The St. Croix macaw (Ara autocthones) or Puerto Rican macaw is an
pre-Columbian site on St. Croix. A second specimen consisting of various bones from a similar site on Puerto Rico was described in 2008, while a coracoid from Montserrat
may belong to this or another extinct species of macaw. The St. Croix macaw is one of 13 extinct macaw species that have been proposed to have lived on the Caribbean islands. Macaws were frequently transported long distances by humans in prehistoric and historical times, so it is impossible to know whether species known only from bones or accounts were native or imported.
As it is only known from bones, the St. Croix macaw's color is not known. Extant macaws can generally be grouped in either large-body or small-body size clusters. Yet, the bones of the St. Croix macaw are intermediate in size between the two, and it was slightly larger than the extinct
Ara
. Like other macaw species in the Caribbean, the St. Croix macaw is believed to have been driven to extinction by humans, as indicated by the fact that its remains were found in kitchen middens.
Taxonomy
In 1934, the archeologist Lewis J. Korn (working under the
extinct. In 1937, the ornithologist Alexander Wetmore identified several species among these bones, including a left tibiotarsus (lower leg bone) of an immature macaw, which was unexpected since no such birds were previously known from St. Croix.[1]
Specimen of the extinct Cuban macaw, the only other Caribbean species of macaw described based on physical remains
Wetmore made the tibiotarsus the
Ara, as Ara autocthones. The specific name is from the Ancient Greekαὐτόχθων (autochthon), meaning native or aborigine. The holotype is housed along with the other bones found at the U.S. National Museum of Natural History, cataloged as USNM 483530. Though numerous other now-extinct macaws had been described from the Caribbean based on old accounts alone, the only other species described based on physical remains at the time was the Cuban macaw (Ara tricolor), which was known from skins. Though Wetmore conceded that many uncertainties were surrounding the bone, especially regarding its affinities to other Caribbean macaws, he thought it appropriate to designate it as a new species.[1][2][3]
In 1978, the ornithologist
indigenous Caribbeans are known to have kept and traded macaws over long distances.[4] In 1983, he indicated that if the macaw had indeed been transported, the specific name would be a misnomer.[5] The zoologist Elizabeth S. Wing agreed in 1989 that the macaw could have been traded,[6] but the ornithologists Matthew I. Williams and David W. Steadman stated in 2001 that given the evidence for other macaws having existed in the region, there was no reason why St. Croix could not have had an indigenous species.[7]
In 1987, the ornithologist Edgar J. Máiz López found several associated bones of a single bird (cataloged as USNM 44834) at the Hernández Colón archeological site on the eastern bank of the
metacarpal), the left femur (lacking the lower end), the right tibiotarsus (lacking part of the upper articular surface), upper and lower portions of the left tibiotarsus, as well as unidentified elements. In 2008, Olson and Máiz López assigned the specimen to Ara autocthones (it had been assigned to Ara sp. in 2004, indicating uncertain classification within the genus Ara), as its tibiotarsus is identical in size to the holotype.[3][8]
Olson and Máiz López considered it likely that Ara autocthones was endemic to the
Amazona and Aratinga have been found in pre-human sites on Puerto Rico, none such belonging to macaws have been found. Olson and Máiz López conceded that macaws are unlikely to be found in cave deposits and noted that the Cuban macaw's fossils had been found in aquatic deposits. They also pointed out that various animal species were transported and kept in captivity by Native Americans – for example the Puerto Rican hutia (Isolobodon portoricensis, an extinct rodent) and the Antillean cave rail (Nesotrochis debooyi, an extinct flightless rail) were both transported to St. Croix and found in kitchen middens.[3]
Olson and Máiz López pointed out that a coracoid from the island of
Joseph M. Forshaw argued in 2017 that the latter was a more appropriate name since he found it more plausible that it naturally occurred on Puerto Rico and had been transported to the Virgin Islands.[11]
As many as 13 now-extinct species of macaw have lived on the Caribbean islands, it has been suggested. Still, many of these were based on old descriptions or drawings and represented only
Bahamas in 1492. Historical records of macaws on these islands, therefore, may not have represented distinct, endemic species; it is also possible that these macaws were escaped or feral birds that had been transported to the islands from elsewhere.[3] The identity and distribution of indigenous macaws in the Caribbean are likely to be resolved only through paleontological discoveries and examination of contemporary reports and artwork.[9][14]
