Pegaster stichos A Cretaceous California starfish example of Paleo History!!

This week, I am in California on my way to Japan! I am visiting the world-renowned Invertebrate Zoology & Geology department at the California Academy of Sciences in San Francisco! 

I used to work here when I was a grad student at San Francisco State University in the 90s and as such I have a long-standing relationship with colleagues at the museum.

While going through the collections, I encountered a specimen of this awesome classic fossil, the Cretaceous Pegaster stichos, a starfish belonging to the family Stichasteridae described by my former PhD advisor, Dan Blake and Dallas Peterson in 1993 in the Journal of Paleontology. Their specimen is below...

                                
The CAS specimen (CASG 68139)  is also from the Cretaceous of California... (my thanks to Dr. Peter Roopnarine @peterroopnarine and Collection Manager Dr. Jean deMouthe for their help!)

If some of you are "old timer" San Franciscans.. you may even recognize that this fossil was originally on display in the old CAS Life Through Time Exhibit!!
                                
These specimens (and others like them) are powerful pieces of evidence for how the distributional ranges of marine animals has changed over time. 

but first.. just a little introduction so we're all on the same page...

The starfish in question belongs to the Stichasteridae, which is a group of forcipulate starfishes. I wrote about the curious pattern of biogeographically arranged lineages in the family tree of these animals awhile back...

Note the purple arrow below. The Stichasterids are down at the base of the tree. Given that the record of this whole group goes back to the Triassic, the fact that they are still around is pretty cool.

BUT most members of the Stichasteridae in MODERN oceans live mostly in the Southern Hemisphere (shown here by Stichaster australis), usually seen in Australia, New Zealand and/or the cold-temperate part of South America

As I've blogged before, shallow water members of this family are often times convergent with sea stars in a different family, the Asteriidae from intertidal habitats in the Northern Hemisphere..

But most members of the Stichasteridae are absent from the Northern Hemisphere EXCEPT in the deep-sea, such as this Neomorphaster we saw in a 2013 Okeanos Expedition, where they can be surprisingly abundant..

The only other EXCEPTION to this occurrence in the northern hemisphere is from FOSSILS!! 

Behold this awesome specimen of the Cretaceous stichasterid, Pegaster stichos!! 

                                 

So, this shows that at ONE TIME, this group of sea stars lived in the Northern Hemisphere and in the Pacific, perhaps even more widely than was previously known. Note also that in this time period, a good chunk of the west coast of North America was underwater...as well as a good parts of Texas and the south..

From NPR: http://media.npr.org/assets/img/2012/10/09/late-cretaceous_wide-e3fc2fd33eac021deb4b6ac5b4d87cb80d50f9f2.jpg?s=6

For most of us, we think of the Cretaceous as the time of the dinosaurs and other big marine reptiles!

from the NPS National fossil DAY page! 

But MANY a starfish and sea urchin was around during those days...

and sea urchins of course!

What happened to them??  Extinction apparently. Or maybe they just moved into more friendly waters?   Why?? Any number of factors including sea level and/or climate change.

I've have documented instances where sea stars have been indicators of past oceans before. Such as the story of Heliaster, which occurs today in the East Pacific but absent from the tropical Atlantic except as Pliocene (3 million year old) fossils

Where do modern faunas come from? They were here and there.. and sometimes we can see them back then....

Brittle Star Diversity! How many are there and where do they live?

Happy New Year! I'm slowly getting caught up with life and finally have time for something meaty!

So, first for 2014 an overview on brittle star (aka ophiuroid) diversity! How many? Where do they live? I wrote a parallel post for starfish last year. You can see it here. 

As with the article on starfish, this one is based on a recent PLOS One paper which is freely available for download here.  It was written by the three TITANS of brittle stars! Sabine Stohr at the Swedish Museum, Tim O'Hara at the Victoria Museum in Melbourne Australia and Ben Thuy at the University of Göttingen, in Göttingen, Germany. The data from their paper is based on the World Ophiuroidea Database. 

