New Botanical and Avian Insights from the Holocene of Murrah Cave in the Trans-Pecos of Texas, USA

Abstract

Murrah Cave is one of a series of cave and rockshelters in the Lower Pecos Canyonlands (far eastern Trans-Pecos) that contain evidence of late Quaternary cultures, fauna, and flora. Excavated in 1937, many faunal and floral specimens from Murrah Cave remain undescribed. Among those materials are a coracoid of a Pied-billed Grebe (Podilymbus podiceps), seeds, and charcoal. The major cultural occupation now is dated between 1000 and 600 ¹⁴C yr B.P. based on textiles. Charcoal dates, however, cluster earlier at around 2500 ¹⁴C yr B.P. with one date at 4800 ¹⁴C yr B.P. The Pied-billed Grebe represents the first occurrence in the Quaternary fossil record for the Trans-Pecos. The floral taxa are found in the Trans-Pecos Canyonlands today, part of the Chihuahuan Desert vegetation community, with some being the first known presence in the Lower Pecos Canyonlands. Two short-term mesic periods begin around 2500 ¹⁴C yr B.P. and 700 ¹⁴C yr B.P. denoted by the return of modern bison and expansion of the grasslands. These brief periods of increased moisture do not fundamentally alter the desert vegetation community. The floral and avian records highlight the potential available data within and the usefulness of old collections in contributing to modern studies.

1. Introduction

The Trans-Pecos region (Figure 1) is the southernmost part of the Basin and Range physiographic province [1,2]. It is characterized by desert mountains and valleys, plateaus and sand hills, and brushlands [3,4]. It is a region of far west Texas west of the Pecos River. The Trans-Pecos forms the northern (i.e., United States) portion of the Chihuahuan Desert (divided by the Rio Grande River). Because the endemic Agave lechuguilla (lechuguilla) is an indicator species of the general boundaries of the Chihuahuan Desert [3,5], adjacent areas frequently are included, e.g., [3,5,6]. Culturally, the area east of the lower Pecos River to the Devils River usually is included in the Trans-Pecos region and identified as the Lower Pecos Canyonlands [7,8]. Both the Pecos and Devils rivers flow into the Rio Grande River, with the lowest elevation for the region, at about 1000 ft (~305 m), at the confluence of the Pecos and Rio Grande rivers [3,4].

Caves and rockshelters in the Lower Pecos Canyonlands (Figure 2) contain a remarkable record of late Pleistocene and Holocene cultures, e.g., [7,8,9,10,11,12,13]. The same deposits also contain evidence of past fauna, e.g., [14,15,16], and flora [17,18,19], although perhaps less well known than the cultural record. Research along Devil’s River, e.g., [7,18,20,21], lower Pecos River [7] and extensive field work in Eagle Nest Canyon [8], a box canyon along the Rio Grande River near Langtry (Val Verde County, Texas), highlights the rich paleobotanical record. Collections generated by the early excavations of the caves and rockshelters along the lower Pecos River in the 1930s [22,23,24,25] also can help fill the knowledge gap in the faunal and floral records. Yet, many of the faunal and floral specimens in these early collections are undescribed or minimally reported.

Murrah Cave (Figure 2) represents this early period of exploration, excavated by William Curry Holden [24] under the auspices of the West Texas Museum (now the Museum of Texas Tech University). Although a diverse faunal assemblage was outlined by Holden [24] with a listing of over 18 vertebrate taxa including multiple birds, that material has never been described or illustrated. Among those undescribed faunal remains is a complete coracoid of a grebe (Podicipedidae) from Murrah Cave. Birds are generally underrepresented in publications describing the past fauna from cave deposits across North America [26]. While the mammalian record, and to a lesser extent the herpetofaunal record, is well outlined, the record of late Quaternary birds is scant [27,28]. The general paucity of the avian record from Texas throughout the Quaternary (see, however, refs. [29,30,31] (regarding the late Quaternary avian record of the Southern High Plains)) reflects the broader pattern in North America. That paucity in Texas exists despite the excellent Pleistocene and Holocene deposits and extensive paleontological and archaeological records. The limited record impairs understanding of the development of modern avifauna. The single grebe element from Murrah Cave, then, is a noteworthy occurrence.

The botanical record fared better in the older reports due to the textiles preserved in the deposits being constructed from various plant fibers. A large sample of cordage, knots, basketry, sandals, netting, and other textile and macrobotanical materials were described from Murrah Cave [24]. The age, cultural context, and taxonomy of those materials remained uncertain. While seeds may have been identified, the use of charcoal for taxonomic identification began in the 1940s [32,33], with Howard [34] being a notable exception. By the 1970s, a greater understanding of past vegetation was being gained from work along the lower Pecos River [17,35,36,37], the Devil’s River [18,20,38,39], and through the extensive work prior to the construction of the Amistad Reservoir at the confluence of the Devil’s River and the Rio Grande River [7].

Accordingly, this study has three objectives. The first is the taxonomic identification, description, and discussion of the grebe from Murrah Cave. The second is the taxonomic identification and discussion of the botanical remains (i.e., seeds and charcoal) from Murrah Cave. The third is the radiocarbon dating of organic materials to gain a better understanding of the age of the deposits. The Murrah Cave macrobotanical remains add to the Pecos River record and enhance the extensive botanical records at Hinds Cave [17] and in Eagle Nest Canyon [19] with taxa not represented in that record. This report is intended as a contribution to the expansion of the late Quaternary avian record of Texas and western North America and the vegetation history of the Lower Pecos Canyonlands.

2. Murrah Cave

Murrah Cave is located in Val Verde County (Texas) on the east bank of the Pecos River approximately 25 miles (~40.2 km) upstream from its confluence with the Rio Grande River (Figure 2). The cave is within a sheer cliff face of Georgetown Limestone (early Cretaceous; Comanchean series) 60 ft (~18.3 m) below the top of the cliff face and about 200 ft (~61 m) above water level at the time of excavation (Figure 3). It is a small cave with only a single entrance (Figure 4 and Figure 5a), and it measures 124 ft (~37.8 m) back into the cliff and varies in width from 24 ft (7.3 m) at the entrance to 45 ft (13.7 m) towards the back of the cave (Figure 5a) [24] (p. 48).

