Know Your Primate: Saadanius hijazensis 

Saadanius hijazensis is a fossil primate dating to the Oligocene at somewhere around 29-28 MYA. Brian Switek has an excellent overview of the finds implications for paleoanthropology.


Order: Primates
Suborder: Anthropoidea
Infraorder: Catarrhini
Superfamily: Saadanioidea
Family: Saadaniidae
Genus: Saadanius
Species: Saadanius hijazensis

As mentioned above, Saadanius hijazensis dates to the Oligocene and was found in Saudi Arabia. It is a medium size catarrhine, with a cranium similar in size to that of the siamang. It has broad molars, spatulate incisors, thin enamel on the teeth, strong midfacial projection, high orbits, long narrow nasal bones, strong temporal lines, a sagittal crest (consequently the authors of the paper assume the specimen is that of a male), lacks a frontal sinus, shallow palate, and a short tubular ectotympanic. Overall, according to the authors of the paper, Saadanius hijazensis shares a preponderance of features with Aegyptopithecus zeuxis. Another suite of features are intermediate between those of Aegyptopithecus zeuxis and Miocene apes. That being the case, the morphology of Saadanius hijazensis can help us recognize basal hominoids:

Early Miocene apes show few modern hominoid synapomorphies, complicating the identification of basal hominoids… The ways in which early Miocene apes differ anatomically from Saadanius and other stem catarrhines are crucial for providing a method for recognizing basal hominoids. For example, ‘dendropithecoids’ have resisted definitive classification because of their primitive postcranial morphology and a lack of information about cranial features such as the form of the ectotympanic… However, possession of frontal sinuses and relatively enormous male canines differentiate them from propliopithecoids, pliopithecoids, Saadanius and basal cercopithecoids, and link them with ‘proconsuloids’ as possible hominoids … [references removed - afarensis]

This is where things get complicated, so some terminological definitions are in order. Crown groups are currently extent species plus the common ancestor of all those currently extant species. Stem groups consist of all species more closely related to the crown group than they are to any other group. The terminology is very flexible so that we can speak of crown group primates (all currently extant primates back to their common ancestor) and stem primates (all species more closely related to primates than to Dermoptera) we can also narrow it and speak of crown groups catarrhines (extant catarrhines back to their common ancestor) and stem catarrhines (species more closely related to catarrhines than to, say, platyrrhines or hominoids). Stem groups give important insights into crown group morphology. As Valentine says (in speaking of phyla):

Stem group taxa expand the morphological features and, usually, the morphological disparity of a phylum beyond that of the crown group, while at the same time they lack the crown-group synapomorphies

Saadanius hijazensis is a stem catarrhine, and, as mentioned above will throw some light on crown group morphology. One way concerns the reconstruction of the last common ancestor of catarrhines. Reconstructions based on on currently extant species of catarrhines yields the following (from Benefit and McCrossin):

Current widely accepted reconstructions of ancestral catarrhine craniofacial morphology are based on the premise that similarities shared by extant colobines and gibbons are conservative retentions from the ancestral Old World higher primate … The colobine/gibbon (and, by inference, ancestral catarrhine) craniofacial morphology is typified by: a cranial vault of moderate to great height with globular frontal squama, broad interorbital septum, short and wide nasal bones, short orthognathous snout, shallow zygoma, short/moderate infraorbital facial height, and abbreviated premaxilla with relatively narrow vertically implanted upper incisors set equally forward… [references removed - afarensis]

Reconstructions of the catarrhine last common ancestor that use fossil material paint a different picture (from Zalmout et al):

Conversely, studies incorporating observations on early Miocene apes and the basal cercopithecoid Victoriapithecus reconstruct an LCA morphotype with a projecting snout and tall face, long, narrow nasal bones and steep frontal with a trigon enclosed by anteriorly convergent temporal lines and supraorbital costae… [references removed - afarensis]

Here is a picture of the find:

Photographic images of the partial cranium SGS-UM 2009-002, type specimen of Saadanius hijazensis gen. et sp. nov. a, Cranium in anterior view. b, Cranium in lateral view, anterior to the left. c, Ventral view of cranium, anterior to the left. d, Anterior view of right temporal bone, ventral at top, lateral to the right. e, Ventral view of right temporal bone, anterior at top, lateral to the left. f, Medial view of right occipital condyle, anterior to the left. g, Ventral view of right occipital condyle, anterior to the left. cf, carotid foramen; egp, entoglenoid process; gf, glenoid fossa; pgp, postglenoid process; smf, stylomastoid foramen; te, tubular ectotympanic

For those that are interested, here are the results of the phylogenetic analysis:

Literature Cited

Benefit and McCrossin (1991) Ancestral facial morphology of Old World higher primates. Proc. Natl. Acad. Sci. USA Vol. 88, pp. 5267-5271

Valentine (2004) On the Origin of Phyla. The University of Chicago Press: Chicago

Zalmout, I., Sanders, W., MacLatchy, L., Gunnell, G., Al-Mufarreh, Y., Ali, M., Nasser, A., Al-Masari, A., Al-Sobhi, S., Nadhra, A., Matari, A., Wilson, J., & Gingerich, P. (2010). New Oligocene primate from Saudi Arabia and the divergence of apes and Old World monkeys Nature, 466 (7304), 360-364 DOI: 10.1038/nature09094

About these ads
Follow

Get every new post delivered to your Inbox.

Join 51 other followers

%d bloggers like this: