Bradley Flynn Posted July 12, 2020 Share Posted July 12, 2020 So I need help with these two specimens. The triangular fossil is in a grey brittle matrix, the other is in a harder matrix. Link to comment Share on other sites More sharing options...
Bradley Flynn Posted July 12, 2020 Author Share Posted July 12, 2020 Link to comment Share on other sites More sharing options...
Bradley Flynn Posted July 12, 2020 Author Share Posted July 12, 2020 Link to comment Share on other sites More sharing options...
Bradley Flynn Posted July 12, 2020 Author Share Posted July 12, 2020 Salter, J.W. 1856. Description of Palaeozoic Crustacea and Radiata from South Africa. Transactions of the Geological Society of London (Series 2) 7(4):215-229 PDF LINK Quote Thanks @piranha Link to comment Share on other sites More sharing options...
I_gotta_rock Posted July 12, 2020 Share Posted July 12, 2020 I think you got it on the shell fossil. The other one looks like a trilobite hash plate. I refuse to give up my childish wonder at the world. Link to comment Share on other sites More sharing options...
piranha Posted July 12, 2020 Share Posted July 12, 2020 1 hour ago, Bradley Flynn said: Salter, J.W. 1856. Description of Palaeozoic Crustacea and Radiata from South Africa. Transactions of the Geological Society of London (Series 2) 7(4):215-229 PDF LINK Quote Thanks @piranha When you copied the post the ID was inadvertently omitted: Burmeisteria herscheli: rostral plate Always glad to assist! 2 Link to comment Share on other sites More sharing options...
Mark Kmiecik Posted July 12, 2020 Share Posted July 12, 2020 FYI -- Triangles have three sides, not four. Mark. Fossil hunting is easy -- they don't run away when you shoot at them! Link to comment Share on other sites More sharing options...
piranha Posted July 12, 2020 Share Posted July 12, 2020 27 minutes ago, Mark Kmiecik said: FYI -- Triangles have three sides, not four. FYI: "The rostral plate is triangular, varying from equilateral to distinctly longer (sag.) than wide, and bears a prominent, hooked, beak-like, median spine." Cooper, M.R. 1982 A Revision of the Devonian (Emsian-Eifelian) Trilobita from the Bokkeveld Group of South Africa. Annals of the South African Museum, 89(1):1-174 PDF LINK 1 Link to comment Share on other sites More sharing options...
Mark Kmiecik Posted July 13, 2020 Share Posted July 13, 2020 Sorry, I'm having some difficulty seeing this shape as a triangle. Mark. Fossil hunting is easy -- they don't run away when you shoot at them! Link to comment Share on other sites More sharing options...
Bradley Flynn Posted July 13, 2020 Author Share Posted July 13, 2020 @Mark Kmiecik I agree that the shape is a quadrilateral, in this image. The two shorter sides that meet at the point are elevated and taper slightly up to the point, giving it a quadrilateral look. If I tilt the rock it takes on a more triangular shape. Hope this makes sense. Link to comment Share on other sites More sharing options...
JohnJ Posted July 13, 2020 Share Posted July 13, 2020 2 hours ago, Mark Kmiecik said: Sorry, I'm having some difficulty seeing this shape as a triangle. "Triangular" is used as a descriptive term meaning it is similar to a triangle...not precisely a triangle. The human mind has the ability to believe anything is true. - JJ Link to comment Share on other sites More sharing options...
piranha Posted July 13, 2020 Share Posted July 13, 2020 1 hour ago, Mark Kmiecik said: Sorry, I'm having some difficulty seeing this shape as a triangle. Obviously this is not an exact triangle, but you're missing the point. Descriptions of morphological features are not always amenable to perfect geometric comparison. Accordingly, the formal description is attempting to convey the overall shape is triangular with a "prominent, hooked, beak-like, median spine". And the OP is certainly on the right track, regardless if the rostral plate does not meet the textbook definition of a triangle. Link to comment Share on other sites More sharing options...
Mark Kmiecik Posted July 13, 2020 Share Posted July 13, 2020 15 minutes ago, piranha said: Obviously this is not an exact triangle, but you're missing the point. Descriptions of morphological features are not always amenable to perfect geometric comparison. Is there something about the word "quadrilateral" that is difficult to understand? Perhaps Cooper could have been more precise in describing it. Imagine someone who has to rely solely on the description, like a blind person, to understand it's shape. The word triangular would be quite misleading. A pentagon is not a trapezoid with a bent base, and one would not expect it to be described as such. Mark. Fossil hunting is easy -- they don't run away when you shoot at them! Link to comment Share on other sites More sharing options...
