Cranial morphology and size variation in fossil hominins

Baab, Karen L., and Kieran P. McNulty. "Size, shape, and asymmetry in fossil hominins: the status of the LB1 cranium based on 3D morphometric analyses." Journal of Human Evolution 57, no. 5 (2009): 608 -- 622. Accessed November 29, 2013. doi:10.1016/j.jhevol.2008.08.011.

This study examines the connection between shape and cranial size over a range of hominin including an African ape species. The reason being, they wish to test whether or not cranial morphology of LB1 remains constant with the elemental pattern of static allometry seen in other various taxa. Various and differing explanations such as insular dwarfism and pathological microcephaly have been attributed to the rare set of morphological characteristics of the Liang Bua hominins. The explanations offer a varied perspective on the remains and its origins.

Associations between 3D cranial shape and size were explored using leading factors analysis in Procrustes form space and in shape space. Furthermore, patterns of static allometry are found within both Plio-Pleistocene hominins and modern humans and were utilized to replicate the expected cranial shapes (size LB1) of each group. Statistically and visually, these hypothetical specimens were distinguished in relation to LB1. Results of most analyses showed that LB1 is the best predictor for a small specimen of fossil Homo, but data remains obscure.

Beals, Kenneth L., Courtland L. Smith, and Stephen M. Dodd. "Brain Size, Cranial Morphology, Climate, and Time Machines." Current Anthropology 25, no. 3 (1984): 301-330. Accessed November 28, 2013. Doi: 10.1086/203138.

Here the authors discuss a bioclimatic model and the reason for its evaluation. It is evaluated to help explain variation in cranial capacity. They used 122 ethnic groups to assess. They also mapped distribution of relative and absolute endocranial volume. Major correlations happen with all of the 9 climatic variables analyzed.

The authors also mention significant foci of adaptation happens in conjunction with solar radiation, winter temperature and vapor pressure. 2.5 cm per degree of equatorial distance signifies the increase in global mean trait. The interactive geometry between shape and cranial size is highlighted, with brachycephalization and encephalization treated as practically linked trends. Breadth is the most significant structural component deciding capacity.

Relations between brain size and body display that human populations under harsh cold stress attain large volumes more from rounder cranial shape than from distinction by total body size. They authors note development of a computerized mapping program and application of it to climatic, anthropometric, and HRAF files. Its ability to generate clinal portrayals through the Pleistocene is examined.

Bookstein, Fred L., Philipp Gunz, Philipp Mitterœcker, Hermann Prossinger, Katrin Schaefer, and Horst Seidler. "Cranial integration in Homo: singular warps analysis of the midsagittal plane in ontogeny and evolution." Journal of Human Evolution 44, no. 2 (2003): 167 -- 187. Accessed November 28, 2013. Doi: 10.1016/S0047-2484(02)00201-4.

The authors create a study that focuses on lasting issues of evolutionary integration and ontogenetic in the hominid cranium form. They obtained information from a sample of 38 crania with 20 modern adult Homo sapiens, 4 archaic Homo, and 14 subadult H. sapiens. They scanned all of the specimens within the sample with a CT scanner with the exception of 1 infant H. sapiens that were instead imaged by MR. They located 84 semilandmarks and landmarks for each specimen.

How they quantified integration was through utilizing the approach of singular warps, which are the latest geometric-statistical method to visualize comparability among regions. They utilized the class patterns of integration, ontogenetic and evolutionary. They were both analyzed and explored through localized patterns of covariation for the ontogenetic and identical patterns for the evolution. Their methodology allowed for separate analysis.

Bruner, Emiliano, and Ralph L. Holloway. "A bivariate approach to the widening of the frontal lobes in the genus Homo." Journal of Human Evolution 58, no. 2 (2010): 138 -- 146. Accessed November 29, 2013. doi:10.1016/j.jhevol.2009.10.005.

This article discusses the most encephalized taxa within the genus Homo. They remark how the heads of the modern and Neanderthal show relatively broader frontal lobes than either australopithecines, or Homo erectus. The current investigation considers whether these differences are correlated with a single size-based or allometric pattern or with a more particular and non-allometric pattern. The authors also examine the relationship between hemispheric length, frontal width, and maximum endocranial width, at Broca's area. It remains an area not often investigated in extinct and extant humans.

