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Anaspids were small marine agnathans that lacked heavy bony shield and paired fins, but have a striking highly hypocercal tail. They first appeared in the Early Silurian, and flourished until the Late Devonian extinction, [17] where most species, save for lampreys, became extinct due to the environmental upheaval during that time.
The latter has lost the paired fins, possibly as a consequence of an adaptation to burrowing habits. [ 2 ] The class Osteostraci (meaning "bony shells") is an extinct taxon of bony-armored jawless fish , termed " ostracoderms ", that lived in what is now North America, Europe and Russia from the Middle Silurian to Late Devonian .
Agnatha (/ ˈ æ ɡ n ə θ ə, æ ɡ ˈ n eɪ θ ə /; [3] from Ancient Greek ἀ-(a-) 'without' and γνάθος (gnáthos) 'jaws') is a paraphyletic infraphylum [4] of non-gnathostome vertebrates, or jawless fish, in the phylum Chordata, subphylum Vertebrata, consisting of both living (cyclostomes) and extinct (conodonts, anaspids, and ostracoderms, among others).
Since then, opinions on the relations among jawless vertebrates have varied. Most workers have come to regard Agnatha as paraphyletic, having given rise to the jawed fishes. Because of shared features such as paired fins, the origins of the jawed vertebrates may lie close to Cephalaspidomorphi.
Stethacanthus ' s unusual fin may have been used in mating rituals. [83] Apart from the fins, Stethacanthidae resembled Falcatus (below). Falcatus: Falcatus is a genus of small cladodont-toothed cartilaginous fishes that lived 335–318 Ma. They were about 25–30 cm (10–12 in) long. [86]
The pair of pectoral fins were modified into a pair of caliper-like, or arthropod-like limbs. In primitive forms, such as Yunnanolepis, the limbs were thick and short, while in advanced forms, such as Bothriolepis, the limbs were long and had elbow-like joints. The function of the limbs is still not perfectly understood, but most hypothesize ...
Sarcopterygii (/ ˌ s ɑːr k ɒ p t ə ˈ r ɪ dʒ i. aɪ /; from Ancient Greek σάρξ (sárx) 'flesh' and πτέρυξ (ptérux) 'wing, fin') — sometimes considered synonymous with Crossopterygii (from Ancient Greek κροσσός (krossós) 'fringe') — is a clade (traditionally a class or subclass) of vertebrate animals which includes a group of bony fish commonly referred to as lobe ...
[3] [4] In 1995, the painted turtle was named as Michigan's state reptile. [5] Reptile habitats in Michigan are generally split into four regions: the northern and southern Lower Peninsula and the eastern and western Upper Peninsula, with differentiations based on climate, soils, underlying bedrock and glacially-derived landforms. Region one ...