Chapter 12

Mammalian Biochronology of Blancan and Irvingtonian (Pliocene and Early Pleistocene) Faunas from New Mexico

GARY S. MORGAN1 AND SPENCER G. LUCAS2

ABSTRACT

Signi®cant mammalian faunas of Pliocene (Blancan) and early Pleistocene (early and medial Irvingtonian) age are known from the Rio Grande and Gila River valleys of New Mexico. Fossiliferous exposures of the Santa Fe Group in the Rio Grande Valley, extending from the EspanÄola basin in northern New Mexico to the Mesilla basin in southernmost New Mexico, have produced 21 Blancan and 6 Irvingtonian vertebrate assemblages; three Blancan faunas occur in the Gila River Valley in the Mangas and Duncan basins in southwestern New Mexico. More than half of these faunas contain ®ve or more species of mammals, and many have associated radioisotopic dates and/or magnetostratigraphy, allowing for correlation with the North American land-mammal biochronology. Two diverse early Blancan (4.5±3.6 Ma) faunas are known from New Mexico, the Truth or Consequences Local Fauna (LF) from the Palomas basin and the Buckhorn LF from the Mangas basin. The former contains ®ve species of mammals indicative of the early Blancan: Borophagus cf. B. hilli, Notolagus lepusculus, Neo- toma quadriplicata, Jacobsomys sp., and Odocoileus brachyodontus. Associated magnetostra- tigraphic data suggest correlation with either the Nunivak or Cochiti Subchrons of the Gilbert Chron (4.6±4.2 Ma), which is in accord with the early Blancan age indicated by the mam- malian biochronology. The Truth or Consequences LF is similar in age to the Verde LF from Arizona, and slightly older than the Rexroad 3 and Fox Canyon faunas from Kansas. The Buckhorn LF has 18 species of mammals, including two rodents typical of the early Blancan, Mimomys poaphagus and Repomys panacaensis. The Buckhorn LF also is similar in age to the Verde LF and has af®nities with the Panaca LF from Nevada. Although the Buckhorn and Truth or Consequences LFs have few taxa in common, the similarities of both faunas with the Verde LF suggest they are close in age. Eight faunas from the central and southern Rio Grande Valley are medial Blancan in age (3.6±2.7 Ma), including the Pajarito and Belen faunas from the Albuquerque basin, the Arroyo de la Parida LF from the Socorro basin, the Cuchillo Negro Creek and Elephant Butte Lake LFs from the Engle basin, the Palomas Creek LF from the Palomas basin, the Hatch LF from the Hatch-Rincon basin, and the Tonuco Mountain LF from the Jornada basin. These faunas are characterized by the presence of taxa absent from early Blancan faunas, including Geomys (Nerterogeomys) paenebursarius, Equus cumminsii, E. scotti, and Camelops, and the absence of South American immigrant mammals found in late Blancan faunas. The Pajarito LF is directly associated with a pumice dated at 3.1 Ma. The Cuchillo Negro Creek and Elephant Butte Lake LFs are in close stratigraphic association with a basalt ¯ow of 2.9 Ma. Magneto- stratigraphy constrains the age of the Tonuco Mountain LF between 3.6 and 3.0 Ma. The Mesilla A fauna from the Mesilla basin and the Pearson Mesa LF from the Duncan basin are late Blancan in age (2.7±2.2 Ma). Both record the association of Nannippus with a South American immigrant, Glyptotherium from Mesilla A and Glossotherium from Pearson Mesa, restricting their age to the interval after the beginning of the Great American Interchange at about 2.7 Ma and before the extinction of Nannippus ca. 2.2 Ma. Magnetostratigraphy

1 Curator of Vertebrate Paleontology, New Mexico Museum of Natural History, 1801 Mountain Road NW, Albu- querque, NM 87104. 2 New Mexico Museum of Natural History, 1801 Mountain Road NW, Albuquerque, NM 87104.

269 270 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279

further constrains the Mesilla A and Pearson Mesa faunas to the upper Gauss Chron, just prior to the Gauss/Matuyama boundary. The Mesilla B and Virden faunas occur higher in the same stratigraphic sequences as the Mesilla A and Pearson Mesa faunas, respectively, and are latest Blancan in age (2.2±1.8 Ma). Both faunas contain taxa restricted to the Blancan, including the camels Blancocamelus and Gigantocamelus from Mesilla B, and Canis lepophagus from Vir- den. The absence of Nannippus, and of Mammuthus and other genera that ®rst appear in the Irvingtonian, support the age. The Tijeras Arroyo fauna from the Albuquerque basin and the Tortugas Mountain and Mesilla C faunas from the Mesilla basin all possess Mammuthus and other mammals indicative of early Irvingtonian age. The association of Mammuthus and Stegomastodon in the Tortugas Mountain LF indicates an age younger than 1.8 Ma, after the arrival of Mammuthus in North America from Eurasia and before the extinction of Stegomastodon at about 1.2 Ma. The co- occurrence of Glyptotherium arizonae, Equus scotti, and the primitive mammoth M. meri- dionalis in Tijeras Arroyo and Mesilla C is typical of southwestern early Irvingtonian faunas. Fossils of M. meridionalis from Tijeras Arroyo and Mesilla C are both closely associated with dates of 1.6 Ma on pumice from the lower Bandelier tuff, making them among the oldest dated mammoths in North America. A fauna from San Antonio Mountain (SAM) Cave in the San Luis basin of northernmost New Mexico lacks large mammals, but the presence of the microtine rodents Mictomys kansasensis, an advanced species of Allophaiomys, Lemmiscus curtatus, and Microtus cf. M. californicus indicates medial Irvingtonian age, between about 1.0 and 0.85 Ma.

INTRODUCTION basin in the Gila River Valley in southwest- ern New Mexico (®g. 12.1). Several addi- There are 31 vertebrate fossil assemblages tional Blancan faunas are known from the currently known from New Mexico that date Gila River Valley in southeastern Arizona to the time interval from the early Blancan (Galusha et al., 1984; Tomida, 1987). North American land mammal ``age'' (NAL- Prior to the 1980s, very few of New Mex- MA), about 4.0 Ma (early Pliocene), through ico's Blancan and Irvingtonian faunas had the medial Irvingtonian NALMA, about 0.8 been mentioned in the literature. In their re- Ma (late early Pleistocene). These faunas are view of the ``Pleistocene'' mammals of concentrated in two areas of the state, the Rio North America, including the Blancan, which Grande Valley and the Gila River Valley (®g. is now known to be entirely Pliocene, KurteÂn 12.1). The Rio Grande bisects the state from and Anderson (1980) did not list a single the Colorado border on the north to the Mex- Blancan or Irvingtonian fauna from New ico and Texas borders on the south, ¯owing Mexico. Tedford (1981) summarized all of through a series of structural basins that are New Mexico's Blancan and Irvingtonian fau- part of the Rio Grande rift system. A nas known at that time, including 12 Blancan through-¯owing Rio Grande apparently orig- faunas and 1 Irvingtonian fauna. Despite inated sometime in the early Pliocene after Tedford's (1981) paper, no sites from New about 5 Ma, and shortly thereafter began de- Mexico were mentioned in the review of positing ¯uvial sediments that preserve ver- North American Blancan and Irvingtonian faunas in Lundelius et al. (1987). Repenning tebrate fossils. Most of the Rio Grande rift (1987) mentioned the early Blancan Truth or basins contain Blancan and/or Irvingtonian Consequences Local Fauna (LF) in his re- vertebrate fossils, from the San Luis basin on view of late Cenozoic microtine rodents from the Colorado border in the northernmost part North America. We summarize all studies on of the state to the Mesilla basin on the Mex- New Mexico Blancan and Irvingtonian fau- ican border in southernmost New Mexico. nas published since Tedford (1981) through The Gila River originates in the Mogollon the end of 2000, and include much new un- Mountains in southwestern New Mexico and published data. ¯ows southwestward, eventually crossing into Arizona. Blancan vertebrate faunas have MATERIALS AND METHODS been recovered from sediments of the Gila Richard Tedford's 1981 paper on the bio- Group in the Mangas basin and the Duncan chronology of late Cenozoic mammalian fau- 2003 MORGAN AND LUCAS: BLANCAN AND IRVINGTONIAN MAMMALS 271 nas from New Mexico provided the impetus Space does not permit us to exhaustively for our long-term project to collect, docu- review all of the 31 currently known New ment, and describe all Blancan and Irving- Mexico Blancan and Irvingtonian faunas and tonian vertebrate faunas from New Mexico. sites. Detailed documentation (e.g., catalogue Beginning in the mid-1980s and continuing numbers, morphological descriptions, and to the present, paleontologists from the New measurements) is not provided for specimens Mexico Museum of Natural History and the described in previous papers. Documentation University of New Mexico have been in- is provided for selected fossils not previously volved in a program to locate new faunas of mentioned in the literature. We give brief de- Blancan and Irvingtonian age throughout scriptions of certain fossils that are of critical New Mexico and to recollect faunas of this importance to mammalian biochronology. age discussed by Tedford (1981). Many new This paper should be considered a status re- Blancan and Irvingtonian faunas have been port because we are actively involved in discovered in New Mexico in the past 15 ®eldwork on Blancan and Irvingtonian fau- years (Lucas and Oakes, 1986; Repenning nas throughout New Mexico. In particular, and May, 1986; Morgan et al., 1998; Morgan comprehensive faunal papers are planned in and Lucas, 1999, 2000a; Rogers et al., 2000), the near future for the Arroyo de la Parida, and extensive new fossil material has been Truth or Consequences, and Pearson Mesa added to many of the faunas described in Local Faunas, and the late Blancan and early Tedford's 1981 paper (Vanderhill, 1986; Irvingtonian faunas from the Mesilla basin. Tomida, 1987; Lucas et al., 1993; Morgan et There are three major collections of Blan- al., 1997; Morgan and Lucas, 1999, 2000a, can and Irvingtonian vertebrate fossils from 2000b). Combining the information in Ted- New Mexico. The New Mexico Museum of ford's 1981 paper, which was based on fos- Natural History and Science (NMMNH) in sils in the collections of the Frick Laboratory Albuquerque and the Frick Collection (F: at the American Museum of Natural History, AM) of the American Museum of Natural and data obtained through our ®eldwork, we History (AMNH) in New York both contain can now provide a fairly detailed review of substantial collections of Blancan and Irving- the Blancan and Irvingtonian fossil record of tonian fossils from throughout the state. The New Mexico. Museum of Arid Land Biology at the Uni- The present paper summarizes the histor- versity of Texas at El Paso (UTEP) has large ical, faunal, stratigraphic, and geochronolog- collections from the Mesilla basin in south- ic data for all known Blancan and Irvington- ern New Mexico. Other New Mexico Blan- ian mammalian faunas from New Mexico. can and Irvingtonian fossils consulted during Faunal lists for sites containing four or more this study include specimens from the Ge- taxa of mammals are provided in tables 12.1 ology Museum in the Department of Earth and 12.2, including 15 Blancan faunas and 4 and Planetary Sciences at the University of Irvingtonian faunas. Numerous additional New Mexico (UNM) in Albuquerque, the sites with fewer than four mammals are dis- New Mexico State University Museum cussed in the text. We follow Woodburne (NMSUM) in Las Cruces, the University of (1987: xiv) for the de®nitions of fauna and Arizona Laboratory of Paleontology (UALP) local fauna. Thus, a fauna is ``an assemblage in Tucson, and the United States Geological of fossil vertebrates of speci®c taxonomic Survey Collection (USGS) in Denver. Site composition obtained from a number of geo- numbers (preceded by NMMNH L-) listed graphically diverse sites.'' A local fauna is throughout the paper refer to NMMNH fossil ``an assemblage of fossil vertebrates of spe- localities. Field notes, map coordinates, and ci®c taxonomic composition recovered from other information on these sites are on ®le in one or a few sites that are closely spaced the Paleontology Collection at the NMMNH. stratigraphically and geographically.'' We follow Woodburne and Swisher (1995) for PREVIOUS WORK use of the age terms early, medial, and late for subdivisions of epochs (e.g., early Plio- Pliocene (Blancan) fossils were ®rst re- cene) and NALMAs (e.g., medial Blancan). ported from New Mexico by Needham 272 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279 2003 MORGAN AND LUCAS: BLANCAN AND IRVINGTONIAN MAMMALS 273

(1936), who described a pair of mandibles of 1928 from Hot Springs and in 1929 from the the gomphotheriid proboscidean Rhynchoth- Mesilla basin. Ted Galusha collected fossils erium and a lower molar of the horse Plesip- in 1946 from the northern edge of the Isleta pus from Santa Fe Group deposits in Arroyo Reservation in southern Bernalillo County. de la Parida, northeast of Socorro in Socorro George Pearce made collections in the Mes- County. Plesippus is now generally regarded illa basin in 1949 and near Buckhorn in the as a primitive subgenus of Equus, and is typ- Mangas basin in 1953. ical of Blancan faunas. Needham also re- Tedford (1981) was the ®rst paleontologist ported several fossil turkey (Meleagris) to summarize the data on New Mexican bones from a pumice deposit of probable ear- Blancan and Irvingtonian faunas, primarily ly Irvingtonian age in an exposure along the based on the previously unpublished material Rio Grande near San Antonio, also in So- in the Frick Collection at the AMNH. Ted- corro County. Denny (1940) identi®ed Equus ford provided a biostratigraphic framework and the gomphotheriid proboscidean Stego- for all subsequent work on New Mexico mastodon from Santa Fe Group deposits Blancan and Irvingtonian faunas, which has north of the Rio Salado on land now within included additional work on many of the fau- the Sevilleta National Wildlife Refuge in the nas he discussed, as well as the discovery of southernmost Albuquerque basin in northern new faunas. Repenning and May (1986) pro- Socorro County. Between 1926 and 1953, vided a faunal list, brief taxonomic descrip- collectors working for the Frick Laboratory tions, and magnetostratigraphy for the early accumulated signi®cant samples of Blancan Blancan Truth or Consequences LF from the and Irvingtonian vertebrates from various lo- Palomas Formation in the Palomas basin calities throughout New Mexico. Very few of near Truth or Consequences in Sierra Coun- these specimens were published until 1981, ty. Lucas and Oakes (1986) described the when Tedford summarized the mammalian medial Blancan Cuchillo Negro Creek LF biochronology of the late Cenozoic basins of from the Engle basin, also from the Palomas New Mexico. Between 1926 and 1929, Jo- Formation in Sierra County. In his doctoral seph Rak collected fossil vertebrates on the dissertation, Vanderhill (1986) presented a Santo Domingo Reservation in the northern detailed review of the vertebrate paleontolo- Albuquerque basin, from Hot Springs (now gy, magnetostratigraphy, and lithostratigra- Truth or Consequences), Palomas Creek, and phy of late Blancan through early Irvington- other sites west of Elephant Butte Lake in ian faunas in the Mesilla basin south of Las the Engle and Palomas basins, and from the Cruces in DonÄa Ana County. Tomida (1987) Mesilla basin south of Las Cruces. Charles provided a faunal list and magnetostratigra- Falkenbach collected fossils with Rak in phy for the late Blancan Pearson Mesa LF

← Fig. 12.1. Map of New Mexico showing the location of all late Hemphillian, Blancan, and Irving- tonian fossil sites. The structural basins are named and indicated by stippling. Sites are numbered from north to south in the Rio Grande Valley (sites 1±29), followed by sites in the Gila River Valley (sites 30±33). Site names and ages are listed here. See text for more detailed information on individual sites. 1, San Antonio Mountain (SAM) Cave, medial Irvingtonian; 2, Puye Formation site, late Hemphillian; 3, Ancha sites, late Blancan; 4, Santo Domingo, late Blancan; 5, Western Mobile, early Irvingtonian; 6, Loma Colorado de Abajo, early/medial Blancan; 7, Mountainview, Blancan; 8, Tijeras Arroyo, early Irvingtonian; 9, Pajarito, medial Blancan; 10, Isleta, Blancan; 11, Los Lunas, Blancan; 12, Belen, medial Blancan; 13, Mesas Mojinas, Blancan; 14, Veguita, Blancan; 15, Sevilleta, Blancan; 16, Arroyo de la Parida, medial Blancan; 17, Fite Ranch, early Irvingtonian; 18, Silver Canyon, Blancan; 19, Elephant Butte Lake, medial Blancan; 20, Cuchillo Negro Creek, medial Blancan; 21, Truth or Consequences, early Blancan; 22, Palomas Creek, medial Blancan; 23, Hatch, medial Blancan; 24, Rincon Arroyo, late Blancan/early Irvingtonian; 25, Tonuco Mountain, medial Blancan; 26, Tortugas Mountain, early Ir- vingtonian; 27, Mesilla A, late Blancan; 28, Mesilla B, latest Blancan; 29, Mesilla C, early Irvingtonian; 30, Buckhorn, early Blancan; 31, Walnut Canyon, latest Hemphillian; 32, Pearson Mesa, late Blancan; 33, Virden, latest Blancan. Map modi®ed from Tedford (1981). 274 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279 ndicated a of mam- rom which the Mesilla tions. Taxa marked with TABLE 12.1 Irvingtonian age is listed in table 12.2. Faunal List of Blancan Mammals from New Mexico mals are included in this table. Smaller ®nds of important Blancan taxa are discussed in the text. There are three distinct biostratigraphic levels in basin according to Vanderhill (1986); the mammals from his Fauna A of late Blancan age and Fauna B of latest Blancan age are listed below. Fauna C of early The Blancan faunas are listed across the top of the table with a superscript letter that corresponds to a reference or references at the end of the table f an asterisk (*) are based on identi®cations of specimens collected after the original paper on the site was published. Only faunas with four or more tax the faunal lists were taken. The faunas are listed in order from the oldest on the left to the youngest on the right. The presence of a species in a fauna is i by ``X'' and its absence by ``Ð''. Species listed as ``X?'' were tentatively identi®ed (e.g., identi®ed with ``cf.'' or ``?'') in the original publica 2003 MORGAN AND LUCAS: BLANCAN AND IRVINGTONIAN MAMMALS 275 ) Continued ( TABLE 12.1 276 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279 ) Continued ( TABLE 12.1 2003 MORGAN AND LUCAS: BLANCAN AND IRVINGTONIAN MAMMALS 277 ) Continued ( TABLE 12.1 278 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279

TABLE 12.2 Faunal List of Irvingtonian Mammals from New Mexico Irvingtonian faunas are listed across the top of the table with a superscript letter that corresponds to references at the end of the table. Tijeras Arroyo, Tortugas Mountain, and Mesilla Basin Fauna C are early Irvingtonian in age, and SAM Cave is medial Irvingtonian. The presence of a species in a fauna is indicated by ``X'' and its absence by ``Ð''. Species listed as ``X?'' were tentatively identi®ed (e.g., identi®ed with ``cf.'' or ``?'') in original publications. Taxa marked with an asterisk (*) are based on identi®cations of specimens collected after the original paper on the site was published. Only faunas with four or more mammal taxa are included. Smaller ®nds of important Irving- tonian taxa are discussed in the text. 2003 MORGAN AND LUCAS: BLANCAN AND IRVINGTONIAN MAMMALS 279

