A review of the piciform avifauna from the upper Pleistocene asphalt deposits of Rancho La Brea, Los Angeles, California, reveals that it comprises at least six species in five genera. We describe a new genus and species, Breacopus garretti, for the largest woodpecker, which was similar in size to the largest living North American species, Dryocopus pileatus. We recognise a new genus and species, Bitumenpicus minimus, for the smallest woodpecker in the palaeoavifauna of Rancho La Brea. We also recognise a new species of Melanerpes, M. shawi. The most common species present in the asphalt deposits is the Northern Flicker, Colaptes auratus, which is predictable because of its ground-foraging habits, which would bring it into contact with the surficial seeps of petroleum more often than those piciforms preferring an arboreal habitat. Habits of the extant species from Rancho La Brea suggest a primarily open environment, with the largest species suggesting the presence of at least scattered large trees. The piciform palaeoavifauna provides support for the hypothesis that southwestern California was a “biogeographic island,” or a region where the insular nature of the habitat promoted speciation during the late Pleistocene.
The fossiliferous asphalt deposits of Rancho La Brea, Los Angeles, California, are well known for the large quantities of late Pleistocene fossils they have produced. For birds, there are an estimated 250,000 specimens in the Rancho La Brea collections of the Natural History Museum of Los Angeles County (LACM). To date, 140 avian species have been recognised from the Rancho La Brea deposits, including 11 described extinct genera and 22 described extinct species (e.g. Howard 1962; Campbell 1995, 2002; Bochenski and Campbell 2006; Campbell and Bochenski 2010, 2013). Additional extinct species have been identified, but not yet described.
This report describes the piciform palaeoavifauna from the asphalt deposits. Woodpeckers are relatively rare in the fossil record, but they occur in fair numbers in the large collections from Rancho La Brea. The first report of piciforms from Rancho La Brea was by Miller (1929), who mentioned the presence of Colaptes auratus (Linnaeus, 1758), the Northern Flicker, and Melanerpes (“Asymdesmus”) formicivorus (Swainson, 1827), the Acorn Woodpecker, in the collections from Rancho La Brea housed in the University of California, Museum of Paleontology (UCMP). Later, Miller (1937) mentioned two other piciforms in that collection: Melanerpes lewis (Gray, 1849), Lewis’ Woodpecker, and what he referred to as the Pileated Woodpecker, Dryocopus pileatus (Linnaeus, 1758), the largest living North American woodpecker. Of the latter, he wrote, “… I chanced upon the unmistakable bones of a Pileated Woodpecker …” (Miller 1937:249), although he did not say which bones of the skeleton he saw. Unfortunately, a thorough search of the Rancho La Brea collections of the UCMP failed to locate the large woodpecker specimens in question, although we did find the specimens he had identified as species of Colaptes Vigors, 1825 and Melanerpes Swainson, 1837.
In her review of the avian assemblages of the various asphalt deposits at Rancho La Brea, referred to as “pits” when excavated, Howard (1962) listed five species of woodpeckers, with another two or three species possible based on unidentified specimens. She cited a total of 32 individuals based on 92 catalogued specimens (17 unidentified to species). An unknown number of uncatalogued specimens from Pit A, also known as Pit 97, were also included in her tabulations. The named species included Colaptes auratus (“cafer”), Dryocopus pileatus, Melanerpes (“Asymdesmus”) lewis, Sphyrapicus sp., and Dryobates sp. We were unable to locate the specimen(s) Howard (1962) referred to Dryobates sp. The specimen she referred to Dryocopus pileatus was a nearly complete carpometacarpus. In the course of our review of the palaeoavifauna from Rancho La Brea, we identified a second large woodpecker specimen, a partial tibiotarsus. Although this specimen was uncatalogued, Howard had left a note with it suggesting that it might also be from D. pileatus. However, in our evaluation of these two large specimens, we found sufficient differences between them and the corresponding bones of D. pileatus to warrant the placement of the former in a new genus and species.
Prior to our review, there were 92 specimens identified and catalogued as woodpeckers. Our review of the entire Rancho La Brea collection, which included several sub-collections uncatalogued or not available at the time of Howard’s publication, resulted in the recognition of 384 additional woodpecker specimens. The total number of catalogued woodpecker specimens from Rancho La Brea in the collections of LACM now stands at 476, representing at least six species, three of which are extinct.
Materials and methods
The largest fossil specimens were compared in detail to 17 comparative specimens of Dryocopus pileatus (9♂, 8♀), the Pileated Woodpecker; to one specimen of D. lineatus (Linnaeus, 1766) (1♂), the Lineated Woodpecker of Central and South America; to D. martius (Linnaeus, 1758) (3?) from Europe, and one specimen each of three species of large woodpeckers of the genus Campephilus Gray, 1840: C. rubricollis (Boddaert, 1783) (1♀), C. melanoleucos (Gmelin, 1788) (1♂), and C. gayaquilensis (Lesson, 1845) (1?).
