Middle Miocene Rodents from Quebrada Honda, Bolivia

Home , Caviinae, Cerro Azul Formation, Chasicoan, Colhuehuapian, Colloncuran, Deseadan

MIDDLE MIOCENE RODENTS FROM QUEBRADA HONDA, BOLIVIA

JENNIFER M. H. CHICK

Submitted in partial fulfillment of the requirements for the degree of

Master of Science

Thesis Adviser: Dr. Darin Croft

Department of Biology

CASE WESTERN RESERVE UNIVERSITY

May, 2009 CASE WESTERN RESERVE UNIVERSITY

SCHOOL OF GRADUATE STUDIES

We hereby approve the thesis/dissertation of

______

candidate for the ______degree *.

(signed)______(chair of the committee)

______

(date) ______

*We also certify that written approval has been obtained for any proprietary material contained therein. Table of Contents

List of Tables ...... ii

List of Figures...... iii

Abstract...... iv

Introduction...... 1

Materials and Methods...... 7

Systematic Paleontology...... 10

cf. Neoreomys huilensis Fields, 1957 ...... 12

Orthomyctera rigens Ameghino, 1889 ...... 20

cf. Prodolichotis mendocina, Rovereto 1914 ...... 24

Prodolichotis sp. nov...... 25

Chasichimys sp. nov...... 30

Gen. et sp. nov...... 34

Prolagostomus profluens Ameghino, 1887 ...... 39

Prolagostomus amplus Ameghino, 1889...... 43 cf. Prolagostomus divisus Ameghino, 1887 ...... 44

Prolagostomus sp. nov...... 45

Discussion...... 47

Paleoecological Implications ...... 47

Evolutionary Trends...... 50

Appendices...... 54

References...... 59

i List of Tables

Table

1. Summary of tooth measurements from Quebrada Honda Orthomyctera rigens specimens...... 21

2. Summary of tooth measurements from Chasichimys sp. nov. specimens ...... 31

3. Summary of tooth measurements from Prolagostomus profluens specimens...... 40

4. Summary of tooth measurements from Prolagostomus amplus specimens ...... 43

ii List of Figures

Figure

1. Miocene South American Land Mammal “Ages” (SALMAs)...... 4

2. Map of South America with Miocene localities ...... 5

3. Occlusal structure terminology ...... 9

4. Right mandible of cf. Neoreomys huilensis ...... 13

5. Right isolated molars from dasyproctid species ...... 15

6. Caviid genera from Quebrada Honda ...... 17

7. Right lower dentition of caviid and eocardiid species ...... 19

8. Right upper dentition for Orthomyctera rigens and O. andina ...... 22

9. Comparison of right lower dentition for cf. Prodolichotis mendocina from

Quebrada Honda (UF 236854) and P. mendocina (MLP 28-X-11-477)...... 24

10. Prodolichotis sp. nov...... 26

11. Comparison of lower right dentition of Prodolichotis sp. nov. and P. pridiana ...... 27

12. Right mandible of Chasichimys sp. nov...... 29

13. Right lower dentition of Chasichimys sp. nov. and other Chasichimys species...... 33

14. Right mandible of a new adelphomyine from Quebrada Honda ...... 34

15. Right lower dentition of adelphomyines ...... 36

16. Prolagostomus specimens from Quebrada Honda ...... 38

17. Right upper dentition of lagostomines ...... 42

18. Left lower dentition of lagostomines ...... 46

iii Middle Miocene Rodents from Quebrada Honda, Bolivia

Abstract

JENNIFER M. H. CHICK

Despite South America’s rich fossil mammal record, relatively little work has focused on middle-latitude faunas of Miocene age; most current understanding of South

American mammals during the middle Miocene derives from the extremes of the continent. Quebrada Honda (Laventan SALMA) in southern Bolivia is intermediate in latitude between these two regions, partly filling this large geographic gap. New collections from Quebrada Honda in 2007 facilitated this analysis of its rodents. The most abundant of these rodents are Prolagostomus and caviids. The octodontid Chasichimys from Quebrada Honda represent the earliest and northernmost occurrences of the genus.

A new genus and species of adelphomyine echimyid is also present, represented by a single specimen with trilophodont, plate-like teeth. The abundance and diversity of rodents with high-crowned teeth suggests that Quebrada Honda was an open, grassland environment with fewer forests.

iv Introduction:

Paleontologists have been intrigued by South America’s fossil record for the past

several hundred years; this is largely due to the continent’s unique geologic history. For

much of the past 65 million year, including most of the Cenozoic era, South America was an island continent, drifting in “splendid isolation” from other land masses (Simpson,

1980; MacFadden and Wolff, 1981). Consequently, fossils from this large time interval, and from the Tertiary period specifically, have yielded valuable information on South

American endemism (Huchon and Douzery, 2001).

Mammalian evolution on the continent is typically split into three phases or strata, each with distinct faunal compositions. The first phase of mammalian evolution in South

America occurred between ~65 and 40 mya, during the Paleocene and much of the

Eocene (Flynn and Wyss, 1998). During this first phase of evolution, tropical and temperate forests dominated the continent; marsupials, xenarthrans, notoungulates, and litopterns proliferated (Huchon and Douzery, 2001). During the second phase, which commenced near the Eocene-Oligocene boundary (40-21mya), platyrrhine primates and caviomorph rodents invaded the continent. This phase was also accompanied by a global cooling event and the replacement of tropical and temperate forests by grasslands

(MacFadden, 2006). The third phase of South American mammalian evolution is marked by the Great Faunal Interchange. This event occurred during the Miocene-Pliocene, when the Panamanian land bridge enabled the immigration of North American taxa into South

America. This intermingling of immigrant and native faunas resulted in the modern

faunal assemblage we see today.

1 In addition to the continent’s interesting geologic past and high degree of endemism, South America is well-known for the quality of its fossil record (Patterson and

Pascual, 1968). Although the majority of fossils are from Argentina, recent efforts have been made to increase the geological sampling of the continent (Croft, 2007). Information

gathered from fossils in Argentina and Colombia, and more recently from Ecuador,

Brazil, Peru, and Uruguay enabled researchers to construct a sequence of provincial

“ages” (Simpson, 1940) unique to South America. These South American Land Mammal

“Ages” (SALMAs) reflect changing faunal assemblages throughout the Cenozoic and

allow paleontologists to correlate the chronologic age of fossil faunas from different

localities on the continent (Flynn and Wyss, 1998). SALMAs are often named after type

localities, and although they are informal biochronologic units, not based on formal

geochronologic units (Flynn and Swisher, 1995), they continue to aid the understanding

of faunal distribution patterns. Additionally, recent radioisotopic and magnetochronologic

analyses have enabled paleontologists to more narrowly constrain many SALMAs

geochronologically, providing more accurate ages for them (Flynn and Swisher, 1995).

Although the most recent SALMA sequence still contains significant temporal “gaps,”

efforts are continuously made to fill them in; improvements in geochronologic studies

(including the integration of radioisotopic dating with magnetic polarity stratigraphy),

combined with the updated faunal lists and the discovery of new faunal sequences will

likely help fill in the temporal hiatuses.

There is much we still seek to learn about mammalian evolution during the long

span of South America’s isolation from other continents, but the Miocene epoch (23.8-

5.3 mya) in particular is of compelling interest for numerous reasons. Not only did

2 monkeys and rodents diversify on the island continent by the early part of the epoch, but the ancient mammalian lineages also modernized from their archaic clades (Flynn and

Wyss, 1998). The late Miocene faunas experienced selective pressures such as competition from invading North American taxa as well as pressures due to a changing global environment. By the late Tertiary, the majority of mammal orders had evolved members with high-crowned (hypsodont) or ever-growing (hypselodont) teeth; this adaptation is correlated with a changed in diet from primarily C3 trees and shrubs to C4 grasses as grasslands spread in South America (MacFadden et al., 1994). The beginning of the Andean uplift during the Miocene also created new, isolated biomes ranging from tropical rain forests to montane grasslands and shrublands, each of which resulted in unique ecological communities.

Nine SALMAs span the Miocene epoch, beginning with the Colhuehuapian and ending with the Montehermosan (Fig. 1). However, much of our knowledge of South

American mammalian evolution during the Miocene derives from the extremes of the continent. Numerous early and late Miocene faunas are known from Argentina (≥ 40º S); specifically, the early Miocene Santacrucian fauna and the late Miocene Montehermosan fauna have been extensively studied by paleontologists of the late nineteenth and early twentieth centuries (See Ameghino, 1887; Scott, 1905; Kraglievich, 1930). The middle

Miocene fauna of La Venta, Colombia (5º N) is also well-known (Kay et al., 1997), but it is the only Laventan fauna that has been described in detail. The fauna is temporally well- constrained to 13.5-11.8 ma (Madden et al., 1997). Other well-sampled middle-late

Miocene faunas are slightly older or slightly younger than La Venta. They include

Collón-Curá (slightly older) and Arroyo Chasicó (slightly younger). These faunas vary in

3 age and geographic location; more middle latitude localities need to be studied in detail to increase our knowledge of mammalian evolution during the Miocene. Many studies have only been preliminary.

Figure 1. Miocene South American Land Mammal “Ages” (SALMAs). The age of Quebrada Honda – the Laventan SALMA – is highlighted. Modified from Croft, 2007.

Middle latitude localities in Bolivia have been studied, yielding valuable information pertaining to mammalian evolution and patterns of distribution. For example,

Salla, in northeastern Bolivia possesses a rich mammalian assemblage; however, radioisotopic dating has contrained the Salla beds to ~25-26.5 ma and it has been correlated with the late Oligocene Deseadan SALMA (MacFadden et al., 1985).

Similarly, Tarija and Ñuapua in southern Bolivia have yielded a number of large

4 mammals, but these localities are Pleistocene in age (Marshall et al., 1984; MacFadden et al., 1994). Another middle latitude locality, the early Miocene Chucal formation of northern Chile, has been studied as well (Croft et al., 2004). While these localities continue to be useful to our understanding of South American mammalian evolution at middle latitudes, they cannot give significant insight into middle Miocene mammalian evolution (Fig. 2).

Figure 2. Map of South America with Miocene localities. Bolivia is highlighted. Modified from Croft et al., 2008.

5 The description of a fossil-bearing site at Quebrada Honda in southern Bolivia by

Hoffstetter (1977) is important because the locality helps to fill in both the temporal and geographic gap previously mentioned. It is located at an intermediate latitude (21º S) between other well-sampled Miocene localities. The fauna is Laventan, and has an extrapolated age of 12.7-13.0 ma; its age has been well-constrained with the aid of numerous paleomagnetic samples correlated with the Magnetic Polarity Time Scale. The site also contains thick stratigraphic sections and numerous datable ash layers

(MacFadden and Wolff, 1981). The Quebrada Honda sediments were deposited in a valley that resulted from uplift of the Cordillera Oriental. The Quebrada Honda and Río

Rosario sites offer large exposures of the geologic section (MacFadden and Wolff, 1981).

The unnamed formation can be divided into three sections: a basal section consisting primarily of reddish-brown silty clays, silts, and sands; a middle section with silty clays and calcareous zones; and a third, rarely exposed section of various silts, clays, sands, gravels, and conglomerates. Units from the first, basal section has yielded many of the fossils known from Quebrada Honda.

As previously mentioned, Quebrada Honda is contemporaneous with La Venta,

Colombia (Croft, 2007). It was originally referred to the “Friasian” SALMA (sensu

Ameghino, 1906). This SALMA has been problematic to paleontologists. “Friasian” faunas come from various localities, and paleontologists debated as to whether their associated biochronologic units were distinct, overlapping, or equivalent (Flynn and

Swisher, 1995) Years of resampling has led to the division of the “Friasian” into

SALMAs younger than Santacrucian and older than Chasicoan (Croft, 2007). Today, the

Friasian refers only to the time period of the type locality, Río Frías (Río Cisnes).

6 Numerous explorations of Quebrada Honda fossils have facilitated preliminary faunal lists (Hofstetter, 1977; MacFadden and Wolff, 1981). More recently, an effort has been

made not only to identify and classify Quebrada Honda taxa, but also to compare them to

other middle Miocene faunas (Croft, 2007). However, these studies focused on large

mammals. The purpose of this research is to describe and identify members an important

and diverse group of mammals – the rodents. Such information is needed because it will

provide a clearer, more complete picture of patterns of mammalian evolution in South

America during the middle Miocene, particularly at middle latitudes.