TABLE 12.2 (Continued) 280 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279 from the Gila Group in the Duncan basin in beginning of the late Pleistocene at 0.13 Ma Hidalgo County. Lucas et al. (1993) re- is de®ned by the onset of the last (Sanga- viewed late Blancan and early Irvingtonian monian) interglacial. vertebrate faunas from Tijeras Arroyo in the Lindsay et al. (1984) and Tedford et al. Albuquerque basin near Albuquerque in Ber- (1987) placed the boundary between the nalillo County. Lucas and Morgan (1996) re- Hemphillian and Blancan NALMAs in the ported the gomphothere Rhynchotherium fal- early Pliocene at about 4.5 Ma. Lundelius et coneri, and brie¯y summarized the remain- al. (1987) stated that this boundary was not der of the mammalian fauna, from the medial well dated, but fell in the interval of about Blancan Arroyo de la Parida LF from the So- 4.4 to 4.0 Ma. Repenning (1987) considered corro basin in Socorro County. Morgan et al. the Hemphillian/Blancan boundary to be (1997) described the latest Hemphillian Wal- somewhat earlier (about 4.8 Ma) based on nut Canyon LF and the early Blancan Buck- the arrival from the Old World of the im- horn LF from the Gila Group in the Mangas migrant microtine rodents Mimomys and Ne- basin in Grant County. Morgan et al. (1998) braskomys. The end of the Hemphillian is reviewed the medial Blancan Tonuco Moun- characterized by a major extinction event, in- tain LF from the Camp Rice Formation in cluding the disappearance of the families the Jornada basin north of Las Cruces in Rhinocerotidae and Protoceratidae, the hors- DonÄa Ana County. Hawley et al. (1969) and es Hipparion, Neohipparion, Pseudhippa- Lucas et al. (1999, 2000) discussed early Ir- rion, Astrohippus, and Dinohippus, and the vingtonian proboscideans and horses from carnivores Agriotherium, Machairodus, and gravel pits in the vicinity of Tortugas Moun- Plesiogulo. tain east of Las Cruces in the northern part Lindsay et al. (1984) discussed several of the Mesilla basin. Morgan and Lucas mammalian genera that appeared at the be- (1999, 2000a) reviewed 10 Blancan and 2 ginning of the Blancan, including the vole Irvingtonian faunas from the Albuquerque Pliophenacomys and the pocket gopher Geo- basin. Morgan and Lucas (2000b) described mys, and also listed a number of genera that 2 late Blancan faunas from Pearson Mesa in appeared in a relatively short interval in the the Duncan basin. Rogers et al. (2000) de- early Blancan at about 3.7 Ma (their Trigon- scribed the Irvingtonian vertebrate fauna ictis appearance datum), including: the rab- from San Antonio Mountain (SAM) Cave bits Nekrolagus and Pratilepus; the rodents from the San Luis basin in northernmost Neotoma and Pliopotamys; the carnivores New Mexico. Chasmaporthetes, Trigonictis, and Ursus; the peccary Platygonus; the camel Camelops; CHRONOLOGY and the deer Bretzia. Lundelius et al. (1987), Tedford et al. (1987), and Woodburne and We follow Berggren et al. (1995) for Swisher (1995) de®ned the beginning of the placement of the Miocene/Pliocene and Pli- Blancan using most of the same genera men- ocene/Pleistocene boundaries and their sub- tioned by Lindsay et al. (1984) and Repen- divisions, and for the boundaries of the geo- ning (1987), in particular Old World immi- magnetic chrons and subchrons. The Mio- grants such as Mimomys, Nebraskomys, cene/Pliocene boundary is 5.32 Ma, and the Chasmaporthetes, Trigonictis, Ursus, Bret- Pliocene/Pleistocene boundary is located zia, and Odocoileus. However, according to near the top of the Olduvai Subchron at 1.81 some authors (e.g., Lindsay et al., 1984; Cas- Ma. The Pliocene is subdivided into the early siliano, 1999), the earliest occurrences of cer- and late Pliocene, with the boundary between tain of these genera are actually well above these subdivisions placed at the boundary the Hemphillian/Blancan boundary, spanning beween the Gilbert and Gauss Chrons at 3.58 an interval in the early Blancan between Ma. The Pleistocene is subdivided into the about 4.5 and 3.7 Ma. Cassiliano (1999) sug- early, medial, and late Pleistocene. The gested that the ®rst appearance of Sigmodon boundary between the early and medial in the Anza-Borrego Desert sequence in Pleistocene is the boundary beween the Ma- southern California at about 4.3 Ma may ap- tuyama and Brunhes Chrons at 0.78 Ma. The proximate the Hemphillian/Blancan bound- 2003 MORGAN AND LUCAS: BLANCAN AND IRVINGTONIAN MAMMALS 281 ary. Mou (1999) documented the earliest ap- siliano (1999) evaluated the biostratigraphic pearance of Blancan mammals from the Pan- record for most of these genera and conclud- aca LF in Nevada at about 4.95 Ma. The ed that none were suitable for de®ning the above discussion indicates that the Hemphil- Blancan/Irvingtonian boundary. He tenta- lian/Blancan boundary is not well dated, but tively placed the Blancan/Irvingtonian can be placed in the time range of about 4.9 boundary in the latest Pliocene between 2.15 to 4.3 Ma. and 1.95 Ma. The ®rst appearance of Mam- Tedford (1981) divided the Blancan into muthus is often used to de®ne the Irvington- three intervals: early Blancan (4.5±3.7 Ma), ian; however, all well-dated mammoths from medial Blancan (3.7±2.5 Ma), and late Blan- North America are younger than 1.8 Ma (Lu- can (2.5±1.5 Ma). Repenning (1987) divided cas, 1995, 1996; Cassiliano, 1999), and are the Blancan into ®ve intervals (Blancan I±V) thus slightly younger than the Plio-Pleisto- based on the biochronology of microtine (ϭ cene boundary. arvicoline) rodents. Repenning's system is The ®rst appearance of immigrants from dependent on the presence of microtines in a outside of North America is generally con- fauna to determine its age, so in many cases sidered to be of utmost importance in estab- it has limited utility. Only one Blancan fauna lishing boundaries between North American from New Mexico, the Buckhorn LF in land-mammal ages (Lundelius et al., 1987; Grant County (Morgan et al., 1997), contains Woodburne, 1996). Thus, the appearance of microtine rodents. Woodburne and Swisher Mammuthus would seem to be the most log- (1995) recognized only two subdivisions of ical time to establish the Blancan/Irvington- the Blancan, early Blancan (4.9±2.7 Ma) and ian boundary, roughly corresponding to the late Blancan (2.7±1.8 Ma), with the bound- Pliocene/Pleistocene boundary at about 1.8 ary between the early and late Blancan cor- Ma. Mammuthus may not be the ideal genus responding to the beginning of the Great to de®ne the beginning of the Irvingtonian American Interchange at about 2.7 Ma. Ted- (e.g., Cassiliano, 1999), but mammoths do ford's (1981) subdivisions of the Blancan are occur in all three early Irvingtonian faunas the most useful for New Mexico faunas, with from New Mexico. For purposes of our dis- slight modi®cations as follows: early Blan- cussion, we will use the ®rst appearance of can (4.5±3.6 Ma)Ðupper boundary corre- Mammuthus to de®ne the beginning of the sponds to the Gilbert/Gauss boundary and Irvingtonian at about 1.8 Ma. Lundelius et the Trigonictis appearance datum of Lindsay al. (1987) used a three-part subdivision of the et al. (1984); medial Blancan (3.6±2.7 Ma)Ð Irvingtonian: early Irvingtonian (1.8±1.0 upper boundary corresponds to the beginning Ma), medial Irvingtonian (1.0±0.6 Ma), and of the Great American Interchange, which is late Irvingtonian (0.6±0.3 Ma). The bound- just slightly below the Gauss/Matuyama ary between the Irvingtonian and Ranchola- boundary; late Blancan (2.7±1.8 Ma)Ðupper brean corresponds to the ®rst appearance of boundary corresponds to the Plio-Pleistocene Bison at about 0.3 Ma. Repenning (1987) boundary, the top of the Olduvai Subchron, subdivided the Irvingtonian into two inter- and the ®rst appearance of Mammuthus. vals (Irvingtonian I and II) based on micro- Lundelius et al. (1987) documented a tran- tine biochronology, and placed the boundary sitional interval between the Blancan and Ir- between the Irvingtonian and Rancholabrean vingtonian, from about 2.2 to 1.8 Ma. Most slightly earlier, at 0.4 Ma. We follow Lun- characteristic Blancan mammalian genera, delius et al. (1987) in recognizing the early, such as Borophagus, Hypolagus, Paenemar- medial, and late Irvingtonian, and the place- mota, Equus (Plesippus), Nannippus, and ment of the Irvingtonian/Rancholabrean Rhynchotherium, became extinct by about boundary at 0.3 Ma. 2.2 Ma (the Nannippus extinction datum of Lindsay et al., 1984). Lundelius et al. de®ned BLANCAN AND IRVINGTONIAN the Irvingtonian on the ®rst appearance of VERTEBRATE FAUNAS FROM Lepus, Microtus, Smilodon, Equus (Equus), NEW MEXICO Euceratherium, and Mammuthus, most of There are 24 Blancan and 7 Irvingtonian which did not appear until after 1.8 Ma. Cas- vertebrate fossil assemblages currently 282 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279 known from New Mexico (®g. 12.1). These date to the late Matuyama Chron, after the range from sites with a single species of Jaramillo Subchron and before the Matuya- mammal to 26 species of mammals in SAM ma/Brunhes boundary (between about 1.0 Cave. All 31 of these assemblages are dis- and 0.78 Ma). A 10th fauna (NMMNH site cussed below, but only those faunas with L-4385) occurs in normally magnetized sed- four or more species of mammals (15 Blan- iments of the Brunhes Chron, but is not in- can and 4 Irvingtonian faunas) are listed in cluded here because it contains no species of tables 12.1 and 12.2. Twenty-eight of these mammals not found in the older sites. assemblages (21 Blancan and 7 Irvingtonian) The combined vertebrate assemblage from are in the Rio Grande Valley and 3 Blancan the nine medial Irvingtonian sites in SAM faunas are in the Gila River Valley in south- Cave includes a minimum of 41 species (fau- western New Mexico. The discussion of fau- nal list from Rogers et al., 2000, complete nas generally proceeds from north to south, list of mammals in table 2): one species of with the Rio Grande Valley sites followed by trout; 2 species of amphibians, tiger sala- the Gila River Valley sites. All sites men- mander (Ambystoma tigrinum), and chorus tioned in the text and the structural basins in frog (Pseudacris triseriata); 3 reptiles, which they occur are indicated on the map horned lizard (Phrynosoma douglassii), rat- in ®gure 12.1. tlesnake (Crotalus viridis), and garter snake (Thamnophis elegans); 9 birds, short-eared SAN LUIS BASIN owl (Asio cf. A. ¯ammeus), least grebe (Tachybaptus cf. T. dominicus), vireo (Vireo SAN ANTONIO MOUNTAIN (SAM) CAVE: sp.), chickadee (Parus sp.), junco (Junco San Antonio Mountain (SAM) Cave is lo- sp.), savannah sparrow (Passerculus cf. P. cated in the San Luis basin about 10 km sandwichensis), sparrow (Ammodramus), south of the Colorado border and 7 km north- and 2 wood warblers (Family Parulidae); and west of San Antonio Mountain in Rio Arriba 26 species of mammals, including a shrew, a County in northernmost New Mexico (®g. bat, 5 carnivores, 2 lagomorphs, and 17 ro- 12.1, site 1). Several factors distinguish SAM dents. The SAM Cave vertebrate assemblage Cave from all other Blancan and Irvington- is dominated by small species, and thus it is ian localities in New Mexico, in particular, very dif®cult to make comparisons with oth- its mode of occurrence and high elevation er New Mexico Irvingtonian faunas, which (Rogers et al., 2000). SAM Cave is a lava are composed primarily of large mammals. tube formed in the Pliocene Servilleta Basalt, Therefore, comparisons are mostly with Ir- and the fossils occur in locally derived cave vingtonian small mammal faunas outside of sediments. All other sites discussed in this New Mexico, in particular, Hansen Bluff, lo- paper are derived from alluvial, ¯uvial, or cated about 40 km northeast of SAM Cave lacustrine sediments associated with the an- in southern Colorado (Rogers et al., 1992). cestral Rio Grande or Gila Rivers. SAM The only larger mammals in SAM Cave are Cave is also considerably higher in elevation the badger Taxidea taxus and the wolf Canis (2737 m) than any other Blancan or Irving- rufus. However, the identi®cation of C. rufus tonian site in New Mexico. Eleven localized from Sam Cave is questionable, and it is sites within SAM Cave have produced ver- more likely to be the Irvingtonian wolf C. tebrate fossils, 10 of which are medial Ir- armbrusteri (see Berta, 1995). vingtonian in age (NMMNH sites L-4385± The age of the SAM Cave vertebrate as- 4390, 4392±4395) and 1 of which is Ran- semblage is determined primarily by the bio- cholabrean (NMMNH site L-4381). Among chronology of its extensive microtine (ϭ ar- the medial Irvingtonian sites, there appears vicoline) rodent fauna (Rogers et al., 2000). to be a range of ages from about 1.0 Ma to The presence of the microtines Mictomys just after the Matuyama/Brunhes boundary at kansasenis, Allophaiomys, Lemmiscus cur- 0.78 Ma (Rogers et al., 2000). In table 12.2 tatus, and Microtus cf. M. californicus helps and in the following discussion, we have ar- date the oldest sites in SAM Cave. The ®rst bitrarily combined the nine medial Irvington- appearance of M. kansasenis is in the late ian sites in Rogers et al. (2000, table 2) that early Irvingtonian Sappa Fauna of Nebraska 2003 MORGAN AND LUCAS: BLANCAN AND IRVINGTONIAN MAMMALS 283

(1.3 Ma; Martin and Schultz, 1985). The ing et al., 2001). In 1999, at a second site presence of an advanced unnamed species of about 10 km farther south and about 2 km Allophaiomys indicates an age greater than west of Turquoise Hill (NMMNH site L- 0.85 Ma, based on comparisons with the 4321), Dan Koning collected a mandible nearby Hansen Bluff fauna (Repenning, with p4±m3 (NMMNH 30493) of the prairie 1992; Rogers et al., 2000). SAM Cave ap- dog Cynomys in a sandy unit about 6 m be- parently documents the evolution of the low the local top of the Ancha Formation. In sagebrush vole Lemmiscus from Allophaiom- a review of the fossil history of prairie dogs, ys between about 1.0 and 0.85 Ma (Rogers Goodwin (1995) noted that the earliest fossil et al., 2000). The occurrence of Microtus cf. record of the genus Cynomys is late Blancan. M. californicus indicates that the fauna is The mandible from the Ancha Formation younger than the beginning of the Jaramillo most closely resembles the extinct species C. Subchron (1.07 Ma; Repenning, 1992). The hibbardi from the late Blancan White Rock red-backed vole Clethrionomys ®rst appears LF in Kansas (Eshelman, 1975). in two SAM Cave sites that date from 0.85 Ma to just above the Matuyama/Brunhes ALBUQUERQUE BASIN boundary. The occurrences of Clethrionomys and Lemmiscus in SAM Cave represent the The Albuquerque basin has often been di- oldest records of these genera in North vided into two separate basins or subbasins, America (Rogers et al., 2000). with the northern third called the Santo Do- The presence of Mictomys kansasenis, Al- mingo basin and the southern two-thirds lophaiomys, Lemmiscus curtatus, and Micro- called the Albuquerque-Belen basin (e.g., tus cf. M. californicus in SAM Cave indi- Tedford, 1981). We follow a more recent cates an age range between about 1.0 Ma and trend, which is to combine these basins and 0.85 Ma (Rogers et al., 2000), which places refer to them as the Albuquerque basin. We this fauna in the early part of the medial Ir- arbitrarily divide the Albuquerque basin into vingtonian. A slightly younger medial Ir- northern and southern portions, with the di- vingtonian site in SAM Cave contains Cleth- viding line being the boundary between Ber- rionomys, and is between 0.85 and 0.78 Ma nalillo and Valencia counties. The Pliocene in age. SAM Cave is younger than other Ir- and Pleistocene stratigraphic units in the Al- vingtonian faunas known from New Mexico, buquerque basin that are known to contain including Tijeras Arroyo, Tortugas Moun- Blancan and Irvingtonian vertebrate fossils tain, and Mesilla Basin Fauna C, all of which include the Ceja and Loma Barbon members are early Irvingtonian. of the Arroyo Ojito Formation of Connell et al. (1999) and the Sierra Ladrones Forma- ESPANÄ OLA BASIN tion. The stratigraphy of Pliocene and Pleis- tocene geologic units in the Albuquerque ba- ANCHA SITES: Blancan mammals are sin is currently in a state of ¯ux, and thus it known from two sites in the southernmost is likely that some of the stratigraphic names EspanÄola basin southwest of Santa Fe in San- recognized here may change in the next few ta Fe County (®g. 1, site 3). These two sites years. represent the northernmost occurrences of SANTO DOMINGO: The Santo Domingo LF Blancan mammals in New Mexico. A vol- (®g. 12.1, site 4) was derived from axial river caniclastic unit correlative with the Ancha gravels of the Sierra Ladrones Formation Formation, exposed in an abandoned cinder (Smith and Kuhle, 1998), east of the Rio quarry near the Santa Fe Airport (NMMNH Grande near the Santo Domingo Pueblo in site L-3116), preserves a trackway Sandoval County (Tedford, 1981). Tedford (NMMNH 25583) of a large camelid, either identi®ed the horses Equus calobatus and E. Camelops or one of the giant Blancan camels scotti from the Santo Domingo fauna, both (e.g., Gigantocamelus). The camel tracks oc- of which are known from the late Blancan cur in a ®ne-grained volcaniclastic deposit and early Irvingtonian. Recent examination that is part of the Cerros del Rio volcanic of fossils from Santo Domingo in the Frick ®eld, dated to between 2.8 and 2.3 Ma (Kon- Collection revealed two additional taxa, the 284 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279

small three-toed horse Nannippus peninsu- LOMA COLORADO DE ABAJO: Loma Colo- latus and the large peccary Platygonus cf. P. rado de Abajo is a prominent hill within the bicalcaratus, both of which are indicative of city limits of Rio Rancho in Sandoval Coun- Blancan faunas. The presence of Nannippus ty, about 20 km northwest of Albuquerque in suggests an age of 2.2 Ma or older. Tedford the northern Albuquerque basin (®g. 12.1, noted that these deposits are interbedded site 6). Between 1990 and 1996, Paul Knight with the Santa Ana Mesa basalts, dated at collected several skulls of small rodents from 2.67 Ma and 2.41 Ma (Smith and Kuhle, indurated, ®ne-grained reddish sandstones 1998), and are overlain by the lower Ban- near the base of the exposed section on the delier Tuff dated at 1.61 Ma (Izett and Ob- south-facing escarpment of Loma Colorado radovich, 1994). The biostratigraphic and de Abajo (NMMNH Site L-1462). The fos- geochronologic constraints indicate an age siliferous level is in the Loma Barbon Mem- between 2.7 and 2.2 Ma for the Santo Do- ber in the upper part of the Arroyo Ojito For- mingo LF. mation of Connell et al. (1999), about 8 m WESTERN MOBILE: Two species of mam- below the base of the overlying Ceja Mem- mals are known from the Western Mobile ber of the same formation. The Loma Colo- gravel pit (NMMNH Site L-1546; ®g. 12.1, rado de Abajo LF consists of just three taxa site 5), located about 3 km northeast of Ber- (Morgan and Lucas, 1999, 2000a), a small nalillo in Sandoval County (Lucas et al., land tortoise and two genera of rodents, 1993; Morgan and Lucas, 2000a). These fos- Spermophilus and Geomys. The same stra- sils, including glyptodont scutes and a pro- tum from which the rodent fossils were col- boscidean tusk fragment, were collected as lected also contains numerous ichnofossils ¯oat and thus lack precise stratigraphic prov- that appear to be rodent burrows. The Loma enance, although they were almost certainly Colorado de Abajo LF is unique among New derived from the Sierra Ladrones Formation. Mexico Blancan faunas in consisting entirely The most diagnostic fossils from the Western of small burrowing vertebrates. Mobile site are ®ve well-preserved interior A ground squirrel of the genus Spermo- carapacial osteoderms of the glyptodont philus is represented in the Loma Colorado Glyptotherium arizonae. These osteoderms de Abajo LF by a partial skull with P4 from are identi®ed as G. arizonae on the basis of a small species in the size range of living S. their large size, comparatively great thick- tridecemlineatus. It is considerably smaller ness, and small, ¯at central ®gure (Gillette than Spermophilus cf. S. bensoni from the and Ray, 1981). G. arizonae also occurs in Blancan of southeastern Arizona (Tomida, the early Irvingtonian Tijeras Arroyo fauna, 1987), a species tentatively identi®ed from located about 30 km south (see below). Most the early Blancan Buckhorn LF in south- other published records of G. arizonae from western New Mexico (Morgan et al., 1997). the southwestern United States are early Ir- The Loma Colorado Spermophilus skull is vingtonian in age, including Gilliland and also smaller than S. pattersoni and S. ma- Rock Creek in Texas, Holloman in tachicensis from the late Hemphillian Ye- Oklahoma (Gillette and Ray, 1981), and poÂmera Fauna in northern Mexico (Wilson, Mesilla Basin Fauna C from the Mesilla ba- 1949; Lindsay and Jacobs, 1985). Three sin in southernmost New Mexico (Vander- specimens from Loma Colorado de Abajo hill, 1986). This glyptodont is also known are provisionally referred to the primitive from two latest Blancan sites in New Mexi- pocket gopher, Geomys (Nerterogeomys) mi- co, Mesilla Basin Fauna B and the Virden nor, including a nearly complete skull, a ros- LF in the Duncan basin in the southwestern trum with a complete dentition, and an eden- part of the state (Morgan and Lucas, 2000b). tulous left mandible. The two skulls are iden- The Western Mobile glyptodont scutes are ti®ed as Geomys on the basis of their bisul- also signi®cant because the location of the cate upper incisors, unrooted cheek teeth, gravel pit at about 35Њ20Ј North latitude rep- and absence of enamel on the posterior sur- resents one of the northernmost records for face of P4. Earlier pre-Blancan geomyids the genus Glyptotherium in North America such as Pliogeomys have rooted cheek teeth. (Gillette and Ray, 1981). The fragmentary mandible lacks cheek teeth, 2003 MORGAN AND LUCAS: BLANCAN AND IRVINGTONIAN MAMMALS 285 but can be identi®ed as a member of the ex- graphic section in Tijeras Arroyo (®g. 12.1, tinct subgenus Geomys (Nerterogeomys)by site 7) has produced two species that are in- the placement of the mental foramen ventral dicative of a Blancan age. This site is here to the masseteric crest (Tomida, 1987). Geo- named the Mountainview Local Fauna to mys (Nerterogeomys) ®rst appears in the ear- eliminate any confusion with the younger Ti- ly Blancan and becomes extinct in the early jeras Arroyo Irvingtonian sites. The fossils Irvingtonian. The Loma Colorado pocket go- from the Mountainview site were derived pher skulls are smaller than most described from a sandstone comprising unit 1 in the skulls of Geomys (Nerterogeomys), and com- stratigraphic section of Lucas et al. (1993). pare most closely to the small species, G. The lowermost part of the section in Tijeras minor, known from the early Blancan Rex- Arroyo, including unit 1, was referred to the road Fauna in Kansas and Verde LF in Ari- Ceja Member of the Arroyo Ojito Formation zona, and the medial Blancan Beck Ranch by Connell et al. (1999). LF in Texas and Benson Fauna in Arizona Lucas et al. (1993) referred a partial man- (Hibbard, 1967; Dalquest, 1978; Czaplewski, dible with p3 from Mountainview to the rab- 1990). Repenning and May (1986) reported bit Hypolagus cf. H. gidleyi. This rabbit is G. minor from the early Blancan Truth or found in late Hemphillian and Blancan fau- Consequences LF from the Palomas Forma- nas, but is unknown from the Irvingtonian tion in Sierra County in central New Mexico. (White, 1987). The horse Equus cf. E. cum- The Loma Colorado mandible is smaller than minsii was identi®ed from this site based on pocket gopher mandibles from the Pajarito a partial skull with a nearly complete denti- and Belen faunas in the Albuquerque basin tion and several associated postcranial ele- referred to G. (Nerterogeomys) paenebursar- ments (Lucas et al., 1993). E. cumminsii oc- ius (see Morgan and Lucas, 2000a). The curs in several medial and late Blancan sites smaller species of G. (Nerterogeomys) that in Texas, but is unknown from the Irvington- are most similar in size to the Loma Colo- ian (KurteÂn and Anderson, 1980). There are rado Geomys (e.g., G. minor) are restricted two other Blancan records of E. cumminsii to the Blancan, whereas the species that sur- from New Mexico, the medial Blancan Ar- vive into the Irvingtonian (e.g., G. anzensis, royo de la Parida LF in Socorro County G. garbanii, and G. persimilis) are larger. (Tedford, 1981; Lucas and Morgan, 1996) The age of the Loma Colorado de Abajo and the late Blancan Pearson Mesa LF in Hi- LF is probably early or medial Blancan. dalgo County (Morgan and Lucas, 2000b). Small species of Geomys (Nerterogeomys), Both mammals from the Mountainview such as G. minor, are typical of faunas of site in the lower portion of the Tijeras Arroyo this age. Also, the medial to late Blancan section, Hypolagus cf. H. gidleyi and Equus (older than 2.2 Ma) Mountainview LF is cf. E. cumminsii, are typical of Blancan fau- known from the Ceja Member of the Arroyo nas, and do not occur in the Irvingtonian. Ojito Formation in Tijeras Arroyo, a unit that The extinction in the late Pliocene of several overlies the Loma Barbon Member. The characteristic Blancan genera (the Nannippus Loma Colorado de Abajo LF is stratigraph- extinction event of Lindsay et al. 1984), in- ically below and thus older than the Blancan cluding Hypolagus, indicates that the Moun- fauna from Tijeras Arroyo. However, these tainview site is older than 2.2 Ma. Equus cf. two faunas have no taxa in common, so more E. cumminsii is absent from early Blancan detailed biostratigraphic comparisons are not faunas (KurteÂn and Anderson, 1980). These possible. two species suggest that Mountainview is MOUNTAINVIEW: Most of the vertebrate medial to late Blancan in age (between 3.6 fossils from Tijeras Arroyo, located just and 2.2 Ma). The absence of Guaje Pumice south of the Albuquerque International Air- from the Ceja Member of the Arroyo Ojito port in Bernalillo County, are derived from Formation in the lower part of the Tijeras the Sierra Ladrones Formation and are early Arroyo section indicates that these beds pre- Irvingtonian in age (Lucas et al., 1993; see date deposition of the Bandelier Tuff at 1.6 below). However, one locality (NMMNH Ma (Lucas et al., 1993). Site L-1458) at the base of the exposed strati- TIJERAS ARROYO: Ten localities in Tijeras 286 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279

