FOSSIL-OF-THE-DAY

March 27, 2016 - ANSWERS

1) What is the Phylum for this organism? ARTHROPODA

2) What is the Subphylum/Class for this organism? (HINT: the name derives from its characteristic jointed appendages anterior to the mouth that form fangs in spiders) CHELICERATA

3) What is the common name for these creatures? EURYPTERIDS

4) What is the nick name for these creatures? SEA SCORPIONS

5) What does the scientific name for this clade mean and from what language does it derive? BROAD (eury) WING (pteron) FOR THEIR SWIMMING PADDLES

6) During what geologic periods did these organisms live? ORDOVICIAN TO PERMIAN

7) In which period was this animal most abundant? SILURIAN BUT DECLINED RAPIDLY THEREAFTER

8) Could fossils of this animal be used as an index fossil?  Explain why or why not. INDIVIDUAL SPECIES MIGHT BE USEFUL, BUT IN GENERAL NO THIS WOULD NOT MAKE A GOOD INDEX FOSSIL SINCE IT DID NOT HAVE A MINERALIZED EXOSKELETON, AND THEY LIVED FOR LONGER PERIODS OF TIME THAT WOULD NOT PROVIDE A NARROW WINDOW OF TIME FOR DATING

9) In what environment did this creature live? VERY SHALLOW MARINE, BRACKISH AND FRESHWATER TIDAL FLATS. SOME ALSO LEFT THE WATER FOR SHORT PERIODS SO AMPHIBIOUS

10)What is the closest living relative of this animal?   HORSESHOE CRABS, MORE REMOTELY, SPIDERS!

a) Does it live in the same environment as the extinct organism? NOT EXACTLY – HORSESHOE CRABS LIVE IN SHALLOW MARINE HABITATS

11) How large could this animal get? THE LARGEST ONES COULD REACH 8 FEET LONG

12) What is the scientific term for this animal’s tail? A TELSON

13)What type of fossilization preserved these animals? CARBONIZATION, HENCE THE BLACK CARBON FILM

14)What type of rock are these fossils most likely to have been preserved in? DOLOSTONE – A SEDIMENTARY CARBONATE ROCK SIMILAR TO LIMESTONE BUT CONTAINING A HIGH PERCENTAGE OF THE MINERAL DOLOMITE (CaMg(CO3)2 FORMED FROM POST-DEPOSITIONAL ALTERATION OF LIME MUD (Calcite CaCO3) WHERE THE CALCIUM IS REPLACED BY MAGNESIUM COMING FROM GROUNDWATER

15)Where in the USA are most fossils of this animal found? (HINT: it is the state fossil of this state) NEW YORK STATE

16)What is the name of the State’s fossil species? EURYPTERUS REMIPES

17) What was the mode of life of this organism? CARNIVORE – PREDATORS/SCAVENGERS

18) What animal might have taken this creature’s ecological niche when it became extinct? (HINT: Romer’s Theory) PLACODERMS

Eurypterids were the first really big predator, and were the largest arthropods of all time.

More Info: http://www.fossilguy.com/gallery/invert/arthropod/eurypterid/

Spindle diagram showing why Romer came up with his theory that Placoderms replaced Eurypterids as the dominant large marine predators:

In this diagram they have broken out the Eurypterids into two Order/Clades called Eurypterina (the nektonic predators) and Stylonurina (bottom “sweep feeding” scavengers). The predators are the ones they think were replaced by Placoderms first, and then Placoderms in turn were replaced by cartilaginous fish (Chondrichthyes) as the dominant nektonic predators. Remember that Agnatha were the jawless fish that sucked food into round jawless mouths. Acanthodii are a type of early bony fish.

So from that prior diagram you should be able to tell what is wrong with this picture…..

Here is a map showing where most Eurypterid fossils are found:

This map shows eurypterid fossil discoveries in the northeastern United States. Upstate New York is home to most of them.

The two biggest sites for Eurypterid fossils found in a geologic group called the Bertie Waterlime: Fiddler’s Green and an area called the Herkimer Pool. The Herkimer pool is named because many eurypterids appear to have gathered there before (or after?) their death.

The Bertie Waterlime

The Bertie Waterlime is a fossil lagerstatten that provides excellent examples of eurypterids and other rare arthropod fossils. Dolostones in the Bertie Group can be used to make cement that cures while under water, thus giving it the name waterlime. Fossils are collected from formations associated with the Bertie and Roundabout groups throughout New York and into Ontario, Canada. The Bertie Waterlime eurypterid containing dolostones represent a hypersaline lagoon. The majority of eurypterids found represent molts. Several species of eurypterids are found in these deposits. Eurypterus remipes is the state fossil for New York. A variety of marine life is preserved in the Bertie Waterlime dolostones. Primitive horseshoe crabs, aquatic scorpians, phyllocarid crustaceans, trilobite-like arthropods, gastropods, orthocone cephalopods, brachiopods, and stromatolites have been collected. A few examples of the land plant Cooksonia have also been recovered. A variety of eurypterid species have been found in deposits around the word representing a time span of 100 million years (Ordovician to Permian). One species of eurypterid reached a length of 2 meters, making it the largest known arthropod to have existed on Earth (Nudds & Selden, 2008, pp. 73-92). 

