., 2010).This genus has a widespread distribution along the Weddellian Biogeographic Province, WBP hereafter (Zinsmeister, 1979), and it is regarded as typical form in the Eocene-Oligocene of Antarctica, but being particularly abundant in Priabonian levels (Reguero et al., 2013), thus, providing additional support for a middle-to-late Eocene age for the fossil bearing levels of Sierra Dorotea studied here.

Río de Las Minas, Punta Arenas
This is located about 10 km west of Punta Arenas (53º08'S; 71º03'W), in the Brunswick Peninsula (Fig. 1).A canyon is conformed by a well-stratified section of the Loreto Formation (Hoffstetter et al., 1957).This unit is about 800 m thick, composed of well-sorted sandstones and including glauconitic and concretionary horizons with frequent intercalated beds containing fossil flora and several coal seams of variable thickness.Fasola (1969) studied palynomorphs from several points along the Río de Las Minas canyon, assigning an Oligocene age for the unit based on this record.The upper section (Otero et al., 2012: fig. 2) includes a single level with chondrichthyan teeth, which was dated on 36.48±0.47Ma based on U-Pb Shrimp radioisotopic date.This age is consistent with the paleobotanic record as well as with the chondrichthyan assemblage which indicate a Priabonian age (Otero et al., 2012 and references therein); in consequence, most of the section of the Loreto Formation exposed at Río de Las Minas is older than the Priabonian.

Material and Methods
Several tens of fragmentary vertebrate remains were recovered by the authors from Río de Las Minas and Sierra Dorotea, during January, 2013 and January, 2014.Among these, the most abundant are chondrichthyan teeth, followed by less frequent bone remains.Most of the collected specimens from Sierra Dorotea were scattered on surface and obtained by sieving, while few of them were directly recovered from their respective hosting levels.The absence of any articulated specimens as well as the broken cusplets in most teeth (even in those recovered in situ) indicate that the vertebrate remains were reworked previous to their final deposit.Isolated teeth were recovered from the recent soil formed by weathering of the fossiliferous sandstone, while in situ material was still included in well-consolidated matrix, being obtained by usage of chisels and direct hammering.Largest bone fragments observed (mostly birds) did not exceed 5 cm, while teeth belonging large taxa were not found.
The chronostratigraphic nomenclature and formal divisions used here follows the scheme of FIG. 2. Stratigraphic section of the upper part of Sierra Dorotea.Small numbers on each level follows the general description by Hunicken (1955, in Hoffstetter et al.,1957: p. 316-319), and complemented with the observations made during this current study.
Family  Ward (1988) and Cappetta and Nolf (2005), although a specific determination is here precluded since the latter species has unresolved taxonomical status.Despite of this, teeth of Carcharias sp. are common in Bartonian-Priabonian strata along the Magallanes Basin, with previous records in Río de Las Minas and Sierra Baguales (Otero et al., 2012(Otero et al., , 2013a)).The genus was also recovered from Maastrichtian beds of the Dorotea Formation in Sierra Baguales (Otero et al., 2013a).
Although teeth of Carcharias spp.are abundant in southernmost South America since the Upper Cretaceous and through the rest of the Cenozoic (Cione et al., 2007), this genus seems to be absent in higher latitudes.To date, no contemporary records are known in Antarctica, suggesting that the austral distribution of the genus could be restricted to the Magallanes Basin.(Long, 1992;Kriwet, 2005;Reguero et al., 2013).This age differs from the records along the Northern Hemisphere, where this species is restricted to the Paleocene (Cappetta, 1987).Description: Teeth small, larger than high; crown triangular and distally recurved, with complete cutting edge and having serrations in the anterior margin; Labial face with an apron that extends ventrally to the root, while in the lingual face there is a projection of the crown (uvula, sensu Cappetta, 1987).The root has rhomboidal basal outline, being narrower than the crown and with several nutritious foramina.

Genus
Remarks: Squalid sharks have been reported in the WBP.Records from Eocene levels of the La Meseta Formation in Antarctica firstly included indeterminate squalids (Welton and Zinsmeister, 1980).These were later precised as the species S. woodbrunei Long, 1992 and S. weltoni Long, 1992.In addition, the genus Centrophorus was also described from the same unit.Previous records in southern South America only include the genus Centrophoroides found in Maastrichtian levels of the Dorotea Formation in Sierra Baguales (Otero et al., 2013a).The new specimens here studied confirm the persistence of squalids in the Magallanes Basin throughout the K/P boundary, while it verifies the widespread distribution of the family along the WBP.(Ameghino, 1893), central Chile (Suárez et al., 2003) and Antarctica (Klug et al., 2008).Its provincial distribution on Paleogene units is also documented in central Chile from likely Paleocene strata (Muñoz-Ramírez et al., 2007;González et al., 2010;Groz and Palma 2013).Although its worldwide record seems to be restricted to the Paleocene (Cappetta, 1987), the genus was found in Ypresian levels of the La Meseta Formation (Cucullaea I Allomember) (A.Cione, personal communication in Reguero et al., 2013).Considering this, the presence of a single tooth in Sierra Dorotea suggests the re-working from older strata that could reach even Ypresian levels.This is also supported by a similar situation detected on Sierra Baguales, with a reworking that could reach to Paleocene levels based on the presence of teeth of the genera Otodus obliquus and Megascyliorhinus cooperi (Otero et al., 2013a).(Cappetta and Ward, 1977) and due the evidence of re-working in lower levels of the Man Aike Formation, Otero et al. (2013a) considered the possibility that the studied specimens could be hosted in levels older than the Bartonian.Otherwise, the known record of the genus Megascyliorhinus extends from the Eocene onwards the Pleistocene.The current find in Priabonian levels of the Loreto Formation proves the occurrence of this taxon in younger beds along the Magallanes Basin.Regionally, the genus (represented by a probable different species with higher crowns) was recovered from Oligocene beds of New Zealand (Keyes, 1984) proving its widespread distribution during the Eocene-Oligocene boundary along the WBP (Zinsmeister, 1979).Remarks: Dental plates of myliobatids are frequent along Eocene units of the WBP (Kriwet, 2005;Reguero et al., 2013;Otero et al., 2012Otero et al., , 2013a)).The new find, although fragmentary, provides evidence on the widespread distribution of Myliobatis along the Magallanes Basin.Kriwet and Gaździcki (2003).Description: Mandibular tooth plate with a single central hypermineralized pad restricted to the distal part of the coronal surface, flanked by narrow tritors on the symphyseal and/or labial edges (Otero et al., 2013b).

Remarks:
The genus Callorhinchus is a widespread taxon along the WBP between the Upper Cretaceous-Eocene.Its presence is documented from upper Maastrichtian levels of the López de Bertodano Formation in Seymour Island, Antarctica (Martin and Crame, 2006;Otero et al., 2013b) and from Eocene levels of the La Meseta Formation, in the same locality (Kriwet and Gaździcki, 2003).

Condrichthyan Paleobiogeography along the Magallanes Basin and Antarctica during the Eocene
The Antarcto-Pacific Eocene diversity of chondrichthyans includes elements with global distribution, as well as others so far restricted to the Southern Hemisphere.Based on the known record, four groups can be separated based on their known paleobiogeographic distribution: i. taxa exclusively restricted to latitudes near 65°S on the Antarctic Peninsula.This group includes the genera Bathyraja, Carcharhinus, Centrophorus, Cetorhinus, Stegostoma, Dalatias, Deania, Heptranchias, Lamna, Pristis, Pseudoginglymostoma, Scoliodon, and Chimaera (Kriwet, 2005;Reguero et al., 2013).These genera are also known in the Northern Hemisphere (Cappetta, 1987 and references therein); ii. a second tentative group comprise those taxa restricted to the Antarctic Peninsula and southernmost South America.So far, only the genera Anomotodon and Callorhinchus fall into this condition (Kriwet, 2005;Otero et al., 2013b), and it is possible that this situation could be a bias of the still incomplete austral record; iii. a third group comprise a larger diversity with widespread taxa along Antarctica and the Magallanes Basin during the Eocene.These are represented by the genera Carcharocles, Galeorhinus, Hexanchus, Ischyodus, Jaekelotodus, Macrorhizodus, Myliobatis, Odontaspis, Palaeohypotodus (known in the Paleocene of the Northern Hemisphere but recovered from upper Ypresian levels of Antarctica; see Reguero et al., 2013), Paraorthacodus (recovered from latest Ypresian levels of Antarctica; see Reguero et al., 2013), Pristiophorus, Squalus, Squatina and Striatolamia, while the genera Abdounia, Carcharias, Carcharoides, Megascyliorhinus, Notorhynchus, and Rhinoptera are to date restricted to southern South America during this lapse; iv.finally, a fourth group include the genera Otodus and Rhizoprionodon which are only known in the northern part of the Magallanes Region (lat.50°48').The distribution of all these taxa is summarized on Table 1.

Chronostratigraphic implications of the new records
The presence of Megascyliorhinus sp. in outcrops of the Loreto Formation at Río de Las Minas is interesting.Chondrichthyan records found in the locality were all recovered from a single level and they represent an assemblage of a well constrained age (Priabonian-Rupelian), while radioisotopic dates indicates a very well defined peak at 36.48±0.47Ma, constraining the age of the fossil-bearing level exclusively to the Priabonian (Otero et al., 2012).Lower levels of the same section include coal seams representing stagnant marshes with abundant vegetation, and the large-scale cross-bedding of some sandstone units that is typical of Gilbert-type bayhead deltas or migrating barrier bars (Le Roux et al., 2010), consistent with an estuarine depositional environment.On the other hand, regional previous records of Megascyliorhinus are only known in the northern part of the Magallanes Basin, being recovered from Bartonian-Priabonian beds of Sierra Baguales (Otero et al., 2013a).Since the teeth from Río de Las Minas do not differ from those from Sierra Baguales, we consider them as probably belonging to the very same species (still indeterminate).Also, due the late Eocene age of the material (radioisotopically controlled in Río de Las Minas), the previous identification of Megascyliorhinus cooperi in Sierra Baguales should be kept only to genus level, being possible that these teeth belong to a still poorly known species typicallt distributed in the Magallanes basin during the late Eocene.
On the other hand, the presence of Paraorthacodus sp. in Sierra Dorotea is very interesting.The genus is well-known in the Upper Cretaceous-Paleocene with a widespread distribution (Cappetta, 1987).An exception to this happens on Ypresian levels of the La Meseta Formation (Cucullaea I Allomember) where the genus Paraorthacodus have been recovered (A.Cione, personal communication in Reguero et al., 2013).Similar is the case of Palaeohypotodus rutoti, species restricted to the Thanetian of the Northern Hemisphere but also recorded in the Ypresian of the Cucullaea I member of La Meseta Formation (Long, 1992;Reguero et al., 2013).This documented extension of its chronostratigraphic range makes plausible their eventual occurrence in Bartonian-Priabonian levels of the Río Turbio exposed at Sierra Dorotea by extension of biochrons.However, an eventual reworking of the material from Ypresian levels and subsequent redepositation on Bartonian-Priabonian horizons of the Río Turbio cannot be ruled, pointing out the need of radioisotopic dates for support this still partial evidence.
The geologic setting of the marine basins in Magallanes and in the southeastern Pacific shows in both cases a general absence of Paleocene beds.Upper Cretaceous (Maastrichtian) marine sediments are commonly contacted with middle-to-late Eocene beds through an erosive unconformity.Such is the case between the the Quiriquina Formation and the Concepción Group (sensu Charrier et al., 2007) in central Chile (Stinnesbeck, 1986), as well as between the Dorotea Formation and the Man Aike-Río Turbio (and likely Loreto) formations in southernmost Chile (Katz, 1963;Charrier and Lahsen, 1969).The only possible Paleocene beds in the Magallanes Basin are represented as an exception in Cerro Dorotea Formation (Hünicken, 1955), which levels conformably overlies the Cerro Cazador (=Dorotea) Formation in outcrops near to Río Turbio, Argentina.Chondrichthyan records from the Quiriquina Basin include Maastrichtian assemblages (Suárez et al., 2003) and more recently, Paleogene assemblages including the genera Paraorthacodus and Palaeohypotodus (Muñoz-Ramírez et al., 2007;González et al., 2010;Groz and Palma-Heldt, 2013).Considering the Pacific Maastrichtian-Eocene discordance, is likely that these records have an Eocene age.Such situation adds support to the existence of a biochron extension for several classically Paleogene taxa but recorded from Eocene levels of the WBP.
The additional specimens here referred to Callorhinchus sp., and Rhinoptera sp., respectively represents their first Eocene occurrence in the Magallanes Basin.The new record of Pristiophorus sp.extends its contemporary occurrence in the southern margin of the basin.The new records of Striatolamia macrota (Agassiz), Carcharias sp., Rhinoptera sp., and indeterminate myliobatids in Bartonian-Priabonian beds of Sierra Dorotea allow complementing the distribution of these taxa between the previous records from Río de Las Minas and Sierra Baguales, respectively.