Arroyo (®g. 12.1, site 8) have produced a dibles, isolated teeth, and postcranials (Lucas signi®cant vertebrate fauna (table 12.2) of et al., 1993; Morgan and Lucas, 2000a). E. early Irvingtonian age (Lucas et al., 1993; scotti is the typical large horse in late Blan- Morgan and Lucas, 2000a). More than 75 m can and early Irvingtonian faunas in the of the Sierra Ladrones Formation is exposed southwestern United States (Hibbard and in Tijeras Arroyo, consisting of sandstones, Dalquest, 1966), and occurs in medial Blan- pumiceous sandstones, and gravels, with mi- can through early Irvingtonian faunas in nor amounts of mudstone and diatomite. New Mexico (Tedford, 1981; Morgan et al., These sediments represent axial river depos- 1998). A complete equid metacarpal from Ti- its of an ancestral Rio Grande. The most im- jeras Arroyo is more slender than metacar- portant lithological marker in these beds is pals of E. scotti, and represents a second, the presence of reworked Guaje Pumice de- smaller species of Equus (Hibbard and Dal- rived from the Bandelier Tuff, Ar/Ar dated quest, 1966; Harris and Porter, 1980). A par- at 1.61 Ma (Izett and Obradovich, 1994), in tial skull of a small Equus occurs higher in the units associated with an Irvingtonian fau- the Tijeras Arroyo section. na (units 6±8 of Lucas et al., 1993). An ex- Lucas and Ef®nger (1991) and Lucas et al. tensive ¯ora of leaves and pollen from a lo- (1993) referred a mandible with left and right calized volcanic ash bed was collected in the m3 from Tijeras Arroyo to the primitive Tijeras Arroyo section (NMMNH Site L- mammoth Mammuthus meridionalis on the 1445). The Tijeras Arroyo ¯ora indicates that basis of its low plate count and extremely the cottonwood forest or bosque currently thick enamel. This is one of only two records found along the banks of the Rio Grande in of mammoths from New Mexico referred to New Mexico dates back to the early Pleis- M. meridionalis, indicating that this fauna is tocene (Knight et al., 1996). almost certainly early Irvingtonian. The oth- The land tortoise Hesperotestudo and ®ve er record consists of several partial teeth, ten- species of mammals, including Glyptother- tatively referred to M. meridionalis, from an ium cf. G. arizonae, Equus scotti, Equus sp., early Irvingtonian fauna in the Mesilla basin Camelops sp., and Mammuthus meridionalis (Vanderhill, 1986). Lucas et al. (1993) re- occur together in the Tijeras Arroyo section ferred a left M3 in a maxillary fragment from above the Mountainview Blancan site dis- Tijeras Arroyo to the mammoth Mammuthus cussed above (Lucas et al., 1993; Morgan imperator. The teeth of M. imperator are and Lucas, 2000a). These species constitute more advanced than M. meridionalis in hav- a fairly typical fauna of early Irvingtonian ing a higher plate count, higher lamellar fre- age. Three additional species of mammals, a quency, and thinner enamel. The M. impe- small species of Equus, the llama Hemiauch- rator specimen was found about 12 m higher enia macrocephala and the mammoth Mam- in the section than the remainder of the Ti- muthus imperator, occur somewhat higher in jeras Arroyo fauna, and thus is somewhat the Tijeras Arroyo section than the remainder younger, although an Irvingtonian age is still of the fauna, but probably are Irvingtonian likely (Lucas et al., 1993). age as well. The presence of mammoths in unit 6 and A caudal osteoderm of a glyptodont from above clearly establishes an Irvingtonian age Tijeras Arroyo (Lucas et al., 1993) probably for the upper part of the Tijeras Arroyo sec- is not diagnostic at the species level, al- tion, as Mammuthus is one of the de®ning though this specimen almost certainly rep- genera for the Irvingtonian NALMA. The resents Glyptotherium arizonae. Tentative re- ®rst appearance of Mammuthus in the New ferral of this osteoderm to G. arizonae is rea- World occurred sometime in the early Pleis- sonable as its association with Mammuthus tocene (early Irvingtonian) between about rules out a Blancan age, and the Ranchola- 1.8 and 1.6 Ma. The mammoth jaws from brean G. ¯oridanum is restricted to the At- Tijeras Arroyo represent one of the oldest lantic and Gulf coastal plains (Gillette and well-documented records of Mammuthus Ray, 1981). The large horse Equus scotti is from North America, based on an Ar/Ar date the most common mammal in the Tijeras Ar- of 1.61 Ma on Guaje Pumice from the Sierra royo Irvingtonian fauna, represented by man- Ladrones Formation in Tijeras Arroyo (Lu- 2003 MORGAN AND LUCAS: BLANCAN AND IRVINGTONIAN MAMMALS 287 cas et al., 1993; Izett and Obradovich, 1994; diagnostic fossils are two pocket gopher Lucas, 1995, 1996). Although the pumice mandibles referred to the extinct subgenus date provides a maximum age for this site, Geomys (Nerterogeomys). The Pajarito man- evidence from other pumice deposits of ex- dibles are similar in size and morphology to actly the same age farther south in the Rio a Geomys mandible from the Belen Fauna Grande Valley (Mack et al., 1996, 1998) in- (see below), all three of which are tentatively dicates that the pumice is very close in age referred to Geomys (Nerterogeomys) paene- to the fossils. The association of M. meri- bursarius, a species originally described dionalis with Glyptotherium arizonae and from the late Blancan Hudspeth LF and Red Equus scotti is indicative of an early Irving- Light LF in southwestern Texas (Strain, tonian age for the Tijeras Arroyo fauna. Cor- 1966; Akersten, 1972). A humerus of the relative early Irvingtonian faunas include the ground squirrel Spermophilus and two rodent Tortugas Mountain LF (Lucas et al., 1999, jaws with incisors but lacking cheek teeth are 2000) and Mesilla Basin Fauna C (Vander- also known from the Pajarito LF. The rodent hill, 1986) from the Mesilla basin in southern jaws represent a smaller species than Geomys New Mexico, Gilliland in Texas (Hibbard or Spermophilus, but cannot be identi®ed and Dalquest, 1966), and Holloman in further pending the discovery of specimens Oklahoma (Dalquest, 1977). with cheek teeth. The camelids from Pajarito PAJARITO: The Pajarito LF is located along represent two species, including an M3 re- the eastern escarpment of the Rio Puerco in ferred to the common Blancan llama, Hem- southern Bernalillo County, extending from iauchenia cf. H. blancoensis, and a carpal the Pajarito land grant to the northern end of from a larger camel, probably Camelops.An the Isleta Reservation (®g. 12.1, site 9). This unidenti®ed cervid is represented by a partial site was discovered in 1946 by Ted Galusha, antler. Fossils occur in both the concretion- Frick Laboratory, who collected a small sam- ary bed, which is just below the pumice dat- ple of vertebrate fossils from just south of ed at 3.12 Ma (Maldonado et al., 1999), and the northern boundary of the Isleta Reser- in the pink sand, which is just above the dat- vation. According to Galusha's ®eld notes ed pumice. One of the two Geomys mandi- (copy kindly provided by Richard Tedford), bles was collected from the concretionary he found fossils in two distinct units, a lower bed and the other from the pink sand. These unit with ``potato-shaped'' concretions and a two specimens are indistinguishable, sug- pinkish sandy unit about 5 m higher in the gesting that these two units are similar in section. We recently collected additional fos- age. The radioisotopic date of 3.1 Ma indi- sils from these same two units on the Pajarito cates a medial Blancan age for the Pajarito land grant just north of the Isleta Reservation LF. This age is in agreement with the evo- boundary. Maldonado and Atencio (1998) lutionary grade of the Geomys mandibles and placed both the concretionary bed and the with the absence of South American immi- pink sand in their ``silt, sand, and clay lith- grant mammals, which ®rst appear in North ofacies of the Isleta Reservation.'' A pumice American faunas about 2.7 Ma. This site that occurs between the two fossil-bearing holds signi®cant potential for new discover- units has been Ar/Ar dated at 3.12 Ϯ 0.10 ies, as only a small amount of the exposed Ma (Maldonado et al., 1999). Tedford (1981) outcrop has been explored for fossils. called this the Laguna site and attributed it ISLETA: In 1999, Dave Love collected a to the Ceja Member, which was recently nearly complete metacarpal of a small ca- placed in the Arroyo Ojito Formation (Con- melid on the east side of the Rio Grande, nell et al., 1999). Morgan and Lucas (2000a) about 3 km northeast of the Isleta Pueblo renamed the Laguna site the Pajarito LF to (®g. 12.1, site 10), from strata that are prob- eliminate any confusion regarding its loca- ably correlative with the Arroyo Ojito For- tion. mation of Connell et al. (1999). The fossil The Pajarito LF consists of eight species was derived from a unit stratigraphically be- of vertebrates: a turtle, a bird, and six species low the pumice-bearing sands of the Sierra of mammals, including three rodents, two Ladrones Formation that contain early Ir- camels, and a deer (table 12.1). The most vingtonian mammals in Tijeras Arroyo, lo- 288 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279 cated about 10 km to the north. This speci- facing escarpment just west of Interstate men is referable to the genus Hemiauchenia, Highway 25 and several kilometers west of but is considerably smaller than metacarpals the Rio Grande. The NMMNH has two col- of the typical Blancan species, H. blancoen- lections of Blancan vertebrates from south- sis, known from several other Blancan faunas west of Belen in Valencia County (®g. 12.1, in New Mexico (e.g., a complete metacarpal site 12). In 1992, Bill Wood collected ver- from the medial Blancan Tonuco Mountain tebrate fossils about 5 km southwest of Belen LF), as well as the type locality, the Blanco (NMMNH Site L-3778). Fossils from this LF in Texas (Dalquest, 1975). A small and site include lower jaws of the gomphotheriid apparently undescribed species of Hemiauch- proboscidean Stegomastodon miri®cus and enia, mostly represented by isolated postcra- postcranial elements of Equus. Christopher nial elements, is found in New Mexico fau- Whittle and several students collected fossils nas ranging in age from early to late Blancan. from conglomeratic sandstone and slightly Based on its stratigraphic position, the small indurated sandstone about 2 km southwest of Hemiauchenia metacarpal from Isleta is Belen (NMMNH Site L-3737), about 4 km probably either medial or late Blancan in north of site L-3778. Fossils from this site age. include a snake, the mole Scalopus, Geomys, LOS LUNAS: The Los Lunas site (®g. 12.1, Equus, and a small antilocaprid. Because of site 11) is located in strata of the Arroyo Oji- the close proximity of sites L-3737 and 3778 to Formation that underlie the Los Lunas southwest of Belen and their occurrence in volcano, about 7 km west of Los Lunas in similar strata referred to the Arroyo Ojito Valencia County (Tedford, 1981). A mandi- Formation, the fossils from these two sites ble of the giant marmot Paenemarmota, a ge- are combined as the Belen Fauna (Morgan nus found in Hemphillian and Blancan fau- and Lucas, 2000a). nas in western North America (KurteÂn and The Belen Fauna (Morgan and Lucas, Anderson, 1980; Zakrzewski, 1998), was 2000a) is composed of ®ve species of mam- collected at this site. The large size of the mals, including Scalopus (Hesperoscalops) Los Lunas mandible suggests referral to P. cf. S. blancoensis, Geomys (Neterogeomys) barbouri, a species that occurs from the early cf. G. paenebursarius, Equus cf. E. caloba- through the late Blancan (Morgan and Lucas, tus, a small antilocaprid, and Stegomastodon 2000a). A K/Ar date of 1.1±1.3 Ma on the miri®cus. A dentary with m1±m3 from the andesite of the Los Lunas volcano (Bachman Belen Fauna is the ®rst mole (family Talpi- and Mehnert, 1978), which overlies the strata dae) ever reported from New Mexico, recent that yielded the Paenemarmota jaw, provides or fossil (Morgan and Lucas, 1999, 2000a). a minimum age for the Los Lunas site (Ted- This mole is referred to Scalopus (Hesperos- ford, 1981). calops), an extinct subgenus of Scalopus re- Several postcranial bones of a large camel stricted to the Blancan. Three species of S. were collected from the Arroyo Ojito For- (Hesperoscalops) have been described, S. se- mation a few kilometers northwest of the Pa- wardensis from the very early Blancan Saw enemarmota site, about 1 km north of New Rock Canyon LF in Kansas, S. rexroadi from Mexico Route 6 (NMMNH Site L-3738; the early Blancan Rexroad and Fox Canyon Morgan and Lucas, 2000a). These speci- faunas in Kansas and the medial Blancan mens, including a partial distal radio-ulna Beck Ranch LF in Texas, and S. blancoensis and a magnum, probably represent a large from the late Blancan Blanco LF in Texas Camelops. A large undescribed species of (Hibbard, 1953; Dalquest, 1975, 1978; Kur- Camelops occurs in several medial and late teÂn and Anderson, 1980). The Belen dentary Blancan faunas elsewhere in New Mexico is tentatively referred to S. blancoensis based (Vanderhill, 1986; Morgan et al., 1998). on its similarity to that species in size and BELEN: Beginning south of the Los Lunas morphological features. A dentary with a volcano and extending south of Belen into complete dentition from Belen is identi®ed northern Socorro County, badlands repre- as the extinct pocket gopher subgenus Geo- senting the Arroyo Ojito Formation of Con- mys (Nerterogeomys). The morphology and nell et al. (1999) are well exposed in an east- size of this mandible are similar to the spe- 2003 MORGAN AND LUCAS: BLANCAN AND IRVINGTONIAN MAMMALS 289 cies G. (N.) paenebursarius, also identi®ed dial Blancan (®g. 12.2) based on similarities from the Pajarito LF, and ®rst described from with other medial Blancan faunas (e.g., Pa- the late Blancan Hudspeth and Red Light jarito) from the Arroyo Ojito Formation in LFs of southwestern Texas (Strain, 1966; the Albuquerque basin. Akersten, 1972). MESAS MOJINAS: An astragalus of a small The most common fossils in the Belen camelid (NMMNH 29936) was collected by Fauna are postcranial elements of horses of Richard Lozinsky in 1986 from the Arroyo the genus Equus, most of which are not di- Ojito Formation, southeast of Mesas Mojinas agnostic at the species level. A nearly com- in the Gabaldon badlands west of Belen in plete metatarsal is tentatively referred to the Valencia County (NMMNH Site L-4253; ®g. large, stilt-legged horse, E. calobatus, a spe- 12.1, site 13). In their review of the early cies known from the late Blancan Santo Do- Hemphillian (late Miocene) Gabaldon Fauna mingo LF (Tedford, 1981) and from late from the Popotosa Formation, which under- Blancan and early Irvingtonian faunas in the lies the Arroyo Ojito Formation, Lozinsky Mesilla basin (Vanderhill, 1986). A well-pre- and Tedford (1991) referred this specimen to served pair of mandibles with right and left Hemiauchenia sp. and noted that it was the m2±m3 is referred to the gomphothere Ste- only fossil recovered from post-Hemphillian gomastodon miri®cus. The presence of seven strata in the Gabaldon badlands. The Gabal- lophids on m3 separates this specimen from don specimen is very similar to two astragali Rhynchotherium and Cuvieronius, and the of a small Hemiauchenia from the early highly complicated enamel with double tre- Blancan Buckhorn LF in southwestern New foiling distinguishes the teeth from the more Mexico (Morgan et al., 1997). This small primitive species S. rexroadensis. species of Hemiauchenia is known from sev- Four mammals in the Belen Fauna are age eral other Blancan faunas in New Mexico. diagnostic. The extinct subgenus Scalopus VEGUITA: A site in the Arroyo Ojito For- (Hesperoscalops) is restricted to the Blancan mation about 1 km east of the Rio Puerco and the species S. blancoensis occurs in the and 10 km northwest of Veguita in northern- late Blancan. Geomys (Nerterogeomys) pa- most Socorro County (NMMNH Site L- enebursarius is known from two late Blan- 2941; ®g. 12.1, site 14) in the southern Al- can faunas in southwestern Texas (Strain, buquerque basin has produced a partial max- 1966; Akersten, 1972), and the medial Blan- illa with left P2±M3 of the large horse Equus can Pajarito LF in the northern Albuquerque scotti (Morgan and Lucas, 2000a). These basin (Tedford, 1981; Morgan and Lucas, teeth are characterized by their large size, 2000a). Stegomastodon miri®cus is known fairly complicated enamel pattern of the fos- from the medial Blancan through the early settes, elongated protocone with a lingual in- Irvingtonian, and Equus calobatus occurs in dentation, and presence of a pli caballin. E. the late Blancan and Irvingtonian (KurteÂn scotti is the common large horse in New and Anderson, 1980). The age of the Belen Mexico faunas ranging in age from medial Fauna is either medial or late Blancan. S. Blancan through early Irvingtonian. A Blan- blancoensis and E. calobatus occur in late can age is more likely considering that most Blancan faunas, but are not known from the sites from the Arroyo Ojito Formation in the medial Blancan, whereas G. (N.) paenebur- southern portion of the Albuquerque basin sarius and S. miri®cus ®rst appear in the me- produce Blancan mammals. dial Blancan. The lack of South American SEVILLETA: Denny (1940) found Blancan immigrants in the Belen Fauna suggests a fossils in sands and gravels, probably derived medial Blancan age, although their absence from the Arroyo Ojito Formation, from could be related to biogeographic factors. bluffs west of the Rio Grande and just north Neotropical mammals are unknown from of the Rio Salado in the southernmost por- Blancan faunas in northern New Mexico; tion of the Albuquerque basin in northern however, Glyptotherium occurs in two early Socorro County (®g. 12.1, site 15). This site Irvingtonian faunas in the Albuquerque ba- is located on land now included within the sin, Tijeras Arroyo and Western Mobile. We Sevilleta National Wildlife Refuge. The fau- tentatively place the Belen Fauna in the me- na reported by Denny consists of the gom- 290 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279 Äola, Albuquerque, Socorro, Engle, and Palomas basins. The chronological Fig. 12.2. Correlation chart showing the relative ages of late Hemphillian, Blancan, and Irvingtonian vertebrate faunas from the northern and central Rio Grande Valleylimits in New of Mexico, the includingfrom the mammalian which San faunas Luis, each are Espan for fauna indicated subdividing or by the site Blancan the was NALMA vertical derived are height is indicated of also to the indicated the boxes within left enclosing (Tedford, the 1981; the box. Repenning, fauna Magnetochronology 1987; or is Woodburne from site and Berggren names. Swisher, 1995). et The al. lithostratigraphic (1995). unit Three systems 2003 MORGAN AND LUCAS: BLANCAN AND IRVINGTONIAN MAMMALS 291 phothere Stegomastodon miri®cus and a Stegomastodon. Lucas and Morgan (1996) tooth of Equus. We have not been able to described and illustrated the mandibles of relocate Denny's fossils, and thus the iden- Rhynchotherium ®rst mentioned by Need- ti®cations are taken from his paper and must ham, and referred them to the species R. fal- be considered tentative. We recently collect- coneri, originally described from the Blanco ed fossils from outcrops of the Arroyo Ojito LF in Texas. Lucas and Morgan (1996) also Formation in this same general area, north of summarized the biostratigraphy of the Ar- the Rio Salado on the La Joya Game Refuge. royo de la Parida LF, including fossils col- We found teeth and postcranial elements rep- lected in 1996 by two students from New resenting two species of Equus, E. simplici- Mexico Tech, Ed Frye and Mike O'Keeffe. dens and a larger horse, tentatively identi®ed We visited the Arroyo de la Parida area sev- as E. scotti. The Sevilleta fauna is similar to eral times during 2000 and collected numer- the medial Blancan Arroyo de la Parida LF, ous additional fossils from 15 different sites derived from the Palomas Formation about (Morgan et al., 2000). 15 km farther south in the northern Socorro The Arroyo de la Parida LF is derived basin. from a 70-m sequence of sands and gravels that constitute the axial river (ancestral Rio SOCORRO BASIN Grande) facies of the Palomas Formation. The strata in the vicinity of Arroyo de la Par- ARROYO DE LA PARIDA: Vertebrate fossils ida are located at the northern end of the So- were ®rst found in Arroyo de la Parida in corro basin, representing one of the northern- 1935, about 6 km northeast of Socorro, So- most occurrences of the Palomas Formation, corro County (®g. 12.1, site 16). Needham which has its type area about 100 km farther (1936) reported a complete pair of lower south in Palomas Creek near Truth or Con- jaws of the gomphotheriid proboscidean sequences in Sierra County (Lozinsky, Rhynchotherium and a lower molar of the 1986). The Arroyo de la Parida LF is com- horse Plesippus (now considered a subgenus posed of 10 vertebrates: the land tortoise of Equus) from an exposure of sands and Hesperotestudo; the ground sloth Megalonyx gravels of the Santa Fe Group on the south cf. M. leptostomus; three horses, Equus cf. E. side of Arroyo de la Parida, about 2 km east cumminsii, E. scotti, and E. simplicidens; two of its con¯uence with the Rio Grande. Ad- camelids, a large Camelops and a small ditional vertebrate fossils were collected Hemiauchenia; the small antilocaprid Cap- from this same exposure by students from the romeryx; and two proboscideans, Rhyncho- New Mexico Institute of Mining and Tech- therium falconeri and Stegomastodon sp. nology (DeBrine et al., 1963). Curt Teichert, This is a fairly typical faunal assemblage a well-known German invertebrate paleon- found in New Mexico Blancan sites, mostly tologist, collected a sample of vertebrate fos- consisting of large grazing ungulates and sils from the vicinity of Arroyo de la Parida dominated by horses of the genus Equus. in 1953, and donated these fossils to the Five mammals from the Arroyo de la Par- American Museum of Natural History. The ida LF are restricted to the Blancan, includ- only locality information associated with ing Megalonyx leptostomus, Equus cummin- Teichert's sample was that the fossils were sii, E. simplicidens, the large Camelops, and collected ``about four miles north of Socorro, Rhynchotherium falconeri. The most age-di- New Mexico.'' Based on the general locality, agnostic of these taxa is Rhynchotherium,a preservation of the fossils, and the compo- gomphothere that became extinct in the late sition of the fauna, there is little doubt that Pliocene at about 2.2 Ma together with sev- Teichert's fossils are from the area that yields eral other characteristic genera of Blancan the Arroyo de la Parida LF. The fossils col- mammals. The lower jaws of R. falconeri lected by Teichert were summarized by Ted- from Arroyo de la Parida were collected near ford (1981), and include three species of the top of the local section of the Palomas horses, Equus simplicidens, E. cf. E. cum- Formation, suggesting that the entire fauna, minsii, and E. cf. E. scotti, the small antilo- most of which occurs some 40 m lower in caprid Capromeryx, and the gomphothere the section, is older than 2.2 Ma. An early 292 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279

