S. T. Hussain

Fossil Evidence for the Origin of Aquatic Locomotion in Archaeocete Whales

Recent members of the order Cetacea (whales, dolphins, and porpoises) move in the water by vertical tail beats and cannot locomote on land. Their hindlimbs are not visible externally and the bones are reduced to one or a few splints that commonly lack joints. However, cetaceans originated from four-legged land mammals that used their limbs for locomotion and were probably apt runners. Because there are no relatively complete limbs for archaic archaeocete cetaceans, it is not known how the transition in locomotory organs from land to water occurred. Recovery of a skeleton of an early fossil cetacean from the Kuldana Formation, Pakistan, documents transitional modes of locomotion, and allows hypotheses concerning swimming in early cetaceans to be tested. The fossil indicates that archaic whales swam by undulating their vertebral column, thus forcing their feet up and down in a way similar to modern otters. Their movements on land probably resembled those of sea lions to some degree, and involved protraction and retraction of the abducted limbs.

Eocene mammal faunas from northern Indo-Pakistan

Abstract We present a summary of the Eocene mammal faunas of Indo-Pakistan based on study of the known faunas and new collections. New taxa described here are the carpolestid Parvocristes oligocollis, the plesiadapid Jattadectes mamikheli (both new families for the subcontinent), the hyaenodontid Paratritemnodon jandewalensis, the arctocyonid Karakia longidens, the raoellid Khirtharia aurea, and the helaletid Jhagirilophus chorgalensis. Based on the faunal evidence and considering the geological setting, we also evaluate the uniformity of the Eocene faunas from northern Indo-Pakistan. Tentatively, we propose that three chronologically distinct faunas occur in Northern Indo-Pakistan. These are, from oldest to youngest, (1) the Banda Daud Shah Fauna, (2) the Ganda Kas Fauna, and (3) the Kalakot Fauna. Although there are broad similarities between these faunas and Eocene faunas of the Northern Hemisphere, the Indian subcontinent retained a highly distinctive fauna in that period.

Additional holotype remains of Ambulocetus natans (Cetacea, Ambulocetidae), and their implications for locomotion in early whales

Abstract Continued excavation at the type locality of Ambulocetus natans led to the recovery of a majority of the axial skeleton of the holotype of this early Eocene cetacean, including both innominates, the sacrum, and most of the thoracic cage and thoracolumbar vertebral column. Additional appendicular, caudal, and cranial materials were also recovered, resulting in a specimen that is now approximately 80 percent complete. This new material allows refined interpretations of its functional morphology. Ambulocetus has a longer thoracolumbar column than that reported for later remingtonocetid and protocetid genera, suggesting that previous estimates of spinal length derived from models of mesonychid ancestry may be inaccurate. Ambulocetus also possesses a co-ossified ecto–mesocuneiform, a character found in some early and middle Eocene artiodactyls, but not mesonychids. New postcranial material provides further evidence of a systemic shift to aquatic locomotion.

Postcranial Osteology of the most Primitive Artiodactyl: Diacodexis pakistanensis (Dichobunidae)

Diacodexis pakistanensis is the smallest and most primitive artiodactyl. It is Known from the ealry Eocene of the Indo‐pakistani subcontinet. It retains a clavicle, has five complete digits in the manus and four in the pes and is digitigrade.

Observer variability in volumetric blood flow measurements in leg arteries using duplex ultrasound

Duplex ultrasound volumetric flow measurements have not found a major clinical use because of variability caused by errors in estimating cross-sectional area (CSA) and in measuring time averaged mean velocity (TAMeV). We determined inter- and intraobserver variation in volumetric blood flow measured at rest in the common femoral artery (CFA) and its main branches, the superficial femoral (SFA) and profunda femoris (PFA) arteries, in 20 normal subjects. The product of TAMeV and CSA was taken as volumetric flow. The coefficient of variation of TAMeV was consistently greater than that of CSA. Interobserver variation for blood flow (16.2%, 20.2% and 40.3% for CFA, SFA and PFA, respectively) was larger than intraobserver variation (13.0%, 15.1%, 21.2%). In conclusion, these data define the minimum changes in VQ that can be realistically detected and indicate that, with modern duplex Doppler equipment, volumetric flow can be used as a reliable haemodynamic measure for monitoring patients before and after surgical or radiological intervention.

