VOLUME 98, NUMBER 4 853 B U Fig. 1. Hum?rus (A, C, E) and scapula (G, I) of holotype of Heliadornis ashbyi, new species (USNM 237226), compared with the same elements of the modem tropicbird Phaethon aethereus Linnaeus (B, D, F, H, J). A-B, Humeri in anconal (cranial) view; C-D, Same in palmar (caudal) view; E-F, Same in dorsal view; G-H, Scapulae in ventral view; 1-J, Same in dorsal view. Scale = 2 cm. Description.?MxhovL^ damaged, there remains enough of the tricipital area of the hum?rus to ascertain that a distinct, circular, pneumatic foramen was present. The small oval scar for M. latissimus dorsi caudalis is situated dorsal to the midline of the shaft, as in Phaethon and other Pelecaniformes except the Fregatidae, in which it is on the midline (Olson 1977b:21). 854 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON /' ':% ' Fig. 2. Coracoid (A, C, E) of holotype o?Heliadornis ashbyi, new species (USNM 237226), com- pared with the same element of the modem tropicbird Phaethon aethereus Linnaeus (B, D, F). A-B, Ventro-lateral view; C-D, Dorsal view; E-F, Lateral view. Scale = 2 cm. Details of the scapular end of the coracoid in Phaethon are quite variable individually, so that comparisons with the fossil are difficult. In Heliadornis the head is not as pointed, and the area of clavicular articulation is not as heavily ossified along the distal margin of ligamental attachment as in Phaethon. Such increased ossification in living versus fossil forms is commonly observed in var- ious parts of the skeleton in diverse groups of seabirds and probably has little systematic significance. The scapula o? Heliadornis differs from that o? Phaethon only in having the shaft somewhat more robust and the acromion slightly less developed. Remarks.?The. highly distinctive reduction and distal displacement of the pectoral crest of the hum?rus in Heliadornis represents an exaggeration of a trend also evident in Phaethon, in which the pectoral crest is somewhat reduced and distally displaced as compared with the probable primitive condition seen in the Eocene frigatebird Limnofregata (Olson 1977b, fig. 19). Because the hum?rus of Heliadornis appears to be more specialized than that of Phaethon, the fossil genus cannot be ancestral to modem tropicbirds. Therefore, Heliadornis represents an extinct lineage in the Phaethontidae and can probably be regarded as the "sister- group" of Phaethon. Functional correlates of the humeral morphology o? Heliadornis are difficult to discern. The reduction of the pectoral crest might represent a trend toward the condition in the Pelecani and Sulae in which there is no deltoid expansion of the hum?rus into a crest at all. Distal displacement of the pectoral crest is also seen in the gigantic pelecaniform pseudodontoms (Pelagomithidae), but in this instance the crest is greatly enlarged, probably in connection with the assumed sustained gliding flight of these birds (Olson 1985). An even more extreme example of reduction and distal displacement of the pectoral crest occurs in the skimmers of the genus Rynchops (Rynchopidae, Charadriiformes), which feed in level flight just at the surface of the water, so the wings cannot be depressed below the horizontal. In the absence of more nearly complete fossil material, it would be of little use to speculate on the mode of life of Heliadornis. i^( 4 December 1985 PROC. BIOL. SOC. WASH. 98(4), 1985, pp. 851-855 A NEW GENUS OF TROPICBIRD (PELECANIFORMES: PHAETHONTIDAE) FROM THE MIDDLE MIOCENE CALVERT FORMATION OF MARYLAND Storrs L. Olson Abstract. ?Three associated bones from the Middle Miocene (Langhian) Cal vert Formation of Maryland are described as a new genus and species of tropicbird, Heiiadornis ashbyi. This constitutes the only Tertiary record for the previously monotypic family Phaethontidae. The morphology of the hum?rus of Heiiadornis was more specialized than in the extant genus Phaethon, hence it probably rep- resents an extinct lineage not ancestral to living tropicbirds. The modem tropicbirds, long so called because "they are never seen far without either Tropick" (Dampier 1697:53), comprise three species in the monotypic family Phaethontidae. They are highly pelagic, plunge-diving birds that usually nest in rocky cliffs and have such reduced hindlimbs that they are incapable of true walking locomotion. In most respects, tropicbirds are so diflerent from other members of the Pelecaniformes that their affinities have frequently been ques- tioned (Sibley and Ahlquist 1972). Nevertheless, apparently derived characters shared with the Pelecaniformes, such as the totipalmate foot, salt glands situated within the orbit, and the lack of an incubation patch, indicate that the Phae- thontidae should be included in that order. Although the tropicbirds are in many respects primitive (Olson 1977b) and may be expected to be at least as old as other families of Pelecaniformes, several of which are known as far back as the early Eocene (Olson 1985), there has hitherto been no Tertiary fossil record of the Phaethontidae. Prophaethon shrubsoiei An- drews (1899), from the Lower Eocene London Clay of England was originally described in the Phaethontidae, but was later elevated to the rank