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April 29, 2013

Dinosaur predecessors gain ground in wake of world’s biggest biodiversity crisis — with photo gallery

Many scientists have thought that dinosaur predecessors missed the race to fill habitats emptied when nine out of 10 species disappeared during the Earth’s largest mass extinction, approximately 252 million years ago. The thinking was based on fossil records from sites in South Africa and southwest Russia.

It turns out that scientists may have been looking for the starting line in the wrong places.

Newly discovered fossils from 10 million years after the mass extinction reveal a lineage of animals thought to have led to dinosaurs taking hold in Tanzania and Zambia in the mid-Triassic period, many millions of years before dinosaur relatives were seen in the fossil record elsewhere on Earth.

“The fossil record from the Karoo of South Africa remains a good representation of four-legged land animals across southern Pangea before the extinction event. But after the event animals weren’t as uniformly and widely distributed as before. We had to go looking in some fairly unorthodox places,” said Christian Sidor, University of Washington professor of biology. He’s lead author of a paper appearing the week of April 29 in the early edition of the Proceedings of the National Academy of Sciences.

The new insights come from seven fossil-hunting expeditions since 2003 in Tanzania, Zambia and Antarctica, funded by the National Geographic Society and National Science Foundation, along with work combing through existing fossil collections. The researchers created two “snapshots” of four legged-animals about 5 million years before and again about 10 million years after the extinction event at the end of the Permian period.

Prior to the extinction event, for example, the pig-sized Dicynodon – said to resemble a fat lizard with a short tail and turtle’s head – was a dominant plant-eating species across southern Pangea. Pangea is the name given to the landmass when all the world’s continents were joined together. Southern Pangea was made up of  what is today Africa, South America, Antarctica, Australia and India. After the mass extinction at the end of the Permian, Dicynodon disappeared and other related species were so greatly decreased that newly emerging herbivores could suddenly compete with them.

“Groups that did well before the extinction didn’t necessarily do well afterward,” said Sidor, who also is the curator of vertebrate paleontology at the UW’s Burke Museum of Natural History and Culture. “What we call evolutionary incumbency was fundamentally reset.”

The snapshot 10 million years after the extinction event reveals, among other things, that archosaurs were in Tanzanian and Zambian basins, but not distributed across all of southern Pangea as had been the pattern for four-legged animals prior to the extinction.  Archosaurs are the group of reptiles that includes crocodiles, dinosaurs, birds and a variety of extinct forms. They are of interest because it is thought they led to animals like Asilisaurus, a dinosaur-like animal, and Nyasasaurus parringtoni, a dog-sized creature with a five-foot tail that scientists in December 2012 announced could be the earliest dinosaur, or else the closest relative found so far.

“Early archosaurs being found mainly in Tanzania is an example of how fragmented communities became after the extinction event,” Sidor said. And the co-authors write: “These findings suggest that . . . archosaur diversification was more intimately related to recovery from the end-Permian mass extinction than previously suspected.”

A new framework for analyzing biogeographic patterns from species distributions, developed by co-author Daril Vilhena, a UW biology graduate student, provided a way to discern the complex recovery, Sidor said.

It revealed that before the extinction event 35 percent of four-legged species were found in two or more of the five areas studied, with some species having ranges that stretched 1,600 miles (2,600 kilometers), encompassing the Tanzanian and South African basins. Ten million years after the extinction event, the authors say there was clear geographic clustering and just 7 percent of species were found in two or more regions.

The techniques – new ways to statistically consider how connected or isolated species are from each other – could be useful for other paleontologists and modern day biogeographers, Sidor said.

In the early 2000s Sidor and some of his co-authors started putting together expeditions to collect fossils from sites in Tanzania that hadn’t been visited since the 1960s and in Zambia where there’d been little work since the ’80s. Two expeditions to Antarctica provided additional materials, as did long-term efforts to examine museum-held fossils that had not been fully documented or named.

Other co-authors from the UW are graduate students Adam Huttenlocker and Brandon Peecook, post-doctoral researcher Sterling Nesbitt and research associate Linda Tsuji; Kenneth Angielczyk of the Field Museum of Natural History in Chicago; Roger Smith, of the Iziko South African Museum in Cape Town; and Sébastien Steyer from the National Museum of Natural History in Paris.

Funding was also received from the Evolving Earth Foundation, the Grainger Foundation, the Field Museum/IDP Inc. African Partners Program and the National Research Council of South Africa.

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For more information:

• Sidor, on sabbatical from UW, spending year at the Field Museum of Natural History in Chicago, office: 312-665-7637, casidor@uw.edu
• Angielczyk, phone: 312-665-7639,  kangielczyk@fieldmuseum.org
• Smith, phone: +27 0 21 481 3879, rsmith@iziko.org.za
• Steyer, phone: +33 662 697 643, steyer@mnhn.fr

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The following fact sheet was developed by the co-authors.

 FAQ : Provincialization of terrestrial faunas following the end-Permian mass extinction

 Major Findings

• The end-Permian mass extinction permitted a significant reorganization of the land-living animal communities living in southern part of the supercontinent of Pangea.
• In addition to causing high levels of extinction, the mass extinction brought about an emptying of ecological niches, which then promoted the diversification of various groups at different places.
• Mass extinctions can have unpredictable long-term effects (e.g., on the makeup of communities and biogeographic provinces).
• Traditional sources of data regarding the effects of the end-Permian extinction on land (viz. Russia and especially South Africa) might not provide as complete a picture of the extinction and subsequent recovery as previously thought.
• The radiation of archosaurs, including dinosaurs, was probably more closely tied to the recovery from the end-Permian extinction than previously realized.

