| Archaeoindris Temporal range:Pleistocene-Holocene | |
|---|---|
 | |
| Archaeoindris fontoynontii skull | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Primates |
| Family: | †Palaeopropithecidae |
| Genus: | †Archaeoindris Standing, 1909 |
| Species: | †A. fontoynontii |
| Binomial name | |
| †Archaeoindris fontoynontii Standing, 1909 | |
 | |
| Subfossil sites forArchaeoindris fontoynontii[1] | |
| Synonyms[2] | |
Lemuridotherium madagascarienseStanding, 1910 | |
Archaeoindris fontoynontii is anextinct giant lemur and the largestprimate known to have evolved onMadagascar, comparable in size to a malegorilla. It belonged to afamily of extinctlemurs known as "sloth lemurs" (Palaeopropithecidae), and because of its extremely large size, it has been compared to theground sloths that once roamed North and South America. It was most closely related toPalaeopropithecus, the second-largest type of sloth lemur. Along with the other sloth lemurs,Archaeoindris was related to the livingindri,sifakas, andwoolly lemurs, as well as the recently extinctmonkey lemurs (Archaeolemuridae). Thegenus,Archaeoindris translates to "ancient indri-like lemur".
Archaeoindris was first described byHerbert F. Standing in 1909 on the basis ofsubfossil fragmentary jaws, althoughCharles Lamberton later discovered a complete skull. Only six bones from the lower skeleton have been found, and excavations in the 1980s offered no leads for new finds. Its remains have been found at only one location:Ampasambazimba, a subfossil site in central Madagascar. Following its initial discovery, some subfossil remains ofMegaladapis grandidieri (a type of extinctkoala lemur) were mistakenly associated withArchaeoindris, while smaller leg bones from a juvenile and a massive adult leg bone were erroneously assumed to belong to two separate species. These errors were gradually corrected between the 1930s and 1980s.
The skeleton ofArchaeoindris was massive and robust, and shared many traits with that ofPalaeopropithecus. The arms were longer than the legs, but no hand or foot bones have been found for comparison with the other sloth lemurs. Size estimates based on the limited remains have varied widely, ranging as high as 244 kilograms (538 pounds), but the most thorough statistical investigation usingregression analyses predicts a mass of 160 kg (350 lb).
Misattributions and limited remains have resulted in varying opinions about the wayArchaeoindris moved, ranging from tree- to ground-dwelling in its environment. Its skeleton suggests it was a deliberate climber that visited the ground to travel.
The diet ofArchaeoindris was mostly leaves, and its habitat—prior to human arrival—was a mix ofwoodlands, bushlands, andsavanna, rich in lemur diversity. Today, the region is dominated bygrasslands, and lemur diversity is very low in the nearestprotected area,Ambohitantely Special Reserve. Although it was a rare lemur, it was stillextant whenhumans first arrived on Madagascar, and it would have been vulnerable to hunting andhabitat loss.
The generic nameArchaeoindris, meaning "ancient indri-like lemur", is derived from theGreek word ἀρχαῖος (archaios, or "ancient") andindris, a common variation of the generic nameIndri.[3] The species name,fontoynontii (sometimes spelledfontoynonti), was selected in honor of Antoine Maurice Fontoynont, the president of the Académie Malgache (Malagasy Academy) at the time. Fontoynont was reported to have been supervising the excavation when it was discovered.[4]
Archaeoindris was a type ofsloth lemur (family Palaeopropithecidae), a recently extinct family of giant lemurs (known assubfossil lemurs) native toMadagascar. Its ancestors were likelyarboreal (tree-dwelling), and this giant sloth lemur has been compared to the extinct giantground sloths of North and South America.[5]
| Phylogeny ofArchaeoindris and its closest lemur relatives[6][7] | |||||||||||||||||||||||||||||||||||||||
|
Archaeoindris was most closely related toPalaeopropithecus,[1] a genus containing the second largest of the sloth lemurs and specialized forsuspensory behavior in its arboreal habitat.[8] Traits of thepostcranium (skeleton below the skull) indicate thatBabakotia was the next most closely related sloth lemur toArchaeoindris andPalaeopropithecus, followed byMesopropithecus,[1] the smallest of the sloth lemurs.[9]
All four genera of sloth lemurs are known to be asister taxon (close relatives) of familyIndriidae, which includes theindri (Indri),sifakas (Propithecus), andwoolly lemurs (Avahi). This relationship is supported by data frommorphological,developmental andmolecular research. Another member of thisclade (related group) is the family ofmonkey lemurs (Archaeolemuridae). Dental features, such as the morphology of theirmolar teeth and the modified number of teeth in theirtoothcomb (a specialized grooming structure found in lemuriforms), have long suggested a relationship.
