Featured Research

from universities, journals, and other organizations

Fossilized Pregnant Fish One Of First Animals To Have Sex

Date:
February 26, 2009
Source:
The Natural History Museum
Summary:
A pregnant fossil fish at the Natural History Museum in London has shed light on the possible origin of sex, according to a new study. Dating from the Upper Devonian period 365 million years ago, the adult placoderm fish Incisoscutum ritchiei is one of the earliest examples of a pregnant vertebrate and contains a five-centimetre-long embryo.

Close-up of the 350-million-year-old fossil fish. The spine runs along the top left and the embryo is below.
Credit: Copyright NHM

A pregnant fossil fish at the Natural History Museum in London has shed light on the possible origin of sex, according to a study published today in the journal Nature by an international team including Museum scientists.

The fossil is an adult placoderm, an extinct group of armoured fish, and it contains a 5cm-long embryo.

It is dated to the Upper Devonian period 350 million years ago and was found in the Gogo formation of western Australia.

The fish species is Incisoscutum ritchiei and this specimen is one of the earliest examples of a pregnant vertebrate and shows that internal fertilisation, or sex, started far sooner than previously thought.

‘This discovery is incredibly important because evidence of reproductive biology is extremely rare in the fossil record,’ says Dr Zerina Johanson, fossil expert (palaeontologist) at the Natural History Museum.

Different types of fertilisation

External fertilisation is believed to be the earliest form of reproduction and scientists used to think the placoderms and other early fish groups used this method. ‘We expected that these early fishes would show a more primitive type of reproduction, where sperm and eggs combine in the water and embryos develop outside the fish,’ says Dr Johanson.

The process of internal fertilisation and giving birth to live young, or viviparity, is more advanced and differentiates some fish and mammals from other animals such as reptiles and amphibians.

Johanson and her colleagues believe it was the main reproductive method for early fish groups such as the placoderms and could have evolved in other fish groups.

‘Sex was far more common in these primitive prehistoric animals,’ adds Dr Johanson. ‘However, copulation appears to be the main way they reproduced, demonstrating that ‘sex’ started a lot sooner than we thought.’

Look again at Museum specimen

The fish fossil has been in the Museum collections since the 1980s. Along with thousands of other fish specimens, they are used in scientific study by Museum scientists and other researchers from around the world.

The Incisoscutum ritchiei fish specimen was originally thought to have died soon after its final meal, because the bones of a smaller can be fish seen within it.

However, recent findings such as embryos found in other placoderms, caused Johanson and her colleagues to take another look at the fossil.

‘The position of the embryo in this fish is the same as that of another found with a placoderm embryo in it in 2008.’ So they decided to reassess the description for the Incisoscutum ritchiei fossil.

The team came to the conclusion that the ‘meal’ was in fact a young fish developing in the womb of an adult.

‘The embryo in Incisoscutum ritchiei was in its final stages of development, inside its mother, waiting to be born,’ continues Dr Johanson.

Pelvic fin

A modification of the pelvic fin on the belly of the adult fish is also significant. This structure, or clasper, would have been used by the male to grip the female during mating.

Placoderms were a diverse group of prehistoric fish. Their head and thorax were covered by articulated armoured plates and the rest of the body had scales or was naked, depending on the species.

Thought to be the most primitive jawed vertebrates, placoderms were the dominant vertebrate group during the Devonian period.

It was thought they went extinct due to competition from the first bony fish and early sharks.

But now research has shown that the last placoderms died out one by one as each of their ecological communities suffered the environmental catastrophes of the Devonian/Carboniferous extinction event.


Story Source:

The above story is based on materials provided by The Natural History Museum. Note: Materials may be edited for content and length.


Journal Reference:

  1. John A. Long, Kate Trinajstic, Zerina Johanson. Devonian arthrodire embryos and the origin of internal fertilization in vertebrates. Nature, 2009; 457 (7233): 1124 DOI: 10.1038/nature07732

Cite This Page:

The Natural History Museum. "Fossilized Pregnant Fish One Of First Animals To Have Sex." ScienceDaily. ScienceDaily, 26 February 2009. <www.sciencedaily.com/releases/2009/02/090225161508.htm>.
The Natural History Museum. (2009, February 26). Fossilized Pregnant Fish One Of First Animals To Have Sex. ScienceDaily. Retrieved August 1, 2014 from www.sciencedaily.com/releases/2009/02/090225161508.htm
The Natural History Museum. "Fossilized Pregnant Fish One Of First Animals To Have Sex." ScienceDaily. www.sciencedaily.com/releases/2009/02/090225161508.htm (accessed August 1, 2014).

Share This




More Plants & Animals News

Friday, August 1, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Ebola Vaccine Might Be Coming, But Where's It Been?

Ebola Vaccine Might Be Coming, But Where's It Been?

Newsy (Aug. 1, 2014) Health officials are working to fast-track a vaccine — the West-African Ebola outbreak has killed more than 700. But why didn't we already have one? Video provided by Newsy
Powered by NewsLook.com
Study Links Certain Birth Control Pills To Breast Cancer

Study Links Certain Birth Control Pills To Breast Cancer

Newsy (Aug. 1, 2014) Previous studies have made the link between birth control and breast cancer, but the latest makes the link to high-estrogen oral contraceptives. Video provided by Newsy
Powered by NewsLook.com
Visitors Feel Part of the Pack at Wolf Preserve

Visitors Feel Part of the Pack at Wolf Preserve

AP (July 31, 2014) Seacrest Wolf Preserve on the northern Florida panhandle allows more than 10,000 visitors each year to get up close and personal with Arctic and British Columbian Wolves. (July 31) Video provided by AP
Powered by NewsLook.com
Florida Panther Rebound Upsets Ranchers

Florida Panther Rebound Upsets Ranchers

AP (July 31, 2014) With Florida's panther population rebounding, some ranchers complain the protected predators are once again killing their calves. (July 31) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins