María E. Pérez

A new rodent (Cavioidea, Hystricognathi) from the middle Miocene of Patagonia, mandibular homologies, and the origin of the crown group Cavioidea sensu stricto

ABSTRACT Cavioidea sensu stricto groups three traditionally recognized families that are characterized by hypsodont, double-heart-shaped cheek teeth and moderate hystricognathy: Eocardiidae, Caviidae, and Hydrochoeridae. Eocardiidae was erected to include a diverse assemblage of extinct and plesiomorphic taxa, whereas Caviidae and Hydrochoeridae (the crown group of Cavioidea) include the lineages with extant representatives (cuyes, maras, and capybaras). A new genus and species of Cavioidea sensu stricto, Guiomys unica, is described here from the middle Miocene of west central Patagonia (Argentina). The new taxon is known from mandibular and maxillary fragments with molars, and isolated cheek teeth. A phylogenetic analysis of Cavioidea sensu stricto shows G. unica as the sister taxon of the clade formed by the crown group of Cavioidea sensu stricto (‘medialis series’). The new species displays characters states intermediate between eocardiids and the ‘medialis series.’ The most outstanding character of Guiomys unica is the autapomorphic position of the notch for the insertion of the masseter medialis pars infraorbitalis muscle, isolated from both the masseteric and horizontal crests. This notch is located at the anterior end of the masseteric crest in eocardiids and represents the plesiomorphic state for Cavioidea sensu stricto. In caviids and hydrochoerids, the notch is located at the anterior end of the horizontal crest, the derived state for this character. G. unica allows reinterpretation of the homologies of the mandibular crests in basal cavioids and clarifies the evolutionary origins of crown-group cavioids (Caviidae + Hydrochoeridae).

Major radiations in the evolution of Caviid rodents: reconciling fossils, ghost lineages, and relaxed molecular clocks.

Background Caviidae is a diverse group of caviomorph rodents that is broadly distributed in South America and is divided into three highly divergent extant lineages: Caviinae (cavies), Dolichotinae (maras), and Hydrochoerinae (capybaras). The fossil record of Caviidae is only abundant and diverse since the late Miocene. Caviids belongs to Cavioidea sensu stricto (Cavioidea s.s.) that also includes a diverse assemblage of extinct taxa recorded from the late Oligocene to the middle Miocene of South America (“eocardiids”). Results A phylogenetic analysis combining morphological and molecular data is presented here, evaluating the time of diversification of selected nodes based on the calibration of phylogenetic trees with fossil taxa and the use of relaxed molecular clocks. This analysis reveals three major phases of diversification in the evolutionary history of Cavioidea s.s. The first two phases involve two successive radiations of extinct lineages that occurred during the late Oligocene and the early Miocene. The third phase consists of the diversification of Caviidae. The initial split of caviids is dated as middle Miocene by the fossil record. This date falls within the 95% higher probability distribution estimated by the relaxed Bayesian molecular clock, although the mean age estimate ages are 3.5 to 7 Myr older. The initial split of caviids is followed by an obscure period of poor fossil record (refered here as the Mayoan gap) and then by the appearance of highly differentiated modern lineages of caviids, which evidentially occurred at the late Miocene as indicated by both the fossil record and molecular clock estimates. Conclusions The integrated approach used here allowed us identifying the agreements and discrepancies of the fossil record and molecular clock estimates on the timing of the major events in cavioid evolution, revealing evolutionary patterns that would not have been possible to gather using only molecular or paleontological data alone.

A New Extinct Genus of Cavioidea (Rodentia, Hystricognathi) from the Miocene of Patagonia (Argentina) and the Evolution of Cavioid Mandibular Morphology

The family Caviidae is represented in modern faunas by cavies and maras, whereas the family Hydrochoeridae is represented by capybaras. The evolutionary origin of these families has been related to a diversity of plesiomorphic fossil forms (recorded from the late Oligocene up to the middle Miocene) traditionally grouped in the family “Eocardiidae”. These fossil forms were included, together with Caviidae and Hydrochoeridae, within the Cavioidea s.s. (sensu stricto), because they share high crowned cheek teeth, double-hearted occlusal surface, short lower incisors, and moderate hystricognathy. Within Cavioidea s.s., caviids and hydrochoerids were interpreted as forming its crown group, because they have unique craniomandibular and dental features. In this contribution, a new taxon of Cavioidea s.s. from the middle Miocene of central Patagonia, Argentina, is described, and its phylogenetic position is determined on the basis of a morphological cladistic analysis in which “eocardiids” were included. The study permits the understanding of the sequence of appearance of characters that originated the highly divergent morphology of crown-group cavioids. The analysis of the sequence of appearance of the characters that traditionally diagnosed the crown group indicates that these changes did not occur at the same time. On the contrary, many of these features seem to have appeared at different nodes of the evolutionary history of Cavioidea s.s. The remarkably derived morphology of modern cavioids is the result of a stepwise appearance of a mosaic of evolutionary innovations that originated gradually along the history of Cavioidea during the late-middle Miocene.