Other anatomical and developmental traits, though, suggested that monkey lemurs might be more closely related to familyLemuridae, which include five genera of lemur, including thering-tailed lemur (Lemur catta). Molecular analysis has shown strong support for the former, placing the monkey lemurs in a clade with the sloth lemurs and indriids.[1]
The family Palaeopropithecidae contains a large number of species compared to most other subfossil lemur families. It includes four known genera and seven species, all of which are now extinct.[10] Among these was the genusArchaeoindris, one of only a fewmonotypic lemurtaxa.[11]
Archaeoindris fontoynontii was first described byHerbert F. Standing in 1909 from two fragments of amaxilla (upper jaw) and a completemandible (lower jaw).[12][13] Thesetype specimens—AM-6239 (maxillae) and AM-6237 (mandible)—are stored in the collection at theUniversity of Antananarivo.[14] The mandible contains a complete set of upper teeth, the left maxillary fragment contains the lastpremolar (P4) and all three molars (M1–M3), and the right maxillary fragment bears both premolars (P2 and P4) and the first molar (M1).[13]
At the time, Standing noted similarities with thedentition ofPalaeopropithecus. Sixteen years after Standing's discovery,Charles Lamberton discovered the first and only completecranium (skull) and associated mandible forArchaeoindris, both of which were well preserved. He published this find in 1934.[13]
Only six postcranial specimens ofArchaeoindris have been found. Two of these belonged to an adult and include a damagedhumerus (upper arm bone) and an almost completefemur (thigh bone). The other four came from an immature individual, and include a damaged humerus, a damagedulna (lower arm bone), and two femurs, both lacking theepiphyses (rounded end of the bone) on both ends.
Archaeoindris is one of the least common of the subfossil lemurs, and the few known specimens were all found atAmpasambazimba in theCentral Highlands.[12] Excavations run by a multidisciplinary Malagasy-American team at this fossil site between 1983 and 1984 yielded no newsubfossil remains, and no other potential sites are known for this species.[15]
Historically, some remains from other subfossil lemurs have been mistakenly attributed toArchaeoindris, resulting in incorrect interpretations of its anatomy and behavior.[12] In 1934, Lamberton missed earlier attribution errors[16] and incorrectly labeled atibia and twofibulae (lower leg bones) from a species ofkoala lemur (Megaladapis grandidieri) as belonging toArchaeoindris. Because of these misattributions and Lamberton's use of the immature bones, his reconstruction was inaccurate.[12][17]
In 1936, Alice Carleton corrected Lamberton by identifying the tibia and fibulae as belonging to a koala lemur. Carleton's corrections were later confirmed and other misattributions were corrected in the 1960s and 1970s byAlan Walker andWilliam L. Jungers.[12][18]
In 1910, 24 years before Lamberton's monograph onArchaeoindris, Standing identified a massive right femur from Ampasambazimba as a new species,Lemuridotherium madagascariense. Although Standing recognized the strong similarities betweenLemuridotherium andArchaeoindris, he placed them in separate genera due to what he perceived as a great size difference.[18] Lamberton was also persuaded by the size difference, partly because he failed to recognize the smaller tibia and fibulae as belonging to the smallerMegaladapis grandidieri. Furthermore, Lamberton did not realize that the smaller femurs he assigned toArchaeoindris belonged to a juvenile.[19]
Although some later authors consideredLemuridotherium asynonym ofArchaeoindris, no one had provided provided a definitive proof until Martine Vuillaume-Randriamanantena in 1988.[18] Vuillaume-Randriamanantena also established associations between thepostcrania andcrania ofArchaeoindris,[16] summarized what is known about the postcranial skeleton, and documented the strong similarity with the genusPalaeopropithecus.[12]
