A new baphetid (stem tetrapod) from the Upper Carboniferous of Tyne and Wear, U.K., and the evolution of the tetrapod occiput

A new genus and species of baphetid, Kyrinion martilli, is described from the Westphalian A (Upper Carboniferous) of Tyne and Wear, England. The skull, braincase, and partial lower jaws are preserved in a nodule of iron-rich seat-earth, in an almost uncrushed state. The occiput and both stapes are in place. The palate and braincase are united by a continuous sheet of denticulated pterygoid and parasphenoid eliminating the interpterygoid vacuities completely, and the parasphenoid bounds deep parasphenoidal tubera; the marginal palatal bones, pterygoid, and dentary are united by interdigitated sutures, rendering the whole skull akinetic. The orbits are approximately triangular, without the "pinching in" that defines an antorbital embayment in other baphetids. The maxilla has a very narrow exposure beneath and posterior to the orbit, and though it and the lacrimal lack lateral line grooves, there is a short stretch on the quadratojugal. Unlike Megalocephalus, the lower jaw symphysis is relatively simple and does not bear a "brassicate" structure and the parasymphysial plate lacks teeth. The stapes is broad and flat distally, with its distal end lying against the palatal bones as in other early tetrapods, but it is difficult to envisage a structural role for this element as suggested by recent hypotheses. The basi- and exoccipitals co-ossified as in some specimens of Greererpeton and Acanthostega, but unlike the latter, the condyle is almost fully ossified. The exoccipitals do not contact the skull roof as they do in temnospondyls, but fully ossified paroccipital processes suture with the tabulars, a feature suggested as synapomorphous for baphetids plus temnospondyls. The specimen also preserves a rib, possibly but not certainly cervical, and an atlas arch. The proatlantes of Loxomma are descibed and figured.