| Saadanius | |
|---|---|
 | |
| Saadanius hijazensis | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Primates |
| Suborder: | Haplorhini |
| Infraorder: | Simiiformes |
| Parvorder: | Catarrhini |
| Superfamily: | †Saadanioidea Zalmoutet al., 2010 |
| Family: | †Saadaniidae Zalmoutet al., 2010 |
| Genus: | †Saadanius Zalmoutet al., 2010 |
| Species: | †S. hijazensis |
| Binomial name | |
| †Saadanius hijazensis Zalmoutet al., 2010 | |
Saadanius is agenus of fossilprimates dating to theOligocene that is closely related to thecommon ancestor of theOld World monkeys andapes, collectively known ascatarrhines. It is represented by a single species,Saadanius hijazensis, which is known only from a single partial skull tentatively dated between 29 and 28 million years ago. It was discovered in 2009 in westernSaudi Arabia nearMecca and was first described in 2010 after comparison with both living andfossil catarrhines.
Saadanius had a longer face than living catarrhines and lacked the advancedfrontal sinus found in living catarrhines. However, it had a bonyectotympanic and teeth comparable to those of living catarrhines. Its discovery provided new information about the early evolution of catarrhines.
Saadanius is known from a single specimen, theholotype, named "SGS-UM 2009-002", stored inJeddah, Saudi Arabia, at the Paleontology Unit of theSaudi Geological Survey (SGS).[1] The specimen was discovered in southwestern Saudi Arabia in February 2009[2] by paleontologist Iyad Zalmout, who had traveled to the region to search forancient whale anddinosaur fossils. While looking for dinosaur fossils in an area that, according to the maps he was working from, contained rock layers that dated to theCretaceous, Zalmout found the jawbone of ananthracotheriid, which dated to theEocene or Oligocene. This indicated that the rock layers were much younger than what was dated on the maps. The following day, he noticed fossil teeth, which he immediately recognized as those of a primate. Zalmout emailed a photo of the teeth to paleontologistPhilip D. Gingerich, with whom he was working as a postdoctoral fellow. Gingerich, an expert on ancient primates and whales, confirmed that it was indeed a primate. Due to a tight schedule, Zalmout had to leave the exposed fossil embedded in the rock for the next few days because collecting it would require days of work.[3] The fossil was soon recovered by a joint expedition involving the SGS and theUniversity of Michigan.[1]
The fossil was formally described in 2010 when its discovery was announced in the journalNature.[2] Thegenus name,Saadanius, comes from the Arabic word,saadan (Arabic:سَعدان), which is the collective term for apes and monkeys. The species name,hijazensis, is a reference to theal Hijaz region, in which it was discovered.[1]
The only known fossil ofSaadanius is a partial skull, preserving much of the face and palate and many of the teeth. Two bite marks, one of which may have been fatal, are visible on the skull.[1] Its enlarged, deep-rootedcanine teeth, thediastema between its canine teeth and secondincisors, and itssagittal crest suggest that the specimen was a male.[1] These features are shared among male Old World monkeys.[2]
Saadanius had a longer face than living catarrhines,[4] more closely resemblingNew World monkeys in appearance,[5] although it was larger, similar in size to thesiamang.[1] It most closely resembles the older fossilAegyptopithecus, but it also shares some similarities with later catarrhines.[1] For example, it lacks the advancedfrontal sinus found in livinghominoids,[1][2][4] but it does possess a tube-shapedectotympanic, found in living catarrhines.Propliopithecoids, the oldeststem group of catarrhines, which date back 35 to 30 mya, lacked a fully developed ectotympanic.[1][4]
The uppermolars were relatively wide, with prominent well-separated cusps. The third upper molar (M3) was larger than the second (M2). Thecanines were relatively smaller than in some later taxa likeProconsul, with an approximately oval cross-section. The nasal aperture is relatively large, though unlike inDendropithecus it does not extend between the roots of the firstincisors. Thenasals are long and narrow and do not touch thepremaxillae.[1]
| Saadanius placement within the catarrhine clade[1] | ||||||||||||||||||||||||
