Wednesday, June 24, 2015

Search Challenge (6/24/15): A couple of fishy questions...

Once in a while I go diving... 

... being a curious sort of fellow, I sometimes find fairly remarkable things.  

And being a SearchResearcher, I wonder about these things I find.  

Not long ago a friend of mine took this photo of me on a dive, hanging onto the rail of a wreck at 50 feet. 

As you can see by my terrified expression, I'm not especially worried about this guy (even though it's somewhat larger than I am). 

I did a bit of research about these sharks (before I got into the water, I should add) so I knew what to expect.  

Along the way, I learned a few additional things about other kinds of fish that I want to pose as Search Challenges.  

So today's Challenges are: 

1.  What kind of shark is right in front of me?  Am I crazy?  Should I be worried about this apex predator?  (If you don't have enough information from this photo, here's another.   Do you have enough information now to figure it out?)  By the way, please don't tell my mother about this... 

2.  Speaking of kinds of sharks, one of the strangest sharks in the ocean today seems to be a holdover from the Cretaceous period.  What kind of shark is that?  Just from that description, can you figure out the genus and species? 

3.  While we're on the subject of large marine predators, I remember reading that there was an order of now-extinct marine reptiles that dominated the seas during  late Triassic and the Jurassic periods.  These giant predators were warm-blooded, and sometimes suffered from the problems of coming up too fast from the briny deep.  What kind of animals were these?  And how do we know they suffered from too rapid ascents?  

4.  If you're really into the topic, for extra credit, in the picture above why does this shark's eye seem to have a white crescent moon in it?  (No, it's not a cataract, nor is he bug-eyed.)  It's a normal sharky thing.  But what's that white thing called?  

As always, be sure to tell us HOW you found out the answer to the Challenge.  We all want to learn from your brilliant search behavior!  

Search on... with sharks!  


  1. Good day, Dr. Russell, fellow SearchResearchers


    [shark eye white part]

    How do sharks see, smell and hear? Has an image of shark eye parts and answers to Challenge questions.

    [nictitating membrane shark]
    [shark nictitating membrane shape]

    Shark senses

    [sharks without nictitating membrane]

    ...the Great White has black eyes in scary pictures, not because it is scary, but because its eyes are rolled back and at that moment, they cannot see.

    Close-up of the eye of a blue shark, showing the nictitating membrane

    [shark identification]

    Shark identification factsheet.

    White shark guide. PDf

    [carcharodon carcharias dangerous]

    Great White Shark (Carcharodon carcharias) Danger. Only if feels attacked or if confuses you with a seal. Yes, could be dangerous.


    1. What kind of shark is right in front of me?
    A. Carcharodon carcharias, White Shark.

    Taxon White Shark
    Kingdom Animalia
    Phylum Chordata
    Class Chondrichthyes
    Order Lamniformes
    Family Lamnidae
    Genus Carcharodon
    Species carcharias


    4. why does this shark's eye seem to have a white crescent moon in it?what's that white thing called?
    A: Some sharks have a third lid known as a nictitating membrane, which will fully protect the eye. Sharks that don't have this feature, such as the great white and the whale shark, roll their entire eyes into the back of their head, giving them a white-eyed look.

    Be right back with Q2 and 3.

  2. a variety of activity…at the Twin Sisters site? or another boat?
    example: Willaurie
    "…Timid and skittish, the blacktip reef shark is difficult to approach and seldom poses a danger to humans unless roused by food. However, people wading through shallow water are at risk of having their legs mistakenly bitten."
    not Caribbean roamers?
    or is it - sans 'reef' - which seems to inhabit the Caribbean Basin waters…?
    "Normally wary of humans, blacktip sharks can become aggressive in the presence of food and have been responsible for a number of attacks on people. "
    (worked off the name on the wet suit rental…'Dan-with-shark-Bahamas-May-2010')
    there be Tigers too - the year before, Stuart Cove's Dive
    a cousin of C. megalodon
    C. megalodon info
    "The blacktip reef shark (Carcharhinus melanopterus) is a species of requiem shark, in the family Carcharhinidae, easily identified by the prominent black tips on its fins (especially on the first dorsal fin and its caudal fin)."
    eye structure
    Tiger example
    Requiem sharks
    different from the nictitating membrane
    Great White eye - not for squeamish, but there is a ballet quality at the end…
    warm blooded/cold blooded
    … diving in the Sea of Curiosity… you don't own stock in the Discovery Channel do you?

