| Agapornis longipes | |
|---|---|
 | |
| Fossilized remains ofA. longipes | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Aves |
| Order: | Psittaciformes |
| Family: | Psittaculidae |
| Genus: | Agapornis |
| Species: | †A. longipes |
| Binomial name | |
| †Agapornis longipes Paviaet al., 2024 | |
Agapornis longipes is anextinct species oflovebird that lived in what is nowGauteng, South Africa during theEarly Pleistocene epoch, about 2.5–1.38 million years ago. Thefossilized remains of this bird were first discovered in theKromdraai fossil site and reported in 1969 by T.N. Pocock, though the species would not be named until decades later in 2024. By the time it was named, 96 bones attributable to this species had been collected over the years from three caves, namely Kromdraai,Swartkrans andCooper's Cave, all located within theCradle of HumankindWorld Heritage Site. Such a large number of fossils is unusual for a small bird, as the fragile bones of birds do not preserve easily and thus are usually found as fragments, yet theA. longipes remains include both complete and incomplete bones.
A. longipes was a small bird, with its wing bones showing that it would have been about the same size as the smallerextant lovebird species, yet itstarsometatarsus (one of the leg bones) was comparable in size to that of the largest living lovebirds. This indicates that the legs of this species were disproportionately long compared to other lovebirds, hence it was given thespecific namelongipes which means'long-footed' inLatin. Though the many preserved specimens show that some individuals were larger than others, the body proportions did not change with size. The proportionally long legs are believed to be an adaptation for feeding on the ground, where the animal would forage forgrass seeds among the dense vegetation of its environment, though it would presumably still breed in tree cavities like modern lovebirds.
Analysis of the fossil assemblage in the three caves whereA. longipes remains have been found suggests that its natural habitat was mostly opengrassland with nearbywoodlands, and in some areas would also have largerocky outcrops or major bodies of water, though the exact conditions vary between the three localities. This environment is largely similar to what is seen in South Africa today, suggesting that this lovebird did not went extinct because of general habitat change, but possibly because of changes to themicroclimate or the loss of a food source. It is believed that at least some of theA. longipes specimens were brought into the caves bywestern barn owls which preyed on the lovebirds and regurgitated the remains aspellets, considering the similarity of the fossil deposits to the debris seen under barn owlroost sites and the presence of barn owl fossils in the same area.
All known fossilized remains ofAgapornis longipes originate from theCradle of Humankind, aWorld Heritage Site about 50 km (31 mi) northwest ofJohannesburg, South Africa and consisting of many fossil-bearing caves. The first to be discovered were found decades before the species was named. In 1969, T.N. Pocock reported that remains of lovebirds belonging to the genusAgapornis have been discovered at theKromdraai fossil site (one of the caves that would later be designated as part of the World Heritage Site). He believed that two species were represented by these specimens, a smaller species around the size of abudgerigar and a larger species, but did not assign any of the specimens to any named species.[1] The presence of at least one lovebird species at Kromdraai was further confirmed in 2010, when Thomas A. Stidham reported that the fossilizedhumerus of a small lovebird had been discovered during excavations at the site between 1977 and 1980, and was being housed in theTransvaal Museum. Stidham also added that the lovebird remains reported by Pocock had been lost.[2] However this turned out to be incorrect, and those remains are actually kept at the Evolutionary Study Institute at theUniversity of the Witwatersrand.[3] Marco Pavia further published two papers reporting fossil remains ofAgapornis, one in 2020 mentioning a humerus at Kromdraai, and the other in 2022 detailing a variety of small bones from the nearbyCooper's Cave. In both papers, Pavia identified the remains only to the genus level, stating that comprehensive analysis is needed for more specific identification.[4][5]
In 2024, a study on the fossil lovebird remains found in the Cradle of Humankind was published. The authors of the study analysed specimens housed in the University of the Witwatersrand and theDitsong National Museum of Natural History, including those formerly studied by Pocock, Stidham or Pavia, and concluded that they represent a single new species. The nameAgapornis longipes was given to this species, with thespecific name derived from theLatin wordslongus (meaning "long") andpēs (meaning "foot"). Bones of this lovebird were uncovered in three caves in the Cradle of Humankind, namely Kromdraai, Cooper's Cave andSwartkrans, and the authors described a series of remains found between 1979 and 1986 by paleontologistBob Brain in detail.[3] Birds have fragile bones, so fossils of small birds such asAgapornis are typically found in small fragments, butA. longipes was unusually represented by 96 bones, some entirely complete and others incomplete.[6]