of a separate family and order by Harrison and Walker (1976). Ordinal separation of Pro- phaethon is not justified, but the differences between it and Phaethon, particularly in the pelvis and hindhmb, warrant the recognition of the family Prophaethontidae (Olson 1977b, 1985). Thus, the three associated bones from the middle Miocene Calvert Formation in Maryland described here, which are referable to the Phae- thontidae, constitute the only fossil record of the family apart from Quaternary remains of extant species. Order Pelecaniformes Sharpe Suborder Phaethontes Sharpe Within the Pelecaniformes, the Calvert fossil can be referred to the suborder Phaethontes by the retention of a procoracoid foramen (lacking in the other suborders), a well developed pectoral crest and a poorly developed acromion process of the scapula (both conditions also occur in the Fregatae but not in the Pelecani or Sulae). 852 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON Family Phaethontidae Bonaparte, 1853 The only skeletal element that can be compared among Phaethon, Prophaethon, and the Calvert fossil is the coracoid; all the fossil specimens, however, are im- perfect. The Calvert fossil resembles the Phaethontidae and differs from the Pro- phaethontidae in having a larger, more expanded procoracoid process and a more robust shaft of the coracoid. Heliadornis, new genus Type-species.?Heliadomis ashbyi, new species; the only included species. Diagnosis.?TUScTS most markedly from Phaethon in the size and shape of the pectoral crest of the hum?rus, which is smaller, more distally situated, with more prominent muscle scars, and in dorsal view has the proximal margin more nearly parallel with the shaft. In addition, the intumescence of the bicipital crest is more proximo-distally elongate, being more ovoid than circular in shape, the impression for M. coracobrachialis cranialis is longer, wider, and incises the bicipital intu- mescence more deeply, so that the proximo-dorsal comer of the latter is more sharply defined and pointed. Etymology. ?Greek, Heliades + omis, bird. In Greek mythology the three He- liades were the daughters of Helios and the sisters of Phaethon; the name, which is masculine, thus reflects the likelihood of the Miocene fossil being the "sister group" of the modem genus Phaethon. Heliadornis ashbyi, new species Figs. 1-2 Holotype. ?Left hum?rus lacking distal end and ventral tubercle, left coracoid lacking sternal end and part of procoracoid process, left scapula lacking posterior half, vertebrate paleontological collections of the National Museum of Natural History, Smithsonian Institution, USNM 237226. Collected in association on 24 Dec 1954 by Wallace L. Ashby. Locality. ?40 m north of south end of second cliiFsouth of Parker Creek, Calvert County, Miuyland. Horizon. ?Zone 11 (of Shattuck 1904), about 60 cm below the base of Zone 12, Calvert Formation, Middle Miocene (Langhian). Measurements of holotype.?Hum?rus: distance from head to distal extent of scar for M. pectoralis, 30.2 mm; depth through head, 5.3; proximo-distal extent of bicipital intumescence, 16.0; width and depth of shaft at approximate midpoint (at level of nutrient foramen), 6.4 x 5.3. Coracoid: dorso-ventral depth through head, 11.0 mm; length and width of glenoid facet, 8.8 x 5.2; width and depth of shaft at approximate midpoint, 5.1 x 4.4. Scapula: width of articular end, 10.0 mm; width and depth of shaft 20 mm from tip of acromion, 3.4 x 1.8, Etymology. ?Dedicated to Mr. Wallace L. Ashby, Jr., who over the past three decades has collected numerous valuable specimens of fossil birds from the Calvert Formation and kept indispensible records of most of his ?nds (see Olson 1984). Recognition of his considerable contribution to knowledge of the Calvert avifauna is long overdue. Diagnosis.?As for the genus. The species was approximately the size of the living species Phaethon aethereus Linnaeus or perhaps slightly smaller. VOLUME 98, NUMBER 4 853 B i / Fig. 1. Hum?rus (A, C, E) and scapula (G, I) of holotype of Heliadornis ashbyi, new species (USNM 237226), compared with the same elements of the modem tropicbird Phaethon aethereus Linnaeus (B, D, F, H, J). A-B, Hrnneri in anconal (cranial) view; C-D, Same in palmar (caudal) view; E-F, Same in dorsal view; G-H, Scapulae in ventral view; I-J, Same in dorsal view. Scale = 2 cm. Description. ?Although damaged, there remains enough of the tricipital area of the hum?rus to ascertain that a distinct, circular, pneumatic foramen was present. The small oval scar for M. latissimus dorsi caudalis is situated dorsal to the midline of the shaft, as in Phaethon and other Pelecaniformes exceipt the Fregatidae, in which it is on the midline (Olson 1977b: 21). 