So, one quick bit of clarification. This article is about brittle stars aka ophiuroids. NOT starfish. Starfish are a different (albeit closely related) group of echinoderms. I provided a brief overview of how to tell apart brittle stars from starfish here.   Note however, that you'll often hear people refer to them as "brittle starfish" or some such thing. Nope. "brittle stars" is good and fine.

Note also that some common names refer to different KINDS of ophiuroids. "Brittle stars" tends to refer to the more conventional types of ophiuroids, such as the ones here and like those above.

On the other hand,  "basket stars" tend to be highly branched and with lots of fleshy arms. These sometimes also get called "serpent stars" if they have only 5 arms.

So terminology is pretty straight forward. Brittle stars AND Basket stars are BOTH different types of ophiuroids (technically.. members of the Class Ophiuroidea).

1. How many species of brittle stars are there??

Answer: As of the 2013 paper there were 2,064 recognized species of brittle stars known in the world. I know for a fact that there have been many more described since then. So, by the end of 2014, I'm guessing we will see closer to 2,075 or even 2,090 species!

In terms of species, brittle stars are by far the MOST diverse of all the living echinoderms. Sea stars follow up in 2nd place (n=~1900 species), followed by the sea cucumbers (Holothuroidea, n=~1250), then sea urchins and sand dollars (n=~950 species) and finally, the living crinoids (n=~600 species).

This has never been a big surprise to invertebrate zoologists. Brittle stars live EVERYWHERE. Under rocks, in the mud, on corals, under corals.. even ON JELLYFISH.

2. How many different KINDS of brittle stars are there? 

Fig. from Stohr et al. 

A more accurate question might be "How many families of brittle stars are there?" This basically represents how many kinds of basic body plans or GROUPS of brittle stars are there? A smattering of the different kinds of brittle stars is represented above.

Here is the table from Stohr et al's paper...

There are 270 genera in 16 different families. So, there's a fair diversity of body plans within the Ophiuroidea but not as much as say, in starfish (which have 370 genera broken up into 36 families). So the bulk of diversity in brittle stars appears to be at the species level. That sounds consistent with their apparent overall strategy of diversification into whatever habitat or niche seems to make itself available, given how many places on the marine bottoms they can be found. There's a high number of species that avails itself of ecological niches.

But more on that below...

3 Which groups of brittle stars are the most diverse??


The MOST diverse of brittle star families? The Amphiuridae! An example shown above, courtesy of the wonderous Arthur Anker!  As of 2013, there were 467 accepted species.

Amphiurids are burrowers and diggers. They find their way into mud, sand, any kind of loose sediment that they can shelter in and under. Once dug in, they throw their arms up through the sediment and out into the water to "fish" for organic particles and other food..  As shown here...


Although amphiurid brittle stars vary in size, many of them are tiny, tiny little critters that fit easily into cracks, crevices and nooks in rocks or other underwater habitat. They live EVERYWHERE.

And the 2nd place winnah??? The Ophiuridae, with 344 species

Ophiurids truly are diverse. They live in the deep-sea, in the shallow tropics, and in temperate waters. There's a LOT of them and often times they are very abundant, often comprising a HUGE amount of biomass where they are found.

We know a fair amount about them, but considering how MANY of them there are? WE probably don't know enough. For example, we didn't know until the 1990s that Ophiura (below) could display some rather vicious predatory behavior...



3. Where do brittle stars live?

Stohr and colleagues have very nicely mapped out the number of species by different biogeographic zones around the world. Their breakdown as follows:

831 species! HIGHEST diversity is in the tropical Indo-Pacific. 
400 species! North Pacific! The temperate/cold-water band including North America and Asia.
350 species! The South Pacific-the temperate water zones around Australia, New Zealand and etc.
333 species! The West Atlantic.
319 species! The Indian Ocean! Examples of new species from the Indian Ocean? Here. 
237 species! The North Atlantic
199 species! South Africa
183 species! East Pacific
123 species! Antarctic
120 species! South America
  73 species! Arctic

What's MOST interesting about these? When one looks at the species diversity by depth, the MOST diverse areas? the Indo-Pacific, South and North Pacific?  A significant amount, sometimes more than 50% of the diversity of these faunas is from the deep-sea (>200 meters!).

