Paleontology provides information about the history of morphological transformations, whereas developmental biology provides information about how such transformations happen at a mechanistic level. As such, developmental evidence enriches paleontology in formulating and assessing hypotheses of homology, character definition, and character independence, as well as providing insights into patterns of heterochrony, evolvability of features, and explanations for differential rates of evolution. The focus of this article is to review a series of case studies that illustrate how our understanding of paleontology is enriched by data generated by developmental biologists. The integration of paleontological and developmental data leads to a greater understanding of evolution than either of these sciences could have reached alone. Our case studies range from fish to mammals and involve somite and vertebral formation, limb loss, hand and foot patterning, and tooth formation.

The Lower Devonian (Lochkovian) Man On The Hill (MOTH) Lagerstätte preserves a large diversity of early vertebrates fossils, including several species of osteostracan. Waengsjoeaspis nahanniensis had previously been named on the basis of material from MOTH and is redescribed herein. The genus Waengsjoeaspis Janvier was originally established in 1985 for two species from Spitsbergen. In addition, the new species Waengsjoeaspis platycornis is recognized. Both species from MOTH lack barbs on their cornual processes. The new species differs from W. nahanniensis in proportions of the cornual processes and of the median field. New specimens from MOTH clarify the condition of the infraorbital sensory line, the mouth, and other morphological features within the genus, and confirm that the dermoskeleton grew like that of Superciliaspis by separate ossification of tesserae, fusion of tesserae to form larger units, and centrifugal growth of these units. The new observations are consistent with the earlier phylogenetic placement of Waengsjoeaspis within a clade basal to the Benneviaspidida and add to the considerable diversity of osteostracans at this important locality.

An increasing number of paleobiological studies use preexisting cladistic data sets to estimate shifting lev-els of morphological disparity over time, and investigate the relative positions of taxa within a multivariate morphospace. Although these patterns are derived from characters selected to reconstruct phylogenetic relationships, it is sometimes suggested that they also reflect functional or ecological variation. We test this assertion using a purpose-built matrix of functional mandibular traits and 24 published cladistic matrices targeting early jawed vertebrates. We find that distance matrices calculated from functional and cladistic data are significantly correlated, but that substantial variation in functional dissimilarity goes unexplained by variation in cladistic dissimilarity. Agreement sequentially improves, but not drastically, when cladistic characters are limited to those pertaining to the skull and then mandible. When dissimilarity matrices are subjected to principal coordinate analysis to yield multivariate morphospaces, we find no clear relationship between phylogenetically independent contrasts for scores on lower functional and cladistic coordinate axes. However, we do find that a majority of variation on the first axis of ordinations based on cladistic characters can be explained by phylogeny, even though the distance matrices underlying these ordinations are phenetic. A resampling procedure reveals a positive, but weak, correlation between cladistic and functional disparity measures for equivalent sets of taxa. Although our results show nonrandom relationships between disparity patterns extracted from functional and cladistic character sets, we conclude that these relationships are not sufficiently strong to allow clear inferences about functional variation to be drawn from data assembled for phylogenetic reconstruction.

Ptychodus (Elasmobranchii, Ptychodontidae) is an enigmatic durophagous shark that lived in Cretaceous seas. Based on multiple articulated tooth plates of Ptychodus mortoni from the Niobrara Chalk in Kansas, the dental pattern of P. mortoni and its paleobiological implications were examined. Each tooth plate consists of one medial tooth row and about nine lateral tooth rows on each side. One individual shark possesses a total of slightly over 550 teeth, with approximately 220 functional upper teeth and 260 functional lower teeth. The largest tooth plate of the species likely measured about 55 cm in length and 45 cm in width. Although this study does not resolve the ordinal placement of Ptychodontidae, it demonstrates that there are two different patterns of tooth plate organization in Ptychodus: a plesiomorphic condition characterized by juxtaposed, non-overlapping tooth rows (e.g., P. decurrens, P. marginalis, and P. occidentalis) and an apomorphic condition characterized by imbricated tooth rows (e.g., P. mortoni). It is hypothesized here that the imbrications of tooth rows in P. mortoni likely helped distribute the bite-induced load on its dentition more widely, and its sharp-tipped crowns were effective in shattering animals with comparably thin, brittle shells (e.g., bivalves and crustaceans). The recognized difference in tooth plate organization adds another level of complexity to the dental evolution of Ptychodus as well as to the already complex evolutionary history of predatory behaviors in cartilaginous fishes.

Specimens of a single but currently undetermined species of the anuran genus Liaobatrachus from the Lower Cretaceous of northeast China, including four articulated skeletons preserved on a single block of sediment plus two skulls and several additional adult skeletons on other slabs, illustrate post-metamorphic developmental stages from early juvenile to fully grown adult. The relative ages of the individuals were estimated based on body size combined with degree of ossification. Postmetamorphic developmental data not only provide a basis for comparisons with other fossil and recent anuran taxa, but also help to identify both age-independent (i.e., size-independent) characters that can be used for taxonomic comparisons among individuals of various sizes (i.e., ages) and age-dependent (i.e., size-dependent, ontogenetically variable) characters that can only be used for comparisons across corresponding developmental stages. Our study revealed that the following characters are independent of size in Liaobatrachus: frontoparietals with a fontanelle between their frontal portions; quadratojugal present; vertebral centra amphicoelous and pierced by a notochordal canal; and free (not ankylosed) ribs attached to diapophyses of second to fourth vertebrae. The tibiofibula/femur and presacral vertebral column/snout-vent length ratios were also found to be size independent. In contrast, ossification of the carpus, distal tarsals, and pubis appears to be ontogenetically variable (i.e., they vary with age), and this is presumably also true of fusion between the tibiale and fibulare. These characters should only be used for comparisons among individuals at a common developmental stage.

A relatively diverse record of European Early Cretaceous pan-cryptodiran turtles has been revealed from the analysis of new specimens and from a review of previously defined taxa. However, knowledge about many of these taxa remains relatively limited. We erect the new taxon, Larachelus morla, gen. et sp. nov., on the basis of a shell from the late Hauterivian—early Barremian of the Iberian Range (Spain). The comparative study of this taxon with the continental European Cretaceous pan-cryptodiran representatives and cladistic analyses reveal L. morla to be a member of the little-known European Early Cretaceous stem Cryptodira. Stem cryptodirans have been recognized from the Early Cretaceous of several continents. The study of L. morla not only confirms the presence of this group in the Early Cretaceous of Europe, it also provides new insights into the European evolution of Pan-Cryptodira. This finding reveals greater diversity in European Early Cretaceous continental pan-cryptodires, highlighting its Hauterivian—Aptian record. This diversity is particularly relevant in the Iberian Range, where several clades of turtles whose coexistence has not been recognized in the Lower Cretaceous of any other region are identified: paracryptodiran members, stem cryptodiran turtles, and representatives of several lineages of the crown group Cryptodira. This very high diversity of continental taxa shows a wide range of morphological diversity that could be related to adaptation to different ecological niches.

Additional information about one of the oldest known gecko-like lizards, Hoburogekko suchanovi from the Early Cretaceous of Mongolia, is provided in light of recent advances in the understanding of gekkotan osteology. The phylogenetic affinities of this taxon were assessed by adding it into an existing morphological data set of 224 taxa coded for 364 characters. The effects of character ordering and scoring on tree topology and the composition of Gekkonomorpha were also explored. The results of the analysis indicate that Gekkonomorpha is highly unstable and additional revision of stem gekkotans (e.g., Parviraptor, Gobekko) is required to refine the basal relationships of this clade. Like modern gekkotans, Hoburogekko possess a tubular frontal bone. In contrast to extant gekkotans, the Meckelian canal is only partially fused and may represent an incipient form of the gekkotan condition. The posterior shelf of the maxilla is wider than in modern gekkotans, perhaps related to a plesiomorphically large jugal. The short, rounded snout may indicate a lifestyle as found in some modern gekkotans found in equivalent xeric environments to the inferred paleoenviroment of the Höövor (Mongolia) locality during the Early Cretaceous.

LACM 128319, which was collected in western Kansas, U.S.A., and is assignable to Platecarpus tympaniticus (Mosasauridae, Plioplatecarpinae), represents arguably one of the most exquisite mosasaur specimens known to date. Measuring 5.67 m from the tip of the snout to the end of the tail, it comprises an exceptionally well-articulated skeleton, accompanied by soft-tissue remains, such as skin impressions and tracheal cartilage. P. tympaniticus is one of the most numerously collected mosasaur taxa in North America, but as most specimens are fragmentary or reconstructed to various degrees, LACM 128319 provides a unique opportunity to document the taxon's osteology from a single skeleton. In this study, we first present a detailed osteological description of LACM 128319. Following this, we present an analysis of the evolution of a streamlined body shape in P. tympaniticus, specifically by comparing the length distribution of the dorsal ribs in relevant anguimorphan taxa. We conclude that both an anterior migration of the rib cage and an increasing regionalization within the dorsal vertebral series are key features contributing to formation of a streamlined body profile in P. tympaniticus, and probably in many other hydropedal members of mosasaurs.

Isolated precloacal vertebrae from the early to middle Miocene Gaillard Cut of Panama represent the first Central American fossil record of the extant boine snake Boa and constrain dispersal of the genus into Central America from South America as no younger than approximately 19.3 Ma. Boa from the Las Cascadas fossil assemblage and the Centenario Fauna represent the oldest record of terrestrial southern vertebrate immigration into Central America, and demonstrate American interchange by the earliest Neogene. Interchange of snakes precedes contiguous terrestrial connection between Central and South America by approximately 17 Ma, necessitating dispersal across an approximately 100 km wide marine strait. The biogeographic history of snakes across the Neotropics is distinct from the mammalian record, and indicates a more complicated assembly of New World vertebrate faunas than previously recognized.

