Sankar Chatterjee

Kurmademys, a New Side-Necked Turtle (Pelomedusoides: Bothremydidae) from the Late Cretaceous of India

Abstract The Maastrichtian Kallamedu Formation of southern India near the village of Kallamedu, Tamil Nadu, has yielded skulls and postcrania of a new genus of side-necked turtle. Kurmademys kallamedensis, new genus and species, is based primarily on a single well-preserved skull. Kurmademys is a pelomedusoid pleurodire belonging to the family Bothremydidae Baur, 1891, with these bothremydid characters: (1) exoccipital-quadrate contact, (2) incisura columellae auris closed by bone, and (3) eustachian tube and stapes separated by bone. Kurmademys is unique among known bothremydids in having extensive temporal emargination, a small postorbital, a large precollumellar fossa, and a foramen posterius canalis carotici interni formed completely by the basisphenoid.

BASAL SAUROPODOMORPHS (DINOSAURIA: SAURISCHIA) FROM THE LOWER JURASSIC OF INDIA: THEIR ANATOMY AND RELATIONSHIPS

Abstract The Upper Dharmaram Formation (Lower Jurassic, Sinemurian) of India has yielded three sauropodomorph dinosaurs, two new taxa and an indeterminate one. Lamplughsaura dharmaramensis n. gen. and sp., represented by several partial skeletons, is a heavily built quadrupedal form (body length ∼10 m). Autapomorphies include teeth with strongly emarginated distal edge; caudal cervical neural spines bearing a vertically oriented ligamentous furrow on cranial and caudal surfaces and a transversely expanded spine table; caudal neural spines bearing a craniodorsally directed spur (proximal caudal vertebrae) or a large process (midcaudal vertebrae); caudal neural spines shorter than transverse processes so former lost first in passing along tail; and a plesiomorphy that is the nontrenchant form of manual ungual I. The Indian dinosaurs were coded for two recent datamatrices for basal sauropodomorphs. The results of this preliminary analysis indicate that Lamplughsaura is either a basal Sauropoda or, less likely, based on Templetons test, a stem sauropodomorph. The second large form, represented by the proximal half of a femur, is a sauropodomorph that is more derived than Saturnalia (Brazil) and Thecodontosaurus (Great Britain) from the Upper Triassic. This is also true for the smaller (body length ∼4 m as adult) Pradhania gracilis n. gen. and sp. which lies outside of the Sauropoda + Plateosauria clade, so it is definitely a stem sauropodomorph. Pradhania is known from fragmentary material; an autapomorphy is the very prominent medial longitudinal ridge on the maxilla.

The Wandering Indian Plate and Its Changing Biogeography During the Late Cretaceous-Early Tertiary Period

Palaeobiogeographic analysis of Indian tetrapods during the Late Cretaceous-Early Tertiary time has recognized that both vicariance and geodispersal have played important roles in producing biogeographic congruence. The biogeographic patterns show oscillating cycles of geodispersal (Late Cretaceous), followed by congruent episodes of vicariance and geodispersal (Early Eocene), followed by another geodispersal event (Middle Eocene). New biogeographic synthesis suggests that the Late Cretaceous Indian tetrapod fauna is cosmopolitan with both Gondwanan and Laurasian elements. Throughout most of the Cretaceous, India was separated from the rest of Gondwana, but in the latest Cretaceous it reestablished contact with Africa through Kohistan-Dras (K-D) volcanic arc, and maintained biotic link with South America via Ninetyeast Ridge-Kerguelen-Antarctica corridor. These two geodispersal routes allowed exchanges of “pan-Gondwana” terrestrial tetrapods from Africa, South America, and Madagascar. During that time India also maintained biotic connections with Laurasia across the Neotethys via Kohistan-Dras Arc and Africa. During the Palaeocene, India, welded to the K-D Arc, rafted like a “Noah’s Ark” as an island continent and underwent rapid cladogenesis because of allopatric speciation. Although the Palaeocene fossil record is blank, Early Eocene tetrapods contain both endemic and cosmopolitan elements, but Middle Eocene faunas have strong Asian character. India collided with Asia in Early and Middle Eocene time and established a new northeast corridor for faunal migration to facilitate the bidirectional “Great Asian Interchange” dispersals.

Rahiolisaurus gujaratensis, n. gen. n. sp., A New Abelisaurid Theropod from the Late Cretaceous of India

Systematic excavations in the fluvial mudstone unit of the Upper Cretaceous Lameta Formation near Rahioli village in Kheda District, Gujarat, have yielded a large-bodied (~8 m long) abelisaurid theropod, Rahiolisaurus gujaratensis, gen. et sp. nov. Abundant skeletal remains represent this new genus and species. Rahiolisaurus provides novel information on foot morphology, hitherto little known in other abelisaurids. Rahiolisaurus gujaratensis is a gracile and slender-limbed abelisaurid that appears to be a distinctive taxon from the sympatric species Rajasaurus narmadensis.

