Afradapis longicristatus Introduction: Afradapis longicristatus was a large-body folivorous adapiform of the the late Eocene (37 ma) (Seiffert, 2009) in Egypt. It presents a new perspective on the Adapiform lineage, and proves Darwinius’ strepsirhine, rather than haplorrhine ancestry. Both afradapis and darwinius are stem strepsirrhines in that they are adapiformes. Despite anthropoid-like characteristics, Afradapis, Darwinius, Aframonius, Caenopithecus, and Mahgarita are phylogentically placed within the stem Strepsirhine clade Caenopithecina (Seiffert, 2009) (Seiffert, 2012) due to their unique astragalar morphology. (Boyer et al., 2010) There is no known extant form of afradapis, Caenopithecinae, or adapiformes. The holotype of Afradapis longicristatus is a mandible with unique dental features of p4 and m3 (CGM 83690), as well as exhibiting an absence of the P2. (Seiffert, 2009) These features correlate with anthropoid-like adaptation that could indicate a pre-anthropoid occupation of the current anthropoid niche. (Seiffert, 2009), (Seiffert 2012). A possible reason for the extinction of afradapis, adapiforms, and stem strepsirrhines is the glaciation of Antartica and the resulting sharp declination of global temperatures and environments.(Kirk et al., 2012),( (Zachos etal., 2001). Binomial nomenclature: “Generic name derived from Afra, Latin, Africa, and adapis, in refernce to Adapis Cuvier, 1821. Specific epithet is from Longi- Latin, long, and cristatus, Latin, crested. “ (Seiffert et al. 2009)
Locality: 60 km south of Cairo, in the Fayum depression of Egypt, lies the Birket Qarun Locality 2 (BQ-2), a freshwater river deposit that contains the holotype of Afradapis. The locality contains the most diverse assemblage of mammalian fauna from the Paleogene.In the Birket Qarun Locality 2, the Umm Rigl Member contained the holotype for Afradapis (Seiffert, 2009), (Seiffert, 2008).
Fossil record: The discovery of the Afradapis holotype at BQ-2 locality in the Fayum of Egypt included several relevant fossils including specimen CGM 8690, a partial left mandible preserving p4-M3 and massetric fossa; specimen DPC 21370J, and DPC 24085A showing a fully ossified symphysis, transverse tori superior and inferior to genial tubercles (Seiffert, 2009), and specimen DPC 21445C , an astragalar bone of the ankle. The astragalar was only recently (2010) attributed to Afradapis and shows Strepsirrhine characteristics of a laterally sloping fibular facet, which provide indications of loris-like locomotion. See Darwinius Debate, and Postcrania Morphology sections. (Seiffert, 2008).
Time period:
The methods to date the fossils found in the Fayum are paleomagnetic reversal stratigraphy, invertebrate biostratigraphic evidence, and sequence stratigraphy (Seiffert, 2009. Analysis of planktic foraminifera of the underlying strata known as the Gehannam Formation restrict the BQ-2 locality maximum age to approximately 38 to 39.5 Ma. Biostratigraphic analysis of the index fossils found at BQ-2, including Nummulites striatus (late Bartonian to early Priabonian in age), Nummulites pulchellus (Priabonian in age), Nummulites beaumonti (Bartonian in age), and Nummulites gizehensis (Lutetian in age) further indicating an Eocene age for the locality. It was unclear, however, if these index fossils were from below the BQ-2 Umm Rigl member. Further age clarification through paleomagnetic reversal analysis indicates that the BQ-2 would be associated with Chron C17n.1n, which yields an age range of 36.51 to 37.24 Ma, or earliest Priabonian in age. Therefore, we can say without a doubt that the holotype for Afradapis most likely came to rest in the area around 37 million years ago in the Eocene. Further, looking at the low global sea level for the Bartonian-Priabonian stages of the Eocene supports the evidence for a fluvial dominated environment for the BQ-2 locality 37 million years ago (Seiffert, 2008) See the section regarding Paleoenvironment below for further information on the BQ-2 locality.
