PaleoBios, Volume IS, Number 4, Pages 63-77, May 24, 1993 Preliminary Report on a Late Pleistocene Vertebrate Assemblage From Bonita, San Diego County, California C. Paul Majors San Diego Natural History Museum, Department of Paleontology, P.O. Box 1390, San Diego, CA 92112 ABSTRACT Although the late Pleistocene marine invertebrate record from coastal San Diego County, California is extensive, the terrestrial vertebrate record from this time iis poorly known. By far, the richest known late Pleistocene terrestrial vertebrate site in the coastal portion of the county is San Diego Society of Natural History locality (SDSNH) 3131 (the Glen Abbey site), in the community of Bonita. This locality occurs in an outcrop of stream terrace deposits in the Sweetwater Valley that were referred by previous authors to the Chula Vista terrace. SDSNH 3131 is here assigned a Rancholabrean age based on the presence of Ectopistes migratorius, Notiosorex crawfordi, Peromyscus maniculatus, and Equus. Other species identified are Callipepla californica, Scapanus latimanus, Reithrodontomys megalotis, and Microtus californicus. The Glen Abbey local fauna is here defined as the Rancholabrean vertebrates of SDSNH locality 3131. INTRODUCTION The late Pliocene to early Pleistocene vertebrate record from eastern San Diego County is extensive but only partially studied (Downs and White, 1968; Kurten and Anderson, 1980). The record of late Pleistocene nearshore marine invertebrates from coastal San Diego County is extensive and well documented, with over 275 species reported (as summarized by Kern, 1977). Until 1980, the only late Pleistocene terrestrial vertebrate localities known in the coastal area have produced limited material of mammals (Hay, 1927; Stock, 1944; Carter, 1957; Jefferson, 1991), save one (Los Angeles County Museum of Natural History locality 3817) that yielded five taxa of small mammals (Leporidae, Thomomys sp., Perognathus sp., Peromyscus sp., and Neotoma; see Jefferson, 1991). This locality and its invertebrate fauna was described by Kern, et al. (1971), who referred to the site as San Diego State College locality 2276. In 1991, Jefferson listed records of Pleistocene terrestrial vertebrates from several sites in San Diego County, including a reference to fossils from San Diego Society of Natural History (SDSNH) locality 3131 - the Glen Abbey Site. The list published by Jefferson was supplied by the author (Majors, 1985). Earlier, Chandler (1982) discussed a fossil passenger pigeon (Ectopistes migratorius), and Hutchison (1987) described mole (Scapanus latimanus) material from the locality. The assemblage reported upon here includes 20 taxa (see Table 1), 14 of which are new to the late Pleistocene of coastal San Diego County. This site was originally discovered in June of 1980 by Richard Cerutti of the San Diego Natural History Museum. The material from SDSNH 3131 is now stored at the San Diego Natural History Museum. This paper is a preliminary report on the fossils from SDSNH 3131, which are under continued study by the author in order to more fully document the faunal diversity of this site and to establish age constraints on deposition of Pleistocene stream terraces within the Sweetwater Valley. This paper presents previously unpublished geologic and faunal data from the Glen Abbey site. LOCALITY DESCRIPTION The locality is exposed in the lower portion of a roadcut along the south side of Bonita Road near the Glen Abbey Mortuary (32°39'20"N; 117°2'33"W; see Figure 1). The base of the roadcut is 21 meters above sea level, the exposed section is about 11 meters thick, and its base is not exposed. Only fluvial deposits are evident at the Glen Abbey outcrop. From 1980 to 1985 several stratigraphic horizons at the site were sampled and screen- washed for micro-vertebrates. The site is richly fossiliferous, with over 490 kilograms (1,000 pounds) of the richest matrix from these samples producing more than 600 specimens of fossil vertebrates. The preservation of these remains is excellent, with individual elements well mineralized and unabraded. Fossil remains are in New Additions to the Pleistocene Vertebrate Record of California (R. G. Dundas and D. J. Lang, eds.), PaleoBios v.15. Page 64 Glen Abbey Local Fauna Majors Table 1. List of taxa present at SDSNH 3131 Amphibia Anura Reptilia fam. Testudinidae Phrynosoma sp. Eumeces sp. cf. Elgaria sp. fam. Anguidae fam. Lacertilia fam. Colubridae Aves Melanitta sp. fam. Accipitridae Callipepla californica Callipepla sp. Ectopistes migratorius Mammalia Scapanus latimanus Scapanus sp. Sorex cf. S. ornatus Notiosorex crawfordi Notiosorex sp. cf. Tadarida sp. cf. Lasiurus sp. fam. Leporidae Sylvilagus sp. Lepus californicus Spermophilus sp. Thomomys cf. T. bottae fam. Heteromyidae Peromyscus maniculatus Peromyscus sp. Reithrodontomys megalotis Neototna sp. Microtus californicus Microtus sp. Equus sp. found in isolated concentrations at the base of the exposure which can be very rich. Because of this patchy distribution, the locality has been sub- divided into five sublocalities (SDSNH 3131-a through 3131-e). Sublocalities 3131-a and 3131-b have produced the majority of fossil material 116 52'3tf 32°S2'30" I I I I I I I I I KILOMETERS Figure 1. Locality map of SDSNH 