Haemodynamic and metabolic responses of the lower limb after high intensity exercise in humans

This study assessed blood flow in the common femoral, superficial femoral and profunda femoris arteries, the effects of vasodilator metabolites and changes in blood pressure and pulse during recovery after high intensity exercise (Wingate test). Mean common femoral artery flow increased sevenfold in response to the exercise. The subsequent decline in mean common femoral artery flow was mono‐exponential with a mean time constant of 19 min. The post‐exercise increase in profunda femoris artery flow (ninefold) was significantly greater than the superficial femoral artery flow (fourfold, P < 0.05). Systolic blood pressure and heart rate decreased monotonically throughout recovery. In contrast, diastolic blood pressure showed a significant fall below baseline at 3 min (P < 0.05) with a return to baseline at 60 min. The greatest drop below baseline (approximately 20 mmHg) occurred around 7 min. Lactate reached a maximum of 13.6 +/− 2.3 mmol ‐1 at 8 min (P < 0.05) and was still significantly above baseline at 60 min. pH remained below 7.2 until 20 min of recovery. The results demonstrate that following high intensity exercise, blood flow to the limbs appears to be controlled by complex interactions of various vaso‐active metabolites, each contributing proportionally more at different times during recovery.

Whale ankles and evolutionary relationships

There are two main hypotheses for the relationships of the mammalian order Cetacea (comprising whales, dolphins and porpoises). The first hypothesis, mainly supported by DNA sequence data,, is that one of the groups of artiodactyls (for example, the hippopotamids) is the closest extant relative of whales and that Artiodactyla are paraphyletic if Cetacea are excluded from it. The second hypothesis, mainly supported by palaeontological data,, identifies mesonychians, a group of extinct archaic ungulates, as the sister group to whales. These two hypotheses are not mutually exclusive, because mesonychians and cetaceans could be sister groups, and this combined clade (Cete) could be the sister group to a group of artiodactyls.

Evolutionary and Functional Anatomy of the Pelvic Limb in Fossil and Recent Equidae (Perissodactyla, Mammalia)

In Equidae, the limb structure adapted for fore and aft running motion first developed during late Paleocene (Hyracotherium). Since then, almost all the modifications contributed in developing a limb structure in which flexion and extension were primary movements. In Hyracotheriinae and Anchitheriinae, the hip and stifle joints were more flexed and had stronger semitendinosus muscles for fore and aft motion of the limb than in Equinae. Hyracotheriinae and Anchitheriinae had unstable hock joint and had significant intertarsal movement. In Hemphillian and earlier Equinae, the intertarsal movement was considerably reduced and in post Hemphillian Equinae it was negligible because of the presence of strong intertarsal ligaments. In the evolution of the horse the development of intertarsal ligaments, reduction of lateral digits and shortening of the astragalar neck contributed in providing the stability at the hock joint. Four types of limb structures are recognized in Equidae: (1) Hyracotheriinae, (2) Anchitheriinae, (3) Tridactyl Equinae, and (4) Monodactyl Equinae.

Attockicetus praecursor, A New Remingtonocetid Cetacean from Marine Eocene Sediments of Pakistan

A new early-to-middle Eocene cetacean from the Kala Chitta Hills of northern Pakistan is described: Attockicetus praecursor new genus and species. It is based on fragmentary cranial material, including a rostral fragment, P3–M3, endocast, and ectotympanic. Attockicetus is the first remingtonocetid from northern Pakistan, and the oldest member of its family. Attockicetus praecursor is smaller than the species of the other remingtonocetid genera, Remingtonocetus, Andrewsiphius, and Dalanistes. It is also more primitive in the retention of large protocones on the upper molars and the anterior position of the orbit. Known material for Attockicetus is fragmentary, but the taxon is important because it extends the geographic and temporal range of remingtonocetids, is one of the few remingtonocetids in which toothcrowns are preserved, and because it is probably the most plesiomorphic remingtonocetid.

New Middle Eocene Archaeocetes (Cetacea:Mammalia) from the Kuldana Formation of Northern Pakistan

ABSTRACT Two new species of fossil cetaceans (Pakicetus calcis and Pakicetus chittas) are described from a new locality in the Kuldana Formation (Lutetian, middle Eocene) of the Kala Chitta Hills in Northern Pakistan. Additional dentitions of the pakicetid Nalacetus ratimitus, the remingtonocetid Attockicetus, and additional dental material of the holotype of Ambulocetus natans are also described. Dental morphology of Nalacetus is intermediate between pakicetids and ambulocetids, as indicated by the presence of an ambulocetid-like P4, but pakicetid-like molars. Premolars of the specimen tentatively described as Attockicetus imply that some pakicetids and remingtonocetids were coeval. Furthermore, the new pakicetid dentitions described here are the most complete to date and further our understanding of pakicetid dental diversity.