Though similar toPalaeopropithecus,Archaeoindris was significantly larger and more robust.[5][14]Archaeoindris was one of the largest primates to ever evolve,[10] and was the largest-known strepsirrhine primate,[13] weighing an estimated 160 kg (350 lb).[2] It was roughly the size of an adult male gorilla,[12] which was first noted by Lamberton.[20]
Since its discovery, size estimates have varied from "larger than a human" to "possibly the largest primate ever". In a study by Jungers from 1990, the area of its molar teeth predicted a mass of 230.5 kg (508 lb), while thefemoral head diameter predicted a mass of 244.1 kg (538 lb).[20] In 1995,Laurie Godfrey estimated a mass of 197.5 kg (435 lb) using the midshaft circumferences of the humerus and femur.[21] Using multipleregressions of thecortical area of the femur in 2008,[22] Jungers and colleagues generated the current best estimate of 161.2 kg (355 lb) with a possible range of 150–187.8 kg (331–414 lb).[23] These estimates were considered to be more accurate since the harder cortical bone in the midshaft of the femur supported an animal's weight, and its thickness better correlated with the animal's mass than the midshaft diameter (which includes both hard cortex andspongy bone).[21] The onlyfossil primate that was probably larger thanArchaeoindris wasGigantopithecus blacki, a close relative oforangutans.[24]
Like all three species ofPalaeopropithecus,Archaeoindris exhibitedderived traits not seen in the two other, less-specialized genera of sloth lemurs.[7] These traits included deflatedauditory bullae and paired protrusions of bone around the nasal opening consisting of part of thepremaxilla and thenasal bones.[14][25][26] Its skull was wider than that ofMegaladapis, but shorter, measuring 269 mm (10.6 in).[2] Its face was shorter than that ofPalaeopropithecus,[5] with its eyes directed further forward. Theneurocranium (braincase) was small[2] and elevated relative to the face, unlikePalaeopropithecus.[27]Postorbital constriction (narrowing of the skull behind the eye sockets) is pronounced.[2] The skull also bore a low, broadsagittal crest (a ridge of bone on the top of the skull to which jaw muscles attach) and robust but smallernuchal crests (ridges of bone on the back of the skull to which neck muscles attach).[2][5][27]
The rims of theorbits (eye sockets) were not as thick as those ofPalaeopropithecus.[25] The area of the orbit was 946 mm2 (1.466 sq in), comparable to that of gorillas. The ratio of its orbit area to the size of itsoptic canal indicates thatArchaeoindris had lowretinal summation, meaning its eyes were as sensitive to light as those of living diurnal lemurs, yet the ratio was not as low as in comparably sized apes, suggestingArchaeoindris had lowervisual acuity than apes do and lackedtrichromatic color vision.[28]
.jpg)
The jaw exhibited a long, robustmandibular symphysis (joining of the two halves of the lower jaw), which fused early during development.[25][29] Itspalate (bones on the roof of the mouth) was rectangular.[14] Like other sloth lemurs, it likely experienced accelerated dental development,[29] and had an adultdental formula of2.1.2.32.0.2.3.[26] Its teeth were also similar to those ofPalaeopropithecus, both in morphology and proportions.[2] The four lowerincisors that would have made up the toothcomb were modified, being shorter and more robust, possibly for feeding purposes.[30] Thecanines were short and stout, but sharp.[31] Also, there was adiastema (gap) between the lower premolars (p2 and p4). Other dental similarities withPalaeopropithecus included small third upper and lower molars (M3 and m3), the first and second molars were narrow and long, and theenamel of its cheek teeth was crenulated (low and rounded), though not as wrinkled and slightly higher-crowned.[2]