3131. recovered to date. These two sublocalities have been screenwashed using 3.2 millimeter (1/8 inch), and 20 and 30 mesh screens (openings of approximately 1.0 mm and 0.6 mm, respectively). The resulting concentrates were sorted by eye and under a microscope. GEOLOGY The most striking geomorphic feature of coastal San Diego County is the occurrence of 14 elevated Pleistocene marine terraces (.Dupre, et al., 1991), ranging from 6 to 160 meters (Kern, 1977) above sea level. These abrasion platforms were cut by marine highstands as mean sea level fluctuated during episodes of Pleistocene global glacial retreat and advance (Kern, 1977), with tectonic uplift leaving them emergent (Dupre, et al., 1991). Following the cutting of these marine terraces each was covered by a thin veneer of either nearshore marine sediments and/or fluvial sediments (after emergence). The lower of these terraces have been dated at 81,000 (Bird Rock terrace), 102,000, 118,000 (Nestor terrace), and 124,000 years old (Dupre, et al., 1991). Once emergent, the marine terraces with their sedimentary covers were dissected by streams, forming many of the coastal valleys seen in the region today (as described by Lawson, 1893; Majors Glen Abbey Local Fauna Page 65 Ellis, 1919; Hanna, 1926; Grant and Gale, 1931). Continued fluctuation of base-levels during these cycles of submergence and emergence have left many of the coastal valleys with a complex sequence of marine, estuarine and fluvial deposits (Ellis, 1919; Carter, 1957; Demere, 1981). It is fluvial deposits such as these that are now preserved as fill terraces on both sides of the present Sweetwater Valley. This is a common pattern of Pleistocene deposition elsewhere in coastal California (see Lawson, 1893; Grant and Gale, 1931; Birkeland, 1972; Dupre, et al., 1991). Eisenberg (1983) discussed the history of Pleistocene fluvial and marine terraces preserved in northern coastal San Diego County. He made tentative correlations between fluvial strath terraces and the Bird Rock, the Nestor, and older marine terraces, as well as intermediate stillstands. Ellis (1919) recognized late Pleistocene terraces in Sweetwater Valley, which he mapped as the marine and estuarine Chula Vista terrace. Carter (1957) discussed the late Pleistocene terraces of Southwestern San Diego County extensively. He found a complex sequence of terraces in the lower Sweetwater Valley, including both marine and fluvial terraces. Among the fluvial terraces, Carter notes the presence of two stacked terraces. The older of these two terraces was characterized as having heavily weathered granodiorite clasts, while the younger fluvial terrace had slightly weathered granodiorite clasts. The deposit exposed at the Glen Abbey site contains slightly weathered granodiorite clasts, thus this deposit may be correlative with Carter's (1957) younger fluvial terrace. The strata exposed at SDSNH 3131 were mapped by Kennedy and Tan (1977) as an unnamed Quaternary stream terrace deposit. As mapped, by Kennedy and Tan (1977), these deposits occur discontinuously throughout the eastern half of Sweetwater Valley, and overlie Pliocene, Oligocene, Eocene, and Jurassic rocks (San Diego Formation, Otay Formation, Sweetwater Formation, Mission Valley Formation, and Santiago Peak Volcanics respectively). Similar Quaternary stream terrace deposits occur in many coastal valleys throughout San Diego County (Ellis, 1919; Carter, 1957; Kennedy and Peterson, 1975; Kennedy and Tan, 1977; Eisenberg, 1983). It is not known whether the stream terrace deposits are offset by the north-south trending La Nacion Fault Zone, which has offset the Early Pleistocene Linda Vista Terrace by as much as 120 meters both to the north and south of the Sweetwater Valley (Artim and Pinckney, 1973), but has not offset the pre-Holocene alluvium of Poggi Canyon to the south (Hart, 1974). Kennedy, et al., (1975) mapped a strand of the La Nacion Fault Zone as offsetting an unnamed Pleistocene deposit at the mouth of the Sweetwater Valley, but did not describe the deposits cut by the fault The relationship of the Sweetwater Valley stream terrace deposits to the adjacent Pleistocene Nestor marine terrace deposits (Kern, 1977) is unknown at present For purposes of the present study, the Quaternary section as exposed at the Glen Abbey Mortuary has been divided into nine broadly defined fades, based on grain size and sedimentary structures (Figure 2). No fades has produced evidence of caliche accumulation, bioturbation, or root structures. These fades are characterized as follows: Fades 1: Compact clayey siltstone with occasional centimeter scale sandy stringers, which appear to be horizontal, color: 5 YR 6/2. No other structures observed. Unfossiliferous. Fades 2: Compact sandy siltstone with granules and pebbles. No observed structure. Fossiliferous (SDSNH 3131-b). Fades 3: Friable laminated medium-grained sandstone with cross-bedded lenses, color: 5 Y 7/2. Fades 4: Compact sandy clay, color: 5 Y 6/2. Clay may be secondary. No observable structure, unfossiliferous. Undulate contact when above fades 3, gradational when above facies 2. Possibly fossiliferous (SDSNH 3131-a?). Facies 5: Friable cross-bedded coarse and fine-grained sand with gravel lag at erosive base, color: 5 Y 8/2. Cross-beds are at least one meter tall, with avalanche faces approaching twenty degrees. Unfossiliferous. Facies 6: Friable cobble/pebble very coarse- grained sandstone with no observed structure. Clasts are angular to well rounded and locally derived. Sparsely fossiliferous (Equus sp. only). Facies 7a: Friable Sctndy, gravelly cobble conglomerate with no observed structure. Clasts are angular to well rounded and locally derived. Unfossiliferous. Facies 7b: Friable sandy, gravelly cobble conglomerate with coarse-tail grading (see Collinson and Thompson, 1984), color: 10 R 3/4. Clasts are angular to well rounded and locally derived. Unfossiliferous. Page 66 Glen Abbey Local Fauna Majors STRATIGRAPHIC COLUMN (METERS, BOTTOM NOT EXPOSED) wmMmmm W* MUD SAND COBBLE GRAIN SIZE FACIES 7b 7a 7c INTERPRETATION CHANNEL FILL (LATERAL ACCRETION) FLOODPLAIN (VERTICAL ACCRETION) CHANNEL FILL (?) FLOODPLAIN (VERTICAL ACCRETION) 3131-e CHANNEL FILL (LATERAL ACCRETION) SAND WAVE (?) PALEOSOL (?) FACIES 2: CHUTE CUT-OFF (?) FACIES 3: LEVEE OR UPPER CHANNEL 3131-a (?) 3131-b 3131-c, 3131-d Figure 2. Generalized stratigraphic column from SDSNH 3131. Fades 7c: Friable sandy, gravelly conglomerate with coarse-tail grading (see Collinson and Thompson, 1984) and bedding. Clasts are angular to well rounded and locally derived. Unfossiliferous. These facies are stacked in a fining/thickening upward sequence (see Figure 2) congruent with the general depositional model for meandering stream deposits proposed by Walker and Cant (1984) (see also Allen, 1970). Facies one represents floodplain deposition (vertical accretion), facies 2 may represent a chute cut-off, and facies 3 through 9 represent various channel fill and point-bar sub- environments (lateral accretion). All sub-localities are within the lowermost 3 meters of the exposed section. 3131-a is now covered, but is most likely within fades 4 (based on exposure of fades 4 deposits in dose proximity to the fossil bearing area, as well as similarity of fossil-bearing matrix to facies 4). 3131-b occurs within facies 2 at street level. Sublocalities 3131-c through 3131-e have only produced fragmentary horse (Equus sp.) material. These sublocalities occur within fades 3 and 6. SYSTEMATIC PALEONTOLOGY To date, SDSNH locality 3131 has yielded no fossil invertebrates. In contrast, representatives of all vertebrate classes, exclusive of fish, have been recovered. This report focuses on identification of the abundant mammal material, comprising over 94% of the total sample. This assemblage is here named the Glen Majors Glen Abbey Local Fauna Page 67 Abbey local fauna. The term local fauna is used as defined by Woodburne (1987, p. xiv): "assemblage of fossil vertebrates of specific taxonomic composition recovered from one or a few sites that are closely spaced stratigraphically and geographically". This definition agrees closely with that of Tedford (1969). The Glen Abbey local fauna is defined as the Rancholabrean vertebrates of SDSNH 3131, and includes the taxa discussed below. The name of the Glen Abbey local fauna is taken from the name of the nearby mortuary. The following list includes remarks on the morphology of selected taxa. Mammalian comparative material used in this study is listed in Appendix 1. Class Amphibia Linnaeus, 1758 Order Anura Rafinesque, 1815 Gen. and sp indet. Referred specimens: SDSNH 44251: mandible fragment; 44252, ilium. Class Reptilia Laurenti, 1768 Order Testudines Batsch, 1788 Family Testudinidae Gray, 1825 Gen. and sp. indet Referred specimens: SDSNH 25147, carapace plates. Order Squamata Oppel, 1811 Suborder Lacertilia Owen, 1842 Family Phrynosomatidae Fitzinger, 1843 Phrynosoma sp. Wiegmann, 1828 Referred specimens: SDSNH 44253, partial parietals. Family Scincidae Gray, 1825 Eumeces sp. Wiegmann, 1834 Referred specimens: SDSNH 44254, R. dentary. cf. Scincidae Gray, 1825 Gen. and sp. indet Referred specimens: SDSNH 44255, maxilla. Family Anguidae Cope, 1864 cf. Elgaria sp. Gray, 1838 Referred specimens: SDSNH 44256, 44257, R. dentaries (2); 44258, L. dentary; 44259, caudal vertebra; 44260, partial caudal vertebra. Discussion: Alligator lizards today live in habitats with abundant organic debris (Shaw, 1950). cf. Anguidae Cope, 1864 Gen. and sp. indet. Referred specimens: SDSNH 44261-44264, vertebrae (4). Suborder Lacertilia Owen, 1842 Gen. and sp. indet. Referred specimens: SDSNH 44265, maxilla; 44266, 44267, left dentaries (2); 44268-44270, vertebrae (3). Suborder Serpentes Linnaeus, 1758 Family Colubridae Oppel, 1811 Gen. and sp. indet. Referred specimens: SDSNH 44271-44274, vertebrae (4). Class Aves Linnaeus, 1758 Order Anseriformes (Wagler, 1831) Family Anatidae Delacour and Mayr, 1946 Melanitta sp. Boie, 1822 Referred specimens: SDSNH 44277, R. radius proximal end. Discussion: Slightly larger than the extant M. parspicillata (R. M. Chandler, pers. comm.). Order Falconiformtes Sharpe, 1874 Family Accipitridae Oderholser, 1919 Gen. and sp. indet. Referred specimens: SDSNH 44278, L. tibiotarsus distal end. Order Galliformes Temminck, 1820 Family Phasianidae Baird, 1858 Callipepla californica (Shaw), 1798 Referred specimens: SDSNH 44279, L. humerus proximal end; 44280,44281, R. scapulae (2). Discussion: This material has been compared to Callipepla californica, Colinus virginianus Page 68 Glen Abbey Local Fauna Majors ridgwayi, Geococcyx calif ornianus, Oreortyx pictus, Rallus limicola, and R. longirostrus. The scapulae compare most closely with Callipepla californica in the morphology of the glenoid facet, acromion process, and furcular articulation. The humerus is nearly identical to C. californica in both size and features of the proximal end. Chandler (R. M., pers. comm.) identified this material in 1985. Callipepla sp. Bonaparte, 1838 Referred specimens: SDSNH 44282, 44283, L. tarsometatarsi (2); 44284, L. carpometacarpus; 44285, R. carpometacarpus. Order Columbiformes Latham, 1790 Family Columbidae Lilijeborg, 1866 Ectopistes migratorius (Linnaeus, 1766) Referred specimens: SDSNH 23085, L. tarsometatarsus. Discussion: Chandler (1982) compared this specimen to Ectopistes migratorius, Columba fasciata, C. leucocephala, Zanaida macroura, and Z. asiatica. It was found that the fossil specimen was similar only to Ectopistes in the five diagnostic characters of the metatarsus discussed by Howard (1937, length, position of tubercle for tibialis anticus muscle, development of proximal ligamentary attachment, position of facet for metatarsal-I, anteroposterior development of external condyle), in addition to three other observed characters (Chandler, 1982, condition of hypotarsus, position of trochlea for digit two relative to digit three, prominence of tubercle for tibialis anticus muscle). This is the third record of the historically abundant but now extinct passenger pigeon from the late Pleistocene of the southwest (Chandler, 1982). Historically, this species did not live further southwest than the northern Mississippi River Valley (Greenway, 1958). Class Mammalia Linnaeus, 1758 Order Insectivora Bowdich, 1821 Family Talpidae Gray, 1821 Scapanus latimanus subsp. cf. S. I. anthonyi Allen Referred specimens: SDSNH 26231, partial rostrum with LI1"3, RI1"3, RC, RP2; 26232, RM^ 26233, LM ; 26234, R. humerus; 26235, partial L. humerus; 26236, L. ulnae (3); 26237, L. femur; 26238, R. clavicle; 44286-44287, LM3 (2). Discussion: Much of this material has been discussed by Hutchison (1987), who assigned it to Scapanus latimanus based on characters of the rostrum and teeth. An assignment of S. latimanus anthonyi rather than S. latimanus occultus is supported by the pattern of tooth reduction in the rostrum. SDSNH 26231 is lacking alveoli for both left and right P , and the left K. Scapanus latimanus anthonyi and S. latimanus occultus may lose one or both P , but the loss of r has been reported for only S. latimanus anthonyi (Hutchison, 1987). The Ms agree closely with S. latimanus anthonyi in size and degree of enamel excursion down the roots. However, these teeth resemble Scapanus malatinus in the presence of a narrow and incomplete precingulid and distinct parastylid (Hutchison, 1987). This is the reason for the tentative referral to Scapanus latimanus anthonyi. Scapanus sp. Pomel, 1848 Referred specimens: SDSNH 44288, L. radius; 44289, L. scapula (partial); 44290, R. clavicle; 44291, R. clavicle (partial); 44292-44293, L. tibia/fibula (2); 44294-44299, ungual phalanges. Discussion: This material was not seen by Hutchison. Family Soricidae Gray, 1821 Sorex cf. S. ornatus Merriam, 1895 Referred specimens: SDSNH 44300, partial L. dentary with partial M , complete M , and partial M . Discussion: SDSNH 44300 possesses several features characteristic of Sorex including features of the mandibular condyles, internal temporal fossa, and position of the mental foramen (Repenning, 1967). The articular facets of the mandibular condyle are continuous along the labial edge of the condyle, and the interarticular area between the facets is only very slightly narrowed. The internal temporal fossa of this specimen is quite large and deep. Finally, the mental foramen appears to lie below the middle Majors Glen Abbey Local Fauna Page 69 of M . All of the above features support an assignment to the genus Sorex (Repenning, 1967; Junge and Hoffmann, 1981). SDSNH 44300 also lacks a post-mandibular foramen which may indicate that the specimen belongs to Sorex ornatus rather than S. trowbridgii (Junge and Hoffmann, 1981). Notiosorex crawfordi (Coues, 1877) Referred specimens: SDSNH 44301, partial R. dentary with M ; 44302, partial L. dentary with M ; 44303, partial R. dentary with I, M . Discussion: Both SDSNH 44301 and 44302 exhibit many mandibular and dental characters which support an assignment to Notiosorex crawfordi. The mandibular condyles are distinct and separated by a narrow bar, the lower condyle is significantly anterior to the upper condyle. The articular facets are separate, the upper facet is triangular and located labial to the lower facet with a groove labial to lower facet. The superior pterygoid fossa is well excavated, and the internal temporal fossa is moderately sized and deep. A pterygoid spicule present. The coronoid process is slender and inclined forward slightly with a moderately low coronoid spicule. The mental foramen is slightly posterior to the midline of Mj (preserved on SDSNH 44301). A labial cingulum is well developed on M and M . The metaconid and the paraconid are close together on M and M . The heel of M is reduced, the entoconid is lost, the