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Two new brachythoracids are described from the Emsian limestones of the Lake Burrinjuck area, both based on skull remains. They are the largest and most advanced arthrodires so far known from the fauna, and amongst the largest fishes recorded anywhere from the Early Devonian. Dhanguura johnstoni gen. et sp. nov. is based on a single incomplete skull with an estimated length of at least 40 cm, which possesses the derived character of a strongly T-shaped rostral plate, not recorded in any other arthrodire from the fauna. Cathlesichthys weejasperensis gen. et sp. nov. was of similar size, and shows a derived dunkleosteid type of development of the posterior skull margin. In both forms the paranuchal plates have narrow anterior margins, suggesting affinities with the family Homostiidae. Some new material of the genus Taemasosteus is illustrated for comparison. Skull characters used in phylogenetic analyses of brachythoracid arthrodires are reviewed; in Dhanguura johnstoni the similar overlap of the nuchal plate onto centrals, central plates onto preorbitals, and preorbital plates onto the rostral plate may reflect a single developmental pattern. The preorbital plates completely separated by the pineal and rostral plates are interpreted as a homoplasy with coccosteomorphs, and instead of a preorbital embayment of the centrals, as seen in that group, this bone has a posterolateral process, as in Arenipiscis. Cathlesichthys is derived in the massive transverse nuchal ridge, one of three defining characters of the Eubrachythoraci, but shows no evidence of an anterior nuchal thickening.
The fragmentary remains of a new dipnoan, Ichnomylax karatajae, sp. nov., have been discovered in the Lower Devonian sediments of Taymir Peninsula, northern Russia. This form is characterized by a prearticular tooth plate consisting of a large, elongated, strongly convex, heel-like posterior region, which is clearly demarcated from the anterior tooth zone. There are three or four anterolaterally-directed rows of large, rounded teeth. Numerous rounded, elongate, enamel-covered denticles are present anteriorly between the tooth rows, as well as medially, laterally, and posteriorly, near the outer edges of the plate. This new species, like Ichnomylax kurnai, can be interpreted as being a basal dipnoan, close to Speonesydrion, another Lower Devonian form. The discovery of this new species of Ichnomylax on the Siberian plate, widely separated from the Southern Australian type locality of I. kurnai, provides additional evidence for rapid dispersal of Early Devonian dipnoans.
Histological examination of one of the prearticular plates revealed the presence of petrodentine in both the body of the plate and in the teeth. We provide a definition, brief description, and discussion on the significance of this unique type of hypermineralized dentine, and conclude that the discovery of petrodentine in such an early stage of dipnoan history has important implications for studies of dipnoan evolution.
A new specimen of the rhizodontid sarcopterygian, Sauripterus taylori (Sarcopterygii, Osteichthyes), from the Late Devonian (Famennian) Catskill Formation of Pennsylvania consists of a well-preserved right pectoral fin, girdle, and associated scales. Rhizodontid affinity is supported by the unique pattern of overlap between the clavicle and cleithrum, the robustness of the pectoral girdle, the presence of elongate and unjointed lepidotrichia in the pectoral fin, and the pattern of connectivity between the endochondral bones of the pectoral fin. The new specimen of Sauripterus provides a three-dimensional and articulated view of basal rhizodontid pectoral girdle and fin anatomy and preserves the first known scapulocoracoid for a Devonian rhizodontid. The glenoid fossa faces posteroventrally, in contrast to the more posterolaterally facing glenoids of other tetrapodomorph fish. The humerus is short proximodistally and possesses an expansive ventral flange for the attachment of the adductor, flexor, and rotatory musculature of the fin. Together, these data suggest that the pectoral fins of Sauripterus were optimized for adduction and flexion against the water column or a solid substrate. To maximize the propulsive force of these motions the distal fin was stiffened by the presence of eight radials, similar in position to the autopodials of tetrapods. However, unlike the digits of tetrapods, the unit that interacts with the environment in rhizodontids is a combined structure consisting of both dermal and endochondral fin skeletons. As recent phylogenetic hypotheses do not support a sister-group relationship between rhizodontids and tetrapods, the similarities between the endoskeletal radials of Sauripterus and the autopodium of tetrapods are independently derived.