New dinosaur species from the Upper Triassic Upper Maleri and Lower Dharmaram formations of Central India

The beginning of dinosaur evolution is currently known based on a handful of highly informative Gondwanan outcrops of Ischigualastian age (late Carnian–early Norian). The richest Triassic dinosaur records of the southern continents are those of South America and South Africa, with taxonomically diverse faunas, whereas faunas from India and central Africa are more poorly known. Here, the known diversity of Gondwanan Triassic dinosaurs is increased with new specimens from central India, which allow a more comprehensive characterisation of these dinosaur assemblages. Five dinosauriform specimens are reported from the probable late Norian–earliest Rhaetian Upper Maleri Formation, including two new sauropodomorph species, the non-plateosaurian Nambalia roychowdhurii and the plateosaurian Jaklapallisaurus asymmetrica , a guaibasaurid and two basal dinosauriforms. The Lower Dharmaram Formation, probably latest Norian–Rhaetian in age, includes basal sauropodomorph and neotheropod remains, providing the second record of a Triassic Gondwanan neotheropod. The currently available evidence suggests that the oldest known Gondwanan dinosaur assemblages (Ischigualastian) were not homogeneous, but more diverse in South America than in India. In addition, the Upper Maleri and Lower Dharmaram dinosaur assemblages resemble purported coeval South American and European beds in the presence of basal sauropodomorphs. Accordingly, the current available evidence of the Triassic beds of the Pranhita–Godavari Basin suggests that dinosaurs increased in diversity and abundance during the late Norian to Rhaetian in this region of Gondwana.

The flight of Archaeopteryx

The origin of avian flight is often equated with the phylogeny, ecology, and flying ability of the primitive Jurassic bird, Archaeopteryx. Debate persists about whether it was a terrestrial cursor or a tree dweller. Despite broad acceptance of its arboreal life style from anatomical, phylogenetic, and ecological evidence, a new version of the cursorial model was proposed recently asserting that a running Archaeopteryx could take off from the ground using thrust and sustain flight in the air. However, Archaeopteryx lacked both the powerful flight muscles and complex wing movements necessary for ground takeoff. Here we describe a flight simulation model, which suggests that for Archaeopteryx, takeoff from a perch would have been more efficient and cost-effective than from the ground. Archaeopteryx may have made short flights between trees, utilizing a novel method of phugoid gliding.

A Late Cretaceous callorhynchid (Chondrichthyes, Holocephali) from Seymour Island, Antarctica

The discovery of chimaeroid tooth plates in late Cretaceous deposits on Seymour Island, Antarctica extends the fossil record of the chimaeriform holocephalian fishes and helps to elucidate their diversification in the southern hemisphere during the Mesozoic era. Like chondrichthyans generally, their phylogenetic history is difficult to follow: only rarely are skeletal elements or associated dorsal fin spines preserved, and most species rest upon isolated tooth plates. Chimaeriform tooth plates of Mesozoic age are known largely from European specimens and a few from the Maastrichtian of eastern North America; that this distribution may be an artifact of sampling, however, is suggested by the reporting of a few tooth plates belonging to Edaphodon in Australia (Long, 1985) and some referable to Ischyodus in New Zealand (McKee, pers. comm.). The paucity of holocephalian material from the Mesozoic has prevented investigators from tracing the origin of the chimaeroid fishes, determining their relationship to the myriacanthoid chimaeriforms, or following the evolution of the three lineages with extant members (classified in the families Callorhynchidae, Rhinochimaeridae, and Chimaeridae). From the evidence in hand, it can be said only that, by the Mesozoic when elasmobranch chondrichthyans were undergoing a radiation, the holocephalians, characterized by their tooth plates and palatoquadrate cartilages fused to the braincase, were diminishing in variety. In the Triassic, the group was already impoverished by the loss of the orders that had flourished in Carboniferous seas; the myriacanthoids and Squaloraja disappeared before the close of the Jurassic, leaving the chimaeroids as the sole surviving holocephalians. Extinct chimaeroids are diagnosed primarily by their tooth plates. In all of these fishes, the dentition consists of three pairs of plates: a large mandibular tooth plate that opposes two plates anchored in the palate, a smaller anterior vomerine and a larger posterior palatine. Internal to a frame of compact dentine, the chimaeroid tooth plate is supported by a network of trabecular dentine and reinforced by pads or rods of hypermineralized tissue that, with the wearing away of the dentine on the oral surface, are exposed as crushing or cutting tritors. The shape and location of these tritors have been used in classifying isolated tooth plates even though it is certain that these features vary somewhat with wear and the age of the fish. The terminology for the tritors and for the margins of the chimaeroid tooth plate are shown in Figure 1.