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Comparative anatomy andcladistic analysis performed when the fossil was discovered indicate thatSaadanius is more closely related to the last common ancestor ofcrown catarrhines than any other known fossil catarrhines, placing the common ancestry of Catarrhini in Arabia and Africa. Other stem catarrhines include propliopithecoids, such asAegyptopithecus, andpliopithecoids, such asPliopithecus. The closer similarities betweenSaadanius and crown catarrhines, particularly its ectotympanic, suggestSaadanius of all known fossil primates most closely resembled the last common ancestor of living catarrhines.[1] Some later studies instead foundSaadanius to be more closely related toOld World monkeys than tohominoids, placing it among crown catarrhines.[6][7]
The discovery ofSaadanius provides new evidence for competing hypotheses about the facial appearance of the ancestral crown catarrhines, or common ancestor. One reconstruction is based on living catarrhine traits and predicts a short face and a rounded braincase, similar to that of a gibbon. Another reconstruction, based on themorphology of earlyMiocene apes and thebasal cercopithecoidVictoriapithecus, predicts that the last common ancestor had a projecting snout and tall face, like that of livingbaboons and the oldest fossil apes and Old World monkeys. The conservative features ofSaadanius, similar to those of the older stem catarrhines, support the latter hypothesis, according to Zalmoutet al.[1][4][3] However, one palaeontologist, Eric Delson, has cautioned that geological pressure may have distorted the shape of the skull.[4]
According to Zalmoutet al.,Saadanius may also help resolve the age of the hominoid–cercopithecoid split.[1][4]Paleoanthropological work has typically placed the divergence between 25 and 23 mya, but genetic-based estimates have placed it in the early Oligocene, approximately 33 mya. Despite the predictions from the genetic tests, little fossil evidence has been found for a last common ancestor between 30 and 23 mya, favoring a later split. Only isolated teeth ofKamoyapithecus hinted at the existence of potential basalhominoids in the late Oligocene (between 24 and 27.5 mya),[1][5] while the oldest fossil Old World monkey,Victoriapithecus macinnesi, dates to 19 mya.[8] With the discovery ofSaadanius, Zalmoutet al. suggested a later split than the genetic data, dating between 29–28 and 24 mya.[1][5] However, Pozziet al. later argued that althoughSaadanius is a significant discovery, because it is a stem catarrhine, it could not be used to date the divergence of the crown group. The presence of stemtaxa in thefossil record does not indicate that crown groups have evolved, and stem taxa may survive for millions of years after the crown taxa appear. For this reason, the fossil record can only suggest a hard minimum boundary for divergence dates, which corresponds to the first appearance of a crown taxon. Furthermore, Pozziet al. pointed out that the supplementary material published by Zalmoutet al. demonstrated that Pliopithecoidea were more closely related to living catarrhines thanSaadanius.[8] In 2013, two other Oligocene catarrhines were announced, the proposed Old World monkeyNsungwepithecus and the hominoidRukwapithecus.[9]
The fossil find has also been seen by the SGS as an important find for Saudi Arabia, because it enriches the fossil record for the region. As a result of the find, both the SGS and the University of Michigan are considering more collaborative field explorations in the country.[3]
Saadanius was found on top of anooliticironstone fossil bed of the middleShumaysi Formation located in the southwest corner of Harrat Al Ujayfa, in western Saudi Arabia, close to Mecca. Other fossils recovered from the same horizon include a few teeth and jaws of the following mammals:[1]
The presence of a gomphothere and mammutid suggests that the deposits are younger than theJebel Qatrani Formation atFayum inEgypt, while the other taxa indicate an older age than theChilga Formation ofEthiopia. This led Zalmout's team to assign an age of 28 or 29 million years to the Shumaysi Formation fauna.[1][4] However, the date has yet to be confirmed by other dating techniques.[4] A 2020 review assigned the Harrat Al Ujayfa locality to theTurkwelian African land mammal age, which started 28.2 million years ago.[10]
Like other catarrhine primates,Saadanius was probably a tree-dweller.[5] During the time it would have lived, theRed Sea had not yet formed, and new plant and animal species would have been arriving from nearbyEurasia as it converged with the Afro-Arabian landmass.[2]
The specimen had serious puncture wounds on the front of the skull, indicating that it had been preyed upon by a largecarnivore.[2] One puncture wound was on the right side of thebraincase and may have been the fatal blow. There was also a bite mark on thefrontal trigone.[1]