metalophid and hypoconid form a curved crest, and the "V" of the hypoconid is not developed. This material is also very close in size to N. crawfordi (N. jacksoni is larger, Repenning, 1967). Taken together, these features indicate that this specimen belongs to Notiosorex crawfordi (Repenning, 1967). Many of the above features are not evident on SDSNH 44303 because of the incompleteness of the specimen (proximal end of dentary missing). Available characters support an assignment to Notiosorex crawfordi. Specifically, the mental foramen lies below the midline of M , the paraconid and entoconid of M are close together, the M has a fairly well developed labial cingulum, and the incisor is simple, without the many crests of Sorex. This specimen is also very close to N. crawfordi in size. Notiosorex sp. cf. N. crawfordi (Coues, 1877) Referred specimens: SDSNH 44304, R. incisor. Discussion: This incisor has a fairly simple cutting edge with two low crests, unlike the specimens of Sorex ornatus and S. trowbridgii examined that have many crests. Notiosorex sp. Baird, 1877 Referred specimens: SDSNH 44305, L. humerus; 44306, R. femur; 44307, L. tibia. Order Chiroptera Blumeribach, 1779 Family Molossidae Gervais, 1855 cf. Tadarida sp. Rafinesque, 1841 Referred specimens: SDEINH 44308, L. maxillary 3 fragment with M ; 44309, R. dentary fragment (edentulous); 44310, R. femur; 44311, L. femur proximal end. Family Vespertilionidae Gray, 1821 cf. Lasiurus sp. Gray, 1865 Referred specimens: SESNH 44312, R. dentary fragment (edentulous); 44313, upper R. canine. Order Lagomorpha Brandt, 1855 Family Leporidae Gray, 1821 Sylvilagus sp. Gray, 1867 Referred specimens: SDSNH 44314, L. maxilla w/P*4 and M1"3; 44315, L. maxilla w/P3"4 and M1" 2; 44316, partial palate (edentulous); 44317, LM ; 44319-44320, LM1 (2); 44322-44323, LM2 (2); 44324- 44325 (2); 44326, RM2; 44327, LP3; 44328, R. femur; 44329, L. femur distal end; 44330, R. humerus distal end; 44331, R. humerus distal end (juvenile); 44332-44333, L. astragalus (2); 44334, R. calcaneum; 44335, L. ischium; 44336, R. innominate (partial); 44337-44338, R. scapula (2); 44339, thoracic vertebra. Lepus californicus Gray, 1837 Referred specimens: SDSNH 44340, R. humerus distal end; 44341, L. scapula. Discussion: Both of the above specimens were compared with Lepus californicus, Lepus Page 70 Glen Abbey Local Fauna Majors atnericanus, and Lepus alleni. The humerus of Levus alleni is much smaller, and has a more robust trochlea than the fossil humerus (SDSNH 44340); while the humerus of L. atnericanus is similar, but has a smaller capitulum; the humerus of L. californicus is nearly identical to the fossil in size, shape and arrangement of the distal articular surfaces and epicondyles. The scapula of Lepus alleni is much larger and has a more robust coracoid process than the specimen from Glen Abbey (SDSNH 44341). Lepus atnericanus has a smaller capitulum than the fossil. The fossil specimen is nearly identical to L. californicus in size as well as shape and arrangement of distal articular surfaces and epicondyles. Order Rodentia Bowdich, 1821 Family Geomyidae Gill, 1872 Thotnotnys cf. T. bottae (Eydoux and Gervais, 1836) Referred specimens: uncat., 148 specimens (includes teeth, dentaries, postcrania, etc.). Discussion: The above uncatalogued material is tentatively referred to the species Thotnotnys bottae because of the following characteristics: all premolars have a convex anterior margin (Hoffmeister, 1986), the molars are pear-shaped (Russell, 1968), and the material agrees well with T. bottae in size. A more detailed analysis of this material is underway by the author. Family Cricetidae Rochebrune, 1883 Peromyscus maniculatus (Wagner, 1845) Referred specimens:: SDSNH 44345-44348, LM1(4). Discussion: The dental terminology used here follows Hooper (1952). These molars exhibit a low mesostyle, an anterior cingulum attached to the anterolabial conule, a posterior cingulum, and a distinct, but shallow, anteromedial fold. Only in SDSNH 44348 is a mesoloph not present, in all other specimens the mesostyle is joined to the paracone by a low mesoloph arising from the posterolingual corner of the paracone. None of the material exhibits an entoloph, entostyle, or anterointernal fold. The above conditions, as well as general shape and size, justify an assignment to Peromyscus maniculatus (see Hooper, 1957). The material of Onychomys examined has a much more pear-shaped M than the fossil material. The following discussion draws from Hooper's (1957) thorough analysis of Peromyscus dental characteristics. Peromyscus crinitus often has a mesostyle on M , but very rarely a mesoloph. Peromyscus californicus usually has neither lophs or styles on M . A mesostyle is often evident on this tooth in P. eremicus, but a mesoloph is very unusual. Peromyscus truei usually has a mesostyle and mesoloph, but has a more robust M than the Glen Abbey material. Peromyscus boylei rarely lacks a mesostyle and a mesoloph that is large and usually does not join the paracone. The M of P. mexicanus often has a mesoloph and a mesostyle, the mesoloph is joined to the mure, and it is very rare for a mesostyle to be present without a mesoloph. The M of P. melanotis usually has a large mesostyle, and a mesoloph. The extinct form P. imperfectus (Dice, 1925) has accessory styles and is close to P. maniculatus in size, however, it appears that the mesostyle is attached to the paracone more labially than P. maniculatus and the Glen Abbey material. Though Peromyscus is highly variable, this material fits easily within the range of morphological variation for P. maniculatus (see Hooper, 1957). Peromyscus sp. Gloger, 1841 Referred specimens: uncat., 101 specimens (includes teeth, dentaries, postcrania, etc.). Reithrodontomys megalotis Howell, 1914 Referred specimens: SDSNH 44349, LM1; 44350, RM1. Discussion: The dental terminology used here is from Hooper (1952). This material is much smaller than both Peromyscus and Onychomys, and is close in size to the specimens of Reithrodontomys examined. Neither fossil specimen has a mesoloph, but SDSNH 44350 has a small mesostyle. Both fossils have an anterior cingulum, and a shallow anteromedian fold. SDSNH 44349 is heavily worn, but still clearly shows a meeting of the major fold and the second primary fold to form a loph from the hypocone to the paracone. This is less well developed in Majors Glen Abbey Local Fauna Page 71 SDSNH 44350. The principal folds (both lingually and labially) of both specimens are "V" shaped in lateral profile, with their mesial ends extending diagonally. Both specimens lack a posterior cingulum. These characters limit assignment of this material to the subgenus R. (Reithrodontomys) of Howell (1914), which includes Reithrodontomys humulis, R. montanus,R. raviventris and R. megalotis (Hooper, 1952). In the southeastern form, R. humulis, the meeting between the major fold and the second primary fold is so extreme as to isolate the anterior cusps from the posterior cusps (Hooper, 1952), this is not the case in the Glen Abbey specimens. The southwestern form R. montanus can be distinguished from this material by its broad "LP shaped principal folds, that extend anteroposterially in their mesial parts (Benson, 1935; Hooper, 1952). Specimens of R. raviventris examined were significantly larger and more pear-shaped than the Glen Abbey material. The closest match found was with R. megalotis, which is slightly larger than the fossils. Reithrodontomys megalotis has "V" shaped principal folds in lateral profile, as well as a loph joining the hypocone and paracone formed by a meeting of the major fold and the second primary fold (Hooper, 1952). Neotoma sp. Say and Ord, 1825 Referred specimens: SDSNH 44351, L. maxilla fragment with M ; 44352, R. dentary fragment w/M ; 44353, R. dentary fragment w/M ; 44354, L. 2 dentary fragment w/M ; 44355, LM ; 44356, RM2; 44357, LM3; 44358, LM3; 44359-44360, L. humerus (2); 44361, R. ilium fragment; 44362- 44363, L. ilium fragment (2); 44364, L. innominate (partial); 44365, R. femur; 44366, R. femur proximal end. cf. Neotoma sp. Say and Ord, 1825 Referred specimens: SDSNH 44367, R. femur fragment. Microtus californicus (Peale, 1848) Referred specimens: SDSNH 44368, LM3; 44369- 44374, LMt (6); 44375, partial R. maxilla w/M1 and M2; 44376, partial palate w/LM1; 44377, partial palate w/LM1, LM2, and RM1; 44378- 44379, partial L. dentaries w/M and M (2). Discussion: All of the fossil specimens exhibit the following: open-rooted molars, cement in re- entrant angles, labial salient angles that are slightly smaller than the lingual angles, and lower molars with thicker enamel on the anterior sides of the salient angles than the posterior sides (the opposite is true for the upper molars). The M material shows a posterior and anterior loop separated by five dearly distinct, closed, alternating triangles of enamel. The anterior loop has a constriction, dividing the loop into two portions. The posterior portion is composed of two rough triangles that open broadly into the anterior part of the loop, that is generally rounded. 3 The M has an anterior loop followed by three alternating, closed, triangles and a posterior loop that has a loph on its lingual side that opens to the rest of the posterior loop. The 3 M is not significantly narrowed posteriorly. In the two dentaries (SDSNH 44378, 44379) the incisor root passes lingually to M and M , then between the alveoli of M and M , and labially past M . SDSNH 44378 is larger and has a more rounded anterior loop than SDSNH 44379. All of the palate elements (SDSNH 44375, 44376, 44377) are close to the same size. The palatines are missing from SDSNH 44377, but are present on SDSNH 44376. There is an excavated pocket facing posteriorly in each of these palatines. The suture line between the maxillae and the palatines reaches anteriorly almost to the anterior loop of M . Each of the three palate elements shows numerous small round pits on the ridge marking the suture between the maxillae. On the basis of the position of the palatine- maxillary suture, the Glen Abbey material can be excluded from the genera Lemmus, Ondatra, Phenacomys, Clethrionomys, Neofiber, and Lagurus as well as the species Microtus richardsoni, and Synaptomys cooperi (Hooper and Hart, 1962). The fossil M material has a slightly less constricted anterior loop than the Microtus pennsylvanicus, M. montanus, and M. townsendi material examined (see Hooper and Hart, 1962). These three species also have Page 72 Glen Abbey Local