Few records of Late Jurassic fishes have been reported previously from Antarctica. They include an indeterminate teleost from the Ameghino (Nordenskjöld) Formation at Longing Gap and two incomplete aspidorhynchiforms from James Ross Island, all of presumed Late Jurassic age. New fish material recently recovered in the Upper Jurassic of Longing Gap is described. The new material consists of one piece of body squamation, which, based on the structure of the scales, corresponds to a new genus and species (Ameghinichthys antarcticus gen. et sp. nov.) of an indeterminate actinopterygian family; one aspidorhynchiform identified as Vinctifer sp. due to the structure and distribution of the scales; and numerous specimens of a new ichthyodectiform, Antarctithrissops seymouri gen. et sp. nov. This new genus differs from European ichthyodectiforms in the shape of the preopercle, the presence of long sensory preopercular branches almost reaching the posterior margin of the bone, and the uncommon structure of the scales, with a fine layer of bone obscuring the circuli.
The presence of Vinctifer in the Antarctic is consistent with its other Gondwanan records. The Ichthyodectiformes, previously known from four European genera, extends the distribution of the group to the southernmost part of the Southern Hemisphere during the Late Jurassic. In contrast to most non-teleostean fishes, the known Late Jurassic teleosts apparently are species endemic to restricted areas in the Southern Hemisphere.
An anatomical study of Microbrachis reveals inaccuracies in previous studies, especially in the palate and cranial proportions. The vomer and the pterygoid reach the midline anteriorly, and the postorbital does not appear to reach the tabular. The skull is higher in our cranial reconstruction than previously thought. A phylogenetic analysis of early stegocephalians places Microbrachis at a fairly basal position in the clade that includes “microsaurs,” lysorophians, and lissamphibians. This analysis corroborates previous suggestions that lissamphibians are part of a clade that includes the taxa classically referred to as “lepospondyls,” and that seymouriamorphs and temnospondyls are not part of Tetrapoda. Statistical tests on another recent amphibian phylogeny reveal that its different placement of the origin of lissamphibians is not statistically more parsimonious than the placement that we suggest. Our analysis also suggests that the first evolutionary radiation of amphibians took place in an aquatic environment because most of the first groups of amphibians to have differentiated, namely adelogyrinids, nectrideans, and Microbrachis, appear to have been aquatic or amphibious taxa. However, the lifestyle of many early amphibians is difficult to assess.
Isolated fragmentary anuran remains from several fossil-bearing levels of the continental succession exposed in the Salla-Luribay basin, Eastern Cordillera, are described herein. The anuran material consists of poorly preserved postcranial bones that are referable to toads of the nearly cosmopolitan genus Bufo, now widely distributed in South America. Moreover, these remains strikingly resemble skeletal elements of extant South American species of the B. marinus group, most of which inhabit humid to semiarid lowlands. Based on the ilial morphology, two species appear to be represented in the Salla Beds: one close to B. arenarum and another, possibly new, that attained large size. This study does not confirm an earlier suggestion that a taxon closely related to the living South American aquatic leptodactylid Caudiverbera is represented in the Salla succession. This record supports an Early Tertiary, or even older, major diversification of bufonids.
A new species of Xinpusaurus Yin in Yin et al., 2000 (Thalattosauria, Thalattosauridae), is described from the Wayao Member of the Falang Formation (Tuvalian, Carnian, Upper Triassic) of Guanling County in Guizhou, southwestern China. It is the third thalattosaur species known from the Guanling faunal assemblage of marine reptiles. The type and only specimen consists of an entire skeleton, including a complete skull. It differs from the type species, X. suni, by its smaller adult size, the larger nasal, the more slender angular and low retroarticular process, the shape of the cervical neural spines, the number of presacral vertebrae, the large size of the scapula, the shape of the radius, the presence of a well ossified carpus, the more slender femur, the smaller hindfin, the presence of a complete row of distal tarsal ossifications, and the proportions of the metatarsals. It is consequently referred to a new species, Xinpusaurus kohi. A new analysis of thalattosaur interrelationships based on 30 cranial and postcranial characters corroborates a sister-group relationship between Xinpusaurus and Nectosaurus from the Carnian of California.
Gastralia are dermal ossifications situated in the ventral abdominal wall. Gastralia may be plesiomorphic for tetrapods, but are only retained in extant Crocodylia and Sphenodon, and possibly as part of the chelonian plastron. In contrast to previously published reports, a similar structural configuration of the gastralia is shared throughout prosauropods and (non-ornithurine) theropods. Within the Prosauropoda and Theropoda, the gastralial system consists of approximately 8 to 21 metameric rows. Each row consists of four bones: two lateral and two medial rods. Gastralia of the cranialmost or caudalmost rows may coalesce, forming a median chevron-shaped gastralium. The lateral gastralia articulate in parallel with the medial gastralia in an elongated groove. The medial gastralia imbricate with contralateral gastralia along the ventral midline, creating a series of cranially directed chevrons. Thus all the gastralia are connected to one another, and operate as a single functional unit. The bones recently identified as sauropod gastralia show no morphological similarities with the gastralia of prosauropods and theropods and are probably sternal elements. No gastralia have been recovered in the Ornithischia.