JohnJ Posted July 13, 2020 Share Posted July 13, 2020 Since the author described it as "varying", his description was precise regarding the different ways it is found. The human mind has the ability to believe anything is true. - JJ Link to comment Share on other sites More sharing options...
piranha Posted July 13, 2020 Share Posted July 13, 2020 39 minutes ago, Mark Kmiecik said: Is there something about the word "quadrilateral" that is difficult to understand? Perhaps Cooper could have been more precise in describing it. Imagine someone who has to rely solely on the description, like a blind person, to understand it's shape. The word triangular would be quite misleading. A pentagon is not a trapezoid with a bent base, and one would not expect it to be described as such. Please read more carefully and check the cited reference. Only the OP used the term 'quadrilateral' in an attempt to clarify its appearance at different viewing angles. Cooper however, was very clear in his description which I quoted verbatim above: "The rostral plate is triangular, varying from equilateral to distinctly longer (sag.) than wide, and bears a prominent, hooked, beak-like, median spine." Link to comment Share on other sites More sharing options...
Mark Kmiecik Posted July 13, 2020 Share Posted July 13, 2020 12 minutes ago, piranha said: Please read more carefully and check the cited reference. Only the OP used the term 'quadrilateral' in an attempt to clarify its appearance at different viewing angles. Cooper however, was very clear in his description which I quoted verbatim above: "The rostral plate is triangular, varying from equilateral to distinctly longer (sag.) than wide, and bears a prominent, hooked, beak-like, median spine." So you're saying the OP was sharp enough to notice that it is a quadrilateral but Cooper wasn't. Got it. Why did you make the word "equilateral" bold and underline it? How is the length of the sides relevant to the difference between a triangle and a quadrilateral? Mark. Fossil hunting is easy -- they don't run away when you shoot at them! Link to comment Share on other sites More sharing options...
piranha Posted July 13, 2020 Share Posted July 13, 2020 Just now, Mark Kmiecik said: So you're saying the OP was sharp enough to notice that it is a quadrilateral but Cooper wasn't. Got it. The OP meant when viewed at an oblique angle it looks quadrilateral. I am 100% confident that Cooper has the matter well sorted. I have exhausted all my best efforts to assist with an explanation. Good luck! Link to comment Share on other sites More sharing options...
Mark Kmiecik Posted July 13, 2020 Share Posted July 13, 2020 4 minutes ago, piranha said: The OP meant when viewed at an oblique angle it looks quadrilateral. I am 100% confident that Cooper has the matter well sorted. I have exhausted all my best efforts to assist with an explanation. Good luck! I wasn't looking for an explanation. I merely made an observation and stated it. Your observation and opinion may vary and I have no issue with that. I fully respect your right to your own. I'm on your side(s). Mark. Fossil hunting is easy -- they don't run away when you shoot at them! Link to comment Share on other sites More sharing options...
piranha Posted July 13, 2020 Share Posted July 13, 2020 After all the back and forth about what triangular means in this context, a recent paper by Rustán et al. 2020 substantiates the formal description of Cooper: The rostral plate of Burmeisteria herscheli is triangular with a median anteroventral spine-like process. And just for good measure ... Salter 1856 to bring it full circle: "This apiculus is the tubercle upon the hypostome or rostral shield, —the latter being conspicuous in this species as a triangular large plate beneath the front margin (fig. 2)." Salter, J.W. 1856. Description of Palaeozoic Crustacea and Radiata from South Africa. Transactions of the Geological Society of London (Series 2) 7(4):215-229 PDF LINK figures from: Rustán, J.J., Waisfeld, B.G., Vaccari, N.E. 2020 The Homalonotid Trilobite Burmeisteria Salter, 1865 in the Lower Devonian of Argentina: New Data in the Context of Southwestern Gondwana. Journal of Paleontology, 94(3):498-512 PDF LINK 1 Link to comment Share on other sites More sharing options...
Bradley Flynn Posted July 14, 2020 Author Share Posted July 14, 2020 Thanks everyone! Link to comment Share on other sites More sharing options...
Bradley Flynn Posted July 14, 2020 Author Share Posted July 14, 2020 Just went through this post again, it's very informative Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now