Context: The Triassic is a geologic period and system which spans 50.9 million years from the end of the Permian Period million years ago (Mya), to the beginning of the Jurassic Period Mya. The Triassic is the first period of the Mesozoic Era. Both the start and end of the period are marked by major extinction events. The Triassic was named in 1834 by Friedrich von Alberti, after the three distinct rock layers ("tri" meaning "three") that are found throughout Germany and northwestern Europered beds, capped by marine limestone, followed by a series of terrestrial mud- and sandstonescalled the "Trias"., In the geologic timescale, the Sinemurian is an age or stage in the Early or Lower Jurassic epoch or series. It spans the time between 199.3 ± 2 Ma and 190.8 ± 1.5 Ma (million years ago). The Sinemurian is preceded by the Hettangian and is followed by the Pliensbachian., The squamosal is a bone of the head of higher vertebrates. It is the principal component of the cheek region in the skull, lying below the temporal series and otic notch and bounded anteriorly by the postorbital. Posteriorly, the squamosal articulates with the posterior elements of the palatal complex, namely the quadrate and pterygoid. The squamosal is bordered anteroventrally by the jugal and ventrally by the quadratojugal., The Early Jurassic epoch (in chronostratigraphy corresponding to the Lower Jurassic series) is the earliest of three epochs of the Jurassic period. The Early Jurassic starts immediately after the Triassic-Jurassic extinction event, 201.3 Ma (million years ago), and ends at the start of the Middle Jurassic 174.1 Ma., Sinoconodon rigneyi is an ancient mammaliamorph or early mammal ( depending on systematic approach ) that appears in the fossil record of China in the Sinemurian stage of the Early Jurassic period , about 193 million years ago . While in many traits very similar to reptiles , it possessed a special , secondarily evolved jaw joint between the dentary and the squamosal bones , which had replaced the primitive reptilian one between the articular and quadrate bones , a trait commonly used to define mammals . Although the animal is closely related to Morganucodon , it is regarded as the most basal of the mammaliaforms . It differed substantially from the more mammalian Morganucodon in its dental and growth habits . Like the reptiles , it was polyphyodont , replacing many of its teeth throughout its lifetime , and it seems to have grown slowly but continuously until its death . Sinoconodon is thus less mammalian than early mammaliaforms like docodonts and morganucodonts . Even the smallest known individuals had already begun the teething cycle of the front teeth , and combined with a poorly ossified jaw , it very probably did not suckle . The combination of reptilian and mammalian features makes it straddle the divide between the two classes anatomically and likely ecologically . There are simply no animals like it alive today ., Juga is a genus of freshwater snails with a gill and an operculum, aquatic gastropod mollusks in the family Semisulcospiridae. , Chronostratigraphy is the branch of stratigraphy that studies the age of rock strata in relation to time., The Pliensbachian is an age of the geologic timescale or stage in the stratigraphic column. It is part of the Early or Lower Jurassic epoch or series and spans the time between 190.8 ± 1.5 Ma and 182.7 ± 1.5 Ma (million years ago). The Pliensbachian is preceded by the Sinemurian and followed by the Toarcian., Subject: sinoconodon, Relation: taxon_rank, Options: (A) branch (B) genus (C) series
Output: genus