The results of the article are not supportive of positive allometry for the frontal lobes width in connection to the primary endocranial diameters within Homo sapiens. The association between frontal width and hemispheric length is depreciated than the association between frontal width and parieto-temporal width. The comparisons to the australopithecines reveal the genus Homo could have shared a non-allometric broadening of the brain at the temporo-parietal areas, which is most clear in Neandertals. Neandertals and modern humans also display a non-allometric broadening of the anterior endocranial fossa at the Broca's cap compared to older, earlier hominins.

Bruner, Emiliano, and Giorgio Manzi. "Paleoneurology of an "early" Neandertal: endocranial size, shape, and features of Saccopastore 1." Journal of Human Evolution 54, no. 6 (2008): 729 -- 742. Accessed November 29, 2013. doi:10.1016/j.jhevol.2007.08.014.

The authors of this article state in 1929, a Saccopastore 1 cranium was found adjacent Rome in 1929. They also note its most likely age is around 120 ka (OIS 5e). Additionally they shared the reason for recognition of the Neandertal morphology is in part due to the analysis by the Italian anthropologist S. Sergi, and afterwards confirmed by various authors. The article provides a complete analysis and description of the endocranial features and shape of this specimen, with considerations on anatomical traits, landmark data, and metrics.

The primary vascular traces and the endocranial diameters parallel the morphology showcased by Middle Pleistocene humans. Although, it lacks several traits described in the European samples which are labeled as ante-Neandertals. The endocranial shape and proportions confirm a definite Neandertal morphology. With the authors mostly taking into account the lateral forming of the frontal lobes as well as the shape of the parietal areas.

Bruner, Emiliano, and Maurizio Ripani. "A quantitative and descriptive approach to morphological variation of the endocranial base in modern humans." American Journal of Physical Anthropology 137, no. 1 (2008): 30-40. Accessed November 29, 2013. doi:10.1002/ajpa.20837.

The authors state the major foci of interest in functional craniology is the cranial base. The morphogenesis and evolution of this structure is not well-known. In fact some see it as a rather controversial area due to the polyphasic stages and multifactorial influences. Connections between endocranial dynamics are anterior with the upper facial structures, the mandibular system is lateral with midsagittally in regards to brain development. In the study, they examined the endocranial morphology of modern humans utilizing 3D landmark-based methods.

Some of these methods are Euclidean distance matrix analysis and geometric morphometrics. Poor integration of variation on the structure of endocranial is noted with only feeble complementary influences among the 3 fossae. The authors explained some considerable variations are correlated with changes in the posterior fossa, with feasible results on the anterior areas. The corresponding independence between the endocranial fossae, along with their structural connection through the meningeal tensors, must be analyzed closely to possibly lead to mosaic changes through phylogeny.

Gordon, Adam D., Lisa Nevell, and Bernard Wood. "The Homo floresiensis cranium (LB1): Size, scaling, and early Homo affinities." Proceedings of The National Academy of Sciences 105, no. 12 (2008): 4650 -- 4655. Accessed November 28, 2013. doi:10.1073/pnas.0710041105.

This article highlights the findings of the skeletal remains of a diminutive small-brained hominin from the Late Pleistocene in cave deposits on the island of Flores, Indonesia. These findings were assigned to a new species, Homo floresiensis. Instead of categorizing it as a new hominin, some feel a drastically different interpretation is that this substance belongs not to a new hominin taxon but to a population of small-bodied present day humans affected, or not affected, by microcephaly. Debaters place emphasis on the shape and size of the endocranial cavity of the type specimen, LB1. The authors also suggest additional research as no study so far has addressed the issue of how scaling would affect shape comparable between a diminutive cranium like LB1 and the bigger crania of modern humans.

Gracia, Ana, Juan L. Arsuaga, Ignacio Martinez, Carlos Lorenzo, Jose M. Carretero, Jose M. Castro, and Eudald Carbonell. "From the Cover: Craniosynostosis in the Middle Pleistocene human Cranium 14 from the Sima de los Huesos, Atapuerca, Spain. "Proceedings of the National Academy of Sciences 106, no. 16 (2009): 6573 -- 6578. Accessed November 29, 2013. doi:10.1073/pnas.0900965106.

