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Monday, 10 June 2013

Mosasaurs From Beyond the Grave by Scott Mardis

(Compiled and edited by Scott Mardis) " The sea saurians of the secondary periods of geology have been replaced in the tertiary and actual seas by marine mammals. No remains of Cetacea have been found in lias or oolite, and no remains of Plesiosaur, or Ichthyosaur, or any other secondary reptile, have been found in Eocene or later tertiary deposits, or recent, on the actual sea-shores; and that the old air-breathing saurians floated when they died has been shown in the Geological Transactions ( vol. V., second series, pg. 512 ). The inference that may be reasonably drawn from no recent carcase or fragment of such having ever been discovered, is strengthened by the corresponding absence of any trace of their remains in the tertiary beds."- Richard Owen, The Times (London), Nov. 11, 1848



Systematics and Morphology of American Mosasaurs

Dale A. Russell

(Originally Published 6 November 1967) pp.178-179

 Elliptonodon compressus Emmons 1858 nomen dubium

Elliptonodon compressus Emmons, 1858, p. 222, figs. 41-42.

TYPE. In Museum of Williams College, from ". . . the miocene near the Cape Fear River, in Bladen county (North Carolina)," (Emmons, 1858, p. 223).

ADDITIONAL REFERENCES. Emmons, 1860, p. 208, fig. 180(2), (5). Cope, 1869b, p. 263;

1869-1870, p. 186. Gilmore, 1928, p. 87. McDowell and Bogert, 1954, p. 152. DISCUSSION. Type and only specimen is a symmetrically bicarinate, somewhat inflated
and gently posteriorly recurved tooth that looks mosasaurian and resembles most
closely teeth of Prognathodon. It differs from any species of this genus however in that
the enamel surface of the tooth is strongly vertically striated. The name Elliptonodon
compressus must be regarded as a nomen dubium due to the incompleteness of the type

and the uncertainty regarding the original horizon of the reworked tooth.

Gilmore (1926, p. 192, pl. 72 figs. 1-2) described and figured a large fragment of a mosasaur dentary from the Coon Creek Formation of McNairy County, Tennessee, mentioning that the teeth were similar to that of Elliptonodon compressus. The dentary probably belongs to
Prognathodon, and its dorsally concave alveolar border resembles that of P. solvayi more closely than the more nearly straight border of P. overtoni.

Holcodus acutidens Gibbes 1851 nomen vanum

Holcodus columbiensis Gibbes, 1850, p. 77 nomen nudum.

Holcodus acutidens Gibbes, 1851, p. 9, pl. 3 figs. 6-9.

Mosasaurus acutidens, Marsh, 18i2b, p. 455.

LECTOTYPE. ANSP 8594, from the "Cretaceous of Alabama," (Gibbes, 1851, p. 9).

ADDITIONAL REFERENCES. Leidy, 1865a, pp. 32, 71, 118, 130, fig. 33, pl. I0 fig. 17.
Cope, 1869b, p. 265; 1869-1870, p. 21O; 1872d, p. 269; 1875, pp. 141, 270. Marsh, 1869,
p. 394. Merriam, 1894, p. 30. Williston, 1897d, p. 185; 1898b, p. 179. Gilmore, 1928, p.
87. McDowell and Bogert, 1954, p. 132.

DISCUSSION. Holcodus acutidens was originaIly proposed by Gibbes for three teeth, one from the Cretaceous of Alabama, a second from the Cretaceous of New Jersey, and a third from the Eocene of Orangeburg, South Carolina. The third tooth has not been located but if it was indeed from the Eocene it could not have been mosasaurian. The second tooth was identified as crocodilian by Leidy (1865a, p. 32), leaving the tooth from Alabama which Williston (1897d, p. 184) treated as a lectotype. This tooth is indistinguishabIe from those of Platecarpus, Ectenosaurus, or Plioplatecarpus and certainly is plioplatecarpine. Because of the inadequacy of the type material Holcodus acutidens must be considered a nomen vanum.

Mosasaurus carolinensis Gibbes 1851 nomen vanum

Mosasaurus caroliniensis Gibbes, 1850, p. 77 nomen nudum.

Mosasaurus carolinienensis Gibbes, 1851, p. 8, pl. 2 figs. 1-3.

TYPE. Specimen not located.
ADDITIONAL REFERENCES. Leidy, 1860, p . 92; 1865a, p. 32. Cope, 1869b, p. 262; 1869-

1870, p. 193; 1875, p. 269.
DISCUSSION. The type is a mandibular fragment probably of a Mosasaurus. It is from
the Pliocene of Darlington, South Carolina, and was derived from the underlying
Cretaceous (Gibbes, 1851, p. 7).

