Marine Mammal Skulls (and Crossbones)

Marine mammal display

Marine mammal display

The ‘Skull and Crossbones’ flag traditionally associated with pirates is, clearly, not the only skull found in/on the ocean. Invertebrates, such as jellyfish and octopus, do not have a vertebral column – meaning they are without a spine, or bones. However, other marine species, including our charismatic marine mammals, do have both skulls and (cross)bones!

Why should we study bones?

Looking at, and studying bones, can provide researchers with insights into the life that an organism once lived. Where the bones in question belong to an extinct species, we can learn more about organisms we will never see.

Lower jaw and teeth

Lower jaw and teeth – Bottlenose dolphin © CBMWC

Skulls are no different. Animal skulls have evolved for millions of years for various purposes: protecting the brain and sensory organs, being one example. However they also have a role in behaviour, meaning that by studying skulls we can learn more about the diet and social patterns of the species in question.

Skull Basics

Teeth: Can indicate diet or hunting method. There are four different types of teeth: incisors, canines, premolars and molars. Generally herbivores (vegetation-eaters) have large incisors to graze on vegetation, and premolars/molars to grind their food. Carnivores (meat-eaters) on the other hand have small incisors, large canines and sharp premolars/molars. Omnivores (eat anything) will have all four teeth types, but their size will vary depending on the species.

Eyes: Eye size and location can indicate if a species is a ‘hunter’ or ‘prey’. Hunters (carnivores and/or omnivores) generally have large and forward facing eyes, allowing them to have binocular vision and good depth perception. Prey (herbivores) instead tend to have sideways facing eyes, to watch for approaching threats (i.e. predators).
Life in the ocean has seen various adaptations of these ‘general rules’ (i.e. cetaceans are more reliant on hearing/echolocation to ‘see’ their environment, than they are on their eyes – even though they are hunters).

Marine Mammal Skulls

Bottlenose Dolphin skull

Bottlenose dolphin (Dolffin trwyn potel)

Bottlenose dolphin skull © CBMWC
Latin Name: Tursiops truncatus.

Skull size: This specimen is approximately 60cm in length.

Size of species: Bottlenose dolphins can grow up to 4m in length here in Cardigan Bay.

Key skull characteristics:

A) As a species which can grow up to 4m in length, the bottlenose dolphin has the largest skull of the marine mammals discussed here. They also have a long, prominent beak.

B) The nostrils point upwards allowing bottlenose dolphins to breathe easily when they surface. This is important because, like us, bottlenose dolphins are mammals.

C) You will see between 18 and 26 teeth on each side of the upper and lower jaws (that’s 72 to 104 teeth!), however these are not used to chew! Instead bottlenose dolphins swallow their meals whole!

Distribution in Wales: Bottlenose dolphins are generally found in coastal waters across north, west, and parts of south-west Wales. They can be found in Cardigan Bay all year round, with this being one of only two locations across the UK where the populations are confirmed as semi-resident.

Fun fact: Bottlenose dolphins produce distinctive, individual whistles by passing air through air sacs in their heads.

Commion Dolphin skull

Common dolphin (Dolffin cyffredin) © CBMWC
Latin Name: Delphinus delphis.

Skull size: This specimen is approximately 42cm in length.

Size of species: Common dolphins grow up to around 2m in length.

Key skull characteristics:

A) Because they grow to around 2m in length, common dolphin skulls are much smaller than those of bottlenose dolphins. Again, you will notice a prominent beak.

B) The nostrils point upwards allowing common dolphins to breathe easily when they surface. This is important because, like us, common dolphins are mammals.

C) Common dolphins have sharp, conical shaped teeth. Though, like bottlenoses, they are not used for chewing – they prefer to swallow their food whole!

Distribution in Wales: Common dolphins are generally an offshore species, however are sighted off the coast of Pembrokeshire more frequently than other coastal areas around Wales.

Fun fact: Common dolphins prefer to swim in deeper waters, and can sometimes be found in huge ‘super-pods’, made up of thousands of individuals.

Harbour porpoise

Harbour porpoise (Llamhidydd harbwr)

Harbour porpoise skull © CBMWC
Latin Name: Phocoena phocoena.

Skull size: This specimen is approximately 26cm in length.

Size of species: Harbour porpoise reach lengths of only 1.5m – 2m.

Key skull characteristics:

A) As the smallest cetacean found in the UK, measuring just 1.5 – 2m in length, the harbour porpoise has a small skull.

B) The nostrils point upwards allowing harbour porpoise to breathe easily when they surface. This is important because, like us, harbour porpoise are mammals.

C) Harbour porpoise have spade-shaped teeth which can be found in their – relatively – short beak.

Distribution in Wales: Harbour porpoise are mostly seen within 6 miles of land across the entirety of the Welsh coast. Despite being shy, they are the most commonly sighted UK cetacean species.

Fun fact: Harbour porpoise are generally quite shy, and are often found swimming alone – unlike dolphins!

Atlantic Grey Seal Skull

Atlantic grey seal (Sêl lwyd atlantig)

Atlantic grey seal skull © CBMWC
Latin Name: Halichoerus grypus.

Skull size: This specimen is approximately 24cm in length.

Size of species: Males Atlantic grey seals can grow up to 3m in length, while females reach up to around 2m.

Key skull characteristics:

A) Atlantic grey seals have large eye sockets for their large eyes. They rely on sight to hunt in dark, murky waters, and also have specialised lenses to focus well underwater.

B) Nostrils are front facing – just like ours! These can be opened and closed using special muscles.

C) Their teeth are very similar to those of a dog: sharp, conical, and perfect for eating fish!

Distribution in Wales: Atlantic grey seals are found across the entirety of the Welsh coast, with around 5,500 individuals found in Cardigan Bay alone. Nearly half of the worlds population is found in the UK.

Fun skull fact: Crabeater seals (found in Antarctica) have sieve-like tooth structures to filter their favourite food: krill.

For more information about our native marine mammal species, why not check out our National Dolphin Day blog post. Or alternatively use CBMWC’s YouTube channel to learn more!

Disclaimer: Cardigan Bay Marine Wildlife Centre holds the appropriate licences to store skulls/bones in this way.

Main image: Various mammal skulls at our ‘Magnificent Mammals’ event at The Welsh Wildlife Centre © CBMWC