Fauna Majors enamel that is nearly equal in thickness on the anterior and posterior sides of the salient angles of both upper and lower molars. The structure of M is most similar to M. californicus and M. pennsylvanicus (Miller, G.S., Jr., 1896), in M. mexicanus, M3 becomes significantly narrower posteriorly (Ellerman, 1966). Though the genus Microtus is highly variable (see Guthrie, 1965) all the fossil material is closest in size and general characters to Microtus californicus. Remarks: Microtus californicus is the only microtine species identified from the late Pleistocene of California, including the rich Los Angeles Basin (Miller, 1971; Jefferson, 1991). Microtus sp. Schrank, 1798 Referred specimens: uncat., 98 specimens (includes teeth, dentaries, postcrania, etc.). Order Perissodaictyla Owen, 1848 Family Equidae Gray, 1821 Eauus sp. Linneaus, 1758 Referred specimens: SDSNH 44380, Molar/premolar fragment; 44381, incisor fragment; 44382, incomplete radius. DISCUSSION Age and bio stratigraphy: The base of the Rancholabrean North American Land Mammal Age (NALMA) was originally defined by Savage (1951) as the first appearance of Bison, a Eurasian immigrant into North America. The Rancholabrean is also characterized by many other taxa of both large and small mammals, many of which are extant (see Lundelius, et al, 1987). As there are currently no reliable means of establishing absolute dates for most of the Rancholabrean (only the latest Rancholabrean is datable by radiocarbon methods, while uranium series and amino acid racemization techniques apply to marine invertebrates; Lowe and Walker, 1984), faunal correlations and fitting of faunas into a glacial/interglacial framework must be used to determine age (Lundelius, et al., 1987). Despite its unreliable date the base of the Rancholabrean appears to lie within the Illinoian Glacial Stage (Lundelius, et al., 1987). The Sangamonian Interglacial, which followed, peaked about 100,000 years ago (Kurten and Anderson, 1980). The Rancholabrean ended with the Wisconsinan Glacial Stage, which began about 70,000 years ago (Flint, 1971). Based on the species identified thus far from the Glen Abbey local fauna, SDSNH locality 3131 and its enclosing stream terrace deposits are either Sangamonian or Wisconsinan in age. An upper age limit of 8,000 to 10,000 years is established by the presence of Equus (Hester, 1960; Meltzer and Mead, 1983). Meltzer and Mead (1983) found that the most reliable youngest dates for Equus in North America were around 10,000 years. A lower age limit of Sangamonian for the Glen Abbey local fauna is based on the presence of Notiosorex crawfordi and Peromyscus maniculatus (Savage and Russell, 1983). The earliest records of Ectopistes migratorius (passenger pigeon) are in the Sangamonian of Florida, and the Mid- Wisconsinan of the West (Brodkorb and Mourer- Cauvire, 1984). There are, however, only three occurrences of this taxon in the late Pleistocene of the West, one of which is from the Glen Abbey site (Chandler, 1982). This limited record cannot provide firm evidence that Ectopistes migratorius was not present in the pre- Wisconsinan west. Scapanus latimanus and Microtus californicus have recorded first appearances in the Irvingtonian NALMA and survive to the present (Hutchison, 1987; Repenning, 1987). Hutchison (1987) has suggested that similarities between the Scapanus latimanus material from the Glen Abbey local fauna and the extinct form S. malanitus (from the Blancan and Irvingtonian of the Anza-Borrego Desert) may indicate a pre-Rancholabrean age for the locality. However, the presence of the Sangamonian to Recent species Notiosorex crawfordi and Peromyscus maniculatus rules this out, but does not preclude an Early Sangamonian age. At present no biostratigraphic age resolution better than pre-Holocene and post-IUinoian is possible for this local fauna. The absence of caliche in the deposit, and the presence of mesic indicators in the Glen Abbey local fauna (see below) suggest that the stream terraces at the Glen Abbey site were deposited under cooler and wetter conditions than today. This may indicate a Wisconsinan age for the Glen Abbey local Fauna. Paleoecology: Much of the Glen Abbey local fauna probably lived in or near the valley which the enclosing stream terrace deposits filled. This is evident from the ecological consistency of the assemblage. Both the passenger pigeon Majors Glen Abbey Local Fauna Page 73 (Greenway, 1958) and the California Quail (Leopold, 1977) are well suited to a wooded riparian habitat, such as that which is present in some coastal valleys of San Diego County today. The passenger pigeon preferred moderately to heavily forested areas for both roosting and nesting (Greenway, 1958). The California quail requires a combination of open feeding areas with patches of "cover", such as is found in chaparral or a wooded grass community (Leopold, 1977). The mole Scapanus latimanus is restricted to soft, moist soils (Palmer, 1937) thus, the river valley may have been an ideal habitat. It is interesting to note that S. latimanus anthonii is today restricted to elevations in excess of 2,000 meters in the Sierra San Pedro Martir of Baja California, Mexico (some 225 kilometers to the south of Bonita). In this