The Bertie Group (the type locality is a Canadian township) is a carbonate sequence of dolostones and limestones with minor shale and mudstone units, evaporites (of gypsum, halite and anhydrite) and intercalated waterlimes that accumulated during multiple oscillations of the Silurian seas. Amongst the numerous waterlime horizons that exist within the Bertie, several species of eurypterid remains have been recovered predominantly within the Phelps Waterlime Member (notably E. remipes) of the Fiddlers Green Formation (a major transgressive-regressive cycle) and the earlier Williamsville Formation (notably E. lacustris) of western New York and the Niagara Peninsula of Ontario, Canada.

A FRESH, BRACKISH OR SALT WATER HABITAT?  Late Silurian waterlimes are thought to have been brackish to hypersaline based upon the prevailing arid landscape and basins of evaporite deposits, salt hoppers and mud cracks without access to normo-saline seas

Eurypterids were shaped like a lobster but they were only distantly related. Some of them measured more than eight feet long! They existed in the shallow seas that covered large parts of what are now eastern North America and western Europe during the Paleozoic Era. They also lived in fresh water environments. These armored beasts inhabited the planet for more than 200 million years, from the earliest Ordovician Period to the middle of the Permian Period.The monster described above was the largest of eurypterids. Most eurypterids, however, were much smaller, less than two feet in length. Most were probably predatory, capturing prey with their claws, but some lack large grasping claws and may have been scavengers or fed on small prey on the bottom. Although they were primarily aquatic (living in both marine and fresh water settings), some forms may have been semi-terrestrial, perhaps in swamps or tidal flats.

Like all arthropods, they had an exoskeleton made of chitin, but unlike many (for example, many crabs, lobsters, and the extinct trilobites), this exoskeleton was not mineralized, which might help explain why fossil eurypterids are so uncommon. Indeed, eurypterids are relatively rare fossils, and not very diverse. There are about 60 described genera encompassing around 300 species. Compare that to the trilobite record of thousands of genera encompassing more than 17,000 species.

Eurypterids were not only the largest arthropods but thought to represent some of the earliest animals to undertake brief amphibious excursions onto land (Selden, 1985; Braddy, 2001). Their arthropodal body architecture made them pre-adapted for adventuring landward with exoskeletons that provided support and water conservation capabilities, flexible legs for walking on land and a respiratory system adaptable to breathing air. Eurypterids never transitioned to a fully land-based lifestyle having gone extinct 250 million years ago, but their phylogenetic relatives certainly did, the closest of which are arachnids (scorpions, spiders, ticks and mites).

This model depicts a eurypterid venturing onto land with Cooksonia growing along the shoreline.About 420 million years, plants such as Cooksonia began their conquest of the land, followed soon by

animals such as eurypterids. They were opportunists in that they took advantage of what they already had, body parts and behavior adapted to an aquatic existence but useful on land as well.

(Model on display in Smithsonian Institution’s Natural History Museum)

SHEDDING ONE’S CHITINOUS SKINThis slab of waterlime (below) displayed in the museum contains a multitude of molted eurypterids and a disarticulated carapace. In fact, most eurypterid fossils are presumed to be molted exoskeletons as opposed to carcasses (Braddy, 1995; Ciurca personal communication, 2012). The problem of distinguishing between eurypterid exuviae and carcasses has remained a paleontological exercise for almost a century (Clarke and Ruedemann, 1912; Tetlie, 2008). One of the challenges is that eurypterid exuviae (molts), like horseshoe crabs, remain so intact defying inclinations to label them as molts.

Typical of all arthropods, eurypterids shed or molted their chitinous, semi-rigid exoskeletons in order to accommodate growth. Similar to cellulose in its supportive function, chitin is a modified polysaccharide like glucose that contains nitrogen.

Contemporary horseshoe crabs (Xiphosurans) and scorpions (Arachnids) are frequently used, phylogenetically-related, modern-analogues for investigating aspects of eurypterid paleo-biology, ecology and behavior (Braddy, 2001; Tetlie 2008). Horseshoe crabs molt perhaps 10 times in its lifetime which provides some explanation for the vast numbers of preserved exoskeletons. 

The actual shedding event is called ecdysis, whereas molting is the term reserved for the entire process that includes a period of inactivity both before and after ecdysis. Molting subjects arthropods to susceptibility from predation during the soft-shell stage. With horseshoe crabs, refugia are sought out, regions in which to safely molt. Reduction of suitable refugia near the end of the Silurian has been cited as a potential cause for eurypterid decline and extinction of some genera (Tetlie, 2007), although others site their decline to quicker, more heavily-armored fish prototypes that developed during the Devonian. [Note from Coach – refugia are protected areas under rocks, small cave, etc. that are sought out as a place to hide and seek refuge by a vulnerable arthropod that has just molted]

DEATH ASSEMBLAGES, MASS MOLTS OR BREEDING GROUNDS?Displayed in the museum are two incredible mirror-image slabs of Bertie waterlime that contain a half-dozen articulated molts and sundry disarticulated bodyparts. Deceivingly, the two halves are not positive and negative casts of upper and lower members of strata entombing the fossils, but are “part” and “counterpart” slabs with each containing a portion of the preserved eurypterids. This is likely a small section of a windrow.

