Spotlight on Students: Understanding Paleoanthropological Studies (Part 1)

The following pieces are written by students who were enrolled in SA 202: Introduction to Anthropology.  In one of the course assignments students were provided a scenario where they had to imagine that they were paleoanthropologists who were asked to comment on a recent hominid discovery, which the paleoanthropological community was at odds about.  The following works are the students who provided the most accurate, and in some cases the most creative, submissions.  Please show your appreciation for their hard work through the comments.

By: Tori Spencer

This is an official report meant to address the recent discovery of hominid remains in West Africa. This species has been dubbed Earthensis premnathi after the discoverer of a similar-looking hominid Earthensis megalisis, Dr.Srikavi Premnath (Premnath, 2018). Despite the extensive research performed by Dr. Premnath and her team on this unique genus, experts are split on the assignment of E. premnathi. Fortunately, there are only two genera left that for anthropologists to decide between as E. premnathi is almost certainly from either the Australopithecine or Homo lineage. I am a paleoanthropologist myself, but I was not on the discovery team of either species nor do I claim the knowledge base with which I could call myself an expert on Earthensis. Still, I am a dedicated educator and will therefore devote this text to explaining how researchers like Dr. Premnath can ultimately place this new hominid. First, I will explain the differences between these hominid groups, then I will describe the features that researchers are likely examining.

Australopithecines

This well studied group is the older of the two and bares a geographic range though Eastern and Southern Africa. Some are even believed to have been capable of processing food with knives (Welsh, Vivianco, & Fuentes, 2017). Physically, species of this genus are of a slender build, relatively large brain, gripping hands, long arms, sexual dimorphism (a difference in the size, weight or appearance of the sexes in a species), and with no sagittal crest (ridged-bone structure that juts from the top of the skull, that can range from a sail like bones structure to a slight point at the top of the head). Their dentition consists of small post-canine teeth (any teeth that sit behind the [flat] molars and premolars) that also bear thick enamel. Finally, as a member of the hominid group, Australopithecines had a forward-tilted foramen magnum (the hole for the spine in the back and bottom of the skull), which suggests at least some form of bipedal (two-legged) locomotion. Still, the length of the arms is more indicative of at least partial arboreal (tree-dwelling) activity (Welsh, Vivianco, & Fuentes, 2017).

Homo

Our modern genus has skeletal remains that date back to 1.8 million years ago (MYA) and were found in Africa, Europe, the Middle East, and Asia. Early Homo species were associated with the use of Olduwan tools and had slightly curved fingers. As with species in the previous genus, physically they bore no sagittal crest, and they possessed comparatively large brains among hominids. In contrast, Homo species had smaller post-canine teeth, large incisors, and a narrower tooth row. Newer members of this group bear relatively flexible feet, were exclusively bipedal (not arboreal), had thick brow ridges (the bone in the forehead that forms a shelf that protects the eyes), and eventually postorbital constriction becomes reduced (the indent in the skull near the temples) (Welsh, Vivianco, & Fuentes, 2017).

After describing these two, it is no wonder that experts are having difficulties sorting Plio-Pleistocene hominids! A pronounced forehead bone here, with a hole in the skull there...  I am sure you are wondering what difference such features really make in distinguishing these two. These two genera share so many features that some scientists use the period of time that remains date back to and geographic dispersal as indicators of lineage. Fortunately, there are key differences with respect to these features, namely, the dentition, the length of the arms, and the cranial space.