Human occupation apparently was restricted to the front 50 ft (~15.2 m) where the floor was comparatively level, after which the floor declines about 30% to the rear [24] (p. 48). Occupation created an ash deposit that varied from 18 in (~45.7 cm) to 52 in (~132 cm) in thickness (Figure 5b). The ash deposit was stratified in part of the cave with a 4 in (~10.2 cm) layer of dust located 18 in (~45.7 cm) below the top of the ash deposit. The ash deposit was excavated in three levels. The ash deposit in the first two levels was removed entirely. The remaining lowest deposit was explored with hand-dug trenches along both sides of the cave. All of the removed sediments were screened through a ¼ in screen, and some objects were photographed in place (Figure 6).

The collection generated was accessioned by the West Texas Museum (X-230; now the Museum of Texas Tech University) but not cataloged. Although excavated in three levels, a disconnect occurred and no provenience information was recorded in the accession records for the individual objects. Holden [24] (p. 53) noted that for his preliminary (and only) report, he was “lump[ing] the layers together” to provide a summary of the findings. Whether Holden intended for the objects from the different levels to be combined physically into a single grouping that disregarded provenience is not known. Holden had his students keep field journals, but those documents never came to the museum’s new facility (opened in 1970) when collections were moved over from the old facility, and their whereabouts today are unknown.

During a review of the collection, the right coracoid (TTU-A3-112) of a grebe was removed from the collection for conservation treatment. No other elements of grebes were present. The coracoid was part of a larger sample of faunal remains. A taxonomic reevaluation and taphonomy of those specimens remained to be done. The collection contained an intermingling of unidentified seeds and charcoal that were part of the sizeable sample of botanical remains recovered from the cave deposits, much of which had been identified preliminarily [24] (pp. 69–73).

3. Materials and Methods

The Murrah Cave collection is housed at the Museum of Texas Tech University. The accession record, photographs from the 1937 work, and Holden’s [24] publication constitute the current associated documents. Inventory records from 1976 to 2025 account for the collection’s objects, provide basic identifications, and indicate cabinet and drawer locations.

Identification of the coracoid (TTU-A3-112) from Murrah Cave was based on a sample of 61 modern skeletal specimens representing seven taxa of grebes from the Western Hemisphere in the collections of the Division of Birds, National Museum of Natural History (NMNH, Washington, DC, USA). The modern sample was composed of Tachybaptus dominicus (n = 1), Rollandia roland (n = 1), Podiceps grisegena (n = 1), Podiceps major (n = 1), Podiceps auritus (n = 20), Podiceps nigricollis (n = 18), and Podilymbus podiceps (n = 19). The large size of the modern sample enabled recognition of individual variation and detection of consistent qualitative distinctions between genera and species. Morphological traits that were consistent within individual taxa but varied between taxa provided a reliable means of distinguishing between extant forms based on the coracoid. Those distinctive morphological traits then were applied to the specimen from Murrah Cave and gave a basis for taxonomic assignment. Measurements were obtained with digital calipers. Morphological terminology followed Howard [40].

The botanical specimens were sent to the Paleoscapes Archaeobotanical Services Team (Bailey, Colorado) for identification. Of these, 14 were representative seed samples and 23 were charcoal samples for tree identification (total 37 samples). Interpretation of those results was undertaken by the senior author and based on the current literature and plant ranges. Taxonomy and taxonomic order followed that of the Flora of North America series, with modifications as warranted.

Organic material samples were submitted to the LTRR & AMS Laboratory at the University of Arizona for radiocarbon dating. Of the 13 samples submitted, five were materials constructed of plant fiber, one of leather, and seven were charcoal. Only loose segments of fiber-based and leather objects were dated so as not to cause further damage to the intact perishable objects. The charcoal samples for dating were subsamples of the same 23 charcoal samples sent for tree identification. The seven samples reflected the seven taxa identified. Radiocarbon ages were calibrated with CALIB Rev. 8.2 [41] using the IntCal20 calibration curve [42].

4. Results

The coracoid from Murrah Cave is identified as belonging to a member of Podicipediformes based on the presence of a strongly ventrally projected coracoid head and the absence of procoracoid prominence, a procoracoid process, and a coracoidal fenestra. These traits are typical of extant grebes [43,44]. The coracoid is distinctly smaller than the large forms Podiceps grisegena, P. major, and Aechmorphus and distinctly larger than the diminutive forms Tachybaptus dominicus and Rollandia roland. The specimen from Murrah Cave is closely aligned, in size (

Table 1. Measurements of the coracoid in species of Podilymbus and Podiceps.

Taxon	Total Length		Width of Sternal Facet
TTU-A3-112	27.7		9.4
Podilymbus podiceps	Female	Male	Female	Male
Mean	29.1	31.7	10.3	11.6
Number of specimens	9	10	9	10
Observed range	27.7–31.3	30.1–33.6	9.1–11.0	10.9–12.4
Podiceps nigricollis
Mean	26.8	27.9	10.1	10.6
Number of specimens	5	5	13	13
Observed range	26.6–26.9	26.5–29.0	9.6–10.7	9.8–11.0
Podiceps auritus
Mean	28.4	29.8	11.1	11.8
Number of specimens	10	10	9	9
Observed range	27.0–30.1	28.0–31.2	10.5–12.0	11.1–12.4

) and form, with P. auritus, P. nigricollis, and Podilymbus podiceps. The latter three species overlap in terms of the size of the coracoid (Table 1) [45].

The morphology of the coracoid differs between Podiceps and Podilymbus. The coracoid of Podilymbus is distinct, relative to Podiceps, in having a narrow coraco-humeral surface, a constriction between the glenoid facet and coracoidal head, a slender diaphysis that is rounded below the scapular facet, and a narrow sterno-coracoidal crest. The glenoid facet is narrow and a distal border of the glenoid facet slopes down distally toward the distal border of the scapular facet. Those relative morphological differences capable of separating the coracoids of Podiceps auritus and Podiceps nigricollis from Podilymbus are illustrated in Figure 7 and listed in

Table 2. Coracoid morphological distinctions separating the coracoids of Podiceps and Podilymbus.