Modern comparative material consulted for identification of the smaller specimens included: Colaptes auratus (7♀, 10♂, 2?); Dryobates albolarvatus (Cassin, 1850) (2♀, 2♂); D. nuttallii (Gambel, 1843) (2♀, 2♂); D. pubescens (Linnaeus, 1766) (1♀, 1♂, 1?); D. scalaris (Wagler, 1829) (1♀, 1♂); D. villosus (Linnaeus, 1766) (1♀, 3♂); Melanerpes formicivorus; M. lewis (4♂, 1?); M. uropygialis (Baird, 1854) (1♀, 1♂); Sphyrapicus nuchalis (Baird, 1858) (1♀, 2♂); S. ruber (Gmelin, 1788) (7♀, 1♂); and S. thyroideus (Cassin, 1852) (2♀). For the genera of woodpeckers discussed herein, we found them to be readily distinguished one from the other based on osteological characters; size is not a defining character for genera. Within genera, the size of individuals of a species is often a distinguishing character, although unique osteological characters are the ultimate test of a palaeospecies. Detailed locality data for each specimen can be found in the master catalogue for Rancho La Brea birds.
Measurements were taken using digital callipers accurate to 0.01 mm, captured directly to computer, and rounded to the nearest 0.1 mm. Most measurements taken are illustrated in Campbell and Bochenski (2010). Selected ratios were computed and scatter diagrams of the ratios were prepared. All specimens, fossil and Recent, were coated with ammonium chloride for photography; photographs by KEC. The small size of most of the specimens made obtaining precise comparative measurements and excellent photographs difficult. Osteological terminology is primarily from Baumel and Witmer (1993), although we use the traditional anterior and posterior as in Howard (1980) in place of the confusing cranial and caudal.
Class Aves Linnaeus, 1758
Order Piciformes Meyer and Wolf, 1810
Family Picidae Vigors, 1825
Genus Breacopus gen. nov.
Type species: Breacopus garretti sp. nov., monotypic.
Differential diagnosis: Holotypic carpometacarpus differs from that of the Recent genera Dryocopus Boie, 1826 and Campephilus, which include the largest woodpeckers in the world, by having (1) Trochlea carpalis with slightly abraded distal portion of dorsal rim not deeply undercut on ventral side, thereby giving a gradual transition, in proximal view, between posterior ends of dorsal and ventral trochlear rims (dorsal rim deeply undercut, giving a notched appearance in proximal view in Dryocopus and Campephilus); (2) Trochlea carpalis with dorsal rim, in dorsal view, broader at base and more rounded proximally than in Dryocopus and Campephilus; (3) attachment site for Lig. ulnocarpo-metacarpale ventrale deep, with distal rim more prominent, curving strongly posteriad distally, and ending well proximal to Spatium intermetacarpale (in Dryocopus and Campephilus the ridge curves less distally and ends closer to the Spatium intermetacarpale); (4) Synostosis metacarpalis proximalis extends distinctly farther distad (i.e. is longer) than in Dryocopus and Campephilus (Fig. 1); (5) Facies articularis digitalis major, in distal view, less pronounced ventrad, which results in a dorsoventrally relatively narrower Facies articularis digitalis major than in Dryocopus and Campephilus; and (6) Spatium intermetacarpale distinctly broader for length, of more uniform width, with broad U-shaped distal end, in ventral view (narrower for length in Dryocopus and Campephilus, with distal end a narrower U-shape).
Although the shape of the Processus intermetacarpalis appears distinctly different in Fig. 1, in dorsal view, some of this difference is a result of abrasion of its posteroproximal edge. In ventral view, the ventral aspect of the Spatium intermetacarpale is clearly broader for length.
Etymology: Brea, after its occurrence in the asphalt deposits of Rancho La Brea; copus, after Greek kopus, “beating.” Gender, masculine.
Breacopus garretti sp. nov.
Holotype: Carpometacarpus. Nearly complete, left, lacking distal portion of Os metacarpale minus, LACM RLB H3605 (Fig. 1).
Type horizon: Rancho La Brea asphalt deposits; upper Pleistocene.
Type locality: Pit 16, Rancho La Brea, Los Angeles, California, USA.
Referred material: Distal left tibiotarsus with shaft (proximal end missing), LACM RLB L776, Pit A of Bliss 29, Rancho La Brea asphalt deposits, Los Angeles, California, USA.
Dfferential diagnosis: As for genus.