Most bones of the postcranial skeleton, including the bones of the hands, feet, vertebral column, ribs,radius (lower arm bone), tibia, and fibula, have not been found forArchaeoindris.[32] As with many cranial features, the postcranial bones that have been discovered are similar to those ofPalaeopropithecus, but significantly larger and more robust. The head of the femur was large and lacked afovea capitis femoris (a small depression in the head of the femur).[2] The femur was short and extremely robust,[14] had a very high collodiaphyseal angle (the angle of the neck and shaft of the bone), and thegreater trochanter was small.[2]
In the adult, the humerus was significantly longer than the femur, while in the immature specimen, both the humerus and ulna were much longer than the femur,[33] making the arms considerably longer than the legs, as also seen inPalaeopropithecus. Yet, the relative length of arms to legs was shorter inArchaeoindris, so although itsintermembral index was over 100, it was lower than that ofPalaeopropithecus.[2][34]
Archaeoindris is thought to have been a leaf-eater (folivorous),[5] a view supported by wear patterns on its teeth.[35] Its fused mandibular symphyses and the likelihood of accelerated dental development suggest that it began processing fibrous foods in the mouth with thorough chewing.[29] Its diet may also have included some fruits and seeds.[36] Like most of the other giant lemurs,Archaeoindris is thought to have beendiurnal because of its relatively small orbits, which are comparable to those of gorillas.[37]
Both Standing and Lamberton assumedArchaeoindris to be a slow-moving tree-dweller likeMegaladapis, primarily due to the misattributed bones. Lamberton also speculated that it would have resembled a ground sloth, a view later supported by Jungers in 1980 after several misattributions had been corrected and having considered its gorilla-like size. Jungers went on to propose that it would have spent most of its time on the ground (terrestrial).
The functional morphology of its hip joint indicates a degree of mobility typically seen in more arboreal animals.[33] Other traits shared withPalaeopropithecus, particularly seen in the femur, suggest thatArchaeoindris spent considerable time in the trees for feeding and possibly nesting,[25][38] although it also would have visited the ground to feed and travel. It is described as a deliberate, scansorial (climbing)browser, and whether it was likePalaeopropithecus in performing hang-feeding is unknown, since hand and foot bones are missing. Given its bulky size, this would be unexpected.[33]
Archaeoindris is known from only one subfossil site, Ampasambazimba, in central Madagascar, and all remains date to the LateQuaternary.[39] The area today is dominated by grasslands, particularly of the grass genusAristida.[40] Prior to human arrival, the area around Ampasambazimba was not completely forested, but more of an open habitat, consisting of a mix of woodlands, bushlands, and savanna.[41] Animal remains at this subfossil site have yielded about 20 species of lemurs living insympatry (sharing the same geographic area). In comparison, the nearbyAmbohitantely Special Reserve today contains only four species, roughly 20% of the area's original lemur diversity.[42]
Despite being the most species-rich family among the giant lemurs, all four genera of sloth lemur, includingArchaeoindris, have gone extinct.[35]Radiocarbon dating of thestratigraphic level of some of theArchaeoindris remains were dated to 8000 BP,[5] while two other specimens were dated to 2362–2149 BP (412–199 BCE) and 2711–2338 BP (761–388 BCE).[43] From these dates, it is likely thatArchaeoindris was still alive on the high plateau in 350 BCE when the first humans reached the west coast of Madagascar,[44] despite being rare by that time. Consequently, it would have been especially vulnerable to hunting andhabitat loss.[5]