Size:
Mean body mass estimates of both a prosimian and all primate regressions indicate a body size range of 2.187 kg to 3.262 kg,based on molar areas and lengths. This is comparatively large in that other members of the family Adapidae are generally just over 1 kg. (Seiffert, 2009).
Morphology: Dental: The holotype of Afradapis contains a partial left mandible with preserved P4-M3, as well as a masseteric fossa. The molars seen in this holotype are similar to those seen in the highly folivorous extant primates Alouatta, and Indri.The preserved dental characteristics of high crests with well developed shearing crests indicate a highly folivorous diet, consisting of abundantly available leaves. This also may point towards a group dynamic similar to that seen in extant folivorous primates. (Seiffert, 2009), (Seiffert , 2012).Afradapis longicristatus Holotype, (Seiffert, 2009).
Dentition:
Afradapis’ lower incisors crowns follow characteristics of known adapiforms in that they are spatulate, and have lingual keels as well as weak lingual cingulids. Lower I1 and I2 and have sharp occlusal edges; lower I1 is flat, while lower I2 is in line with I1 towards the middle, but then curves distally - alveoli for lower I1-2 are not very procumbent.
The upper incisors for Afradapis have rounded occlusal surfaces, and are asymmetric - edges are unlikely to have resulted in a continuous blade. There was likely a small interincisal gap due to a lack of midline contact - developed mesial processes on the upper central incisor crowns, and no interproximal wear facet on any of the isolated upper incisors. The robust lower canine of Afradapis’ protrudes above the occlusal plane - indication of contact with the anterior edge of the upper canine on distal heel. Sharp mesial, distal edges, reduced lingual cingulum and deep mesial groove on upper canine. No evidence of sexual dimorphism. The absence of a second premolar is a very anthropoid diagnostic trait. This morphological feature may indicate either convergent evolution (See below for distinction from the Anthropoid clade), or the necessary adaptation in order for Afradapis to occupy the specific folivorous niche with competition to Anthropoids (See below section on Darwinius debate). Lower P3 has long honing facet which is the result of wear against the distal face of the upper canine; lower P3 is longer and taller than lower P4, and has more obliquely planted roots - primary crest long axes oblique relative to long axis of tooth row. Reconstruction of Holotype from above fragments (Seiffert, 2009). On lower M1-2 hypoconulid is very small or absent, but there is a large hypoconulid lobe present on lower M3. Upper molars size decreases, sporting rounded distal margins visible distally along the toothrow. Upper M1-2 show well-developed mesostyles, a clear buccal cingula, hypocones derived from the posterior cingulum and trenchant postprortcristae and prehypocristae. On preprotocrista - large paraconule present but no metaconule. Upper M3 has a strongly convex distal margin, tiny metacone, hupocone and paraconule cusps, and an expanded talon. (Seiffert, 2009). Folivorous Characteristics: Afradapis molars have high crests with well-developed shearing crests, similar to the highly folivorous extant primates Alouatta, and Indri. “Afradapis’ elaborate shearing crests indicate that the species was likely to have been highly folivorous as well.” (Seiffert, 2009) It is likely that the similar molar morphology of Caenopithecids including Afradapis to the molar morphology of Anthropoids (=Simiiformes) means that the Caenopithecids occupied a dietary niche of folivory. This may indicate that Caenopithecids (and most likely their relative adapiformes) actually competed with early Anthropoids for control of the niche. With the eventual paleoclimate change towards the Eocene-Oligocene boundary, anthropoids obviously started to take advantage of some Caenopithecid disadvantage. Further out-competing of anthropoids over Caenopithecines and Afradapis made them reach extinction by the end of the (C) Afradapis longicristatus (Strepsirrhini, Caenopithecinae, earliest late Eocene, Egypt). D) Aframonius dieides (Strepsirrhini, Caenopithecinae, latest Eocene, Egypt). (Seiffert, 2012). Eocene. Further information on extinction below (Seiffert, 2009), (Seiffert, 2012).