Materials and Methods:

Fossils collected from the Quebrada Honda site in southern Bolivia in May 2007

were used for this study. They are housed in the Universidad Autónoma Tomás Frías in

Potosí, Bolivia. Dental measurements were made using digital calipers and measured to

the nearest 0.1 mm. Quebrada Honda rodents collected from the 1978 exploration are

also included in this study. This 1978 summer exploration sampled fossil vertebrates and

collected geological data from Quebrada Honda (plus Tarija and Ñuapua); this lead to a

preliminary publication of the Quebrada Honda fauna (MacFadden and Wolff, 1981).

The Quebrada Honda collection also includes specimens collected from nearby Río

Rosario; the specimens from the 1978 study are housed at the Florida Museum of Natural

History in Gainesville, Florida. Specimens from the following institutions were studied

firsthand to aid rodent identification: the Museo Nacional de Historia Natural in La Paz,

Bolivia; the Museo Argentino de Ciencias Naturales in Buenos Aires, Argentina; and the

7 Princeton University (collection now at Yale University in New Haven, Connecticut).

Published sources were also used as supplemental resources.

Terminology: Nomenclature of occlusal structures follows Wood and Patterson (1959) and Patterson and Wood (1982), except in dasyproctids, where nomenclature follows

Kramarz (1998). Uppercase letters denote upper teeth and lowercase letters denote lower teeth. Rodents possess upper and lower pairs of incisors (I/i), upper and lower pairs of premolars (P4/p4), and upper and lower pairs of three molars (M1-3/m1-3). Deciduous premolars (DP4/dp4) are maintained through adulthood in some taxa. The suffix –id is used to denote structures of lower dentition. A flexus/flexid is considered a valley structure which remains open along the side of the tooth crown. A fossette/fossettid is a flexus/flexid that becomes isolated (closed off from the side of the tooth crown) due to wear (Fig. 3). Hypsodont dentition is characterized by high-crowned teeth, as opposed to brachydont dentition, which is low-crowned. Hypselodonty refers to ever-growing, rootless or open-rooted dentition. Hypsodonty indices follow Verzi (1999), and were calculated by dividing the m1 height by the m1 anterobuccal-posteriorlingual length.

Figure 3. Occlusal structure terminology. Nomenclature is given for lower (A) and upper (B) dentition of caviids, lower (C) and upper (D) dentition of chinchillids, and lower dentition of adelphomyines (E), dasyproctids (F), and octodontids (G). Anterior is to the right. Drawings are not to scale.

Institutional abbreviations: DC-BO, specimens from Quebrada Honda 2007 exploration,

Universidad Autónoma Tomás Frías in Potosí, Bolivia (not catalogued); UF, Florida

Museum of Natural History, Gainesville, Florida; MACN, Museo Argentino de Ciencias

Naturales in Buenos Aires, Argentina; MLP, Museo Nacional de Historia Natural, La Paz,

Bolivia; YPM-PU, Princeton University (now housed at Yale University, New Haven,

Connecticut); UCMP, University of California Museum of Paleontology.

9 Results:

SYSTEMATIC PALEONTOLOGY

Class MAMMALIA Linnaeus, 1758

Order RODENTIA Bowdich, 1821

Suborder HYSTRICOGNATHI Wood and Patterson, 1955

Infraorder CAVIOMORPHA Wood and Patterson, 1955

Comments—Caviomorph rodents are New World members of the

suborder Hystricognathi, which differ from other rodents in numerous bone, skull, and

molecular characters (Huchon and Douzery, 2001). In South America, they date back to

the early Oligocene Tinguirirican SALMA of Chile, when two specimen, a dasyproctid or

dinomyid and a chinchillid were discovered (Wyss et al., 1993). However, rodents are

not found in abundance in the fossil record until the late Oligocene Deseadan SALMA of

Bolivia and Patagonia. Many of the most primitive members of South American rodent

families can be traced to the Deseadan with a fair degree of certainty (Vucetich et al.,

1999). The majority of rodent families are believed to have radiated and diversified around the late Oligocene or early Miocene. At least 160 living and extinct rodent genera

have been identified from South America, and those genera belong to 13 extant and four extinct families (Vucetich et al., 1999). These families belong to four superfamilies

(although some systematic and molecular data conflict as to which families belong

10 where): Erethizontoidea, Cavioidea, Chinchilloidea, and Octodontoidea (McKenna and

Bell, 1997; Huchon and Douzery, 2001).

Superfamily CAVIOIDEA Fischer de Waldheim, 1817

Family DASYPROCTIDAE Gray, 1825

Comments—McKenna and Bell (1997) recognize the Dasyproctinae as a

subfamily of Agoutidae. More recently, however, researchers have treated these two

groups in different ways. The Agoutinae is sometimes considered to be a subfamily of the

Dasyproctidae. Alternatively, many taxonomists have recognized Dasyproctidae and

Agoutidae as separate families (Cabrera, 1961; Woods, 1984), and I will treat them as such.

Genus Neoreomys Ameghino, 1887

Type Species—Neoreomys australis Ameghino, 1887

Included Species—the type, N. huilensis, N. pinturensis

Comments—Although Ameghino originally named nine Santacrucian species of

Neoreomys, others have concluded that the differences in morphology and size between

those species are due to ontogenetic variation (Kramarz, 2006); the type species named

by Ameghino is considered to be the one true species from the Santa Cruz formation

(Scott, 1905). Walton (1997) referred to the Laventan species as “N.” huilensis stating

that the differences between it and N. australis, such as differences in incisor widths and

11 premolar occlusal patterns, may justify a change in genus, but no new generic assignment

has been published thus far.

Differential Diagnosis—Neoreomys, like other dasyproctids, has high-crowned,

lophate cheek teeth with thick enamel (Walton, 1997). It differs from many dasyproctids

in its tetralophodont teeth. Neoreomys is smaller than Megastus. Neoreomys is similar to

Alloiomys, but Alloiomys possesses more rounded teeth with less persistent buccal flexids,

particularly the metaflexid. Alloiomys also lacks anterofossettids on lower molars.

Neoreomys differs from Australoprocta and the small dinomyid “Scleromys” in that the

metaflexid does not join the hypoflexid. Australoprocta also has a larger anterofossettid

than Neoreomys (Kramarz, 2008), and the buccal flexids of “Scleromys” extend farther lingually than those of Neoreomys. Cephalomys differs from Neoreomys in its persistent

mesoflexid (Kramarz, 2005), and the hypoflexid of Neoreomys is less penetrating and

more posteriorly displaced than in Cephalomys.

Age and Distribution— Santa Cruz Formation, southern Argentina, early

Miocene age, Santacrucian SALMA (Kramarz, 2002); Pinturas Formation, southern

Argentina, early Miocene age, Santacrucian SALMA (Kramarz, 2002); Collón-Curá

Formation, northwestern Argentina, middle Miocene age, Colloncuran SALMA

(Vucetich et al., 1993); La Victoria Formation, Colombia, middle Miocene age, Laventan

SALMA (Walton, 1996), unnamed formation of Quebrada Honda, southern Bolivia, middle Miocene age, Laventan SALMA (Croft, 2007).

cf. Neoreomys huilensis Fields, 1957

12 Holotype—UCMP 37973, left mandible with p4-m3 and base of i1

Referred Material—UF 26915, right mandible with m1

Locality—Unit 2 of Section 1 of Quebrada Honda

Figure 4. Right mandible of cf. Neoreomys huilensis (UF 26915) in occlusal (above) and buccal (below) views, anterior to the right. Scale bar equals 5 mm.

Description—The referred material is the anterior portion of a large right

mandible (Fig. 4). The mandible is long and narrow in occlusal view, and is

approximately 15 mm deep from the alveolus. The diastema, although incomplete, is 12

mm and the symphysis is large. The specimen bears one isolated molar, with remnants of

dentine from a premolar. The broken jaw does not reveal any m1 roots. The m1 extends

14 mm below the alveolar surface and 5.5 mm above it. It has a length of 6.1 mm and a width of 4.9 mm. The buccal conids are thick, separated by a deeply penetrating flexid containing cement. The metaflexid extends midway through the tooth and is perpendicular to the long axis of the jaw. Enamel is relatively uniform, but slightly thicker along the posterior surface of the ectolophid; enamel is thin surrounding the

13 anterofossettid, likely due to wear. The entoconid is slightly separated from the large metaconid by a small flexid, a possible remnant of the mesofossettid. The posterolophid and ectolophid are more concave than the hypolophid and anterolophid, which are less curved.

Differential Diagnosis—N. huilensis is smaller than other species in the genus

(Fig. 5). However, since the only specimen from Quebrada Honda is an isolated lower molar, variations in size and the developmental stage of the specimen cannot be properly analyzed. In general, N. huilensis differs from N. australis and N. pinturensis in its lack of an anterolophid posterior projection; however, this character does not occur in all N. australis specimens (Kramarz, 2006). N. australis does distinctly differ from N. huilensis in its wider, more rounded hypoconid. Since Walton (1997) differentiated N. huilensis from N. australis based on incisor and premolar characters, this information alone cannot be used to identify the isolated Quebrada Honda molar. However, the Quebrada Honda specimen does share a similar occlusal pattern with Walton’s “N.” huilensis IGM 183327 as well as specimens described by Fields (1957).

Figure 5. Right isolated molars from dasyproctid species. A, cf. Neoreomys huilensis (UF 26915) m1; B, N. pinturensis (MACN Pv SC2211) m1 or m2; C, “N.” huilensis (IGM 183327) m1-m2; D, N. australis m1 or m2; E, “N.” huilensis (IGM 183683) m2-m3; F, Alloiomys sp. (MLP 76-VIII-30-4) m1; G, Australoprocta fleaglei (MACN CH 1784) m2. Anterior is to the right. Scale bar equals 2 mm.

Family CAVIIDAE Waterhouse, 1839

Comments—Caviids have hypselodont cheek teeth that are triangular in shape

with deep sulci. Enamel is reduced or absent on the lingual occlusal surfaces of lower teeth, and they are rounded on the lingual side and more narrow on the buccal side. On each tooth, a narrow isthmus extends diagonally from one prism to the other. The

Quebrada Honda caviids differ from eocardiids such as Eocardia and Luantus in that the prisms of the eocardiid teeth are separated by a thicker flexus/flexid, and the p4 anterior

15 prisms of eocardiids are less developed (Scott, 1905). The P4 of Eocardia resembles a

single, rounded triangle, whearas the P4 of the Quebrada Honda caviids have at least two

distinct triangular prisms (Ameghino, 1889).

Subfamily DOLICHOTINAE Pocock, 1922

Comments—Characters differentiating dolichotines from caviines include the

diastema longer than the upper tooth row length (Quintana, 1998), the absence of the

nasolacrimal formen in lateral view, and the position of the mesopterygoid fossa at the

level of the anterior and posterior prisms of M2 (Ubilla and Rinderknecht 2003). Other

characters are less useful in distinguishing between the subfamilies; diverging borders of

M3 is a synapomorphy of the subfamilies according to Quintana (1998), but may have

been a trait shared by the subfamilies’ ancestor (Ubilla and Rinderknect, 2003). Caviines

also differ from dolichotines in an elongation of the anterior prism of P4. The cheek teeth

of dolichotines have cement on the innermost portions of the hypoflexus/hypoflexid

(Walton, 1990). Dolichotines can be distinguished from cardiomyines in that

cardiomyines possesses a true third, triangular prism on P4. Also, the teeth of cardiomyines have deeper flexids (on the lingual surface for lower dentition and buccal surface for upper dentition) that give each prism a heart-shaped appearance (Rovereto,

1914).

Figure 6. Caviid genera from Quebrada Honda. Occlusal and buccal views of Orthomyctera rigens (UF 236860) (left) and cf. Prodolichotis mendocina (UF 236854) (right). Anterior is to the right. Scale bar equals 5 mm.

Genus Orthomyctera Ameghino, 1889

Type Species— O. rigens Ameghino, 1889

Included Species—the type, O. andina

Comments—Ameghino named nine Montehermosan species of Orthomyctera, eight of which have since been referred to other genera, most commonly Dolichotis.

Rovereto (1914) also considered O. rigens as belonging to Dolichotis, but recent analyses have suggested that the two genera are not closely related (see below).

Differential Diagnosis—Orthomyctera differs from Prodolichotis in having a slight elongation of the anterior p4 prism that is not considered a true third prism (Fig. 7).