Blancan age for the Arroyo de la Parida LF San Marcial basin at the very northern end can be ruled out by the presence of E. scotti of Elephant Butte Lake in southern Socorro and Camelops, both of which ®rst appear in County (NMMNH site L-3682; ®g. 12.1, site New Mexico faunas during the medial Blan- 18). The Silver Canyon site consists of three can. The absence of South American immi- taxa of mammals, a rodent tentatively iden- grants suggests an age greater than 2.7 Ma. ti®ed as the wood rat Neotoma, the horse Eq- Megalonyx is the only Blancan mammal of uus, and an indeterminate gomphothere. The South American origin that was not a partic- most common fossils are proboscidean tooth ipant in the Great American Interchange. Me- and tusk fragments and postcranials, identi- galonyx or its progenitor arrived from South ®able only as Gomphotheriidae. Equus is America in the late Miocene about 9 Ma. M. represented in the fauna by postcranial re- leptostomus is fairly widespread in early mains. A mandible of a fairly large rodent through late Blancan faunas. The Arroyo de appears to be referable to Neotoma, although la Parida LF is interpreted to be medial Blan- the teeth are too worn for a species-level can in age (3.6±2.7 Ma), and is similar to the identi®cation. The age of this fauna cannot Cuchillo Negro Creek LF from the Palomas be determined on the basis of the fossil ma- Formation in the Engle Basin near Truth or terial currently known, although a Blancan Consequences. age is most likely considering that all other FITE RANCH: Tedford (1981) reported post- vertebrate faunas so far known from the Pal- cranial bones of Equus and Camelops col- omas Formation are Blancan. lected by George Pearce in 1953 from pum- ice-bearing sands on the Dean Fite Ranch ENGLE BASIN near San Antonio in the Socorro basin, So- corro County (®g. 12.1, site 17). Specimens ELEPHANT BUTTE LAKE: Joseph Rak and in the F:AM collections from Fite Ranch Charles Falkenbach of the Frick Laboratory consist of an astragalus of Equus and a par- collected fossil vertebrates in the late 1920s tial metatarsal of Camelops. Needham (1936) from axial river gravels of the ancestral Rio reported a partial humerus, radius, and ulna Grande in the Engle and Palomas basins in of the turkey Meleagris, apparently from this the vicinity of Hot Springs (now called Truth same locality (Tedford, 1981). Needham (p. or Consequences) in Sierra County. Fossils 537) described this locality as ``a bed of from the Engle basin on the western side of pumicite . . . about three and one half miles Elephant Butte Lake north of Truth or Con- northeast of San Antonio, Socorro County, sequences are called the Elephant Butte Lake along the east bluff of the Rio Grande. It [the Fauna (®g. 12.1, site 19). Tedford (1981) at- bed of pumicite] is underlain by some thirty tributed these strata to the Sierra Ladrones feet of light-colored gravel and sand and buff Formation, but they have since been referred silt, typical of the Santa Fe formation as de- to the Palomas Formation (Lozinsky, 1986). veloped east of the Rio Grande near Socor- The precise localities and stratigraphy of ro'' (i.e., Arroyo de la Parida). Tedford noted these fossils are not known; however, they that the pumice-bearing sands on the Fite were certainly derived from the Palomas For- Ranch were attributed to the Bandelier erup- mation, and are similar in age to the nearby tions, indicating an age of 1.6±1.2 Ma (Izett Cuchillo Negro Creek LF (see below). Mam- et al., 1981; Izett and Obradovich, 1994). mals identi®ed by Tedford from Elephant This would suggest an early Irvingtonian Butte Lake are the horse Equus simplicidens, age, although the fossil vertebrates from Fite the tapir Tapirus, and the giant camel Gi- Ranch are not age diagnostic. gantocamelus. Since 1981, additional fossils referable to the Elephant Butte Lake Fauna SAN MARCIAL BASIN have been collected in the vicinity of Rock Canyon on the western shore of Elephant SILVER CANYON: Gary Morgan, Mike Butte Lake about 5 km north of Truth or O'Neill, and Brenda Wilkinson collected a Consequences, and include the giant tortoise small sample of fossils in 1998 from the Pal- Hesperotestudo, a mandible of Gigantoca- omas Formation near Silver Canyon in the melus cf. G. spatula, and a skull of the gom- 2003 MORGAN AND LUCAS: BLANCAN AND IRVINGTONIAN MAMMALS 293 phothere Stegomastodon cf. S. rexroadensis. late Hemphillian and early Blancan species E. simplicidens and Gigantocamelus are in- B. hilli. The larger and more highly derived dicative of the Blancan, and S. rexroadensis species B. diversidens appears in the late ear- suggests an early or medial Blancan age. ly Blancan and survives until the late Blan- Tedford considered these sites to be medial can (Wang et al., 1999). An edentulous man- Blancan because of their close stratigraphic dible from Cuchillo Negro Creek represents association with a basalt ¯ow dated at 2.9 Ϯ the ®rst New Mexico Pliocene record of the 0.3 Ma from Mitchell Point on the western ringtail Bassariscus. The only Blancan spe- side of Elephant Butte Lake (Bachman and cies of Bassariscus, B. casei from the early Mehnert, 1978). Blancan Rexroad Fauna in Kansas, is distin- CUCHILLO NEGRO CREEK: Vertebrate fossils guished from the extant B. astutus on the ba- from the Palomas Formation north of Cuch- sis of dental characters that cannot be ob- illo Negro Creek in the Engle Basin in Sierra served in the Cuchillo Negro Creek jaw. County (®g. 12.1, site 20) were named the Lucas and Oakes (1986) identi®ed the pal- Cuchillo Negro Creek LF by Lucas and Oak- ate of a horse from the Cuchillo Negro Creek es (1986). Fossils were collected from the LF as Equus simplicidens. Two associated Cuchillo Negro Creek area in 1983 and 1984 upper molars found in 1998 match the orig- by University of New Mexico ®eld crews inal dental sample. Although these teeth have and in 1998 and 1999 by NMMNH ®eld several features that differ somewhat from crews. Lozinsky (1986) recognized two in- typical E. simplicidens (e.g., fairly compli- formal members of the Palomas Formation cated fossettes and slight lingual indentation in this area, the axial facies consisting of of the protocone), this species is the only about 30 m of sand with lenses of gravel and Blancan Equus that is similar in morphology clay and the piedmont facies consisting of and size to the teeth from Cuchillo Negro about 50 m of sandy silt and conglomerate. Creek. There are three taxa of camelids from Most of the fossils were derived from the Cuchillo Negro Creek. The typical large axial facies, which was deposited by an an- Blancan llama Hemiauchenia blancoensis cestral Rio Grande. A basalt ¯ow dated at was reported previously (Lucas and Oakes, 2.9 Ma from Mitchell Point, about 15 km 1986). A small species of Hemiauchenia is north of the Cuchillo Negro Creek sites, in- known from an adult distal tibia. This ap- ter®ngers with the axial facies of the Palomas parently undescribed species of llama occurs Formation (Lozinsky, 1986). in six Blancan faunas in New Mexico. A The Cuchillo Negro Creek LF is com- large undescribed species of Camelops, rep- posed of 10 species (Lucas and Oakes, 1986; resented by a large proximal phalanx from this report): 3 turtles, including a small land Cuchillo Negro Creek, occurs in several oth- tortoise of the genus Hesperotestudo, the er Blancan faunas in New Mexico (Morgan mud turtle Kinosternon, and an aquatic mem- et al., 1998). ber of the family Emydidae, and 7 mammals, A proboscidean is represented at Cuchillo including the borophagine canid Borophagus Negro Creek by a pair of mandibles with hilli, the procyonid Bassariscus sp., the equid heavily worn m3s (Lucas and Oakes, 1986) Equus cf. E. simplicidens, the camelids Ca- and by a recently collected partial m3 in me- melops sp., Hemiauchenia blancoensis, and dium wear. The mandibles have a short, Hemiauchenia small sp., and the gompho- straight symphysis lacking tusks. The m3s of theriid proboscidean Stegomastodon re- these two specimens are similar in size and xroadensis. dental features, including the presence of six A nearly complete dentary with i2±3, c, lophids and a simple trefoil pattern. The and p2±m2 identi®ed as Borophagus diver- combination of six lophids on the m3 and the sidens by Lucas and Oakes (1986) was re- absence of lower tusks excludes all other ferred to B. hilli by Wang et al. (1999). Al- Blancan genera of proboscideans except Ste- though most Borophagus fossils from the gomastodon. The smaller number of lophids early Blancan were referred to B. diversidens on m3 and simple trefoiling distinguish the by previous authors, these specimens are Cuchillo Negro Creek teeth from the more more similar in size and morphology to the advanced species S. miri®cus, and suggest re- 294 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279 ferral to the early to medial Blancan S. rex- Truth or Consequences LF is composed of roadensis. about 20 m of poorly consolidated sand and Lucas and Oakes (1986) proposed a me- pebbly sand, with two interbedded mudstone dial Blancan age (about 3.0 Ma) for the layers, referred to the Palomas Formation. Cuchillo Negro Creek LF, based on biostra- Most of the vertebrate fossils occur in green- tigraphy and correlation with the 2.9 Ma ish to reddish mudstones in the lower third Mitchell Point basalt. They suggested that of the roadcut. The preservation of fossils in the Cuchillo Negro Creek LF is similar to the these mudstones is excellent, and includes Rexroad Fauna in Kansas and the Benson numerous mandibles, maxillae, and partial Fauna in Arizona. The presence of Came- skulls of both small and large mammals. We lops, a genus that supposedly did not appear recently recovered fossils of aquatic species, until after 3.7 Ma (Lindsay et al., 1984), is including a duck and two partial shells of indicative of a medial Blancan age, and Ste- emydid turtles, in ®ne sand at the base of the gomastodon rexroadensis occurs in both ear- local section. Fine-grained units are uncom- ly and medial Blancan faunas. The absence mon and discontinuous within the axial river of South American immigrant mammals in- facies of the Palomas Formation, which is dicates a pre-late Blancan age (older than 2.7 dominated by sands and gravels. Ma). The presence of Borophagus hilli sug- The Truth or Consequences LF, as origi- gests an early Blancan age according to nally described by Repenning and May Wang et al. (1999), although this same spe- (1986), consisted of 13 species: 4 reptiles, cies occurs in the medial Blancan Hagerman including the mud turtle Kinosternon, the Fauna in Idaho. A more precise age deter- box turtle Terrapene, the fence lizard Sce- mination for the Cuchillo Negro Creek LF loporus, and the coachwhip snake Mastico- must await the discovery of additional age- phis; and 9 mammals, including the rabbits diagnostic taxa, or other data such as mag- Hypolagus vetus and Notolagus lepusculus, netostratigraphy. In the near future, we in- the pocket gopher Geomys (Nerterogeomys) tend to determine the relative stratigraphic minor, the cotton rat Sigmodon, the rice rat position of this fauna compared to the better cf. Oryzomys, the wood rat Neotoma quad- known early Blancan Truth or Consequences riplicata, the horse Equus (Plesippus), the LF, located about 5 km farther south. deer Odocoileus brachyodontus, and the gomphothere Stegomastodon. Recent addi- PALOMAS BASIN tions to the fauna include an aquatic emydid turtle, another snake, a duck and a galliform TRUTH OR CONSEQUENCES: The Truth or bird, and six mammalsÐa shrew, the mole Consequences LF is derived from ®ne- Scalopus, a small sciurid, the large canid grained sediments of the Palomas Formation Borophagus cf. B. hilli, the peccary Platy- in a roadcut on Interstate 25 about 2 km gonus cf. P. bicalcaratus, and the small an- south of Truth or Consequences in Sierra tilocaprid Capromeryx. The Truth or Conse- County (Repenning and May, 1986; ®g. 12.1, quences LF is now composed of 23 species, site 21). The site was discovered by Arthur including 15 mammals (table 12.1), making Harris of the University of Texas at El Paso it one of the most diverse Blancan vertebrate and then worked in the early 1980s by faunas from New Mexico. Charles Repenning and Steven May of the Many of the mammals from the Truth or U.S. Geological Survey in Denver. Gary Consequences LF are age diagnostic, several Morgan, Paul Sealey, and Spencer Lucas be- of which suggest an early Blancan age. Re- gan work at this site in 1997 and have added penning and May (1986) referred the small numerous taxa to the fauna, including both rabbit to Notolagus lepusculus, a species large and small species (table 12.1). Repen- named by Hibbard (1939) from the late early ning and May recovered most of their fossils Blancan Rexroad 3 Fauna of Kansas (Blan- by excavation, whereas the more recent can II of Repenning, 1987). The larger rabbit NMMNH collections have been obtained pri- was identi®ed as Hypolagus vetus, a species marily through screenwashing. known from the Hemphillian through the The stratigraphic section that includes the medial Blancan (White, 1987). The pocket 2003 MORGAN AND LUCAS: BLANCAN AND IRVINGTONIAN MAMMALS 295 gopher was referred to the small species Repenning and May (1986) suggested an Geomys (Nerterogeomys) minor, described early Blancan age (between 4.2 and 4.0 Ma, from Rexroad 3 (Hibbard, 1950, 1967). The early Blancan II of Repenning, 1987) for the primitive wood rat Neotoma (Paraneotoma) Truth or Consequences LF based on both quadriplicata is intermediate in size between biostratigraphy and magnetostratigraphy. Re- the oldest species of pack rat, N.(P.) saw- penning and May (1986) correlated the Truth rockensis from the very early Blancan Saw or Consequences magnetostratigraphic sec- Rock Canyon LF in Kansas, and N. (P.) tion of 11 normally magnetized samples quadriplicata from Rexroad 3 (Hibbard, from three levels to the Nunivak Subchron 1941, 1967). Repenning and May (1986) ten- of the Gilbert Chron, primarily on the basis tatively referred a small sigmodontine rodent of the similarity of its fauna with other fau- to the extant genus Oryzomys. Czaplewski nas from the Nunivak or the next oldest nor- (1987) noted that the Oryzomys from Truth mal subchron in the Gilbert (Sidufjall), and or Consequences was similar to his new ge- a more primitive aspect than faunas (e.g., nus Jacobsomys from the early Blancan Rexroad 3) derived from the next youngest (about 4 Ma) Verde LF in Arizona, but was normal subchron in the Gilbert (Cochiti). smaller than the Verde species J. verdensis. They gave an age range of 4.20±4.05 Ma for The Sigmodon from Truth or Consequences, the Nunivak, but the age of this subchron has referred here to S. medius, may represent one since been revised downward to 4.62±4.48 of the earliest records of this genus. Cza- Ma (Berggren et al., 1995). The correlation plewski (1987) also recorded S. medius from of the Truth or Consequences magnetostrati- the Verde LF. graphic section to the Nunivak Subchron The Truth or Consequences LF consists should be considered tentative since it was primarily of microvertebrates. Because of the based on a few samples through a limited rarity of large mammals, it is dif®cult to stratigraphic section (Mack et al., 1993). We make biostratigraphic comparisons with oth- intend to measure a longer stratigraphic sec- er New Mexico Blancan faunas, most of tion of the Palomas Formation through the which are composed of large vertebrates. The Truth or Consequences LF, in hopes of de- cervid Odocoileus brachyodontus, identi®ed termining the stratigraphic position of this from Truth or Consequences by a maxillary fauna relative to three other nearby Blancan fragment and antler, was ®rst described from faunas from the Palomas Formation, Cuchi- the early Blancan Fox Canyon Fauna of Kan- llo Negro Creek and Elephant Butte Lake to sas (Oelrich, 1953). Odocoileus appears in the north and Palomas Creek to the south. the early Blancan as an immigrant from the We anticipate that a more detailed magneto- Old World. It is one of the genera whose ®rst stratigraphic section eventually will be taken appearance helps to de®ne the beginning of through this section. the Blancan (e.g., Woodburne and Swisher, PALOMAS CREEK: Joseph Rak and Charles 1995). The rostrum of a large peccary is sim- Falkenbach collected fossil vertebrates in ilar to the large species Platygonus bicalcar- 1927 and 1928 from exposures of the distal atus. Although the genus Platygonus sup- piedmont facies of the Palomas Formation posedly appeared at the beginning of the me- southwest of Hot Springs (ϭ Truth or Con- dial Blancan at about 3.6 Ma (Lindsay et al., sequences) in Palomas Creek, Sierra County 1984), an occurrence in the early Blancan (Tedford, 1981; ®g. 12.1, site 22). Palomas would not be surprising. A p2 of Borophagus Creek is the type area of the Palomas gravel, is similar in size and morphology to the p2 now called the Palomas Formation (Lozin- of B. hilli from Cuchillo Negro Creek, a spe- sky, 1986). The Palomas Creek LF is in the cies known elsewhere from the late Hem- Palomas basin about 8±10 km southwest of phillian and early Blancan (Wang et al., the Truth or Consequences LF. Palomas 1999). Fossils of Equus (Plesippus), Cap- Creek has a fairly diverse Blancan fauna romeryx, and Stegomastodon are too incom- composed of nine species (table 12.1, after plete for further identi®cation. Nannippus Tedford, 1981): the tortoise Hesperotestudo and camelids are both absent from the Truth and eight mammals, including the pocket go- or Consequences LF. pher Geomys (Geomys); the cotton rat Sig- 296 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279 modon medius; the horses Nannippus pen- NMMNH ®eld crews collected vertebrate insulatus, Equus simplicidens, and E. cf. E. fossils in 1990 and 1998 from the Camp Rice cumminsii; a peccary; a large Camelops; and Formation about 5 km west of Hatch (®g. the mastodont Mammut raki. Nannippus, E. 12.1, site 23). The Camp Rice Formation is simplicidens, E. cumminsii, and the large Ca- unconformably underlain by Miocene red melops are characteristic of New Mexico beds of the Rincon Valley Formation in the Blancan faunas. The absence of South Amer- vicinity of Hatch. This is similar to a strati- ican immigrants suggests a pre-late Blancan graphic section about 30 km southeast of age. The type mandible of Mammut (ϭ Mas- Hatch in the Jornada basin near Tonuco todon) raki (Frick, 1933) from Palomas Mountain, where the Tonuco Mountain LF Creek is one of the few known Blancan was collected (Morgan et al., 1998). The Mammut, and the only one referred to a spe- only fossil previously reported from Hatch is cies other than M. americanum, the typical a partial skeleton of the long-nosed snake Pleistocene mastodon (Lucas and Morgan, Rhinocheilus (Lucas et al., 1995). 1999). On the basis of fossils in the NMMNH Magnetostratigraphy and radioisotopic collection, the Hatch LF is composed of 12 dates provide additional geochronologic data species: the land tortoises Gopherus and pertaining to the age of Palomas Formation Hesperotestudo, the mud turtle Kinosternon, in the Palomas basin (Mack et al., 1993, Rhinocheilus, and eight species of mammals 1998). K/Ar dates on basalts in the Palomas (table 12.1) including two unidenti®ed rab- basin include a ¯ow dated at 4.5 Ϯ 0.1 Ma bits, the pocket gopher Geomys (Nerterogeo- in the western part of the basin that is either mys) cf. G. (N.) paenebursarius, the badger below or within the lowermost Palomas For- Taxidea, a small cat probably of the genus mation and a ¯ow dated at 3.1 Ϯ 0.1 Ma Lynx, the horse Equus, the camelid Hem- interbedded with alluvial fan conglomerates iauchenia cf. H. blancoensis, and the small of the Palomas Formation in the eastern part antilocaprid Capromeryx. Land tortoises are of the basin (Seager et al., 1984; Mack et al., the most abundant members of the Hatch 1998). A magnetostratigraphic section in the fauna. Specimens of mammals are less com- Palomas Formation from Palomas Creek mon, particularly ungulates. Equus is repre- sampled mostly reversely magnetized strata sented by fragmentary teeth, Hemiauchenia referred to the Matuyama Chron, but includ- by postcranial remains, and Capromeryx by ed about 10 m of normally magnetized strata a single tooth. Two leporids are present based referred to the Gauss Chron at the bottom of on two distal femora of very different size. the section (Mack et al., 1993). The precise Taxidea is identi®ed from a distal radius. stratigraphic position of the Palomas Creek Badgers are known from two other New fossils is unknown, but the paleomagnetic Mexico Blancan faunas, Buckhorn and Ton- data strongly suggest the fauna was derived uco Mountain (Morgan et al., 1997, 1998). from low in the section. The combination of The small cat is represented by a maxillary magnetostratigraphy and biostratigraphy in- fragment with a partial P4 (NMMNH 25308) dicates a medial Blancan (3.6±2.7 Ma) age that compares well in size and other features for the Palomas Creek LF. to Lynx rexroadensis, known from late Hem- phillian and Blancan faunas (MacFadden and HATCH-RINCON BASIN Galiano, 1981). Two pocket gopher mandi- bles (NMMNH 25324, 25329) from Hatch HATCH: Blancan and early Irvingtonian are similar to mandibles referred to Geomys fossils occur in the Camp Rice Formation in (Nerterogeomys) paenebursarius from the southern New Mexico, from Hatch and Rin- Belen and Pajarito Faunas in the Albuquer- con Arroyo in the Hatch-Rincon basin in que basin (Morgan and Lucas, 2000a). northern DonÄa Ana County south through the The age of the Hatch LF is somewhat un- Jornada and Mesilla basins and into Texas. certain because most of the mammalian taxa Hawley (1978) mentioned the presence of are not identi®able below the generic level. Blancan fossils from the vicinity of Hatch, A medial Blancan age is suggested by the but did not list any taxa. Paul Sealey and faunal and stratigraphic similarity to the 2003 MORGAN AND LUCAS: BLANCAN AND IRVINGTONIAN MAMMALS 297