Measurements (mm): [Means and standard deviations of 17 Recent comparative specimens of Dryocopus pileatus in parentheses.] Holotypic carpometacarpus: total length, 32.2 (31.3 ± 1.05); proximal width, 9.5 (9.3 ± 0.44); proximal depth, 4.5 (4.7 ± 0.26); width of carpometacarpus, measured at its mid-length, 6.4 (5.9 ± 0.38); width of Spatium intermetacarpale, measured at its mid-length, 4.4 (3.4 ± 0.34); depth of Os metacarpale majus, measured at its mid-length, 3.5 (3.1 ± 0.21); distal width, 8.1 (7.7 ± 0.49); distal depth of Facies articularis digiti major, 3.0 (2.9 ± 0.16). Tibiotarsus: shaft width, measured just proximal to Tuberositas retinaculi extensoris medialis, 3.7 (3.9 ± 0.48); shaft depth, measured just proximal to Tuberositas retinaculi extensoris medialis, 3.1 (3.4 ± 0.18); distal width, 6.4 (6.5 ± 0.34).
Etymology: We name this species for Kimball L. Garrett, Collections Manager, Department of Ornithology, Natural History Museum of Los Angeles County, in recognition of his decades of service building the modern avian comparative osteology collection at the Museum, without which the identification of many taxa from the Rancho La Brea deposits would not be possible.
Description: The holotypic carpometacarpus resembles that of species of the order Piciformes in overall morphology and derived features, in particular by having (1) a well-developed Processus intermetacarpalis that joins with the Os metacarpale minus; (2) Os metacarpale minus with a broad distal end that protrudes far distad (although not as far as in Passeriformes); (3) a fossa in the ventral surface of the Synostosis metacarpalis distalis; and (4) Facies articularis digitalis major with a very large protuberance in its posterior part that projects distad.
The carpometacarpus of Breacopus garretti superficially resembles that of the Recent North American Dryocopus pileatus (Figs. 1 and 2). However, it differs from the Recent species of Dryocopus and Campephilus by having those characters listed in the Diagnosis of the genus and a combination of other features that include the following: (1) Trochlea carpalis, despite having both dorsal and ventral rims slightly abraded, are more rounded proximally, in dorsal and ventral views, respectively (ventral rim is more angular proximally and dorsal rim is more flattened proximally in D. pileatus and D. lineatus; in species of Campephilus the dorsal rim is relatively narrower anteroposteriorly); (2) Fossa infratrochlealis broader and deeper than in D. pileatus, D. lineatus, C. melanoleucos and C. gayaquilensis, but not much deeper than in the much smaller C. rubricollis; (3) the area between Fossa infratrochlealis and the articular facet for the Lig. ulnocarpo-metacarpale ventrale is moderately pronounced and, in proximal view, it is relatively flattened (it bulges ventrad in proximal view in D. pileatus, C. gayaquilensis, and C. rubricollis, but not as much in D. lineatus and C. melanoleucos); (4) Processus extensorius, in dorsal view, is relatively wider proximodistally, more robust, and projects less proximad than in D. pileatus, D. lineatus, C. rubricollis, C. melanoleucos, and C. gayaquilensis; (5) Os metacarpale majus, in anterior view, with a relatively moderately deep, elongated depression just distal to Processus extensorius (the depression is shallower in D. pileatus, D. lineatus, C. rubricollis, C. melanoleucos, and C. gayaquilensis).
The tibiotarsus referred to Breacopus garretti (Fig. 3) is badly abraded, but several characters stand out. It differs from Recent species of Dryocopus and Campephilus by having (1) Sulcus extensorius broader than in D. pileatus, D. lineatus, C. rubricollis, C. melanoleucos, and C. gayaquilensis); (2) Pons supratendineus narrower proximodistally than in some D. pileatus specimens and D. lineatus, but broader proximodistally than in Campephilus (C. rubricollis, C. melanoleucos, and C. gayaquilensis); (3) Canalis extensorius with distal opening large and more rounded (smaller and elongated mediolaterally in D. pileatus, D. lineatus, C. rubricollis, C. melanoleucos, and C. gayaquilensis); (4) Condylus lateralis less rounded and less pronounced anteriad, joining gradually with shaft, in lateral view (more rounded and joins shaft more abruptly in D. pileatus, D. lineatus, C. rubricollis, C. melanoleucos, and C. gayaquilensis); (5) Tuberositas retinaculi extensoris medialis much longer proximodistally and positioned more distal on the shaft (shorter proximodistally in all Dryocopus and Campephilus species examined; positioned more proximal on the shaft in D. pileatus and D. lineatus, more distal on shaft in Campephilus); (6) Tuberculum retinaculi m. fibularis broken away, but remnants of base suggest it was smaller than in Dryocopus and Campephilus.