Similar to other articles, these authors report on a previously undescribed human Middle Pleistocene immature specimen. The specimen is labeled Cranium 14 and was examined and picked up from the Sima de los Huesos (SH) site. The Sima de los Huesos is located in Atapuerca, Spain. This specimen comprises the oldest evidence in human evolution of an extremely rare pathology in humans, lambdoid single suture craniosynostosis (SSC).

The authors note both the ecto- and endo-cranial abnormalities detected in this specimen are extreme. Evidence from specimen suggests that this extremeness implies that the SSC happened prior to birth, and that facial asymmetries, along with motor/cognitive disorders, were likely to be correlated with this condition. This specimen helps better understand sociobiological behavior in Middle Pleistocene humans. It does so by providing unique information few other specimens have offered

Gunz, Philipp, and Katerina Harvati. "The Neanderthal "chignon": Variation, integration, and homology." Journal of Human Evolution 52, no. 3 (2007): 262 -- 274. Accessed November 28, 2013. doi:10.1016/j.jhevol.2006.08.010.

The occipital bun ("chignon") is noted extensively as a Neanderthal derivative characteristic. It contains the posterior convexity/projection of the occipital squama and is correlated with lambdoid flattening on the parietal. The authors discuss and define a 'hemibun' which is located in some Upper Paleolithic Europeans and is believed by some authors to demonstrate interbreeding between early modern Europeans and Neanderthals. Still, 'Bunning' is harder to quantify, and the term has been used on a range of morphological patterns.

Additionally, its practicality in phylogenetic reconstruction as well as its homologous status crosswise fossil and modern humans have been argued. The authors present a geometric morphometric study that quantitatively assesses the chignon, evaluates its practicality in separating Neanderthals from modern humans, and its degree of similarity to Upper Paleolithic 'hemibuns.' They measured the three-dimensional coordinates of nearly spaced points along the midsagittal plane from bregma to inion and of anatomical landmarks in a large series of recent human crania and several Middle and Late Pleistocene European and African fossils.

Gunz, Philipp, Fred L. Bookstein, Philipp Mitteroecker, Andrea Stadlmayr, Horst Seidler, and Gerhard W. Weber. "Early modern human diversity suggests subdivided population structure and a complex out-of-Africa scenario." Proceedings of the National Academy of Sciences 106, no. 15 (2009): 6094 -- 6098. Accessed November 28, 2013. doi:10.1073/pnas.0808160106.

The article discusses and examines the interpretation of genetic evidence in relation to modern human origins and its dependency, among several factors, on evaluations of the structure and differences within ancient populations. They note lack of genetic information available from the time of the first appearance of anatomically modern humans. They first appear from 60,000 to 200,000 years ago. Instead they exploit the phenotype of neurocranial geometry to make comparisons on the difference in early modern human fossils compared to other Homo fossil groups and the most recent modern humans.

Differences are analyzed through the mean-squared Procustes distance from the average shape in the group with basis on several hundred neurocranial points of interest. They noted the sample showed much variation covering over 1.8 million years. They also stated that recently completed models of modern humans, some are contrary to other data. It is important to consider researching more samples in order to have a more consistent conclusion.

Lieberman, D.E. "The evolution and development of cranial form in Homosapiens."Proceedings of the National Academy of Sciences 99, no. 3 (2002): 1134 -- 1139. Accessed November 28, 2013. doi:10.1073/pnas.022440799.

Lieberman discusses the lack of unanimity over the defining Homo sapiens in the fossil record. Thus, the author examines cranial variation among recent and Pleistocene human fossils by using a model of cranial growth to classify particularly derived features, specifically autapomorphies, that accurately analyzes fossils associated to "anatomically modern" H. sapiens (AMHS) from those associated to assorted taxa of "archaic" Homo spp. (AH) and to assess hypotheses about the differences in cranial development that dominate the ancestry of modern human cranial form. In regards pattern, AMHS crania are notably characterized by two common structural autapomorphies: neurocranial globularity and facial retraction. Morphometric analysis of the ontogeny of these autapomorphies demonstrates that the preliminary advances that led to current human cranial form evolve from a sequence of shifts in cranial base angle, facial length, and cranial fossae length and width. These morphological differences, some of which might have happened due to the relative size expansions in the temporal and possibly the frontal lobes, happen previously in ontogeny, and their effects on facial retraction and neurocranial globularity differentiate AMHS from AH crania.

