Anthro Assignment

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Nada Allet
Mark Prentice
Human Evolution
March 29th 2018
MARGINS!!!
You have discovered several intact fossil remains of what appears to be male and female
representatives of a previously unknown ancient nonhuman primate species. How would you
go about reconstructing their mode of locomotion, their dietary pattern and their mating
behavior?
Fossils are precious clues to understand the way of living of species that no longer exist on our
planet. It is possible to extract information from various components of an organism’s remains to
know about its locomotion, diet and mating process. To know the composition of the diet of the
species, teeth are the more convenient body part to analyze for the reason that they are well
preserved as fossils. According to Chris Stringer and Peter Andrews’ "The Complete World of
Human Evolution", the tooth structure is influenced by what a species eats, more specifically the
tooth surfaces and enamel. The two researchers in palaeoanthropology note that when eating, food
particles leave scratches on the teeth invisible to the naked eye, and these marks varies depending
upon the type of food that is ingested. They state that leaf eaters have more significant tooth ridges
than fruit eaters, whereas hard fruit, nut and seed eaters have large teeth and low crowns. For
instance, Paranthropus boisei, one of our hominid ancestors, had big molars for chewing hard
fruits and seeds. (Stringer & Andrews p.191), which can serve as a comparison to find the diet of
an unknown primate species. Today’s frugivore primates, such as the chimpanzee, have large
incisors teeth to prepare fruits for digestion (Stringer & Andrews p.191). The tooth enamel, the
hard surface of the teeth, can also give clues with its thickness. Stringer and Andrews add that a
thick enamel is proof of fruit eating habits and a thin enamel, of leaf eating habits. Since fruits are
easily deformable during chewing and have a rich food value, frugivores have a greater variety of
tooth types and shorter guts compared to folivores, since it requires less digestion work and energy
than digesting leaves. (Stringer & Andrews p.191) As said with chimps, these dentition and diet
information of existing nonhuman primates species could give many ideas of an unknown species’
nutrition. In "Primate Origin" published in 2009, Shawn Lehman states that "the comparative
method, as it applies to palaeoanthropology, is based on inferences gleaned from studies of form
and function in extant primates" (p.5). As shown in his study, insect eating primates tend to have
short and sharp teeth to break the outer hard shell of insects. In consequence, they have sharp cusps
and thick enamel. Primates that open bark and wood with their teeth have projecting forward
anterior dentition. Moreover, Lehman says that it could be hard to distinguish eating from social
use of some teeth. Sometimes, primates use their teeth to bite, defend or intimidate other
individuals (class notes, Prentice). Lehman’s study shows that for leaf-eaters, the sharper incisors
are used to cut the leaves and the huge molars and premolars, to chew the leaves right before
digestion. According to Lehman, the chewing action is a revealing sign of alimentation. He
explains that different muscles, connecting the mandible to the rest of the skull, are activated for
the act of chewing to happen. The size and location of these muscles and their attachment to the
indicate the biting force a species has. (Lehman, p.8) Lehman makes the relation that the larger
the chewing muscles and attachment are, the harder the food the species was feeding to.
Furthermore, the environment where the fossils were found could tell a lot about their diet. Modern
frugivores apes are found in tropical forests to permanently have access to fruits, as an instance
(Stringer & Andrews p. 200) The above characteristics could be useful when analyzing the crane
and teeth of the unknown fossilized skeletons to understand the dietary pattern.
Most credit for the proofs of the locomotion of a species is given to the skeleton morphology. It is
possible to look at the eye orbits to know if the species was using its locomoting during the night
or day. Large eye orbits on the skull would indicate the species to be mostly active in the night
when small orbits would make it active during the day (The Primates Powerpoint, Febrary 13th
2018). The foramen magnum is on the back of the crane for quadrupedal primates, which shows
that they tend to adopt a lean posture (class notes, Prentice). Upright primates have their foramen
magnum under the skull, causing a straight position (class notes, Prentice). In "Primate Origin",
Shawn Lehman mentions that Arboreal quadrupeds, primates living among trees, have a narrow
axial skeleton. He notes that they are recognizable with their long tail and digits to easily cling to
trees and branches. Lehman found that they have short forelimbs, but hindlimbs of equal length.
These primates are always in a flexed position, causing bending in elbows and knees (Lehman,
p.8). Thus, their knees and elbows are adapted to support the posture. All of these features allow
for the Arboreal quadrupeds to lower their center of gravity and have an easier time moving from
branch to branch and from tree to tree (Lehman, p.8). Lehman’s study points out that terrestrial
quadrupeds are more adapted to speed than arboreal quadrupeds. These primates have long and
extended forelimbs and hindlimbs, a short tail and small digits (Lehman, p.8). Their skeletal
structure is adapted for strong propulsive forces to jump, as their longer hindlimbs than forelimbs
show, as the study shows. Lehman remarks that terrestrial quadrupeds have a narrow tibia to help
flex and extend their body during a leap. In addition, he states that suspensory primates are
characterized as having longer forelimbs than hindlimbs, and that they lack a tail. Their mobile
shoulders and hips make them able to change position frequently (Lehman, p.9). He explains the
utility of their curved fingers, which is to hold to branches. There is enough knowledge of extant
nonhuman primates to categorize the mode of locomotion of the unknown species.
Joseph J. Werner’s "Mating Behavior in Australopithecus and Early Homo: A Review of The
Diagnostic Potential of Dental Dimorphism." published in 2014, suggests that the difference in
body and canine size between males and females nonhuman primates indicates the mating behavior
of a primates species. Bigger males than females used their canines to fight against other males for
female mates. (Werner 2014) Thus, these males also have larger canines than their female
homologues, he adds. Then, Werner explains that there is a higher chance for that species to live
in a polygamous group. If that is not the case, he explains, and there is no significant difference in
the female and male size of the body and canines, the species is said to be monogamous or
polyandrous. In his book "Sexual Selection and the Origins of Human Mating System" published
in 2009, Alan F. Dixson emphasizes that there is also a difference between the structure of the
larynx between female and male primates. He evaluates that the difference is greater among
polygynous species than monogamous and polyandrous nonhuman primates. Sexually mature
polygamous males use low sounds the most to show their desire for sexual intercourses (Dixson
2009). Since the skeletons are of a female and male representative, the fossils could be compared
to see any presence of dimorphism in their size. The neck bones can be analyzed too to see if there
is a difference in size.
Works Cited
http://www.pearsoned.ca/highered/showcase/lehman/media/lehm_ch05.pdf
http://rasmussen.libanswers.com/faq/32328
https://ir.lib.uwo.ca/cgi/viewcontent.cgi?article=1307&context=totem
https://books.google.ca/books?id=VRTniKE2liYC&pg=PA178&lpg=PA178&dq=mating+behaviours+fos
sils+primates&source=bl&ots=edBY6bTO6h&sig=wNPx0xIbCCCM2BAd9-tI_DeVLI&hl=fr&sa=X&ved=0ahUKEwiM4v696_HZAhVL8IMKHS3ZAF04FBDoAQgzMAI#v=onepage&q=
mating%20behaviours%20fossils%20primates&f=false