Tim O'Hara has been working on the zonation and patterns in deep-sea ophiuroids for quite awhile. Here is an example of some of his work...

5. How long have brittle stars been around??


Most sensible scientists would agree that ophiuroids and asteroids diverged at some point in the Paleozoic with modern-looking brittle stars appearing sometime in the mid to late Paleozoic, some 440-485 million years ago or so.  So, yes. Brittle stars have a very old lineage as do most echinoderms. Older than dinosaurs and certainly older than humans.

But most "good" fossils of brittle stars are largely observed in Mesozoic rocks. There are actually quite a lot of brittle star fossils out there but many of them were identified using pretty substandard taxonomy by geologists using out of date identification concepts (long story)..

And so, long story short, only now are we actually assessing fossils and looking at their real significance in the history of marine invertebrates.

Author Ben Thuy for example, has been able to take the skeletal elements from living brittle stars and compare them with fossil skeletal elements, discovering the presence of deep-sea faunas in the Cretaceous and in younger rocks..

For people who appreciate brittle stars, we live in good times. We have three active brittle star workers, including that ever so rare beast... a brittle star paleontologist!   And we now even have a new Japanese worker who specializes on basket and serpent stars

How long will it be until that 2,064 hits 3000?

Starfish Mystery! 3 Oceans,2 Hemispheres,but ONE species?!

Today a post about a NEW paper currently available as advance ONLINE at Marine Biology (yes, there's a paywall) authored by myself and Dave Foltz my colleague (with help from Scott Fatland) at Louisiana State University, and five multi-nationalcollaborators whose role will become clear.

This project originally began because we were studying a relationship between two near-Arctic sea star species. One in the sub-Arctic North Pacific (called Hippasteria spinosa) which occurs widely in Alaska/the Aleutians Islands, Washington, etc.

Hippasteria is a cold-water animal and is important as a predator of deep-sea corals and cnidarians. Here was a blog about some prior species I've worked on...

Image by Davidtodd via Flickr

and Hippasteria phrygiana which lives in the North Atlantic near the Arctic Ocean around the United Kingdom, Norway, off the coast of Massacusetts in North America etc.

Often times, when you see two very similar looking species in far Northern parts, separated by the Arctic Ocean

You can test the relationships between these species using genetics to determine if they are closely related.  Sometimes you can even determine if they are literally the SAME species perhaps separated by time and the history of the region.  Ice bergs and glaciers perhaps??

As it turns out, we found something intriguing...

The more we sampled these 2 species, the more we realized that scientists had assumed that Hippasteria was present from North Pacific to Arctic to North Atlantic.. it turns out no one had ever collected any from the Arctic!! (i.e., nothing in between!)

And to add more to the mystery, there were taxonomic accounts which indicated that there were accounts of the Atlantic species, H. phrygiana in unusual places..namely.. New Zealand!!

We looked at the distribution of this and related species..it turned out that H. phrygiana or species which closely resembled it were present all over the world!

A two-year effort on the part of myself and Dave Foltz was launched!

We managed to obtain samples of Hippasteria from all colleagues over the world!  Our coverage spanned 3 oceans across 2 hemispheres!

• the North Pacific-Aleutian Islands/Alaska
• the South Pacific-Chile, Solomon Islands and New Zealand
• the Kerguelen Islands in the South Indian Ocean (sub Antarctic), 
• the North Atlantic, the North Pacific-Aleutian Islands

We gratefully acknowledge all of the the co-authors and other scientists who helped us obtain the data we used in the paper!

What we found was pretty amazing. It turns out that from all the populations of similar looking Hippasteria around the world?

There was only ONE species.

We extracted tissue and DNA from multiple populations and found that the genetic differences among the many populations found around the world were minute.  SO minute that there was really no reason they should be regarded as separate species..

BUT there was structure. Different populations show SOME natural differences relative to other populations.

The following two diagrams show what's called "haplotype networks" for the two genes that we studied. The size of the circle indicates the sample size, whereas the different colors shows the region and the lines show the connectivity between the regions sampled..

Fig. 2 Network for COI haplotypes

We sampled two genes but I've only shown one network so that you get the idea.  Basically, there ARE population differences between the populations in the North vs. South Pacific vs. the ones in the North Atlantic..

One Species Around the World! 

You can think of this in the same way that human beings show differences (also called heterogeneity) between populations but are all basically considered the same species. In population genetics-its often the amount of difference between isolated populations that mounts up to indicating different species.

There's actually a LOT of animals that belong to only one species that are found all over the world (other than humans that is!)

Usually though, its small species (such as the brittle star Ophiactis) (see here) that get carried everywhere or perhaps things that swim like jellyfish...


BUT this is still kind of unusual. One species that lives on the sea bottom?? From a group of animals not known to be quick travellers or even particularly well travelled?  This species' spread is probably via the marine larvae which were carried via ocean currents...

Widely distributed species often wreak havok with people who describe species (i.e. taxonomists).

Do differences between populations mean many species? Or do they mean one species occurring widely?

In this case-its ONE species. This also has a pretty huge impact on taxonomy. In the old days, many species were identified as new because they were found in new places, or far away from where prior species were known. A lot of the technology to test these relationships was not yet available...

But now that we know,  ALL those species names that fall within the range of our study will be suppressed (via international rules) by the oldest name-Hippasteria phrygiana.  So, for example, the North Pacific Hippasteria spinosa (described in the 20th Century) will now be called H. phrygiana (described in the 19th Century) because they've been shown to effectively be the same.


Another spin- HOW FAST did they Spread Out? and from where?

Further dynamics!

• There was apparently NO gene flow across the Arctic and we couldn't find any records of this species currently present in the Arctic. So, in one sense they took the long way around....
• Modelling studies of the genes showed that the three populations had been diverging with little or no connection  (i.e. gene flow) for the past 50 to 75,000 years (roughly the late Pleistocene when). 
• That means that this species spread out over the world's oceans QUICKLY (not even a million years!) and not that long ago! That in itself is pretty surprising...

• Could the distribution of these animals (originally spread via swimming marine larvae) be affected by glacial (i.e. ice) cover?  

• Although evidence was not concrete-it seems likely that Hippasteria spread out from the Pacific to the Atlantic. 
• This was not a case of spread from human transport. We know this because one of the genes we looked at had changed too much to have occurred in a human time frame.

So there you have it!  A story about a species of starfish living in THREE Oceans! Evolved wide and Quickly!  Not invasive and not an animal that floats around the world as an adult! 

Deep-Sea Brittle Stars Occur in Lateral Bands!!

This week's blog is based on a new paper (here) by Tim O'Hara (Museum Victoria), Ashley Rowden (the New Zealand Institute of Water and Atmosphere) and Nicholas Bax from the Commonwealth Scientiifc and Industrial Research Organisation in Hobart, Australia.

This paper has been making the rounds in the popular media (here) and the blogosphere (and here)...
First, a little bit of background so that everyone can appreciate the story with the same starting point..

Faunas & What is Biogeography?
At some basic level, I think that most people realize that most organisms, including plants and animals, do not occur all around the world at equal levels.

For example- If you are an aquarium hobbyist, you've probably noticed that some fish are "cold" salt whereas others are tropical or "hot" salt. That's because the animals that live at those different temperatures are originally from different specific locations in the world.

You can often find complete "sets" of particular organisms also known as faunas (or floras for plants) specific to these regions.

Thus, the fauna (i.e., the set or assemblage) of animals and plants you find in the cold/temperate water kelp forest (on the left) will be VERY different from those which you find in the tropical-hot water reef habitat on the right.Scientists take this basic definition one step further. There is an active field of study known as biogeography, which seeks to determine the significance of where organisms live.

This includes the evolution/character, structure, and history of how particular groups associated with specific regions came to be distributed in those regions. How do these regions transition into others? What dictates those distributions? These are big questions in biogeography.

Among the scientists who often work in biogeography are specialists called taxonomists who can identify the many different types of organisms present in each specific region. And based on this, they can characterize different biogeographic areas.