New rodents (Mammalia) from the late Oligocene of Cabeza Blanca (Chubut) and the first rodent radiation in Patagonia

Caviomorph rodents, the New World Hystricognathi, are one of the most characteristic groups of South American mammals. Although they have been in the continent at least since the middle Eocene, those of the Deseadan Land mammal Age (early–late Oligocene) are the best source to understanding their early history due of their good record, large geographic distribution and good temporal calibration of many of the local faunas. Here, we describe the following new taxa from the classical locality of Cabeza Blanca: Octodontoidea Acaremyidae Galileomys baiosn. sp., Octodontoidea incertae sedis Ethelomys loomisin. gen.,n. comb., Acarechimys leucotheaen. sp., Protacaremys? adilosn. sp., Chinchilloidea incertae sedis Loncolicu tretosn. gen., n. sp., Incamys menniorumn. sp., Caviomorpha incertae sedis Llitun notucan. gen., n. sp., Leucokephalos zeffiaen. gen., n. sp. and Cephalomyidae Cephalomys ceciaen. sp. The DP4 of an ‘eocardiid’, Asteromys punctus? is described for the first time. These new taxa allow us to reinterpret the relationships of some of the previously known Deseadan species and genera. They show a great early diversification at least for extra Andean Patagonia, involving at least three of the main caviomorph lineages: octodontoids, chinchilloids and cavioids.

The putative cardiomyines (Rodentia, Cavioidea) of the middle Miocene of Patagonia (Argentina) and the differentiation of the Family Hydrochoeridae

The putative cardiomyines (Rodentia, Cavioidea) of the middle Miocene of Patagonia (Argentina) and the differentiation of the Family Hydrochoeridae Maria G. Vucetich a & Maria E. Perez a b a Departamento Cientifico Paleontologia de Vertebrados, Museo de La Plata, Paseo del Bosque s/n B1900FWA, La Plata, Buenos Aires, Argentina b Museo Paleontologico “Egidio Feruglio,” Av. Fontana Nro. 140, U9100GYO, Trelew, Chubut, Argentina

The first Eocardiidae (Rodentia) in the Colhuehuapian (early Miocene) of Bryn Gwyn (northern Chubut, Argentina) and the early evolution of the peculiar cavioid rodents

ABSTRACT Caviidae and Hydrochoeridae (extant Cavioidea s.s.), probably the most peculiar among rodents, are characterized by their evergrowing double-heart-shaped cheekteeth. They have classically been rooted in Eocardiidae, which ranges from Deseadan to ‘Colloncuran’ (late Oligocene-middle Miocene) in Patagonia, although in the Deseadan and Colhuehuapian (early Miocene) remains are very scanty. For the Colhuehuapian, only one species coming from the southern cliff of the Colhué Huapi Lake (Gran Barranca, Chubut, Argentina) was known so far. In this paper, the first Colhuehuapian eocardiids from outside Gran Barranca are reported: Luantus minor, sp. nov., and Chubutomys leucoreios, sp. nov. They are represented by two fragmentary mandibles and a few isolated cheek teeth, from the Trelew Member of the Sarmiento Formation at Bryn Gwyn, lower valley of the Chubut River, Chubut. The new species enlarge the knowledge of eocardiid diversity, and reinforce the hypothesis of a basal dichotomy for the group. L. minor represents one of the smallest species of the series Asteromys + Luantus + Phanomys + Eocardia, which likely gave rise to modern Cavioidea s.s. C. leucoreios pertains to a group of species with precocious hypsodonty and apparently low diversity, but without modern descendant.

