help identifying possible fossil from coastal California

[Kane]

lol. Don't be trying to protect @ynot -I think he might have the right ID!

[Fossildude19]

7 minutes ago, ynot said:

Isn't a tusk just a modified tooth? (Just to save face for Ynot.)

 

Tony

 

You are correct. They are "modified" incisors.  

[Peat Burns]

I don't think walrus tusk has the polygonal structures in the center (secondary dentine).  It's less regular in shape and appearance (at least in mature tusks).  But maybe tooth / tusk of some kind is gaining steam... (although the longitudinal grain reminiscent of wood fiber is perplexing)... the polygonal "cell-like" pattern is also perplexing.  Rudist sounded like a possibility, but I'm not very familiar with their internal structure.

[ynot]

16 minutes ago, Peat Burns said:

walrus tusk has the polygonal structures in the center (secondary de

I think that is a defining structure for walrus dentine.

[Peat Burns]

18 minutes ago, ynot said:

I think that is a defining structure for walrus dentine.

Walrus secondary dentine looks like "marble" or some say "oatmeal" in macroscopic view.  I have a piece of fossil walrus tusk in my collection, and it looks like laminated swirls and is very "punky"

 

Internet image of walrus tusk c.s.

 

Specimen in question

 

Maybe juvenile structure?  But not reminiscent (to me anyway) of mature walrus tusk osteodentine

[Peat Burns]

Here's a picture of my fossil walrus tusk core as verified by @Boesse

 

I've never looked at it under high magnification, though...

[jsones]

I'm way out of my league here, but I just wanted to throw out another possibility.  We've been sending some of these photos around, and another suggestion includes a barnacle -- Tamiosoma gregaria.  [Interestingly, it was once considered a rudist!]

 

Any thoughts about that?

 

I found a few pictures of Tamiosoma here:

 

http://picssr.com/photos/casgeology/page8?nsid=46329675@N02

 

Jackie

[Peat Burns]

32 minutes ago, jsones said:

I'm way out of my league here, but I just wanted to throw out another possibility.  We've been sending some of these photos around, and another suggestion includes a barnacle -- Tamiosoma gregaria.  [Interestingly, it was once considered a rudist!]

 

Any thoughts about that?

 

I found a few pictures of Tamiosoma here:

 

http://picssr.com/photos/casgeology/page8?nsid=46329675@N02

 

Jackie

You might be on to something there.  Here is a thread with a similar object (although lacking pics that show the polygonal structures) that ended up being identified as a barnacle:

 

Cross section of barnacle shell:

[Boesse]

A barnacle piece had crossed my mind but I wasn't sure how to make sense out of it. It's not a walrus tusk, owing to points brought up above.

[jsones]

For reference, here's an example of Tamiosoma gregaria (formerly Balanus gregarius) from:

 

The sessile barnacles (Cirripedia) contained in the collections of the U. S. National museum; including a monograph of the American species, by Henry A. Pilsbry.  1916

[doushantuo]

Very worn Rudist,if you ask me

[ynot]

Oh well, I learned something today!

 

 

[Peat Burns]

23 minutes ago, ynot said:

Oh well, I learned something today!

 

 

Me too.  The next time one of these plant/tooth/coral specimens comes up, I'm going to try to remember to consider rudists and barnacles...  

 

It's amazing what local knowledge and geographic familiarity can contribute to identifying random bits.  

 

Btw.  I need to buy or trade for a rudist.  I have never held one and don't have a single one in my collection. ..

[westcoast]

Tusk. But why has the one on the right got a fossil tree preserved in it? Looks like Tony was right with plant ID as well

[ynot]

8 hours ago, westcoast said:

Tusk. But why has the one on the right got a fossil tree preserved in it? Looks like Tony was right with plant ID as well

I have to bow out on this one.

I think a rudist is the correct answer here (not plant or tusk). 

And it was Al Dente who said it first.

[abyssunder]

I admit that it looks almost like a radiolitid rudist, but not quite that. IMHO, the best way to be certain of what the specimen in question could be, is a medial longitudinal section through it.
Just to be clear, Balanus gregarius is a barnacle, a strange one. It was wrongly identified by Conrad being a rudist (Radiolites). Later Conrad recognised its relationship to the genus Balanus.

 

"
Suborder BALANOMORPHA Pilsbry, 1916
Family BALANIDAE Leach, 1817
Genus Balanus Da Costa, 1778
Subgenus Balanus
Balanus gregarius (Conrad, 1856)

 

Tamiosoma gregaria Conrad, 1856, p. 315; 1857a, p. 72, pi. 4, fig. 18; Gabb, 1869, p. 61, pi. 18, figs. 22a-d; Dall, 1902, p. 5.
Balanus estrellanus Conrad, 1857b, p. 195, pi. 8, fig. 1; 1877, p. 156.
Radiolites gregaria Conrad, 1864, p. 214.
Balanus H. estrellanus Conrad, 1876, p. 273.
Balanus gregarius (Conrad). Pilsbry, 1916, p. 126, pi. 28, figs. 1-3, pi. 29; Zullo, 1964, p. 360; Durham and Addicott, 1965, p. 14, pi. 1, figs. 2, 3, 6, 8 (not pl. 2, figs. 4, 7).
Balanus (Tamiosoma) cf. B. (T.) gregarius (Conrad). Woodring, in Woodring, Stewart, and Richards, 1940, p. 96, pi. 36, figs. 2-5, 8, 9.
Balanus concavus concavus Bronn. Ross, 1962, p. 14, figs. 6, 7.

 

Balanus gregarius, in the broad sense, is a common fossil encountered in Miocene and Pliocene deposits of the San Francisco Bay Area, Salinas Valley, and San Joaquin Valley in California, and in Pliocene rocks at Rosario in Baja California. As indicated by the preceding synonymy, there has been considerable confusion regarding its identification and affinities. Conrad (1856, 1857a, 1864), who originally described B. gregarius from its distinctive vesiculose basis, considered it to be a rudistid pelecypod. Later, Conrad (1876) and Dall (1902) recognized its relationship to the genus Balanus, but did not have the opercular valves available to them. The valves were first described by Woodring, in Woodring et al. (1940), but because the delicate beaks of the terga were missing in the specimens examined, Woodring (op. cit.) was led to conclude that B. gregarius was closely related to B. concavus Bronn. The marked similarity of the scuta of B. gregarius to those of various subspecies of B. concavus was also responsible for Ross' (1962) record of B. concavus concavus on the basis of a scutum from the Pliocene of Rosario, Baja California.
The reassignment of this scutum to B. gregarius is supported by the occurrence in the same deposit (UCMP Loc. 4300) of undoubted B. gregarius whose scuta are identical in form to that figured by Ross (op. cit.).
When well preserved, intact opercular valves of B. gregarius are available, the marked resemblance of this species to the extant Pacific Coast species B. aquila Pilsbry becomes immediately apparent. The resemblance is so great as to suggest that the two species are conspecific (Zullo, 1964), but a more detailed study of fossil populations, their variation, and their comparison with living B. aquila is needed before any conclusions can be drawn." - V. A. Zullo. 1969. THORACIC CIRRIPEDIA OF THE SAN DIEGO FORMATION, SANDIEGO COU NTY , CALIFORN IA. CONTRIBUTIONS IN SCIENCE No. 159.

 

 

[jsones]

Hi, everyone,

 

Thanks so much for working on this identification.  I really appreciate the help!

 

In case it's of interest, I also took a photo from above, looking down at the wider end:

[westcoast]

For some reason that whole section of the thread on rudists was missing for me...but we seem to have gone from solitary to colonial coral to plant then tooth then tusk then rudist with a mention for barnacle.  That usually means rudist is the right answer... 

[Rockwood]

2 hours ago, westcoast said:

  That usually means rudist is the right answer... 

I've toyed with this thought often. In the end is it strictly scientific though ? 

[abyssunder]

I don't think it's a rudist, looks more like the barnacle mentioned above, in a worn condition. Try to compare with the samples from plates 28, 29 of USNM Bulletin 93.

 

 

Also, Balanus gregarius (Conrad, 1856) among other Balanus species is listed in E. C. Wilson, D. E. Bing. 1970. Type specimens of fossil invertebrata in the Los Angeles County Museum of Natural History, exclusive or paleoentomology (CS181).

 

 

[westcoast]

I'm  exhausted but delighted. I'm finally getting this straight in my mind after reading the posts properly.. It's a barnacle that looks like a rudist. I haven't come across Balanus gregarius before and would never have considered cirripede as an option for that specimen. Hats off to TFF.

[Boesse]

The rudist-like shape likely relates to barnacle crowding - we're all used to thinking of barnacles that are "perfect" in shape and sitting on rocks without being crowded; when they get crowded, they cannot grow the foot plate out any further, and instead just grow outward like a tube.

 

For some reason I'm still not satisfied, but now that it's not a walrus, it's a bit out of my wheelhouse.

[jsones]

Thanks so much for including that other plate from Pilsbry 1916.  We've positioned the photo from the plate and the current specimen side-by-side for comparison (see below).

 

Also, I've been doing some research on Tamiosoma (formerly Balanus) gregaria.  They are known for having unusual, elongate bases...and it's thought that the shape might have been an adaptation for living in the mud.  Karen Whittlesey studied Tamiosoma and referred to them as "mudstickers" in her thesis.

 

 

 

 

 

 

[abyssunder]

You are correct, and the best way to see the resemblence is to put them side-by-side (I usually make this). The specimen in question is an elongated one, that's the reason why it looks strange, like a worm or rudist. I'm not sticking at the species B. gregarius , but it can be taken as reference for it's typical and confusing morphology, nicely described in Pilsbry, 1916 (USNM Bul. 93).