So, what does this have to do with the paper again??

Brittle stars are a good model organism for understanding how life is distributed on the sea bottom because they are abundant in the deep-sea and are consistently EVERYWHERE. They live in mud, under rocks, in sponges...some brittle stars even live on EACH other!Because brittle stars are important components of this region..and especially in the deep-sea, their distribution may hold clues to the biogeography, evolution and distribution of all organisms in this area which is ultimately important for marine resource planning and etc.

Enter the considerable talents of Tim O' Hara at the Museum Victoria who is one of the world's foremost experts on brittle stars!
He developed a large data set derived from 295 research expeditions, across an equator to pole sector of the Indian, Pacific and Southern oceans. This literally means identifying thousands of specimens from scientific expeditions, museums, universities and other places where brittle stars are found. The study area covers 1/8 of the globe using data from 24 museums!

Multivariate analyses (i.e., statistical) of this dataset were performed (also by O'Hara and etc.) and they found the following...

1. Brittle star faunas in different depth zones is different.
This includes:

1. A "shelf" zone, from 0-250 meters.
2. A bathyal zone from 250-2000 meters.

(data for below 2000 m apparently was too poorly sampled to yield results) This shows the depth vertically...
This figure (Fig. 1 in their paper) does a much nicer job of showing it on the map... (note the keys to different colors in the lower left hand corner).

(Figure 1 from O'Hara et al., 2011)

Brittle stars from shelf vs. those in bathyal regions are VERY different from one another-Except in the Antarctic where cold water basically forms a homogeneous environment all throughout the shelf-bathyal region.

So far so good. This goes along with what's been known.

Historically, its been thought that the geographical faunas of brittle stars would all be clustered based on ocean basin.. In other words.. different brittle star faunas for different discrete regions in the Indian and Pacific ocean basins. it turns out this was NOT the case...

2. Bathyal (deep-sea) brittle star faunas were observed to occur in latitudinal (i.e., "lateral") BANDS across the Indo-Pacific region!!

(Fig. 2 from O'Hara et al., 2011)

RED for Tropical species, such as this Acanthophiothrix purpurea

(photograph by Julian Finn, Museum Victoria)

GREEN for temperate species, such as this Conocladus australis

(photograph by Julian Finn, Museum Victoria)

and BLUE for POLAR species...such as this Ophiosteira sp.Although the three faunas appear very distinct, they don't show a very clear transition.

The geographical boundaries between the groups was rarely distinct. Many of the species ranges overlap and intergrade (you can see the colors in Fig. 2 blending together in many places).

So, the boundaries were transitional and not sharply, distinct disjunctions between biogeographical regions as was historically assumed.

Unfortunately, there are no clear clues as to what may be the cause of the overall "lateral band" pattern. An evolutionary hypothesis (i.e., a phylogeny) for brittle stars is unavailable and fossil brittle stars of the appropriate age aren't really common..

The authors speculate on possible reasons in this area are distributed in this manner.

1. Water temperature?
2. Primary Productivity? (i.e., food)
3. Oceanographic reasons-current flows, etc. that might affect settlement of the larvae

As much work as this represents, this likely represents only the FIRST step towards understanding the distribution and biogeography of animals such as these in the deep-sea.

Remember also that brittle stars are the MOST diverse group within the Echinodermata, boasting over ~2159 species! How will additional discoveries of fossils?? Or new species? Or developing evolutionary histories?? affect these patterns?

Understanding distributions like this aren't just academic questions, they are also used to help management plans of the ocean for deep-sea mining of oil and gas. Possibly to help develop a network of marine protected areas.

All from the humble brittle star...

Sun Star Stories! The 3 Million Year old Tale of fossil Heliaster from Florida!

(photo by Tom Niesen, San Francisco State University)

Today! A little lesson in Geology and how ONE species of starfish can tell you something cool about 3 million years of evolution! Details are from this paper by Douglas Jones and Roger Portell at the Florida Museum of Natural History.

The subject of our story, is a multi-armed starfish, Heliaster microbrachius whose living members are found in the East Pacific (South & Central America).
In fact, Heliaster is part of a species complex (a cluster of closely related species present in a discrete geographic range) throughout this region and different variable body forms can be encountered on the Pacific side from Mexico to Central America to Chile. Effectively, Heliaster is ONLY found in this part of the world.

That is, until they found a fossil one in Florida!

(Fig. 4 from Jones & Portell)

The fossil below was found in fossil deposits from the Pliocene (about 2.2-2.5 Mya) of Florida!

Most fossil starfish break apart and wash away after they've died..but these have pretty heavily armored bodies and were likely buried quickly and so, preserved well as fossils.

(Figure 1 from Jones & Portell, 1988)

Here are some photos from the oral surface (the underside) of a living Heliaster for comparison...

...with the surface of the fossil! The details are amazingly well preserved! Its not often you can identify a fossil starfish to species with confidence.

The specimens (apparently over 360 were collected) were exceptionally well preserved, so well preserved they were able to positively identify it as Heliaster microbrachius, a species that continues to be around even today.

That would mean that this species at one time, woudl have lived from Florida ALL the way to Mexico/Central America and along the "Pacific" coast!!

WHAT? But how does THAT make sense? For something from the PACIFIC to be found SO FAR away from where the living ones are found?? How did that happen?

To understand this little mystery..let's learn a little interesting geology about Central America...

North and South America are connected by a narrow strip of land called the Isthmus of Panama.

(from Wikipedia)

But the Panamanian isthmus was NOT ALWAYS THERE. and that's important to know.

Its formation is considered by some to be one of the most important geological events of the last 60 million years, in part because its formation, triggered glaciation in the Arctic-among other reasons which I'll outline below.

Here is a series of great geological maps with arrows showing currents from the Woods Hole Oceanographic Institution website, which shows the geological and current history of this area.

So, about 10 Million Years Ago (well AFTER the time of dinosaurs, and well into the time of mammals-Click here to see examples of Miocene mammals) there was NO "Isthmus of Panama".

(from the WHOI website)

It was essentially an OPEN channel, called the Central American Seaway through which an ocean current traveled connecting the "Atlantic" with the Pacific Ocean. Bear in mind, that also means that there was LIFE here. And it was connected ACROSS the Central American Seaway.

(from the WHOI website)

Over time, tectonics triggered uplift and formation of the isthmus-effectively BLOCKING currents from flowing through the seaway that had been there before.

This blockage essentially CREATED the modern day Gulf Stream and led to glaciation of the Arctic. You can see the complete story at the WHOI website..but the current flow below shows this very nicely...

(from the WHOI website)

The formation of the isthmus created a land bridge for terrestrial animals, birds, plants, and etc.. setting up the Great American Interchange as outlined below....

(from Wikipedia!)

But a bridge for the land-critters is a BARRIER for marine organisms.
Based on the fossil deposits (2.2-2.5 million years) and the age of the land bridge, the authors bracket the age of the Heliaster fossil at about 2.5-3.5 Million years ago.. suggesting that it might have been present well AFTER the land bridge sealed off the populations between the Pacific and Atlantic.

There is a fairly sizeable fauna of mollusks and other invertebrates that are also found as part of the fossil deposit where this species was found. These all point towards continuity BETWEEN the populations in the "East Pacific" (Mexico, Central America, etc.) and Florida about 2-3 million years ago.

(from Wikipedia!)

The isolation between Pacific and Atlantic would have led to NUMEROUS changes in salinity, water temperature among any number of other factors that might have resulted in the dieoffs of these faunas.

The currents changed and not only does the environment change but the water's nutrient flow and so on.

(from the WHOI website)

So, the land bridge formation was a kind of "starfish natural disaster" of sorts- as it cut off this small population of this species from the rest..and the subsequent changes in the marine environment likely led to their localized extinction.

(Figure 1 from Jones & Portell, 1988)

Interestingly, there are still quite a few species that persisted AFTER the isthmus was formed and the barrier was formed by the land bridge...but that is a story for another day...

(from Wikipedia..)