Locomotion; Astragalar An astragalar, or Talus-bone of Afradapis (DPC 21445C) has been discovered in the Birket Qarun (BQ2); the morphology of this ankle-bone provides new information about the possible phylogeny of Afradapis, regarding its place as either Strepsirrhine or Haplorhine. Living strepsirrhine and haplorhine primates have notably different astragalar morphology, for example: the position of the tendon groove of the flexor fibularies in relation to the tibial facet, as well as the orientation of the fibular facet relative to the lateral tibial facet. This can also be understood as “laterally sloping” fibular facet for strepsirrhines, and “vertical and straight-sided” fibular facet for haplorhines (Boyer et al., 2010). The astragalar morphology of Afradapis appears to place it with Strepsirrhines: “The astragalus of Afradapis bears a strongly sloping fibular facet, adding support to its placement (along with other adapiforms) among strepsirrhines.”(Boyer et al., 2010). Afradapis astragalar morphology (Boyer et al., 2010) The locomotion of Afradapis can be extrapolated from its astragalar morphology, which is highly loris-like, indicating that Afradapis was most likely a slow-climbing arborealist, similar to modern lorisids.(Boyer et al., 2010), (Kirk et al., 2012), (Seiffert, 2012). Morphological characteristics discussed in this section help provide insight to the phylogenetic placement of the much discussed Darwinius. See below. Phylogeny: Darwinius Debate: Darwinius masillae is a relative Caenopithecine of Afradapis. It exhibits similar anthropoid-like dental morphological characteristics that assigned it as the "missing link" between Tarsiers and early Anthropoids (haplorhines). The astragalar of the ankle bone, another important phylogenetic identifier, was found as well but provided no diagnostic result. However, the 2009 discovery of Afradapis included the astragalar bone of the ankle (DPC-21445C) as well, which displayed signs of a strepsirhine laterally sloping fibular facet. “Franzen et al (2009) argued that Darwinius has a characteristically haplorhine “vertical and straight-sided” fibular facet on its astragalus, and employed this observation as one of the key lines of evidence in support of Darwinius’ alleged haplorhine affinities.” (Boyer et al., 2010). The discovery of Afradapis clearly defines Afradapis and Darwinius as cercamoniinae strepsirrhines instead of haplorhines (Dalton, 2009)
The two genera's clear relation in both phylogeny (Caenopithecines) and geologic time (Eocene) indicate that the family Caenopithecidae is most likely therefore strepsirhine in origin. Seiffert explained that Darwinius' astragalar is not indicative of either haplorhine or strepsirhine relation due to damage during fossilization. This may be due to the fact that Seiffert only examined a cast, and not the original. However, the relationship of Afradapis and Darwinius, along with a clear strepsirhine astragalar from Afradapis, gives enough evidence that Darwinius is infact a strepsirhine and not a haplorhine. (Seiffert, 2009), (Dalton, 2009).
Environment and Ecology: Paleoenvironment: The Birket Qarun Locality 2 (BQ-2) is a terrestrially deposited alluvial formation with no evidence of a marine or near-shore origin. It is the earliest known terrestrial deposit of Egypt since the Cretaceous. The BQ-2 locality represents an area of periodic flooding as seen through stratigraphic analysis. The presence of limonitic limestone indicates deposition via bogs that were periodically flooded with no more than one meter of water. This flooding buried the newly formed surface with coarse materials, and eventually continually finer materials.Vertebrate fossils are found in the coarse material (including Afradapis). The process would repeat which yeilds the periodic deposition of coarse grained to fine grained rock in the lithological column for BQ-2 (See (Seiffert, 2008), Fig 3.). The abundant vertebrate fossils found at the BQ-2 unit lack evidence of abrasion, indicating little post-mortem transportation of the organism before burial and fossilization. This lack of transportation before burial along with an abundance of arboreal primate remains in and around the BQ-2 and overall Fayum deposits indicates the presence of a forest at or near the location during the time of deposition. Furthermore, inquiries into the date of deposition and subsequent burial of Afradapis at BQ-2 yields a result of 36.51 to 37.24 Ma (millions of years before present), or earliest Priabonian in age, during the early Late Eocene. Two different stratigraphic analyses led to this conclusion: first, a biostratigraphic study of the planktonic foraminifera Nummulites, and second, a paleomagnetic reversal stratigraphy study by Kappelman et al., 1992 (Seiffert, 2008) (Zachos, 2001).