	Podilymbus podiceps	Podiceps auritus and Podiceps nigricollis
1	Coraco-humeral surface is relatively narrow and located internally	Coraco-humeral surface is relatively wide and is located proximally
2	Transition from glenoid facet to the head is constricted	Transition from the glenoid facet is relatively broad
3	Glenoid facet relatively narrow	Glenoid facet relatively broad
4	Diaphysis distal to the scapular facet is rounded ventrally	Diaphysis distal to the scapular facet is flattened ventrally
5	Distal border of the glenoid facet slopes distally toward the distal border of the scapular facet	Distal border of the glenoid facet is level with or extends distal to the distal border of the scapular facet
6	Diaphysis is relatively slender	Diaphysis is relatively broad
7	Sterno-coracoidal crest is narrow, with a flat external border	Sterno-coracoidal crest is wide and sub-triangular

. Podilymbus and species of Podiceps exhibit considerable sexual dimorphism and that dimorphism is evident in the skeleton (Table 1) [46,47]. Nonetheless, the characters described here (Figure 7, Table 2) provide a consistent means of distinguishing between both sexes of these similarly sized North American grebes. The morphology of the post-cranial skeleton in the three species is very similar. As a result, some of the traits reported here represent relative differences in form and are best understood through direct comparisons of relevant skeletal material. The coracoid from Murrah Cave (TTU-A3-112) exhibits the morphology of Podilymbus podiceps (Table 2) and is assigned to this taxon.

The seeds yielded 10 taxa from 7 families (Figure 8), while charcoal produced 7 taxa from 6 families (

Table 3. Identified taxa by family for the Murrah Cave representative seed and charcoal samples.

Seeds
Catalog Number	Family	Taxon	Common Name	Counts
TTU-A3-465	Juglandaceae (Walnut Family)	Juglans microcarpa	Texas walnut	11
TTU-A3-461	Fagaceae (Oak Family)	Quercus cf. fusiformis	Texas live oak	2
TTU-A3-584	Cactaceae (Catus Family)	Opuntia spp.	prickly pear	26
TTU-A3-593	Ebenaceae (Ebony Family)	Diospyros texana	Texas persimmon	1
TTU-A3-592	Fabaceae (Legume Family)	Senegalia berlandieri	guajillo	1158
TTU-A3-462		Prosopis glandulosa	honey mesquite	64
TTU-A3-596		Dermatophyllum secundiflora	Texas mountain laurel	2
TTU-A3-597	cf. Rhamnaceae (Buckthorn Family)		buckthorns	22
	Asparagaceae (Asparagus Family)
TTU-A3-581		Agavoideae	agave	2
TTU-A3-464		Yucca cf. treculeana	Torrey’s yucca	90
Charcoal
TTU-A3-585 TTU-A3-682	Fagaceae (Oak Family)	Quercus-Leucobalanus	white oak group	6
TTU-A3-679	Ebenaceae (Ebony Family)	Diospyros texana	Texas persimmon	5
TTU-A3-579 TTU-A3-675 TTU-A3-680	Fabaceae (Legume Family)	Prosopis glandulosa	honey mesquite	21
TTU-A3-681 TTU-A3-678		Dermatophyllum secundiflora	Texas mountain laurel	21
TTU-A3-594	Zygophyllaceae (Creosote-bush or Caltrop Family)	cf. Guaiacum angustifolium	Texas lignum-vitae	4
TTU-A3-683	Oleaceae (Olive Family)	Fraxinus cf. greggii	Gregg’s ash	2
TTU-A3-684	Scrophulariaceae (Figwort Family)	Leucophyllum frutescens	cenizo	2

). Four of the charcoal-based taxa did not overlap with the seed taxa (Table 3). This situation, then, provided a broader view of the plants being brought into the cave and habitats within the surrounding area (14 taxa from 10 families;

Table 4. Composite of recently identified botanical taxa by form and habitat for Murrah Cave.

Family	Taxon	Common Name	Form	* Habitat	Tolerances
Juglandaceae (Walnut Family)	Juglans microcarpa	Texas walnut	Tree	Canyons, along or near watercourses	Heat, cold, drought
Fagaceae (Oak Family)	Quercus cf. fusiformis	Texas live oak	Shrub to tree	Limestone mesas, canyon, and flats near watercourses	Heat, cold, high drought
	Quercus-Leucobalanus (white oak group)	White oak	Tree	** Q. polymorpha-watercourse; Q. vaseyana-limestone canyons, watercourses, and high mountains; Q. fusiformis-limestone mesas, canyons, and flats near watercourses;	Heat, cold, high drought
Cactaceae (Catus Family)	Opuntia	Prickly pear cactus	Shrub	Limestone hills, mesas, and canyons; desert to semi-desert, grassland to woodland;	Heat, drought
Ebenaceae (Ebony Family)	Diospyros texana	Texas persimmon	Shrub to small tree	Limestone desert to semi-desert, along intermittent water courses and on slopes	Heat, high drought
Fabaceae (Legume Family)	Senegalia berlandieri	Guajillo	Shrub	Rocky limestone substrates along and near the Rio Grande	Heat, high drought
	Prosopis glandulosa	Honey mesquite	Shrub to small tree	Desert, grassland, mesic mountain	Heat, high drought
	Dermatophyllum secundiflora	Texas mountain laurel	Shrub	Limestone watercourses	Heat, cold, drought
cf. Rhamnaceae (Buckthorn Family)			Shrub to small tree	Desert, grassland, brushy flats and arroyos
Zygophyllaceae (Creosote-bush or Caltrop Family)	cf. Guaiacum angustifolium	Texas lignum-vitae	Shrub	Intermittent watercourses and brushlands	Heat, cold
Oleaceae (Olive Family)	Fraxinus cf. greggii	Gregg’s ash	Shrub to tree	Limestone hills, mesas, and canyons and near the Rio Grande	Heat, cold
Scrophulariaceae (Figwort Family)	Leucophyllum frutescens	Cenizo	Shrub	Desert hillsides, arroyos, scrublands	Heat, cold, drought
Asparagaceae (Asparagus Family) agave subfamily)	Agavoideae	Agave subfamily	Shrub-forb	Desert
	Yucca cf. treculeana	Torrey’s yucca	Shrub	Hills, mesas, slopes, desert scrub and grasslands	Heat, cold, drought

* Powell and Worthington [3]; Flora of North America series. ** Simpson et al. [48].

