The pelycosaurs were dominant on land in the Permian, and went under at the Permian–Triassic extinction event. The therapsids were dominant on land in the Lower Triassic, but by the Upper Triassic the dinosaurs had taken over.
The mammal-like reptiles are traditionally divided into a primitive group and an advanced group, known respectively as pelycosaurs and therapsids. Pelycosaurs are a paraphyletic group of six primitive families of synapsids. They were all rather lizard-like with sprawling gait and possibly horny scutes. The therapsids contain the more advanced synapsids, having a more erect pose and possibly hair, at least in some forms. The latter are the ancestors of mammals. Thus both of the two synapsid groups represent evolutionary grades: the pelycosaurs have given rise to the therapsids, who in their turn have given rise to the mammals.
The therapsids ('beast face') used to be called mammal-like reptiles. This was a mistake, because they were never reptiles. The split between Synapsids and Sauropsids (the group which gave rise to reptiles) took place long before therapsids evolved.
There are a number of characteristics which cannot be seen on fossils, but which are of great importance. Mammals are distinguished from reptiles by fundamental differences in the development of the blood system. These differences are such that it would be almost impossible for mammals to be derived from reptiles.
This supports the division of amniotes into sauropsida and synapsida.
Synapsids evolved a fenestra (hole) behind each eye orbit on the lower part of the skull. It allows better attachment sites for jaw muscles than the original anapsid condition.
A parallel development took place in the diapsida, who evolved two rather than one opening behind each eye.
Originally, the opening in the skull left the inner cranium only covered by the jaw muscles, but in higher therapsids and mammals the sphenoid bone has expanded to close the opening.
Synapsids had differentiated teeth. These include the canines, molars, and incisors.
The trend towards differentiation is found in some labyrinthodonts and early anapsid reptilians. They have enlarged first teeth on the maxilla, forming a form of proto-canines. This trait was subsequently lost in the sauropsid line, but developed further in the synapsids. Early synapsids could have 2 or even 3 enlarged 'canines', but in the therapsids, the pattern had settled to one canine in each upper jaw half. The lower canines developed later.
Note: in evolutionary terms, the mammals are entirely within the Synapsida. Their status as a separate class is traditional Linnaean taxonomy: as a clade they are a sub-group of the Therapsida.
The Pilgrim's Progress
The Pilgrim's Progress is an English language book written by John Bunyan. It was published in two parts: the First Part in 1678, and the Second Part in 1684. Its full title is The Pilgrim's Progress from this World to that which is to come. It is regarded as one of the most important books in English literature. It is a Christian allegory.
The book uses the dream story of a journey through the English county of Bedfordshire, to London. Bunyan uses this to tell the idea of Christianity from a Protestant point of view. Although the journey is imaginary, the places are based upon real places in 17th century Bedfordshire. The difficulties faced by "Christian", the main character, is meant to be an allegory of the difficulties faced by a true Christian in keeping to the 'straight and narrow path'. The author was jailed for preaching his opinions, yet after the book was published, it was translated into over 200 languages.
Bunyan started to write the book in jail. He got into trouble for preaching without a licence. Bunyan, who was a Reformed Baptist, did not qualify for a licence. Only ministers of the Church of England were allowed to preach. He spent 12 years in Bedford jail. He might have been freed if he had promised not to preach, but he refused. He was let out only when the law changed, in 1672. He was jailed again for a short time in 1677.
The book is divided into two parts, and is 108,260 words long. Each part is a continuous narrative, with no chapter divisions. When the first part was published in 1678, it immediately became extremely popular. Part Two was published in 1684. There were 11 editions of the first part during John Bunyan’s lifetime, and two editions of the second part.
The story is an allegory about a man called Christian, who goes on a journey, and meets many strange people. Christian is an 'everyman' character: he represents the reader or any ordinary person. Eventually he gets to the Celestial City. The strange people he meets are characters who represent good and bad things in life. The story is therefore an allegory of the life of a good Christian. To be precise, it is an allegory of the Protestant view of Christianity. It includes, as characters, the giants 'Pope' and 'Pagan', allegories of Roman Catholicism and paganism as persecutors of Protestant Christians. 'Pagan' is dead, indicating the end of pagan persecution, and 'Pope' is alive but decrepit (elderly), indicating the diminished power and influence of the Roman Catholic pope. The many indirect references to the Bible is a sure sign of Protestant belief. The Bible had not long been available in English, and its translation was opposed by the church in the reign of Henry VIII.
Many of the places Bunyan describes are based on places he knew in the Bedfordshire countryside. For example, the Slough of Despond is thought to be the marshes in Tempsford (now on the A1 road). House Beautiful is thought to be Houghton House (now a ruin), just outside Ampthill. The character of the Evangelist is that of his friend John Gifford, who was the leader of a non-conformist group at St John’s Church, Bedford. The heavy burden (the load), which Christian carries on his back, represents his sins: the things he has done wrong, and which trouble him. However, the burden is also based on the heavy anvil which he carried on his back as he walked from place to place. He worked as a tinker (someone who mends pots and pans).
Later, the Land of Beulah is Middlesex County, the Very Deep River is the Thames, and the Celestial City is London.
Part One tells how a man called Christian makes his way from the 'City of Destruction' (Earth) to the 'Celestial City' (Heaven) of Zion. Christian finds himself weighed down by a great burden which he gets from reading a book (obviously the Bible). He wonders what he can do to be saved. The character Evangelist appears several times during the story, pointing him in the right direction. Evangelist shows Christian the way to the 'Wicket Gate'. Christian tries to persuade his family to join him on the journey, but they refuse, so he leaves them behind.
The first person he meets is called Mr. Worldly Wiseman, who says he can be saved by looking at the law, and that Mr. Legality can help him. Evangelist stops him from going that way. He must go to the Wicket Gate.
At the Wicket Gate the gatekeeper, Goodwill, tells him to keep to the straight path. In the Second Part, Goodwill is shown to be Jesus himself. To Christian's query about relief from his burden, Goodwill directs him forward to the 'place of deliverance'.
Christian goes to the House of the Interpreter, where he is shown pictures and that show ideas of the Christian faith. Then he gets to the 'place of deliverance'. This is meant to be the hill with the cross where Jesus died. There his burden falls off his back, so he is very relieved. Three shining ones give him the greeting of peace. They give him new clothes and a passport to the Celestial City (heaven). This is like a Christian Baptism.