Prodolichotis has a well-developed anterior p4 prism, and typically has a cheek teeth row length nearly twice the size of Orthomyctera (Ubilla and Rinderknecht, 2003). Similarly,

17 Orthomyctera differs from Kerodon (subfamily Caviine) in that the anterior p4 prism of

Kerodon is elongated to the point where it is considered a well-defined third prism

(Ubilla and Rinderknecht, 2003). Pliodolichotis has a more well-developed M3 third prism than Orthomyctera, as well as a shorter, more heavily pitted palate (Ubilla and

Rinderknecht, 2003). Orthomyctera differs from both Propediolagus and Pediolagus in that the latter genera have large sulci between lobes (Brizuela and Tauber, 2006).

Propediolagus also has more cement between lobes. Orthomyctera differs from

Dolichotis in that Dolichotis has tooth rows that converge to the point where P4s nearly touch (Brizuela and Tauber, 2006). Orthomyctera differs from Dolicavia (subfamily

Caviine) in that Dolicavia has equal anterior and posterior lobes of P4, a shorter and broader M3 prism, and deeper sulci between lower molar lobes (Prado and Cerdeño,

1998). Orthomyctera has a shorter diastema and shorter lower incisors than other genera

(Fields, 1957). Orthomyctera is also distinct in that the posterior prisms of lower cheek teeth often curve slightly posteriorly (Walton, 1990).

Figure 7. Right lower dentition of caviid and eocardiid species. A, Orthomyctera rigens (DC BO 5-14-07-171); B, Dolichotis patagonum; C, Dolicavia sp.; D, Cardiomys sp.; E, Prodolichotis pridiana (UCMP 36761); F, Eocardia montana (UPM-PU 015386). Anterior is to the right. Scale bar equals 5 mm. Modified from Walton, 1990.

Comments—Ameghino (1889) noted many similarities in tooth morphology between Orthomyctera and the genus Dolichotis. Presumably Orthomyctera was placed

in the subfamily Dolichotinae because of these shared characters, and this classification

has been maintained by McKenna and Bell (1997). However, Quintana (1998) and Ubilla

and Rinderknecht (2003) believe that the genus Orthomyctera should not be classified as

a dolichotine. Instead, they agree that it shares many morphological features with

19 members of the subfamily Caviinae, including a molar series equal to or longer than

diastema in length, elongation of the anterior p4 prism, and similar skull size. Also,

Orthomyctera is generally smaller than other dolichotine genera (O. rigens, a large

species of the genus, has a cheek teeth row length of approximately 12.5 mm as

compared to approximately 23 mm for Pediolagus salincola, a medium-sized

dolichotine). Additionally, dolichotines have thick bridges connecting cheek teeth prisms,

but O. rigens and, to a lesser extent, O. andina have narrow bridges. For these reasons,

Orthomyctera may in fact be more closely related to the caviines (Quintana, 1998).

Age and Distribution— unnamed formation of Quebrada Honda, southern

Bolivia, middle Miocene age, Laventan SALMA; Arroyo Chasicó Formation, central

Argentina, late Miocene age, Chasicoan SALMA (Bondesio et al., 1980b); Quehua

Formation, southwestern Bolivia, middle-late Miocene age, Huayquerian SALMA

(Hoffstetter, 1986; Marshall and Sempere, 1991); Muyu Huasi Formation, Bolivia, late

Miocene, Huayquerian SALMA (Hoffstetter, 1986; Marshall and Sempere, 1991);

Tunuyan Formation, Argentina, late Miocene, Montehermosan SALMA (Rovereto, 1914).

Orthomyctera rigens Ameghino, 1889

Holotype—MACN-Pv-1661-62, skull with left and right P4-M3

Referred Material—DC BO 5-14-07-171, DC BO 5-14-07-173, DC BO 5-14-

07-208, DC BO 5-14-07-217, UF 236854, UF 236858, UF 26914 (lower dentition), DC

BO 5-13-07-162, DC BO 5-14-07-181, DC BO 5-15-07-238, UF 236853, UF 236859,

UF 236860 (upper dentition)

20 Table 1. Summary of tooth measurements (in mm) from Quebrada Honda Orthomyctera rigens specimens, including mean, range, and standard deviation (SD) values for anteroposterior length (APL) and transverse width (TRW).

Orthomyctera rigens

APL TRW N mean range SD mean range SD p4 3 2.9 2.0-3.1 0.5 2.5 2.4-2.5 0.3 m1 5 3.4 2.7-3.5 0.5 3.0 2.7-3.3 0.3 m2 6 3.2 3.0-4.5 0.5 4.1 2.7-3.2 0.3 m3 4 4.2 2.8-4.2 0.2 3.0 2.8-3.0 0.2 p4-m3 1 15.0 P4 7 3.1 2.7-3.5 0.3 2.7 2.1-3.3 0.4 M1 10 3.3 2.7-3.7 0.3 3.0 2.7-3.3 0.2 M2 7 3.2 2.7-3.4 0.3 2.9 2.4-3.3 0.3 M3 3 4.4 3.9-4.6 0.5 3.0 2.7-3.2 0.4 P4-M3 1 15.0

Localities— Río Rosario, equivalent to Unit 4, above lower gray sandstone; Río

Rosario lower red beds (approximately equivalent to Unit 2, below the first gray interval); and Río Rosario, unspecified lower levels

Description—The referred specimens are small dolichotines with narrow, slightly rounded teeth (Fig. 6). The palate is shallow; it is approximately 15 mm as its widest point (between the posterior prisms of M3s) and 5 mm at its narrowest point (between anterior prisms of P4). The upper tooth row measures 15 mm (Table 1). Upper prisms are of roughly equivalent size, with shallow buccal sulci and deep hypoflexids. Hypoflexid enamel is roughly 1 mm thick. The posterior prisms of M1 and M2 are posteriorly curved.

The posterior prisms of M3 are independent, slightly rounded, and perpendicular with the long axis of the jaw. In lower dentition, teeth have a similar teardrop shape, often with anterior prisms anteriorly curved. Enamel is thick on buccal surfaces and reduced on lingual surfaces. The buccal sulci are most penetrating in m1 and m2, and posteriorly

21 shifted in m2 and m3. Hypoflexid cement is thinner than in upper dentition, and ranges

from 0.5 mm to 0.7 mm in thickness. The posterior prism of m3 is often more rounded

than in other molars. This prism has a greater length, reduced width, and a more curved

buccal surface. The anterior portion of p4 is rounded, but is not independent from the rest

of the tooth.

Differential Diagnosis—O. rigens differs from O. andina in that O. andina has a

more independent, less-rounded p4 prism, whereas that of O. rigens often resembles a

mere rounded anterior flange. The M3 third prisms of O. rigens and O. andina are both perpendicular to the medial prisms (Ubilla and Rinderknecht, 2003); however, the M3 of

O. andina is more rounded than that of O. rigens (Fig. 8). In upper cheek teeth of O.

rigens and O. andina, the hypflexus is wider and it is more open lingually than in other

dolichotines. However, the hypoflexus of O. andina is wider and contains more cement than that of O. rigens. O. rigens is also larger than O. andina.

Figure 8. Right upper dentition for (A) Orthomyctera rigens (DC BO 5-15-07-238) and (B) O. andina (MACN Pv 8350), anterior to right. Scale bar equals 2 mm.

Genus Prodolichotis Kraglievich, 1932

Type Species—P. prisca Kraglievich, 1932

Included Species—the type, P. lacunosa, P. mendocina, P. molfinoi, P. perfecta,

P. pridiana

Differential Diagnosis—Prodolichotis is a medium- to large-sized dolichotine. It

differs from Orthomyctera in its typically larger size. The p4 of Prodolichotis has a third

prism (or a well-developed flange), whereas Orthomyctera only has two prisms, with the

anterior prism slightly rounded or possesses a slight elongation only. The cranium of

Prodolichotis is similar to that of the living Dolichotis (Kraglievich, 1932). Similarly, the

lower incisor of Prodolichotis and Dolichotis extend farther back than in Orthomyctera.

Comments—Ubilla and Rinderknecht (2003) proposed a revision of the genus, stating that the criteria used by Kraglievich (1930) and Fields (1957) are insufficient to

account for the variation in size and numerous other characters. However no such

revision has taken place.

Age and Distribution— La Victoria Formation, Colombia, middle Miocene age,

Laventan SALMA (Walton, 1997); unnamed formation of Quebrada Honda, southern

Bolivia, middle Miocene age, Laventan SALMA; Ituzaingo Formation, central Argentina,

late Miocene age, Huayquerian SALMA (Cione et al., 2000); Camacho Formation,

southwestern Uruguay, late Miocene, Huayquerian SALMA (Ubilla and Rinderknecht,

2003); Chiquimil Formation, northeastern Argentina, Chasicoan SALMA (Marshall and

23 Patterson, 1981); Monte Hermoso Formation, central Argentina, Montehermosan and

Chapadmalan SALMAs (Walton, 1990).

cf. Prodolichotis mendocina, Rovereto 1914

Holotype—MACN 8551, left mandibles with p4-m3

Referred Material—UF 236854, right and left mandibles with p4-m3

Figure 9. Comparison of right lower dentition for (A) cf. Prodolichotis mendocina from Quebrada Honda (UF 236854) and (B) P. mendocina (MLP 28-X-11-477) anterior to right. Scale bar equals 2 mm.

Locality—Quebrada Honda: Unit 2 of Section 1

Description—The referred specimen pertains to a small dolichotine with molars

comprised of two prisms. It is similar in size to O. rigens, although slightly larger. The p4 contains a third, anterior prism that is more independent than in O. rigens. The lingual sulci are very shallow; consequently, the lingual surfaces of the teeth are straighter. The hypoflexids curve anteriorly at their deepest points. In m1, the buccal faces are oriented

24 towards the anterior portion of the jaw, whereas other the other molars are more

perpendicular with the long axis of the jaw.

Differential Diagnosis—P. mendocina is smaller than most other dolichotines,

with a p4 anterior prism that is less developed than in other members of the genus. It is

similar to Orthomyctera, except the anterior p4 prism is more elongated and more

independent. The p4 of P. mendocina is also more obliquely oriented than in

Orthomyctera, where the p4 is more perpendicularly oriented. It differs from P. molfinoi

in being smaller, with a more developed anterior prism of p4 (Kraglievich, 1940). The latter is also 15% larger. Although the Quebrada Honda species is similar in size and tooth morphology, the p4 anterior prism of the Quebrada Honda species is more elongated than P. mendocina, and the anterior surface of the medial prism is more concave in the Quebrada Honda species (Fig. 9). The anterior prisms of the molars are more anteriorly tilted in the Quebrada Honda species, resulting in more open hypoflexids.

However, given one Quebrada Honda specimen, it is unclear whether these differences constitute distinct species, or whether they are due to intraspecific variation.

Prodolichotis sp. nov.

Referred Material—UF 66003, right mandible with p4-m2

Figure 10. Prodolichotis sp. nov. (UF 66003) in occlusal (above) and buccal (below) views, anterior to right. Scale bar equals 5 mm.

Locality—unspecified Quebrada Honda or Río Rosario locality

Description—The referred material is an incomplete left mandible bearing p4-m2.

This small dolichotine possesses molars made of two prisms. The incomplete tooth row is

10.93 mm in length and 3.11 mm at its widest point (the anterior prism of m2). The jaw is

thick and extends approximately 6.5 mm below the alveolar surface. The high-crowned

teeth are up to 5 mm thick from alveolus to crown. The p4 has a true third prism, which is slightly larger than the medial one (Fig. 10).

Differential Diagnosis—The species differs from most Prodolichotis species in that it is much smaller. It is most similar to Prodolichotis pridiana, and they share the

following characters: the middle and anterior prisms of p4 are the same size, the anterior

prism is slightly blunt and projects slightly posteriorly (Fields, 1957; Walton, 1990).

Although Walton (1990) acknowledges a larger size range for P. pridiana than Fields

(1957), the Quebrada Honda species is smaller than the smallest La Venta species (which

include juveniles). The bridges connecting the prisms are thicker than in P. pridiana, yet

26 have less enamel; additionally, the lingual surfaces of p4-m2 lack enamel in the Quebrada

Honda species. The lingual sulci of P. pridiana are also deeper, particularly the m2

sulcus, and anterior prisms extend farther lingually than posterior ones in all molars (Fig.

11).

Figure 11. Comparison of lower right dentition of (A) Prodolichotis sp. nov. (UF 66003) and (B) P. pridiana (UCMP 36761), anterior to right. Scale bar equals 2 mm.

Superfamily OCTODONTOIDEA Simpson, 1945

Family OCTODONTIDAE Waterhouse, 1839

Comments—The family Octodontidae is represented by living and extinct small or medium-sized caviomorph rodents from South America (Waterhouse, 1839).

Octodontids are characterized by hypsodont molars and have a tendency towards simplified molar patterns (Verzi, 1999); the latter character includes the gradual loss of flexids and an often sigmoid or figure-eight shaped occlusal morphology. Verzi et al.

(1994) distinguish octodontids from other families of the Octodontoidea based on

27 discontinuity between the masseteric notch and crest of the mandible; in addition to this,

octodontids possess a unique molar flexid closure sequence, with the metaflexid forming

a fossettid before the mesoflexid. Other characters, such as degree of hypsodonty and

replacement versus retention of the deciduous premolar, are less reliable diagnoses at the

familial level. The earliest confirmed octodontids are known from the late Miocene

Chasicoan SALMA (Vucetich et al., 1999). Although the taxonomy of earlier supposed

octodontids remains unclear, they likely belong to the Echimyidae or Acaremyidae

(Wood, 1949; Reig, 1986).

Subfamily CTENOMYINAE Reig, 1958

Comments—There is skepticism as to whether this subfamily should be treated as such, or whether the taxonomic unit should be recognized as a separate family from the Octodontidae (Wood, 1955; McKenna and Bell, 1997; Vucetich et al., 1999).

Regardless, this group of rodents was previously believed to have diverged from octodontines at least by the Chasicoan (Quintana, 1994).

Genus Chasichimys Pascual, 1967

Comments—this genus was placed in the family Echimyidae and subfamily

Heteropsomyinae due to its superficial resemblance to extant echimyids, and McKenna and Bell (1997) maintain this classification. However, this large subfamily contains several genera which may be eumysopines or even octodontids. Based on its similar

28 mandible configuration and flexid closure sequence, Verzi (1999) believes that

Chasichimys is actually a primitive octodontid ancestor of the subfamily Ctenomyinae.

Type Species—Chasichimys bonaerense Pascual, 1967

Included Species—the type, “C. morphotype a”, C. scagliai

Differential Diagnosis—Chasichimys is similar to Acarechimys in that both

genera have trilophodont molars with non-opposing lingual and buccal flexids and

hypoflexids angled towards the anterior portions of the molars. Chasichimys differs from

Acarechimys in its flexid closure sequence and its more penetrating hypoflexid as

compared to the mesoflexid and metaflexid (Pascual, 1967). With wear, the molar

metaflexid closes before the mesoflexid; this is characteristic of other octodontids, such

as Chasicomys (a different genus from Chasichimys) and Phtoramys (Verzi, 1999).

However, Chasicomys has a more derived, simplified molar pattern than Chasichimys

and the lophids of Phtoramys are more transverse than those of Chasichimys.

Figure 12. Right mandible of Chasichimys sp. nov. (DC BO 5- 12-07-135) in occlusal (above) and buccal (below) views, anterior to the right. Scale bar equals 2 mm.

29 Age and Distribution— unnamed formation of Quebrada Honda, southern

Bolivia, middle Miocene age, Laventan SALMA; Arroyo Chasicó Formation, central

Argentina, late Miocene age, Chasicoan SALMA (Pascual, 1967); Cerro Azul Formation,

central Argentina, late Miocene age, Chasicoan and Huayquerian SALMAs.

Comments—Walton (1990) refers specimen IGM-DU 88-242 (left mandible with dp4-m3) from La Venta to Acarechimys minutissimus with question. However, this

specimen exhibits a different wear pattern than that of other Acarechimys species from La

Venta; the metaflexid becomes isolated before the mesoflexid in this specimen. I think a

revision of these rodents from La Venta is necessary, because it is likely that some

specimens belong to the genus Chasichimys.

Chasichimys sp. nov.

Referred Material—DC BO 5-12-07-96, DC BO 5-12-07-97, DC BO 5-12-07-

134, DC BO 5-12-07-135, DC BO 5-12-07-147, DC BO 5-13-07-150, DC BO 5-13-07-

152, DC BO 5-13-07-158, DC BO 5-13-07-160, DC BO 5-14-07-174, DC BO 5-14-07-

183 (lower dentition) and DC BO 5-13-07-140 (upper dentition)

30 Table 2. Summary of tooth measurements (in mm) from Chasichimys sp. nov. specimens, including mean, range, and standard deviation (SD) values for anteroposterior length (APL) and transverse width (TRW).

Chasichimys sp. nov. APL TRW N mean range SD mean range SD i1 1 3.3 1.6 diastema 2 3.3 3.2-3.4 0.1 dp4 7 1.9 1.7-2.0 0.1 1.4 1.2-1.5 0.1 m1 8 1.8 1.6-2.0 0.2 1.6 1.4-2.1 0.2 m2 9 1.8 1.6-2.1 0.3 1.8 1.6-2.1 0.2 m3 4 1.7 1.4-1.8 0.4 1.5 1.4-1.6 0.4 dp4-m3 1 5.9 M1 1 1.6 1.5 M2 1 2.0 1.8

Localities—Unit 2 of Section 1 of Quebrada Honda, below the first gray interval;

Unit 3 of Section of Quebrada Honda, in soft, gray beds just above basal red beds; Río

Rosario, unspecified lower levels; Río Rosario, lower red beds (approximately equal to

Unit 2 of Section 1 of Quebrada Honda).

Description—The referred material includes small octodontids with simple, sigmoid dental patterns (Fig. 12). The dental series is approximately 6 mm long and approximately 2 mm wide (Table 2). The incisor is 1.5-2 mm thick and separated from the tooth row by a 3.3 mm diastema. The rooted teeth are brachydont, approximately 1.7 mm from root to crown. In little worn teeth (DC BO 5-12-07-135 and DC BO 5-13-07-

160), lophids are thin and slightly concave. Hypoconids and protoconids are well-defined and have sharp buccal surfaces. Little worn dp4s exhibit some variability in occlusal pattern; most notably, the metafossettid varies in size, and the anterofossettid is circular or semi-circular. With increased wear, the metaflexid becomes an isolated fossettid,

31 followed by the mesoflexid. This wear pattern results from the more penetrating

mesoflexid, which persists longer than the metaflexid. Enamel is thicker and more

uniform at the base of the tooth, since little worn teeth have much thinner enamel than

well worn teeth. In addition to the thickened enamel, the lophids (especially the entolophid and anterolophid) become thicker with wear. The hypoflexid is more

penetrating than the lingual flexids, and persists even in the most worn specimen (DC BO

5-13-07-152).

Differential Diagnosis—The Quebrada Honda Chasichimys species is similar to

C. bonaerense (MLP 60-IV-28-3) in occlusal pattern (Fig. 13). However, C. bonaerense has lower molars with more penetrating, less rounded hypoflexids when compared to a

Quebrada Honda specimen of a comparable wear state. The mesoflexid of m1 in C. bonaerense is also more penetrating, with a narrow, anterior projection. The anterior surfaces of the lower molars of C. bonaerense are perpendicular with the long axis of the tooth row, whereas, in the Quebrada Honda species, these surfaces are more obliquely oriented. All other members of this genus are more hypsodont than the Quebrada Honda species; for example, C. bonaerense has an average hypsodonty index of 1.9 (Verzi,

1999), as compared to an average of 0.7 in the Quebrada Honda species.

Figure 13. Right lower dentition of Chasichimys sp. nov. (A-D) and other Chasichimys species (E-G). A, DC BO 5-13-07-160 dp4-m1; B, DC BO 5-12- 07-135 dp4-m3; C, DC BO 5-12-07-134 dp4-m2; D, DC BO 5-13-07-150 m1- m3 (shown as right); E, C. bonaerense (MLP 60-VI-18-108) m1; F, C. bonaerense (MLP 55-IV-28-3) m1-m2; G, C. scagliai (MLP 55-IV-28-4) dp4- m1 (shown as right). Anterior is to the right. Scale bar equals 1 mm.

Family ECHIMYIDAE Gray, 1825

Comments—Echimyids are diverse Neotropical extant and fossil rodents

(Carvalho and Salles, 2004). The oldest echimyids are from the Deseadan SALMA of

Bolivia (Hoffstetter and Lavocat, 1970). Members of this family vary in tooth morphology, but possess molars with more persistent metaflexids than mesoflexids

(Verzi et al., 1994).

Subfamily ADELPHOMYINAE Patterson & Pascual, 1968

33 Comments—Adelphomyines exhibit a tendency towards hypsodonty (Kramarz,

2001) and m2 is often the largest in the molar series (Deseadomys, Prostichomys,

Stichomys). Members of this subfamily possess trilophodont or tetralophodont molars

with oblique lophids that tend to form plates.

Gen. et sp. nov.

Referred Material—DC BO 5-15-07-230, right mandible with m1-m3

Figure 14. Right mandible of a new adelphomyine from Quebrada Honda (DC BO 5-15-07-230) in occlusal (above) and buccal (below) views, anterior to the right. Scale bar equals 2 mm.

Locality—Unit 2 of Section 1 of Quebrada Honda, low in section, at the base, below first gray interval

Description—The referred material is a right mandible that bears m1-m3 (Fig.

14). In lateral view, the jaw appears thick, with the masseteric fossa beginning below the

34 first molar. The broken incisor is approximately 0.5 mm thick. The teeth are hypsodont, extending 2 mm above the alveolus. The m1 is the smallest molar, and m3 is slightly larger than m2. This incomplete dental series is less than 10 mm in length. The premolar socket is 3.8 mm in length. The molars are formed by a series of thin plates with uniform, thin enamel. In m2, the posterolophid is thicker than the entolophid; the opposite trend occurs in m3. The anterolophid is thin in all molars, particularly at the most anterobuccal point; here, the mesoflexid curves anteriorly. The metaflexid, by comparison, is straighter and less penetrating. The hypoflexid is less penetrating than the lingual flexids and curves posteriorlingually.

Differential Diagnosis—This genus differs from Stichomys, Prostichomys,

Xylechimys and Deseadomys in that it lacks a metafossettid. It is similar to Adelphomys in that the hypoflexid and metaflexid are separated only by a very narrow isthmus, but the molar lophids of this genus are slightly more transverse than in Adelphomys. The

Quebrada Honda genus differs from Paradelphomys in that the hypoflexid and mesoflexid of Paradelphomys are not separated by an isthmus, and form one flexid in little worn molars. It is similar to Ricardomys in that the molars are composed of three plate-like crests, but Ricardomys is less wide transversely, with more curved buccal flexids. The hypoflexids of the Quebrada Honda genus are more penetrating and anteriolingually shifted (Fig. 15).

Figure 15. Right lower dentition of adelphomyines. A, DC BO 5-15-07-230 m1- m2; B, Ricardomys longidens (IGM 183847) dp4-m2 (shown as right); C,

Paradelphomys fissus (MLP 125) dp4-m1 (shown as right); D, Adelphomys candidus (YPM-PU 15090) dp4-m2 (shown as right); E, Stichomys sp. dp4-m3;

F, Prostichomys bowni (MACN SC 3856) dp4-m2 (shown as right). Anterior is to the right. Scale bar equals 2 mm.

Age and Distribution—unnamed formation of Quebrada Honda, southern

Bolivia, middle Miocene age, Laventan SALMA

Superfamily CHINCHILLOIDEA Bennett, 1833

Family CHINCHILLIDAE Bennett, 1833

Comments—Chinchillids have open-rooted cheek teeth, often with parallel lophs/lophids. The enamel is reduced on the buccal surfaces of lower and upper cheek teeth (Bennett, 1833) in chinchillids from younger faunas. The subfamilies Lagostominae and Chinchillinae likely diverged before or during the Deseadan (Vucetich and Verzi,

1993). Chinchillines possess a more complex occlusal pattern, often with two

flexi/flexids. Lagostomine teeth have two lophs/lophids, which are separated by only one

flexus/flexid; the enamel of this flexus/flexid in particular tends to be reduced in

lagostomines from younger faunas.

Subfamily LAGOSTOMINAE Wiegmann, 1832

Genus Prolagostomus Ameghino, 1887

Type Species—Prolagostomus pusillus, Ameghino 1887

Included Species—the type, P. divisus, P. profluens, P. imperialis, P. amplus, P.

obliquidens, P. rosendoi

Differential Diagnosis—Prolagostomus is similar to Pliolagostomus in that both genera have bilobed cheek teeth with oblique lophids. However, Pliolagostomus possesses molar laminae with relatively straight anterior and posterior margins, whereas

37 those of Prolagostomus are more rounded. Also, the M3 of Pliolagostomus has a smaller,

more triangular third prism that is more lingually oriented than that of Prolagostomus.

