Saturday, June 9, 2012

Ancient Marine Reptiles ~ Family Redux

I did not set out to fashion a post that carried on the theme from the last one – fossil hunting families – but that’s what I appear to have done, though it has an added twist – a fossil family.

I wonder if visitors to the Smithsonian’s National Museum of Natural History were aware of the recent, rare privilege they had of seeing a marvelous fossil being worked on.  Well, to be honest, it wasn’t much to look at, initially rather more puzzling than breathtaking.  But if you had an idea what it was (that is, were willing to read the brief explanation placed near it), you learned that its looks were deceiving.  This specimen, formally described in a 2009 publication, was undergoing some additional preparation in the FossiLab, the Museum’s paleontological preparatory lab situated on the exhibit floor, just down from the dinosaurs.  Visitors had a view of this fossil through the lab’s large glass windows.  (Though the fossil is still on display as of the date of this post, I’ve written this in the past tense for reasons that will be obvious at the conclusion.)

A stack of thin, black disks, like miniature poker chips, rises from the small block of gray matrix found in the Sundance Formation, Wyoming.  This material is 161.2 to 155.6 million years old (Oxfordian Age of the Upper Jurassic).  In a 2009 article, biologist F. Robin O’Keefe and his co-authors posited that these disks (12 – 15 mm wide and 2 – 3 mm thick) are embryonic ichthyosaur vertebrae.  These vertebrae were found encased in matrix lying amid the ribs and gastralia (the “belly ribs”) of the fossilized remains of an adult plesiosaur, a different kind of animal.  O’Keefe, et al., described the ichthyosaur as “a voided embryo rather than a neonate,” and its presence in the plesiosaur as evidence of scavenging.  (Viviparity or live birth is an attribute of ichthyosaurs.)   (F. Robin O’Keefe, et al., A Plesiosaur Containing an Ichthyosaur Embryo as Stomach Contents From the Sundance Formation of the Bighorn Basin, Wyoming, Journal of Vertebrate Paleontology, December 2009.)

I hope visitors who saw the ichthyosaur embryo were inclined to take the few steps necessary to see the adult ichthyosaur and plesiosaur skeletons on display nearby. These ancient marine reptiles were indeed monstrous denizens of the Mesozoic seas, nothing soft and cuddly about them (though O’Keefe may beg to differ regarding the plesiosaur – see below).  Ichthyosaurs went extinct in the Early Cretaceous, while the plesiosaurs, in a diminished capacity, outlasted them, but ended their run presumably with the mass extinction at the end of the Cretaceous.  One of the Early Jurassic ichthyosaurs (species unknown) on display at the NMNH is shown below.

When I first saw the ichthyosaur embryo fossil being prepped, a tiny bell rang in the recesses of my memory, and, eventually, the connection was made.  It’s what brings a fossil hunting family and a fossil family into this posting.

In 2011, O’Keefe and paleontologist L.M. Chiappe posited that, along with ichthyosaurs and some other ancient marine reptile taxa during the Mesozoic Era (251.0 to 65.5 million years ago), plesiosaurs also gave birth to live young.  They based their hypothesis on the fossil skeleton of a Late Cretaceous short-necked plesiosaur skeleton which, within its body cavity, contains what appear to be the fossil remains of a plesiosaur fetus.  O’Keefe and Chiappe reached their conclusion from the position of the plesiosaur juvenile within the adult skeleton, the fact that both individuals are members of the same species, the limited ossification of the juvenile skeleton, and that the juvenile remains are unmarked by stomach acid.  This would be the first evidence of viviparity for plesiosaurs.  (Viviparity and K-Selected Life History in a Mesozoic Marine Plesiosaur (Reptilia, Sauropterygia), Science, August 12, 2011.)  (Warning:  paywall at the Science site.)

O’Keefe and Chiappe pushed the envelope a bit when they went on to suggest that, given the reproductive strategy they attribute to the plesiosaur (giving birth to a single, live offspring) is the same as that of odontocete cetaceans (toothed whales), the plesiosaurs may have exhibited social behavior similar to those marine mammals.  This would have included extensive parental attention to newborns and membership in larger social networks.  Though they acknowledged that additional evidence must be marshaled, they asserted, “it is certain that plesiosaur life history differed markedly from that of other Mesozoic marine reptiles.”  In the photograph below, a Cretaceous plesiosaur swims on display at the NMNH.

And it’s here that a fossil hunting family enters the picture.  Well, actually, the family entered the picture long before O’Keefe and Chiappe published their findings.  In 1987, nearly a quarter of a century earlier, Charles Bonner and his father Marion had came upon these plesiosaur fossils while hiking on their ranch in Logan County, Kansas.  Suspecting they were something special, the Bonners excavated the fossil remains and shipped them to the Natural History Museum, Los Angeles County.  Only recently, as these fossils were brought out for display was their import realized.  (Daniela Hernandez, Plesiosaurs Carried Young Like a Mammal, Study Finds, Los Angeles Times, August 11, 2011.)  This is another of those stories of fossils coming into their own only after lingering in storage-induced obscurity.

Bonner.  It’s a family name with cachet among fossil collectors.  Marion, the patriarch of the family, was a renowned amateur fossil collector.  He and his wife Margaret raised a fossil collecting family of eight children.  Among the children, Orville went on to become the head preparator at the University of Kansas’ Museum of Natural History.  In 2010, scientists named a new genus of huge plankton-eating Cretaceous fish Bonnerichthys in honor of the Bonner family.  Ah, one more tale of delayed understanding of a fossil’s significance.  In 1971, son Charles discovered the fossil which was the basis of the identification of the new species nearly 40 years later, and Marion invested many months in 1971 and 1972 excavating the remains which were then shipped to the museum at the University of Kansas.  (Kathy Hanks, Man, His Fossil Finds Were In A Class By Themselves, The Hutchinson News, February 22, 2010.)

Fossils and families, fossil families – endlessly fascinating, as is time in paleontology.  I don’t mean the creation of fossils, but what happens subsequently.  Fossils produced over millions of years may be discovered only to then languish decades, even centuries, on a shelf (often literally), or not.  Case in point, the ichthyosaur embryo fossil.  The large plesiosaur fossil which encased it was discovered in 2004, extracted and prepped in 2005.  The initial paper describing the ichthyosaur embryo within the plesiosaur came out just four years later.

And now, in the past several days, the embryo material was being prepped still further for analysis.  The various stages of paleontological prepping can take a protracted period of time, or not.  I took the photographs shown at the beginning of this posting about five days ago.  Here’s the most important of the small chunks I saw today upon another visit.  Blink and you may miss it.

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