Lieberman, Daniel E. "Speculations about the selective basis for modern human craniofacial form." Evolutionary Anthropology 17, no. 1 (2008): 55 -- 68. Accessed November 28, 2013. doi:10.1002/evan.20154.

In recent years, researchers have uncovered a wealth of information concerning the place of origin and time of humans, namely Homo sapiens. Discovery of more sites, new fossils help uncover more about the species. With more accurate analysis thanks to better dates, modern and fossil DNA, and so forth. The results of numerous analyses have mostly disproved the multiregional model of human evolution Lieberman states.

For the most part, the evidence typically supports some version of the out-of-Africa model. This of course is in accordance to which humans from 200,000 years or so ago first evolved in Africa. Subsequently the peoples of that time period then migrated to other parts of the world. Even with the increase in knowledge, there are still debates on human origins. These debates primarily address if and how much hybridization happened between modern humans and Neanderthals.

Mitteroecker, Philipp, and Fred Bookstein. "THE EVOLUTIONARY ROLE OF MODULARITY AND INTEGRATION IN THE HOMINOID CRANIUM." Evolution62, no. 4 (2008): 943 -- 958. Accessed November 29, 2013. doi:10.1111/j.1558-5646.2008.00321.x.

This article highlight several aspects of the human skull involving the role of evolution on cranial vaults of hommins. The integration and modularity in the hominoid cranium is also identified with additional information discussed on origins and so forth. The article addresses several instances of specimen collecting and identification. The authors also stress the need for more research in the field of hommins.

Neubauer, Simon, Philipp Gunz, and Jean-Jacques Hublin. "Endocranial shape changes during growth in chimpanzees and humans: A morphometric analysis of unique and shared aspects." Journal of Human Evolution 59, no. 5 (2010): 555 -- 566. Accessed November 29, 2013. doi:10.1016/j.jhevol.2010.06.011.

The article opens with comparison of human's closest and extinct relatives. The findings revea humans possess a big, intricate, and specialized brain embedded in an originally shaped braincase. There is where the authors quantitatively compare endocranial shape differences during ontogeny in chimps and humans. They used the CT scans of 60 chimps and 58 humans varying in age from birth to adulthood. They also created virtual endocasts to analyze and measure 29 three-dimensional endocranial landmarks along with several hundred semilandmarks on the endocranial surface and curves.

Pearson, Osbjorn M. "Statistical and biological definitions of "anatomically modern" humans: Suggestions for a unified approach to modern morphology." Evolutionary Anthropology17, no. 1 (2008): 38 -- 48. Accessed November 28, 2013. doi:10.1002/evan.20155.

Pearson begins with an introduction stating how so much of the current literature on the origin of modern humans has been deviled by debaters' inability to concur on what establishes "anatomically modern" morphology. The upside to constant and ongoing disagreement has been a continual set of debates over whether specimens are or are not anatomically modern. Pearson explains the specimens are: Florisbad cranium, Klasies River Mouth mandibles, Vindija Neanderthals, or Skhul-Qafzeh hominins. All of these specimens show modern characteristics.

Rightmire, G.P. "Homo in the middle pleistocene: Hypodigms, variation, and species recognition." Evolutionary Anthropology 17, no. 1 (2008): 8 -- 21. Accessed November 29, 2013. doi:10.1002/evan.20160.

Rightmire begins with the general acceptance of evolution of modern humans in Africa. This consensus was recent with its emergence coming in the last 20 years thanks in part to molecular evidence in connection with findings from paleontology and prehistory. Archeological traces, patterns of DNA variation among living populations, and morphology of fossils, help to trace the deep roots of modern humans in Africa. Thus, it also aids in identifying how it began to disperse into other regions only late in the Pleistocene.

Rightmire, Phillip G. "Brain size and encephalization in early to Mid-Pleistocene Homo."American Journal of Physical Anthropology 124, no. 2 (2004): 109-123. Accessed November 28, 2013. doi:10.1002/ajpa.10346.

Significant difference in the brain have happened during the span of human evolution. Both relative and absolute size increases can be noted for species of Homo, climaxing in the appearance of present day humans. One species that is uniquely well-shown by fossil crania is Homo erectus. The author states the mean capacity for thirty individuals is 973 cm3. This group exhibits significant variation, but with only a slight increase in brain size detected from other specimens of later periods. Other Middle Pleistocene crania vary from those of the main group Homo erectus.