pdo_mysql extension is not installed

#0 /Library/Tenon/WebServer/WebSites/www.dardart.net/lib/Zend/Db/Adapter/Abstract.php(441): Varien_Db_Adapter_Pdo_Mysql->_connect()
#1 /Library/Tenon/WebServer/WebSites/www.dardart.net/lib/Zend/Db/Adapter/Pdo/Abstract.php(230): Zend_Db_Adapter_Abstract->query('SET NAMES utf8', Array)
#2 /Library/Tenon/WebServer/WebSites/www.dardart.net/lib/Varien/Db/Adapter/Pdo/Mysql.php(281): Zend_Db_Adapter_Pdo_Abstract->query('SET NAMES utf8', Array)
#3 /Library/Tenon/WebServer/WebSites/www.dardart.net/app/code/local/Mage/Core/Model/Resource/Type/Db/Pdo/Mysql.php(45): Varien_Db_Adapter_Pdo_Mysql->query('SET NAMES utf8')
#4 /Library/Tenon/WebServer/WebSites/www.dardart.net/app/code/local/Mage/Core/Model/Resource.php(87): Mage_Core_Model_Resource_Type_Db_Pdo_Mysql->getConnection(Object(Mage_Core_Model_Config_Element))
#5 /Library/Tenon/WebServer/WebSites/www.dardart.net/app/code/local/Mage/Core/Model/Resource/Setup.php(62): Mage_Core_Model_Resource->getConnection('core_setup')
#6 /Library/Tenon/WebServer/WebSites/www.dardart.net/app/code/local/Mage/Core/Model/Resource/Setup.php(120): Mage_Core_Model_Resource_Setup->__construct('core_setup')
#7 /Library/Tenon/WebServer/WebSites/www.dardart.net/app/code/local/Mage/Core/Model/Config.php(263): Mage_Core_Model_Resource_Setup::applyAllUpdates()
#8 /Library/Tenon/WebServer/WebSites/www.dardart.net/app/code/local/Mage/Core/Model/App.php(263): Mage_Core_Model_Config->init(Array)
#9 /Library/Tenon/WebServer/WebSites/www.dardart.net/app/Mage.php(434): Mage_Core_Model_App->init('', 'store', Array)
#10 /Library/Tenon/WebServer/WebSites/www.dardart.net/app/Mage.php(455): Mage::app('', 'store', Array)
#11 /Library/Tenon/WebServer/WebSites/www.dardart.net/index.php(66): Mage::run()
#12 {main}