Agapornis longipes was a small species of parrot with relatively large legs compared to other lovebirds. Its wing bones are comparable in size to those of the extantFischer's,Lilian's andblack-cheeked lovebirds, suggesting it was about as large as these small modern forms. However, thetarsometatarsus (a bone in the lower leg) ofA. longipes is closer in size to that of larger lovebird species such as theblack-winged androsy-faced lovebirds. This makes the ratio ofhumerus to tarsometatarsus length inA. longipes the smallest of all knownAgapornis species, indicating this species had long legs for a lovebird.Intraspecific variation in size is known inA. longipes, with some individuals being larger than others, though the ratio of wing length to leg length remains the same regardless of an individual's size.[3] When remains of the species were first studied in 1969, it was thought that larger and smaller individuals represent two separate species.[1] However, this size variation is within the range seen in extant lovebird species. In addition, no extant lovebird species overlap in distribution with one another, making it unlikely thatA. longipes lived alongside a second species of lovebird.[3]
Only onescapulocoracoid (a unit of theshoulder girdle) of this species has been found, and thesternal part of it is not preserved. Theclavicular facet of the scapula is large, with a protrusion on itsventral (lower) side, and overhangs a deepfossa (depression or hollow). On thedorsal (upper) side of the groove of thesupracoracoideus muscles, there is a roundedtubercle. Thehumerus has a prominent dorsal tubercle and a deep attachment for thebrachialis muscle, making it more similar to that of the extinctAgapornis attenboroughi than any extant lovebirds. Theulna ofA. longipes has a curved shaft like that of all other lovebirds, but otherwise differs from them in having a less protruding, stouterolecranon (elbow protrusion) and a carpal tubercle which protrudesventrally rather thandistally (towards the underside instead of the wing tip).[3] Thecarpometacarpus has an elongated, ridge-likepisiform process, which is aderived feature unique to theAgapornis genus.[7] There is also a continuous ridge connecting the pisiform process to thealula process, a feature not seen in other lovebird species.[3]
A singletibiotarsus ofA. longipes is known, and is similar in structure to that of other lovebirds (and unlike most other African parrots). The tarsometatarsus has a canal where both theflexor hallucis longus muscle and theflexor digitorum longus muscle would have been attached, and a separate canal is present for the superficial flexor tendons. Such a canal structure of the tarsometatarsus is also known in otherAgapornis species, as well as the related hanging parrots of the genusLoriculus. InA. longipes, the trochlea (pulley-like grooved structure) at the head of the thirdmetatarsal protrudes further and is wider at theproximal end than in any living lovebird species, and the tarsometatarsus is also straighter and narrower at the proximal end.[3]
Because all but one living species of lovebirds eat mainlygrass seeds and secondarily feed on fruit, it is believed thatAgapornis longipes had a similar diet.[8][9][10] While some extant lovebirds search for food in trees, the ones with comparably longer legs relative to their wings (namely thegrey-headed,yellow-collared andFischer's lovebirds) feed on the ground.[10]A. longipes has the proportionally longest legs of all known lovebirds, suggesting that it lived primarily on the ground rather than in trees, feeding on grass seeds in the tall, dense vegetation of the South African grasslands.[3] Even so, the breeding habits ofA. longipes are still presumably similar to those of living lovebirds, which require tall trees with either natural cavities or holes made by other birds (such asAfrican barbets andwoodpeckers) to lay their eggs in.[3][10] It was reported by T.N. Pocock in 1969 that onehumerus found at theKromdraai fossil site was of an immature bird, suggesting that the surrounding area was used as anesting ground forA. longipes rather than simply being part of itsnon-breeding range.[1]