  3. Question 2 and 3

    [cretaceous period sharks related today]

    Frilled Shark

    [Frilled Shark]

    Results shows videos, Wikipedia, and links. Also learned about: Extant taxon

    It looks like something out of "Alien" but has more in common with "Jurassic Park." Video

    [Frilled Shark genus]

    Chlamydoselachus anguineus is the only living species in the Family Chlamydoselachidae.

    [frilled shark first discovered]

    First recognized between 1879 and 1881.

    2. Speaking of kinds of sharks, one of the strangest sharks in the ocean today seems to be a holdover from the Cretaceous period. What kind of shark is that? Just from that description, can you figure out the genus and species?
    A: Frilled Shark. Genus:Chlamydoselachus. Species:C. anguineus

    Q3. First, read what "Briny deep" meant.

    [Triassic Jurassic periods sea predators warm-blooded quick ascent issues]

    Ichthyosaur? in wikipedia Ctrl-F # ascend, and Jurasic and others check.


    In wikipedia "Ichthyosaurs" says: They were particularly abundant in the later Triassic and early Jurassic Period, until they were replaced as the top aquatic predators by another marine reptilian group, the Plesiosauria, in the later Jurassic and Cretaceous Period. In the Late Cretaceous ichthyosaurs became extinct for unknown reasons.

    3.I remember reading that there was an order of now-extinct marine reptiles that dominated the seas during late Triassic and the Jurassic periods. These giant predators were warm-blooded, and sometimes suffered from the problems of coming up too fast from the briny deep. What kind of animals were these? And how do we know they suffered from too rapid ascents?
    A. Need to search more.

  4. Replies
    1. Great memory, Remmij! and excellent findings.

      Now, I will visit your links. I am sure, new knowledge and fun will come.

      I was reading about Hippos. [Hippo dangerous] and found: "The bite of a three-meter-long great white shark pushes four tons of pressure through every square centimeter of tooth."

      Then, this morning [ Shark word origin] Etimology

    2. Many times, life appears to give us much more about what we are reading and looking. And once again this is the case. Of course, maybe if time was different, I wouldn't read it because Ichthyosaur's story are new for me. In any case, here is the link. 'Ghost image' shows how ichthyosaur ruled the seas

    3. Wow, Remmij, I'm impressed. I didn't remember using that photo before!

  5. Post #2
    Responses from Reddit/Scuba “Looks like a regular reef shark to me judging by the eyes, snout, body shape” and suggested link. I would agree that they do look the same as the image in this challenge.

    I just saw Remjii’s response (very clever) referring back to the June 2014 image posted. However this link would suggest to me that the shark might not be a black-tip because as stated in this link (very similar but slight difference in anal fin)
    “Blacktip (C. limbatus ): The blacktip shark has a pale white anal fin, unlike the dusky colored anal fin of the Caribbean reef shark .” They are obviously very similar in appearance. Here’s the page on the black-tip reef shark

    1. thorough and reasoned analysis, as always, Rosemary… Dan is diabolical in his ability to prompt esoteric discussions - I never imagined I would be reading
      about the chromatic parameters of anal fins, dusky, black spotted, or otherwise, as a means to identify carcharhinus varieties and yet…
      but then I never thought I would have to search the meaning of a one frame comic either…
      or one frame, six words…
      For Sale: Baby-sized saddle, bobcat
      Hemingway (also did battle with sharks & other fish off Cuba)

      that aside, you make a good case for the shark type… looked at your "Numerous Caribbean reef sharks attracted to a bait ball." photo
      and was attracted to the adjacent Wiki photo because it seemed to have a similar railing to what Dan had in his photos…
      and, indeed, it was from Stuart Cove's — with similar sharks identified as Caribbean Reef sharks feeding.
      Saw that there was source info, so followed that and found numerous photos of the area and
      all sharks being IDed as Caribbean Reef sharks… thought it was interesting Joi opted for the bite resistant chain mail shark suit - Dan's Mum might agree with that.
      Joi feeding, full size
      also see:
      flickr/Joi/Stuart Cove's
      Joi feeding, note eye — and how they line up for the buffet
      Joi Ito, cam & helmet - again, Dan's Mom might endorse the sea helmet noggin protection…
      with all that, I'm willing to go with your CRS ID until the ground… ummm water truth is dispensed by DrD
      hopefully, Dan was able to get some of these Yellowtail Snappers away from los tiburones and produce some most excellent fish tacos…

      even thought Black Tips, Caribbean Black Tip Reef?, Bulls, Tigers, Spinners, etc.: even GWs all cruise the basin. MaryLee on twitter
      ML site
      Katharine and Betsy
      and then there's always Bruce

      btw, still on an art kick… the Metropolitan seems to confirm Dan in Havana… in the late 1700s…
      Thomas J. Watson Library - Metropolitan Museum of Art
      Kahn Academy
      detail, blood in the water - Chrome?