Dentition

As noted before, Australopithecines had larger molars and canines than the other (Australopithecus platyops, Australopithecus garhi, Australopithecus anamensis, Australopithecus afarensis, Australopithecus deyiremeda, and Australopithecus robustus),  (Welsh, Vivianco, & Fuentes, 2017). Finally, the enamel is one of the most pronounced features in this genus (encompassing all aforementioned species except A. garhi and now including the species Australopithecus tugenensis). Features more common to Homo species include smaller molars, larger incisors, and even a post-molar gap occasionally (Homo habilis, Homo erectus, Homo antecessor, Homo neanderthalensis, Homo sapiens), (Welsh, Vivianco, & Fuentes, 2017). Dentition can therefore be a reliable indicator of lineage due to its rather divisive evolutionary divergence; either premolar teeth are larger or postmolar teeth are larger with thick enamel. This may suggest differences in diet between these groups. The only outlier to this feature is Homo rudolfensis who possesses large molars, but this species’ status within the Homo lineage is also under question (may belong to the Paranthropus genus) and Australopithecus sediba who bares the next most divisive feature.

Arm Length

Arm length, as previously mentioned, is an indicator of lifestyle.  The Australopithecines have longer arms (A. anamensis, A. afarensis, Australopithecus africanus and A. sediba) that suggest partial arboreal occupation, whereas the Homo lineage bares shorter, stockier frames and limbs as seen in H. erectus, Homo ergaster and H. antecessor, which is associated with groups that were capable of tool use, carrying young, overland movement, and who appeared to care of their elderly, (Welsh, Vivianco, & Fuentes, 2017). This may suggest that food and resources were gathered and stored differently by these groups.

Cranial Space

Again, this feature is sufficiently divisive, or at least offers a best fit model for new unknown species because there is a clear trend of growing cranial space as time progresses. Additionally Australopithecines are often described as having “fairly large brain cavities,” but this appears to be the middle size when compared with the smaller brained Paranthropus group and the larger-brained Homo species. Next, the brain size of the Homo species is compared to modern human brain sizes, not other hominids (Welsh, Vivianco, & Fuentes, 2017). Outliers to this identifier are H. floresiensis who had very small heads, Homo naledi who is described as having an ‘Australopithecus sized brain case’ (Welsh, Vivianco, & Fuentes, 2017). Finally, many Australopithecines are more closely associated with larger jawbones, not cranial space (Australopithecus deyiremeda), whereas Homo species are associated with small, rounded or missing chins (H. floresiensis, H. sapiens) (Welsh, Vivianco, & Fuentes, 2017). This too represents a possible divergence between these groups where one develops strong chewing muscles whereas the other develops larger brain space. Two outliers of this distinction are A. sediba who exhibits “mosaic evolution” or features from both groups and A. naledi, which is very similar to Australopithecus and whose categorization is also contested (Welsh, Vivianco, & Fuentes, 2017).

So here we have three traits that would help distinguish these two genera of hominid. All of the example specimens and features suggest one group or the other may lead to categorization when used in combination. For example, several individual species display a feature from another group, such as the species A. sediba who bares teeth and jaw sizes similar to Homo species. Its other characteristic (long-arms) is suggestive of arboreal life though, and therefore suggests that its placement is within the Australopithecines. Here is hoping that the research team that studies the Earthensis genus can employ similar logic to their endeavors.

References

1. Premnath, Srikavi. “Spotlight on Students: Hominid Discoveries.” Physical Anthropology, Student Post. Humerus Revelations of the Naked Ape.. Blogspot.com. Dr, Christine Boston, 15 December 2018
2. Welsch, R. L., Vivanco, L. A., & Fuentes, A. (2017). Anthropology: Asking Questions About Human Origins, Diversity, and Culture. New York, NY: Oxford University Press.

By: Rebecca Johanns

Discovering new fossils always brings excitement to paleoanthropologists, especially when found in areas known to have been inhabited by modern humans’ ancestors and other Hominidae species. When these fossils are discovered there is always a big question of whether these fossils belong to an already known species or a new species that may help fill any missing holes in humans’ lineage. When deciding whether the fossil is a modern human ancestor, paleoanthropologists must look at different characteristics of the fossil. These characteristics such as cranial capacity, jaw and teeth size and features, and type of locomotion can help not only identify if the fossil belongs in the superfamily Hominidae but also discern if it is a hominid and the specific type of species. Each of these characteristics vary among hominids and show the evolution of the group as well as how modern humans compare to today’s primates. 