In contrast to the reduction of the gastralia in other amniote groups, theropod gastralia show elaborate modification. The anatomy of the gastralial system indicates a more active function than abdominal support or protection. The gastralia may have affected the shape and volume of the trunk in theropods, and may have functioned as an accessory component of the aspiration pump, increasing tidal volume. Moreover, if the caudal region of the lungs in some theropods had differentiated to form abdominal air-sacs, the gastralia might have ventilated them. Gastralial aspiration may have been linked to the generation of small pressure differences between potential cranial and caudal lung diverticula, which may have been important for the evolution of the unidirectional airflow lung of birds.
We describe an articulated specimen of the titanosaurian sauropod Epachthosaurus sciuttoi from the early Late Cretaceous Bajo Barreal Formation of Chubut Province, central Patagonia, Argentina. The skeleton was found in tuffaceous sandstone, with its hindlimbs flexed and its forelimbs widely extended. It is slightly deformed on its left side. The skull, neck, four or five cranial dorsal vertebrae, and several distal caudals are missing.
Epachthosaurus is diagnosed by the following autapomorphies: middle and caudal dorsal vertebrae with accessory articular processes extending ventrolaterally from the hyposphene, a strongly developed intraprezygapophyseal lamina, and aliform processes projecting laterally from the dorsal portion of the spinodiapophyseal lamina; hyposphene-hypantrum articulations in caudals 1–14; and a pedal phalangeal formula of 2-2-3-2-0. The genus shares the following apomorphies with various titanosaurians: caudal dorsal vertebrae with ventrally expanded posterior centrodiapophyseal laminae; six sacral vertebrae; an ossified ligament or tendon dorsal to the sacral neural spines; procoelous proximal, middle, and distal caudal centra with well-developed distal articular condyles; semilunar sternal plates with cranioventral ridges; humeri with squared proximolateral margins and proximolateral processes; unossified carpals; strongly reduced manual phalanges; craniolaterally expanded, nearly horizontal iliac preacetabular processes; pubes proximodistally longer than ischia; and transversely expanded ischia. Epachthosaurus is considered the most basal titanosaurian known with procoelous caudal vertebrae.
Rapetosaurus krausei (Sauropoda: Titanosauria) from the Upper Cretaceous Maevarano Formation of Madagascar is the best-preserved and most complete titanosaur yet described. The skull of Rapetosaurus is particularly significant because most titanosaurs are diagnosed solely on the basis of fragmentary postcranial material, and knowledge of the titanosaur skull has remained incomplete. Material referred to Rapetosaurus includes the type skull from an adult that preserves the basicranium, rostrum, mandible, and palate. A second, juvenile skull preserves most of the braincase and cranial vault, as well as some of the palate and lower jaw. Here we provide a detailed description of Rapetosaurus cranial anatomy and highlight comparative relationships among known titanosaur and other neosauropod skulls. The Rapetosaurus skull is similar to those of diplodocoids in its overall shape, with retracted external nares and an elongated snout. However, extensive tooth distribution and bone articulations surrounding the external narial region and orbit are more similar to those of macronarians like Camarasaurus and Brachiosaurus. The maxilla, basicranium, paroccipital process, and pterygoid are among the most diagnostic elements of the Rapetosaurus skull, along with the enlarged antorbital fenestra, anteroventrally oriented braincase, and mandible. Titanosaur crania exhibit a greater diversity than previously recognized and, in light of Rapetosaurus, it is apparent that there is not a narrowly constrained bauplan for the skull of titanosaurs. Broad generalizations about evolution based on previously known, fragmentary fossils require re-evaluation. Ultimately, Rapetosaurus will be key in resolving titanosaur higher-level and ingroup phylogeny.
The hadrosaurid Nipponosaurus sachalinensisNagao, 1936, was the first dinosaur discovered in Japan. Here we establish its ontogenetic stage, diagnostic characters, and systematic position by redescribing and phylogenetically analyzing the type and sole specimen of Nipponosaurus. The unfused neurocentral sutures of all vertebrae suggest that the type specimen of Nipponosaurus is subadult. Furthermore, it can be diagnosed by the following characters: (1) the coronoid process of the surangular is robust, (2) the neural spine of the axis is only slightly developed, and (3) the lateral margin of the first phalanx on digit IV is strongly deflected. The phylogenetic analysis, using 78 characters for seven ingroup and six outgroup taxa, indicates that Nipponosaurus belongs within Lambeosaurinae as the sister taxon to Hypacrosaurus altispinus.
