Synapsida

Synapsid diversity 3

Skull synapsida 1

Eothyris head

Sea Otter kuchang kushiro hokkaido

Archaeothyris BW

Ophiacomorphs2

Synapsida is a group of amniotes that includes mammals and their extinct relatives. Synapsids first appeared in the Carboniferous period and became the dominant terrestrial vertebrates during the Permian period. They are distinguished from other amniotes by having a single temporal fenestra, an opening in the skull behind each eye, which allows for the attachment of larger jaw muscles. This article provides an overview of the Synapsida, including their evolutionary history, characteristics, and significance.

Characteristics

Synapsids are characterized by their distinctive skull morphology, particularly the presence of a single temporal fenestra on each side of the skull. This feature contrasts with the Diapsida, which have two openings, and Anapsida, which have none. The temporal fenestra in synapsids allows for the expansion of the jaw muscles, giving them a more powerful bite. Other characteristics include differentiated teeth (incisors, canines, premolars, and molars) and a more upright limb posture compared to earlier amniotes.

Evolutionary History

The evolutionary history of Synapsida is marked by several significant events. They first emerged in the late Carboniferous period, with early members being small, lizard-like creatures. During the Permian period, synapsids diversified and became the dominant land vertebrates. This era saw the rise of several important groups, including the Pelycosauria, which are often mistakenly referred to as "sail-backed dinosaurs," and the more advanced Therapsida.

The end of the Permian period was marked by the Permian-Triassic extinction event, the largest mass extinction in Earth's history, which led to a significant decline in synapsid diversity. However, one group of therapsids, the Cynodontia, survived and gave rise to the first mammals in the Late Triassic period.

Classification

Synapsida is divided into several major groups, including:

• Pelycosauria: An early and diverse group of synapsids that were dominant during the early Permian. They are not a natural group (monophyletic) but are useful for describing early synapsid evolution.
• Therapsida: A more derived group that includes mammals and their direct ancestors. Therapsids show more advanced characteristics, such as a more upright posture and complex teeth.
• Cynodontia: A subgroup of therapsids that includes modern mammals and their immediate ancestors. Cynodonts display features that are characteristic of mammals, including a secondary palate and more complex jaw muscles.

Significance

Synapsids are of significant interest to paleontologists and evolutionary biologists because they represent the evolutionary lineage that led to mammals. Studying synapsids helps scientists understand the evolutionary transitions that occurred from simple amniote ancestors to complex modern mammals, including the development of endothermy (warm-bloodedness), hair, and lactation.

Conclusion

Synapsids play a crucial role in understanding the evolutionary history of mammals. Their fossil record provides valuable insights into how environmental changes and mass extinctions have shaped the evolution of terrestrial vertebrates. As research continues, more discoveries about this fascinating group are likely to emerge, shedding light on the complex journey from early synapsid ancestors to the diverse array of mammals present today.