Cranial anatomy of the Late Triassic phytosaur Machaeroprosopus, with the description of a new species from West Texas

The skull anatomy of a new species of the phytosaur Machaeroprosopus is described for the first time on the basis of two specimens from the Upper Triassic Cooper Canyon Formation of Texas. Additional information is provided by a third specimen referred to Machaeroprosopus sp. A paranasal bone, an additional paired element of the narial region, is identified. Important new data are presented for the braincase, including the morphology of the epipterygoid and presphenoid, an anterior process of the prootic, an anteroventral process of the laterosphenoid, and a parasphenoid process. Machaeroprosopus lottorum n. sp. is characterised by four apomorphies: a supratemporal fenestra closed on the skull roof with bevelled anterior rim, a comparatively short squamosal, a flat and rugose narial rim, and medially extended palatines that come close to form an ossified secondary palate. With respect to the supratemporal fenestra, the supraoccipital-parietal complex and several features of the squamosal, Machaeroprosopus lottorum n. sp. bridges the morphological gap between species previously referred to the genera Pseudopalatus and Redondasaurus. A parsimony analysis of known species of Machaeroprosopus supports the hypothesis that the development of the rostral crest in Machaeroprosopus is a sexually dimorphic feature, and questions the validity of the genus Redon- dasaurus. Consequently, Redondasaurus is here considered a junior synonym of Machaeroprosopus.

Vegaviidae, a new clade of southern diving birds that survived the K/T boundary

The fossil record of Late Cretaceous–Paleogene modern birds in the Southern Hemisphere includes the Maastrichtian Neogaeornis wetzeli from Chile, Polarornis gregorii and Vegavis iaai from Antarctica, and Australornis lovei from the Paleogene of New Zealand. The recent finding of a new and nearly complete Vegavis skeleton constitutes the most informative source for anatomical comparisons among Australornis, Polarornis, and Vegavis. The present contribution includes, for the first time, Vegavis, Polarornis, and Australornis in a comprehensive phylogenetic analysis. This analysis resulted in the recognition of these taxa as a clade of basal Anseriformes that we call Vegaviidae. Vegaviids share a combination of characters related to diving adaptations, including compact and thickened cortex of hindlimb bones, femur with anteroposteriorly compressed and bowed shaft, deep and wide popliteal fossa delimited by a medial ridge, tibiotarsus showing notably proximally expanded cnemial crests, expanded fibular crest, anteroposterior compression of the tibial shaft, and a tarsometatarsus with a strong transverse compression of the shaft. Isolated bones coming from the Cretaceous and Paleogene of South America, Antarctica, and New Zealand are also referred to here to Vegaviidae and support the view that these basal anseriforms were abundant and diverse at high southern latitudes. Moreover, vegaviids represent the first avian lineage to have definitely crossed the K–Pg boundary, supporting the idea that some avian clades were not affected by the end Mesozoic mass extinction event, countering previous interpretations. Recognition of Vegaviidae indicates that modern birds were diversified in southern continents by the Cretaceous and reinforces the hypothesis indicating the important role of Gondwana for the evolutionary history of Anseriformes and Neornithes as a whole.

Palaeoecology, Aerodynamics, and the Origin of Avian Flight

Data from hundreds of small, exquisitely preserved feathered coelurosaurs and early birds from the Early Cretaceous Jehol Group, Liaoning Province, China, suggest that avian flight probably began in the trees (arboreal or trees-down theory) rather than on the ground (cursorial or ground-up theory). The quality of preservation of the Jehol biota and the sediment in which they were preserved accords with recurrent mass mortality events, the animals being asphyxiated, buried by ash falls and swiftly preserved. The inferred palaeoecology of the Jehol biota indicates they lived in a forest environment bordering a large lake. New information on the origin of flight by the Jehol fossils is presented; it includes various transitional stages of flight—from wingless, tree climbing coelurosaurs to parachuting, to gliding, to fully winged, active flying birds. The fossils show development of adaptations necessary to enable wing-assisted climbing: highly recurved claws on hands and feet; long fingers, wrist joints that swivelled, and stiffened tails. Several feathered paravian coelurosaurs, exemplified by Epidendrosaurus, Epidexipteryx, and Scansoriopteryx with wings suitable for climbing, became arboreal, yet were flightless. Their arboreal lifestyles contradict arguments previously advanced supporting the cursorial (ground-up) theory of the origin avian flight. The cursorial model fails to explain climbing adaptations of protobirds, different stages of flight, and development of neurosensory specializations in early birds. Rather, the climbing adaptations of protobirds support an arboreal setting for the evolution of flight. These adaptations include, for example, different stages of flight from a perch, gradual brain enlargement for three-dimensional orientation, acquisition of vision and acute sight, and neurosensory specialization for hearing and balance. We have identified six evolutionary stages of avian flight represented by phylogeny and transitional fossils—arboreal leaping, parachuting, biplane gliding, monoplane gliding, undulating flight, and manoeuvring flapping flight. Arboreal life is suggested to have promoted enlargement of the brain, increased visual acuity, and development of more sophisticated vision. A computer model to simulate the flight performance of protobirds and early birds has been developed that corroborates the argument for the above evolutionary pathway.