A few NJ Cretaceous trips

[Pagurus]

You sure do get the most out of each trip. Terrific finds for just three trips! Thanks for posting them.

[non-remanié]

Thanks all.  Its definitely not always this productive.  

[non-remanié]

10 hours ago, Plax said:

am liking the Wenonah matrix. Great material reminiscent of bygone years collecting at Big Brook. Am thinking that "Navesink 1" sequence at BB is Mt Laurel to the south and west. Lithology above the lag is surely Navesink. Not sure what to call formations these days with the sequence updates. Guess we could call them sequences or formations and specify which is being discussed? Or Navesink "formation" (= lithology) is late Campanian and Maastrichtian.

  I didn't know the ammonite fauna from the Navesink Formation in Monmouth County was late Campanian. Learn something new every day!

 

Don,

 

I remembered that the Navesink2 sequence is actually New Egypt/Tinton fm.  But a lot of fairly recent papers do show the Navesink base as Maastrichtian so its hard to say where the disconnect is.   The ammonite fauna, Nostoceras hyatti zone is well calibrated as latest Campanian.  Although some of the ammonites are definitely reworked,  I've collected enough in situ basal Navesink specimens to see that some hyatti zone specimens are definitely not reworked.  Therefore that portion of the Navesink must be Campanian.  It probably is the case that the Navesink you see at Big Brook was extremely slowly deposited and most of it is actually Maastrichtian but all the age diagnostic ammonites only occur in the latest Campanian base.  Only that basal lag might be truly Campanian.  What the basal lag looks like and its thickness varies greatly at different outcrops even within the same creek.  Its pretty clear that nearly all the vertebrate material comes from the base.

[non-remanié]

Joseph,

 

As for the hybodont fin spines, there's a lot of factors to consider.  But basically I think the NJ specimens are too rare, fragmentary and worn to say much about.  Many specimens are reworked and heavily abraded.  This one isn't abraded but is only a fragment so we don't know what the denticles on the trailing edge looked like.   I do think its likely that the tubercules fall off some specimens prior to fossilization.   I believe the same phenomena is common in dermal denticles referred to Brachyrhizodus/ Rhombodus by some.   That would mean the presence or lack of tubercules on specimens is preservational rather than representative of different species.  

[The Jersey Devil]

3 hours ago, non-remanié said:

Joseph,

 

As for the hybodont fin spines, there's a lot of factors to consider.  But basically I think the NJ specimens are too rare, fragmentary and worn to say much about.  Many specimens are reworked and heavily abraded.  This one isn't abraded but is only a fragment so we don't know what the denticles on the trailing edge looked like.   I do think its likely that the tubercules fall off some specimens prior to fossilization.   I believe the same phenomena is common in dermal denticles referred to Brachyrhizodus/ Rhombodus by some.   That would mean the presence or lack of tubercules on specimens is preservational rather than representative of different species.

 

Hello Steve,

That makes sense, although some unworn specimens that have both the leading and trailing edges present seem to have faint tubercles which can't easily be seen, but can be better felt. The striations definitely distinguish the two (or more) spine types. Maybe it has to do with the age or sex of the shark. The fin spines of the first dorsal fin and the second dorsal fin should be very similar, except the one from the second dorsal fin is smaller, so I guess it doesn't have to do with spine position.

 

So both the Wenonah and the basal Navesink are latest Campanian, with the Navesink being just slightly younger?

 

I've also noticed that pretty much all the Serratolamnas that are found in the streams are laterals. Do you possibly know why significantly less anteriors are found?

 

Joseph

[non-remanié]

Yes Joseph there are a fair amount of specimens in which you can feel the faint tubercules somewhat better than see them.  But I think our knowledge of the hybodonts is pretty incomplete to begin with.  The tooth roots almost never are preserved and the tooth design is pretty generic anyway.   There's just a lot of issues that in my opinion need to be clarified better before we can postulate about the spines.   But it is useful to note the differences as you have. 

 

There is still a very significant time gap between the Wenonah ( or even the Mt. Laurel) and the basal Navesink, as much as 2-4my.

 

As for Serratolamna, I could imagine that its more likely for the anteriors to be overlooked.   I don't think they are as pronounced as Serratolamna from the Maastrichtian, like the common NC ones.   I do have some anteriors from the Englishtown fm.  They look similar to the 2 John posted in this old thread.   

 

http://www.thefossilforum.com/index.php?/topic/60487-hypotodus-verticalis

[The Jersey Devil]

On 6/22/2018 at 8:14 PM, non-remanié said:

Yes Joseph there are a fair amount of specimens in which you can feel the faint tubercules somewhat better than see them.  But I think our knowledge of the hybodonts is pretty incomplete to begin with.  The tooth roots almost never are preserved and the tooth design is pretty generic anyway.   There's just a lot of issues that in my opinion need to be clarified better before we can postulate about the spines.   But it is useful to note the differences as you have. 

 

There is still a very significant time gap between the Wenonah ( or even the Mt. Laurel) and the basal Navesink, as much as 2-4my.

 

As for Serratolamna, I could imagine that its more likely for the anteriors to be overlooked.   I don't think they are as pronounced as Serratolamna from the Maastrichtian, like the common NC ones.   I do have some anteriors from the Englishtown fm.  They look similar to the 2 John posted in this old thread.   

 

http://www.thefossilforum.com/index.php?/topic/60487-hypotodus-verticalis

 

So "latest" Campanian does not necessarily refer to the very end of the Campanian at ~72my, but sort of at the end of it. So the Wenonah/Mt. Laurel are approximately 76-74my and the Navesink is around 72my. Thanks for the other info.

[Echinoid]

Wow! Great finds, especially the ratfish

[frankh8147]

Nice stuff Steve, those brooks are really hitting!

[non-remanié]

Joseph, after some back and forth about the larger specimen between Nostoceras mendryki, N. colubriformis and N. pauper, Ralph concluded they both were likely N. pauper.    Ralph also said he believed all the basal Navesink ammonites are reworked from older beds.   This is the most obvious answer to age of the basal  Navesink  discrepancy especially as I already thought this was the case with the vertebrates.    I have collected one hyatti that I might dispute is not reworked, but it may actually be from a small lens of sediment that is older than basal Navesink.