The Extant Phylogenetic Bracket approach is applied to infer the kind of soft tissue that would have been associated with the bifurcated neural spines of the cervical vertebrae of sauropods. A median ligament (“ligamentum nuchae” or lig. supraspinale) extends along the tips of the neural spines and attaches to them in the cervical region of extant avian and non-avian diapsids, thus enabling a parsimonious inference that a homologous ligament would also have attached to the same sites in extinct diapsids, including sauropods. In the extant ratite bird, Rhea americana, “lig. nuchae” splits ventrally into two halves as the neural spines become bifurcated in the posterior cervical region, thereby maintaining its connection to both tips of each bifurcated neural spine. This shows the conservative nature of the connection between “lig. nuchae” and its osteological correlate. Furthermore, this ligament and the notches of the bifurcated neural spines enclose another ligament, lig. elasticum interspinale, that arises from the non-bifid neural spine of the most posterior “cervico-dorsal” and gives off branches inserting on the posterior surfaces of the neural spines of the middle to posterior cervicals in Rhea. This ligament in Rhea is suggested to be a good modern analog to the structure occupying the notches of the bifurcated neural spines of sauropods. A hypothetical reconstruction of the proposed ligament system is given using Camarasaurus and Apatosaurus as examples.
Pyozia mesenensis, gen et sp. nov. is the second varanopid synapsid from the Middle Permian Krasnoschelsk Formation of Russia. Pyozia is a basal varanopid similar to Archaeovenator in having teeth that lack lateral compression or serration, lacking a caniniform tooth or region on the maxilla, and possessing four premaxillary teeth. Pyozia uniquely possesses a medial contact of the maxilla with the quadratojugal with no lateral exposure allowing the jugal to form part of the skull's ventral margin, and rounded interpterygoid vacuities just anterior to the basipterygoid articulations. Phylogenetic analysis places Pyozia as sister taxon to the terminal dichotomy of Mycterosaurinae and Varanodontinae. The newly described Upper Carboniferous Archaeovenator is again found to be the most basal varanopid.
The Permian saw a large-scale changeover of the synapsid fauna, with derived, but ecologically similar, taxa, replacing more primitive “pelycosaurs.” Leaf-shaped tooth-bearing caseids were replaced in the Middle and Late Permian by herbivorous pareiasaurs with similar dentition, and Edaphosaurus was replaced by therapsids capable of processing plant material. The large predators of Sphenacodontidae were similarly replaced by therapsid predators. The small to medium sized predator niche, however, was continuously occupied by varanopids. The discovery of the basal Pyozia suggests that varanopids maintained their diversity in the Middle Permian.
Four distinct stages have been identified in the ontogeny of Diictodon feliceps based on variations in cortical thickness, organization of primary osteons, porosity, incidence of growth marks, and extent of endosteal reconstruction. In general, the cortex comprises fibrolamellar bone tissue suggesting rapid bone deposition and growth. In the initial two stages of growth, when up to 70% of adult size is attained, no growth marks interrupt the fibrolamellar tissue, indicating a sustained, fast growth. Growth marks appear late in ontogeny and indicate periods of slow or complete cessation of growth after which, fast growth resumed. Although growth was interrupted and much slower in the later stages, D. feliceps probably had an indeterminate growth strategy. Variations in cortical thickness, porosity, organization of primary osteons, and incidence of annuli and LAGs are observed between elements of the same individual, suggesting variable inter-elemental growth. The propodials had faster appositional growth than did the epipodials, with the humerus having grown much faster than the femur in the same individual. The high cortical thickness (RBT) and correspondingly low k values suggest that the limbs were selected for impact loading. The relatively high RBT and low k value of the humerus compared to other limb bones indicates that the forelimbs were more modified for postural support and digging.
Tashkumyrodon desideratus, gen. et sp. nov. from the Middle Jurassic (Callovian) Balabansai Formation near Tashkumyr in Kyrgyzstan is described from a single lower molar. The tooth exhibits the typical structure of a docodont lower molar with the main cusp a connected by crests to the lingual cusps (c and g) and to the mesial cusp b. Tashkumyrodon is plesiomorphic in retaining well developed crests c-d and d-f, and derived in reduction of crest b-g. By formation of crests b-e and e-g (derived), Tashkumyrodon resembles Tegotherium from the Late Jurassic of Mongolia and Sibirotherium from the Early Cretaceous of West Siberia, Russia. Tegotherium is more derived than Tashkumyrodon by the more prominent anterior basin (“pseudotalonid”) and the reduction of the crests distal to cusp c. The Asian docodonts probably represent the sister group of all remaining docodonts, an Euramerican clade characterized by retention of crest b-g and reduction of cusp e as well as crest b-e. Simpsonodon from the Middle Jurassic of England is convergently similar to Tegotherium in development of a “pseudotalonid” and reduction of distal crests.