nearby Tonuco Mountain LF (Morgan et al., JORNADA BASIN 1998). A pre-late Blancan age is indicated by the lack of South American immigrant mam- TONUCO MOUNTAIN: The Tonuco Mountain mals that appeared in faunas after 2.7 Ma. A LF is a medial Blancan vertebrate assem- magnetostratigraphic section in the Camp blage from the Cedar Hill area southeast of Rice Formation at Hatch Siphon, located sev- Tonuco Mountain (also called San Diego Mountain) in northern DonÄa Ana County, eral kilometers west of the badlands that pro- southern New Mexico (Morgan et al., 1998; duced the Hatch LF, samples essentially the ®g. 12.1, site 25). The fossils are derived entire Gauss Chron, including both the Ka- from the axial river facies of the Camp Rice ena and Mammoth Subchrons (Mack et al., Formation in the western Jornada Basin. The 1993). The lowermost part of the section stratigraphic section of the Camp Rice For- does not cross the Gilbert/Gauss boundary mation at Cedar Hill consists of about 50 m and is thus younger than 3.6 Ma, whereas the of sandstone and conglomerate, with a minor upper 10 m samples the Matuyama Chron. component of sandy mudstone, and is un- The Hatch Siphon section is similar to the conformably underlain by Miocene red beds magnetostratigraphic section for Cedar Hill of the Rincon Valley Formation (Morgan et that contains the medial Blancan Tonuco al., 1998). Mountain LF (Mack et al., 1993; Morgan et The Tonuco Mountain LF is composed of al., 1998; see below), further supporting a 16 species: the mud turtle Kinosternon, the medial Blancan age for the Hatch LF. land tortoises Gopherus and Hesperotestudo, RINCON ARROYO: Several fragmentary a duck, and 12 mammals including an inde- teeth and partial metapodials of Equus were terminate rabbit; the badger Taxidea; the collected from the Camp Rice Formation in coyote-like canid Canis lepophagus; the bor- Rincon Arroyo by Paul Knight and Paul ophagine canid Borophagus sp.; the horses Sealey. Rincon Arroyo is in the Hatch-Rin- Nannippus peninsulatus, Equus simplicidens, con basin in northern DonÄa Ana County and E. scotti; the peccary Platygonus cf. P. about 10 km east of Hatch (®g. 12.1, site 24). bicalcaratus; the camelids Camelops, Hem- The most signi®cant aspect of Rincon Ar- iauchenia blancoensis, and a small Hem- royo is the detailed geochonologic data avail- iauchenia; and the gomphothere Cuvieron- able for the stratigraphic section, including ius. Among these taxa, Borophagus, C. le- magnetostratigraphy (Mack et al., 1993) and pophagus, N. peninsulatus, E. simplicidens, a dated pumice-clast conglomerate (Mack et P. bicalcaratus, and H. blancoensis are in- al., 1998). The lower half (about 50 m) of dicative of the Blancan, and several of these the Rincon Arroyo section is in the Gauss taxa help to further limit the age of this fauna Chron and the upper portion (also about 50 within the Blancan. E. simplicidens is absent from very early Blancan faunas, Platygonus m) is in the Matuyama Chron, and includes and Camelops supposedly do not appear until the Reunion, Olduvai, and Jaramillo sub- the beginning of the medial Blancan (Lind- chrons (Mack et al., 1993). Between the Ol- say et al., 1984), and most Blancan records duvai and Jaramillo subchrons in the upper of Nannippus in the southwestern United part of the section is a pumice-clast conglom- States predate the Gauss/Matuyama magnetic erate dated at 1.60 Ma, which correlates with reversal at 2.6 Ma. The absence of South the lower Bandelier eruption (Mack et al., American immigrants suggests the fauna is 1998). The Rincon Arroyo section crosses older than 2.7 Ma, the earliest date for the the Blancan/Irvingtonian boundary at the top onset of the Great American Interchange. of the Olduvai Subchron in the upper third The biostratigraphic data restrict the age of of the section. Unfortunately, Rincon Arroyo the Tonuco Mountain LF to the medial Blan- is not particularly fossiliferous, and the few can (between 3.6 and 2.7 Ma). A magneto- fossils recovered so far are not age diagnos- stratigraphic study of the Camp Rice For- tic. Future ®eld work in Rincon Arroyo mation at Cedar Hill helps to further con- hopefully will yield additional mammal fos- strain the age of this fauna (Mack et al., sils from this well-dated section. 1993). The entire Cedar Hill section is within 298 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279 the Gauss Chron (younger than 3.6 Ma), and fauna was based on the Frick fossils (F:AM) the fossiliferous interval is below the top of now housed in the AMNH. The largest col- the Kaena Subchron (older than 3.0 Ma). The lection of fossils from the Mesilla basin was combination of biostratigraphic and magne- amassed from the 1950s through the 1980s tostratigraphic data limit the age of the Ton- by William Strain, Arthur Harris, and their uco Mountain LF to the medial Blancan, be- students at the University of Texas at El Paso tween 3.6 and 3.0 Ma. (UTEP). The UTEP and F:AM collections formed the basis for the detailed review of MESILLA BASIN the vertebrate paleontology, lithostratigraphy, and magnetostratigraphy of the Mesilla basin Two Blancan and two early Irvingtonian faunas by Vanderhill (1986) in his doctoral vertebrate faunas occur in the Camp Rice dissertation. Beginning in 1999, ®eld crews Formation in the Mesilla Basin, DonÄa Ana from the NMMNH began collecting fossils County, southern New Mexico (Tedford, from the Camp Rice Formation in the vicin- 1981; Vanderhill, 1986; Lucas et al., 1999, ity of Chamberino and La Union in the 2000). In his doctoral dissertation, Vanderhill southern Mesilla Basin, and discovered a mi- (1986) referred to these faunas as Faunule A crovertebrate site near Chamberino in the lat- (late Blancan), Faunule B (latest Blancan/ est Blancan portion of the Camp Rice For- earliest Irvingtonian), and Faunule C (early mation. The discussion of the southern Mes- Irvingtonian) of the Mesilla basin, but did illa Basin faunas is primarily abstracted from not apply formal names to them. We follow Vanderhill's (1986) unpublished dissertation, the letter designations of Vanderhill (1986) with additional data from recent ®eld work. for the faunas from the southern Mesilla ba- TORTUGAS MOUNTAIN: Vertebrate fossils sin, from Chamberino south to the Mexican have been known for 40 years from gravel border near Santa Teresa; however, we use pits in the northern Mesilla Basin (Ruhe, the terms Mesilla Basin Fauna A, B, and C 1962; Hawley et al., 1969). The Tortugas (shortened to Mesilla A, B, and C) to con- Mountain LF includes fossils collected from form to the nomenclature as discussed above two gravel pits near Tortugas Mountain, sev- under Methods (i.e., the Mesilla basin ver- eral kilometers east of Las Cruces in DonÄa tebrate assemblages ®t the de®nition of fau- Ana County (Lucas et al., 1999, 2000; ®g. nas, rather than faunules or local faunas). 12.1, site 26). These pits expose axial river The three faunas from the southern Mesilla sands and gravels of an ancestral Rio Grande basin are stratigraphically superposed and in the upper part of the Camp Rice Forma- differ in age, as documented by both biostra- tion. A palate of Stegomastodon, two man- tigraphy and magnetostratigraphy (Vander- dibles of Cuvieronius, and isolated teeth of hill, 1986), and thus should eventually be as- Mammuthus were collected from a gravel pit signed formal names to eliminate confusion. on the northwestern side of Tortugas Moun- The Tortugas Mountain LF includes two ear- tain (NMMNH site L-3537). A palate of Cu- ly Irvingtonian sites in the northern Mesilla vieronius,aMammuthus tooth, and several basin (Lucas et al., 1999, 2000) that were teeth and postcranial elements of Equus were included in Fauna (ϭ Faunule) C by Van- found from about the same stratigraphic level derhill (1986). Mesilla Basin Fauna C is here in the Inman Gravel Pit (NMMNH site L- restricted to the early Irvingtonian fauna 3649), about 3 km north of Tortugas Moun- from the southern Mesilla basin. tain (Hawley et al., 1969; Tedford, 1981; Vertebrate fossils were ®rst collected in Vanderhill, 1986; Lucas et al., 1999, 2000). the southern Mesilla basin in 1929 by Joseph With the exception of several Equus fos- Rak of the Frick Laboratory. George Pearce, sils ®gured in Hawley et al. (1969) that we also of the Frick Laboratory, returned to the cannot locate, the Tortugas Mountain LF southern Mesilla basin in 1949 and accu- consists of three species of proboscideans mulated a sizeable collection, including a gi- (Lucas et al., 1999, 2000), the gomphotheres ant tortoise shell, several glyptodont shells, Cuvieronius tropicus and Stegomastodon and a nearly complete tapir skeleton. Ted- miri®cus and the mammoth Mammuthus im- ford's (1981) summary of the Mesilla basin perator. Tortugas Mountain is only the sec- 2003 MORGAN AND LUCAS: BLANCAN AND IRVINGTONIAN MAMMALS 299 Fig. 12.3. Correlation chart showing the relative ages of late Hemphillian, Blancan, and Irvingtonian vertebrate faunas from the southern Rio Grande Valley and Gilafor River ®gure Valley 12.2. in New Mexico, including the Hatch-Rincon, Jornada, Mesilla, Mangas, and Duncan basins. Other notes as 300 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279 ond site that records the co-occurrence of part of the sequence (Vanderhill, 1986; ®g. Cuvieronius, Stegomastodon, and Mammu- 12.1, site 27). The vertebrate assemblage thus, the other being the early Irvingtonian from Mesilla A is composed of only six spe- Gilliland LF from the Seymour Formation in cies (table 12.1; from Vanderhill, 1986): the Texas (Hibbard and Dalquest, 1966). Cuvi- cat®sh Ictalurus, the softshell turtle Apalone eronius is not particularly age diagnostic in (ϭ Trionyx), the glyptodont Glyptotherium, North America, as this genus ®rst appears in the horses Nannippus peninsulatus and Eq- the Blancan and survives until the early Ran- uus cf. E. calobatus, and the llama Hem- cholabrean (Morgan and Hulbert, 1995). iauchenia blancoensis. The presence of However, the association of Stegomastodon Glyptotherium con®rms a late Blancan or and Mammuthus is important biochronolog- younger age (younger than 2.7 Ma) for this ically because these two genera have only a fauna, as the ®rst appearance of South Amer- limited period of overlap in the early Irving- ican immigrants, including Glyptotherium,in tonian, after the arrival of Mammuthus across North American faunas de®nes the beginning the Bering Land Bridge from Eurasia (about of the late Blancan. The presence of Nannip- 1.6 Ma) and before the extinction of Stego- pus indicates an age greater than 2.2 Ma. mastodon (about 1.2 Ma). The presence of Magnetostratigraphic data for the Camp Mammuthus clearly establishes an Irvington- Rice Formation strata from which the Mes- ian age for the Tortugas Mountain LF. At pre- illa A fauna was derived further restrict its sent there are no con®rmed records of mam- age (Vanderhill, 1986). Mesilla A occurs in moths in North America older than 1.6 Ma normally magnetized sediments in the upper (Lucas, 1995, 1996; Cassiliano, 1999). The Gauss Chron between the Kaena Subchron mammoth teeth from the Tortugas Mountain (3.04 Ma) and the Gauss/Matuyama bound- LF, identi®ed as M. imperator by Lucas et al. ary (2.58 Ma). Mesilla A is one of only six (1999, 2000), are very similar to mammoth southwestern Blancan faunas that documents teeth from other early Irvingtonian sites, in- the presence in the upper Gauss Chron (be- cluding M. haroldcooki from Gilliland, Texas tween 3.0 and 2.6 Ma) of South American (Hibbard and Dalquest, 1966) and Holloman, immigrant mammals. Although 2.7 Ma is of- Oklahoma (Dalquest, 1977) and M. hayi ten cited as the ®rst appearance datum for from Leisey Shell Pit, Florida (Webb and South American immigrants in North Amer- Dudley, 1995). The youngest well-dated re- ica, and is used here as the boundary be- cord of Stegomastodon miri®cus is from Tule tween the medial and late Blancan, the tim- Canyon in the Texas Panhandle, where this ing of the ®rst appearance in southwestern species is associated with mammoths and Blancan faunas of mammals that participated several species of horses in a volcanic ash at in the Great American Interchange is not the base of the Tule Formation dated at be- ®rmly established, but occurred sometime tween 1.3 and 1.2 Ma (Izett, 1977; Tedford, between 3.0 and 2.6 Ma. There are no con- 1981; Madden, 1983). An age between 1.6 ®rmed records of Interchange mammals in and 1.2 Ma is indicated for the Tortugas Blancan faunas north of Mexico that predate Mountain LF based on the association of the Kaena Subchron at 3.04 Ma. However, Mammuthus and Stegomastodon. several new records of South American im- MESILLA BASIN FAUNA A: There are three migrants from central Mexico appear to be vertebrate faunas from the Camp Rice For- early Blancan (Miller and Carranza-Casta- mation in the southern Mesilla basin, from nÄeda, 2001, 2002). Chamberino south to Santa Teresa near the MESILLA BASIN FAUNA B: Mesilla Basin border with Mexico (Vanderhill, 1986). Fau- Fauna B (hereafter shortened to Mesilla B) nas A and B are late Blancan in age, and is the most diverse late Blancan fauna in Fauna C is early Irvingtonian. Mesilla Basin New Mexico (®g. 12.1, site 28). Vanderhill Fauna A (hereafter shortened to Mesilla A) (1986: table 1) listed 16 species from Mesilla is the oldest and least well known of the B: two turtles, the aquatic emydid Trachemys three southern Mesilla basin faunas, probably and the land tortoise Hesperotestudo; and 14 because exposures of the lower part of the mammals including Glyptotherium arizonae, section are less extensive than in the upper the mylodont gound sloth Paramylodon cf. 2003 MORGAN AND LUCAS: BLANCAN AND IRVINGTONIAN MAMMALS 301

P. harlani, the rabbits Aluralagus virginiae 1987; Repenning, 1987), is best regarded as and a larger Lepus or Sylvilagus, the small latest Blancan owing to the absence of Mam- cat cf. Lynx rufus, the sabercat Smilodon muthus and other typical Irvingtonian genera gracilis, the horses Equus cf. E. calobatus (Lindsay et al., 1990). There are also late and E. scotti, the large tapir Tapirus haysii, Blancan records of G. arizonae from Florida the camelids Blancocamelus meadei, Gigan- (Morgan and Hulbert, 1995). The rabbit Al- tocamelus cf. G. spatula, and Camelops, the uralagus virginiae appears to be restricted to deer Odocoileus, and the gomphothere Cu- Blancan/Irvingtonian transitional faunas. The vieronius. Our recent ®eldwork in the Camp only other faunas where A. virginiae has Rice Formation near La Union has added been identi®ed (referred to Hypolagus virgi- four species of large mammals to the Mesilla niae by Tomida, 1987), Curtis Ranch and the B fauna (table 12.1). San Simon Power Line, both in southern Ar- We recently discovered a new microver- izona, are similar in age to Mesilla B. Smi- tebrate site near Chamberino in the southern lodon gracilis and Tapirus haysii are typical Mesilla basin (NMMNH site L-2971), from of early Irvingtonian faunas, but both are the same stratigraphic level as Vanderhill's known from the late Blancan. Previous Mesilla B. This site occurs stratigraphically southwestern records of S. gracilis are re- about 5 m below the lowest occurrence of stricted to the early Irvingtonian, but this sa- Mammuthus in the Chamberino section. The bercat occurs in several Florida late Blancan Chamberino microsite is being actively faunas (Berta, 1987; Morgan and Hulbert, screenwashed at the present time. Prelimi- 1995). T. haysii is known from late Blancan nary identi®cations add at least 11 species to faunas in Texas and Colorado (Strain, 1966; the Mesilla B fauna: two snakes, a lizard, a Hager, 1974; Hulbert, 1995). small passerine bird, and seven mammals in- Magnetostratigraphic data for Mesilla B cluding the mole Scalopus, the ground squir- (Vanderhill, 1986) indicate that the zone con- rel Spermophilus, the pocket gopher Geomys, taining this fauna spans the time period from the heteromyid rodent Dipodomys, the cotton the Gauss/Matuyama boundary to the Oldu- rat Sigmodon, the grasshopper mouse Ony- vai Subchron (between about 2.6 and 1.8 chomys, and the skunk Spilogale. Combining Ma). Faunal evidence suggests that Mesilla Vanderhill's Faunule B with our Chamberino B falls in the younger half of this interval, site, the Mesilla B fauna now has 25 species as typical Blancan taxa that went extinct by of mammals, making it the most diverse about 2.2 Ma (Hypolagus, Nannippus, and Blancan mammal fauna in New Mexico. Rhynchotherium) are absent from this fauna. Mesilla B has a diverse assemblage of Pending the discovery of additional age-di- mammals, but only a few taxa are age di- agnostic taxa in the Mesilla B fauna, partic- agnostic. Many species occur in both late ularly among small mammals, this fauna is Blancan and early Irvingtonian and younger here considered to be latest Blancan (latest faunas. Vanderhill (1986) correlated Mesilla Pliocene) in age, between 2.2 and 1.8 Ma. B with the transitional interval between the MESILLA BASIN FAUNA C: The uppermost Blancan and Irvingtonian (2.2±1.8 Ma). Two portion of the Camp Rice Formation in the genera typical of the Blancan, the giant cam- southern Mesilla basin (®g. 12.1, site 29) els Blancocamelus and Gigantocamelus, oc- contains Mammuthus, and is thus Irvington- cur in Mesilla B. The presence of the South ian or younger in age. Mesilla Basin Fauna American immigrant xenarthrans Glyptoth- C (hereafter shortened to Mesilla C) is cor- erium arizonae and Paramylodon cf. P. har- relative with the early Irvingtonian Tortugas lani con®rms that Mesilla B is late Blancan Mountain LF near Las Cruces (Lucas et al., or younger. G. arizonae is supposedly re- 1999, 2000) in the northern Mesilla basin. stricted to early Irvingtonian sites elsewhere Among Irvingtonian faunas in New Mexico, in the southwest (Gillette and Ray, 1981). Mesilla C has the most diverse sample of However, the type locality of G. arizonae, large vertebrates (table 1, from Vanderhill, Curtis Ranch in the San Pedro Valley of Ar- 1986), consisting of 17 species: the land tor- izona, although considered earliest Irvington- toises Gopherus and Hesperotestudo and 15 ian by most workers (e.g., Lundelius et al., species of mammals, including Glyptother- 302 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279 ium arizonae; Paramylodon harlani; the me- from the Camp Rice Formation near La galonychid ground sloth Megalonyx wheatle- Union, in the vicinity where many of the fos- yi; the beaver Castor canadensis; the wolf sils from both Mesilla B and C were col- Canis armbrusteri; a smaller coyote-like Ca- lected. A pumice dated at 1.59 Ma occurs nis sp.; the bobcat Lynx rufus; three horses, about 30 m below the La Mesa surface (local Equus cf. E. calobatus, E. scotti, and a large top of the Camp Rice Formation in the La Equus, Camelops cf. C. hesternus; the cervid Union section) and a pumice dated at 1.32 Navahoceros lascrucensis; the deer Odoco- Ma occurs about 10 m below the top of the ileus; the gomphothere Cuvieronius tropicus; section (Mack et al., 1996: ®g. 2). Although and the mammoth Mammuthus cf. M. meri- these radioisotopic dates cannot currently be dionalis. precisely correlated with the magnetostratig- The ®rst appearance of Mammuthus in raphy and biostratigraphy, it appears that all North America as an immigrant from Eurasia of the Mesilla C fossils were collected from occurred sometime around 1.6 Ma (Lucas, above the 1.59 Ma pumice date, which pro- 1995, 1996; Cassiliano, 1999). The primitive vides a maximum age for this fauna. It is mammoth Mammuthus meridionalis, identi- likely that some fossils assigned to Mesilla ®ed from Mesilla C (Vanderhill, 1986), oc- C were collected from strata above the 1.32 curs only in early Irvingtonian faunas, and is Ma pumice date. The combination of bio- quickly replaced by (or evolved into) more stratigraphy, magnetostratigraphy, and radio- advanced mammoths variously referred to M. isotopic dates suggests an age between 1.6 haroldcooki, M. hayi, and M. imperator, and 1.1 Ma for Mesilla C (Vanderhill, 1986; which are also present in the early Irvington- Mack et al., 1996). ian. Although Glyptotherium arizonae is sup- posedly restricted to early Irvingtonian fau- MANGAS BASIN nas in the southwestern United States (Gil- lette and Ray, 1981), fossils referred to this BUCKHORN: The Buckhorn LF is derived species from Mesilla B and Virden appear to from 14 sites located between 3 and 10 km be latest Blancan. The large wol¯ike canid northwest of Buckhorn in northern Grant Canis armbrusteri is found only in Irving- County, southwestern New Mexico (Morgan tonian faunas, with the oldest record of this et al., 1997; ®g. 12.1, site 30). The fossils species from the early Irvingtonian Leisey occur in unconsolidated sands, silts, and Shell Pit LF in Florida (Berta, 1995). The muds through a stratigraphic interval of living beaver Castor canadensis is restricted about 20 m in the upper part of the Gila to Irvingtonian and younger faunas in North Group in the Mangas basin. The abundance America. A supposed late Blancan record of of aquatic vertebrates in several of the Buck- C. canadensis from the Haile 15A LF in horn sites, including ®sh, frogs, ¯amingos, Florida (Robertson, 1976) is based on a fe- rails, and ducks, as well as the lithology of mur that is not diagnostic at the species level. the sediments, suggests a freshwater deposi- Mesilla C is most similar to early Irving- tional environment, possibly a large lake. tonian faunas from the southern Great Plains, The Buckhorn LF is the most diverse Blan- such as Gilliland and Rock Creek in Texas can vertebrate faunal assemblage known (Hibbard and Dalquest, 1966) and Holloman from New Mexico, composed of 33 species, in Oklahoma (Dalquest, 1977), that contain including 14 lower vertebrates and 19 mam- Glyptotherium arizonae, Paramylodon har- mals (Morgan et al., 1997). The nonmam- lani, Equus scotti, E. calobatus, and Mam- mals include three species of small ®sh, the muthus sp. Magnetostratigraphy for the in- frog Rana, the salamander Ambystoma, two terval that produces the Mesilla C fauna unidenti®ed colubrid snakes, a lizard, and six (Vanderhill, 1986) suggests correlation with birdsÐthe ¯amingo Phoenicopterus, two the upper Matuyama Chron, spanning the ducks, a rail, the turkey cf. Meleagris, and a time interval from just after the Olduvai Sub- small perching bird. The mammalian fauna chron (1.81 Ma) to just prior to the Jaramillo of 19 species includes a microchiropteran Subchron (1.07 Ma). Mack et al. (1996) ob- bat; a rabbit; the ground squirrel Spermophi- tained Ar/Ar dates on three pumice beds lus cf. S. bensoni; Repomys cf. R. panacen- 2003 MORGAN AND LUCAS: BLANCAN AND IRVINGTONIAN MAMMALS 303 sis; the vole Mimomys poaphagus, Peromys- Kansas (Hibbard, 1938, 1941, 1950, 1967; cus sp., and Baiomys sp.; four carnivores in- Repenning, 1987). cluding the badger Taxidea, a bear, a small There are currently no radioisotopic dates feline, and a large machairodontine; two or magnetostratigraphic data that would pro- horses, Nannippus peninsulatus and Equus vide additional information on the age of the simplicidens; a peccary, three camelids, Ca- Buckhorn LF. There are several volcanic ash melops sp., Hemiauchenia blancoensis, and beds in the Buckhorn section, but they are a small Hemiauchenia, an indeterminate ru- too altered to provide accurate radioisotopic minant, and Stegomastodon. dates. The latest Hemphillian Walnut Canyon Many of the mammals from the Buckhorn LF occurs in Gila Group strata about 25 km LF are indicative of a Blancan age, including southeast of the Buckhorn LF (Morgan et al., Mimomys, Repomys cf. R. panacaensis, Nan- 1997; ®g. 12.1, site 31). The latest Hemphil- nippus peninsulatus, Equus simplicidens, and lian age (earliest Pliocene; 5.0±4.5 Ma) of Hemiauchenia blancoensis. Several taxa al- the Walnut Canyon LF provides a maximum low for a more precise placement within the age for the Buckhorn LF. These two faunas Blancan. The presence of a primitive species have no taxa in common, indicating that the of the arvicoline rodent Mimomys and the ab- Hemphillian/Blancan boundary occurs some- sence of Neotropical immigrants suggest a where in the section separating them. Further pre-late Blancan age (older than 2.7 Ma). ®eldwork in the region between Buckhorn The occurrence of Equus simplicidens and a and Walnut Canyon should allow a more pre- large species of Mimomys (subgenus Ogmo- cise stratigraphic placement of these two fau- dontomys) excludes very early Blancan fau- nas. nas. The evolutionary stage of two of the Buckhorn rodents, Mimomys (Ogmodonto- mys) poaphagus and Repomys cf. R. pana- DUNCAN BASIN caensis, is most consistent with a late early PEARSON MESA: Exposures on Pearson Blancan age (between about 4.2 and 3.6 Ma; Mesa south of the Gila River in the Duncan Blancan II of Repenning, 1987) for the Buckhorn LF. basin along the New Mexico-Arizona border The Buckhorn LF and the Truth or Con- have produced a diverse assemblage of late sequences LF from the central Rio Grande Blancan vertebrate fossils from strata of the Valley both appear to be early Blancan in age Gila Group (®g. 12.1, sites 32, 33). Most of on the basis of comparisons with early Blan- Pearson Mesa is located in Hidalgo County can faunas outside of New Mexico; however, in southwestern New Mexico, but the north- the mammalian faunas from these two sites western point of the mesa extends into have virtually no age-diagnostic taxa in com- Greenlee County in southeastern Arizona. mon, particularly among the small mammals. About three-fourths of the 76 NMMNH fos- Mimomys, the extinct ``cricetid'' genus Re- sil sites located on Pearson Mesa are in New pomys, and the tiny sigmodontine Baiomys Mexico and the rest are in Arizona. The occur in the Buckhorn LF, whereas the Truth stratigraphic section at Pearson Mesa con- or Consequences LF is dominated by the sists of more than 60 m of sandstones, mud- wood rat Neotoma, the cotton rat Sigmodon, stones, and sedimentary breccias referred to and the small extinct sigmodontine genus Ja- the Gila Group. The lower 15 m of this sec- cobsomys. The Buckhorn and Truth or Con- tion contains the three-toed horse Nannippus sequences faunas must have sampled differ- peninsulatus and the horse Equus simplici- ent habitats or perhaps differ enough in age dens, together with rarer specimens of many to have allowed signi®cant change in the other taxa, the most signi®cant of which is small mammal fauna. Other early Blancan the mylodont ground sloth Glossotherium cf. faunas that are broadly correlative with G. chapadmalense. This assemblage, the Buckhorn are the Verde LF in Arizona (Cza- Pearson Mesa LF (Tomida, 1987; Morgan plewski, 1987, 1990), the Panaca LF in Ne- and Lucas, 2000b; ®g. 12.1, site 32), is in- vada (May, 1981; Mou, 1997, 1999), and the dicative of a late Blancan age. A latest Blan- Rexroad 3 and Fox Canyon faunas from can fauna, the Virden LF (®g. 12.1, site 33), 304 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279 occurs in the upper 20 m of the section at South American immigrants in North Amer- Pearson Mesa, and is discussed below. ican faunas, following the onset of the Great The Pearson Mesa LF consists of 16 spe- American Interchange at about 2.7 Ma, de- cies of vertebrates: the land tortoise Gopher- ®nes the beginning of the late Blancan. The us, a large and a small species of the land only time interval during which these two tortoise Hesperotestudo, the box turtle Ter- genera coexisted in southwestern faunas was rapene, a heron, and 11 mammals, including between 2.7 Ma (the beginning of the Inter- Glossotherium cf. G. chapadmalense; a small change) and 2.2 Ma (the Nannippus extinc- cat and a larger machairodontine sabercat; tion datum of Lindsay et al., 1984). A paleo- the pocket gopher Geomys (Nerterogeomys) magnetic section from Pearson Mesa (Tom- cf. G. persimilis; the horses Nannippus pen- ida, 1987) further restricts the age of the low- insulatus, Equus cumminsii, E. scotti, and E. er portion of the section, including the simplicidens; the peccary Platygonus bical- Pearson Mesa LF, to the upper Gauss Chron caratus; the camelid Hemiauchenia blan- (3.0±2.6 Ma). Combining the biostratigraph- coensis; and the gomphothere Stegomasto- ic and magnetostratigraphic data for the don rexroadensis. The presence of Nannip- Pearson Mesa LF would seem to tightly con- pus in the Pearson Mesa LF indicates an age strain the age of this fauna between 2.7 Ma greater than 2.2 Ma, whereas Glossotherium (earliest appearance of Glossotherium) and does not appear in North American faunas 2.6 Ma (Gauss/Matuyama boundary). Al- until the late Blancan, indicating an age less though the timing of the ®rst arrival of South than 2.7 Ma. Other taxa from the Pearson American immigrants in North America is Mesa LF that provide some indication of age not precisely known, Pearson Mesa is im- include Geomys (N.) persimilis, Platygonus portant because it is one of only six sites in bicalcaratus, and Stegomastodon rexroad- the southwestern United States that records ensis. G. (N.) persimilis occurs in medial the presence of South American Interchange Blancan through early Irvingtonian sites in mammals in the Gauss Chron, indicating an the southwestern United States. Tomida age greater than 2.6 Ma. (1987) noted that the presence of this pocket VIRDEN: A substantial thickness (about 30 gopher in the lower part of the Pearson Mesa m) of Gila Group strata in the middle of the section suggested placement in the upper- Pearson Mesa section has not yet produced most Gauss Chron. Platygonus bicalcaratus fossils, including a 9-m-thick breccia at the apparently is restricted to medial and late top of this unfossiliferous interval that may Blancan faunas, and Stegomastodon rexroad- represent a hiatus (Morgan and Lucas, ensis occurs in the early and medial Blancan. 2000b). Just above this breccia, at about the The mandible of Stegomastodon upon which 45 m level in the section and continuing for this record is based (F:AM 23338) is from about the next 10 m, vertebrate fossils occur an imprecisely located site in the vicinity of at several localities on Pearson Mesa. This Pearson Mesa, and is of unknown strati- fauna differs signi®cantly from the underly- graphic position. A mandible of similar mor- ing Pearson Mesa LF, and is here named the phology, referred to S. rexroadensis, occurs Virden Local Fauna for the nearby village of in the medial Blancan Cuchillo Negro Creek Virden, New Mexico (®g. 12.1, site 33). Ex- LF (Lucas and Oakes, 1986). The medial posures in the upper portion of the Pearson Blancan Duncan Fauna is located near Dun- Mesa section are not as extensive and tend can, Arizona, less than 10 km northwest of to be more vertical than lower in the section, Pearson Mesa (Tomida, 1987), and thus it is and consequently the Virden LF is not as possible that the S. rexroadensis mandible abundant or diverse as the Pearson Mesa LF. was derived from lower in the Gila Group Nonetheless, the presence of Glyptotherium section than strata that produce the Pearson arizonae and the absence of Nannippus in Mesa LF. the Virden LF indicate that this fauna is The association of Nannippus with Glos- younger than the Pearson Mesa LF, either lat- sotherium provides the most signi®cant bio- est Blancan or earliest Irvingtonian in age. stratigraphic information regarding the age of The only taxa these faunas share are a large the Pearson Mesa LF. The ®rst appearance of land tortoise and Equus scotti. 2003 MORGAN AND LUCAS: BLANCAN AND IRVINGTONIAN MAMMALS 305