  6. Post #3 Second question-
    Query [“cretaceous period” sharks]

    “Cretaceous (144-65 million years ago)... The Ischyrhiza was an ancestor” And at Wikipedia we find “Ischyrhiza is an extinct genus of cartilaginous fish from the Cretaceous and Paleogene belonging to the primitive Batoidea family Sclerorhynchidae.”

  7. My Post #1 went astray - here's my google docs shared link

    1. # 4 now is lost I think in the internet black hole - but no matter, here it is again.

      Post #4

      Question 3 - Query [dinosaur got the bends] I chose this term because earlier I saw articles that referred to the water species as dinosaurs.

      “Ichthyosaurs from the late Jurassic and Cretaceous suffered the bends, says Bruce Rothschild at the University of Kansas in Lawrence, but it was not clear if their Triassic predecessors did too.

      Analysing thousands of ichthyosaur fossils from all three periods, Rothschild and his team found that virtually none from the Triassic got the bends, compared with 15 to 20 per cent for the later periods.”

      With these comments I am not sure we can say Ichthyosaurs got the bends in the Triassic period. The article was in 2012 so I’ll look to see if anything more has been written up since that time.

    2. To determine if more uptodate information could be found on whether or not Ichthyosaurs (fish lizards) during the Triassic period in fact did get the bends, I chose to stay focused on Bruce Rothschild of U of Kansas. I found he has been quoted many times regarding the Ichthyosaurs. I haven’t found any update from him since 2012.

      This site has an interesting write-up that appears to come from “Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.”

      It is apparent that opinions differ but here we see a specific mention of “Triassic Ichthyosaurs” so I believe they existed in that period however interesting to note differing opinions on the subject of their demise.

      “Ichthyosaur fossils also show the animals were prone to the decompression sickness commonly referred to as the "Bends". Triassic Ichthyosaurs show no signs of such trauma, while later species from the Jurassic and Cretaceous show decompression sickness in many specimens. This may be due to the appearance of large predators such as large sharks during these later periods that forced ichthyosaurs into making emergency trips to the surface. The inability of Ichthyosaurs to handle such trauma from emergency surfacing is hypothesized by John Haymond, Bruce Rothschild et al to have helped contributed to their extinction, though opinions differ on why.”

  8. First I looked at the exif data and again nothing. What do you have against exif data? ;-)

    Noticed the name on the dive suit [ stuart cove ] and found the web page for a service offering shark experiences. I watched the video for the shark feeding and the narrator mentions caribbean reef sharks. Since your picture shows a wreck, I watched the video for wreck dives. In that video the narrator mentions grey reef sharks. Looking at the grey reef sharks, I determined they weren't grey reef sharks as there habitat is not in the Caribbean.

    1. Caribbean reef shark. Yes you are crazy. You should be aware and on your guard, but they don't normally attack humans. "Hi. Mrs. Russell? Do you know what your son did?"

    2. Frill Shark. Got an image from searching [ shark Cretaceous today ]. Genus: Chlamydoselachus Species: C. anguineus from Wikipedia.

    3. Searched [ late Triassic and the Jurassic periods marine "bends" ] I had to put bends in quotes to eliminate results with bend.
    Answer - ichthyosaurs. They found "bone lesions from a disease called dysbaric osteonecrosis, or DON" on the bones similar to those caused by the bends in humans.

    4. nictitating membrane by searching [ sharks eye covering ]

    Search path -

    1. May be a repost - Fred Your observation of the name on the wetsuit. Well Done! Dr. Dan has taught us well. With Remmij's find of the photo & your observation it looks like everyone is really on their game. Nice post.