Four Paleocene petrosal bones from the Itaboraí fissure fillings of Brazil belong to two metatherian morphotypes. They are compared with ear regions of other fossil and recent marsupials. The results of a parsimony analysis using thirty-eight characters from the petrosal and ear region are partly congruent with recent studies and confirm that characters from the ear region are highly informative for phylogenetic reconstruction. Metatheria are diagnosed by five petrosal synapomorphies: stapedial artery absent in adults; reduced, intramural prootic canal; extrabullar internal carotid artery; inferior petrosal sinus between petrosal, basisphenoid, and basioccipital; and cava supracochleare and epiptericum completely separated. The stem group of South American and Australian metatherians is composed of the Paleocene taxa Pucadelphys, one of the oldest known metatherians from South America, and Petrosal Type II from Itaboraí. Among the South American-Australian metatherians two clades are defined here. The crown clade is composed of Australian taxa plus Dromiciops (here referred to Australidelphia sensu stricto), while they plus Caenolestes form the Australidelphia sensu lato. Petrosal Type I from Itaboraí is the most basal taxon of Australidelphia sensu lato, the latter diagnosed by three significant synapomorphies: ventral part of the mastoid rounded and bulbous owing to enlargement of the fossa subarcuata; posttemporal foramen absent; and foramen for a branch of the transverse sinus present on the posterior edge of the ventral pars canalicularis.
The fossil record of megatheriine ground sloths extends back to the middle Miocene, but only Pleistocene megatheriines are reasonably well understood. The taxonomy of pre-Pleistocene genera and species is not well-established. A partial megatheriine skeleton lacking the skull from the Pliocene Toro Negro Formation (La Rioja Province, Argentina) was originally assigned to Plesiomegatherium sp. This specimen forms the basis of Pyramiodontherium scillatoyanei, sp. nov. Py. scillatoyanei is notable for a relatively prominent humeral deltopectoral crest, a relatively short, robust calcaneum, and the largest crural index among sloths. The stronger humeral crests possibly imparted a relatively stronger ability in grappling. The higher crural indices of megatheriines and particularly of Pyramiodontherium, compared to those of mylodontids, suggest greater agility.
The type species of Plesiomegatherium is Plesiomegatherium hansmeyeri, but unfortunately the genus was originally diagnosed almost entirely using the type species of Pyramiodontherium, Py. bergi. Few, if any, features can be used to define Plesiomegatherium. A second species assigned Plesiomegatherium, Pl. halmyronomum, is probably not congeneric with Pl. hansmeyeri, but sufficient evidence to unequivocally remove it from this genus is lacking. A third species, Plesiomegatherium triangulatum, is a nomen vanum.
A relatively complete skull of Hypsosteiromys with a well-preserved natural cranial endocast was recovered from the Colhuehuapi Member, Sarmiento Formation (lower Miocene) at Gran Barranca, Chubut Province, Argentina. The only known skull of this genus, it differs from those of other erethizontids because it is continuously very low, the ascending ramus of the premaxillae extends behind the posterior margins of the nasals, and the external auditory meatus has a ventral furrow. Comparison of the endocast with the brains of extant Erethizontidae demonstrates remarkable neuromorphological homogeneity, despite differences in size. Erethizontid brains have rounded, telencephalic hemispheres with prominent frontal lobes and small olfactory bulbs, and lack temporal lobes and neocortical sulci. Thus, the Gran Barranca skull shows that the external neuromorphology of erethizontids has not changed substantially since at least the early Miocene.
Almost two thousand mandibular teeth of the short-necked giraffid, Sivatherium hendeyi, from Langebaanweg, South Africa, were examined for dental pathologies. Enamel hypoplasia is present in 0 to 34 percent of deciduous teeth and 40 to 75 percent of permanent teeth. No linear enamel hypoplasias were found in the deciduous teeth, while 20 to 35 percent of the permanent teeth have this defect. The linear defects at the base of the first molar are thought to relate to stress associated with weaning. The defects in the later erupting permanent teeth are, however, widely distributed over tooth crowns. Several linear defects are present on some teeth suggesting that these stress episodes were periodic. We propose that poor environmental conditions, possibly seasonal nutritional stress, are responsible for the observed enamel hypoplasia in the permanent dentition of S. hendeyi. This study provides new insight into the current understanding of the paleoenvironment at Langebaanweg, South Africa.