Conclusions
The studied material includes the first record of Megascyliorhinus sp., Pristiophorus sp., Callorhinchus sp., and Rhinoptera sp. in late Eocene levels of the Loreto Formation exposed at Río de Las Minas, Punta Arenas, southernmost Chile.The radioisotopic date and the relative age obtained from the previously recognized chondrichthyan assemblage confirm the Priabonian age of the fossil-bearing level, while the depositional environment and the taphonomic condition of most of the teeth preserving even their delicate cusplets, allow discarding the reworking of the material from older levels.Since M. cooperi have been considered as a typical Ypresian taxon, we propose an extension of its biochron along the southeastern Pacific at least until the Priabonian.The new records extend the number of chondrichthyan genera found in the upper section of the Loreto Formation from 12 to 16.
On the other hand, it is described the first occurrence of Striatolamia macrota, Palaeohypotodus rutoti, Carcharias sp., Squalus sp., Rhinoptera sp., Paraorthacodus sp. and indeterminate myliobatids in Bartonian-Priabonian levels of the Río Turbio Formation exposed at Sierra Dorotea, near Puerto Natales.Previously, the genus Paraorthacodus was considered as typically Paleocene, with the exception of confirmed records from Ypresian levels of La Meseta Formation in Seymour Island Antarctica, and likely Eocene records from central Chile.Considering the general absence of Paleocene marine strata along the Pacific and in the Magallanes Basin, this new record extends its biogeographical occurrence into southern South America indicating its presence in Bartonian-Priabonian levels, and suggesting an extension of its previous known Biochron (Upper Cretaceous-Ypresian), although, the re-working of the recovered specimen from older strata in Sierra Dorotea cannot be discarded.The additional taxa described from the latter locality complements their contemporary distribution along the Magallanes Basin, proving the existence of a faunal continuity along the latter, based on the austral-most records from Río de Las Minas and the northern-most records from Sierra Baguales.From the 16 genera recognized in the upper section of the Loreto Formation at Río de Las Minas, 13 of them are now recognized to be also present in Bartonian-Priabonian levels at Sierra Baguales.This faunal correlation supports that the deposition on each locality was nearly contemporary and occurred in a very similar environment.These results also indicate a noticeable degree of correlation between part of the Man Aike Formation at Sierra Baguales, the upper slopes of the Río Turbio Formation at Sierra Dorotea, and finally, the upper section of the Loreto Formation at Río de Las Minas.

FIG. 1 .
FIG. 1. Map indicating the two localities where the studied material was recovered.A. Río de Las Minas, Punta Arenas; B. Sierra Dorotea, Puerto Natales.

Palaeohypotodus Glickman, 1964 Palaeohypotodus rutoti (Winkler, 1874) Fig. 3H-I Type species
Río de Las Minas, Punta Arenas, southernmost Chile.Upper levels of the Loreto Formation, Late Eocene (Priabonian).Scale bar equals 10 mm.sharp and medially recurved lateral cusplets on each side of the crown; base of the crown overhanging the root and having profuse vertical folds; root with well-separated branches and lingual bulk.

Order Synechodontiformes Duffin and Ward, 1993 Family Palaeospinacidae Regan, 1906 Genus Paraorthacodus Glikman, 1958
Teeth axially broader than dorsoventrally high, with short, triangular but slender crown having two or three triangular lateral cusplets; both lingual and labial surfaces of the crown bear striations extended between from tip to base; the root is distinctive, with a flat base having several parallel nutritious grooves that extend over the lingual face; presence of a lingual bulk on the root.
Remarks: The genus Paraorthacodus have been recorded in the Upper Cretaceous of Argentina
Regionally, identical teeth have been recovered from lower levels of the Man Aike (=Río Baguales) Formation in Sierra Baguales, north of Magallanes Region, being firstly referred to M. cooperi by Otero et al. (2013a) due its narrow morphologic affinities.Since this species was originally recovered from Ypresian beds of England