Known from a large number of fossil remains, including 24 specimens of at least seven individuals fromCooper's Cave,A. longipes was likely a common animal in its natural habitat, being the fifth most common bird in terms of percentage of identified remains at this site and the third most common in terms of number of individuals represented.[5] The species may be similarly abundant in Kromdraai, where it is known from 23 specimens, but since these remains are spread across multiplestratigraphic layers, it is difficult to verify the true abundance of this bird there.[3] Some of theA. longipes specimens from Kromdraai and Cooper's Cave come from deposits with numerous small animal remains, which are believed to be debris from fossilizedowl pellets. In particular, the remains in the Kromdraai deposits are most similar to debris underroost sites ofwestern barn owls, and fossils attributed toTyto cf. alba are known from both localities. This suggests that barn owls used these caves as roosting spots and were at least an occasionalpredator ofA. longipes.[1][5]
Fossilized remains ofAgapornis longipes have been discovered in three caves, namely theKromdraai fossil site,Cooper's Cave andSwartkrans. These caves are situated within theUNESCO World Heritage Site of theCradle of Humankind in South Africa, so named because this area bears fossils of earlyhominins spanning from theLate Pliocene toLate Pleistocene epochs. However, in spite of extensive searches, specimens of this lovebird have not been recorded from localities other than the aforementioned three caves. The environment thatA. longipes inhabited was similar to thesavanna andveld grasslands of modern South Africa. Living in the Cradle of Humankind, the species lived alongside a wide variety of other animals, including the homininsParanthropus andHomo. Because the environment ofA. longipes has not changed significantly, it is likely that the bird was driven to extinction by microclimatic changes or the extinction of a food source rather than a change in the general environment.[3]
Specimens ofA. longipes were first discovered in Kromdraai, but the exactstratigraphic unit from which they originate is unclear. The stratigraphy of Kromdraai was revised in 2022, when the fossil-bearing units of the site were assigned letters, with "Unit A" being the youngest and "Unit O" being the oldest. Fossils excavated before 2014 (including theA. longipes specimens) therefore cannot be easily compared with this modern stratigraphy and their exact age is uncertain.[11] However, the KromdraaiA. longipes specimens have been broadly considered to represent individuals which lived about 2.5 million years ago, near the boundary of thePliocene andPleistocene epochs.[3] Study of the fossil assemblage at Kromdraai suggests the area had an open, semi-arid grassland habitat differing little from the current environment. The area would also have had a rockyoutcrop or cliff over 10 meters high, as evidenced by the fact that the most abundant bird species in the Kromdraai fossil assemblage, the bald ibisGeronticus thackerayi, would have been a rock-dwelling animal that had a breeding colony in this area.[4][12] This rocky structure was likely influenced by erosion from a largestream orriver, and the presence of a water body is further supported by the fact that fossils of ducks belonging to the genusAnas are represented. Agallery forest would have flanked this water body, as evidenced by fossils of forest-dwelling birds such as theblack sparrowhawk (Astur melanoleucus) and a green pigeon of the genusTreron, and some particular species such as the pygmy owlGlaucidium ireneae and a roller of the genusCoracias would have required tree cavities to nest in.[4]
A wide variety of animals known from the Kromdraai fossil assemblage, including hominins such asParanthropus robustus and an early species ofHomo.[11] The large herbivores of this ecosystem are represented by a range of bovids, with the most numerous being the wildebeestConnochaetes taurinus prognu, while other bovid fossils from Kromdraai include those of thecommon eland (Taurotragus oryx), theoribi (Ourebia ourebi),Numidocapra crassicornis and a species ofMegalotragus. The mammalian carnivores represented in this fossil assemblage include mustelids such as theAfrican clawless otter (Aonyx capensis),honey badger (Mellivora capensis) and the small weaselPropoecilogale bolti, hyenas such as thebrown hyena (Parahyaena brunnea),striped hyena (Hyaena hyaena) and an early aardwolf (Proteles amplidentus), felids such asDinofelis barlowi,Megantereon whitei and theleopard (Panthera pardus), canids such as theblack-backed jackal (Lupulella mesomelas),Cape fox (Vulpes chama) and a species ofLycaon, and civets such as theAfrican civet (Civettictis civetta) andCivettictis braini.[13][14]
In Swartkrans, fossils ofA. longipes have been uncovered from the Lower Bank of Member 1, the oldest of the fossil-bearing deposits in this cave.[3] Use of theisochron dating method has shown that the Member 1 deposits were formed about 2.22 million years ago during theEarly Pleistocene epoch, making theA. longipes remains from this site geologically younger than those at Kromdraai.[15] Analysis of the faunal assemblage suggests that the Swartkrans fauna originates from a mosaic of habitats made up largely of veld grassland withriparian woodland.[3] The landscape might have comprised a succession from riverine grassland with someacacia trees, to bushy hillsides, and finally to plains with open woodland. Minimum temperatures were slightly higher than today. Annual rainfall was likely between 310–550 mm (12–22 in), less than the modern annual rainfall of 650 mm (26 in), and there may have been a slight shift in therainy season, with less rain in summer and more in winter compared to today.[16]