area, current mean annual temperature is about 12 degrees celsius, and average annual rainfall is between 500 and 600 millimeters (Mexico, 1984); while the current mean annual temperature for Bonita is 16 degrees celsius and average annual rainfall is 255 millimeters (Close, et al., 1970). This record of Scapanus latimanus anthonii is a late Pleistocene range extension of some 250 kilometers North, and a marked decrease in elevation range, this may indicate cooler and wetter conditions at this time. Peromyscus maniculatus is the most abundant mammal in California at present (Ingles, 1965) and lives in nearly all comunities and habitats of San Diego (Bond, 1977), therefore does not refine the paleoecological consideration of this assemblage. Microtus californicus and Reithrodontomys megalotis also fit well within this general system, preferring grassy or marshy areas close to water (Bond, 1977). Sorex ornatus prefers damp areas on slopes of both coastal and inland San Diego County today (Bond, 1977). The members of the assemblage which do not at first appear to fit into the ecological picture of a wooded stream valley are Notiosorex crawfordi (desert shrew) which is xeric adapted (Ingles, 1965), and Melanitta (surf scoter), a shorebird (Unitt, 1984). However, the desert shrew is known to move into almost any habitat, provided that there is not a viable competitor (Harris, 1985). Also, the Glen Abbey site is currently within six kilometers of San Diego Bay. During a highstand of sealevel (i.e. during an interglacial), the shoreline may have been much closer to the fossil locality than this. SUMMARY The Glen Abbey local fauna has a gross similarity to other Rancholabrean assemblages from southern California, and the southwestern United States (Schultz, 1938; Miller, W. E., 1971; Kurten and Anderson, 1980; Harris, 1985; Jefferson, 1991), especially so for the Los Angeles Basin (Miller, W. E., 1971; Jefferson, 1991), including Rancho La Brea (Stock, 1972). This faunal affinity, as well as the age of the Glen Abbey local fauna and its associated stream terrace deposits, may come to be better understood as study of the Glen Abbey local fauna progresses. This will include study of the material not discussed here. A survey of this material has revealed the presence of a possible duck {Anas), the squirrel Spermophilus, and the heteromyid rodents Dipodomys and Perognathus. Mesic indicators within the Glen Abbey local fauna suggest a Wisconsinan age assignment. Hopefully, further study will clarify the age of this local fauna. ACKNOWLEDGEMENTS The author thanks the following for their critical thoughts and assistance: Patrick Abbott, J. David Archibald, Jim Berrian, Annalisa Berta, Richard Cerutti, Robert Chandler, Greg Pregill, Brad Riney, Mark Roeder, Steve Walsh, and Robert Zimdar. The author is very grateful to Matthew Colbert and Thomas Demere for their patience, understanding, and many critical reviews. A debt of thanks is owed to Philip Unitt for his assistance with the collections under his care at the San Diego Natural History Museum (Department of Birds and Mammals). In addition, the comments of George Jefferson and an anonymous reviewer were crucial in shaping this paper. REFERENCES Allen, J. R. L. 1970. Studies in Fluviatile Sedimentation: A Comparison of Fining- upwards Cyclothems, with Special Reference to Coarse-member Composition and Interpretation. Journal of Sedimentary Petrology 40(l):298-323. Artim, E. R., and C. J. Pinckney. 1973. La Nacion Fault System, San Diego, California. 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Los Angeles County Museum of Natural History, Science Series Number 20, Paleontology Number 11,81p. Tedf ord, R. H. 1969. Principles and Practices of Mammalian Geochronology in North America. Proceedings of the North American Paleontological Convention, 666-703. Unitt P. 1984. The Birds of San Diego County. San Diego Society of Natural History, Memoir 13,276p. Majors Glen Abbey Local Fauna Page 77 Walker, R. G., and D. J. Cant. 1984. Sandy Woodburne, M. O. (ed.). 1987. Cenozoic Mammals Fluvial Systems. Pages 71-89 in. Facies of North America: Chronology and Models, second edition, (Walker, R. G., ed.), Biostratigraphy. University of California Geoscience Canada Reprint Series 1. Press, Berkeley, 336p. Appendix 1. The following list of mammalian comparative material includes only recent specimens from the San Diego Natural History Museum's Department of Birds and Mammals. Sorex ornatus: SDSNH 22943,22999, 23305. Sorex trowbridgii: SDSNH 23310, 23336. Notiosorex crawfordi: SDSNH 22946, 23001, 23002, 23394. Lepus alleni: SDSNH 23484. L. americanus: SDSNH 23489, 23499. L. californicus: SDSNH 23339, 23614, 23483. Thomomys bottae: SDSNH 21413, 22991, 23006, 23103. Peromyscus californicus: SDSNH 23055. P. crinitus: SDSNH 992, 7448,32084. P. eremicus: SDSNH 23401, 23638. P. eremicus eremicus: SDSNH 20916, 20917. P. maniculatus: SDSNH 21440, 22924, 22940. P. maniculatus gameli: SDSNH 23118. P. truei gilberti: SDSNH 23324. Onychomys torridus: SDSNH 23403. Reithrodontomys megalotis: SDSNH 22907, 22919, 22920. R. raviventrisi SDSNH 20010, 20011. Microtus californicus: SDSNH 22925, 22926, 23326. M. montanus: SDSNH 7802. M. pennsylvanicus: SDSNH 6723, 6724. M. townsendii: SDSNH 9789.