A revision of the fossil genus Phanomys Ameghino, 1887 (Rodentia, Hystricognathi, Cavioidea) from the early Miocene of Patagonia (Argentina) and the acquisition of euhypsodonty in Cavioidea sensu stricto

Cavioidea sensu stricto (Cavioidea s.s.) is one of the most divergent lineages within the South American Hystricognathi, and is currently represented by cavies, maras (Caviidae), and capybaras (Hydrochoeridae). Caviids and hydrochoerids have been interpreted as forming the crown group, whereas the stem group of Cavioidea s.s. is formed by “Eocardiidae”, a paraphyletic group recorded in the late Oligocene to middle Miocene, mainly in Patagonia. One of the most interesting features of Cavioidea s.s. is the record of evolution of hypsodonty, which develops relatively slowly compared to other groups of caviomorphs, enabling this process to be followed in the fossil record. Phanomys is recorded in Patagonia during the late early Miocene, and since its description this genus has been considered close to euhypsodont genera. The objective of this paper is to: (1) report new material of Phanomys; (2) re-describe the two species of the genus; (3) determine the phylogenetic position of Phanomys among Cavioidea s.s. by morphological cladistic analysis; and (4) explore the sequence of appearance of characters related to the origin of euhypsodonty. The new materials assigned to Phanomys mixtus are the first mandibular fragments and palate known, yielding valuable morphological, ontogenetic, and phylogenetic information. Phanomysvetulus is recognized as a valid species, although better material is needed for a more robust definition. The phylogenetic analysis shows that Phanomys is the sister group of euhypsodont Cavioidea s.s. The evolutionary history of Cavioidea s.s. demonstrates that character states previously thought to correlate with the degree of hypsodonty (e.g. absence of fossettes/ids) do not all appear at the same time during the evolution of the group. Although the evolutionary trend in Cavioidea s.s. shows progressively increasing hypsodonty, the morphological changes inferred from this phylogenetic analysis indicate that hypsodonty and other character states were temporally decoupled during the evolution of the group during the Oligocene and early Miocene.KurzfassungDie Cavioidea sensu stricto repräsentieren eine der divergierenden Linien innerhalb der su?damerikanischen Hystricognathi und sind zurzeit durch Meerschweinchen, Maras (Caviidae), und Wasserschweine vertreten. Caviiden und Hydrochoeriden wurden als die Kronen-Gruppe der Cavioidea s.s. interpretiert, während die “Eocardiidae”, eine paraphyletische Gruppe aus dem späten Oligozän bis mittleren Miozän aus Patagonien, als Stamm-Gruppe dargestellt wurden. Eine der interessantesten Merkmalsentwicklungen von Cavioidea s.s. ist die Evolution der Hypsodontie, die sich im Vergleich zu anderen Gruppen von Caviomorphen relativ langsam entwickelte; dies ermöglicht es, diesen Prozess bei Fossilien zu erkennen. Phanomys ist aus dem Ende des frühesten Miozän von Patagonien bekannt, und seit ihrer Erstbeschreibung wurde diese Gattung in die Nähe von euhypsodonten Taxa gestellt. Das Ziel dieses Beitrags ist es, neues Material von Phanomys vorzustellen, die beiden Arten dieser Gattung neu zu beschreiben, ihre phylogenetische Stellung innerhalb der Caviodea s.s. durch eine kladistische Analyse mit morphologischen Merkmalen zu untersuchen und die Sequenz des Merkmalserwerbes von mit Euhypsodontie verbundener Merkmale zu untersuchen. Bei dem neuen Material handelt es sich um den ersten Rest des Unterkiefers und des Gaumens von Phanomys mixtus, und diese Reste ergeben wichtige morphologische, ontogenetische und auch phylogenetische Informationen. Bei Phanomys vetulus handelt sich um eine gültige Art, obwohl besseres Material für eine befriedigende Definition nötig ist. Die phylogenetische Analyse zeigt, dass Phanomys die Schwestergruppe der euhypsodonten Cavioidea s.s. darstellt. Die Evolution der Cavioidea s.s. zeigt, dass die Merkmale, die bisher in direktem Zusammenhang mit dem Grad der Hypsodontie gestellt wurden (z.B. Abwesenheit von fossettes/ids) nicht zur gleichen Zeit während der Entwicklung der Gruppe erscheinen. Obwohl die evolutionäre Entwicklung bei den Caviodea s.s. einen Trend zu zunehmender Hypsodontie aufweist, zeigen die morphologischen Veränderungen, basierend auf dieser phylogenetischen Hypothese, dass diese Merkmale und der Erwerb der Hypsodenties in der Evolution der Gruppe im Oligozän und frühen Miozän zeitlich entkoppelt waren.