).

All of the taxa are found in the Trans-Pecos Canyonlands today and are part of the northern Chihuahuan Desert vegetation community [3]. Drought-tolerant taxa (10 of 14; 71.4%; Table 3 and Table 4) dominate. The majority of the seed taxa are from shrub-to-tree forms, while all of the charcoal taxa reflect shrub-to-tree forms (Table 3 and Table 4). Texas walnut, Texas live oak, honey mesquite, Texas mountain laurel, and Gregg’s ash (Table 4) form part of the modern riparian community of the Pecos River as well as the various Trans-Pecos watercourses. Away from the watercourses, honey mesquite and Gregg’s ash also can be found on the open scrub and grasslands where they more likely occur in shrub form.

Several records are of taxonomic note. Among the seeds, the original notation of Quercus–live oak-type acorn has been referred to Quercus cf. fusiformis (Texas live oak; Table 3). Of the live oak group, only Q. fusiformis occurs in the Trans-Pecos region today. It is restricted to Terrell and Val Verde counties along the Pecos and Devils rivers [3,5]. The other species in the live oak group (Q. virginiana, Q. geminata, and Q. minima) are southeastern coastal region oaks. Today’s range of Q. virginiana (Southern live oak) extends west into the coastal lower Brazos River basin [49] (p. 503). Hester [18] (p. 111) notes preserved leaves of live oak (Q. virginiana) from deposits dated to 9000 ¹⁴C yr B.P. ~10,200 calendar years) in Baker Cave along the Devils River (Figure 2). Its presence may reflect the beginning of a range contraction to the east with more mesic conditions. The rest of the plant and animal remains from Baker Cave indicate a semi-arid environment [7,18].

White oaks, identified in the Murrah Cave charcoal (Table 3), dominate the oaks of the Trans-Pecos region today. Of the currently recognized oak species recorded as part of the Trans-Pecos region’s vegetation today [3,5], 17 are within the white oak group, representing ~65.4% of the oak species. Most occur in discontinuous or isolated populations within the mountain ranges of the Trans-Pecos region. Of the three found in Val Verde County today, two occur along the lower Pecos and Devils rivers, Quercus vaseyana (Vasey oak) and Q. fusiformis (Texas live oak) [3,5,49]. The only known U.S. population of Quercus polymorpha (net-leaf white oak), a Mexico to Guatemala species, occurs in a protected ravine along the Devils River about 30 km (18.6 miles) above the confluence with the Rio Grande River [48,49]. Being among the most likely candidates represented in the charcoal (Table 3), the habitats and tolerances of these three species listed in Table 4.

Within the agave subfamily Agavoidaea, Torrey’s yucca and at least one other, as yet undetermined, were identified from seeds (Table 3). That undetermined taxon of Agavoidea could be either an agave or another yucca (Table 3). Among the agave possibilities, four of the five Trans-Pecos agaves today are associated with the Trans-Pecos mountain ranges and their grassy foothills. Lechuguilla (Agave lechuguilla), however, is a widespread taxon that occurs today in the Lower Pecos. It is present in the cave deposits in the recovered fibrous materials. Most of the yuccas are associated with the Trans-Pecos mountain ranges. Although Torrey’s yucca is the most widespread and common yucca in the Trans-Pecos, at least three other yuccas occur today in Val Verde County [3,5].

The original notation of Yucca torreyi type has been referred to as Yucca cf. treculeana (Table 3). Although Y. torreyi is still in widespread use, e.g., [3,19], Y. torreyi has been subsumed under Y. treculeana [50] (p. 428) and followed here.

The seven taxa based on charcoal samples have been radiocarbon dated (Table 3 and

Table 5. Murrah Cave radiocarbon dates based on textiles and charcoal.

Arizona Lab Number	Catalog Number	Material	Radiocarbon Date	AD/BC	Calendar Calibration (cal AD/BC)		Calendar Calibration (cal BP)
					Median Probability	95.4% cal Age Range	Median Probability	95.4% cal Age Range
AA116297	TTU-A3-573	Textile–segment	633 ± 30	1317 AD	1350 cal AD	1290–1396 cal AD	600 cal BP	555–660 cal BP
AA116298	TTU-A3-574	Textile–mat segment	705 ± 30	1245 AD	1290 cal AD	1266–1392 cal AD	660 cal BP	560–680 cal BP
AA116299	TTU-A3-575	Textile–mat segment	666 ± 30	1284 AD	1320 cal AD	1279–1392 cal AD	630 cal BP	560–670 cal BP
AA116300	TTU-A3-670	Textile–basket segment	995 ± 30	955 AD	1050 cal AD	994–1154 cal AD	900 cal BP	800–960 cal BP
AA116301	TTU-A3-672	Textile–loin cloth fringe segment	638 ± 30	1312 AD	1350 cal AD	1287–1396 cal AD	600 cal BP	550–660 cal BP
AA116302	TTU-A3-671	Textile–fiber twine segment	627 ± 30	1323 AD	1350 cal AD	1295–1397 cal AD	600 cal BP	550–650 cal BP
AA117334	TTU-A3-579	Charcoal–Prosopis cf. glandulosa	4785 ± 19	2835 BC	3575 cal BC	3625–3528 cal BC	5520 cal BP	5480–5580 cal BP
AA117337	TTU-A3-594	Charcoal–cf. Guaiacum angustifolium	2620 ± 16	670 BC	800 cal BC	809–788 cal BC	2750 cal BP	2740–2750 cal BP
AA117332	TTU-A3-679	Charcoal–Diospyros texana	2529 ± 16	579 BC	675 cal BC	786–565 cal BC	2620 cal BP	2510–2730 cal BP
AA117336	TTU-A3-681	Charcoal–Dermatophyllum secundiflora	2612 ± 16	662 BC	800 cal BC	807–780 cal BC	2750 cal BP	2730–2760 cal BP
AA117333	TTU-A3-682	Charcoal–Quercus-Leucobalanus group	2573 ± 16	623 BC	785 cal BC	799–770 cal BC	2730 cal BP	2720–2750 cal BP
AA117338	TTU-A3-683	Charcoal–Fraxinus cf. greggii	2630 ± 16	680 BC	805 cal BC	811–791 cal BC	2750 cal BP	2740–2760 cal BP
AA117335	TTU-A3-684	Charcoal–Leucophyllum frutescens	2539 ± 16	589 BC	755 cal BC	790–570 cal BC	2700 cal BP	2520–2740 cal BP

). These dates firmly fix each taxon in time, documenting trees growing in the vicinity of the cave during the late Holocene. The charcoal-based dates reflect the problem of mixed deposits and present a contrast to the textile-based dates (Table 5).

