The morphology and histological structure of the humerus and femora of the stem karaurid salamander Kulgeriherpeton ultimum Skutschas et al., 2018, from the Lower Cretaceous Teete locality, Republic of Sakha (Yakutia) is described. The microanatomical and histological structure of K. ultimum is characterized by the presence of a thick compact primary cortex formed by a parallel-fibered bone; the absence (in the humerus) or presence of a small medullary cavity in the mid-diaphysis; the presence of a medullary cavity expanding towards the epiphyses, which continues in the proximal and distal parts as a complex network of branching canals, partially replaced by erosion bays; the presence of primary vascular canals and growth marks in the primary cortex; the presence of remnants of unresorbed cartilage and the Kashchenko’s line; active secondary remodeling with the formation of erosion bays similar to those in large-sized salamanders (other stem karaurid salamanders and cryptobranchids). Skeletochronological analysis of the humerus of K. ultimum showed that, at the time of the animal’s death, its individual age was 13–16 years, and the absence of a reduction in the distance between cyclic growth marks in the peripheral part of the cortex indicates that it belonged to an actively growing individual that had not reached its maximum possible size. The similarity in the morphology of the humerus and femur of K. ultimum and extant aquatic neotenic salamanders (absence of a dorsal crest on the humerus for the attachment of m. subcoracoscapularis, lower, forward-displaced trochanter of the femur, and shallow ventral fossa (fossa trochanterica) on the femur), as well as the presence of remnants of cartilage and preservation of Kashchenko’s line in the internal structure of limb bones, confirm conclusions about aquatic life style and neotenic nature of stem karaurid salamanders.

This paper describes the morphology and histological structure of the femora of salamanders of the genus Kiyatriton K. krasnolutskii from the Middle Jurassic (Bathonian) Berezovsk Quarry locality in Krasnoyarsk krai and K. leshchinskiyi from the Lower Cretaceous (Aptian) Shestakovo 1 locality in the Kemerovo Region. The femora of Kiyatriton are characterized by the presence of a large spur-like trochanter, a developed high trochanteric crest, a large ventral fossa (fossa trochanterica), and a bean-shaped proximal end in cross-section. The histological structure is characterized by the presence of a thick, almost avascular cortex formed by both the primary periosteal bone and secondary endosteal bone; a thick periosteal cortex, which consists of a parallel-fibred bone matrix and bears cyclical growth marks (annuli and LAGs), including double LAGs; a thick endosteal cortex consisting of a lamellar bone matrix; the presence of a small medullary cavity; the presence of the Katschenko’s line; and the absence of a calcified cartilage and bone remodeling (erosion bays, secondary osteons, and resorption of the walls of the medullary cavity). The similarities in the morphological and histological structure of the femora of Kiyatriton and small-sized modern metamorphosing salamanders (large spur-like trochanter of the femur, deep ventral fossa, rounded proximal end of the femur, avascular periosteal cortex with growth marks, thick layer of endosteal bone forming the inner part of the cortex, and small medullary cavity) indicate that members of the genus Kiyatriton were metamorphosing salamanders with a terrestrial adult stage. The similarity in the structure of the femora of different-aged Middle Jurassic and Early Cretaceous representatives of Kiyatriton indicates that the biological features (growth pattern and the presence of metamorphosis) have not changed for about 40 million years.

This paper describes the microanatomical and histological structure of different-sized femora and hypocentra of the archegosauroid amphibian Platyoposaurus stuckenbergi from the Middle Permian (Urzhum horizon, Estemmenosuchus uralensis zone) of Eastern Europe. Age variability is discussed in a comparative context, along with the ecology of the species. P. stuckenbergi femora are characterized by the complete absence of calcified cartilage and the presence of up to 15 lines of arrested growth (LAGs); hypocentra have an osteoporotic structure, lacking both calcified cartilage and LAGs. Microanatomical and morphological features indicate the predominantly aquatic lifestyle of Platyoposaurus as an active predator in river and lake habitats.

This study describes the microanatomical and histological structure of the femur and hypocentra of the neotenic temnospondyl amphibian Dvinosaurus campbelli from the Late Permian locality Gorokhovets, Vladimir Region (Upper Vyatkian Substage, subzone Chroniosuchus paradoxus of the Scutosaurus karpinskii zone). The femur of D. campbelli is characterized by a "pachyosteous" structure (dense thick periosteal cortex in the diaphysis) and a large number of growth marks (about 57); the hypocentrum has an "osteoporotic" structure. The neotenic nature of D. campbelli is confirmed by the presence of unresorbed cartilage in the skeletal elements of large-sized forms. Microanatomical and morphological features indicate that D. campbelli was an ambush feeder (using concealment during hunting).

The first finding of the docodontan (a lower molar ofSibirotheriumsp.) from the Bol'shoi Kemchug 3 locality (Ilek Formation, Lower Cretaceous) in Krasnoyarsk Territory is described.Sibirotherium rossicum, one of the youngest docodontans in the geological record, is known from the Ilek Formation of the Shestakovo 1 locality (Kemerovo Region). Previously, only indeterminable remains of docodontans had been found in the localities of the Ilek Formation (Bol'shoi Terekhtyul' 2 and Bol'shoi Ilek) on Krasnoyarsk Territory.