Having a larger, more complex brain is one of the most obvious characteristics of a hominid. While modern humans’ brain size is even larger than early human ancestors, the brain size of those ancestors are still larger than most living primates and other extinct species in the Hominoidea superfamily. Brain size can be identified by looking at the cranium or skull of the fossils. A large cranium signifies a larger brain. Fossils found from six to two million years ago are much smaller than today’s humans but slightly larger than other living primates and organisms of the fossils time. This increase in brain capacity is a result of the hominid species’ new ability of bipedal locomotion and capability to make some simple tools. As evolution continued affecting these hominids, brain size continued to grow rapidly differentiating these hominids from other species dramatically. Changes in climate also had an effect on even later hominid species, continuing the increase in brain capacity to help these hominid species survive and adapt in the changing complex world (No Author, 2019). Early species of the genus Australopithecus had a cranial capacity of about 450 to 500 cubic centimeters (cc) compared to early Homo species such as Homo habilis, who had a cranial capacity averaging 600 cc. Later Homo species, such as Homo ergaster, had a cranial capacity reaching up to 1,200 cc. Modern humans—Homo sapiens—have a cranial capacity of 1,400, which is more than double the size of early Homo species and roughly three times the capacity of Australopithecines (No Author, 2019). Observing the size of the cranium can help determine if the fossil is hominid and even distinguish the genus or species of the fossil, which can be very beneficial to discovering new species and possible missing links in the human lineage.

A fossil’s jaw and teeth can help identify the species of a fossil. Today’s modern humans greatly differ from apes and chimpanzees in the jaw and teeth. This variation comes from a long line of evolution in different species in hominids. In general, modern humans have smaller jaws and teeth than closely related living primates. Early hominid species closely resemble today’s primates, allowing paleoanthropologists to better place a fossil in the species and time period it comes from. Differences between early hominids and modern hominids vary greatly and can tell a lot about the type of environment the species lived in, which can help identify the species a fossil belongs to. For example, modern humans’ jaws do not project outward as much as primates of similar size. Certain teeth differ greatly between hominid species. Such teeth are the molars and premolars as well as the canines and incisors. Early hominid species, who resemble living primates, had smaller crowns on their premolars and their second molar was typically their largest molar tooth, whereas modern humans’ first molars are typically the largest. Canines, in general, have reduced in size greatly through each new species. The canines’ reduction in size allowed for the premolars and molars to become larger in more recent hominid species. Tooth size alone can hint at what genus or species the fossil is from, and then by looking further at the details of the teeth as well as the size and angle of the jaw, paleoanthropologists can determine an even more accurate guess of the species. Australopithecines and other early hominids will generally have larger jaws with a larger canine-to-molar ratio whereas modern humans and recent Homo sapien ancestors have smaller jaws with a smaller canine-to-molar ratio (Emes et al., 2011).  The jaws and teeth of the superfamily Hominidae are very similar, making it difficult to differentiate between species sometimes; however, discerning the fossil as resembling living primates or Homo sapiens more can help identify if the fossil is of a hominid species and if so, how close of an ancestor it is to modern humans.

Another key feature distinguishing today’s modern human species from all other species is bipedalism. Bipedal locomotion is “the use of two legs rather than four for movement,” (Welsch et al., 2017). While some other primate species have the capability of bipedal locomotion, they are more quadrupedal and prefer using all four limbs for movement. It is believed that the bipedal movement first appeared in the Orrorin tugenensis species about six million years ago (McHenry and Johanson, 2018). The evolution of the pelvis allowed for the species to become more dependent on bipedal locomotion. The pelvis in apes, chimpanzees, and relatives of the modern human species such as Australopithecine and other Homo species is longer, narrower and reaches from the pelvic ring upward into the back. In hominid species, however, the pelvis is shorter and extends outward rather than upward, allowing the pelvis to hold the upper body weight and protect the intestines. Both Australopithecines and Homos used bipedal locomotion and had similar hip bone structure; however, there are still small differences that distinguish the two genera from each other. Some Australopithecines’ pelvis structure like the one found in Lucy’s species, Australopithecus afarensis, are flatter and angled more to the side. Their hip bone differs from the Homo species’ in that when viewed from the front, the pelvis appears to be more plate-like whereas the homo sapiens and our recent ancestors have a more bowl-shaped pelvis (Vansickle, 2016). Looking closely at the shape of the pelvis of the fossil can help identify if the species is hominid and a possible ancestor of the modern human.

