What is the Difference Between Gracile and Robust

The main difference between gracile and robust is that gracile species had smaller cheek teeth, pronounced prognathism, less flared cheeks, and no sagittal crest, but robust species had enormous cheek teeth, robust jaws and massive jaw muscles, sometimes anchored to a bony crest running along the top of the skull. Furthermore, gracile species were frugivores that lacked heavy vegetation, but robust species were herbivores that consumed heavy, gritty vegetation. 

Generally, gracile and robust are two terms commonly used to describe different species of the extinct genus Australopithecus. Also, they belong to the tribe Hominini and apparently evolved in eastern Africa around 4.2 million years ago.  

Key Areas Covered 

1. Gracile Australopithecus
     – Taxonomy, Characteristics, Behavior
2. Robust Australopithecus
     – Definition, Characteristics, Behavior
3. What are the Similarities Between Gracile and Robust
     – Outline of Common Features
4. What is the Difference Between Gracile and Robust
     – Comparison of Key Differences  

Key Terms 

Australopithecus, Cheek teeth, Diet, Gracile, Jaw Muscles, Paranthropus, Robust

Gracile Australopithecus – Taxonomy, Characteristics, Behavior

The gracile form is one of the two groups of species of the genus Australopithecus. Also, these species include A. anamensis (4.0 Mya), A. afarensiss (Lucy) (3.5 Mya), A. africanus (Taung Child) (3.0 Mya), A. garhi (2.5 Mya), and A. sedeba (2.3 Mya).

Figure 1: A. africanus

Importantly, the main significant feature of these gracile species is their generalism rather than specialization in hard-to-process herbivorous food. That means; they are frugivores adapted to a fruit-based diet. On that account, they had a lighter appearance in their facial and cranial features. Thereby, they lacked bony crests for the attachment of heavy chewing muscles. Still, they had smaller cheek teeth. Also, their anterior dentition was emphasized. But, they had a pronounced prognathism, which is the bulging out of the lower jaw or mandible.

Figure 2: A .afarensis

The term ‘gracile’ is used to describe anatomically modern humans (AMH) and Epipaleolithic humans that are Combe-Cepelle, a Paleolithic and Epipaleolithic site situated in the Couze valley in the Périgord region of southern France. Here, anatomically modern humans refer to H. sapiens having an anatomy consistent with the range of phenotypes seen in contemporary humans from varieties of extinct archaic humans. However, Epipaleolithic humans lived in a period intervening between the Upper Paleolithic and Neolithic in the Stone Age. The Epipalaeolithic hunter-gatherers are nomadic, made relatively advanced tools from small flint or obsidian blades, known as microliths, that were hafted in wooden implements.  

Robust Australopithecus – Taxonomy, Characteristics, Behavior

The robust form is the other group of species of the genus Australopithecus with opposite features to the gracile counterpart. In general, Paranthropus is another term for the robust Australopithecines. In this, there are three significant species that represent the robust form. They are A. robustus (2.5 Mya), A. boisei ( 2.5-1.4 Mya), and A. aethiopicus (2.5 Mya). Also, these species were sympatric with the gracile forms and later with early Homo throughout their existence.

Figure 3: DNH 7, The Most Complete Skull of A. robustus

In contrast to the gracile forms, robust forms adapted to consume heavy and gritty vegetation as they are herbivores. Therefore, their diet was specialized. On that account, they had large cheek teeth, robust mandible as well as a heavy bony architecture (i.e. zygomatic arch), which supports strong chewing muscles. Additionally, they had very large projecting brow ridges and projecting face

Figure 4: A. boisei

Moreover, the term ‘robust’ is used to describe archaic humans and early modern humans that are Cro-Magnon (H. s. sapiens). Here, archaic humans include Neanderthals and Middle and Lower Paleolithic hominins with transitional features and intermediate between H. erectus, Neanderthals, and early anatomically modern humans (AMH). But, early modern humans lived in the Middle Paleolithic period. Also, they include Jebel Irhoud, Omo, Herto, Florisbad, Skhul, and Peștera cu Oase, exhibiting a mix of archaic and modern traits. 

Similarities Between Gracile and Robust  

• Gracile and robust are two terms, describing different species of the genus  Australopithecus of the tribe hominini.  
• They apparently evolved in eastern Africa around 4.2 million years ago.    
• They are literally extinct and their fossils found in South Africa and  East Africa.  
• Feature-wise,  they have a low lying braincase. Also, the cranial and facial morphology of them indicates different diets and thus separate niches. Besides, it helps to explain the co-evolution of these two groups in the same landscapes for 2 million years.    
• It has been suggested that the latest australopithecine species gave rise to the earliest members of Homo.    
• Nevertheless, the terms gracile and robust can also be used to describe humans. 

Difference Between Gracile and Robust 

Definition 

Gracile refers to any member of the species, belonging to the genus Australopithecus with relatively a lighter build, especially in the skull and teeth, but robust refers to the species of the genus Australopithecus, especially belonging to the contested genus, Paranthropus. 

Classification 

Gracile species of Australopithecus include A. anamensis, A. afarensiss, A. africanus, A. garhi, and A. sedeba, while robust species of Australopithecus include A. robustus, A. boisei, and A. aethiopicus. 

TimeLine 

Gracile species appeared ~ 4 Mya but disappeared ~ 2 Mya, whereas robust species persisted from ~ 4–1 Mya.  

Facial Morphology 

Gracile species had pronounced prognathism, less flared cheeks, and smaller cheek teeth, but robust species had very large projecting brow ridges, projecting face, post-orbital restriction, flared cheekbones, large jaws, big molars, and heavy facial muscles. 

Cranial Morphology 

Gracile species had no sagittal crest, while robust species had a sagittal crest. 

Diet 

Gracile species were frugivores that lacked heavy vegetation, but robust species were herbivores that consumed heavy, gritty vegetation. 

Adaptation Ability 

Gracile species had a generalized diet and they could adapt quickly, but in contrast, robust species had a specialized diet, and they could not adapt quickly. 

Reproduction 

Gracile species showed less sexual dimorphism, while robust species showed considerable sexual dimorphism. 

Conclusion 

In brief, gracile forms refer to the species of the genus Australopithecus, excluding Paranthropus. Therefore, the main characteristic facial features of these species include smaller cheek teeth, pronounced prognathism, and less flared cheeks. Also, they had no sagittal crest. On that account, gracile species were frugivores that had a fruit-based diet. In contrast, robust species of the same genus are also known as Paranthropus. Basically, they had enormous cheek teeth, robust jaws, and massive jaw muscles. However, they had a sagittal crest. Hence, robust species were herbivores that consumed a heavy and gritty diet. Therefore, the main difference between gracile and robust is the facial and cranial features, which led to their type of diet in Australopithecus.

References:

1. “Human Evolution: A Description of Fossil Hominids and Their Origins.” ArchaeologyInfo.com, Available Here.
2. Constantino, P. J. (2013) The “Robust” Australopiths. Nature Education Knowledge 4(1):1. Available Here.

Image Courtesy:

1. “Australopithecus africanus – Cast of taung child” By Didier Descouens – Own work (CC BY-SA 4.0) via Commons Wikimedia   
2. “A.afarensis” By Esv assumed – Own work (Public Domain) via Commons Wikimedia   
3. “DNH7” By DrHerries – Own work (CC BY-SA 4.0) via Commons Wikimedia   
4. “MEH Paranthropus boisei 29-04-2012 11-50-46 2592×3888” By Nachosan – Own work (CC BY-SA 3.0) via Commons Wikimedia