The oldest avialans that comprise birds and their predecessors emerged during the Mid-Late Jurassic period and are undoubtedly depicted by Archaeopteryx from Germany’s Late Jurassic era. Avialans are members of the Coelurosuria clade Paraves, which also comprises troodontids and dromaeosaurs (Rauhut and Foth, 2020, p. 27). The Anchiornithidae of China’s Mid-Late Jurassic are speculated to be avialans, but they have also been discovered as a distinct family of paravians. These dinosaurs and early birds share characteristic features, most prominently the exact shape of the pelvis, a lengthy vertebral tail, pecked paws, hollow bones, and a tooth-filled mouth.
Modern bird characteristics, including a beak and breastbone, are yet to evolve. The earliest-known bird is Archaeopteryx, a fossil species first found in Germany in the mid-1860s (“Deep Time. Mesozoic Era” (a)). It flew, based on the outline of the bird’s feathers. The latest research in northeast China affirms the hypothesis that theropods developed wings for insulation before birds converted their purpose for flight. The identification of wings on some dinosaurs has complicated a past clear differentiation between them and birds. Cladistic studies have consistently demonstrated that birds and certain dinosaur species constitute a well-defined lineage. Most paleontologists ostensibly believe that birds are evolved dinosaurs.
Mammals evolved from cynodonts toward the close of the Triassic period and diversified extensively throughout the Jurassic. The majority of Jurassic mammals are documented only from fragmented teeth and jaw separation, but preserved fossils have revealed a wide range of behaviors (“Deep Time. Mesozoic Era” (b)). True mammals evolved traits such as a more petite body, a more expansive brain volume, molars for cutting rather than tearing food, a middle ear with bones, and one jaw bone. At the same time, the oldest primates were solitary, nocturnal, and rodent-like.
The Paleocene epoch represents the start of the Tertiary and Cenozoic eras. The period, which started approximately 65M years ago and proceeded to the modern-day, is the third known epoch of Earth’s history (“Cenozoic Era: (248 mya-present) para 5). This period accounts for the present positions of the continents and their current occupants, such as humans. As a result of the disappearance of certain classes of large animals, the Cenozoic period is often recognized as the Period of Mammals, enabling smaller animals to survive and diversify when their rivals became extinct. Due to the long period represented by the era, it is preferable to address the animal community by the era’s milestones instead of in broad generalities.
Although mammals may have developed millions of years ago, the earliest documented primate specimens date from about 60 million years ago. Groups of mammal species classified as either anthropoid or prosimian vary in size from gorillas to pygmy mice. Cone opsin variants from a wide range of modern primates aided the evolution of opsin genetic phylogenies (Scholtyßek and Kelber, 2017, p. 978). All mammal optical photopigments belong to the opsin genes from the five genetic groups related to rod photopigments and the other four to cone pigments. A single gene is connected to the rod photopigments as the rest represent cone pigment. The four cone photopigment genome families appeared early in vertebrate development, possibly in 540 Ma. In these groups, gene-sequence heterogeneity produces photopigments for modification to absorb selectively through narrow limits of peak sensitivities. Colour vision enables animals to discern variations in the patterns of spectral energies approaching the eye with high accuracy.
Reference List
Deep Time. Mesozoic Era: (248-65 mya).(a) Evolution. Web.
Deep Time: Cenozoic Era: (248 mya-present). Evolution. Web.
Deep Time: Mesozoic Era: (248-65 mya).I (b) Evolution. Web.
Rauhut, O.W. and Foth, C., (2020). The origin of birds: Current consensus, controversy, and the occurrence of feathers. In The Evolution of Feathers (pp. 27-45). Springer, Cham.
Scholtyßek, C. and Kelber, A., 2017. “Color vision in animals: From color blind seals to tetrachromatic vision in birds.” Der Ophthalmologe: Zeitschrift der Deutschen Ophthalmologischen Gesellschaft, 114(11), pp.978-985.