Anoiapithecus brevirostris: An Interesting Miocene Ape

I have mentioned this find in several posts in a “hey look at this” kind of way, but wanted to go into the subject in a little more detail. The fossil was discovered in Catalonia, Spain, and dates to ~11.9 MYA. The fossil is described in PNAS – subscription required and is accompanied by open access supplementary material (which has one figure mislabeled). There are a number of interesting issues in the article and I will look at a few of them here.

I have posted one of the pictures from the paper, but more formally this is what was found:

The face of IPS43000 … lacks the nasals and the right maxilla, some parts of the orbits, and parts of both zygomatics. The palate is nearly complete, lacking only the left C1 and M3, as well as the incisors; part of the frontal also is preserved. The mandible preserves the symphysis and a large portion of the 2 corpora, but lacks the 2 rami; the left I1 and C1-M2 series and the right C1-M1 series are preserved. Complete eruption of the M3 indicates that IPS43000 belongs to an adult individual, because the slight displacement of this tooth from the alveolar plane merely results from bone distortion at the level of M2-M3.

Which, of course, does not say much about the actual anatomy. IPS43000 has reduced nasal and alveolar prognathism (more about that below), a short maxilla, high, downwardly inclined zygomatic roots, a well developed frontal sinus (more about that below, as well), reduced maxillary sinus, temporal lines which meet (this means that a sagittal crest would have been present), wide deep palate, thick enamel, molars with low crowns, globulous cusps and restricted basins, robust mandible with highly divergent rami, a mandible with a weak superior torus and a strong inferior torus (= simian shelf).

What justifies placing the find in a new genus and species? The answer to that involves one of my pet peeves about the way paleoanthropology is perceived by the press and the public. I have written about this elsewhere (and in a different context). Basically, one compares the morphology of the fossil in question with those of other species – both extant and extinct – and determines how similar or different they are. There are, of course, a number of factors that can effect anatomy and to try and get around that comparisons are made to ranges of variation (usually to the range of variation of a given trait in extant species, but to extinct ones, as well, whenever possible). Moya-Sola et al compared Anoiapthecus to a wide variety of Miocene apes and extant monkeys and apes. Here is a taste:

Anoiapithecus differs from all known Miocene Eurasian hominoids by the very orthognathous face, because of reduced mid- and lower facial prognathism, with the glabella and orbits situated very anteriorly (close to the premolars and C1 on the vertical plane); it further differs from the above-mentioned taxa except Oreopithecus by the presence of a sagittal crest. More specifically, Anoiapithecus further differs from proconsulids and afropithecids by the possession of hominid facial synapomorphies, including the wide nasal aperture widest at the base, the high face, the deep palate, and the configuration of the nasals.

Two points need to be made about the above quote. First, Moya-Sola et al use a slightly different taxonomic scheme than some, so to clarify any confusion afropithecids include the following (from the Supplementar material):

Family Afropithecidae*, Andrews, 1992
Subfamily Afropithecinae*, Andrews, 1992
Tribe Afropithecini*, Andrews, 1992
Genus Afropithecus*, R. E. Leakey and M. G. Leakey, 1986
Genus Heliopithecus*, Andrews and Martin, 1987
Genus Morotopithecus*, Gebo et al., 1997
Subfamily Kenyapithecinae*, Andrews, 1992
Tribe Kenyapithecini*, Andrews, 1992
Genus Kenyapithecus*, L. S. B. Leakey, 1962
Genus Griphopithecus*, Abel, 1902
Tribe Equatorini*, Cameron, 2004
Genus Equatorius*, Ward et al., 1999
Genus Nacholapithecus*, Ishida et al., 1999
Family Hylobatidae, Gray, 1870
Genus Hylobates, Illiger, 1811
Family Hominidae, Gray, 1825
Subfamily incertae sedis
Tribe Dryopithecini*, Gregory and Hellman, 1939
Genus Dryopithecus*, Lartet, 1856
Genus Pierolapithecus*, Moyà-Solà et al., 2004
Genus Anoiapithecus*, gen. nov.

One of the oddities of this scheme (not shown) is the the genus Gorilla and the genus Pan are placed in the same tribe. At any rate, they also did morphometric analysis which focused mainly on the cranial facial angle. This is the part of the study that received a lot of attention in the press. One of the things that characterizes human evolution is the reduction of prognathism. In a word humans have flat faces (brevirostris, if you will) so the comparisons were inevitable. Fortunately, most of the press accounts correctly identified the similarity between Anoiapithecus brevirostris and humans correctly as convergence. There are a number of ways to measure the craniofacial angle. The first that I am aware of was that of Huxley in Evidence as to Man’s Place in Nature (although Huxley mentions Owen in this connection). There Huxley defined the cranial facial angle as the angle between the most anterior point on the maxilla, the most anterior point on the sphenoid and the most anterior point on the foramen magnum. A number of other ways of measuring cranial facial angle have been proposed in the intervening years and some of them are problematic. For example, infant apes have more orthognathic faces than adult apes (hence the idea that humans are neotenic apes). Additionally, factors such as the expansion of the frontal sinus and the development of a pronounced glabella can reduce the angle (by pushing the upper facial skeleton anteriorly – there are also other issues with measuring CFA that I won’t go into in this post). Anoiapthecus) has an expanded frontal sinus and an anteriorly situated glabella (it is, however an adult specimen as the third molar had erupted). Perhaps the best way to measure prognathism involves taking measurements from porion (the most superior point on the margin of the external auditory meatus – you can see porion in this picture). Unfortunately, the fossil did not include the external auditory meatus so Moya-Sola et al used a line joining glabella and prosthion (M in this picture) with the plane of the tooth row. This measurement was then compared to that of a wide variety of living and fossil primates – including early Homo and the australopithecines. The result is that Anoiapithecus has a CFA most similar to that of Homo and the australopithecines (there is a wide degree of variation in the latter two groups so CFA isn’t useful in distinguishing among them).

One of the other issues raised in the paper revolves around the issue of where the Hominidae evolved, and which species they evolved from. This will be the subject of a future post (hopefully by next weekend).

Literature

Aiello and Dean (1990) An Introduction to Human Evolutionary Anatomy

Moy-Sola et al (2009) A unique Middle Miocene European hominoid and the origins of the great ape and human clade. PNAS Published online before print June 1, 2009, doi: 10.1073/pnas.0811730106

About these ads
Follow

Get every new post delivered to your Inbox.

Join 51 other followers

%d bloggers like this: