Navigation Links
Getting a leg up on whale and dolphin evolution
Date:9/24/2009

When the ancestors of living cetaceanswhales, dolphins and porpoisesfirst dipped their toes into water, a series of evolutionary changes were sparked that ultimately nestled these swimming mammals into the larger hoofed animal group. But what happened first, a change from a plant-based diet to a carnivorous diet, or the loss of their ability to walk? A new paper published this week in PLoS One resolves this debate using a massive data set of the morphology, behavior, and genetics of living and fossil relatives. Cetacean ancestors probably moved into water before changing their diet (and their teeth) to include carnivory; Indohyus, a 48-million year-old semi-aquatic herbivore, and hippos fall closest to cetaceans when the evolutionary relationships of the larger group are reconstructed.

"If you only had living taxa to figure out relationships within this group of animals, you would miss a large amount of diversity and part of the picture of what is going on," says Michelle Spaulding, lead author of the study and a graduate student affiliated with the American Museum of Natural History. "Indohyus is interesting because this fossil combines an herbivore's dentition with adaptations such as ear bones that are adapted for hearing under water and are traditionally associated with whales only."

The origin of whales, dolphins, and porpoiseswith their highly modified legs and lack of hairhas long been a quandary for mammalogists. About 60 years ago, researchers first suggested that cetaceans were related to plant-eating ungulates, specifically to even-toed, artiodactyl mammals like sheep, antelope and pigs. In other words, carnivorous killer whales and fish-eating dolphins were argued to fit close to the herbivorous hoofed animal group. More recent genetic research found that among artiodactyls, hippos are the cetaceans' closest living relatives.

Because no one would ever link hippos and whales based on their appearance, fossil evidence became an important way to determine the precise evolutionary steps that cetacean ancestors took. Traditionally, the origin of whales was linked to the mesonychids, an extinct group of carnivores that had singly-hoofed toes. The recent discovery of Indohyus, a clearly water-adapted herbivore, complicates this picture (as new fossils often do) because of ear bones similar to those of modern cetaceans, which are theorized to help the animal have heard better while under the water.

To tease apart different potential evolutionary histories (whether carnivory or water adaptations occurred first; the mesonychid or Indohyus relatedness ideas), Spaulding and colleagues mapped the evolutionary relationships among more than 80 living and fossil taxa (in other words, species and/or genera). These taxa were scored for 661 morphological and behavioral characters (such as presence of hair or the shape of and ankle bone). Forty-nine new DNA sequences from five nuclear genes were also added to the mix of more than 47,000 characters; both morphological and genetic data build on previous analyses by authors Maureen O'Leary of Stony Brook University and John Gatesy of University of California at Riverside. In addition, Indohyus, carnivores (dogs and cats), and an archaic group of meat-eating mammals called creodonts were included.

The team found that the least complex evolutionary tree places Indohyus and similar fossils close to whales, while mesonychids are more distantly related. Hippos remain the closest living relatives. These results suggest that cetacean ancestors transitioned to water before becoming carnivorous but that the meat-eating diet developed while these ancestors could still walk on land.

"How do you put flesh and movement onto a fossil?" asks author O'Leary. "The earliest stem whale probably ate prey in water while still being able to walk on land. Indohyus has some adaptations for hearing under water but also ate plants, while Ambulocetus (a walking whale that lived about 50 million years ago) seems to have been carnivorous."

"There is deep conflict in the evolutionary tree," says Spaulding. "The backbone of the tree is robust and stable, but you have these fairly large clades that move around relative to this backbone(Indohyus and mesonychids) We need to really re-examine characters carefully and see what suite of traits are the truly derived in different taxa to fully resolve this tree."


'/>"/>

Contact: Kristin Elise Phillips
kphillips@amnh.org
212-496-3419
American Museum of Natural History
Source:Eurekalert  

Related biology news :

1. Getting plants to rid themselves of pesticide residues
2. Getting to the root of science in a nutty way
3. Getting down to cancer basics
4. Getting into hot water
5. Many middle-aged and older Americans not getting adequate nutrition
6. Getting warmer? Prehistoric climate can help forecast future changes
7. Getting to the root of the matter
8. Getting better with a little help from our micro friends
9. Getting wise to the influenza virus tricks
10. The sea ice is getting thinner
11. New species discovered on whale skeletons
Post Your Comments:
*Name:
*Comment:
*Email:
Related Image:
Getting a leg up on whale and dolphin evolution
(Date:6/22/2016)... Md. , June 22, 2016  The American College ... Trade Show Executive Magazine as one of the ... on May 25-27 at the Bellagio in Las ... on the highest percentage of growth in each of the ... of exhibiting companies and number of attendees. The 2015 ACMG ...
(Date:6/22/2016)... , June 22, 2016 On Monday, ... call to industry to share solutions for the Biometric ... U.S. Customs and Border Protection (CBP), explains that CBP ... are departing the United States , ... and to defeat imposters. Logo - ...
(Date:6/20/2016)... , June 20, 2016 Securus ... justice technology solutions for public safety, investigation, corrections ... the prisons involved, it has secured the final ... (DOC) facilities for Managed Access Systems (MAS) installed. ... additional facilities to be installed by October, 2016. ...
Breaking Biology News(10 mins):
(Date:6/23/2016)... ... 2016 , ... UAS LifeSciences, one of the leading manufacturers ... Probiotics, into Target stores nationwide. The company, which has been manufacturing high quality ... list of well-respected retailers. This list includes such fine stores as Whole Foods, ...
(Date:6/23/2016)... 23, 2016 Houston Methodist Willowbrook Hospital ... Sports Association to serve as their official health ... Methodist Willowbrook will provide sponsorship support, athletic training ... association coaches, volunteers, athletes and families. ... Sports Association and to bring Houston Methodist quality ...
(Date:6/23/2016)... SAN FRANCISCO , June 23, 2016   ... it has secured $1 million in debt financing from ... to ramp up automation and to advance its drug ... for its new facility. "SVB has been ... goes beyond the services a traditional bank would provide," ...
(Date:6/23/2016)... , June 23, 2016 Apellis Pharmaceuticals, ... 1 clinical trials of its complement C3 inhibitor, ... and multiple ascending dose studies designed to assess ... of subcutaneous injection in healthy adult volunteers. ... either as a single dose (ranging from 45 ...
Breaking Biology Technology: