Female dolphins may be able to experience the same pleasure from sex as humans, a groundbreaking new study has found.

Scientists found that female bottlenose dolphins have large and well-developed clitorises which are located close to the opening of their vaginas, meaning that any penetration would stimulate them and could cause an orgasm.

It has been long-believed that male dolphins have sex for pleasure because some have been seen masturbating and even penetrating each other's blow holes.

Female bottlenose dolphins have large and well-developed clitorises which are located close to the opening of their vaginas, meaning that any penetration would stimulate them and could cause an orgasm

The erectile tissue of the clitoris (centre) is surrounded by dense muscle and connective tissue

While research into the pleasure animals get from sex is relatively limited, bonobo monkeys and pigs are thought to be two species which also enjoy the act.

Some scientists believe that working out whether the females in a species can orgasm is a good indication as to whether sex is pleasurable because females do not need to orgasm to become pregnant.

Bonobo monkeys are thought to use sex as a way to 'de-stress' while scientists believe pigs - who can ejaculate for up to half an hour - also have sex for pleasure.

Italian researchers Alfonso Troisi and Monica Carosi spent 238 hours watching Japanese Macaques and saw 240 acts of sex.

In a third of those copulations, they saw what they called female orgasmic responses.

According to the BBC they said: 'The female turns her head to look back at her partner, reaches back with one hand, and grasps the male'.

Hyenas, goats, sheep and fruit bats have been known to take part in oral sex.

If animals take part in oral sex it could suggest they derive pleasure from having an orgasm because oral sex cannot result in pregnancy.

Over the course of six years, researchers amassed 116 hours of behavioural observations of two male brown bears, which included 28 acts of oral sex.

The dolphin researchers said the structure of the tissue in the dolphin clitoris suggests it may expand, for example, in response to stimulation.

Left: Computer reconstruction of the clitoris of the bottlenose dolphin showing the erectile tissue of the clitoris (yellow) embedded in the surrounding muscle and connective tissue (green). Right: Another computer reconstruction which shows the erectile tissue (purple) embedded in the muscle (yellow)

Previous studies on sex in dolphins has suggested that it plays an important role in social bonding and happens all year round - even during periods when they cannot conceive

They discovered that the skin under the clitoral hood contains 'bundles' of nerves that may increase sensitivity and the potential for pleasure, as has been found in the human clitoris.

Previous studies suggest sex plays an important role in social bonding among dolphins, as seen in other social species.

Researchers said that dolphins have sex all year round - even during periods when they cannot conceive - which could show that they have sex for pleasure rather than just to procreate.

Study co-leader Dr Dara Orbach, a research associate at Mount Holyoke College in the US, said: 'In other mammalian species with year-round copulation, such as humans and bonobos, sex is known to be pleasurable for females, often through clitoral stimulation that leads to orgasm.

Bonobo monkeys are believed to enjoy sex because they are known for same-sex intimate interactions which couldn't possibly result in a pregnancy. They are also thought to use sex as a way to 'de-stress'

Pigs - who can orgasm for up to half an hour - are also believed to enjoyed sex. Female pigs have their clitorises located inside their vagina, which suggests that any penetrative sex would stimulate them

'Our anatomical observations suggest the clitoris is functional in bottlenose dolphins, but further research, including physiological and behavioural analyses, are necessary to test if sexual experiences can be pleasurable for female dolphins.'

The research team studied 11 dolphins that had died naturally and were collected under a permit authorised by the National Marine Fisheries Service in the US.

To explore the anatomy of the dolphin clitoris, they performed dissections, created 3-D CT scans, fixed the tissues in paraffin wax and stained them to examine their structure in detail.

They found that dolphins have a clitoral hood where two areas of extensive erectile tissue merge into a single body, a shape and structure very similar to the human clitoris.

In both humans and dolphins, the erectile tissue of the clitoris is larger than the clitoral hood.

The researchers said that the thin, folded nature of the skin around the clitoral hood suggests the dolphin clitoris may expand during periods of engorgement and increased sensitivity.

The research team studied 11 dolphins that had died naturally and were collected under a permit authorised by the National Marine Fisheries Service in the US

However, the dolphin clitoris is located in a different position relative to the vaginal opening than in humans.

Dr Orbach said: 'In dolphins, the clitoris is positioned at the entrance of the vaginal opening and in direct contact with the penis during copulation, unlike the external position of the clitoris in humans.

'The location of the clitoris near the vaginal opening indicates it can potentially be easily stimulated during copulation.'

However, the researchers did not any evidence of a vestibular bulb - an area of erectile tissue that surrounds the vaginal opening in humans and contributes to orgasms.

Dr Orbach added: 'Very little is known about female reproductive morphology in most wild vertebrate species.

'This research provides a comparative framework to explore other functions of sex that may not be unique to humans.

'We are on the precipice of a deeper understanding of the relationship between form and function of genitalia.'

In an interview with Inside Science Dr Patricia Brennan said: 'Of course, one can't prove that an animal experiences pleasure just by examining its anatomy.

'But it would be hard to measure direct signs of orgasm in a dolphin - for one thing, they don't have any toes to curl.'

Dr Brennan believes that unless contrary findings are produced, it would make sense to assume that dolphin clitorises work in the same way as human clitorises.

She is due to present the findings of the study at the American Association of Anatomists annual meeting in Orlando, Florida.