Comment: Breacopus garretti is the second large woodpecker to be described from the upper Pleistocene of North America, Campephilus dalquesti Brodkorb, 1971 being the first. Unfortunately, C. dalquesti is known only from a fragmentary distal tarsometatarsus, so it is not possible to compare it directly to the two specimens of B. garretti. However, morphologically, B. garretti is closer to Dryocopus than Campephilus, so if the assignment to genus of C. dalquesti is correct, B. garretti is unlikely to be closely related to C. dalquesti.
Although the specimens were not compared to comparable bones of the Ivory-billed Woodpecker, Campephilus principalis (Linnaeus, 1758), the largest known North American woodpecker, the generic differences noted between Breacopus and the species of Campephilus available are sufficient to discount the possibility that Breacopus represents the Ivory-billed Woodpecker. Further, the preference of the Ivory-billed Woodpecker for old-growth forest stands in the southeastern United States and northeastern Mexico would make it unlikely that it would appear in semi-arid southwestern California.
Specimens identified as possibly of the Pileated Woodpecker were reported from cave deposits in the eastern United States by Shufeldt (1897) and Goslin (1955). The former specimen was a well-worn ulna, and the latter reference did not indicate which bones were seen.
Genus Melanerpes Swainson, 1837
Comment: The genus Melanerpes is represented in North America by six species: M. lewis (Lewis’ Woodpecker), M. erythrocephalus (Linnaeus, 1758) (Red-headed Woodpecker), M. formicivorus (Acorn Woodpecker), M. uropygialis (Gila Woodpecker), M. aurifrons (Wagler, 1829) (Golden-fronted Woodpecker), and M. carolinus (Linnaeus, 1758) (Red-bellied Woodpecker). Of these, only M. lewis, M. formicivorus, and M. uropygialis have a modern range that includes California. Of the latter three, M. lewis is by far the largest and its skeletal elements can be separated from the other two on the basis of size. Melanerpes lewis also is larger than the other three North American species of the genus not occurring in California today. Melanerpes lewis is fairly common in the Rancho La Brea collections, being represented by 92 specimens from at least 18 individuals. We did not record any specimens of the smaller species of Melanerpes from the Rancho La Brea collections, although specimens of smaller sized species of other genera were found. Also, Miller (1929) did report the presence of M. formicivorus from Rancho La Brea in the UCMP collections, but we could not confirm its presence. In addition to the living M. lewis, we found a number of specimens of an extinct species referable to the genus Melanerpes and comparable in size to M. lewis, which we describe here.
Melanerpes shawi sp. nov.
Holotype: Tarsometatarsus. Complete, right. LACM RLB L530.
Type horizon: Rancho La Brea asphalt deposits; upper Pleistocene.
Type locality: Pit A of Bliss 29, Rancho La Brea, Los Angeles, California USA.
Differential diagnosis: The holotypic tarsometatarsus of M. shawi is distinguished from that of M. lewis, whose size range it falls within, by having (1) Eminentia intercondylaris taller, more slender, with smaller base, in anterior view; (2) Cotyla lateralis with posterolateral extension shorter, in proximal view; (3) Hypotarsus extending less laterad, in proximal view; (4) Trochlea metatarsi IV shorter anteroposteriorly and lacking a distal projection; (5) Trochlea accessoria with anterior edge partly hidden behind Trochlea metatarsi III, in anterior view (anterior edge clearly visible between Trochlea metatarsi III and IV in M. lewis).
Etymology: We name this species for Christopher Shaw, former Collections Manager and volunteer at the Rancho La Brea tar pits, to honour his many decades of service and dedication to the preservation and study of the palaeontological resources of Rancho La Brea.
Referred material: [All catalogue numbers preceded by acronym LACM RLB.] Complete right scapula, L707; humeral end left coracoid, L696; complete left humerus, F9756; complete left (2) and right ulnae, G8812, L627, G8821, respectively; proximal right ulna, R14745; distal right radius, R35971; complete right and left carpometacarpi, L602, L589, respectively; complete left femur, L755; almost complete right tibiotarsus, L719; complete right (2) and left tarsometatarsi, G5656, P23–7332, and R12358, respectively; proximal right and left tarsometatarsi, L771 and R14313, respectively. The 18 specimens give a minimum number of four individuals.
Measurements (mm): (Except for holotypic tarsometatarsus, only total length of complete specimens is given.) [Means and standard deviations of 6 Recent comparative specimens of Melanerpes lewis in parentheses.] (Holotypic tarsometatarsus length, 26.0, proximal width, 4.9, distal width, 4.8, mid-shaft width, 1.7); humerus, 38.6; ulna (3 specimens), 43.6, 48.3, 49.9 (39.0 ± 1.23); carpometacarpus (2 specimens), 22.7, 23.3 (23.1 ± 0.36); femur, 25.4 (26.2 ± 0.56); tibiotarsus, 38.0 (40.2 ± 1.01); tarsometatarsus (3 specimens), 24.4, 25.1, 25.4 (25.8 ± 0.66).
Description: The scapula of Melanerpes shawi differs from that of M. lewis in having (1) Acromion more slender, with elongated, slender curvature in dorsolateral view (lacks curvature, more bulky in M. lewis).
The coracoid of Melanerpes shawi differs from that of M. lewis in having (1) Processus acrocoracoideus shorter, in dorsal view; (2) Facies articularis humeralis longer, in dorsal view; and (3) attachment of M. biceps brachii nearly overlapping dorsal end of Facies articularis humeralis (does not come close to overlapping in M. lewis).
The humerus of Melanerpes shawi (Fig. 5) differs from that of M. lewis by having (1) Caput humeri less rounded proximally, in anterior view; (2) Caput humeri extends farther distad, in posterior view; (3) Incisura capitis shallower, in anterior view; (4) Crista bicipitalis less pronounced ventrad; (5) Crista deltopectoralis flaring less dorsad in posterior view; (6) Condylus ventralis less rounded, extending less distad; (7) Condylus dorsalis smaller overall, not reaching as far proximad, relative to proximal end of attachment of anterior articular ligament; (8) Processus flexorius not projecting as far distad, less rounded, in anterior view.
The ulna of Melanerpes shawi differs from that of M. lewis in having (1) Cotyla dorsalis smaller, less concave, with more rounded rim; (2) Tuberculum Lig. collateralis ventralis small, rounded projection (larger, more shelf-like in M. lewis); (3) Depressio M. brachialis not as deep or well-marked; (4) Tuberculum carpale shorter, not projecting as far anteriad.
The radius of Melanerpes shawi differs from that of M. lewis in having (1) Sulcus tendinous more distinct, well defined on both sides (in M. lewis, clearly defined from one side); (2) distal end broader, with deeper Depressio ulnaris.
The carpometacarpus of Melanerpes shawi (Fig. 6) differs from that of M. lewis in having (1) Os metacarpale majus more robust, in ventral view, best seen in distal half of bone; (2) Trochlea carpalis with dorsal rim broader, in dorsal view, and united with ventral rim of trochlea by a slight ridge posteriorly (dorsal and ventral portions separated by depression in M. lewis); (3) Spatium intermetacarpale wider, more open proximally; (4) Processus intermetacarpalis positioned more distally; (5) Synostosis metacarpale distalis more robust; (6) Facies articularis digitoris major bulging slightly dorsad and ventrad, in distal view (bulging more in both directions in M. lewis).
The femur of Melanerpes shawi (Fig. 7) differs from that of M. lewis by having (1) Facies articularis antitrochanterica not expanded posteriad, in proximal and lateral view; (2) neck shorter; (3) Facies lateralis of Corpus femoris not expanded anteriad in its proximal part, in lateral view; (4) Trochlea fibularis less expanded posterolaterad, in distal view.
The tibiotarsus of Melanerpes shawi differs from that of M. lewis by having (1) Crista cnemialis lateralis extending straight laterad, in proximal view (flaring somewhat anteriad in M. lewis); (2) Condylus medialis projecting less anteriad, in medial view; (3) Condylus lateralis with anterolateral part expanding less laterad, in distal view; (4) Incisura intercondylaris narrower mediolaterally (this character corresponds to the taller and more slender Eminentia intercondylaris in the tarsometatarsus of M. shawi).
Comment: The characters distinguishing Melanerpes shawi apply equally well to both Recent and fossil specimens of M. lewis.
Melanerpes lewis (Gray, 1849)
Referred material: Melanerpes lewis is represented by 89 specimens, representing a minimum of 19 individuals. Online Resource 1 presents a complete listing of all specimens referred to this taxon. In addition, four other specimens were referred to Melanerpes sp. cf. M. lewis.
Small woodpeckers of Rancho La Brea
There are two modern genera comprising very small woodpeckers in North America: Dryobates and Sphyrapicus Baird, 1858. The former has nine species, three of which include southwestern California in their modern range and could be expected to have occurred in the Los Angeles Basin in the Pleistocene: D. villosus, D pubescens, and D. nuttallii. Dryobates villosus is the largest of the three, and D. pubescens is the smallest North American woodpecker. Dryobates nuttallii is separable from both by size. Howard (1962) listed one individual of Dryobates sp., but no specimen of that genus was listed in the catalogue. We did not find any specimens that we could refer to Dryobates.
The genus Sphyrapicus comprises four species, although there is some disagreement as to the validity of each because three of the four are said to interbreed (Johnson and Johnson 1985; Seneviratne et al. 2016, and papers cited therein). Only one of the four, S. ruber, includes southwestern California in its modern range. Brodkorb (1971a, b) listed S. varius as being recorded from Rancho La Brea, citing Howard (1962), although she listed only Sphyrapicus sp. in her report. Specimens of S. ruber are slightly larger than those of D. nuttallii. We present characters distinguishing the two species when appropriate.
We describe a new genus and species of a third small woodpecker similar in size to Dryobates nuttallii on the basis of osteological characters.
Genus Sphyrapicus Baird, 1858
Sphyrapicus ruber (Gmelin, 1788)
Referred material: We identified 26 specimens, representing a minimum of four individuals, as Sphyrapicus ruber. A list of the referred specimens is presented in Online Resource 1. Howard (1962) listed one individual as Sphyrapicus sp. in her report. Three specimens of Sphyrapicus sp. were previously recorded in the catalogue (LACM RLB F9985, G97 and G5663), but only the first two of the three could be located. We identified F9985 as S. ruber, but we determined that G97 could not be positively identified to species.
Description: The scapulae of Sphyrapicus ruber differ from those of Dryobates nuttallii by having (1) Acromion terminating in broad, not narrow, rounded point, in medial view; and (2) Tuberculum coracoideum broad-based, larger, not as pointed at terminus.
The humeri of Sphyrapicus ruber differ from those of Dryobates nuttallii by having (1) Crista bicipitalis not projecting as far ventrad, with a more rounded terminus, and with ventral terminus not extending as far distad, in posterior view; (2) Tuberculum ventrale with broader base, tapering more quickly to terminus, in ventral view; (3) Caput humeri projecting farther proximad, with Incisura capitis positioned farther from proximal terminus, in anterior view; (4) Tuberculum dorsale less pronounced, in posterior view; (5) Crista pectoralis not flaring as much dorsad, in posterior view; (6) Fossa M. brachialis deeper, with more prominent ventral bordering ridge; and (7) Processus flexorius not extending as far distad beyond Condylus ventralis, in anterior view. Humeri of S. ruber are slightly larger than those of D. nuttallii, smaller than those of D. villosus; more robust than both.
The tibiotarsi of S. ruber differs from those of D. nuttallii by having (1) Crista cnemialis not projecting as far laterad; and (2) Crista patellaris not extending as far proximad.
The tarsometatarsi of S. ruber differ from those of D. nuttallii by (1) being larger; (2) proximal end with hypotarsal complex curving less laterad; (3) Crista lateralis hypotarsi broader, protruding less posteriad; (4) Sulcus hypotarsi broader; (5) Trochlea metatarsi II not projecting as far posteriad or mediad; and (6) Trochlea metatarsi IV not extending as far laterad.
Comment: Of the four species of Sphyrapicus that occur in North America, the one species most likely to have occurred in southern California in the Pleistocene, and the only one to inhabit the region today, is Sphyrapicus ruber.
Genus Colaptes Vigors, 1825
Colaptes auratus (Linnaeus, 1758)
Referred material: Howard (1962) referred to Colaptes auratus 18 individuals based on 60 catalogued specimens and an unknown number of uncatalogued specimens. We add to that number 257 additional specimens for a total of 317 specimens representing a minimum of 38 individuals. The small increase in individuals, as opposed to the large increase in specimens, is attributed to the readily recognisable, based on morphology, but uncatalogued, tarsometatarsi from Pit A being included in Howard’s tabulation, whereas the remainder of the elements from that highly productive site were not identified to species. In addition to the specimens identified to species, four carpometacarpi were referred to cf. Colaptes sp. No morphological characters separated the fossil specimens of C. auratus from Recent comparative material of C. auratus. For a complete listing of all specimens of Colaptes auratus, see Online Resource 1.
Description: Colaptes auratus is the largest of the small woodpeckers from Rancho La Brea, and it is easily distinguished based on size.
Genus Bitumenpicus gen. nov.
Type species: Bitumenpicus minimus sp. nov., monotypic.
Differential diagnosis: The holotypic tarsometatarsus differs from that of species of Sphyrapicus and Dryobates by having (1) Facies dorsalis flatter and relatively wider; (2) Shaft more robust (Figs. 8 and 9), with medial side straighter, less curving leading to Trochlea metatarsi II; (3) Eminentia intercondylaris with lateral side only slightly curved, in posterior view; (4) Crista lateralis hypotarsi with posterior terminus not curving mediad (shorter and much wider in Sphyrapicus); (5) Sulcus hypotarsi broader, in proximal view; (6) Trochlea metatarsi II with slightly abraded tip, but directed more mediad than posteriad, not projecting distad beyond medial rim of Trochlea metatarsi III; (7) Trochlea metatarsi IV with posterior portion only slightly extending laterad beyond base, with medial edge closer to lateral edge of Trochlea III; and (8) Trochlea accessoria not extending as far distad, in anterior view, and with more slender base.
