Dentalium mcganna, 2019

Charles L. Powell, Ii, Clites, Erica C. & Poust, Ashley W., 2019, Miocene marine macropaleontology of the fourth bore Caldecott Tunnel excavation, Berkeley Hills, Oakland, California, USA, PaleoBios 36, pp. 1-34 : 15-17

publication ID	https://doi.org/ 10.5070/P9361044567
publication LSID	lsid:zoobank.org:pub:EFED8DE6-E976-43A5-BD7B-F478EF0B6FF9
persistent identifier	https://treatment.plazi.org/id/7A6D87C5-FFC8-1E02-7A11-4F8EFD41F810
treatment provided by	Felipe
scientific name	Dentalium mcganna
status	sp. nov.

Treatment

DENTALIUM ( FISSIDENTALIUM ?) MCGANNA POWELL, CLITES, AND POUST N. SP.

FIGS. 27-30 View Figure 27 View Figure 28 View Figure 29 View Figure 30

Diagnosis —The coarse radial and moderate to fine concentric sculpture forming a checkerboard pattern both high on the sculpture and low between the radial and concentric sculpture is distinctive to this species, as is large size. The pattern can vary along the length of the shell and radial sculpture can be difficult or impossible to see on casts.

Holotype — UCMP 251012 View Materials .

Paratypes — UCMP sp. nos. 14436, 218713, 218799, 412728 .

Referred Specimens —Caldecott Tunnel locality UCMP IP13001: UCMP sp. nos. 251010, 410431, 412779; Caldecott Tunnel locality UCMP IP13003: UCMP sp. nos. 218690, 218701, 218712, 218719, 218729, 218730, 218801, 218829, 251018, 251024, 251032, 410426, 410925; Caldecott Tunnel locality UCMP IP13004: UCMP sp. nos. 218803, 410434, 410435, 412731, 410438. See Appendix 3 for details.

Type Locality — UCMP IP13003: Caldecott Fourth Bore, Sobrante first shale, specimens collected from the “First shale” of the Sobrante Formation as described by Page (1950). Note that contractors were not allowed to enter the tunnel, so this designation as “First shale” of the Sobrante is approximate.

Other occurrences — Known from the Tsm and possibly Claremont Formation exposed at or near the west side of the Caldecott Tunnel’s fourth boring, Berkeley Hills , Oakland , California. Specimens were recovered from spot collecting and talus piles attributed to Tsm based on the position of the excavator near the west end of the boring and the dark to medium gray fine grained rocks the fossils were preserved in. One specimen ( UCMP 412728 View Materials ) is preserved in medium sand and is questionably attributed to the Claremont shale .

In addition to the Caldecott Tunnel material a single specimen from the Gallaway Formation (=Gallaway Beds of the Mendocino coast of Weaver (1944) fide Addicott, 1967; UCMP locality D7149) collected near Point Arena, Mendocino County, northern California present in the UCMP collection and reported on by Phillips et al. (1976). Phillips et al. (1976) using benthic foraminifers determined an age of Zemorrian California provincial benthic foraminiferal stage age (33.5–22 Ma; GeoWhen Database, http://www.stratigraphy.org/bak/geowhen/ stages/Zemorrian.html, visited 7/2018), while W. Addicott (in Phillips et al., 1976, p. 148) indicated a “Vaqueros” California provincial molluscan stage age (32.6–19.5 Ma; Smith 1991) for these outcrops, slightly older than either the Tsm unnamed glauconitic mudstone or Claremont Formation in the Berkeley Hills. This specimen ( UCMP 14436 View Materials ) is included here as a paratype of D. mcganna ( Fig. 30 View Figure 30 ) and extends the geographic and age range of this new species from Contra Costa County to Mendocino County and from middle Miocene back to the early Miocene .

Etymology —This species is named in honor of Mary McGann (USGS) for her friendship, continuous help and support to the senior author over many years.

Description —The holotype is the longest and one of the best preserved specimens measuring ~6.7 cm long and ~0.7 cm at its widest ( Fig. 24 View Figure 24 ). It has a circular or oval cross-section (compression of the rocks makes an exact determination impossible), is moderately curved and tapered. It shows coarse radial sculpture consisting of up to 12 ribs on one side crossed with variable weight concentric sculpture, which varies along the length of an individual specimen and varies between specimens from strong to nearly absent due to intraspecific variation and preservation. The radial and concentric sculpture together form a square checkerboard pattern high in the middle of each individual square formed by the sculpture and low on the margins. The interspaces are fine and much smaller than the ribs. The apex was not observed.

Discussion —The subgenus Fissidentalium has large, solid shells, circular in outline and sculptured by numerous longitudinal striae and an apex mostly with a long slit on the convex side. While in Dentalium s. s. the apex is weakly to strongly polygonal and the shell has a number of rounded ribs numbering less than 20 (Keen 1971). Diagnostic features are not observable but the large size and deep water habitat are indicative of the subgenus Fissidentalium .

Miocene California and Pacific Northwest Dentalium include D. laneensis Hickman, 1969 , D. petricola Dall, 1909 ) (new name for Teredo substriata Conrad, 1849 , in part), D. pseudonyma Pilsbry and Sharp, 1898 (new name for Teredo substriata Conrad, 1849 ), in part; syn. D. conradi Dall, 1909 , n. nom. fide Clark (1918)], D. radiolineata Clark, 1918 , D. radiolineata sobrantensis Clark, 1918 , and D. schencki Moore, 1963 . These taxa are distinguished from D. mcganna n. sp. as follows: D. laneensis is smaller and lacks prominent concentric growth lines; D. petricola lacks sculpture; D. pseudonyma is much smaller and does not show growth lines; in D. radiolineata the interspaces are as wide as the ribs, and the ribs fade above and below the middle of the shell easily distinguishing it from the present species. Lastly, D. schenecki , differs in being smaller and having a smooth, strongly tapered shell.