Evolutionary Development


The five fetal skulls of the pantropical spotted dolphin significantly aid in the description of the evolutionary development of dolphins. The presence of rostral tactile hairs and skin pigmentation represents the early fetal life. The dolphin on its early life exhibits developmental order of the intramembranous and endochondral factors and morphological development in the cranium. Telescoping, the nasal anatomy and the aquatic hearing of the dolphins greatly aid in the analysis of the cranial evolution.

The length of the skull increases with age, but variations occur due to the vast shape change of the cranial bones. The telescoped skull shows that the facial bones in the archaocetes mainly the premaxilla and the maxilla from the elongate rostrum and the nasal openings through posterior extension. The mysticete skull shows a reduced isthmus between the braincase and the rostrum. The evolved dolphins show an increased size of the skull and the buccal cavity to allow processing of large amounts of water required in filter feeding (de Muizon, Lambert, & Bianucci, 2018). The restructuring of the skull in odontocete facilitates production of sound and echolation through beam production.

During echolocation, the odontocetes generate some high sound frequencies that are transformed into a forward transmission beam for environmental survival. The increased utilization of echolation reduced the need for olfaction among the early dolphins. The rays through the mandibular aid in detecting obstacles, predators, and prey through interpretation of returning echoes in the water (Little et al., 2015). The nasal bones in a well-developed dolphin are nodular, elevated and compressed from the anterior-posterior unlike in most terrestrial mammals. The nasal bones resemble those of terrestrial mammalian to show the evolution but differ in the dorsal positioning on the surface of the skull.

The transition from terrestrial to obligate aquatic can be observed through the external body nares of the dolphins such as reduction from the posterior rostrum to the forehead.



Dolphin 2

The difference in substrate thickness between the air and the water contributed to the development of fusiform body shape to reduce drags in the aquatic environment. The tail flukes aid significantly reducing the drag when moving at high speeds due to the balanced thickness ratio detected using a CT scan. The shape of the fluke and the large leading radius edge reduced the tendency for flow and stall to generate lift. The evolution of flukes is convergent as observed in the dugongs, manatees and the sirenians. The flipper developed from the front limb significantly aid in locomotion in water by increasing lift, executing turns for braking. The narrowness of the flippers increases the speed in swimming while the broadness helps in slow turns. The five digits present on the flippers give an ancestral connection with the terrestrial relatives. The differences in the osteology of the flippers among the dolphins provide a clue on the vestigial hind limb.


Zebra 1

The pelage of the zebra plays a significant role in protection, adaption to the environment for insulation and tactile. The zebra fur is highly sensitive as observed by several species in the historical chart of study. The lines on the fur form a definite pigmentation that plays significant roles in the adaptation of the zebra to the internal and external environment. The quagga zebra currently under extinction after rampant hunting in South Africa showed to have the stripe pattern on the form part only (Gosling, 2017). DNA research regarding the stripes showed that stripes varied with the environment but collectively meant to protect and balance insulation. The stripes according to evolution reduced fly bites which through their visual system view the zebras as different animals.

The flehmen response profoundly characterizes the Olfactory system of the zebra. The changes in the environment that required a high level of detection led to the development of the Jacobson’s organ. The organ receives pheromones and scents to facilitate the response thus essential in communication. The curling of the upper lip created a connection through the nostril and the olfactory bulb in the brain thus increasing their size to aid in communication.

The auditory system of the zebra developed significantly due to the social living which required communication. The ear pinnae increased in size because it was used as a mood detecting organ. The changes in size, shape, and position significantly aid zebras and other animals to understand emotional stability. Sound communication led to an increase in the size of the eardrums and coiling of the ossicles to interpret the sound (Liu et al., 2016). The highly coiling of the cochlea resulted from the high pitched barks made to communicate especially danger.

Zebra 2

The visual system of zebra is termed as excellent due to their ability to view objects from far. Zebras evolved from the ungulates family with the eyes located on the sides of the head for a wide field of view. The sharpening of the visual system as characterized by the evolutionary changes in the size of the pupil and lens resulted due to the changes in environmental adaptation. The increase in the number of predators caused an increase in the visual power filed and the size of the retina. Zebras exhibited night vision though not much developed as a result of movements and increased predators.

The food gathering system of the zebras entails direct feeding on main grasses with occasional diets on shrubs, leaves, and barks. The presence of incisors on both jaws is a unique feature absent in most herbivores.  The digestive system evolved to allow absorption of nutrients, especially when feeding on lower nutritional foods. The digestive system changed to suit the environments that had reduced sources of food (Liu et al., 2016). The dentition is unique with strong jaw muscles to allow digestion of hard foods such as the barks, especially during drought.