Etymology: Bitumenpicus, from Latin bitumen, asphalt; picus, woodpecker; in reference to the deposits in which it was discovered. Gender, masculine.
Bitumenpicus minimus sp. nov.
Diagnosis: As for genus.
Type horizon: Rancho La Brea asphalt deposits; upper Pleistocene.
Type locality: Pit A of Bliss 29, Rancho La Brea asphalt deposits, Los Angeles, California, USA.
Etymology: minimus, Latin, in reference to it being the smallest woodpecker known from Rancho La Brea.
Referred material: [All catalogue numbers preceded by acronym LACM RLB.] Complete left humerus, L575, proximal end right ulna, L674; distal end left ulna, L679; complete left radius, L769; one proximal right and one distal left radius, L770, PMS3725, respectively; right carpometacarpus, L615. All referred specimens are from Pit A of Bliss 29 of the Rancho La Brea asphalt deposits. The eight specimens represent a minimum of one individual.
Measurements (mm): [Arithmetic means and standard deviations of 4–11 Recent comparative specimens of Dryobates nuttallii, depending on the element, in parentheses]: Holotypic tarsometatarsus, total length 17.9 (18.7 ± 0.62); width at mid-shaft, 1.5 (1.2 ± 0.07). Humerus length, 26.2 (25.2 ± 0.49); radius length, 26.1 (27.4 ± 0.32); carpometacarpus length, 13.4 (13.6 ± 0.56).
Description: The holotypic tarsometatarsus resembles species of the order Piciformes in overall morphology and derived features, in particular by having a Trochlea accessoria. All referred specimens are similar in size to Dryobates nuttallii and smaller than Sphyrapicus ruber. Comparisons are given relative to D. nuttallii, but most characters differentiating Bitumenpicus minimus from D. nuttallii also differentiate it from S. ruber.
Humerus differs from that of Dryobates nuttallii by having (1) Bicipital crest more robust ventrally and not projecting as far ventrad, in posterior view; (2) Tuberculum ventrale shorter, with more rounded distal end, in proximal view; (3) Crista pectoralis flaring more dorsad, more deeply excavated proximally, in anterior view; (4) Epicondylus dorsalis shorter; (5) Epicondylus ventralis larger, extending farther ventrad and longer anteroposteriorly; and (6) shaft more robust, without slight curve ventrad proximally.
The proximal ulna of Bitumenpicus minimus differs from that of Sphyrapicus ruber and Dryobates nuttallii by having (1) Olecranon process narrower; (2) Cotyla ventralis less rounded; and (3) Cotyla dorsalis small, rounded, without a prominent projection to dorso-distal corner. The distal ulna differs by having (1) Condylus dorsalis shorter, more rounded in dorsal view, without antero-proximal corner in dorsal view (but slightly abraded); (2) Tuberculum carpale smaller, projecting less anteriad, without anterodistal corner projecting distad; and (3) much smaller size. The radius of B. minimus differs from that of S. ruber by having (1) rim of Cotyla humeralis more rounded; and (2) the distal end with Sulcus tendinous less constrained.
Carpometacarpus differs from that of Dryobates nuttallii by having (1) Processus extensorius relatively shorter and broader proximodistally, in ventral view, thinner in anterior view; (2) Trochlea carpalis with ventral rim more rounded, shorter proximodistally, in ventral view; (3) Synostosis metacarpalis proximalis relatively broader anteroposteriorly; (4) Os metacarpale minus with proximal end coming off Synostosis metacarpalis proximalis more toward centre of bone, in ventral view; (5) Synostosis metacarpale distalis with ventral surface less excavated, or concave; (6) Spatium intermetacarpale broader, more open, or not tapering proximad, in ventral view (might be an effect of breakage, but if so, not visible); (7) Os metacarpale majus, excluding distal extension of Processus intermetacarpalis, broader anteroposteriorly, in ventral view, best seen in distal portion of bone; and (8) rounded facet for attachment of Phalange digitalis majoris III positioned closer to projection of Synostosis metacarpale distalis.
Small Piciformes indet.
In addition, we found in the collection eight specimens of a size similar to Sphyrapicus, but they can only be identified as small Piciformes indet. They are complete humerus (G97); distal right (L617, R62398) and distal left (R66124) carpometacarpi; proximal left (R61565), distal right (L526), and distal left (L522, MT31) tarsometatarsi. [All catalogue numbers preceded by acronym LACM RLB.]