 Facts about the end-Permian mass extinction (AKA Permo-Triassic mass extinction)

• The end-Permian extinction was the largest in Earth History. Nearly 90% of life disappeared.
• The end-Permian mass extinction event is poorly known on land. Most of the data available today come from the marine realm.
• The end-Permian mass extinction is dated to 252.3 Ma (based on radiometric dates from marine beds in China).
• On land, many diverse groups of Permian animals went extinct. The groups that radiated after the extinction in the Triassic include recognizable members of many of the groups of land vertebrates we still have today: mammals, crocodilians, turtles, lizards, and dinosaurs (which include birds).

 Species involved in the analysis

• Archosaurs.  Archosaurs are a group including modern crocodiles, modern birds, their common ancestor and all of its descendants, including the dinosaurs. Many of the oldest known archosaurs, including the oldest close relatives of dinosaurs and possibly the oldest true dinosaur, are known from the Middle Triassic of Tanzania and Zambia.
• Cynodonts.  Cynodonts are the group from which mammals later evolved.  If this group had perished at the end-Permian extinction, mammals wouldn’t be around today.
• Dicynodonts.  These were the dominant herbivores of the Permian. They were cat- to hippo-sized and distantly related to mammals. They survived the extinction and re-diversified in the Triassic, before becoming extinct at the end of the Triassic.
• Temnospondyls.  These amphibians, which could reach giant sizes, were mostly freshwater top predators like crocodiles today. They survived the extinction but underwent a drastic faunal turnover in the Triassic, with many species going extinct and new species originating.
• Pareiasaurs and other reptiles. Pareiasaurs were mostly large-bodied terrestrial herbivores with robust skulls ornamented by bosses or horns. They were victims of the end-Permian extinction. However, other reptiles like procolophonids survived the extinction and went on to diversify in the Triassic.

 Age

• The Permian Period lasted from 300 to 252 million years ago.  The Permian fossils in this study are about 257 Ma (i.e., Late Permian).
• The Triassic Period lasted from 252 to 201 million years ago. The Triassic fossils in this study are about 242 Ma (i.e., Middle Triassic).

 Geography

• During most of the Permian and Triassic, the continents were coalesced into a single landmass named Pangea.
• The southern portion of Pangea is called Gondwana, and included what is now Africa, Madagascar, South America, Antarctica, Australia, and India.
• The areas in which we collected fossils in Africa were much farther south in the Permian and Triassic than they are today. For example, the Ruhuhu Basin of southern Tanzania is currently ~10.5° S latitude, but in the Late Permian it was about ~50° S.

 Fossils and fieldwork leading to this paper

• Tanzanian fossils were collected in the Ruhuhu valley of southern Tanzania in 2007, 2008, and 2012. They are temporarily on loan to our team for research but will eventually return to be housed at the National Museum of Tanzania in Dar es Salaam.
• Zambian fossils were collected in the Luangwa valley of northeastern Zambia in 2009 and 2011. They are temporarily on loan to our team for research but will eventually return to the National Heritage Conservation Commission in Lusaka.
• Antarctic fossils were most recently collected in 2003 and 2010 are housed at the Burke Museum (Univ. Washington).
• South African fossils are the product of long-term fieldwork projects and are stored at a variety of museums in Cape Town, Johannesburg, Pretoria, etc.

Our paper DOES NOT say:

• Anything about the causes of end-Permian mass extinction.
• Anything about the extinction in the marine realm.
• Anything about global climate change at the end of the Permian.

Funding:
National Geographic Society (to C.A.S.)
National Geographic Society (to J.S.S.)
National Science Foundation (to C.A.S.)
Evolving Earth Foundation (to S.J.N.)
The Grainger Foundation (to K.D.A.)
Field Museum/IDP, Inc. African Partners Program (to K.D.A.)
NSF Graduate Research Fellowships (to B.R.P.)
National Research Council (to R.M.H.S.)

Potential Commentators (not affiliated with this research):
Robert Reisz, University of Toronto (robert.reisz@utoronto.ca)
David Jablonski, University of Chicago (djablons@uchicago.edu)
Paul Olsen, Columbia University (polsen@ldeo.columbia.edu)
Randy Irmis, University of Utah (irmis@umnh.utah.edu)
Hans Sues, Smithsonian Institution (suesh@si.edu)

Co-author emails:
USA
Christian Sidor (Univ. Washington): casidor@uw.edu
Daril Vilhena (Univ. Washington): daril@uw.edu
Kenneth Angielczyk (Field Museum): kangielczyk@fieldmuseum.org
Sterling Nesbitt (formerly UW, now Field Museum):
Adam Huttenlocker (Univ. Washington): huttenla@uw.edu
Brandon Peecook (Univ. Washington): bpeecook@uw.edu
Linda Tsuji (Univ. Washington): latsuji@uw.edu

South Africa
Roger Smith (Iziko South African Museum, Cape Town): rsmith@iziko.org.za

France
J.Sébastien Steyer (CNRS and Muséum national d’Histoire naturelle, Paris): steyer@mnhn.fr

Tag(s): Christian Sidor • College of Arts & Sciences • Department of Biology • dinosaurs • University of Washington

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