A new Middle Triassic sauropterygian, Qianxisaurus chajiangensis, gen. et sp. nov., is described on the basis of a skeleton from the Zhuganpo Member (Ladinian) of the Falang Formation, Xingyi, southwestern Guizhou Province, China. It is primarily characterized by a premaxilla with eight teeth, marginal teeth with a slightly constricted peduncle and short conical crown, snout longer than the rest of skull, postorbital with a truncated dorsal process and forked posterior process, a very small supratemporal fenestra, a short retroarticular process posteriorly truncated and lacking a dorsal concavity, an elongate trunk with 28 vertebrae, a stout sacrum with four vertebrae, a longitudinal groove on proximodorsal surface of the dorsal ribs, and a coracoid with a narrow lateral portion and a foot-shaped medial portion. Q. chajiangensis appears similar to the European pachypleurosaurs, but a global phylogenetic analysis failed to support close relationships with these taxa. Instead, Q. chajiangensis is an eosauropterygian and most probably the sister group of a clade consisting of the European pachypleurosaurs and the Nothosauroidea. The discovery of Q. chajiangensis certainly enriches our knowledge of the early history of the Eosauropterygia and leads to a better understanding of the phylogenetic relationships among known eosauropterygians.

Placodus gigas is an unarmored placodont marine reptile (Diapsida, Sauropterygia) known from the Middle Triassic of Europe, most commonly found in the shallow marine carbonate facies of the German Muschelkalk (lower Anisian to middle Ladinian, approximately 243–235 Ma). Generally, the morphology of the skull is well understood, with the exception of the braincase, which is partially obscured by dermatocranial bone. Two skulls that display well-preserved and intact chondrocranial elements were scanned using industrial micro-computed tomography (µCT), thus revealing parts of the braincase that were previously obscured and allowing a new three-dimensional reconstruction of the region to be constructed. This includes a complete osteological description, the first reconstruction of a sauropterygian vestibular apparatus, and a new virtual cranial endocast. The morphology of the braincase and sphenoid region has been revised, revealing the position of the hypophyseal pit. The enigmatic ‘alisphenoid bridge’ has been reinterpreted as being a dorsally extended dorsum sellae. The vestibular apparatus is shown to have strongly dorsoventrally compressed vertical semicircular canals, a commonly observed morphology of other marine reptiles, and an ‘alert’ head position of about 20°, indicating a highly aquatic lifestyle. Because placodonts are the sister group to all other sauropterygians, these new data are of great comparative and phylogenetic significance, providing insight into some of the morphological and functional changes that occurred on the stem leading to the more derived sauropterygians.

We describe a three-dimensionally prepared specimen of Baryphracta deponiae from the middle Eocene of Messel (Darmstadt, Germany). Based on a phylogenetic analysis that included the addition of 20 novel scorings for characters previously unavailable for this taxon and the recoding of four additional characters, we found B. deponiae to be nested within Diplocynodon. We propose the new combination Diplocynodon deponiae. The name Baryphracta is thus a junior synonym of Diplocynodon. The small species D. deponiae (∼1 m in total length) shares several features with other species of Diplocynodon, including the presence of two subequal alveoli in the maxilla and dentary, exclusion of the splenial from the symphysis, and the shape of the iliac blade. However, it also differs in a few characters, including the presence of molariform teeth and the extension of osteoderms along the limbs and tail. Such osteodermal cover, which developed very early in ontogeny, easily distinguishes even small-sized specimens of D. deponiae from the co-occurring Diplocynodon darwini. The crocodylian fauna of Messel shows an astonishing diversity including at least seven taxa, with two belonging to the same genus. The two congeners exhibit differences in dentition and size that likely allowed for niche partitioning that minimized competition, thereby allowing them to be syntopic.

Jeholosaurus shangyuanensis is a small ornithischian dinosaur from the Lower Cretaceous Yixian Formation of the Lujiatun locality, Liaoning Province, China. Here, we provide the first detailed description of its postcranial skeleton based on the holotype and four other well-preserved skeletons, and compare it with material of other primitive cerapodans. Jeholosaurus can be diagnosed on the basis of one postcranial autapomorphy, relating to the absence of parapophyses from the anterior dorsal vertebrae, and a unique combination of postcranial characters, but its anatomy is otherwise similar to that of many other basal ornithischians. A phylogenetic analysis incorporating these new postcranial data confirms previous suggestions that Jeholosaurus is a basal ornithopod and that it forms a clade with Changchunsaurus and Haya; Koreanosaurus and Yueosaurus might also belong to this clade, though additional material of both will be required to test this hypothesis. The name Jeholosauridae is proposed for this apparently endemic group of Cretaceous East Asian taxa.

The taxonomy and paleobiology of the Upper Permian dicynodont Cistecephalus have been much debated over the last century. Fossils of Cistecephalus have been identified as belonging either to one species or up to six species and hypotheses concerning their lifestyle range from aquatic to arboreal and fossorial. Earlier studies of Cistecephalus focused mainly on macroanatomical characteristics, whereas the current assessment examines a combination of anatomical features, as well as bone histology and microanatomy to unravel its biology. The allometries of a skull growth series that were examined in the present study imply that all Cistecephalus specimens belong to a single species. Furthermore, our data suggest that the variability in the occurrence of supraorbital ridges, which are raised in some specimens and leveled in others, is a feature of sexual dimorphism. Histological thin-sections of a humerus, an ulna, a femur, and ribs from two Cistecephalus specimens were studied to evaluate life history traits of this taxon. The comparison of ribs from a subadult and a fully grown specimen allows an estimation that sexual maturity was attained when the skull length was between 5.9 and 6.5 cm. The compact microstructure of the sampled Cistecephalus bones implies aquatic and/or fossorial adaptations, refuting an arboreal lifestyle. We propose that the high degree of binocular vision evident in Cistecephalus developed in response to predatory (insectivory) and/or nocturnal habits and that it is unrelated to a scansorial lifestyle.

Two incisors and five postcanine teeth of complex crown morphology were found in the lower levels of the Burgersdorp Formation of the Beaufort Group, corresponding to the basal Subzone A of the Cynognathus Assemblage Zone (late Olenekian). All the teeth bear a single root and the postcanines show two rows of mesiodistally aligned cusps and a central basin or groove. Among the postcanines, two general patterns of crown morphology are recognized on the basis of relative length of the cusp rows, number of cusps per row, and width of the central area. Phylogenetic affinities of the described specimens remain unclear, and thus they are regarded as Eucynodontia incertae sedis. However, comparisons with non-mammalian cynodonts with labiolingually expanded postcanines show that they are most similar to those of Aleodon, Candelariodon, and some haramiyids. Many cynodont taxa such as Aleodon, Candelariodon, Cromptodon, haramiyids, and tritylodontids, which are probably not closely related to each other, have labiolingually expanded postcanines with cusps arranged mesiodistally in rows and a central basin; thus pointing to the homoplastic nature of dental morphologies in the cynodont lineage. The teeth presented here are the oldest record of therapsid teeth with crowns having parallel rows of cusps, representing a temporal extension of approximately 10 million years for this crown pattern.

The oldest Miocene continental fauna in the Guadix-Baza depression from southern Spain is described in this paper. The small mammals remains from Cortijo de la Piedra fossil localities have a latest Vallesian (early Tortonian) age, and provide evidence of late Vallesian continental environments, which were unknown until now in southern Iberia. The age of the reported assemblage is previous to the establishment of the Guadix-Baza Basin sensu stricto. It represents the oldest Miocene continental mammalian fauna found thus far in southern Iberia, and proves the presence of connections with the foreland. The small mammals from Cortijo de la Piedra display a similar size and morphology as those recorded on the mainland, showing no particular traits that might be interpreted as insular features. These continental faunas suggest that the North-Betic Foreland Basin was at least partially closed at the end of the early Tortonian.

†Pardinamys humahuaquensis, a new genus and species of Phyllotini (Rodentia, Cricetidae), is described on the basis of 111 cranial, mandibular, and dental remains belonging to at least 29 individuals. The fossils were recovered from a microvertebrate assemblage found in late Pliocene deposits (between 3 and 2.5 Ma ago) from the Uquía Formation, central Jujuy Province, northwestern Argentina. †Pardinamys is morphologically intermediate between the extant genera Eligmodontia and Calomys and can be differentiated from these taxa by the combination of several traits, including short masseteric crest, with upper and lower ramus similarly developed; coronoid process well developed; anteromedian flexus in M1 only present in very young individuals, without any trace of anteromedian style; M1 and M2 with developed second minor fold; large M2 and M3; and metaflexus, paracone, and metacone of M3 well developed. The morphologic characteristics of the new genus and the other sigmodontines found in the Uquian assemblage (at least three extinct genera) suggest an important radiation before the establishment of the modern communities in the central Andean region and indicate the need for a reevaluation of the divergence-age estimates for the group. The recovered taxa indicate the presence of open environments during depositional times, within arid or semiarid conditions, unlike previous reconstructions for this geologic unit. The finding reveals the need for improving the fossil record of sigmodontines in the central Andean region and its importance to understanding the radiation of this group in a more inclusive South American context.