Relative to many other taxa reported as present in the Rancho La Brea palaeoavifauna, woodpeckers are limited in number, which might be expected of a primarily arboreal group. The only exception is the Northern Flicker, Colaptes auratus, which is primarily an open ground feeder. Ground-foraging would more often bring it directly into contact with the surface seeps of petroleum, ensuring entrapment and potential fossilization. Of the three extant species from Rancho La Brea, C. auratus is also the most widespread geographically. For the relatively abundant Melanerpes lewis, it is also possible that the habit of pursuing flying insects would bring it into accidental contact with the petroleum seeps more often than those species that drilled for insects or gleaned them from the surfaces of vegetation.
Despite their limited presence in the Rancho La Brea deposits, the woodpeckers do provide some information regarding the environment of southwestern California in the late Pleistocene. For example, the large Breacopus garretti is suggestive of stands of large, tall trees, which would be necessary to provide nesting cavities sufficiently large to accommodate these woodpeckers. Miller (1937:249) wrote that the presence of specimens of what he interpreted to be the Pileated Woodpecker in the Rancho La Brea deposits suggested “a substantial coniferous forest” in the area around Rancho La Brea, which he considered unlikely based on the known biotic association of the Rancho La Brea region at the time of his writing. The fact that the known specimens of the large woodpecker from Rancho La Brea do not belong to the Pileated Woodpecker but, instead, to the similar-sized new species, Breacopus garretti, and if it can be assumed that the specimens seen by Miller were also probably not of that species, then the problem of biotic association he noted goes away. We can only speculate as to the preferred habitat of the extinct B. garretti. It need not have been the same as for the Pileated Woodpecker, although, as noted, based on the size of the bird it probably sought out areas with large trees, but not necessarily dense forests of large trees.
Both Melanerpes lewis and Sphyrapicus ruber inhabit open forest and woodlands, and a mix of oak, aspen, and coniferous forests. Together with Colaptes auratus, these species are all indicative of a relatively open landscape. For detailed information on the life habits and distributions of the species of extant woodpeckers, see Del Hoyo et al. (2002).
Southwestern California can be regarded as a “biogeographic island,” or insular habitat, that is surrounded by the Pacific Ocean, high mountains, and extreme deserts (Campbell and Bochenski 2010, 2013). Such geographic barriers could be difficult for sedentary species to cross, preventing them from interbreeding with representatives of their ancestral lineages living outside southwestern California. This could easily lead to allopatric speciation, as was probably the case in some extinct late Pleistocene owls (Campbell and Bochenski 2010, 2013, 2015), the extinct California Turkey (Bochenski and Campbell 2006), and probably other non-migratory species. The relatively high number of extinct species found in the Rancho La Brea deposits (22+ out of 140 identified) also indirectly supports the “island” hypothesis. For instance, in Poland, which is about twice the size of southern California, but which does not have such geographic barriers, only one extinct species, out of about 130 identified, has been described from upper Pleistocene deposits (Bochenski et al. 2012). Most woodpeckers, including Dryocopus pileatus, which is the Recent species most similar morphologically to Breacopus garretti, are sedentary birds (Del Hoyo et al. 2002). Thus, we may assume, although it is impossible to prove, that geographic isolation of southwestern California probably played a role in the evolution of the extinct woodpeckers of Rancho La Brea.
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We thank Alison Stenger for financial support that allowed Z.M.B. to visit the Rancho La Brea collections, and Elizabeth and Jan Szupinski for hosting him during his stay in Los Angeles; K. Garrett, Collection Manager, LACM Ornithology, for assisting with access to modern piciforms; A. Farrell, Collection Manager, Rancho La Brea, for assistance with cataloguing specimens; G. Takeuchi, Rancho La Brea, for loan assistance; C. Cicero and R. Bowie (University of California Museum of Vertebrate Zoology), and J. Dumbacher and M. Flannery (California Academy of Sciences) for loans of modern Dryocopus pileatus specimens; and P. Holroyd, Senior Museum Scientist, University of California, Museum of Paleontology, for access to, and loan of, woodpecker specimens from, the UCMP collections from Rancho La Brea. We thank F. Hertel for commenting on an early draft of the manuscript, and G. Mayr and T.H. Worthy for their careful, detailed reviews of the manuscript, which helped us to improve this work. P. Koenigshof and S. Weber facilitated publication of the manuscript.
Availability of data and material
The specimens studied are in the collections of the Natural History Museum of Los Angeles County.
Dr. Alison Stenger provided funds to support Dr. Bochenski’s travel to California.
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This Excel file contains the following information about all extant and unidentified specimens of Piciformes described in this paper: catalogue number, genus, species, element, side, and fragment. (XLSX 26 kb)
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Campbell, K.E., Bochenski, Z.M. A review of the woodpeckers (Aves: Piciformes) from the asphalt deposits of Rancho La Brea, California, with the description of three new species. Palaeobio Palaeoenv (2021). https://doi.org/10.1007/s12549-020-00444-1
- Rancho La Brea
- Late Pleistocene
- Asphalt deposits