Description
Mean length and ranges of carpometacarpus (yellow squares) and tibiotarsus (green circles; red circle is the St. Croix macaw) of all macaws, with links to the species
Since only bones are known of the St. Croix macaw, nothing can be said about its coloration.[10] While the holotype tibiotarsus appears to belong to a fully grown individual, the fact that the bone is slightly spongy at the ends indicates it was immature. This left tibiotarsus is 77.7 mm (3.06 in) in total length, 9.4 mm (0.37 in) in breadth from side to side across the lower end, and the smallest breadth from side to side of the shaft is 3.9 mm (0.15 in). Though similar to the same bone in the Cuban macaw, it is wider from side to side (comparisons between the lower ends of their tibiotarsi indicate it was a slightly larger bird). It is slender compared to those of larger macaws. The holotype tibiotarsus is intermediate in size between those of large macaws such as the scarlet macaw (Ara macao) and the military macaw (Ara militaris), and the small chestnut-fronted macaw (Ara severus). Compared to the tibiotarsi of extant macaws, the bone is more slender and has a slightly greater hindwards development of the upper end. Apart from this, its only distinguishing feature is that its dimensions do not fall within those of other known species. The slender proportions of the bone and more elongated ridges around the upper end show it is a macaw and distinguishes it from the Amazon parrots such as the large imperial amazon (Amazona imperialis).[1]
The tibiotarsus of the assigned specimen is essentially identical in size to the holotype. It is 74.5 mm (2.93 in) from the upper articular surface, 47.2 mm (1.86 in) from the lower end of the fibular crest to the external
sternal facet, 26.5 mm (1.04 in) from the base of the procoracoid process to the internal corner of the sternal facet, the glenoid facet is 10.5 by 6.1 mm (0.41 by 0.24 in) wide and deep, the shaft is 5.2 by 4.4 mm (0.20 by 0.17 in) wide and deep at midpoint, and the sternal facet is 10.5 mm (0.41 in) wide. The upper width of the humerus is 19.9 mm (0.78 in), the depth through its external tuberosity is 12.8 mm (0.50 in), the depth of its head is 6.2 mm (0.24 in), the width of the lower end is about 15.5 mm (0.61 in), and the height and width of the radial condyle is 7.4 by 5.0 mm (0.29 by 0.20 in). The carpometacarpus is 55.8 mm (2.20 in) long, its upper depth is 14.3 mm (0.56 in), the trochlea (a grooved structure where bones join) is 5.7 mm (0.22 in) wide, and the shaft is 4.5 by 5.0 mm (0.18 by 0.20 in) at midpoint. The upper part of the radius is 6.0 mm (0.24 in) at its greatest diameter. The estimated length of the femur is 51.5 mm (2.03 in), its upper width is 12.5 mm (0.49 in), the depth through its trochanter is 8.2 mm (0.32 in), the head is 6.2 mm (0.24 in) deep, and the shaft is 4.9 by 5.4 mm (0.19 by 0.21 in) wide and deep at its midpoint.[3]
Known bones of this macaw marked in red on an illustration of an unrelated parrot skeleton
Olson and Máiz López stated that extant macaws fall into two size-clusters, representing large and small species. In contrast, the St. Croix macaw was distinct in being intermediate between the two clusters, with only the
pectoral attachment on the humerus is less excavated compared to those two macaws. In contrast, the capital groove (a groove separating two parts of the humerus's head) is wider. The head of the femur is more massive, and when seen from the back, is more excavated under the head, neck, and trochanter. In contrast, the femur's more robust shaft is similar to that of Ara but dissimilar to Anodorhynchus. The tibiotarsus is more robust with a flared lower extremity. The tibiotarsus' length is shorter than in the blue-throated macaw but longer than in Lear's macaw. In contrast, the lengths of the coracoid, carpometacarpus, and femur are smaller than in either.[3]
Olson and Máiz López ruled out the specimen from Puerto Rico belonging to the Amazon parrots by pointing out characters found only in Ara macaws. The coracoid is more elongated and has a relatively narrow shaft, and the ventral lip of the glenoid facet (equivalent to the
pronation muscles in the wing) on the humerus is placed farther upwards. The femur has a proportionally larger head, and the tibiotarsus has a narrower internal condyle and a distinctive inner cnemial crest that is more pointed and extends further upwards.[3]
Extinction
All the endemic Caribbean macaws were likely driven to extinction by humans (in prehistoric and historical times), though hurricanes and disease may have contributed. Native Caribbeans hunted macaws and held them captive for later use as food, but also as pets. Since they are known from kitchen midden deposits, the macaws from Puerto Rico and St. Croix were evidently also used for subsistence.[9][15] It is likely that the St. Croix macaw became extinct due to these factors, but the date it happened is unknown.[10]