Many different characteristics differentiate hominid species from other species in the superfamily Hominidae, but three features are among the most important in making this distinction: cranial capacity, jaw and teeth size, and type of locomotion. Modern hominids have larger cranial capacity than early hominids who have roughly the same or slightly larger brain size than other species in the Hominidae group. Primates and early hominids typically have larger jaws that project outward and a larger canine-to-molar ratio compared to later hominids who have smaller jaws at a flatter angle and a larger molar-to-canine ratio. Bipedal locomotion is very unique in the Hominidae group but especially with hominids. While some Hominidae species are capable of bipedal locomotion, their primary means of movement is quadrupedal. Using these three distinct characteristics can help place fossils into the Hominidae group and then aid in identifying if the fossil is of a hominid species or not. Comparing the fossil to living primates and modern humans can help discern if the fossil is of an early hominid species or later species because early hominid species closely resemble today’s primates.

Works Cited

Emes et al. “On The Evolution of Human Jaws and Teeth: A Review.” Bull Int Assoc

Paleodont., vol. 5, no. 1, 2011. Retrieved from https://hrcak.srce.hr.

McHenry, Henry and Johanson, Donald C. “Australopithecus.” Encyclopedia Britannica, 2018.

Retrieved from https://www.britannica.com/topic/Australopithecus.

“The human brain.” Maropeng and Sterkfontein Caves, 2019. Retrieved from

https://www.maropeng.co.za/content/page/the-human-brain.

Vansickle, Caroline. “An Updated Prehistory of the Human Pelvis.” American Scientist, 2016.

Retrieved from https://www.americanscientist.org/article/an-updated-prehistory-of-the-human-pelvis.

Welsch et al. Anthropology: Asking Questions About Human Origins, Diversity, and Culture. E-

book, Oxford University Press, 2017.

 “What does it mean to be human?” Smithsonian National Museum of Natural History, 2019.

Retrieved from http://humanorigins.si.edu/human-characteristics/brains.

By Charles Townsend

In the world of paleontology, the discovery of a new potential addition to the hominid classification is an exciting proposition taken with a great amount of care. A discovery of this kind would require plenty of information to determine said fossil’s classification, as there are many attributes of hominin fossils that would require attention to determine where it falls in our ancestry. As such, classifications of this kind are not easy to immediately assume and, in the case of a hypothetical new fossil, the only hints we have as to determining anything about it is its morphological features. Since the hominin ancestry possesses an extensive history with extensive evolutionary changes, paleoanthropologists have made it their lives work to analyze these features to determine where they may lie in the hominid timeline. For this piece, we will be focusing on a few morphological features of similar fossils and utilize these features to determine whether or not a new hominid species would be part of the Australopithecine or Homo genus.

Hominids gain their classification through the understanding of various biological principles and specific features that must be present to gain that classification. One of the most pertinent features to determine whether or not a fossil is a hominid is its brain, more specifically its size. In comparison to the modern human brain, most of our hominid ancestors boast much smaller brains evidenced by the smaller sizes of their crania. The importance of brain size is it serves as one of the primary indicators for determining whether or not a hominin fossil is considered part of the Australopithecus or Homo genus (Welsch et al. 202). In the case of Australopithecines, the size of their brains represents one-third to one-half the size of modern human cranial capacity, averaging 300-500 cubic centimeters, while the early transitional humans, which consist of Homo genus, have a cranial capacity range of 509-752 cubic centimeters (O’Neil, pg. 1). In general, though not always true, the smaller the braincase the higher likelihood of the fossil being Australopithecus in classification.