Figure 16. Prolagostomus specimens from Quebrada Honda. A, P. profluens

(DC BO 5-12-07-87) upper dentition; B, P. amplus (DC BO 5-13-07-129d) left p4-m3; C, Prolagostomus sp. nov. (DC BO 5-13-07-133) p4-m3 (shown as left);

D, cf. P. divisus (DC BO 5-12-07-106) p4-m2 (shown as left). Anterior is to the right. Scale bar equals 2 mm.

Age and Distribution—Santa Cruz Formation, southern Argentina, early

Miocene age, Santacrucian SALMA (Kramarz, 2002); Pinturas Formation, southern

Argentina, early Miocene age, Santacrucian SALMA (Kramarz, 2002); Collón-Curá

Formation, northwestern Argentina, middle Miocene age, Colloncuran SALMA

(Bondesio et al., 1980a); unnamed formation of Quebrada Honda, southern Bolivia, middle Miocene age, Laventan SALMA; Arroyo Chasicó Formation, eastern Argentina, late Miocene age, Chasicoan SALMA

38 Comments—Interestingly, lagostomines have not been found in all Laventan-age

formations in South America. While the subfamily is abundant in Quebrada Honda, it is noticeably absent in La Venta, Colombia (Walton, 1997). Lagostomines are abundant at

Quebrada Honda, and researchers have previously identified Prolagostomus profluens, P.

imperialis, and P. divisus from some of the Florida specimens of this locality (see Croft,

2007). Others believe that the Quebrada Honda (and slightly younger, but similar

Nazareno) chinchillids are not the same as the Santacrucian Prolagostomus species

(Takai et al., 1984; Oiso, 1991). Still others have labeled Quebrada Honda chinchillids as

simply Prolagostomus-Pliolagostomus group members, or even Lagostomus group

members (Hoffstetter, 1977; MacFadden and Wolff, 1981).

Prolagostomus profluens Ameghino, 1887

Holotype—MLP 15-70, left mandible with i1, p4-m1

Referred Material— DC BO 5-12-07-88, DC BO 5-12-07-98, DC BO 5-12-07-

103, DC BO 5-12-07-104, DC BO 5-12-07-107, DC BO 5-12-07-109, DC BO 5-13-07-

127, DC BO 5-13-07-129b, DC BO 5-13-07-129e, DC BO 5-13-07-141, DC BO 5-13-

07-142, DC BO 5-13-07-146, DC BO 5-13-07-148, DC BO 5-13-07-154, DC BO 5-13-

07-155, DC BO 5-13-07-163, DC BO 5-13-07-165, DC BO 5-14-07-170, DC BO 5-14-

07-185, DC BO 5-14-07-204, DC BO 5-14-07-205, DC BO 5-14-07-221, DC BO 5-15-

07-232, DC BO 5-15-07-234, DC BO 5-15-07-237, DC BO 5-15-07-241, UF 26920, UF

236856, UF 26932, UF 26912, UF 26942, UF 66001, UF 26935, UF 27897, UF 236855,

39 UF 26940, UF 26924 (lower dentition), DC BO 5-12-07-87, DC BO 5-12-07-102, DC

BO 5-14-07-177, DC BO 5-14-07-225, UF 26916, UF 26917, UF 236857, UF 26927, UF

66002 (upper dentition)

Table 3. Summary of tooth measurements (in mm) from Prolagostomus profluens specimens, including mean, range, and standard deviation (SD) values for anteroposterior length (APL) and transverse width (TRW).

Prolagostomus profluens APL TRW N mean range SD mean range SD i1 1 1.8 1.4 diastema 1 8.9 p4 27 2.4 1.8-3.3 0.4 3.4 2.3-4.7 0.6 m1 33 3.0 2.2-3.8 0.5 3.8 2.8-4.2 0.6 m2 26 2.9 2.2-3.9 0.5 3.7 2.2-4.2 0.5 m3 19 2.8 2.2-3.9 0.5 3.3 2.1-3.8 0.3 p4-m3 1 12.2 P4 10 2.5 2.1-3.7 0.3 3.4 2.8-4.1 0.5 M1 14 2.6 2.2-3.2 0.3 3.6 2.8-4.5 0.5 M2 15 2.5 2.0-4.2 0.3 3.4 2.3-4.2 0.4 M3 8 2.7 2.4-4.9 0.3 2.7 2.5-4.6 0.3 P4-M3 4 10.1 9.6-10.5 0.7

Localities—Unit 2 of Section 1 of Quebrada Honda, low in section, at the base,

below first gray interval; above soft gray beds of Unit 3 of Section 1 of Quebrada Honda;

Río Rosario, equivalent to Unit 4 of Section 1 of Quebrada Honda, above lower gray sandstone; Río Rosario, lower red beds, roughly equivalent to Unit 2 of Section 1 of

Quebrada Honda, high in section in buff sandstone; Río Rosario: unspecified lower levels

(roughly equivalent to Units 2-4 of Quebrada Honda)

40 Description— Chinchillid with hypselodont, bilobed, and slightly rounded teeth.

Lower cheek teeth are long and narrow. Lingual surfaces of lower cheek teeth are slightly more narrow than the buccal surfaces, especially for p4, which is v-shaped. There is only one specimen with a complete diastema (DC BO 5-13-07-139), which 8.9 mm long. The incisor, although broken, is thick, with a transverse width of 1.8 mm (Table 3). In lower cheek teeth, m2 is the largest, m1 and m3 are both slightly smaller, and p4 is the smallest.

Lower cheek teeth are obliquely oriented with respect to the long axis of the tooth row, especially p4. Enamel is reduced on the buccal surfaces, especially on the anterior portions of the second lophs, where enamel is essentially absent. Upper cheek teeth are slightly more box-shaped than lower teeth (they are less long and narrow). Enamel is reduced on the buccal surfaces of both lophs of upper cheek teeth. M3 possesses a third prism which is more obliquely oriented than the other lophs. The third prism is separated from the second loph by a cement fold (Fig. 16).

Differential Diagnosis— Prolagostomus profluens is larger than P. pusillus

(which has a tooth row measuring only 9 mm). P. profluens differs from P. divisus in that its third M3 prism is less obliquely oriented. The lower cheek teeth of P. divisus also have lophs of roughly equivalent size, whereas the second lophids of P. profluens are slightly smaller. Additionally, in P. profluens, the second lophid of m3 is more parallel to the first lophid; it also extends further lingually than the second lophid of P. divisus. In P. divisus, p4 is considerably smaller than m1 and m2. P. profluens differs from P. imperialis in that the upper cheek teeth of P. imperialis are more narrow. The M3 third prism of P. imperialis is more developed; the prism is obliquely oriented and there is no

indication of a cement fold between it and the rest of the tooth. The m3 of P. imperialis

41 also has the greatest antero-posterior length of the cheek teeth; m3 is slightly smaller than m1 and m2 in other members of the genus, which are also smaller species by comparison

(Scott, 1905). P. profluens is slightly smaller than P. amplus, and the lower cheek teeth of

P. amplus are all the same size. P. profluens differs from P. rosendoi in that P. rosendoi

has upper cheek teeth with vestiges of cement on the buccal surfaces (Vucetich, 1984)

(Fig. 17). Also, the first lophs of upper cheek teeth extend further externally in P. rosendoi. P. obliquidens differs from all other members of the genus in possessing a p4

which is parallel to the long axis of the jaw (Scott, 1905).

Figure 17. Right upper dentition of lagostomines. A, Prolagostomus profluens (DC BO 5-14-07-225) (shown as right); B, Prolagostomus divisus (YPM-PU 15570) (shown as right); C, Prolagostomus rosendoi (MLP 76-VIII-30-3); D, Pliolagostomus notatus (MLP 15-100). Anterior is to the right. Scale bar equals 2 mm.

42 Prolagostomus amplus Ameghino, 1889

Holotype—mandible with p4-m3 (location is unknown at this time)

Referred Material— DC BO 5-12-07-106a, DC BO 5-13-07-129d, DC BO 5-15-

07-246, UF 26919 (lower dentition)

Table 3. Summary of tooth measurements (in mm) from Prolagostomus amplus specimens, including mean, range, and standard deviation (SD) values for anteroposterior length (APL) and transverse width (TRW).

Prolagostomus amplus APL TRW N mean range SD mean range SD p4 3 2.7 2.3-3.1 0.4 2.9 2.6-3.4 0.4 m1 4 2.7 2.4-3.0 0.3 2.9 2.6-3.4 0.4 m2 4 2.8 2.4-3.3 0.4 2.9 2.5-3.4 0.4 m3 3 2.8 2.5-3.1 0.3 3.1 2.8-3.3 0.3 p4-m3 2 11.3 10.3-12.5 1.7

Localities—Unit 2 of Section 1 of Quebrada Honda, low in section, at the base, below first gray interval; above soft gray beds of Unit 3 of Section 1 of Quebrada Honda;

Río Rosario, lower red beds, roughly equivalent to Unit 2 of Section 1 of Quebrada

Honda, high in section in buff sandstone; unspecified locality from Quebrada Honda or

Río Rosario

Description—The referred material consists of lower dentition. In a complete mandible, such as DC BO 5-13-07-129d, the tooth row is 11.6 mm long and 4.2 mm at its thickest point (the anterior prism of m2). The buccal and lingual faces of the molars are roughly equivalent. The lingual flexids are small, but never absent from the molars.

Enamel is absent from the buccal faces of the molars, and the buccal flexids show

43 vestiges of cement. The buccal face of each anterior lophid extends further than the

lingual face; the opposite trend occurs at the lingual surface, where posterior lophids

extend further than anterior ones. The enamel separating each molar lophid is straight and of uniform thickness, although it curves anteriorly as it reaches the lingual surface.

Differential Diagnosis—P. amplus differs from other members of the genus in possessing a lower tooth row with teeth of roughly equivalent size. In the other members of the genus, p4 is typically the smallest tooth, m1 and m2 are the biggest, and m3 size varies.

cf. Prolagostomus divisus Ameghino, 1887

Holotype— MLP 26-IV-6, skull with left and right P4-M3

Referred Material— DC BO 5-12-07-106 (lower dentition)

Locality—Unit 2 of Section 1 of Quebrada Honda, low in section, at the base, below first gray interval; above soft gray beds of Unit 3 of Section 1 of Quebrada Honda

Description—The referred material is a portion of a right mandible bearing p4-

m2 (Fig. 18). This partial tooth row is 7.4 mm in length; despite this incompleteness, I

estimate that the Quebrada Honda specimen is 10% smaller than the average P. profluens

specimen. The p4 is 30% smaller than the two molars, and its lingual extension is about

half of that of the molars. The anterior lophid of p4 is thicker and more rounded than the

second lophid, which is thinner, with more parallel anterior and posterior faces. The

posterior lophids of the molars are more perpendicularly oriented than the anterior

44 lophids, and enamel is absent from the lingual faces of the posterior lophids. Similarly, the enamel is reduced or absent on the lingual surface of anterior lophids.

Differential Diagnosis—The most diagnostic character for P. divisus is its small p4. However, P. divisus is much larger than the Quebrada Honda specimen; YPM-PU

15882 has an anterioposterior length of 15 mm (Scott, 1905). The Quebrada Honda specimen has an extrapolated length of only 9.7 mm. Since the p4 of the Quebrada Honda specimen has fully-developed lophids and enamel, it is not likely to be deciduous.

However, it is still unclear whether the size difference is due to ontogenetic differences.

Prolagostomus sp. nov.

Referred Material— DC BO 5-13-07-133 (lower dentition)

Locality— Río Rosario, equivalent to Unit 4 of Section 1 of Quebrada Honda, above lower gray sandstone

Description—This medium-size chinchillid is roughly the same size as other

Quebrada Honda chinchillids; it is 13.6 mm in length, and 5.1 mm at its thickest point

(the posterior lophid of m1). Enamel is absent from buccal faces, as are any remnants of cement. The anterior lophid of m1 and the posterior lophid of m2 are elliptical, while the anterior lophid of m2 and both lophids of m3 are posteriorly concave (crescent-shaped).

The posterior lophid of m1 extends 0.6 mm further lingually than the anterior lophid; this occurs, to a lesser extent, in m2.