854 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON Fig. 2. Coracoid (A, C, E) of holotype of Heliadomis askbyi, new species (USNM 237226), com- pared with the same element of the modern tropicbird Phaethon aethereus Linnaeus (B, D, F). A-B, Ventro-lateral view; C-D, Dorsal view; E-F, Lateral view. Scale = 2 cm. Details of the scapular end of the coracoid in Phaethon are quite variable individually, so that compeirisons with the fossil are difficult. In Heliadomis the head is not as pointed, and the area of clavicular articulation is not as heavily ossified along the distal margin of ligamental attachment as in Phaethon. Such increased ossification in living versus fossil forms is commonly observed in var- ious parts of the skeleton in diverse groups of seabirds and probably has little systematic significance. The scapula of Heliadomis differs from that o? Phaethon only in having the shaft somewhat more robust and the acromion slightly less developed. Remarks.?Ths highly distinctive reduction and distal displacement of the pectoral crest of the hum?rus in Heliadomis represents an exaggeration of a trend also evident in Phaethon, in which the pectoral crest is somewhat reduced and distally displaced as compared with the probable primitive condition seen in the Eocene frigatebird Limnofregata (Olson 1977b, fig. 19). Because the hum?rus of Heliadomis appears to be more specialized than that of Phaethon, the fossil genus cannot be ancestral to modem tropicbirds. Therefore, Heliadomis represents an extinct lineage in the Phaethontidae and can probably be regarded as the "sister- group" of Phaethon. Functional correlates of the humeral morphology of Heliadomis are difficult to discern. The reduction of the pectoral crest might represent a trend toward the condition in the Pelecani and Sulae in which there is no deltoid expansion of the hum?rus into a crest at all. Distal displacement of the pectoral crest is also seen in the gigantic pelecaniform pseudodontoms (Pelagomithidae), but in this instance the crest is greatly enlarged, probably in connection with the assumed sustained gliding flight of these birds (Olson 1985). An even more extreme example of reduction and distal displacement of the pectoral crest occurs in the skimmers of the genus Rynchops (Rynchopidae, Charadriiformes), which feed in level flight just at the surface of the water, so the wings cannot be depressed below the horizontal. In the absence of more nearly complete fossil material, it would be of little use to speculate on the mode of life of Heliadomis. VOLUME 98, NUMBER 4 855 Mainly because of their clifF-nesting habits, modem tropicbirds occur very infrequently in Quaternary deposits, even on islands where they are known to breed (Olson 1975, 1977a). The holotype of Heliadornis is the only Tertiary specimen of tropicbird yet known, despite the fact that in recent years thousands of fossils of marine birds have been recovered from Miocene and Pliocene deposits along the middle Atlantic coast of eastern North America, and in Florida, CaU- fomia, and South Africa. No Tertiary fossil deposits containing marine birds have yet been found in what would have been truly tropical waters. The great rarity of the Phaethontidae in the fossil record would be understandable if Tertiary tropicbirds were also restricted to low latitudes and were as extremely pelagic in their habits as the modem birds. Acknowledgments For their valuable contributions and not inconsiderable patience I thank Wally Ashby, who waited more than 30 years for this specimen to be described, and Anne Curtis, who waited more than 10 years to see her illustrations of it put to use. I am grateful to Cyril A. Walker, British Museum (Natural History) for lending the coracoid from the holotype of Prophaethon shrubsolei for comparison in this and other studies. For bibUographic assistance I thank Leslie Overstreet, and for comments on the manuscript, Ralph Eschelman and Clayton E. Ray. Literature Cited Andrews, C. W. 1899. On the remains of a new bird fronn the London Clay of Sheppey. - Proceedings of the Zoological Society of London 1899:776-785. Dampier, W. 1697. New voyage round the world. 2nd ed., corrected.?London: James Knapton. Harrison, C. J. O., and C. A. Walker. 1976. A reappraisal of Prophaethon shrubsolei Andrews (Aves).?Bulletin of the British Museum (Natural History), Geology 27:1-30. Olson, S. L. 1975. Paleomithology of St. Helena Island, South Atlantic Ocean.-Smithsonian Con- tributions to Paleobiology 23:1-49. . 1977a Additional notes on subfossil bird remains from Ascension Island, ?Ibis 119:37-43. . 1977b. A Lower Eocene frigatebird from the Green River Formation of Wyoming (Pele- caniformes: Fregatidae). ?Smithsonian Contributions to Paleobiology 35:1-33. . 1984. A brief synopsis of the fossil birds from the Pamunkey River and other Tertiary marine deposits in Virginia. In L. W. Ward and K. Kraft, eds., Stratigraphy and paleontology of the outcropping Tertiary beds in the Pamunkey River region, central Vii^inia coastal plain. ? Guidebook for Atlantic Coastal Plain Geological Association 1984 Field Trip. Pp. 217-223, 2 plates. . 1985. The fossil record of birds. In D. Famer, J. King, and K. Parkes, eds., Avian biology, volume 8.?New York: Academic Press. Pp. 79-238. Shattuck, G. B. 1904. Geological and paleontological relations, with a review of earlier investiga- tions.-Maryland Geological Survey, Miocene I :xxxii-cxxxvii. Sibley, C. G., and J. E. Ahlquist 1972. A comparative study of the egg white proteins of non- passerine birds.?Peabody Museum ofNaturalHistory, Yale University,Bulletin39:vi + 276 pp. Department of Vertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560.