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Saadanius

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Saadanius
Temporal range:29–28Ma
↓
"Saadanius hijazensis"
Saadanius hijazensis
Scientific classificationEdit this 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

Saadaniusis agenusof fossilprimatesdating to theOligocenethat is closely related to thecommon ancestorof theOld World monkeysandapes,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 ArabianearMeccaand was first described in 2010 after comparison with both living andfossil catarrhines.

Saadaniushad a longer face than living catarrhines and lacked the advancedfrontal sinusfound in living catarrhines. However, it had a bonyectotympanicand teeth comparable to those of living catarrhines. Its discovery provided new information about the early evolution of catarrhines.

Taxonomy

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The specimen was found with the palate and teeth facing upward.

Saadaniusis 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 whaleanddinosaurfossils. 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 theEoceneor 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]Thegenusname,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 Hijazregion, in which it was discovered.[1]

Description

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Front and side view ofSaadanius hijazensis.

The only known fossil ofSaadaniusis 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,thediastemabetween its canine teeth and secondincisors,and itssagittal crestsuggest that the specimen was a male.[1]These features are shared among male Old World monkeys.[2]

Saadaniushad a longer face than living catarrhines,[4]more closely resemblingNew World monkeysin 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 sinusfound in livinghominoids,[1][2][4]but it does possess a tube-shapedectotympanic,found in living catarrhines.Propliopithecoids,the oldeststem groupof catarrhines, which date back 35 to 30 mya, lacked a fully developed ectotympanic.[1][4]

The uppermolarswere relatively wide, with prominent well-separated cusps. The third upper molar (M3) was larger than the second (M2). Thecanineswere relatively smaller than in some later taxa likeProconsul,with an approximately oval cross-section. The nasal aperture is relatively large, though unlike inDendropithecusit does not extend between the roots of the firstincisors.Thenasalsare long and narrow and do not touch thepremaxillae.[1]

Phylogeny

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Saadaniusplacement within the catarrhine clade[1]
Catarrhini

Propliopithecoidea(Aegyptopithecus)

Pliopithecoidea(Pliopithecus)

Saadanius

crown catarrhines
(living and fossil)

Comparative anatomyandcladistic analysisperformed when the fossil was discovered indicate thatSaadaniusis more closely related to the last common ancestor ofcrowncatarrhines 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 betweenSaadaniusand crown catarrhines, particularly its ectotympanic, suggestSaadaniusof all known fossil primates most closely resembled the last common ancestor of living catarrhines.[1]Some later studies instead foundSaadaniusto be more closely related toOld World monkeysthan tohominoids,placing it among crown catarrhines.[6][7]

Animated 3D view of the skull

The discovery ofSaadaniusprovides 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 themorphologyof earlyMioceneapes and thebasalcercopithecoidVictoriapithecus,predicts that the last common ancestor had a projecting snout and tall face, like that of livingbaboonsand 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.,Saadaniusmay also help resolve the age of the hominoid–cercopithecoid split.[1][4]Paleoanthropologicalwork 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 ofKamoyapithecushinted at the existence of potential basalhominoidsin 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 althoughSaadaniusis 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 stemtaxain thefossil recorddoes 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 monkeyNsungwepithecusand 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]

Paleoecology

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Saadaniuswas found on top of anooliticironstonefossil bed of the middleShumaysi Formationlocated 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 FormationatFayuminEgypt,while the other taxa indicate an older age than theChilga FormationofEthiopia.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 theTurkwelianAfrican land mammal age, which started 28.2 million years ago.[10]

Like other catarrhine primates,Saadaniuswas probably a tree-dweller.[5]During the time it would have lived, theRed Seahad not yet formed, and new plant and animal species would have been arriving from nearbyEurasiaas 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 thebraincaseand may have been the fatal blow. There was also a bite mark on thefrontal trigone.[1]

References

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  1. ^abcdefghijklmnopqrsZalmout, I. S.; Sanders, W. J.; MacLatchy, L. M.; Gunnell, G. F.; Al-Mufarreh, Y. A.; Ali, M. A.; Nasser, A. -A. H.; Al-Masari, A. M.; Al-Sobhi, S. A.; Nadhra, A. O.; Matari, A. H.; Wilson, J. A.; Gingerich, P. D. (2010). "New Oligocene primate from Saudi Arabia and the divergence of apes and Old World monkeys".Nature.466(7304): 360–364.Bibcode:2010Natur.466..360Z.doi:10.1038/nature09094.PMID20631798.S2CID205220837.
  2. ^abcdefSample, I. (14 July 2010)."Ape ancestors brought to life by fossil skull of 'Saadanius' primate".The Guardian.
  3. ^abcRoss-Flanigan, N. (14 July 2010)."Fossil find puts a face on early primates".University of Michigan News Service.
  4. ^abcdefghLaursen, L. (14 July 2010)."Fossil skull fingered as ape–monkey ancestor".Nature.NatureNews.doi:10.1038/news.2010.354.
  5. ^abcdGhosh, P.(14 July 2010)."Fossil links humans and monkeys".BBC News.Archived fromthe originalon 15 July 2010.
  6. ^Gilbert, Christopher C.; Ortiz, Alejandra; Pugh, Kelsey D.; Campisano, Christopher J.; Patel, Biren A.; Singh, Ningthoujam Premjit; Fleagle, John G.; Patnaik, Rajeev (2020-09-09)."New Middle Miocene ape (Primates: Hylobatidae) from Ramnagar, India fills major gaps in the hominoid fossil record".Proceedings of the Royal Society B: Biological Sciences.287(1934): 20201655.doi:10.1098/rspb.2020.1655.PMC7542791.PMID32900315.
  7. ^Nengo, Isaiah; Tafforeau, Paul; Gilbert, Christopher C.; Fleagle, John G.; Miller, Ellen R.; Feibel, Craig S.; Fox, David L.; Feinberg, Josh; Pugh, Kelsey D.; Berruyer, Camille; Mana, Sara; Engle, Zachary; Spoor, Fred (2017)."New infant cranium from the African Miocene sheds light on ape evolution".Nature.548(7666): 169–174.Bibcode:2017Natur.548..169N.doi:10.1038/nature23456.PMID28796200.S2CID4397839.
  8. ^abPozzi, L.; Hodgson, J. A.; Burrell, A. S.; Disotell, T. R. (2011)."The stem catarrhine Saadanius does not inform the timing of the origin of crown catarrhines"(PDF).Journal of Human Evolution.61(2): 209–210.Bibcode:2011JHumE..61..209P.doi:10.1016/j.jhevol.2011.02.008.PMID21497373.
  9. ^Stevens, Nancy J.; Seiffert, Erik R.; O'Connor, Patrick M.; Roberts, Eric M.; Schmitz, Mark D.; Krause, Cornelia; Gorscak, Eric; Ngasala, Sifa; Hieronymus, Tobin L.; Temu, Joseph (2013)."Palaeontological evidence for an Oligocene divergence between Old World monkeys and apes"(PDF).Nature.497(7451): 611–614.Bibcode:2013Natur.497..611S.doi:10.1038/nature12161.PMID23676680.S2CID4395931.
  10. ^Van Couvering, John A.; Delson, Eric (2020-12-01). "African land mammal ages".Journal of Vertebrate Paleontology.40(5): e1803340.Bibcode:2020JVPal..40E3340V.doi:10.1080/02724634.2020.1803340.S2CID229372221.
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