The Virden LF consists of seven species: and the absence of diagnostic Blancan indi- the land tortoise Hesperotestudo and six cators (e.g., Nannippus) suggests that the mammals, including Glyptotherium arizonae, Virden LF is distinctly younger than the un- the coyote-like canid Canis lepophagus, Eq- derlying Pearson Mesa LF, probably either uus scotti, Camelops, a small Hemiauchenia, latest Blancan or earliest Irvingtonian (be- and an indeterminate proboscidean. The tween 2.2 and 1.6 Ma). The presence of Ca- glyptodonts in the Virden LF, represented by nis lepophagus, a species unknown from the osteoderms, a cranial fragment, and several Irvingtonian, suggests that a latest Blancan postcranial elements, are referable to the age is more likely. Tomida's (1987) Pearson large species G. arizonae. Glyptodonts ®rst Mesa paleomagnetic stratigraphy does not in- appear in southwestern faunas in the early clude the upper 20 m of the section (Morgan late Blancan (upper Gauss Chron) in sites and Lucas, 2000b), and thus we currently equivalent in age to the Pearson Mesa LF have no magnetostratigraphic data for this (e.g., Hudspeth and Cita Canyon in Texas fauna. Paleomagnetic samples from the up- and 111 Ranch in Arizona), but these occur- per portion of the section recently collected rences represent the smaller species G. tex- by G. Mack should help clarify the age of anum. Glyptodonts are unknown from the the Virden LF. Pearson Mesa LF. Although previous records of G. arizonae indicated that this species was BIOCHRONOLOGY AND restricted to the early Irvingtonian in the CORRELATION southwestern United States (Gillette and Ray, 1981), there are now late Blancan records of There are 24 Blancan and 7 Irvingtonian this species from Curtis Ranch in Arizona, sites in New Mexico that have produced fos- Mesilla B, and Virden, as well as Florida sil mammals. Four or more species of mam- (Morgan and Hulbert, 1995). mals are known from 15 of the Blancan and Associated mandibles of a medium-sized 4 of the Irvingtonian sites (faunal lists in ta- canid, similar in size and morphology to the bles 12.1 and 12.2, respectively). Throughout coyote-sized species Canis lepophagus, were the preceding discussion, we have provided found in association with Glyptotherium os- information on the ages of the 31 sites and teoderms in the upper portion of the Pearson the biochronology of the individual taxa. Mesa section. C. lepophagus is restricted to Here we summarize the biochronology of the Blancan, including the late Blancan Cita New Mexico Blancan and Irvingtonian sites, Canyon and Red Light faunas in Texas (Ak- with correlation to well-known faunas from ersten, 1972) and the late Blancan 111 Ranch elsewhere in western North America. These fauna in Arizona (Galusha et al., 1984; Tom- data are preliminary because we are still ac- ida, 1987). A pair of lower jaws from Virden tively involved in ®eldwork at several of the represents a small species of Hemiauchenia. richer sites, particularly those with diverse These mandibles are from an adult with well- small mammal faunas (e.g., Buckhorn, worn teeth, but are very small compared to Chamberino, and Truth or Consequences). other known species of Hemiauchenia, such New taxa are still being added to the various as the Blancan H. blancoensis and the Ir- faunal lists, but for most of the sites listed in vingtonian and Rancholabrean H. macroce- tables 12.1 and 12.2, enough taxa are present phala. A small Hemiauchenia occurs in sev- to provide an accurate indication of age, at eral New Mexico Blancan faunas, including least within the major subdivisions of the two Cuchillo Negro Creek, Tonuco Mountain, NALMAs (e.g., medial Blancan, early Ir- and Buckhorn, as well as two early Irving- vingtonian). We also review all relevant ra- tonian sites in Florida (Morgan and Hulbert, dioisotopic dates and magnetostratigraphic 1995). Equus scotti is one of the most com- data pertaining to New Mexico Blancan and mon horses found in southwestern early Ir- Irvingtonian sites. The correlation charts in vingtonian faunas, but this species also oc- ®gures 12.2 and 12.3 summarize the current curs in medial and late Blancan sites in New state of our knowledge on the age of the sites Mexico. discussed in the text. Figure 12.4 correlates The presence of Glyptotherium arizonae the New Mexico Blancan and Irvingtonian 306 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279 Fig. 12.4. Correlation chart showing the relative ages of late Hemphillian, Blancan, and Irvingtonian vertebrate faunas from New Mexico compared to faunas of similar age from Arizona and Texas. Other notes as for ®gure 12.2. 2003 MORGAN AND LUCAS: BLANCAN AND IRVINGTONIAN MAMMALS 307 faunas with well-known faunas from Arizona Buckhorn sites in the composite Gila Group and Texas. Not all of the Blancan and Ir- section in the central Mangas basin. The vingtonian sites from New Mexico are in- Walnut Canyon LF compares closely to the cluded in the correlation charts. All sites list- YepoÂmera Fauna, one of the youngest known ed in tables are included in the correlation Hemphillian faunas (Lindsay et al., 1984), charts, as well as selected faunas with fewer whereas the Buckhorn LF is early, but not than four mammals that contain age-diag- earliest, Blancan. These age relationships nostic taxa. suggest two possibilities: (1) there may be a With two exceptions, all Pliocene verte- hiatus in the Gila Group section or (2) there brate faunas in New Mexico are Blancan, may be an older, and as yet undiscovered, ranging in age from about 4.5 to 1.8 Ma. earliest Blancan fauna in the intervening un- There is a restricted interval of time in the measured section. Although separated by less earliest Pliocene (between 5.3 and 4.9±4.5 than 1 m.y., the Walnut Canyon and Buck- Ma, depending on the placement of the Hem- horn faunas have no taxa in common, indi- phillian/Blancan boundary) that is included cating that the major extinction event docu- within the next older NALMA, the Hem- mented at the Hemphillian/Blancan bound- phillian. Most Hemphillian faunas are late ary (Lindsay et al., 1984; Tedford et al., Miocene in age (9.0±5.3 Ma), including the 1987) occurs somewhere in the section be- well-known faunas from the type area of the tween these two sites. The horses Astrohip- Chamita Formation in the EspanÄola basin in pus and Dinohippus are common in the Wal- northern New Mexico (MacFadden, 1977; nut Canyon LF, but both disappear at the end Tedford, 1981), which are late early to early of the Hemphillian. The microtine rodent Mi- late Hemphillian (about 7±5.5 Ma). The Wal- momys, a Eurasian immigrant and one of the nut Canyon LF from the Gila Group in the genera whose ®rst appearance in North Mangas basin in southwestern New Mexico America de®nes the beginning of the Blan- (Morgan et al., 1997; ®g. 12.1, site 31; ®gs. can (Repenning, 1987; Tedford et al., 1987), 12.3, 12.4) has two horses, Astrohippus sto- is one of the most common mammals in the cki and Dinohippus mexicanus, that are very Buckhorn LF. similar to horses from the latest Hemphillian Repenning (1987) subdivided the Blancan (earliest Pliocene) YepoÂmera Fauna from into ®ve ``subages'' (Blancan I±V) based on Chihuahua in northern Mexico (Lance, 1950; microtine (ϭ arvicoline) rodent biochronol- MacFadden, 1984). The lower Puye Forma- ogy. Although Repenning's system is very tion in the EspanÄola basin (®g. 12.1, site 2) useful if a site contains one or preferably has produced a palate with most of the upper more species of microtine rodents, he pro- cheek teeth of D. mexicanus, indicating that vided only limited data for other mammal at least part of the Puye Formation is latest groups. Only one Blancan fauna in New Hemphillian in age as well (®gs. 12.2, 12.4). Mexico, the Buckhorn LF, contains micro- The Mangas Basin in southwestern New tines. Faunas dominated by large mammals, Mexico is the only place in the state where which include most Blancan faunas from a Blancan fauna occurs in stratigraphic su- New Mexico, are dif®cult to correlate using perposition above a Hemphillian fauna. We Repenning's microtine biochronology. Lun- measured two stratigraphic sections in Gila delius et al. (1987) and Woodburne and Group sediments in the Mangas Basin in Swisher (1995) used a two-part subdivision Grant County (Morgan et al., 1997), a 76-m of the Blancan: early Blancan (ϭ Rexroadian section incorporating the latest Hemphillian of Schultz et al., 1978; BL1 of Woodburne Walnut Canyon Horse Quarry (NMMNH site and Swisher, 1995) and late Blancan (ϭ Se- L-2922) and a 57-m section incorporating necan of Schultz et al., 1978; BL2 of Wood- several sites included in the early Blancan burne and Swisher, 1995). The boundary be- Buckhorn LF (in particular, the Buckhorn tween their early and late Blancan corre- microvertebrate site, NMMNH site L-2912). sponds to the arrival at about 2.7 Ma of im- We have not yet been able to correlate these migrant xenarthrans and caviomorph rodents two sections, although the Walnut Canyon from South America and several microtine fossils occur at least 50 m below the lowest rodents from Eurasia. We have found it use- 308 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279 ful, following Tedford (1981), to subdivide Blancan I). If the White Bluffs LF is 4.3 Ma the early Blancan of Lundelius et al. (1987) in age, then this fauna represents the oldest and Woodburne and Swisher (1995), a time documented occurrence of many of the gen- interval of nearly 2 Ma (between about 4.5 era listed above, including Trigonictis, Ur- and 2.7 Ma), into the early and medial Blan- sus, Nekrolagus, Thomomys, Platygonus, and can, with the boundary between these suba- Mammut. The ®rst appearance of Neotoma ges corresponding to the boundary between appears to be in the Saw Rock Canyon LF the Gilbert and Gauss Chrons at about 3.6 in Kansas, which most workers (e.g., Lun- Ma. Where possible, we correlate New Mex- delius et al., 1987; Repenning, 1987) regard ico Blancan and Irvingtonian faunas with as one of the earliest Blancan faunas in North Repenning's microtine biochronology. America (early Blancan I, 4.8±4.3 Ma). First appearances of Eurasian immigrant Many of the genera used to de®ne the begin- mammals have been used to de®ne the be- ning of the Blancan occur in the Anza-Bor- ginning of the Blancan (between 4.9 and 4.3 rego Desert stratigraphic sequence, but have Ma) in North America, including: the mus- their lowest occurrence well above the Hem- telid Trigonictis, the hyaena Chasmaporthe- phillian/Blancan boundary (Cassiliano, tes, the bear Ursus, the microtine rodents Mi- 1999). Cassiliano suggested that the lowest momys and Nebraskomys, and the cervids stratigraphic occurrence of the cotton rat Sig- Bretzia and Odocoileus (Lundelius et al., modon in the Anza-Borrego sequence at 1987; Tedford et al., 1987; Woodburne and about 4.3 Ma may be close to the Hemphil- Swisher, 1995). However, according to Lind- lian/Blancan boundary. say et al. (1984), some of these ®rst appear- Two of the most diverse Blancan faunas ances occurred later, at about 3.7 Ma, which from New Mexico, the Truth or Consequenc- they designated the Trigonictis appearance es LF from the Palomas Formation in the Rio datum. In addition to Trigonictis, other gen- Grande Valley (Repenning and May, 1986) era they listed as ®rst appearances about 3.7 and the Buckhorn LF from the Gila Group Ma include Chasmaporthetes, Ursus, the rab- in the Gila River Valley (Morgan et al., bits Nekrolagus and Pratilepus, the pocket 1997), are early Blancan in age. Even though gopher Thomomys, the wood rat Neotoma, these two faunas have almost no age-diag- the muskrat Pliopotamys, the peccary Pla- nostic mammals in common, comparisons tygonus, the camel Camelops, and the mas- with Blancan faunas outside of New Mexico todont Mammut. indicate that the Truth or Consequences and In part, the discrepancy in the ages of the Buckhorn faunas are similar in age (late early ®rst occurences of certain genera used to de- Blancan ϭ Blancan II, about 4.2±3.8 Ma). ®ne the Blancan is related to differences of Repenning and May (1986) considered the opinion regarding the age and correlation of Truth or Consequences LF to be early Blan- the White Bluffs LF in Washington (Gustaf- can based on the somewhat more primitive son, 1978, 1985), the earliest Blancan fauna nature of its mammalian fauna compared to that contains a diverse sample of both large the Fox Canyon and Rexroad 3 faunas from and small mammals. Most other very early Kansas. The primitive wood rat Neotoma Blancan faunas (e.g., Concha in Chihuahua, (subgenus Paraneotoma) from Truth or Con- Mexico; Saw Rock Canyon, Kansas; and sequences is intermediate in size between the Verde, Arizona) consist predominantly of smaller N. sawrockensis from the earliest small mammals (Lindsay et al., 1984; Cza- Blancan Saw Rock Canyon LF and the larger plewski, 1987, 1990; Lundelius et al., 1987; N. quadriplicata from early Blancan Rexroad Repenning, 1987). Lindsay et al. and Lun- 3 (Repenning and May, 1986). The Truth or delius et al. considered White Bluffs to be Consequences Neotoma is similar to N. early Blancan (3.9±3.7 Ma; Blancan II of Re- vaughani from the early Blancan (Blancan II, penning, 1987), but not earliest Blancan, and about 4.2 Ma) Verde LF in Arizona (Cza- a correlative of the Fox Canyon Fauna in plewski, 1990). The small sigmodontine ro- Kansas and slightly older than the Hagerman dent Jacobsomys from Verde appears to be Fauna in Idaho. Repenning thought White present at Truth or Consequences (Czaplew- Bluffs was considerably older (about 4.3 Ma, ski, 1987). The deer from Truth or Conse- 2003 MORGAN AND LUCAS: BLANCAN AND IRVINGTONIAN MAMMALS 309 quences, Odocoileus brachyodontus, was gle tooth of Repomys from Buckhorn is sim- ®rst described from Fox Canyon (Oelrich, ilar to R. panacaensis from Panaca (May, 1953). Truth or Consequences shares three 1981). The Buckhorn LF is most similar to species of small mammals with the early late early Blancan (Blancan II of Repenning, Blancan Rexroad 3 Fauna, Notolagus lepus- 1987) faunas such as Fox Canyon, Rexroad culus, Geomys minor, and Sigmodon medius. 3, and Verde, and appears to be somewhat G. minor and S. medius also occur in the younger than early Blancan (Blancan I) fau- Verde LF, which seems to have the closest nas such as Panaca, White Bluffs, and Saw faunal similarity with Truth or Consequenc- Rock Canyon. Repenning (1987) placed the es. Panaca LF in the medial Blancan (Blancan The Truth or Consequences LF occurs in III, about 3.3 Ma), whereas Mou (1997, normally magnetized sediments that were 1999) considered Panaca to be much older, correlated with the Nunivak Subchron of the early Blancan I (4.9±4.6 Ma). There are no Gilbert Chron (Repenning and May, 1986). other geochronologic data associated with These authors gave an age range of 4.20± the Buckhorn LF that would help determine 4.05 Ma for the Nunivak, but the currently its age. The stratigraphic section that pro- recognized age range of this subchron is duced the Buckhorn LF contains several vol- somewhat older, from 4.62±4.48 Ma (Berg- canic ash beds, but these are too highly al- gren et al., 1995). A K/Ar date of 4.5 Ma on tered for radioisotopic dating. In the near fu- a basalt ¯ow below or within the lowermost ture, we hope to obtain magnetostratigraphic Palomas Formation provides a maximum age data for the Gila Group section containing for the Truth of Consequences LF (Seager et both the early Blancan Buckhorn LF and the al., 1984; Mack et al., 1998). A more com- latest Hemphillian Walnut Canyon LF. plete magnetostratigraphic section must be Three faunas derived from the Palomas obtained for the strata of the Palomas For- Formation in the Rio Grande Valley, Cuchi- mation containing the Truth or Consequences llo Negro Creek, Elephant Butte Lake, and site before this fauna can be accurately cor- Palomas Creek, are considered medial Blan- related to the geomagnetic polarity time scale can following Tedford (1981) and Lucas and (GPTS). We suspect that the Truth or Con- Oakes (1986), although the presence of the sequences LF actually may correlate to the large canid Borophagus hilli from Cuchillo next youngest normal subchron in the Gil- Negro Creek (see discussion below) may be bert, the Cochiti, with an age range of 4.29± indicative of an early Blancan age (Wang et 4.18 Ma (Berggren et al., 1995). Repenning al., 1999). The Elephant Butte Lake and (1987) considered Truth or Consequences to Cuchillo Negro Creek faunas consist almost be similar in age to Verde, somewhat youn- entirely of large mammals, and thus have ger than White Bluffs, and slightly older than few taxa in common with the Truth or Con- Rexroad 3 and Fox Canyon. sequences LF. They share two species, Equus The Buckhorn LF has 18 species of mam- simplicidens, found throughout much of the mals compared to 15 species from the Truth Blancan, and Stegomastodon rexroadensis, or Consequences LF; however, many of the restricted to early and medial Blancan fau- Buckhorn taxa are not age diagnostic or are nas. Borophagus hilli from Cuchillo Negro identi®ed only to the family or genus level Creek, and tentatively identi®ed from Truth (Morgan et al., 1997). The most age-diag- or Consequences, occurs primarily in late nostic mammals from the Buckhorn LF are Hemphillian and early Blancan faunas (e.g., the rodents Mimomys (Ogmodontomys) Saw Rock Canyon and White Bluffs), but is poaphagus and Repomys cf. R. panacensis. known from at least one medial Blancan fau- The Buckhorn Mimomys is most similar to na, Hagerman, Idaho (Wang et al., 1999). M. poaphagus from Fox Canyon and Rex- Tedford placed the Elephant Butte Lake sites road 3 (Hibbard, 1941, 1950; Zakrzewski, in the medial Blancan because of their strati- 1967) and Verde (Czaplewski, 1990), larger graphic association with a basalt ¯ow from than M. panacaensis from the Panaca LF in Mitchell Point at the northern end of Ele- Nevada, and differing from the latter species phant Butte Lake (K/Ar date of 2.9 Ϯ 0.3 in certain dental features (Mou, 1997). A sin- Ma; Bachman and Mehnert, 1978). Lucas 310 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279 and Oakes (1986) assigned the Cuchillo Ne- ly associated with an Ar/Ar date of 3.12 Ma gro Creek LF to the medial Blancan, and cor- on pumice (Maldonado et al., 1999), estab- related this fauna with Rexroad and Benson. lishing a medial Blancan age. The Palomas Creek LF shares one species Four species of mammals from the Belen of small mammal, Sigmodon medius, with LF provide an indication of age (Morgan and the Truth or Consequences LF, but S. medius Lucas, 2000a). A mole mandible is most sim- also occurs in medial Blancan faunas, in- ilar to Scalopus (Hesperoscalops) blancoen- cluding the type locality, Benson, Arizona sis from the late Blancan Blanco LF in Texas (Martin, 1979). A mandible from Palomas (Dalquest, 1975). Geomys (Neterogeomys) Creek is the only record of the extant sub- paenebursarius also occurs in the Pajarito genus of Geomys known from the Blancan and Hatch faunas, as well as in two late of New Mexico. Other mammals from this Blancan faunas in southwestern Texas fauna indicative of a Blancan age are Nan- (Strain, 1966; Akersten, 1972). Equus calo- nippus peninsulatus, a large Camelops, and batus is known elsewhere in New Mexico Mammut raki. The presence of Nannippus from the late Blancan Santo Domingo LF and absence of Neotropical immigrants sug- and from late Blancan and early Irvingtonian gest a pre-late Blancan age (older than 2.7 faunas in the Mesilla basin (Tedford, 1981; Ma), whereas the presence of Camelops in- Vanderhill, 1986). Stegomastodon miri®cus dicates a post-early Blancan (younger than is restricted to medial Blancan through early 3.6 Ma). Mammut is rare in the Blancan, but Irvingtonian faunas. Two mammals from Be- is known from the early Blancan White len do not occur elsewhere prior to the late Bluffs LF and the medial Blancan Hagerman Blancan (S. blancoensis and E. calobatus), Fauna. A magnetostratigraphic section from whereas two other species (G. paenebursar- Palomas Creek suggests the fossils came ius and S. miri®cus) are known from medial from strata referred to the upper Gauss Chron Blancan faunas. The similarity in stratigraph- (Mack et al., 1993), indicating a medial ic occurrence to the nearby Pajarito LF and Blancan age (between 3.0 and 2.7 Ma) for the absence of South American immigrants the Palomas Creek LF. indicates a medial Blancan age is more likely Further study of the mammalian taxa and (between 3.1 and 2.7 Ma). other geochronologic data should eventually The Arroyo de la Parida LF from the Pal- clarify the age relationships among the four omas Formation in the Socorro basin has ®ve vertebrate faunas from the Palomas Forma- species of mammals that are restricted to the tion in the vicinity of Elephant Butte Lake, Blancan (Morgan et al., 2000), Megalonyx including Truth or Consequences, Elephant leptostomus, Equus cumminsii, E. simplici- Butte Lake, Cuchillo Negro Creek, and Pal- dens, a large Camelops, and Rhynchotherium omas Creek. The stratigraphic sections con- falconeri. Early Blancan can be ruled out by taining these four faunas have not been pre- the presence of E. cumminsii, E. scotti, and cisely correlated to one another to determine Camelops, all of which ®rst appear during their relative positions within the Palomas the medial Blancan. Rhynchotherium became Formation and their stratigraphic position extinct in the late Blancan at about 2.2 Ma. with respect to relevant radioisotopic dates. The absence of South American immigrants We hope to obtain detailed magnetostrati- suggests an age greater than 2.7 Ma. The graphic sections for the individual sites con- mammalian fauna indicates a medial Blancan taining Blancan faunas. age (3.6±2.7 Ma) for the Arroyo de la Parida Five other sites from the Rio Grande Val- LF. No other geochronologic data are cur- ley, Pajarito, Belen, Arroyo de la Parida, rently available for Arroyo de la Parida. Oth- Hatch, and Tonuco Mountain (®g. 12.1), are er faunas from the Palomas Formation far- medial Blancan in age (3.6±2.7 Ma). In ad- ther south in the Engle and Palomas basins dition to mammalian fossils, three have as- are either early or medial Blancan. sociated magnetostratigraphy and/or radio- The Hatch LF from the Camp Rice For- isotopic dates. The Pajarito LF is not diverse, mation in the Hatch-Rincon basin shares but contains Geomys (Neterogeomys) cf. G. Geomys (Nerterogeomys) paenebursarius paenebursarius and Camelops, and is direct- with the Pajarito and Belen faunas. A medial 2003 MORGAN AND LUCAS: BLANCAN AND IRVINGTONIAN MAMMALS 311

Blancan age is further indicated by the lack However, many of these taxa are either un- of South American immigrants and the fau- known from New Mexican Blancan faunas nal and stratigraphic similarity to the Tonuco (e.g., Chasmaporthetes, Trigonicitis, Ursus) Mountain LF (Morgan et al., 1998). A mag- or also occur in early Blancan faunas (e.g., netostratigraphic section in the Camp Rice Neotoma, Platygonus). Furthermore, no me- Formation at nearby Hatch Siphon (Mack et dial Blancan fauna currently known from al., 1993) does not cross the Gilbert/Gauss New Mexico has a rich microvertebrate sam- boundary but samples most of the Gauss ple, although several sites do contain small Chron, including both the Kaena and Mam- mammals, including Geomys (Nerterogeo- moth Subchrons, and is thus between 3.6 and mys) paenebursarius from Pajarito, Belen, 2.6 Ma. The Hatch Siphon section is similar and Hatch, Scalopus (Hesperoscalops) blan- to the Cedar Hill magnetostratigraphic sec- coensis from Belen, and Geomys (Geomys) tion (Mack et al., 1993) that contains the sp. and Sigmodon medius from Palomas Tonuco Mountain LF (Morgan et al., 1998), Creek. A medial Blancan age can be ®rmly further supporting a medial Blancan age for established for the Pajarito, Hatch, and Ton- the Hatch LF (between 3.6 and 2.7 Ma). uco Moutain faunas from associated geo- The Tonuco Mountain LF from the Camp chronologic data. Pumice Ar/Ar dated at 3.12 Rice Formation in the Jornada basin has six Ma (Maldonado et al., 1999) is in direct as- species of mammals that are indicative of the sociation with the Pajarito LF. An Ar/Ar date Blancan: Canis lepophagus, Borophagus sp., of exactly the same age (3.12 Ma) on a pum- Nannippus peninsulatus, Equus simplicidens, ice-clast conglomerate from Hatch Siphon Platygonus cf. P. bicalcaratus, and Hem- (Mack et al., 1998) can be correlated with iauchenia blancoensis. E. simplicidens is ab- the Hatch LF. A magnetostratigraphic section sent from very early Blancan faunas, Ca- from Hatch Siphon (Mack et al., 1998) can melops and E. scotti appear in the medial be correlated with the Gauss Chron (3.58± Blancan, and most Blancan records of Nan- 2.58 Ma). A magnetostratigraphic section nippus predate the Gauss/Matuyama magnet- from Cedar Hill (Mack et al., 1993) can be ic reversal at 2.6 Ma. The absence of South directly correlated with the Tonuco Mountain American mammals suggests the fauna is LF and indicates an age between 3.58 and older than 2.7 Ma. The biostratigraphic data 3.04 Ma. restrict the age of the Tonuco Mountain LF Because the medial Blancan is dif®cult to to medial Blancan. A magnetostratigraphic characterize biostratigraphically, an argu- section in the Camp Rice Formation at Cedar ment could be made that it should be includ- Hill (Mack et al., 1993) can be directly cor- ed in the early Blancan (e.g., Lundelius et related with the Tonuco Mountain LF. The al., 1987; Woodburne and Swisher, 1995). Cedar Hill section is entirely within the Careful study of early Blancan (e.g., White Gauss Chron, and the fossiliferous interval is Bluffs) and medial Blancan (e.g., Hagerman) below the top of the Kaena Subchron (older faunas that have extensive samples of both than 3.0 Ma). Biostratigraphic and magne- large and small mammals, as well as asso- tostratigraphic data constrain the age of the ciated magnetostratigraphy and radioisotopic Tonuco Mountain LF to the early medial dates, should help to clarify the faunal and Blancan (3.6±3.0 Ma). time relationships between these two inter- About 10 sites in New Mexico of medial vals. The best solution might be to recognize Blancan age (3.6±2.7 Ma) are among the Repenning's ®ve Blancan microtine zones least well constrained by biostratigraphy in (Blancan I±V) as subdivisions of the Blancan the state. Many medial Blancan sites are that are de®ned by their faunas of both mi- identi®ed primarily by lack of characteristic crotine rodents and other mammals. For now early or late Blancan taxa, rather than by the we recognize a medial Blancan interval that presence of taxa that are diagnostic of the corresponds with the Gauss Chron (3.58± medial Blancan. Lindsay et al. (1984) listed 2.58 Ma), with the exception that the upper a number of genera whose ®rst appearance boundary is de®ned by the ®rst appearance at about 3.7 Ma de®nes the beginning of of Neotropical immigrant mammals at about what we recognize as the medial Blancan. 2.7 Ma, slightly before the end of the Gauss. 312 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279