The Lower Bank deposits at Swartkrans have preserved remains of many different animals which would have coexisted withA. longipes. As with Kromdraai, the most famous of these are the hominins, which includeParanthropus robustus and an earlyHomo species.[17] Other primate fossils from the Lower Bank include those of the monkeysTheropithecus oswaldi,Dinopithecus ingens andCercopithecoides williamsi. The majority of the large herbivores in this environment were bovids, with extant species such as thespringbok (Antidorcas marsupialis),klipspringer (Oreotragus oreotragus),steenbok (Raphicerus campestris) andrhebok (Pelea capreolus) living alongside prehistoric taxa such asAntidorcas bondi and a species ofMegalotragus, though equids such asEquus capensis andHipparion lybicum were also present. Carnivoran fossils are also abundant in the Lower Bank, mostly representing extant species such as thelion (Panthera leo),leopard (Panthera pardus),African wildcat (Felis lybica),brown hyena (Parahyaena brunnea),black-backed jackal (Lupulella mesomelas),Egyptian mongoose (Herpestes ichneumon) andAfrican clawless otter (Aonyx capensis), though there are also extinct species such as the hyenaChasmaporthetes nitidula. Other mammals represented in this fossil assemblage include the hyraxesProcavia antiqua andProcavia transvaalensis, theaardvark (Orycteropus afer), a springhare belonging to the genusPedetes, and a pangolin of the genusManis.[18]
Cooper's Cave is an extensive system and includes multiple distinct localities which have produced fossils, with theA. longipes specimens originating from a locality known as Cooper's D.[19]Uranium-lead dating conducted in 2009 suggests that the Cooper's D deposits are approximately 1.5 to 1.4 million years old, while a more recent study from 2019 refined that estimate to an age of about 1.38 million years, dating to theEarly Pleistocene epoch.[20][21] Though geologically younger, the fossil assemblage at Cooper's D suggests an environment similar to that at Kromdraai, with open savanna being the dominant habitat, while rocky outcrops and woodland were also present. However, while rock-dwelling species made up most of the birds in Kromdraai, Cooper's D instead preserves more open grassland birds and almost no water-associated birds, suggesting that the environment had gradually become drier and more open by the time the Cooper's D deposits formed.[5]
At Cooper's D, by far the most abundant birds in the fossil assemblage werefrancolins (Francolinus sp.), which are open grassland birds and support the idea that this environment was dominated by savanna. Other birds in this assemblage include extant birds such as thewestern barn owl (Tyto alba), theharlequin quail (Coturnix delegorguei), theblack sparrowhawk (Astur melanoleucus), theLudwig's bustard (Neotis ludwigii). Some of the present bird remains belong to extant genera, such as a buttonquail of the genusTurnix, a swift of the genusApus, a guineafowl of the genusNumida, two falcons of the genusFalco, and a vulture of the genusGyps, though it cannot be determined exactly which species they are. Extinct species such as the crowCorvus bragai and the pygmy owlGlaucidium ireneae are also represented, as are indeterminate remains attributed to the familiesAccipitridae,Scolopacidae,Sturnidae,Coliidae andOtididae.[5] Mammal fossils are also abundant at Cooper's D, with among the most famous being those of the early homininParanthropus robustus, though non-hominin primates such asGorgopithecus,Theropithecus andPapio are also represented.[20][22][23] Bovids are also well-represented, with remains of both modern species such as thegreater kudu (Tragelaphus strepsiceros),common eland (Tragelpahus oryx), andspringbok (Antidorcas marsupialis), and those of extinct forms such asAntidorcas recki andMegalotragus having been found.[24] Though rarer than the bovids, fossils of equids such asEquus capensis andEurygnathohippus cornelianus are also known from Cooper's D.[25] The apex predators in this ecosystem were large felids of the generaDinofelis,Megantereon,Panthera andAcinonyx, as well as hyenas including thebrown hyena (Parahyaena brunnea),striped hyena (Hyaena hyaena),Crocuta ultra andChasmaporthetes nitidula.[26][27] Smaller carnivores at Cooper's D include felids of the generaFelis andCaracal, the mustelidsPropoecilogale bolti and thehoney badger (Mellivora capensis), and mongooses such as theEgyptian mongoose (Herpestes ichneumon) andmarsh mongoose (Atilax paludinosus).[26][28][29]
