New research conducted by Size Graf sheds light on the animals with largest and smallest brain size across the various vertebrate classes. The results indicate that the Ostrich does not have the largest brain size among birds, and Bony-eared Assfish does not have the smallest brain-body mass ratio across vertebrates.

CLAYMONT, Del., Jan. 31, 2024 /PRNewswire/ — There are some uncertainties about what animal has the largest or smallest brain size (and brain-body weight ratio) across several vertebrate classes. To gain better insights, Size Graf has performed comprehensive research to find out for sure the animal with biggest and tiniest brain in each of mammals, birds, fish, reptiles and amphibians.

The research findings, which are based on datasets from many scientific journals, revealed the bird with largest brain size is actually a giant species of Penguin called the Emperor Penguin, not the Ostrich as wrongly assumed. This Penguin species has a brain weight of around 48 grams versus 42 grams for the Ostrich (difference of six grams).

The research also indicated the vertebrate with smallest brain-body mass ratio is the Whale Shark, not the Bony-eared Assfish as commonly accepted. The brain of Whale Shark constitutes only about 0.003% of body weight while it’s 0.03% for the Bony fish species.

Whale Shark

When it comes to the biggest brain size among reptiles, most people probably know that record belongs to Crocodiles, but the specific species was unknown. However, the new research revealed the Crocodile with largest brain is the American Crocodile. It has a brain that weighs up to around 16 grams, which is two grams more than the reptile with second biggest brain.


“We wanted to know for certain what animal has the biggest and smallest brain size across each vertebrate class instead of taking what others say for granted,” says Hassan Alnassir, founder and owner of Size Graf. “the research allowed us to correct some major misconceptions around this topic including that the bird with largest brain size is Emperor Penguin not Ostrich and the animal with smallest brain-body weight ratio among vertebrates is the Whale Shark not Bony-eared Assfish.”

To read the full details of the research and learn more about the animals with largest and smallest brain size, check out The Animals with Largest & Smallest Brain Size (by Class).

In case you want to review the raw research data or ask some questions about the results, you can contact Hassan Alnassir through the email

About Size Graf
Size Graf is a website that offers free tools and graphics related to size (or height) in some way.

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