Moving towards the front of the skull, the face of a hominin can lead to many clues as to the classification of one of these fossils. The reason the face of a hominin fossil is important for classification is that the relative size, structure, and types of the teeth and jaw can greatly determine many dietary factors. Also, as a general trend but most certainly not a universal rule, the larger the cranium of hominin ancestors the smaller the face of a hominin would become (as a product of smaller teeth and jaws) (McHenry and Johanson, Relation to Homo). This rule is best represented in the characteristics of early Australopithecine fossils, like Australopithecus africanus that boasts a slightly jutting jaw and comparably larger teeth to that of Homo erectus which is characterized with smaller molar teeth and a face shape considerably closer to modern humans (Welsch et al. 206-207, 220-221).

Although the face and skull are primarily used to identify hominin fossils, another essential trait used to classify these remains would be that of the legs, arms, and pelvis.

Generally speaking, most of the hominin ancestors that fall in the timelines of Austrolopithicus and Home Genus would have obtained some form of bipedal locomotion made possible due to the forward placement of the foramen magnum in the back of the skull. The real question, in this case, would be as to how reliant on bipedal locomotion the hominin in question would have been based on morphological differences between different fossils. Early Australopithecine fossils, like Australopithecus anamensis and Australopithecus afarensis, both have long arms which suggest they were partly arboreal; coupled with bipedal anatomy strengthen this suggestion (Welsch et al. 204-205). As for the Homo genus hominins, like Homo erectus, they possess longer legs and shorter arms, clearly suggesting almost exclusive bipedal locomotion (Welsch et al. 200-201).

Presently, if a new hominin fossil were to be introduced to the paleoanthropological world, several of the indicated characteristics in the paragraphs above would be used to assist in the fossil’s classification as either being Australopithecine or Home genus. If the fossil were to have a cranial capacity larger than 500 cm cubed, with a smaller jaw and teeth, and a skeleton that indicated a preference to bipedal locomotion, it would be safe to assume the fossil is likely Homo genus. If the fossil maintained a small cranial cavity, a jutting jaw with large canines and a bent spine with long arms then it is safe to say that the fossil is very likely Australopithecus. That being said, these are only a few of the many features that can indicate the placement of these fossils in the hominin ancestor timeline and there are far more specific factors that can adjust how these fossils are categorized like shape of the spine, size of the body, shape of the hands, the presence of primitive tools, and much more.

If the introduction of a new fossil were to be made known to paleoanthropologists, especially one that does not strictly sit in any existing categorization, it may take the assessment of many characteristics to determine its placement in the hominin timeline. Although the above features can be utilized to determine the categorization of these fossils, several of these features overlap and sometimes contradict the consensus of what they represent. Since none of these traits   is 100% conclusive as to determining the classification of a hominin fossil, paleoanthropologists must assess every possible quality of these remains to make an educated decision. Therefore, if a new fossil was discovered and its classification has yet to be determined, many of the features stated in this paper serve as an excellent starting point.

Works Cited:

●     Welsch, Robert L. et al. Anthropology: Asking Questions about Human Origins, Diversity, and Culture. New York City, Oxford University Press, 2017.

●     O’Neil, Dennis. “Early Transitional Fossils.” Palomar.edu, 2012, https://www2.palomar.edu/anthro/homo/homo_1.htm

●     McHenry, Henry, and Donald C. Johanson. “Australopithcus.” Encyclopedia Britannica, Encyclopaedia Britannica, inc. 15 November 2018, https://www.britannica.com/topic/Australopithecus/Australopithecus-afarensis-and-Au-g arhi

●     “Homo.” Encyclopedia Britannica, Encyclopaedia Britannica, inc. 9 January 2019, https://www.britannica.com/topic/Homo