(Photographed at the R.A. Langheinrich Museum of Paleontology)

One of the many questions surrounding eurypterids is whether large aggregations of molts are reflective of refugia or transportation from a freshwater estuary to a region of hypersaline waterlime for burial. Not surprisingly, other hypotheses exist. Based on fossil remains (which may falsely confer a taphonomic or collection bias), one theory suggests that “breeding grounds” were utilized in mudflats and sandbars for survival protection accounting for the large eurypterid assemblages (“mass molts”) or for ecdysis (“mass molts”) (Braddy, 2001). Mass mortality (“death assemblages”) seems less likely an explanation, since the remains are concentrations of exuviae rather than carcasses (Vrazo, 2011). As mentioned, possibly storms brought exuviae down river into muddy deltaic sediments near and offshore for burial, even additionally mixing with marine biotas (Ciurca, 2010). Horseshoe crabs were transported and preserved in the hypersaline Jurassic lagoons of Solnhoffen (Barthel, 1994).

Amongst the articulated eurypterid molts, notice the disarticulated carapace and the beautifully preserved spinose appendages. The chitinous exoskeletons have a brown color largely due to carbonization. The

original components of the cuticle have undergone in situ polymerization during diagenesis (Gupta, 2007). The prevalence of "ventral-up" specimens is not necessarily an indication of supine-ecdysis (Tollerton,

1997) but may be related to transportation and burial (Tetlie, 2007).(Photographed at the R.A. Langheinrich Museum of Paleontology)

Allan Lang and the massive Pterygotus that he excavated from his quarry

(Photographed at the R.A. Langheinrich Museum of Paleontology)

The following will give you a good feel for how fossils are actually recovered in the field at these Eurypterid sites:

After several feet of overburden consisting of unconsolidated Pleistocene glacial till and topsoil have been removed, heavy earth-moving equipment is used to exhume the underlying Fiddler’s Green Formation. The target is the 1 to 1.5 meter thick, fossil-bearing waterlime of the Phelps Member. The excavated rock face in the photo provides a scale of the excavating operation.

Rather than hack away at the dense dolostone by hand, a laborious and time-consuming process, extracted large blocks are allowed to weather a series of harsh Central New York winters (of which I can testify to having grown up in nearby Syracuse). Assisted by winter’s repetitive freezing and thawing, the rock tends to readily cleave along frost planes that have developed. 

Once the rock has fully weathered, the seasoned waterlime is ready. Notice the two “foreign” boulders of glacial erratic amongst the talus of waterlime. Allan is hard at work doing what he both loves and knows best.

Allan instructs that by aligning a hammer and chisel at the right angle within a frost plane and followed by a lot of pounding the dolostone will split apart. Notice the fine-grained, layered nature of the waterlime’s limy muds.

Finally, a firm, two-handed pull lifts the heavy, newly exfoliated façade and exposes the treasures that have been trapped for over 400 million years. Seeing my enthusiasm, Allan cautioned that typically hundreds of slabs must be split apart in order to find one good eurypterid. Unknowingly, I was about to defy those odds.

Call it beginner’s luck, but on my first attempt I uncovered a massive, foot-long claw from the eurypterid Pterygotus! This was the portion of the claw attached to the head structure, referred to as a fixed ramus, whereas the movable grasping-end is the free ramus. Together they clamp down on the eurypterid’s prey similar to a lobster-claw. Based on the size of the claw, my guess for the Pterygotus was 6-8 feet in length.

Still partially buried within the matrix of the waterlime, the claw’s massive teeth are readily discernible.

 (Modified from an illustration by William L. Parsons, Buffalo Museum of Science)

On my second slab-splitting attempt, I uncovered two small molts of Eurypterus eurypterids. Allan marks noteworthy fossils with yellow chalk. They will eventually be transported down to his lab where they are carefully excised from the matrix of the waterlime, cleaned and professionally prepared with micro-air abrasion, a laborious and skill-requiring process.

Notice the conchoidal fractures in the waterlime that cleaves similar to a broken soda bottle. Allan refers to their appearance as “dishes.” Conchoidal fractures transect more than one bedding plane and often contain eurypterid fossils. In all, we sectioned three or four slabs.

This is a close-up of the newly-exposed veneer of waterlime seen above. Seen from the ventral aspect, two Eurypterus remipes are seeing the light of day for the better part of 415 million years.   

After my rewarding visit to the quarry, we headed back down to the museum. I was anxious to see what surprises Allan had unearthed over the years. Please see my next post Part III – The R.A. Langheinrich Museum of Paleontology.