All of the textile-based radiocarbon dates are from the last 1000 years (Table 5) and indicate more than one time period of occupation. Nevertheless, they all fall within the Flecha Interval (1000–400 ¹⁴C yr B.P.) in the current Lower Pecos Canyonlands cultural chronology ([7] (p. 61), [13] (p. 268)). This result is more restricted than the now-recognized age range of the projectile points recovered in Murrah Cave [24], the earliest of which date to the Eagle Nest Interval (5500–4100 ¹⁴C yr B.P.; Middle Archaic) [7] (pp. 62,69).

On the other hand, all of the charcoal-based radiocarbon dates are much earlier in time. Of the seven dates, six cluster around 2600–2500 ¹⁴C yr B.P. (Table 5). This cluster falls within the latter part of the Cibola Interval (3150–2300 ¹⁴C yr B.P.; ([7] (pp. 62, 77–78), [13] (p. 268)). The remaining seventh date is an outlier. It is the oldest date at ~4800 ¹⁴C yr B.P. (Table 5) and within the Eagle Nest Interval.

5. Discussion

The Pied-billed Grebe (Podilymbus podiceps) is relatively common and widespread throughout the Americas [51]. A foot-propelled diver, the Pied-billed Grebe inhabits a range of aquatic settings, both freshwater and brackish, including marshes, lakes, rivers, and streams [51,52]. Extant populations are present across Texas, including the Trans-Pecos where the species occurs year-round [53,54,55] including the lower Pecos River [55]. The Murrah Cave specimen represents the first occurrence of a grebe in the Quaternary fossil record for the Lower Pecos Canyonlands as well as the Trans-Pecos in general.

Grebes are highly specialized for life in aquatic habitats. The extreme posterior position of the hind limbs of grebes is ideal for their diving hunting behavior but makes locomotion on land awkward, and most species cannot take flight from land [56]. Accordingly, grebes offer clear evidence of the presence of aquatic habitats in the past. Preferred habitat includes dense emergent vegetation and a combination of shallow water for nesting and deeper water for diving hunting of vertebrate and invertebrate prey [56,57]. Pied-billed Grebes are flexible, however, and they also occur in less favorable and more ephemeral settings, including shallow water settings, ponds as small as 1.3 hectares, and even sewage ponds [51,54].

A review of 123 individual publications (peer-reviewed journal articles and relevant gray literature) revealed a total of eight grebe occurrences (

Table 6. Late Quaternary occurrence of grebes in Texas (USA).

	Taxon	Locality	Age (14C yr)	Reference
1	Podilymbus podiceps	Ingleside, San Patricio County	Late Pleistocene	[58]
2	Podilymbus podiceps	Howard Ranch l.f., Hardeman County	Late Pleistocene (16,775 BP)	[59]
3	Podilymbus podiceps	Macy Fork l.f., Garza County	Late Pleistocene (11,550–11,000 BP)	[29]
4	Podilymbus podiceps	Lubbock Lake (41LU1; Plainview l.f.), Lubbock County	Early Holocene (10,000 BP)	[31]
5	Podiceps cf. nigricollis	Lubbock Lake (41LU1; Plainview l.f.), Lubbock County	Early Holocene (10,000 BP)	[31]
6	Podilymbus podiceps	Murrah Cave (41VV351), Val Verde County	Late Holocene	This paper
7	Podilymbus podiceps	Leonard K site (41AU37), Austin County	Late Holocene (2470–1590 BP)	[60,61]
8	Podilymbus podiceps	Taddlock site (X41WD39), Wood County	Late Holocene (1010–950 BP)	[62]

) in Texas for the entire 2.588 million years of the Quaternary. Quaternary occurrences of grebes in Texas are clustered within the late Quaternary (Figure 9; Table 6), with no occurrences known prior to the late Pleistocene. Records of grebes are sparse across the Pleistocene of western North America [27], and the entire fossil record of Podicipediformes has been described as scant [43]. The grebe’s presence in the cave deposits presumably is the product of transport by humans or other bone-accumulating vertebrates (e.g., predatory birds, carnivorans, pack rats). The coracoid has not been radiocarbon dated and may or may not be contemporaneous with the dated materials (Table 5).

Sedimentary deposits in caves often are complex, may lack superposition and lateral continuity, and associated objects may experience multiple episodes of transport and redeposition [63,64,65]. Those factors challenge straightforward interpretation of the evidence preserved in caves. In this case, interpretation is challenged further by the historical nature of the sample and a lack of provenience data. Studies of site formation processes in Eagle Nest Canyon downstream from Murrah Cave on the Rio Grande (Figure 2) indicate that bioturbation by people (domestic activities and trampling) and floodwaters are primary factors in formation and disturbance, although animal bioturbation had a secondary role [66,67]. With Murrah Cave located high above the Pecos River on a cliff face, flooding seems an unlikely factor. The data presented here contribute to addressing those challenges. The new radiocarbon ages provide the means to reconstruct the spatio-temporal relationships between macrobotanical materials recovered in the 1937 excavation. The robust existing regional record offers a framework for interpreting data from Murrah Cave in a broader context.

The cultural record of the Lower Pecos region is primarily an extensive Holocene one [7] but with indications extending it back into the late Pleistocene [68,69,70]. All of the Murrah Cave radiocarbon dates fall within the current chronology of the projectile points recovered from the cave [7]. They, therefore, are considered reliable. Due to the lack of provenience data, however, they do not date a specific feature or individual activity area.

The Murrah Cave textile-based radiocarbon dates indicate periodic reoccupation of the cave over a 400-year period in the latter part of the late Holocene. This major cultural occupation is within the Flecha Interval. All charcoal-based radiocarbon dates, however, reflect two earlier time periods that hint at possible multiple occupations not recognized by Holden [24] and lend support for the potential earlier occupations indicated by the recovered projectile points.

