synapsiiden

Synapsids are a major group of amniote vertebrates that includes all mammals and their extinct ancestors. The group is defined by a single pair of temporal fenestrae, or openings, in the skull located behind the eye socket. This anatomical feature distinguishes them from the diapsids, which have two pairs of such openings, and the anapsids, which have none.

The earliest known synapsids appeared in the Late Carboniferous period, around 312 million years ago. Initially, they were small, lizard-like creatures, but over time, they diversified into a wide range of forms. Prominent among their extinct members are the pelycosaurs, such as Dimetrodon, which are often mistaken for dinosaurs but predate them by millions of years. Pelycosaurs were characterized by their sail-like structures on their backs, the function of which is still debated but may have been for thermoregulation or display.

Later, more mammal-like synapsids, known as therapsids, evolved. Therapsids showed increasingly mammalian characteristics, including more upright posture, differentiation of teeth, and possibly endothermy. Cynodonts, a subgroup of therapsids, are considered the direct ancestors of mammals.

Mammals themselves emerged from the cynodont lineage during the Triassic period. Despite the rise of dinosaurs, early mammals were generally small and nocturnal, occupying ecological niches that allowed them to survive alongside the dominant reptiles. The subsequent extinction of the non-avian dinosaurs paved the way for mammals to diversify and occupy a vast array of ecological roles, leading to the incredible diversity of mammalian life seen today. The study of synapsids is crucial for understanding the evolutionary transition from reptiles to mammals and the broader history of vertebrate life.