The evolution of the locomotion in zebra based on the four gaits was based on the interaction with the environment. The pectoral girdle developed a unique positioning that allows a wavy movement during attach. The stamina level of the pelvic and the pectoral girdle increased as the exposure to predators became high for escape purposes. Domestication as a human activity contributed to the evolution of the lumbar vertebrae to help balance especially during transport.

Lion 1

The pelage of the lions is sensitive and mostly used as a communication tool through licking. The sensitivity of the fur increased due to reduced forest habitats thus forced to live in the opening. The color of the fur ranges over brown as an adaptation to the grasslands where most preys are found. The color domineered as part of the camouflaging tactics to increase survival rate. The brown color allows a balanced absorption of light and heat thus plays the role of insulation especially after the reduction of forest habitats that could provide shade.


Long nostrils characterize the olfactory system due to the continuous use of the smell sense in detecting prey and predator. The Jacobson’s organ in lions is well developed to facilitate facial expressions made on sniffing a chemical signal. The olfactory bulb of the brain is highly developed to coordinate the different communication expressions such as raised muzzle and closed mouth. Lions tend to use chemical and visual signals in communication thus a high developed olfactory system.

The auditory system of the lion is developed as characterized by the large eardrum to accommodate the repertoire of vocalizations. The cochlea s highly developed because the sound is a core part of communication. The pinnae are large to collect sound from the surrounding environment as an adaptive measure. The intensity of the vibrations made is based on the size of the auditory part of the brain leading to puffing, roaring, and bleating.  The ear ossicles are classified into three to aid in differentiating the several forms of sounds produced by the lion.


Lion 2

The visual system of the lion characterized by sharpness due to the perfect placement of the orbit to facilitate a wide field of view. The size of the pupil varies in proportion to regulate light due to the changes in habitat especially living in the open grounds. The lens has a high magnification due to living in the forest where clear visual results were required to facilitate survival. The tapetum lucidum increased in thickness to prevent injuries during hunting.

The evolution of the masticatory system of the lion is based on the type of prey and hunting process. The jaw muscles increased as a result of continuous capturing of heavy-weight prey. The short and powerful attack used by the lion in hunting led to the development of a long side of the tongue and flexible lips. The incisors are substantial and significant due to the quick grasp of prey during hunting (Mosser, Kosmala, & Packer, 2015).  The constant breakage of bones led to the sharp carnassial teeth which makes it easy during feeding. Living in caves led to the enlargement of the incisors because the practice to drag the prey into the habitat for consumption.

The locomotion and prey capturing system of lions have a universal evolution system due to the high level of dependency. The hypercarnivore nature explains the presence of a wide range of prey which explains the origin of most features. Lions have initially been gigantic, but due to changes in habitat, lions reduced in size, but some features remained large. The scapula of the lion on the front limb is large to facilitate the capturing of the prey. The front paw of the lion with retractable claws developed from the gigantic origin as a hunter to hold the prey in position. The paw with retracted claws made a move easy and less noisy thus easy to get to the targeted prey (de Oliveira et al., 2017).  The flexibility of the spine evolved from the hunting roles and the type of habitat the caves. The flexibility of the spine allowed movement of the lion in different habitats, especially in the forest.




de Muizon, C., Lambert, O., & Bianucci, G. (2018). River dolphins, evolution. In Encyclopedia of marine mammals (pp. 829-835). Academic Press.

de Oliveira, L. R., Gehara, M. C., Fraga, L. D., Lopes, F., Túnez, J. I., Cassini, M. H., … & García, N. (2017). Ancient female philopatry, asymmetric male gene flow, and synchronous population expansion support the influence of climatic oscillations on the evolution of South American sea lion (Otaria flavescens). PloS one12(6), e0179442.

Gosling, M. (2017). Biting flies, lions, and the evolution of zebra stripes. Ecology98(8), 2227-2229.

Liu, Y., Zong, Q. G., Zhou, X. Z., Foster, J. C., & Rankin, R. (2016). Structure and evolution of electron “zebra stripes” in the inner radiation belt. Journal of Geophysical Research: Space Physics121(5), 4145-4157.

Mosser, A. A., Kosmala, M., & Packer, C. (2015). Landscape heterogeneity and behavioral traits drive the evolution of lion group territoriality. Behavioral Ecology26(4), 1051-1059.

Pyenson, N. D., Vélez-Juarbe, J., Gutstein, C. S., Little, H., Vigil, D., & O’Dea, A. (2015). Isthminia panamensis, a new fossil inioid (Mammalia, Cetacea) from the Chagres Formation of Panama and the evolution of ‘river dolphins’ in the Americas. PeerJ3, e1227.