In size they range from squares of side . In most cases they have a pierced boss at the back to accommodate a cord for handling or for use as personal adornment. In addition a large number of sealings have survived, of which only a few can be matched to the seals. The great majority of examples of the Indus script are short groups of signs on seals. Seals have been found at Mohenjo-daro depicting a figure standing on its head, and another, on the Pashupati seal, sitting cross-legged in what some call a yoga-like pose (see image, the so-called Pashupati, below). This figure has been variously identified. Sir John Marshall identified a resemblance to the Hindu god, Shiva. A human deity with the horns, hooves and tail of a bull also appears in the seals, in particular in a fighting scene with a horned tiger-like beast. This deity has been compared to the Mesopotamian bull-man Enkidu. Several seals also show a man fighting two lions or tigers, a "Master of Animals" motif common to civilisations in Western and South Asia. Trade and transportation IVC may have had bullock carts identical to those seen throughout South Asia today, as well as boats. Most of these boats were probably small, flat-bottomed craft, perhaps driven by sail, similar to those one can see on the Indus River today;. An extensive canal network, used for irrigation, has however also been discovered by H.-P. Francfort. During 4300–3200 BCE of the chalcolithic period (copper age), the Indus Valley Civilisation area shows ceramic similarities with southern Turkmenistan and northern Iran which suggest considerable mobility and trade. During the Early Harappan period (about 3200–2600 BCE), similarities in pottery, seals, figurines, ornaments, etc. document intensive caravan trade with Central Asia and the Iranian plateau. Judging from the dispersal of Indus civilisation artefacts, the trade networks economically integrated a huge area, including portions of Afghanistan, the coastal regions of Persia, northern and western India, and Mesopotamia, leading to the development of Indus-Mesopotamia relations. Studies of tooth enamel from individuals buried at Harappa suggest that some residents had migrated to the city from beyond the Indus Valley. Ancient DNA studies of graves at Bronze Age sites at Gonur Depe, Turkmenistan, and Shahr-e Sukhteh, Iran, have identified 11 individuals of South Asian descent, who are presumed to be of mature Indus Valley origin. There was an extensive maritime trade network operating