Holden [24] (pp. 53–54) placed the projectile points into nine classes following a modified scheme of Pearce and Jackson [23] and noted that the classes occurred throughout the ash deposit. Vertical distribution of any one class was not limited to any of his excavation levels, although half the points were recovered within 2 ft (~61 cm) of the cave walls. Bioturbation through living activities may account for the redistribution of some material. Both Pearce and Jackson [23] (p. 74) and Martin [22] (p. 13) made similar observations with their respective excavations at Fate Bell and Shumla Caves (Figure 2).

While bioturbation may account for the co-occurrence of all point types, it does not explain the tight clustering of the textile-based radiocarbon dates to the one chronological interval. That situation may be a matter of sampling. Because charcoal was not kept intentionally, the extant charcoal in the collection is associated with other plant materials and fibrous objects intentionally collected. The seeds were sifted from the ash heap (notation on the accession card; Figure 6) that most likely accounts for the incidental presence of charcoal found among the seeds in their storage containers. Although fiber-based textiles apparently were recovered in all levels, Holden [24] (p. 65), Figure 5 notes that all sleeping mats were found at the surface or within 15 in (~38 cm) of the surface and packed with ashes. Further, only fibrous and leather objects that had an associated separated piece have been dated. It is possible that other fibrous and leather objects in the collection could date to earlier chronological intervals. The style and construction of fibrous sandals (primarily made of yucca and lechuguilla) changes through the Holocene [7,21,71]. An analysis of the Murrah Cave sandals may help clarify the radiocarbon dates and chronology of occupations. Nevertheless, a major occupation period has taken place between 1000 and 600 ¹⁴C yr B.P. (Flecha Interval).

While the presence of charcoal in the collection is fortuitous, that situation does not explain why this charcoal exclusively dates to earlier time periods. The dichotomy between the textile-based dates and the charcoal-based dates is puzzling. Bioturbation may explain the mixing of earlier charcoal in more recent deposits, but usually that process is not unidirectional. With point styles of the Flecha Interval found throughout the ash deposit vertically, a reasonable expectation would be that charcoal from that interval could be found in the deeper, earlier levels. That being the case, presumably the younger charcoal would have had an equal possibility of unintentional retention with the sifted seeds. The old wood effect does not appear to be a factor as all dates are consistent with the known regional projectile point and cultural chronology. Further radiocarbon dating of both charcoal and textiles may resolve the conundrum. Although Holden [24] (p. 50) left intact most of the lowermost ash deposit (his third level), excavating that remaining deposit is no longer possible. The cave has now been gutted of all deposits by vandals. Nevertheless, the trees represented by the dated charcoal (Table 3 and Table 5) were growing in the area at that time.

The seeds and charcoal identified (Table 3 and Table 4) expand upon the 14 floral taxa initially identified from Murrah Cave by Holden [24] (

Table 7. Identified botanical taxa of Holden [24] for Murrah Cave.

Family	Taxon	Common Name	Form	* Habitat	Tolerances
Ephedraceae (Mormon tea or Joint-fir Family)	Ephedra spp.	Mormon tea	Shrub	Desert shrub grassland	Heat, cold, drought
Juglandaceae (Walnut Family)	Juglans microcarpa	Texas walnut	Tree	Canyons, along or near watercourses	Heat, cold, drought
Fagaceae (Oak Family)	Quercus	Oak	Shrub to tree	Limestone mesas, canyon, and flats near watercourses	Heat, cold, high drought
Cactaceae (Catus Family)	Opuntia	Prickly pear cactus	Shrub	Limestone hills, mesas, and canyons; desert to semi-desert, grassland to woodland	Heat, drought
Fabaceae (Legume Family)	Senegalia berlandieri	Guajillo	Shrub	Rocky limestone substrates along and near the Rio Grande	Heat, high drought
	Prosopis glandulosa	Honey mesquite	Shrub to small tree	Desert, grassland, mesic mountain	Heat, high drought
	Dermatophyllum secundiflora	Texas mountain laurel	Shrub	Limestone watercourses	Heat, cold, drought
Bignoniaceae (Bignonia Family)	Chilopsis linearis	Desert willow	Tree	Streams, riverbanks	Heat, cold, high drought
Poaceae (Grass Family)	Aristida spp.	Needle grass	Grass	Hillsides, grasslands	Drought
Asparagaceae (Asparagus Family, agave subfamily)	Yucca cf. treculeana	Torrey’s yucca	shrub	Hills, mesas, slopes, desert scrub, and grasslands	Heat, cold, drought
	Agave lechuguilla	Lechuguilla	Shrub-forb	Desert shrub grassland	Heat, cold, drought
Asparagaceae (Asparagus Family, nolinoid subfamily)	Dasylirion texanum	Sotol	Grass-like	Desert flats, grasslands, shrub grassland	Heat, cold
	Nolina texana	Texas bear grass	Grass-like	Hillsides, grasslands, shrublands	Heat, cold, drought
Amaryllidaceae (Amaryllis family)	Allium spp.	Wild onion	Herb	Hills, grasslands, desert, desert mountains	Cold, drought

* Powell and Worthington [3]; Flora of North America series.

). In comparing the recent results (Table 4) with Table 7, about half of the taxa in each table do not overlap. The composite findings, then, for Murrah Cave plant remains consist of 21 taxa (

Table 8. Composite of recent and Holden [24] identified botanical taxa for Murrah Cave.