    2. I was wondering how long it would take the SRS crew to notice that! ;-) Nice job, Fred!

  9. Nicely done, Fred as RRR says!

    [marine predators decompression sickness ]

    Mechanics and Physiology of Animal Swimming. By Linda Maddock, Q. Bone, Jeremy M. V. Rayner, Marine Biological Association of the United Kingdom, Society for Experimental Biology (Great Britain)

    Decompression syndrome in plesiosaurs

    [marine predators decompression sickness jurassic period]

    Additionally examination of the joints of Ophthalmosaurus has revealed damage to the bones caused by decompression sickness‭ (‬better known as‭ ‘‬the bends‭’)‬.‭ ‬This is where the body moves‭ ‬from‭ ‬higher to lower pressure levels faster than the body can adjust which causes gases that are dissolved in the blood stream to be released.‭ ‬This indicates that Ophthalmosaurus would have had to dive very deep in order for it to be able to sustain these kinds of injuries.

    But this article says:
    Dinosaurs-like creatures may have injured themselves during leisurely deep-sea diving trips and not from resurfacing too quickly, as previously thought.

    [bends jurassic creatures]

    Fleeing from these predators — in particular, sharks — might have forced ichthyosaurs to make emergency trips to the surface, causing the bends, the researchers saidAnother researcher: he suggests, might have gotten the bends if herded into and trapped in shallow water by predators. Article continues, While whales and dolphins developed systems that permitted them to excrete excess nitrogen and avoid decompression sickness, ichthyosaurs seem to have become extinct before doing the same. The bends probably caused painful symptoms for the reptiles, the researchers say, and impaired their ability to find food and flee predators.

    1. nice searching on decompression Ramón - got me wondering about other current animals - penguins, turtles, whales, seals and the like…
      you might be interested in glancing at these… easy to forget how complicated a simple breath is…

      good BBC piece… still much unknown
      decompression sickness, diving not required
      Dysbarism dissolved gas
      Caisson disease
      scarred bones and the Bends - even working as a bricklayer…
      an example of the impact

    2. Good Morning, Remmij. Thanks for your links. As you said, breathing is not so easy. And the information you shared is very interesting. I am still on link 2 (BBC) I found interesting links to read in your links so lots of reading.

      Nice cat photo :)

  10. 1 What kind of shark is right in front of me?

    [how to identify sharks by their fins] NOAA at work here.

    Careful analysis suggests this is Bull Shark.,-part-1/bull-shark

    I think this confirms it. The bull shark has relatively large eyes and black markings on the underside of the pectoral fins. The first dorsal fin is broad and slightly curved at the tip and the anal fin notch forms an obtuse angle... bull shark, which is found inshore,

    However, a grandson, a Shark Week aficionado tells me its a reef shark, a grey reef shark.

    Bull sharks are dangerous says Jonathon Bird of Blue World. If so, this could be why your mother shouldn't know of this venture. Reef shark, not so much.

    [5 gill] finds Shark Week video and answers next question in the first vid

    2 Speaking of kinds of sharks, one of the strangest sharks in the ocean today seems to be a holdover from the Cretaceous period. What kind of shark is that? Just from that description, can you figure out the genus and species?

    Shark Week video right off the top says sixgill is the type you are after here. adds useful stuff

    Hexanchus griseus

    3 What kind of animals were these? And how do we know they suffered from too rapid ascents?

    I guessed mosasuars/elasmosaurs and used this along with rapid ascent and found

    "Microscopic evidence found by Martin and Rothschild in the fossilized bones of mosasaurs indicates that they were susceptible to decompression sickness (also known as 'the bends'), a condition caused by the formation and expansion of nitrogen bubbles in the blood and tissues during a rapid ascent from a deep dive."

    Confirmed by Fossil Behavior Compendium By Arthur J. Boucot, George O. Poinar, Jr. mention this but point out that the evidence Martin and Rothschild present

    "can be caused by other means." [google Books]

    4 why does this shark's eye seem to have a white crescent moon in it?

    Wikipedia shark

    To protect their eyes some species have nictitating membranes. This membrane covers the eyes while hunting and when the shark is being attacked.

    or it may be eyelid for the same reason but it does not come right across the eye.

    But after some study I think its the 'carpet of light' the tapetum lucidum It will show as brightness around the pupil.

    The aforementioned aficionado says its the nictating membrane

    jon tU

  11. very rare Sinatra reef shark @ Stuart Cove's…
    ol blue eyes
    the dive audio