Eocene-Oligecene Extinction: Paleobiogeography of a pan-Tethys dispersal of adapiforms (Walsh, Dworsky, 2013) The Eocene-Oligocene boundary marked one of five significant extinction events in the course of geologic time. However, it was not nearly as destructive as other extinction events, but was rather an anomaly of the extinction rate at the time. Causes for the event, which in turn is believed to have killed out Afradapis, are not fully known. However, a drastic increase in global cooling near the end of the Eocene likely coincided with the development of an Antarctic ice sheet ^6. Most likely, this cooling caused by the southern hemispherical glaciation altered the habitat of the primates in the Fayum of Egypt, where Afradapis was found, which in turn gave anthropoids some significant advantage over the now extinct adapiformes, Caenopithecines, and Afradapis. This event was completely different than the usual causes for extinction events such as an extraterrestrial bolide impact. In fact, it was a gradual declination of global temperatures over a long period of time, possibly around 300,000 years. Because of this longevity of the extinction event, we can see that the primates affected by the event may not have become extinct all at once. Instead, some genera survived into the early early Oligocene, while others may have died out before the extent of the event (Seiffert, 2007) (Zachos, 2001).
Developing Hypotheses of Paleobiogeographical Distributions: The phylogeny relating to African Afrimonious, Darwinius and Afradapis as well as the European Caenopithecus lemuroides indicates at least one geographic dispersal across the Tethys sometime in the mid-late Eocene (Seiffert, 2009). Independent evolution (on separate land masses) of caenopithecus and afradapis (in a split later than aframonius) derived dental features from primitive ancestor of caenopithicine and afradapis, but not afromonius. Could the astragalar morphology of European Darwinius as compared to the later African Afradapis show some kind of geographic morphological adaptation, as in Afradapis would need its specialized astragalar in order to survive in Africa? The presentation and comparison of the later European Caenopithecus's astragalar may prove this if it astragalar is visibly similar to that of Darwinius. References: Boyer. (2010). Astragalar Morphology of Afradapis, a Large Adapiform Primate from the Earliest Late Eocene of Egypt. American Journal of Physical Anthropology, 143, 383-402. Dalton, R. (2009). Fossile Primate Challenges Ida's Place. Nature , 461, 1040. Kirk. (2012). Morphology of the Petrosal and Bony Labyrinth in Afradapis longicristatus (Primates, Adapiforms). Journal of Vertebrate Paleontology , 32. Seiffert, E. (2007). Evolution and Extinction of Afro-Arabian Primates Near the Eocene-Oligocene Boundary. Folia Primatologica , 78, 314-327. Seiffert, E. (2008). Geology Paleoenvironment and Age of Birket Quarum Locality 2, Fayum. In E. Simons, Fleagle, & Gilbert (Eds.), Search for Origins. Springer. Seiffert, E. (2009). Convergent Evolution of Anthropoid-like Adaptations in Eocene Adapiform Primates. Nature, 461, 1118-1122. Seiffert, E. (2012). Early Primate Evolution in Afro-Arabian . Evol. Anthropol. , 26, 239-253. Seiffert, E. (2012). Morphology and Relationships of Large-Bodied Afradapis from the Late Eocene of Egypt. American Journal of Physical Anthropology, Annual Meeting Supplement 50, 212.