All praise be to Allah.
In al-Mawsoo‘ah al-‘Arabiyyah al-‘Aalamiyyah it says: The dinosaurs of the Jurassic period (138-205 million years ago) include the tallest known dinosaur, namely the diplodocus, which reached a height of 27 m, as well as other dinosaurs such as the plated or armoured stegosaurus, the Allosaurus, and the camptosaurus.
The dinosaurs were reptiles that lived millions of years ago. The word dinosaur is derived from two Greek words meaning “terrible lizard”. However the dinosaurs were not really lizards, although the size of some of them was terrifying; the largest dinosaur was the biggest animal that ever lived on dry land, with a weight that was many times that of a fully grown elephant. There are a very few types of whales that grow to a size bigger than these dinosaurs.
The first dinosaurs appeared on earth 220 million years ago. These creatures dominated dry land for approximately 150 million years and lived on most continents on earth and in various environments, such as swamps and flat plains. They became extinct suddenly 63 million years ago. End quote.
There is nothing in the texts of the Qur’aan or Sunnah to confirm or deny the existence of these creatures. In the Holy Qur’aan there are some verses which some scholars have understood to mean that there were creatures that existed on earth before Adam (peace be upon him), such as the verse in which Allah, may He be exalted, says (interpretation of the meaning):
“And (remember) when your Lord said to the angels: ‘Verily, I am going to place (mankind) generations after generations on earth.’ They said: ‘Will You place therein those who will make mischief therein and shed blood, – while we glorify You with praises and thanks (Exalted be You above all that they associate with You as partners) and sanctify You.’ He (Allah) said: ‘I know that which you do not know’”
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said: The words of the angels “Will You place therein those who will make mischief therein and shed blood?” make it very likely that they were successors to some creatures who came before them and that there were creatures on earth before that who shed blood and spread mischief. So the angels asked their Lord, may He be glorified and exalted: “Will You place therein those who will make mischief therein and shed blood” as was done by those who came before them?
End quote from Tafseer al-Qur’aan al-Kareem, 1/30
The dinosaurs may have been among those creatures.
It is not strange that there were creatures of this great size. It is proven in the saheeh Sunnah that Adam (peace be upon him)was sixty cubits tall, as was narrated by al-Bukhaari (3326) and Muslim (2841) from Abu Hurayrah (may Allah be pleased with him), that the Prophet (blessings and peace of Allah be upon him) said: “Allah created Adam sixty cubits tall, then He said: Go and greet those angels and listen to how they greet you, for that will be your greeting and the greeting of your descendants.
So he went and said, As-salaamu ‘alaykum (peace be upon you) and they said: Al-salaam ‘alayka wa rahmat Allaah(peace be upon you and the mercy of Allaah. So they added (the words) wa rahmat Allah. Everyone who enters Paradise will be in the form of Adam. Mankind continued to diminish in size until now.”
It also says in the Sunnah that when the earth’s blessing is restored to it at the end of time, one pomegranate at that time will be sufficient for a group of people, and they will seek shade beneath its skin, as was narrated by Muslim (2937) from an-Nawwaas ibn Sam‘aan (may Allah be pleased with him): the Prophet (blessings and peace of Allah be upon him) said, when speaking of the descent of ‘Eesa (peace be upon him) and Allah’s destruction of Ya’jooj and Ma’jooj: “Then Allaah will send rain which will not be kept out by any house of clay or hair; it will wash the earth and leave it like a mirror.
Then it will be said to the earth: Bring forth your fruits and restore your blessing. On that day a group of people will eat from a pomegranate and shelter beneath its skin. Milk will be blessed until a milch-camel will be sufficient for a crowd of people, and a milch-cow will be sufficient for a tribe of people, and a milch-sheep will be sufficient for a family of people.”
To sum up: Islam does not deny that these creatures existed or that they were of this great size, but the fact remains that when they speak of their lifespans and the details of their forms and lives, this is the field of science and speculation combined.
The Muslim should not be preoccupied with that and he should not waste time discussing it or believe that it is a matter that has any impact on his religious commitment or belief, because he knows that the Qur’aan and Sunnah were revealed to guide people and show them the right way; their focus is not history, geography, earth science or biology, although they indicate many facts that have to do with these fields. There are some kinds of animals that are not mentioned in Qur’aan and Sunnah at all, even though they existed at the time the Qur’aan was revealed.
And Allah knows best.