Not sure if this may help, but the authors refer to "animal models" - maybe this could be a lead to further references...  Sorry for not being able to be of better help!

http://www.ncbi.nlm.nih.gov/pubmed/22777037

For Tiago and anyone else who might be interested in the topic of this question, I have recently found some information about age of suture fusion in Barone, R. (1976) Anatomie comparée des animaux domestiques, Tome 1er - Ostéologie, 2e édition. Paris : Vigot Frères, Editeurs (I'm afraid one cannot find the book freely on-line).

In page 53, the author provides a table with the age of fusion of major cranial and post-cranial sutures (including synchondroses, which he calls sutures) in humans, horses, cattle, sheep, goats, pigs and dogs. In all those animals, the spheno-occipital synchondrosis ('suture sphéno-basilaire') fuses just before full maturity, thus denoting it a fair trait to estimate adulthood in skeletal specimens lacking age-related information.

I am not yet fully convinced that this trait behaves the same way in all Primates, Perissodactyla, Artiodactyla, or Carnivora, but it is a start...

Good to know! I'd guess it might be something like that!

The important question porbably is, what means maturity. Is it sexual maturity (in the sense of fertile germ cells or as age at first reproduction) or is it skeletal maturity (in the sense of all or most epiphyses fusing or even completely fused). Often the second is taken as a proxy for the first. In ungulates this can be quite variable. Like sheep ewes that can be inseminated under favorable consitions as early as with 7 month. We are curating a collection of skulls and parts of the postcranium of Soay sheep with known age-at-death. Some epiphyses show signs of fusion in the course of the second year. In the third year all epiphyses start fusing and show last remnants up to the beginning of the fourth year. Fusion of the basioccipital to the basisphenoid is occuring in the second year of life. So in these creatures this fusion is somewaht inbetween (potential) sexual maturity and skeletal maturity. I would expect it to vary considerably between other genera and even more between orders.

Very interesting information, Carsten. I'm actually thinking that would make an awesome study - comparing spheno-occipital fusion with sexual maturity (possibly also with general skeletal maturity) across several mammal species.

Still on the topic of my question, and for information that might be useful to others, I found a recent paper where they have a short review on the existing literature (Rager et al. 2014, 

https://www.researchgate.net/publication/257814494_Timing_of_Cranial_Suture_Closure_in_Placental_Mammals_Phylogenetic_Patterns_Intraspecific_Variation_and_Comparison_With_Marsupials

; please find in this paper the full references for the citations that will follow). According to the authors, the few studies of timing of cranial suture closure in Placentalia up to 2014 (plus a few more added by myself) dealt with:

- primates (e.g., Krogman, 1930; Schultz, 1941; Chopra, 1957; Wang et al., 2006; Cray et al., 2008; Flores & Barone, 2012);

- carnivorans (Schweiker, 1930; García-Perea 1996; Brunner et al., 2004; Segura & Flores, 2009; Goswami et al., 2013; Segura, 2013);

- hystricognath rodents (Wilson & Sánchez-Villagra, 2009);

- a bat (Giannini et al., 2006);

- manatees (Hoson et al., 2009);

- pigs and peccaries (Herring, 1972, 1974);

- deer (Sánchez-Villagra, 2010);

- artiodactyls in general [inc. a brief comparison with cetaceans] (Bärmann & Sánchez-Villagra, 2012);

[- a dolphin (Castillo et al., 2015, Mastozoología Neotropical, 22(1):141-148), but they do not study the spheno-occipital synchondrosis]

- afrotherians (e.g. Hoson et al., 2009; Rager et al., 2014); 

- xenarthrans (Rager et al., 2014);

- marsupials (e.g., Gardner, 1973; Flores et al., 2006; Rager et al. 2014).

In all these studies, though with considerable variation (e.g. between sexes, and among species), the spheno-occipital synchondrosis seems to fuse just before or around the age of full maturity, possibly with the following exceptions: delayed fusion in Giraffa and Okapia; very late fusion in Camelus. The spheno-occipital synchondrosis however seems to be seldom totaly closed (meaning becoming completely unnoticeable), particularly in rodents; it seems to totaly close in Lynx, though.

I fully agree with Carsten that skeletal maturity, while often being used as a proxy for sexual maturity, is by no means equivalent to it. However, for the moment I am interested only in skeletal maturity, as must necessarily be diagnosed in dry bones found in old museum collections (where specimen information has been lost or never gathered) or in a zooarchaeological dig (where specimen information is not available). That said I will follow your identified sheep collection with great interest, Carsten; I know of no similar collection and I can foresee that that one will become an invaluable reference collection.

Article Timing of Cranial Suture Closure in Placental Mammals: Phylo...