I read this in English in the late 70s in primary school.

What I remember:

• Two boys are somehow caught up in a time travel scenario. I think their father may have been the inventor of the time machine.
• Their initial journey takes them back about 200 million years.
• They meet an animal they identify as a cynogasaurus. At least, that's what my memory told me. Google tells me my memory may be playing tricks and they met a cynognathus instead. It was definitely cynogsomething.
• They somehow jump forward to caveman times with the cynogasaurus/cynognathus in tow.
• They befriend a similarly-aged kid who's a member of a particular tribe, possibly the leopard tribe.
• The leopard tribe are enemies of the zebra tribe. It's possible I've got both animals wrong.
• Each tribe has a sacred animal. Disputes between the tribes are settled by their sacred animals fighting.
• Somehow the kids have caused the death of "their" tribe's sacred animal so they offer the cynogawhatsit, which the cave-people call Nog, in its place. Nog wins the fight and stays on as the sacred animal when the kids leave.

It's possible the book is Lester Del Rey's "Tunnel Through Time", the subject of a few queries here over the years. The cover looks familiar and some details match. However no question or answer mentions the cynog* creature, sacred animals or the fight, which are what I recall about the book.

I read this in English in the late 70s in primary school.

What I remember:

• Two boys are somehow caught up in a time travel scenario. I think their father may have been the inventor of the time machine.
• Their initial journey takes them back about 200 million years.
• They meet an animal they identify as a cynogasaurus. At least, that's what my memory told me. Google tells me my memory may be playing tricks and they met a cynognathus instead. It was definitely cynogsomething.
• They somehow jump forward to caveman times with the cynogasaurus/cynognathus in tow.
• They befriend a similarly-aged kid who's a member of a particular tribe, possibly the leopard tribe.
• The leopard tribe are enemies of the zebra tribe. It's possible I've got both animals wrong.
• Each tribe has a sacred animal. Disputes between the tribes are settled by their sacred animals fighting.
• Somehow the kids have caused the death of "their" tribe's sacred animal so they offer the cynogawhatsit, which the cave-people call Nog, in its place. Nog wins the fight and stays on as the sacred animal when the kids leave.

Edit: I thought it may have been Lester Del Rey's "Tunnel Through Time", the subject of a few queries here over the years. The cover looks familiar and some details match. However two comments have verified that it doesn't feature the cynog* creature, sacred animals or the fight, which are what I recall about the book.

I read this in English in the late 70s in primary school.

What I remember:

• Two boys are somehow caught up in a time travel scenario. I think their father may have been the inventor of the time machine.
• Their initial journey takes them back about 200 million years.
• They meet an animal they identify as a cynogasaurus. At least, that's what my memory told me. Google tells me my memory may be playing tricks and they met a cynognathus instead. It was definitely cynogsomething.
• They somehow jump forward to caveman times with the cynogasaurus/cynognathus in tow.
• They befriend a similarly aged kid who's a member of a particular tribe, possibly the leopard tribe.
• The leopard tribe are enemies of the zebra tribe. It's possible I've got both animals wrong.
• Each tribe has a sacred animal. Disputes between the tribes are settled by their sacred animals fighting.
• Somehow the kids have caused the death of "their" tribe's sacred animal so they offer the cynogawhatsit, which the cave-people call Nog, in its place. Nog wins the fight and stays on as the sacred animal when the kids leave.

It's possible the book is Lester Del Rey's "Tunnel Through Time", the subject of a few queries here over the years. The cover looks familiar and some details match. However no question or answer mentions the cynog* creature, sacred animals or the fight, which are what I recall about the book.

I read this in English in the late 70s in primary school.

What I remember:

• Two boys are somehow caught up in a time travel scenario. I think their father may have been the inventor of the time machine.
• Their initial journey takes them back about 200 million years.
• They meet an animal they identify as a cynogasaurus. At least, that's what my memory told me. Google tells me my memory may be playing tricks and they met a cynognathus instead. It was definitely cynogsomething.
• They somehow jump forward to caveman times with the cynogasaurus/cynognathus in tow.
• They befriend a similarly-aged kid who's a member of a particular tribe, possibly the leopard tribe.
• The leopard tribe are enemies of the zebra tribe. It's possible I've got both animals wrong.
• Each tribe has a sacred animal. Disputes between the tribes are settled by their sacred animals fighting.
• Somehow the kids have caused the death of "their" tribe's sacred animal so they offer the cynogawhatsit, which the cave-people call Nog, in its place. Nog wins the fight and stays on as the sacred animal when the kids leave.

It's possible the book is Lester Del Rey's "Tunnel Through Time", the subject of a few queries here over the years. The cover looks familiar and some details match. However no question or answer mentions the cynog* creature, sacred animals or the fight, which are what I recall about the book.

I read this in English in the late 70s in primary school.

What I remember:

• Two boys are somehow caught up in a time travel scenario. I think their father may have been the inventor of the time machine.
• Their initial journey takes them back about 200 million years.
• They meet an animal they identify as a cynogasaurus. At least, that's what my memory told me. Google tells me my memory may be playing tricks and the met a cynognathus instead. It was definitely cynogasomething.
• They somehow jump forward to caveman times with the cynogasaurus/cynognathus in tow.
• They befriend a similarly aged kid who's a member of a particular tribe, possibly the leopard tribe.
• The leopard tribe are enemies of the zebra tribe. It's possible I've got both animals wrong.
• Each tribe has a sacred animal. Disputes between the tribes are settled by their sacred animals fighting.
• Somehow the kids have caused the death of "their" tribe's sacred animal so they offer the cynogawhatsit, which the cave-people call Nog, in its place. Nog wins the fight and stays on as the sacred animal when the kids leave.

It's possible the book is Lester Del Rey's "Tunnel Through Time", the subject of a few queries here over the years. The cover looks familiar and some details match. However no question or answer mentions the cynog* creature, sacred animals or the fight, which are what I recall about the book.

I read this in English in the late 70s in primary school.

What I remember:

• Two boys are somehow caught up in a time travel scenario. I think their father may have been the inventor of the time machine.
• Their initial journey takes them back about 200 million years.
• They meet an animal they identify as a cynogasaurus. At least, that's what my memory told me. Google tells me my memory may be playing tricks and they met a cynognathus instead. It was definitely cynogsomething.
• They somehow jump forward to caveman times with the cynogasaurus/cynognathus in tow.
• They befriend a similarly aged kid who's a member of a particular tribe, possibly the leopard tribe.
• The leopard tribe are enemies of the zebra tribe. It's possible I've got both animals wrong.
• Each tribe has a sacred animal. Disputes between the tribes are settled by their sacred animals fighting.
• Somehow the kids have caused the death of "their" tribe's sacred animal so they offer the cynogawhatsit, which the cave-people call Nog, in its place. Nog wins the fight and stays on as the sacred animal when the kids leave.

It's possible the book is Lester Del Rey's "Tunnel Through Time", the subject of a few queries here over the years. The cover looks familiar and some details match. However no question or answer mentions the cynog* creature, sacred animals or the fight, which are what I recall about the book.