Differential Diagnosis—The Quebrada Honda specimen differs from other

Prolagostomus species in the crescent-shaped m3. Most other members of the genus

45 (except P. imperialis) have reduced or absent enamel on the lingual surfaces of the lower

molars; the lingual enamel is much thicker in all lower teeth of the Quebrada Honda specimen (whereas P. imperialis has reduced lingual enamel on p4). Another striking

character of this specimen is the lingual extension of the m1 posterior lophid. This occurs

slightly in P. profluens, but the lingual surface is not thick and rounded as in the

Quebrada Honda specimen.

Figure 18. Left lower dentition of lagostomines. A, Prolagostomus amplus (DC BO 5- 13-07-129d) (shown as left); B, Prolagostomus sp. nov. (DC BO 5-13-07-133) (shown as left); C, cf. Prolagostomus divisus (DC BO 5-12-07-106) (shown as left); D, Prolagostomus profluens (DC BO 5-12-07-88); E, Prolagostomus imperialis (YPM-PU 15602) (shown as left); F, Pliolagostomus notatus (YPM-PU 15087). Anterior is to the right. Scale bar equals 2 mm. 46 Discussion:

The Quebrada Honda fauna is a key component of our understanding of South

American mammal evolution during the Miocene. A detailed study of the fauna has

paleoecological implications and can further our knowledge of biostratigraphy.

Analyzing character states of the Quebrada Honda specimens can help to place them in

an evolutionary context as well. Although larger mammals from Quebrada Honda have

been studied in detail and have yielded valuable information about middle latitude

Miocene faunas, an analysis of its rodents, a crucial part of the puzzle, was previously

lacking.

Paleoecological Implications

The Quebrada Honda rodent community is dominated by chinchillids. They make

up 61.5% of the rodent families (as indicated by the number of specimens). Caviids are

the second most abundant family, making up 19.2% of the rodent families. Octodontids

account for 16.7% of rodent diversity, and echimyids and dasyproctids each make up

1.3% of rodent families. Chinchillids and caviids are open range rodents with

hypselodont teeth. Modern chinchillids occupy temperate Andean regions (non-tropical)

(Walton, 1997). Extant caviids have a smaller range than their ancestors; they are found

in arid to semiarid environments of southern Bolivia, Paraguay, and Patagonia (Ubilla

and Rinderknecht, 2003). All of the Quebrada Honda specimens, except for the

octodontids, possess either hypsodont or hypselodont teeth – an adaptation to eating more

abrasive foods such as grasses. There is an apparent absence of forest dwelling rodents such as erethizontids and dinomyids from Quebrada Honda, and a low proportion of

47 echimyid specimens. Although sampling error may be responsible for this apparent trend, erethizontids and dinomyids tend to be larger rodents than the ones found at Quebrada

Honda. This would suggest that any sampling error is not due to size, and therefore suggests that forests (and forest-dwelling rodents) were indeed scarce. Forests may have only existed in small, isolated patches; this habitat mosaic phenomenon also occurred during the “Friasian” of Patagonia (Vucetich, 1984). Based on the large proportion of chinchillids and caviids at Quebrada Honda, the paleoenvironment was probably most similar to the regions inhabited by living members of these families with abundant grasses and shrubs.

Rodents are an incredibly diverse group of mammals, and typically make up a large percentage of Miocene faunas. Members of this diverse order often account for 30-

40% of the non-primate terrestrial mammal species in a given locality. Indeed, the 10 species from Quebrada Honda make up 38% of the mammal species at the locality. Other traditionally “Friasian” faunas contain 13-26 rodent genera (Walton, 1997), whereas the

Quebrada Honda fauna only contains 10 species belonging to six genera. Taken together, the data suggest that the rodents at Quebrada Honda were closely related, and these taxa were well-adapted to their environment.

Perhaps one of the best sampled and most thoroughly analyzed paleofaunas is from La Venta, Colombia. Although Quebrada Honda is more than 3,000 km south of La

Venta, some degree of similarity between fossil rodents was expected, given that both faunas are referred to the Laventan SALMA. Caviids can be found at both localities, and the species are certainly similar and probably related. The most common caviid at La

Venta is Prodolichotis pridiana (Walton, 1997). Two other genera, a large and a small

48 dolichotine species, have also been proposed (Walton, 1990; Walton, 1997).

Prodolichotis sp. nov. from Quebrada Honda is similar to P. pridiana in several characters. The Quebrada Honda species also closely resembles the small dolichotine

species, Dolichotinae gen. 2, small. The most common caviid from Quebrada Honda,

Orthomyctera rigens, is absent from La Venta and is associated with Patagonian faunas

that are more than 4 ma younger, including some pertaining to the Chasicoan,

Huayquerian, and Montehermosan SALMAs. Another genus, Neoreomys, is found at

Quebrada Honda and La Venta. However, this genus is also found in Colhuehuapian

through Friasian SALMAs of Patagonia as well (Walton, 1997). As previously mentioned,

Chasichimys may occur at La Venta; the genus is found at Quebrada Honda and from

Chasicoan and Huayquerian localities.

Despite these similarities between La Venta and Quebrada Honda faunas, they are also very different. For example, chinchillids, the most abundant and diverse rodent family at Quebrada Honda, are completely absent from La Venta. Their absence at La

Venta is consistent with the notion that the environment in northern South America was

tropical during the middle Miocene (MacFadden et al., 1985). The presence of these

families in Patagonian SALMAs that are older and younger than Laventan suggests that a

similar temperate environment persisted for a long period of time at southern parts of the

continent. Additionally, the least common rodent from Quebrada Honda, a new

aldelphomyine, is the only echimyid from the locality, and is represented by one

individual. Other echimyids, namely Acarechimys and Ricardomys, are abundant at La

Venta. Dinomyids and erethizontids are also noticeably absent from Quebrada Honda and

common at La Venta.

49 While La Venta is the most extensively studied Laventan locality, the middle

Miocene Fitzcarrald fauna of Peru is another likely Laventan assemblage. A preliminary

faunal analysis of this middle latitude locality suggests that it is more similar to La Venta than Quebrada Honda, at least in terms of rodents (Antoine et al., 2007). Two dinomyids

and a dolichotine caviid have been referred to species common at La Venta. The caviid,

Prodolichotis pridiana is likely similar to the Quebrada Honda species. The fossil rodents

at this locality do not appear to be very similar to those from Arroyo Chasicó or Collón-

Curá in Argentina (Antoine et al., 2007). The exploration of this fauna suggests that

tropical environments extended further south than La Venta during the middle Miocene.

Although geographically nearby, Quebrada Honda’s rodents are different from this

Laventan fauna. This suggests that Quebrada Honda had a similar paleoenvironment and

a similar biogeographic history to localities in Patagonia, specifically those pertaining to

younger Chasicoan and Huayquerian SALMAs. Another newly explored locality, “El

Petiso” in northeastern Chubut, has yielded specimens similar to middle Miocene species,

particularly a small dolichotine (which may be similar to the one from La Venta or

Quebrada Honda) and an Alloiomys species. Lagostomines, echyimids, and octodontids

have also been preliminarily identified (Villafañe et al., 2008).

Evolutionary Trends

This analysis of the Quebrada Honda rodents has extended the evolutionary

histories for Orthomyctera and Chasichimys. The Quebrada Honda species of

Orthomyctera represents the earliest occurrence of the genus, extending its temporal

distribution by 4 million years. Previously, Orthomyctera had been found in Chasicoan

50 and younger faunas of Argentina and Bolivia. Similarly, Chasichimys was known from

Chasicoan and Huayquerian faunas. The occurrence of this genus at Quebrada Honda represents the northernmost occurrence of the genus, and increases its geologic distribution by 2,000 km.

In addition to a clear hypsodonty trend among Quebrada Honda rodent taxa, other character states and tooth morphologies are noteworthy. Lagostomine chinchillids, particularly those from younger faunas, exhibit a tendency towards reduced lingual and buccal enamel, particularly near the flexi/flexids that divide each tooth into lophs/lophids

(Vucetich and Verzi, 1993). Vestiges of cement also become increasingly rare in lagostomines from younger faunas. Lagostomines from the Santacrucian (P. pusillus, P. divisus, P. profluens, P. imperialis, P. amplus, and P. obliquidens) and Colloncuran

(including P. rosendoi) often have very reduced or absent buccal enamel on upper cheek teeth, but lingual enamel is present. However, there are some exceptions (such as MLP

15-101, Santacrucian Prolagostomus sp.) that have roughly uniform cement on buccal and lingual surfaces, as do those from the Pinturas Formation (Kramarz, 2002). By the

Chasicoan, members of this genus often lack upper dentition buccal and lingual enamel

(as in MLP 55-IV-28-43). Interestingly, the Quebrada Honda chinchillids more closely resemble the older Santacrucian and Colloncuran species in their maintenance of lingual enamel on upper cheek teeth. This suggests that lingual enamel was lost after the

Laventan, but chinchillids of similar age need to be analyzed from Patagonia to strengthen this argument.

A similar, but more uncertain evolutionary trend is observed in lower dentition for

Prolagostomus. Species from older faunas exhibit some reduction in enamel. However,

51 fewer species (P. divisus and P. imperialis) exhibit pronounced lingual enamel coupled

with buccal enamel absence. Other species (P. profluens in particular) lack enamel on

both lingual and buccal surfaces. Indeed, by the Chasicoan, enamel is absent from these

surfaces of lower cheek teeth (as in MLP 55-IV-28-42). By comparison, the Quebrada

Honda species seem to be a transitory state. While lower molars of P. amplus and P.

profluens have reduced or absent lingual and buccal enamel, lower premolars have

thicker lingual enamel. The two rarest Quebrada Honda species (Prolagostomus sp. nov.

and cf. P. divisus) have thicker lingual enamel. Prolagostomus sp. nov. possesses

uniformly thick lingual enamel on all lower teeth, while anterior and flexid enamel is

thickest for cf. P. divisus.

Chasichimys specimens from Quebrada Honda are the only low-crowned rodents

from the locality. However, all other Chasichimys species (all from younger faunas)

have much higher hypsodonty indices (Verzi, 1999). It is no surprise that this genus

evolved from brachydont ancestors; however, the analysis of the Quebrada Honda species

suggests that the acquisition of more hypsodont teeth occurred during the Mayoan.

This analysis of rodent specimens from Quebrada Honda has numerous far-

reaching implications. It suggests that the paleoenvironment was temperate to semiarid.

Although habitats may have been patchy to some extent, the abundance and diversity of

rodents with high-crowned teeth suggests a predominance of grasses and shrubs, with few forests. Faunal similarities between Quebrada Honda and La Venta and Patagonia suggest that north-south species intermingling was more prevalent than previously considered, thus refuting the argument that geographic barriers prevented dispersal during the Miocene. This study also provides older first occurrences of Orthomyctera and

52 Chasichimys in the fossil record and give important insight into the evolution of lagostomine and ctenomyine lineages. This information has, and will continue to facilitate a more detailed understanding of South American mammalian evolution and dispersal patterns during the Miocene.

Appendix 1. Anteroposterior length (APL) and transverse width (TRW) measurements (in mm) for Orthomyctera rigens dentition.

p4 m1 m2 m3 Specimen Number APL TRW APL TRW APL TRW APL TRW DC BO 5-14-07-171 3.1 2.4 3.5 3.2 4.5 3.2 4.2 2.9 DC BO 5-14-07-173 2.0 2.4 3.4 2.7 3.5 3.0 4.3 2.8 DC BO 5-14-07-208 3.0 2.8 3.4 2.8 3.9 3.0 DC BO 5-14-07-217 3.0 2.5 3.5 3.3 4.1 3.2 UF 236858 2.7 2.7 3.1 2.7 UF 26914 3.0 2.8

P4 M1 M2 M3 Specimen Number APL TRW APL TRW APL TRW APL TRW DC BO 5-13-07-162 right 3.3 2.8 3.3 3.3 DC BO 5-13-07-162 left 3.5 3.3 DC BO 5-14-07-181 3.1 3.0 DC BO 5-15-07-238 right 3.1 3.3 3.2 3.0 3.3 2.8 4.1 3.2 DC BO 5-15-07-238 left 3.5 3.1 3.1 3.1 4.6 2.7 UF 236853 right 3.2 3.7 2.8 2.7 2.4 UF 236853 left 3.2 3.1 3.3 3.0 3.2 2.9 3.9 UF 236859 right 2.8 2.1 3.1 UF 236859 left 2.7 2.5 3.0 2.7 UF 236860 right 3.2 2.7 2.7 3.1 3.1 2.9 UF 236860 left 3.5 3.4 2.8 3.1

Appendix 2. Anteroposterior length (APL) and transverse width (TRW) measurements (in mm) for cf. Prodolichotis mendocina dentition. p4 m1 m2 m3 Specimen Number APL TRW APL TRW APL TRW APL TRW UF 236854 right 3.3 2.6 4.0 3.3 4.2 3.2 4.4 2.8 UF 236854 left 3.4 3.1 4.1 3.0 4.5 3.5 4.2 3.4

Appendix 3. Anteroposterior length (APL) and transverse width (TRW) measurements (in mm) for Prodolichotis sp. nov. dentition.

p4 m1 m2 m3 Specimen Number APL TRW APL TRW APL TRW APL TRW UF 66003 3.4 2.6 4.0 3.1 3.5 3.1

Appendix 4. Anteroposterior length (APL) and transverse width (TRW) measurements

(in mm) for Chasichimys sp. nov. dentition.

dp4 m1 m2 m3 Specimen Number APL TRW APL TRW APL TRW APL TRW DC BO 5-12-07-96 1.7 1.8 1.6 1.6 DC BO 5-12-07-97 1.7 1.2 DC BO 5-12-07-134 2.0 1.4 2.0 1.8 1.6 2.0 DC BO 5-12-07-135 1.8 1.2 1.6 1.7 1.6 1.7 1.6 1.4 DC BO 5-12-07-147 1.9 1.2 1.9 1.7 1.7 1.8 DC BO 5-13-07-150 1.5 1.6 1.7 1.9 2.0 1.4 1.4 DC BO 5-13-07-152 1.8 1.8 1.9 1.9 1.5 1.4 DC BO 5-13-07-158 1.7 2.0 DC BO 5-13-07-160 1.9 1.5 1.8 1.4 DC BO 5-14-07-174 2.0 1.4 2.0 1.7 1.6 1.6 DC BO 5-14-07-183 1.9 1.5 1.8 2.1 2.1 2.1

Appendix 5. Anteroposterior length (APL) and transverse width (TRW) measurements (in mm) for adelphomine gen. et sp. nov. dentition.

dp4 m1 m2 m3 Specimen Number APL TRW APL TRW APL TRW APL TRW DC BO 5-15-07-230 2.4 2.1 3.0 2.5 3.2 2.6

Appendix 6. Anteroposterior length (APL) and transverse width (TRW) measurements (in mm) for Prolagostomus profluens dentition.

p4 m1 m2 m3 Specimen Number APL TRW APL TRW APL TRW APL TRW DC BO 5-12-07-88 2.8 2.3 3.4 4.1 DC BO 5-12-07-98 3.1 3.2 3.1 4.0 2.7 3.2 3.1 3.1 DC BO 5-12-07-103 3.5 3.9 3.1 3.2 DC BO 5-12-07-104 3.4 4.0 DC BO 5-12-07-107 3.1 3.4 2.8 2.9 DC BO 5-12-07-109 2.8 3.1 3.1 3.1 3.1 3.1 DC BO 5-13-07-127 2.1 3.0 DC BO 5-13-07-129b 2.5 3.0 3.1 3.7 3.8 3.2 3.3 3.2 DC BO 5-13-07-129e 2.4 2.8 3.0 4.0 2.3 3.5 2.4 2.8 DC BO 5-13-07-141 3.3 3.4 3.3 3.8 2.2 3.3 3.4 2.3 DC BO 5-13-07-142 3.1 3.5 3.4 4.2 3.0 3.0 3.3 3.8 DC BO 5-13-07-146 2.3 3.1 3.8 3.9 3.3 3.8 2.9 3.0 DC BO 5-13-07-148 2.4 2.8 3.0 3.0 2.2 2.9 DC BO 5-13-07-154 2.5 2.3 DC BO 5-13-07-155 3.0 3.4 3.4 4.0 3.4 2.8 DC BO 5-13-07-163 2.4 4.5 2.2 3.1 3.0 2.2 3.8 3.1 DC BO 5-13-07-165 2.2 3.5 2.3 3.0 DC BO 5-14-07-170 2.2 3.3 3.4 2.3 2.9 2.1 DC BO 5-14-07-185 3.1 4.0 3.1 4.2 2.7 3.6 3.3 DC BO 5-14-07-204 2.3 3.5 2.4 3.2 3.4 DC BO 5-14-07-205 2.7 2.8 3.1 3.4 3.3 3.3 3.2 2.9 DC BO 5-14-07-221 1.8 2.8 2.4 2.9 DC BO 5-15-07-232 2.3 2.8 2.9 3.5 DC BO 5-15-07-234 2.4 3.3 2.6 3.5 2.6 3.6 DC BO 5-15-07-237 2.1 2.8 2.5 3.3 2.2 2.8 DC BO 5-15-07-241 3.0 2.4 3.2 3.2 3.4 4.2 3.9 3.0 UF 26920 2.3 3.6 2.8 3.8 2.6 3.8 UF 236856 1.9 2.9 2.7 3.4 UF 26932 2.5 3.9 2.9 3.5 UF 26912 2.7 3.1 3.9 UF 26942 2.4 3.5 3.0 4.1 3.0 3.6 3.1 3.1 UF 66001 3.0 3.2 2.9 UF 26935 3.0 3.1 UF 27897 2.6 4.7 3.8 3.5 4.2 3.4

56 UF 236855 2.8 2.7 3.0 2.8 UF 26924 2.9 3.1 2.9 3.5 2.5 2.9

P4 M1 M2 M3 Specimen Number APL TRW APL TRW APL TRW APL TRW DC BO 5-12-07-87 right 3.8 4.1 3.1 3.8 4.0 4.2 4.9 4.3 DC BO 5-12-07-87 left 3.7 4.0 3.2 3.8 4.2 4.0 4.8 4.2 DC BO 5-12-07-102 2.3 2.8 2.9 3.0 2.7 2.9 DC BO 5-14-07-177 right 2.2 3.1 2.2 3.1 2.1 3.5 DC BO 5-14-07-177 left 2.1 2.8 2.5 3.0 2.4 2.8 2.6 2.7 DC BO 5-14-07-225 2.3 3.0 2.0 2.3 2.4 2.7 UF 26916 right 2.6 3.7 2.8 4.5 2.8 3.8 UF 26916 left 2.9 3.7 3.0 4.4 2.7 3.8 3.8 3.3 UF 26917 right 2.3 2.9 2.6 3.4 2.6 3.0 UF 26917 left 2.4 2.5 2.4 UF 236857 right 2.6 3.4 3.0 3.1 2.9 3.5 UF 236857 left 2.8 3.4 3.0 3.5 2.9 3.8 UF 26927 2.5 2.5 2.5 UF 66002 right 2.5 3.4 2.4 3.1 UF 66002 left 2.8 3.3

Appendix 7. Anteroposterior length (APL) and transverse width (TRW) measurements (in mm) for Prolagostomus amplus dentition.

p4 m1 m2 m3 Specimen Number APL TRW APL TRW APL TRW APL TRW DC BO 5-12-07-106a 2.3 2.7 2.4 2.6 2.4 2.7 DC BO 5-13-07-129d 2.5 2.6 2.4 2.6 2.7 2.5 2.5 2.8 DC BO 5-15-07-246 3.1 3.4 3.0 3.4 3.3 3.4 3.1 3.3 UF 26919 3.0 3.0 2.8

Appendix 8. Anteroposterior length (APL) and transverse width (TRW) measurements (in mm) for cf. Prolagostomus divisus dentition.

p4 m1 m2 m3 Specimen Number APL TRW APL TRW APL TRW APL TRW DC BO 5-12-07-106 2.1 2.1 2.4 2.9 2.9 3.0

Appendix 9. Anteroposterior length (APL) and transverse width (TRW) measurements (in mm) for Prolagostomus sp. nov. dentition.

p4 m1 m2 m3 Specimen Number APL TRW APL TRW APL TRW APL TRW DC BO 5-13-07-133 2.9 3.4 3.0 4.2 3.3 3.5 2.9 3.1

58 References:

Ameghino, F. 1887. Enumeración sistemática de las especies de mamíferos fósiles coleccionados por C. Ameghino en los terrenos eocenos de la Patagonia austral. 1:1-24.

Ameghino, F. 1889. Contribución al conocimiento de los mamíferos fósiles de la República Argentina. Actas de la Academia Nacional de Ciencias de Córdoba 6:1-1027.

Ameghino, F. 1894. Enumération synoptique des espèces mammifères fossiles des formations éocènes de Patagonie. Boletín de la Academia Nacional de Ciencias, Córdoba 13:259-452.

Ameghino, F. 1906. Les formations sédimentaires du crétacé supérieur et du tertiaire de Patagonie avec un parallèle entre leurs faunes mammalogiques et celles de l'ancien continent. Anales del Museo Nacional de Buenos Aires 3:1-568.

Antoine, P-O., R. Salas-Gismondi, P. Baby, M. Benammi, S. Brusset, D. de Franceschi, N. Espurt, C. Goillot, F. Pujos, J. Tejada, and M. Urbina. 2007. The middle Miocene (Laventan) Fitzcarrald fauna, Amazonian Peru. Cuadernos del Museo Geominero 8: 19-24.

Bennett, E. T. 1833. On the family of Chinchillidae, and on a new genus referable to it. Proceedings of the Zoological Society of London: 57-60.

Bergqvist, L. P., A. M. Ribeiro, and J. Bocquentin-Villanueva. 1998. Primata, roedores e Litopternas do Mio/Plioceno da Amazõnia sul-ocidental (Formação Solimões, Bacia do Acre), Brasil. Geología Colombiana 23:19-29.

Bondesio, P., J. Rabassa, R. Pascual, M. G. Vucetich, and G. J. Scillato-Yané. 1980a. La Formación Collón Curá de Pilcaniyeu Viejo y sus alrededores (Río Negro, República Argentina). Su antigüedad y las condiciones ambientales según su distribución, su litogénesis y sus vertebrados. Actas del Segundo Congreso Argentino de Paleontología y Bioestratigrafía y Primer Congreso Latinoamerica de Paleontología 3:85-99.

Bondesio, P., J. H. Laza, G. J. Scillato-Yané, E. P. Tonni, and M. G. Vucetich. 1980b. Estado actual del conocimiento de los vertebrados de la Formación Arroyo Chasicó (Plioceno temprano) de la Provincia de Buenos Aires. Actas del Segundo Congreso Argentino de Paleontología y Bioestratigrafía y Primer Congreso Latinoamerica de Paleontología 3:101-127.

Brizuela, R. and A. Tauber. 2006. Estratigrafía y mamíferos fósiles de la Formación Toro Negro (Neógeno), Departamento Vinchina, noroeste de la provincial de La Rioja, Argentina. Ameghiniana 43 (2): 257-272.

Carvalho, G. A. S., and L. O. Salles. 2004. Relationships among extant and fossil

59 echimyids (Rodentia: Hystricognathi). Zoological Journal of the Linnean Society 142:445-477.

Cione, A. L., M., M. Azpelicueta, M. Bond, A. A. Carlini, J. R. Casciotta, M. A. Cozzuol, M. de la Fuente, Z. Gasparini, F. J. Goin, J. Noriega, G. J. Scillato-Yané, L. Soibelzon, E. P. Tonni, D. Verzi, and M. G. Vucetich. 2000. Miocene vertebrates from Entre Ríos Province, eastern Argentina. El Neogeno de Agentina, INSUGEO, Serie Correlación Geológica 14:191-237.

Croft, D. A. 2007. The middle Miocene (Laventan) Quebrada Honda Fauna, southern Bolivia, and a description of its notoungulates. Palaeontology 50:277-303.

Croft, D. A., and F. Anaya. 2004. A new hegetotheriid from the middle Miocene of Quebrada Honda, Bolivia, and a phylogeny of the Hegetotheriidae. Journal of Vertebrate Paleontology 24:48-49A.

Croft, D.A., J.J. Flynn, & A.R. Wyss. 2008. The Tinguiririca Fauna of Chile and the early stages of “modernization” of South American mammal faunas. Arquivos do Museu Nacional 66 (1):191-211.

Fields, R. W. 1957. Hystricomorph rodents from the late Miocene of Colombia, South America. University of California Publications in Geological Sciences 32:273- 404.