Family	Taxon	Common Name
Ephedraceae (Mormon tea or Joint-fir Family)	Ephedra spp.	Mormon tea
Juglandaceae (Walnut Family)	Juglans microcarpa	Texas walnut
Fagaceae (Oak Family)	Quercus	Oak
	Quercus cf. fusiformis	Texas live oak
	Quercus-Leucobalanus	White oak group
Cactaceae (Catus Family)	Opuntia	Prickly pear cactus
Ebenaceae (Ebony Family)	Diospyros texana	Texas persimmon
Fabaceae (Legume Family)	Senegalia berlandieri	Guajillo
	Prosopis glandulosa	Honey mesquite
	Dermatophyllum secundiflora	Texas mountain laurel
cf. Rhamnaceae (Buckhorn Family)		Buckhorn
Zygophyllaceae (Creosote-bush or Caltrop Family)	cf. Guaiacum angustifolium	Texas lignum-vitae
Oleaceae (Olive Family)	Fraxinus cf. greggii	Gregg’s ash
Scrophulariaceae (Figwort Family)	Leucophyllum frutescens	Cenizo
Bignoniaceae (Bignonia Family)	Chilopsis linearis	Desert willow
Poaceae (Grass Family)	Aristida spp.	Needle grass
Asparagaceae (Asparagus Family, agave subfamily)	Yucca cf. treculeana	Torrey’s yucca
	Agave lechuguilla	Lechuguilla
Asparagaceae (Asparagus Family, nolinoid subfamily)	Dasylirion texanum	Sotol
	Nolina texana	Texas bear grass
Amaryllidaceae (Amaryllis Family)	Allium spp.	Wild onion

) from 14 families, diversifying the recovered flora. Four of the non-overlapping taxa (Diospyros texana, cf. Guaiacum angustifolium, Fraxinus cf. greggi, Leucophyllum frutescens; 57%) come from the taxonomic identification of the charcoal. These taxa are constituents of the cluster that dates to around 2600–2500 ¹⁴C yr B.P. While three of the taxa are known in the regional record [17,19], Guaiacum angustifolium (Texas lignum-vitae) is new to the Quaternary paleobotanical record for the Lower Pecos Canyonlands as well as the Trans-Pecos in general.

Furthermore, the Murrah Cave record expanded and complemented the rest of the regional record. The composite macrobotanical record from Murrah Cave was compared to other Lower Pecos Canyonlands composite records that, based on published data, appeared to be contemporaneous. The paleobotanical research with Hinds Cave, on the Pecos River downstream from Murrah Cave (Figure 2), was focused on food (that included extensive work with coprolites), fuel, and pollen [17,34,35,36,37,72,73]. Hinds Cave was stratified and has a radiocarbon-dated chronology spanning the Holocene. In identifying the macrobotanical remains, Dering [17] placed them into four chronological periods. The Late Postglacial ranged from 4000 BP to the present and encompassed units 2, 3, and 4 [17] (p. 65). This 4000-year period encompassed several intervals in the now-constructed Lower Pecos Canyonlands cultural chronology.

Hinds Cave unit 2 has a radiocarbon date of 2,280 ¹⁴C yr B.P. [17] (p. 65) that places it in the Cibola-Flanders Sub-interval (~2300 ¹⁴C yr B.P.; [7] (pp. 62, 78). Unit 2 post-dates by 200–300 radiocarbon years the major cluster of Murrah Cave charcoal-based dates (2600–2500 ¹⁴C yr B.P.) and pre-dates its textile-based dates by more than a 1000 years. Nevertheless, the plant taxa recovered in unit 2 [17] (p. 34) (Table 4) are the closest age comparison with the results from Murrah Cave. The unit 2 flora consists of 38 taxa. In comparison with the Murrah Cave taxa (Table 8), seven Murrah Cave taxa are not found in the macrobotanical remains of unit 2. Of these seven, most taxa reflect the xeric uplands of desert shrub grassland (Ephedra, Aristida, Leucophyllum frutescens, Yucca cf. treculeana, Nolina texana) while the remaining taxa signal the more mesic waterways of the canyonlands (cf. Guaiacum angustifolium, Chilopsis linearis). Dering [17] (pp. 65, 66) notes that the vegetation during his Postglacial period reflected the extant local flora and remained stable throughout that 4,000-year period. The one exception is the possible shift on the landscape of increased sotol (Dasylirion texanum) at the expense of lechuguilla (Agave lechuguilla). Although the Murrah Cave data cannot address this issue, the Murrah Cave macrobotanical results expand and enhance the findings of Hinds Cave unit 2. The local flora of the Lower Pecos area based on Hinds Cave unit 2 and Murrah Cave is typical of the Lower Pecos Canyonlands today.

Eagle Nest Canyon is west of the confluence of the Pecos and Rio Grande rivers in a reentrant box canyon along the Rio Grande River (Figure 2). The current systematic paleobotanical research in Eagle Nest Canyon is focused on food, fuel, and fibrous construction materials [19]. Research at the various sites within the canyon has resulted in an extensive compilation of identified taxa encompassing the last 11,000 ¹⁴C yr B.P. Nevertheless, the plants identified in Murrah Cave (Table 8) add six taxa to that list. Of these, only one (Aristida) reflects the xeric uplands while the others (Quercus cf. fusiformis, Senegalia berlandieri, Chilopsis linearis, cf. Guaiacum angustifolium, Fraxinus cf. greggii) are found primarily along the more mesic waterways of the canyonlands. Three of these waterway trees (Quercus cf. fusiformis, cf. Guaiacum angustifolium, Fraxinus cf. greggii) can occur in the brushlands and mesas of the uplands particularly in shrub form [3].

At Skiles Shelter, within Eagle Nest Canyon, the dominant occupation is radiocarbon dated to the period 1000–350 ¹⁴C yr B.P. [66,74]. This time span falls primarily within the cultural Flecha Interval and the major occupation of Murrah Cave. In comparing the taxa between the two sites, Murrah Cave contributes 12 taxa beyond what was identified at Skiles Shelter (the six from the Eagle Nest Canyon composite list and an additional six more not present specifically at Skiles Shelter). This represents a significant expansion for the time period. Most of the taxa reflect the more mesic waterways. In comparing the taxa recovered from Hinds Cave unit 2, Murrah Cave, and Skiles Shelter, the greatest broadening is in the diversity of tree taxa growing along the canyonlands waterways. That increased diversity is based on the Murrah Cave record. Again, the Murrah Cave macrobotanical record expands and enhances the records at Hinds Cave unit 2 and Eagle Nest Canyon/Skiles Shelter.

The Murrah Cave macrobotanical record reflects taxa found in sites throughout the Lower Pecos Canyonlands (Figure 2). These records indicate a past flora similar to the extant flora existing today in the non-mountainous areas of the Trans-Pecos, specifically the Pecos Plains and Stockton Plateau (Figure 1) [3,5]. Although vegetational distribution and abundance may differ, the same plants are found throughout the uplands and waterways. In this situation, what is local and what is regional can be blurred. Local landscape harvested by people, however, is a different matter. Although animals, particularly packrats, may have contributed to the Murrah Cave macrobotanical remains, they most likely would have sampled the vegetation in the immediate area of the cave.

Both environmental and cultural aspects influence the macrobotanical remains recovered from archaeological sites. Unlike pollen, macrobotanical remains usually come from the vicinity where they were found and reflect the local vegetation. Humans, however, are selective in what they use from the available plant resources on the landscape. This selectivity provides an incomplete record of the vegetation record, furthered biased by preservation factors and excavation methodology and techniques. Macrobotanical records, however, from contemporaneous sites across the landscape can create a composite that helps flesh out the local vegetation record.

Defining local is critical to determining the extent of the landscape encompassed. Dering [17] (p. 44) estimates the local area for Hinds Cave at a ~35 km (21.7 mi) radius based on daily home range ethnographic data [75,76]. Using that estimate for Murrah Cave (Figure 10), the projected local area, as might be expected, encompasses both the uplands and the riparian lower Pecos River. The same situation occurs with Hinds Cave unit 2 and Eagle Nest Canyon/Skiles Shelter projections (Figure 10). More important is the overlapping radii of the three projections. These intersections provide credence to an expanded view of the local vegetation using a composite record. They construct and form a lens in which to view a piece of the landscape similar to a catchment area.

Wells [77] (p. 82) notes that much of the current landscape of the Chihuahuan Desert is a Holocene occurrence with its vegetation pattern transitioning in the early Holocene with increased aridity. Larrea (creosote bush) is an extreme xerophyte that enters the Chihuahuan Desert post-11,500 ¹⁴C yr B.P. It dominates the lowest and most arid sections of the modern Chihuahuan Desert [76]. Larrea occurs in the Lower Pecos Canyonlands record around 9000 ¹⁴C yr B.P. at Baker Cave [18] (p. 111). The canyonlands, then, are transitioning to a semi-arid environment and desert vegetation by this time.

Van Devender [78,79], however, places the transition for the northern Chihuahuan Desert post-8000 ¹⁴C yr B.P. based on dated packrat middens in far northwestern Trans-Pecos (Hueco Mountains, Hudspeth County; Figure 1). On the other hand, Larrea is part of the diet of the Shasta ground sloth (Nothrotheriops shastensis) found in a cave in the more central Trans-Pecos Sierra Vieja (Presidio County; Figure 1). The presence of Larrea is based on analysis of dung dated to ~11,000 ¹⁴C yr B.P. [80]. The dated Larrea record from Baker Cave [18] is in far northeastern Trans-Pecos along the Devil’s River (Val Verde County; Figure 1 and Figure 2). These study locations are hundreds of miles apart at very different elevations. With the size and complexity of the northern Chihuahuan Desert/Trans-Pecos region, that transition to arid, desert conditions throughout the region may well have been time-transgressive.

Although on a trajectory of increased aridity through time, two short-term periods of mesic conditions are indicated by the presence of modern bison (Bison bison) and expansion of the grasslands [7]. These brief late Holocene periods of increased moisture most likely caused vegetation distributional shifts across the landscape. They, however, did not fundamentally alter the desert vegetation community. Hinds Cave unit 2, dated at 2280 ¹⁴C yr B.P., is slightly younger than the first mesic period. Bison have not been reported for unit 2 but bighorn sheep (Ovis canadensis) occur at this time [73]. While bighorn sheep occupy the Trans-Pecos mountain ranges today, they are not known to inhabit the canyonlands [6]. Bison occur in the Murrah Cave faunal remains alongside typical Lower Pecos Canyonlands flora. While their presence may indicate either mesic period based on radiocarbon dates, the Murrah Cave bison most likely reflect the more recent mesic period that encompasses the major cultural occupation of the cave.

6. Conclusions

The Lower Pecos Canyonlands are within the northeastern area of the modern Chihuahuan Desert. Murrah Cave is located within a canyon cliff along the lower Pecos River. Radiocarbon dating (Table 5) provides the first radiometric evidence of the age of the archaeological materials from Murrah Cave. Radiocarbon dates on textiles indicate a major cultural occupation dating between 1000 and 600 ¹⁴C yr B.P. within the Flecha Interval. Charcoal-based radiocarbon dates cluster around 2600–2500 ¹⁴C yr B.P. All of the available age data indicate a late Holocene age for Murrah Cave.

Although a prime wintering area for birds and major migration pathway [53], little is known of the Trans-Pecos late Quaternary avian fossil record. Pied-billed Grebes occur year-round today in the Trans-Pecos [55]. Yet, its late Holocene presence in Murrah Cave is the first occurrence in the Trans-Pecos Quaternary fossil record.

Understanding the impacts of Quaternary changes on North American avifauna has important implications for understanding the patterns and processes of Pleistocene and Holocene faunal change as well as the impacts of future climatic change. The limited record of birds in the Quaternary may be attributable to a lack of expertise and interest in avian osteology, limited comparative skeletal material, and what screen-washing methodology [31,81,82,83] is applied if any. Despite those challenges, avian samples exist in collections. Unidentified avian skeletal remains from the Lower Pecos Canyonlands, e.g., [14,16,21,84,85], indicate that samples are already present in institutional collections. The potential exists for some of these samples to contribute significantly to the late Quaternary fossil record and climatic impacts. The Murrah Cave coracoid is one example of such existing material.

Macrobotanical results from Murrah Cave have expanded and enhanced the substantial record of late Quaternary vegetation for the canyonlands, e.g., [17,18,19,36]. All of the Murrah Cave plant taxa are part of the current northern Chihuahuan Desert vegetation community [3]. That community has been developing for at least the last 9000 ¹⁴C yr B.P. in the Lower Pecos Canyonlands. Two late Holocene short-term mesic periods modulate the trajectory of increased aridity. Although Murrah Cave falls within one of those periods, its macrobotanical record is typical of the Lower Pecos Canyonlands today. Identified taxa reflect the desert shrub grassland of the uplands and the riparian community of the Pecos River. The Murrah Cave record is dominated by drought-tolerant taxa. Distributional shifts on the landscape, then, are most likely what occurred during the mesic periods, such as the expansion of the grassland rather than range changes for plant taxa. These findings underscore the importance of maintaining and revisiting old collections for contributions they can still make today.