31-696: Lissamphibia ? † Westlothiana ? † Adelospondyli ? † Aïstopoda ? † Lysorophia † " Microsauria " † " Nectridea " Lepospondyli is a diverse taxon of early tetrapods. With the exception of one late-surviving lepospondyl from the Late Permian of Morocco ( Diplocaulus minimus ), lepospondyls lived from the Visean stage of the Early Carboniferous to the Early Permian and were geographically restricted to what
62-612: A monophyletic group, it has been considered an evolutionary grade of basal ("primitive") lepospondyls, although there is growing consensus that a large subset of fossorially-adapted microsaurs, the Recumbirostra , is monophyletic. Lysorophia may belong within the Recumbirostran clade, distinct from other derived lepospondyls. Nectridea may also be paraphyletic, consisting of a range of more anatomically-specialized lepospondyls. The name Holospondyli has been proposed for
93-497: A 1995 paper by Robert Carroll argued that lepospondyls were actually a monophyletic group closer to reptiles. Carroll considered them closer to reptiles than the seymouriamorphs , but not as close as the diadectomorphs . Many phylogenetic analyses since Carroll (1995) agreed with his interpretation, including Laurin & Reisz (1997), Anderson (2001), and Ruta et al. (2003). A few have still considered lepospondyls ancestral to amphibians, but came to this conclusion without changing
124-1390: A clade including aïstopods, and nectrideans, and possibly adelospondyls, although not all recent phylogenetic analyses support the grouping. The following cladogram , simplified, is after an analysis of tetrapods and stem-tetrapods presented by Ruta et al. in 2003: Batropetes fritschi Tuditanus punctulatus Pantylus cordatus Stegotretus agyrus Asaphestera intermedia Saxonerpeton geinitzi Hapsidopareion lepton Micraroter erythrogeios Pelodosotis elongatum Rhynchonkos stovalli Cardiocephalus sternbergi Euryodus primus Microbrachis pelikani Hyloplesion longicostatum Odonterpeton triangulare Brachydectes spp. Acherontiscus caledoniae Adelospondylus watsoni Adelogyrinus simorhynchus Dolichopareias disjectus Scincosaurus crassus Keraterpeton galvani Batrachiderpeton reticulatum Diceratosaurus brevirostris Diplocaulus magnicornis Diploceraspis burkei Ptyonius marshii Sauropleura spp. Urocordylus wandesfordii Lethiscus stocki Oestocephalus amphiuminum Phlegethontia linearis The "lepospondyl hypothesis" of modern amphibian origins proposes that lissamphibians are monophyletic (that is, they form their own clade) and that they evolved from lepospondyl ancestors. Two alternatives are
155-401: A group with elongated bodies and very small limbs; Aïstopoda , a group of limbless, extremely elongated snake-like forms; Adelospondyli , a group of presumably aquatic forms that resemble aïstopods, but have more solidly built skulls; and Nectridea , another diverse group that includes terrestrial and aquatic newt-like forms. Microsauria is generally considered paraphyletic ; rather than being
186-717: A meter in length, but most were much smaller), and they are assumed to have lived in specialized ecological niches not taken by the more numerous temnospondyl amphibians that coexisted with them in the Paleozoic. Lepospondyli was named in 1888 by Karl Alfred von Zittel , who coined the name to include some tetrapods from the Paleozoic that shared some specific characteristics in the notochord and teeth . Lepospondyls have sometimes been considered to be either related or ancestral to modern amphibians or to Amniota (the clade containing reptiles and mammals). It has been suggested that
217-415: A notch on either side near the symphysis (chin). The symphysis itself is formed by a rough area of bone on the left and right dentaries. This rough patch is formed by a complex system of ridges, which have been described as "brassicate" (textured like a cauliflower ). Only Megalocephalus is known to share this brassicate patch with colosteids. The mandibles were also unique in the fact that they possessed
248-449: A suite of anatomical features shared between lissamphibians and a group of Paleozoic temnospondyls called dissorophoids . Under this hypothesis, Lepospondyli either falls outside crown group Tetrapoda (the smallest clade containing all living tetrapods, i.e. the smallest clade containing Lissamphibia and Amniota), or is closer to amniotes and therefore part of Reptiliomorpha . However, some phylogenetic analyses continue to find support for
279-462: Is a family of stegocephalians ( stem-group tetrapods ) that lived in the Carboniferous period. They possessed a variety of characteristics from different tetrapod or stem-tetrapod groups, which made them historically difficult to classify. They are now considered to be part of a lineage intermediate between the earliest Devonian terrestrial vertebrates (such as Ichthyostega ), and
310-489: Is a cladogram from Ruta et al. (2003) that supports the "temnospondyl hypothesis", showing the position of Lepospondyli within crown group Tetrapoda: Lissamphibia + Temnospondyli Caerorhachis bairdi Eoherpeton watsoni Proterogyrinus scheelei Archeria crassidisca Pholiderpeton scutigerum Anthracosaurus russelli Lissamphibia The Lissamphibia (from Greek λισσός (lissós, "smooth") + ἀμφίβια (amphíbia), meaning "smooth amphibians")
341-607: Is a group of tetrapods that includes all modern amphibians . Lissamphibians consist of three living groups: the Salientia ( frogs , toads , and their extinct relatives), the Caudata ( salamanders , newts , and their extinct relatives), and the Gymnophiona (the limbless caecilians and their extinct relatives). Salientians and caudatans are likely more closely related to each other than to caecilians. The name Batrachia
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#1732771954429372-447: Is an artificial ( polyphyletic ) grouping with some members closely related to extinct stem tetrapod groups and others more closely related to modern amphibians or reptiles. Early phylogenetic analyses conducted in the 1980s and 1990s often maintained the idea that lepospondyls were paraphyletic, with nectrideans close to colosteids and microsaurs close to temnospondyls, which were considered to be ancestral to modern amphibians. However,
403-741: Is commonly used for the clade combining salientians and caudatans. A fourth group, the Allocaudata (also known as Albanerpetontidae ) is also known, spanning 160 million years from the Middle Jurassic to the Early Pleistocene , but became extinct two million years ago. For several decades, this name has been used for a group that includes all living amphibians, but excludes all the main groups of Paleozoic tetrapods, such as Temnospondyli , Lepospondyli , Embolomeri , and Seymouriamorpha . Most scientists have concluded that all of
434-422: Is now Europe and North America . Five major groups of lepospondyls are known: Adelospondyli ; Aïstopoda ; Lysorophia ; Microsauria ; and Nectridea . Lepospondyls have a diverse range of body forms and include species with newt-like, eel- or snake-like, and lizard -like forms. Various species were aquatic, semiaquatic, or terrestrial. None were large (the biggest genus, the diplocaulid Diplocaulus , reached
465-433: Is now called Batrachia and includes frogs and salamanders . In the early to mid 20th century, a biphyletic origin of amphibians (and thus of tetrapods in general) was favoured. In the late 20th century, a flood of new fossil evidence mapped out in some detail the nature of the transition between the elpistostegalid fish and the early amphibians . Most herpetologists and paleontologists , therefore, no longer accept
496-543: The "temnospondyl hypothesis", in which lissamphibians originated within Temnospondyli, and the "polyphyly hypothesis", in which caecilians originated from lepospondyls while frogs and salamanders (collectively grouped within Batrachia ) evolved from temnospondyls. Of the three hypotheses, the temnospondyl hypothesis is currently the most widely accepted among researchers. Strong support for this relationship comes from
527-402: The back of the head, unlike temnospondyls and other " labyrinthodonts ". However, they did possess large mandibular and palatal fangs (on the lower jaw and the roof of the mouth), in addition to smaller marginal teeth (at the edge of the mouth), like "labyrinthodonts". The skull was overlaid with wide sensory grooves known as lateral lines , which extended from rear edge of the skull to the tip of
558-604: The clade Lissamphibia . For a long time, the Lepospondyli were considered one of the three subclasses of Amphibia , along with the Lissamphibia and the Labyrinthodontia . However, the dissolution of "labyrinthodonts" into separate groups such as temnospondyls and anthracosaurs has cast doubt on these traditional amphibian subclasses. Much like "Labyrinthodontia", some studies proposed that Lepospondyli
589-443: The different groups ancestral to all modern tetrapods, such as temnospondyls (probably ancestral to modern amphibians ) and reptiliomorphs (ancestral to amniotes such as mammals , reptiles , and birds ). Colosteids had elongated bodies, with an estimated 40 vertebrae, not including the tail. The skull is relatively flat and composed of many separate bones, like that of other stegocephalians. Colosteids lacked otic notches at
620-407: The grooves, rather than the nostrils. The mandibular fangs were larger than the palatal ones, though those on the palate were still large. Colosteids were unique compared to most stegocephalians in the fact that a pair of palatal fangs were present on the premaxillary bones at the tip of the snout. In conjunction with the forward position of these fangs, the dentary bones of the lower jaw developed