Flynn, J. J., and C. C. Swisher, III. 1995. Cenozoic South American Land Mammal Ages: Correlation to global geochronologies; pp. 317-333 in W. A. Berggren, D. V. Kent, M.-P. Aubry and J. Hardenbol (eds.), Geochronology, Time Scales, and Global Stratigraphic Correlation. SEPM (Society for Sedimentary Geology) Special Publication No. 54.

Flynn, J. J., and A. R. Wyss. 1998. Recent advances in South American mammalian paleontology. Trends in Ecology and Evolution 13:449-454.

Hoffstetter, R. 1977. Un gisement de mammifères miocènes à Quebrada Honda (Sud Bolivien). Comptes Rendus de la Académie des Sciences, Paris, Série D 284:1517-1520.

Hoffstetter, R. 1986. High Andean mammalian faunas during the Plio-Pleistocene; pp. 218-245High Altitude Sub-Tropical Biogeography. Oxford University Press, Oxford.

Hoffstetter, R., and R. Lavocat. 1970. Découverte dans le Déséadien de Bolivie des genres pentalophodontes appuyant les affinities africaines des rongeurs Coviomorphes. Comptes Rendus de la Académie des Sciences, Paris, Série D 271:172-175.

Huchon, D. and E. J. P. Douzery. 2001. From the old-world to the new-world: a molecular chronicle of the phylogeny and biogeography of hystricognath rodents.

60 Molecular Phylogenetics and Evolution 20 (2): 238-351.

Kay, R. F., R. H. Madden, R. L. Cifelli, and J. J. Flynn (eds.). 1997. Vertebrate Paleontology in the Neotropics: the Miocene Fauna of La Venta, Colombia. Smithsonian Institution Press, Washington, D.C.

Kraglievich, L. 1930. La Formacíon Friaseana del Río Frías, etc., y su fauna de mamíferos. Physis X:127-166.

Kramarz, A. G. 2001a. Un nuevo roedor Adelphomyinae (Hystricognathi, Echimyidae) del Mioceno Medio - Inferior de Patagonia, Argentina. Ameghiniana 38:163-168.

Kramarz, A. G. 2001b. Registro de Eoviscaccia (Rodentia, Chinchillidae) en estratos colhuehuapenses de Patagonia, Argentina. Ameghiniana 38:237-242.

Kramarz, A. G. 2002. Roedores chinchilloideos (Hystricognathi) de la Formación Pinturas, Mioceno temprano-medio de la provincia de Santa Cruz, Argentina. Revista del Museo Argentino de Ciencias Naturales 4:167-180.

Kramarz, A. G. 2005. A primitive cephalomyid hystricognath rodent from the early Miocene of northern Patagonia, Argentina. Acta Palaeontologica Polonica 50:249-258.

Kramarz, A. G. 2006. Neoreomys and Scleromys (Rodentia, Hystricognathi) from the Pinturas Formation, late Early Miocene of Patagonia, Argentina. Revista del Museo Argentino de Ciencias Naturales 8:53-62.

Kramarz, A. G. 2008. Un Nuevo Dasyproctidae (Rodentia, Caviomorpha) del Mioceno inferior de Patagonia. Ameghiniana 35 (2): 181-192.

MacFadden, B. J. 2006. Extinct mammalian biodiversity of the ancient New World tropics. Trends in Ecology & Evolution 21:157-165.

MacFadden, B. J., K. E. Campbell, Jr., R. L. Cifelli, O. Siles, N. M. Johnson, C. W. Naeser, and P. K. Zeitler. 1985. Magnetic polarity stratigraphy and mammalian fauna of the Deseadan (Late Oligocene-Early Miocene) Salla Beds of northern Bolivia. Journal of Geology 93:223-250.

MacFadden, B. J., Y. Wang, T. E. Cerling, and F. Anaya. 1994. South American fossil mammals and carbon isotopes: a 25 million-year sequence from the Bolivian Andes. Palaeogeography, Palaeoclimatology, Palaeoecology 107:257-268.

MacFadden, B. J., and R. G. Wolff. 1981. Geological investigations of Late Cenozoic vertebrate-bearing deposits in southern Bolivia. Anais do II Congresso Latino- Americano de Paleontología 2:765-778.

Madden, R. H., J. Guerrero, R. F. Kay, J. J. Flynn, C. C. Swisher, III, and A. H. Walton. 1997. The Laventan Stage and Age; pp. 499-519 in R. F. Kay, R. H. Madden, R.

61 L. Cifelli and J. J. Flynn (eds.), Vertebrate Paleontology in the Neotropics: the Miocene Fauna of La Venta, Colombia. Smithsonian Institution Press, Washington, D.C.

Marshall, L. G., A. Berta, R. Hoffstetter, R. Pascual, O. A. Reig, M. Bombin, and A. Mones. 1984. Mammals and stratigraphy: Geochronology of the continental mammal-bearing Quaternary of South America. Palaeovertebrata, Mém. extr. 1983:1-76.

Marshall, L. G., and B. Patterson. 1981. Geology and geochronology of the mammal- bearing Tertiary of the Valle de Santa María and Río Corral Quemado, Catamarca Province, Argentina. Fieldiana: Geology, New Series:1-80.

Marshall, L. G., and T. Sempere. 1991. The Eocene to Pleistocene vertebrates of Bolivia and their stratigraphic context: a review; pp. 631-652 in R. Suárez-Soruco (ed.), Fósiles y Facies de Bolivia - Vol. I Vertebrados. Yacimientos Petrolíferos Fiscales Bolivianos, Santa Cruz, Bolivia.

McKenna, M. C., and S. K. Bell. 1997. Classification of Mammals Above the Species Level. Columbia University Press, New York, 631 pp.

Oiso, Y. 1991. New land mammal locality of middle Miocene (Colloncuran) age from Nazareno, southern Bolivia; pp. 653-672 in R. Suárez-Soruco (ed.), Fósiles y Facies de Bolivia - Vol. I Vertebrados. Yacimientos Petrolíferos Fiscales Bolivianos, Santa Cruz, Bolivia.

Pascual, R. 1967. Los roedores Octodontoidea (Caviomorpha) de la Formación Arroyo Chasicó (Plioceno inferior) de la Provincia de Buenas Aires. Revista del Museo de la Plata (Paleontología) 5: 259-282.

Patterson, B., and R. Pascual. 1968b. New echimyid rodents from the Oligocene of Patagonia, and a synopsis of the family. Breviora 301:1-14.

Patterson, B., and A. E. Wood. 1982. Rodents from the Deseadan Oligocene of Bolivia and the relationships of the Caviomorpha. Bulletin of the Museum of Comparative Zoology 149:371-543.

Pocock, R. I. 1922. On the external characters of hystricomorph rodents. Proceedings of the Zoological Society of London 25:365-427.

Prado, J. L., and E. Cerdeño. 1998. Los mamíferos Pliocenos de la fauna local Querquén Grande (provincia de Buenos Aires, Argentina). Estudios Geológicos (Madrid) 54:75-83. Quintana, C. A. 1994. Ctenominos primitivos (Rodentia, Octodontidae) del Mioceno de la Provincia de Buenas Aires, Argentina, Boletín de la Real Sociedad Española de Historia Natural 89: 19-23. Quintana, C. A. 1998. Relaciones filogenéticas de roedores Caviinae (Caviomorpha, Caviidae), de América del Sur. Boletin de la Real Sociedad Espanola de Historia

62 Natural, Seccion Biologica 94:125-134.

Reig, O. A. 1986. Diversity patterns and differentiation of high Andean rodents. In Evolutionary biology of transient unstable populations (A. Fontevidela, ed.) Springer-Verlag, New York, 293 pp.

Rovereto, C. 1914. Los estratos araucanos y sus fosíles. Anales del Museo Nacional de Historia Natural de Buenos Aires 25:1-247.

Scott, W. B. 1905. Mammalia of the Santa Cruz Beds. Volume V, Paleontology. Part III, Glires; pp. 384-490 in W. B. Scott (ed.), Reports of the Princeton University Expeditions to Patagonia, 1896-1899. Princeton University, E. Schweizerbart'sche Verlagshandlung (E. Nägele), Stuttgart.

Simpson, G. G. 1940. Review of the mammal-bearing Tertiary of South America. Proceedings of the American Philosophical Society 83:649-710.

Simpson, G. G. 1980. Splendid Isolation: the Curious History of South American Mammals. Yale University Press, New Haven, Connecticut, 266 pp.

Takai, F., B. Arózqueta, T. Mizuno, A. Yoshida, and H. Kondo. 1984. On fossil mammals from the Tarija Department, southern Bolivia. The Research Institute of Evolutionary Biology, Publication No. 4, 63 pp.

Ubilla, M., and A. Rinderknecht. 2003. A Late Miocene Dolichotinae (Mammalia, Rodentia, Caviidae) from Uruguay, with comments about the relationships of some related fossil species. Mastozoología Neotropical 10:293-302.

Verzi, D.H. 1999. The dental evidence on the differentiation of the ctenomyine rodents (Caviomorpha, Octodontidae, Ctenomyinae). Acta Theriologica 44: 263-282.

Verzi, D. H., E. C. Vieytes, and C. I. Montalvo. 2004. Dental evolution in Xenodontomys and first notice on secondary acquisition of radial enamel in rodents (Rodentia, Caviomorpha, Octodontidae). Geobios 37:795-806.

Verzi, D. H., M. G. Vucetich, and C. I. Montalvo. 1994. Octodontid-like Echimyidae (Rodentia); an upper Miocene episode in the radiation of the family. Palaeovertebrata 23: 199-210.

Villafañe, A. L., M. E. Pérez, M. A. Abello, E. Bedatou, and M. Bond. 2008. Nueva localidad fosilífera del Mioceno medio en el noroeste de la Provincia del Chubut. Congreso Latinoamericano de Paleontología de Vertebrados: 265.

Vucetich, M. 1984. Los roedores de la Edad Friasense (Mioceno medio) de Patagonia. Revista del Museo de La Plata (Nueva Seria) 8:47-126.

Vucetich, M. G., and M. Bond. 1982. Los primeros Isotemnidae (Mammalia, Notoungulata) registrados en la Formación Lumbrera (Grupo Salta), del noroeste

63 argentino. Ameghiniana 19:7-18.

Vucetich, M. G., and D. H. Verzi. 1991. Un nuevo Echimyidae (Rodentia, Hystricognathi) de la edad Colhuehuapense de Patagonia y consideraciones sobre la sistematica de la familia. Ameghiniana 28:67-74.

Vucetich, M. G., M. M. Mazzoni, and U. F. J. Pardiñas. 1993. Los roedores de la Formación Collón Cura (Mioceno medio), y la Ignimbrita Pilcaniyeu. Cañadón del Tordillo, Neuquen. Ameghiniana 30:361-381.

Vucetich, M. G., and D. H. Verzi. 1993. Un nuevo Chinchillidae del Colhuehapense ("Mioceno inferior") de Gaiman (Chubut); su aporte a la comprension de la dicotomia Vizacachas-Chinchillas; pp. 115IX jornadas argentinas de paleontologia de vertebrados. Asociacion Paleontologica Argentina, Buenos Aires, Argentina.

Vucetich, M. G., D. H. Verzi, and J. L. Hartenberger. 1999. Review and analysis of the radiation of the South American Hystricognathi (Mammalia, Rodentia). Comptes Rendus de la Académie Des Sciences, Paris, Serie II, Fascicule A -Sciences De La Terre et Des Planetes 329:763-769.

Walton, A. H. 1990. Rodents of the La Venta fauna, Miocene, Colombia: Biostratigraphy and paleoenvironmental implications. Ph.D. Dissertation, Southern Methodist University, Dallas, 159 pp.

Walton, A. H. 1997. Rodents; pp. 392-409 in R. F. Kay, R. H. Madden, R. L. Cifelli and J. J. Flynn (eds.), Vertebrate Paleontology in the Neotropics: the Miocene Fauna of La Venta, Colombia. Smithsonian Institution Press, Washington, D.C.

Wood, A. E. 1949. A new Oligocene rodent genus from Patagonia. American Museum Novitates:1-54.

Wood, A.E. and B. Patterson. 1959. Rodents of the Deseadan Oligocene of Patagonia and the beginnings of South American rodent evolution. Bulletin of the Museum of Comparative Zoology 120: 281-428.

Wyss, A. R., J. J. Flynn, M. A. Norell, C. C. Swisher, III, R. Charrier, M. J. Novacek, and M. C. McKenna. 1993. South America's earliest rodent and recognition of a new interval of mammalian evolution. Nature 365:434-437.