A new acaremyid rodent (Caviomorpha, Octodontoidea) from Scarritt Pocket, Deseadan (late Oligocene) of Patagonia (Argentina)

ABSTRACT Octodontoidea is the most diverse caviomorph clade presently represented in South America by Octodontidae, Echimyidae, and Abrocomidae. Some evidence suggests that in the past they were taxonomically even more diverse, including several independent lineages with no modern representatives, sometimes considered as families. One of them is Acaremyidae, known until now from the Colhuehuapian—Colloncuran (early to early—middle Miocene) of Patagonia. Here we describe a new octodontoid rodent from the Deseadan (late Oligocene) of Scarritt Pocket (Patagonia): Changquin woodi, gen. et sp. nov. Cladistic analysis indicates that the new species is an acaremyid related to the Santacrucian (early Miocene) Sciamys. Acaremyidae was recovered as a monophyletic group. C. woodi, gen. et sp. nov., the oldest representative of Acaremyidae, extends the family biochron back to the late Oligocene, and indicates that acaremyids differentiated before the Deseadan. C. woodi represents the first Deseadan octodontoid displaying protohypsodont cheek teeth, showing that the Deseadan was a period of important diversification for octodontoids, as it was for the cavioids. C. woodi adds a new element to the faunal differences observed between Patagonian and Bolivian Deseadan faunas. A new U-Pb laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) date (27.17 ± 0.54 Ma) for Scarritt Pocket is provided.

Mandibular remains of Procardiomys martinoi Pascual, 1961 (Hystricognathi, Cavioidea) from the Arroyo Chasicó Formation (early late Miocene) of Argentina: anatomy and the phylogenetic position of the genus within Caviidae

Hydrochoerinae is a clade of caviomorph rodents broadly distributed in South America, which includes the maximum body size recorded among extant rodent taxa. The most basal forms of this group are an assemblage of small to medium body size extinct taxa with a plesiomorphic dentition, traditionally clustered in the group cardiomyines. One of the oldest known cardiomyine is Procardiomys martinoi (Chasicoan South American Land Mammal Age SALMA; early late Miocene), which was known only from the holotype, a fragmentary palate with the left and right molar series. New mandibular remains from the Arroyo Chasicó Formation (Chasicoan SALMA) are described and identified here as belonging to P. martinoi because they share a unique combination of characters (as well matching in size) with the upper dentition of the holotype. These materials help in critically reviewing the taxonomic identification of the mandibular remains previously assigned to Procardiomys and allow testing the phylogenetic affinities of this taxon within Caviidae. P. martinoi is depicted as one of the most basal forms of Hydrochoerinae, placed basally on the lineage leading to extant capybaras after the split between the common ancestor of Kerodon and Hydrochoerus. http://zoobank.org/F60356E0-CB8E-48C2-BF86-429E347A9579

The Taxonomic Status of the Pliocene Capybaras (Rodentia) Phugatherium Ameghino and Chapalmatherium Ameghino

Abstract. Living capybaras are a unique group of rodents. They have ever-growing cheek teeth with a complicated occlusal morphology that changes even after birth. Concerning fossil capybaras this morphological change, associated with increasing size, led to regard them as taxonomically highly diverse, including small species with simple dental morphology, and large species with complicated cheek teeth, considered as primitive and derived, respectively. Recently, it was proposed that the different morphs found in each locality actually represent individuals of different ontogenetic stages of a population or successive populations, rather than a multiplicity of coeval species in different stages of evolution. For the Pliocene, the richest locality for capybaras is Farola Monte Hermoso on the southern coast of Buenos Aires Province. This locality yielded four nominal species of capybaras, three of them are a small morph (Phugatherium cataclisticum Ameghino, “Anchimysops villalobosi” Kraglievich, “A. ultra” Kraglievich) and the other a large one (“Chapalmatherium perturbidum” (Ameghino)). In this paper we propose that they represent juveniles and adults of one species, P. cataclisticum. In order to evaluate the phylogenetic position of Phugatherium within Cavioidea a cladistic analysis was performed modifying a previously published combined matrix of morphology and DNA sequences. Phugatherium forms a monophyletic group and is the sister group of modern capybaras. Within Phugatherium the most basal species is P. novum Ameghino, whereas the type species P. cataclisticum is the sister group of P. saavedrai Hoffstetter, Villarroel and Rodrigo.