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An anapsid is an amniote whose skull lacks one or more skull openings (fenestra, or fossae) near the temples. [1] Traditionally, the Anapsida are considered the most primitive subclass of amniotes, the ancestral stock from which Synapsida and Diapsida evolved, making anapsids paraphyletic.
Turtles have an anapsid skull, but this was likely acquired secondarily from a diapsid ancestor. Synapsida – One low opening (beneath the postorbital and squamosal bones). A monophyletic group including mammals and their ancestors. Euryapsida – One high opening (above the postorbital and squamosal bones).
A = Anapsid, B = Synapsid, C = Diapsid. It was traditionally assumed that first reptiles were anapsids, having a solid skull with holes only for the nose, eyes, spinal cord, etc.; [10] the discoveries of synapsid-like openings in the skull roof of the skulls of several members of Parareptilia, including lanthanosuchoids, millerettids, bolosaurids, some nycteroleterids, some procolophonoids and ...
“It shows that early turtle evolution was not a straightforward, step-by-step accumulation of unique traits but was a much more complex series of events that we are only just beginning to ...
All anapsid skulls lack a temporal opening while all other living amniotes have temporal openings. [115] It was later suggested that the anapsid-like turtle skulls may be due to backward evolution rather than to anapsid descent. [116] Fossil evidence has shown that early stem-turtles possessed small temporal openings. [105]
Compared to many other ostracoderms, such as the Heterostraci and Osteostraci, anaspids did not possess a bony shield or armor, hence their name.The anaspid head and body are instead covered in an array of small, weakly mineralized scales, with a row of massive scutes running down the back, and, at least confirmed among the birkeniids, the body was covered in rows of tile-like scales made of ...
This placement within the diapsids suggests that the turtle lineage lost diapsid skull characteristics, since turtles possess an anapsid skull. This would make Parareptilia a totally extinct group with skull features that resemble those of turtles through convergent evolution.
This is an accepted version of this page This is the latest accepted revision, reviewed on 17 January 2025. Group of animals including lepidosaurs, testudines, and archosaurs This article is about the animal class. For other uses, see Reptile (disambiguation). Reptiles Temporal range: Late Carboniferous–Present Pre๊ ๊ O S D C P T J K Pg N Tuatara Saltwater crocodile Common box turtle ...