651-427: The grouping is polyphyletic , with aïstopods being primitive stem-tetrapods, while recumbirostran microsaurs are primitive reptiles. All lepospondyls are characterised by having simple, spool-shaped vertebrae that did not ossify from cartilage , but rather grew as bony cylinders around the notochord. In addition, the upper portion of the vertebra, the neural arch, is usually fused to the centrum (the main body of
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#1732771954429682-479: The internal and external relationships of the remaining lepospondyl taxa. The former places the remaining lepospondyls into a single clade along the amniote stem. The latter does not treat the relationships of nectrideans or adelospondyls, but finds microsaurs to be early amniotes, and places lysorophians within microsaurs. Five main groups of lepospondyls are often recognized: Microsauria , a superficially lizard- or salamander-like and species-rich group; Lysorophia ,
713-580: The lepospondyl hypothesis. The analysis by Vallin and Laurin (2004) found lissamphibians to be most closely related to lysorophians, followed by microsaurs. Pawley (2006) also found lysorophians to be the closest relatives of lissamphibians, but found aïstopods and adelogyrinids rather than microsaurs to be the second most closely related groups. Marjanović (2010) found holospondyls to be the most closely related group to lissamphibians, followed by lysorophians. Under this hypothesis, lepospondyls would be crown tetrapods and temnospondyls would be stem tetrapods. Below
744-479: The one leading to frogs and salamanders, and an early Permian date for the separation of the frog and salamander groups. The stem-caecilian Funcusvermis , described in 2023, retained many dissorophoid temnospondyl features, supporting a monophyletic Lissamphibia within clade Temnospondyli. [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] Colosteidae Colosteidae
775-441: The position of lepospondyls compared to seymouriamorphs and diadectomorphs. Lepospondyl and tetrapod classification is still controversial, and even recent studies have had doubts about lepospondyl monophyly. For example, a 2007 paper has suggested that adelospondyls are stem-tetrapods close to colosteids and a 2017 paper on Lethiscus has Aïstopoda in the tetrapod stem based on their primitive braincase. These studies differ in
806-498: The primary groups of modern amphibians— frogs , salamanders and caecilians —are closely related. Some writers have argued that the early Permian dissorophoid Gerobatrachus hottoni is a lissamphibian. If it is not, the earliest known lissamphibians are Triadobatrachus and Czatkobatrachus from the Early Triassic . Some, if not all, lissamphibians share the following characteristics. Some of these apply to
837-412: The snout. Most aquatic stegocephalians have their lateral lines dip, unbroken, under the nostrils once they reach the tip of the snout, or alternately disconnect into separate grooves separated by the nostrils. However, colosteids evolved a unique alternative; their lateral lines droop below the nostrils so far that they contact the marginal teeth, so that the edge of the skull is responsible for subdividing
868-480: The soft body parts, hence do not appear in fossils. However, the skeletal characteristics also appear in several types of Palaeozoic amphibians: The features uniting the Lissamphibia were first noted by Ernst Haeckel , even though in Haeckel's work, Lissamphibia excluded the caecilians . Nevertheless, Haeckel considered the caecilians to be closely related to what he called Lissamphibia (gr. λισσός, smooth), which
899-419: The two prevailing theories of lissamphibian origin are: One of the hypotheses regarding their ancestors is that they evolved by paedomorphosis and miniaturization from early tetrapods. Molecular studies of extant amphibians based on multiple-locus data favor one or the other of the monophyletic alternatives and indicate a Late Carboniferous date for the divergence of the lineage leading to caecilians from
930-513: The vertebra). The position of the Lepospondyli within the Tetrapoda is uncertain because the earliest lepospondyls were already highly specialized when they first appeared in the fossil record. Some lepospondyls were once thought to be related or perhaps ancestral to modern salamanders (Urodela), but not the other modern amphibians. This view is no longer held and all modern amphibians (frogs, salamanders, and caecilians ) are now grouped within
961-505: The view that amphibians have arisen twice, from two related but separate groups of fish. The question then arises whether Lissamphibia is monophyletic as well. The origin and relationships of the various lissamphibian groups both with each other and among other early tetrapods remain controversial. Not all paleontologists today are convinced that Lissamphibia is indeed a natural group, as there are important characteristics shared with some non-lissamphibian Palaeozoic amphibians. Currently,