Five faunas from New Mexico are late American Faunal Interchange) and 2.2 Ma Blancan in age (2.7±1.8 Ma): Santo Domin- (the Nannippus extinction datum of Lindsay go, Mesilla Basin Faunas A and B, Pearson et al., 1984). Magnetostratigraphic data for Mesa, and Virden. Late Blancan faunas are Mesilla A indicate correlation with the upper recognized by the ®rst appearance of Neo- Gauss Chron (Vanderhill, 1986), restricting tropical immigrant mammals at about 2.7 the age of this fauna to older than 2.58 Ma. Ma. With the exception of Santo Domingo, The Pearson Mesa LF also documents the the remaining four late Blancan faunas from association of Nannippus with a Neotropical New Mexico have one or more taxa of Neo- immigrant, the mylodont ground sloth Glos- tropical immigrants. Repenning (1987) also sotherium chapadmalense. The ®rst appear- noted several ®rst appearances of Eurasian ance of Glossotherium and Glyptotherium,as microtine rodents at about this same time well as several other Neotropical immigrants (Blancan V), including the lemming genera discussed below, identi®es the onset of the Mictomys and Synaptomys. Microtine rodents Great American Interchange at about 2.7 Ma, are unknown from New Mexican late Blan- and de®nes the beginning of the late Blan- can faunas. The ®ve late Blancan faunas can. A magnetostratigraphic section from from New Mexico appear to separate into Pearson Mesa (Tomida, 1987) further re- two groups, three faunas (Santo Domingo, stricts the age of the lower portion of the Mesilla A, and Pearson Mesa) that contain section, including the Pearson Mesa LF, to Nannippus, and are thus older than 2.2 Ma the upper Gauss Chron (3.0±2.6 Ma). Bio- (early late Blancan, 2.7±2.2 Ma), and two stratigraphy and magnetostratigraphy for faunas (Mesilla B and Virden) that lack Nan- Pearson Mesa and Mesilla A seem to tightly nippus, and thus appear to be younger (latest constrain the ages of these faunas between Blancan, 2.2±1.8 Ma). 2.7 Ma (earliest appearance of Neotropical The Santo Domingo LF from the Sierra immigrants) and 2.6 Ma (Gauss/Matuyama Ladrones Formation in the Albuquerque ba- boundary). sin has four species of mammals, none of The exact timing of the onset of the Great which are de®nitively late Blancan. The pres- American Interchange in North America has ence of Nannippus peninsulatus suggests the not been ®rmly established, although it is fauna is older than 2.2 Ma, whereas Equus well documented that the ®rst appearance of calobatus and E. scotti occur in medial Blan- South American immigrants in the south- can through early Irvingtonian faunas. Ac- western United States occurred in the upper cording to Tedford (1981), the strata that pro- Gauss Chron, sometime between the top of duced the Santo Domingo LF are interbed- the Kaena Subchron (3.04 Ma) and the ded with the Santa Ana Mesa basalts, K/Ar Gauss/Matuyama boundary (2.58 Ma). Six dated at 2.67 and 2.41 Ma (Smith and Kuhle, late Blancan sites in the southwestern United 1998), and are overlain by the lower Ban- States record the ®rst appearance of South delier Tuff, Ar/Ar dated at 1.61 Ma (Izett and American mammals in the upper Gauss Obradovich, 1994). The combination of bio- Chron: 111 Ranch (Galusha et al., 1984) and stratigraphy and radioisotopic dates con- Wolf Ranch (Harrison, 1978) in Arizona, strains the age of the Santo Domingo LF be- Pearson Mesa (Tomida, 1987; Morgan and tween 2.7 and 2.2 Ma. Lucas, 2000b) and Mesilla Basin Fauna A Mesilla Basin Fauna A from the Camp (Vanderhill, 1986) in New Mexico, and Cita Rice Formation in southernmost New Mex- Canyon (Lindsay et al., 1976) and Hudspeth ico (Vanderhill, 1986) and the Pearson Mesa (Strain, 1966; Vanderhill, 1986) in Texas. At LF from the Gila Group in southwestern 111 Ranch, the best documented of these six New Mexico (Morgan and Lucas, 2000b) are faunas (Galusha et al., 1984), Neotropical similar in age. The association of Glyptothe- mammals appear in the uppermost Gauss, rium with Nannippus in the Mesilla A fauna and thus the date of 2.7 Ma has often been clearly establishes a late Blancan age, as the cited as the ®rst appearance datum for Neo- only interval during which these two genera tropical immigrants in North America (e.g., coexisted in southwestern faunas was be- Woodburne and Swisher, 1995), as well as tween 2.7 Ma (the beginning of the Great the boundary between the early and late 2003 MORGAN AND LUCAS: BLANCAN AND IRVINGTONIAN MAMMALS 313

Blancan (or medial and late Blancan as used from Blancan/Irvingtonian transitional fau- here). The ®rst appearance datum for two nas, including Curtis Ranch and San Simon genera of Neotropical xenarthrans (Glypto- Power Line in southern Arizona (Tomida, therium and Glossotherium) and two genera 1987). Three other species from Mesilla B, of Neotropical caviomorph rodents (Neocho- Glyptotherium arizonae, Smilodon gracilis, erus and Erethizon) is within the upper and Tapirus haysii, are more typical of early Gauss Chron, including: Glossotherium at Irvingtonian faunas, but are also known from Pearson Mesa and Cita Canyon; Glyptothe- the late Blancan. The type locality of G. ar- rium at Cita Canyon, Hudspeth, Mesilla A, izonae, Curtis Ranch in Arizona, although and 111 Ranch; the capybara Neochoerus at considered early Irvingtonian by most work- 111 Ranch; and the porcupine Erethizon at ers (e.g., Lundelius et al., 1987; Repenning, Wolf Ranch. Several other sites document 1987), has more recently been placed in the the occurrence of Neotropical immigrants in latest Blancan (Lindsay et al., 1990). There the early Matuyama Chron (2.6±2.2 Ma), in- are also ®ve late Blancan records of this cluding the Blanco LF in Texas (Dalquest, glyptodont from Florida (Morgan and Hul- 1975; Lindsay et al., 1976, 1984) and the bert, 1995). Likewise, most records of S. Anza-Borrego Desert in California (Opdyke gracilis are from the early Irvingtonian, but et al., 1977; Cassiliano, 1999). Two addition- this small sabercat is also known from sev- al genera of Neotropical xenarthrans, the ar- eral Florida late Blancan faunas (Berta, madillo Dasypus and the pamapthere Hol- 1987). T. haysii occurs in late Blancan faunas mesina, as well as Glossotherium and Neo- in Texas and Colorado (Strain, 1966; Hager, choerus, occur in the early Matuyama Chron 1974; Hulbert, 1995). Mammuthus is absent in the Macasphalt Shell Pit LF in southern from Mesilla B, but appears higher in the Florida (Morgan and Ridgway, 1987; Jones same stratigraphic sequence in Mesilla C. et al., 1991; Morgan and Hulbert, 1995). No Magnetostratigraphic data for Mesilla B early or medial Blancan (4.5±2.7 Ma) sites (Vanderhill, 1986) place this fauna in the north of Mexico are known to contain Neo- time interval between the Gauss/Matuyama tropical mammals involved in the Great boundary and the Olduvai Subchron (2.6±1.8 American Interchange. However, several fau- Ma). Biostratigraphic evidence indicates that nas from central Mexico suggest that the ini- Mesilla B belongs in the younger half of this tial migration of South American mammals interval (2.2±1.8 Ma). across the Panamanian Isthmus may have oc- The Virden LF from the Duncan basin in curred as early as 4.7 Ma (Miller and Car- the Gila River Valley has Glyptotherium ar- ranza-CastanÄeda, 2001, 2002). We use 2.7 izonae but lacks Nannippus, indicating that Ma for the beginning of the Interchange in this fauna is younger than the Pearson Mesa the southwestern United States, with the un- LF, derived from Gila Group strata about 45 derstanding that detailed stratigraphic and m lower in the same section. Although glyp- geochronologic studies of sites in central todonts ®rst appear in southwestern faunas in Mexico may eventually push back the rec- the early late Blancan (about 2.7 Ma), these ognized age of onset of Interchange in trop- early occurrences represent the smaller spe- ical North America. cies G. texanum. As discussed above, G. ar- Mesilla B and the Virden LF occur higher izonae is now known from both latest Blan- in the same stratigraphic sequences as the can and early Irvingtonian faunas in the Mesilla A and Pearson Mesa faunas, respec- southwest, as well as late Blancan and early tively. The Mesilla B mammalian fauna con- Irvingtonian faunas in Florida (Morgan and tains three taxa restricted to the Blancan, the Hulbert, 1995). Canis lepophagus from Vir- large camelids Blancocamelus, Gigantoca- den is restricted to the Blancan, and occurs melus, and an undescribed Camelops. Other in the late Blancan Cita Canyon and Red typical Blancan genera such as Nannippus Light faunas in Texas (Akersten, 1972) and are absent from Mesilla B, suggesting the the late Blancan 111 Ranch in Arizona (Gal- fauna is younger than 2.2 Ma. The rabbit Al- usha et al., 1984; Tomida, 1987). The pres- uralagus virginiae, identi®ed from Mesilla B ence of C. lepophagus strongly indicates a (Vanderhill, 1986), is known elsewhere only Blancan age for the Virden LF, while the 314 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279 presence of G. arizonae further suggests that ¯uvially transported pumice beds at about the fauna is very late Blancan. 1.6 Ma was essentially synchronous with the Mesilla B and Virden appear to be similar formation of the lower Bandelier tuff in the in age based on the occurrence of the large Jemez volcanic ®eld in northern New Mex- Glyptotherium arizonae and the absence of ico. Nannippus and Mammuthus. Taxa restricted The Tortugas Mountain LF from the north- to the Blancan are known from each fauna, ern Mesilla basin (Lucas et al., 1999, 2000) including Blancocamelus and Gigantocame- contains three proboscideans, Cuvieronius lus from Mesilla B and Canis lepophagus tropicus, Stegomastodon miri®cus, and Mam- from Virden. Nannippus does occur in lower muthus imperator. Mammuthus arrived from stratigraphic units in both the Mesilla Basin Eurasia in the early Pleistocene about 1.6 and Pearson Mesa sections, suggesting that Ma. The youngest well-dated record of Ste- the Mesilla B and Virden faunas are younger gomastodon is from Tule Canyon in the Tex- than the Nannippus extinction datum at 2.2 as Panhandle, where it is associated with Ma. Mammuthus is absent from Mesilla B, Mammuthus in a volcanic ash at the base of but occurs higher in the same stratigraphic the Tule Formation dated between 1.3 and sequence in the Mesilla C fauna. Biostratig- 1.2 Ma (Izett, 1977; Tedford, 1981; Madden, raphy, magnetostratigraphy, and radioisoto- 1983). Thus, the co-occurrence of Stegomas- pic dates constrain the age of Mesilla B to todon and Mammuthus de®nes a restricted the latest Blancan (2.2±1.8 Ma). Biostrati- interval of time in the early Irvingtonian, be- graphic correlation indicates that the Virden tween about 1.6 and 1.2 Ma, after the arrival LF belongs in this age range as well. of Mammuthus and before the extinction of Three early Irvingtonian faunas from New Stegomastodon. The Tortugas Mountain LF Mexico contain more than ®ve species of is similar in age to the Gilliland LF in Texas, mammals: Tijeras Arroyo, Tortugas Moun- which is the only other fauna that documents tain, and Mesilla Basin Fauna C (®gs. 12.2± the association of Cuvieronius, Stegomasto- 12.4; table 12.2). Mammuthus, whose ®rst don, and Mammuthus (Hibbard and Da- appearance de®nes the beginning of the Ir- lquest, 1966). vingtonian (Lundelius et al., 1987), is known Among New Mexico's early Irvingtonian from all three of theses faunas. The co-oc- faunas, Mesilla C in the southern Mesilla ba- currence in the Tijeras Arroyo fauna of Glyp- sin has the most diverse sample of large totherium arizonae, Equus scotti, and Mam- mammals (Vanderhill, 1986). Three species muthus is typical of southwestern early Ir- from Mesilla C clearly establish an Irving- vingtonian faunas (1.6±1.0 Ma), including tonian age, Mammuthus cf. M. meridionalis, Gilliland in Texas (Hibbard and Dalquest, the wol¯ike Canis armbrusteri, and the bea- 1966) and Holloman in Oklahoma (Dalquest, ver Castor canadensis. The primitive mam- 1977). Mandibles of Mammuthus meridion- moth M. meridionalis occurs only in early alis from Tijeras Arroyo represent one of the Irvingtonian faunas, C. armbrusteri ®rst ap- most primitive mammoths known from pears in the early Irvingtonian and becomes North America (Lucas and Ef®nger, 1991; extinct in the late Irvingtonian (Berta, 1995), Lucas et al., 1993). This specimen is also one and the extant C. canadensis is limited to of the oldest well-documented records of Irvingtonian and younger faunas. The Mesi- Mammuthus from North America (Lucas, lla C fauna is very similar to early Irving- 1995, 1996), based on its association with tonian faunas from the southern Great Plains, pumice derived from the lower Bandelier tuff including Gilliland and Rock Creek in Texas (Lucas et al., 1993). The lower Bandelier tuff (Hibbard and Dalquest, 1966) and Holloman has an Ar/Ar date of 1.61 Ma (Izett and Ob- in Oklahoma (Dalquest, 1977), that docu- radovich, 1994). Although this date provides ment the association of Glyptotherium ari- a maximum age for the Tijeras Arroyo mam- zonae, Paramylodon harlani, Equus scotti, moth, similar ages on pumice deposits farther E. calobatus, and Mammuthus. The magne- south in the Rio Grande Valley, including the tostratigraphy of Mesilla C (Vanderhill, southern Mesilla basin (Mack et al., 1996, 1986) suggests correlation with the interval 1998), suggest that deposition of widespread in the Matuyama Chron from just after the 2003 MORGAN AND LUCAS: BLANCAN AND IRVINGTONIAN MAMMALS 315

Olduvai Subchron (1.81 Ma) until just prior the ®rst appearance of Mammuthus and the to the Jaramillo Subchron (1.07 Ma). Ar/Ar placement of the Blancan/Irvingtonian dates of 1.59 Ma and 1.32 Ma on pumice boundary. Mammuthus occurs in a fairly beds from the Camp Rice Formation near La complete stratigraphic sequence that spans Union agree, suggesting an age between 1.6 the late Blancan and early Irvingtonian. The and 1.1 Ma for Mesilla C (Vanderhill, 1986; stratigraphic sequence of the Camp Rice For- Mack et al., 1996). mation in the vicinity of La Union and We recognize the beginning of the Irving- Chamberino in the southern Mesilla Basin tonian based on the ®rst appearance of Mam- contains two diverse superposed mammalian muthus in the early Pleistocene between 1.8 faunas, the latest Blancan Mesilla B and ear- and 1.6 Ma. Cassiliano (1999) could not pre- ly Irvingtonian Mesilla C, as well as the late cisely determine the position of the Blancan/ Blancan Mesilla A at the base of the section Irvingtonian boundary, suggesting an age that documents the association of Nannippus range between 2.15 Ma and 1.95 Ma (latest and Glyptotherium. Further study of this im- Pliocene). He analyzed the utility of several portant sequence is ongoing, and will include genera to de®ne the Blancan/Irvingtonian detailed correlation of magnetostratigraphy boundary (e.g., Mammuthus, Smilodon, Le- (Vanderhill, 1986), radioisotopic dates (Mack pus), and found none of these genera to be et al., 1996), lithostratigraphy, and biostratig- appropriate. One of the most dif®cult prob- raphy. lems encountered by Cassiliano (1999) was The youngest Irvingtonian fauna in New that Mammuthus, the most frequently cited Mexico is San Antonio Mountain (SAM) genus for de®ning the beginning of the Ir- Cave from the San Luis basin near the Col- vingtonian, is absent from the two most com- orado border. Magnetostratigraphy and mi- plete stratigraphic sequences in North Amer- crotine rodent biochronology constrain the ica that span the Blancan/Irvingtonian age of the SAM Cave fauna to the medial boundary, the San Pedro Valley in Arizona Irvingtonian; however, SAM Cave contains (Johnson et al., 1975; Lindsay et al., 1990) nine individual sites with a range of ages be- and the Anza-Borrego Desert (also known as tween about 1.0 and 0.7 Ma (Rogers et al., the Fish Creek-Vallecito Creek section) in 2000). The four oldest sites in SAM Cave southern California (Opdyke et al., 1977; contain the microtines Mictomys kansasensis, Cassiliano, 1999). an advanced species of Allophaiomys, Lem- Two stratigraphic sequences from New miscus curtatus, and Microtus cf. M. califor- Mexico, Tijeras Arroyo and the southern nicus, indicating ages between about 1.0 and Mesilla Basin, contain early Irvingtonian 0.85 Ma, in the early part of the medial Ir- faunas with Mammuthus superposed above vingtonian. A slightly younger medial Ir- Blancan faunas. Mammuthus fossils from Ti- vingtonian site in SAM Cave contains Cleth- jeras Arroyo and Mesilla C, referred to M. rionomys, and is between 0.85 and 0.78 Ma meridionalis, are among the oldest dated in age. The occurrences of Lemmiscus and mammoths in North America, as both are Clethrionomys in SAM Cave represent the closely associated with radioisotopic dates of oldest records of these two genera in North 1.6 Ma on pumice from the lower Bandelier America. tuff. Mammoths from Wellsch Valley, Sas- katchewan (Barendregt et al., 1991) and ACKNOWLEDGMENTS Thornton Beach, California (Madden, 1980, 1995) were thought to be older than 1.5 Ma, We are particularly grateful to Richard but both sites are now known to be consid- Tedford for his help and encouragement dur- erably younger (Barendregt et al., 1991; Lu- ing our project to collect and describe New cas, 1995, 1996; Cassiliano, 1999). All other Mexico's Blancan and Irvingtonian faunas. early Irvingtonian records of Mammuthus are Our original motivation for this undertaking younger than 1.5 Ma. came from Dr. Tedford's 1981 paper on the The southern Mesilla Basin may possess mammalian biochronology of the late Ce- one of the most important stratigraphic se- nozoic basins of New Mexico. Before his pa- quences in North America for determining per, the Pliocene and early Pleistocene ver- 316 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279 tebrate record of New Mexico had been vir- Berta, A. 1987. The sabercat Smilodon gracilis tually ignored. We thank Greg McDonald for from Florida and a discussion of its relation- reviewing several of our previous papers and ships (Mammalia, Felidae, Smilodontini). Bul- letin of the Florida State Museum, Biological for sharing with us his comprehensive Science 31(1): 1±63. knowledge of North American Blancan fau- Berta, A. 1995. Fossil carnivores from the Leisey nas. Greg McDonald, Nicholas Czaplewski, Shell Pits, Hillsborough County, Florida. In and Lawrence Flynn provided helpful com- R.C. Hulbert, Jr., G.S. Morgan, and S.D. Webb ments on this paper. Numerous people have (editors), Paleontology and geology of the Leis- assisted us in the ®eld collecting Blancan and ey Shell Pits, early Pleistocene of Florida. Bul- Irvingtonian fossils in New Mexico, espe- letin of the Florida Museum of Natural History cially Paul Sealey, Warren Slade, and Jerry 37, Pt. II: 463±499. Cassiliano, M.L. 1999. Biostratigraphy of Blancan MacDonald, and also including the late John and Irvingtonian mammals in the Fish Creek± Estep, Ed Frye, Jerald Harris, Paul Knight, Vallecito Creek section, southern California, Peter Kondrashov, Thomas Logan, Wayne and a review of the Blancan-Irvingtonian Oakes, Mike O'Keefe, Mike O'Neill, Pete boundary. Journal of Vertebrate Paleontology Reser, Jay Sobus, Christopher Whittle, Bren- 19: 169±186. da Wilkinson, and Bill Wood. Collectors for Connell, S.D., D.J. Koning, and S.M. Cather. the Frick Laboratory who worked on Blan- 1999. Revisions to the stratigraphic nomencla- ture of the Santa Fe Group, northwestern Al- can and Irvingtonian sites in New Mexico buquerque Basin, New Mexico. New Mexico include Charles Falkenbach, Ted Galusha, Geological Society Guidebook 50: 337±353. 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