"Recent mosasaur discoveries from New Jersey and Delaware, USA:stratigraphy, taphonomy and implications for mosasaur extinction", W.B. Gallagher, Netherlands Journal of Geosciences, 84 (3) (2005), pp-241-245

(Pg.244)- "The only mosasaurs that are stratigraphically higher occur in the Hornerstown Formation. The basal Hornerstown Formation has an abundantly fossiliferous horizon sometimes called the Main Fossiliferous Layer, or MFL for short. This bed produces mosasaur remains, but these are usually single isolated bones, often quite worn looking – some of the vertebrae from this layer are quite abraded, for example. So it has been argued that this material is reworked from underlying Cretaceous beds. But there are also mosasaur braincases and fresher-looking teeth as well from the MFL, although these are relatively more durable elements that would be more resistant to damage. A number of other Late Cretaceous fossils are found in this layer, including the shark Sqaulicorax, the teleost Enchodus, and

several genera of ammonites. There is some question over the age of this bed – is this a latest Maastrichtian deposit, or is it of early Paleocene age with some reworked Cretaceous fossils

in it? The MFL may be a time-averaged remanié deposit, with Cretaceous fossils accumulating under winnowed low sediment circumstances (Gallagher, 1993). An alternative hypothesis for the origin of this bed is that the MFL represents a lag deposit of Cretaceous fossils left in the wake of an impact tsunami, with subsequent input from Paleocene mortality."

 "Age and provenance of Cretaceous marine reptiles from the South Island and Chatham Islands, New Zealand", Graeme J. Wilson et. al, New Zealand Journal of Geology & Geophysics, 48(2005), pp. 377-387

 (Pg. 384)-Three samples from a block containing mosasaur bones were examined. Zfr 164a (L18959), from the underside of the block, contains a well-preserved diverse dinoflagellate assemblage of Lower Haumurian (S. haumuriense Zone) taxa plus a slightly less common component of Paleocene (Teurian) taxa belonging to the Palaeocystodinium golzowense Zone. The Lower Haumurian taxa include S. haumuriense (abundant), O. spinosa, O. porifera, I. cf. greenense, Nelsoniella semireticulata, N. aceras, Trichodinium cf. castanea, and V. spinulosa. The Teurian component includes Palaeoperidinium pyrophorum, Deflandrea foveolata, Cassidium fragile, Alisocysta cf. circumtabulata, and Cerodinium speciosum. In

the original description of S. haumuriense, Wilson (1984b) noted that the species occurred both at Haumuri Bluff and in the Takatika Grit of Chatham Island. Zfr164b (L18960) from near abone andZfr164c (L18961) from between bones yielded a similar mix of early Haumurian and Teurian
assemblages, although their diversities are less. These mixed Lower Haumurian and Teurian assemblages mirror almost exactly the assemblages described from elsewhere in the Takatika Grit (Wilson 1982b) and indicate that the Chatham's mosasaur was derived (together with
several of the palynomorphs) from Lower Haumurian and subsequently emplaced into Teurian sediments, or occurs as part of a lag deposit. The series of caudal vertebrae that comprise mosasaur specimen Zfr 164 are preserved in such a way as to suggest they have maintained their original life relationship to one another. Their in-line arrangement would seem to preclude their having been eroded from Cretaceous deposits and re-worked into Paleocene deposits. It seems more likely that they were buried in Cretaceous sediment, exhumed or partially exhumed in situ, before being re-buried in Paleocene sediment."

"Late Cretaceous marine reptiles (Elasmosauridae and Mosasauridae) of the Chatham Islands, New Zealand", Christopher P. Consoli and Jeffrey D. Stilwell, Cretaceous Research 30 (2009), pp.991–999

(Pg. 992)-"Marine reptile elements from the Takatika Grit, Chatham Islands have previously been mentioned but never formally described. This paper describes in detail a new marine reptile assemblage from the Chatham Islands. It is also one of the youngest marine reptile assemblages occurring close to the Cretaceous-Paleogene boundary from the high-latitudes of the Southern Hemisphere. The time slice from the Campanian to the Danian (Late Cretaceous-early Paleogene) witnessed the submergence of a finger-like tract of land informally known as the Chatham Peninsula. The well-constrained New Zealand biostratigraphic record has resulted in a mid-Campanian to mid-Danian age range for the Takatika Grit due to its rich dinoflagellate assemblages, correlated to the zonation proposed for New Zealand by Crampton et al. (2000). The Takatika Grit comprises mainly mid-Campanian species typical of the Satyrodinium haumuriense Zone plus a slightly less conspicuous Lower Paleocene component (Palaeocystodinium golzowense Zone). This zonation was based on samples that were removed from matrix on and around an unidentified mosasaur from the nodular-phosphorite bone package (NPB).In addition to the Campanian and Danian palynomorphs, Wilson(1982) recorded New Zealand taxa characteristic of the Cretaceous-Paleogene(KPg)boundary. The palynomorphic data indicate that the phosphate nodules and fossils of the NPB are Late Cretaceous in age, but due to sedimentary starvation and reworking, Paleocene microfossil taxa are recorded. Mosasaurine mosasaurs and the elasmosaurid plesiosaurs were all found in the uppermost horizons of the nodular-phosphorite bone package (NPB) along Maunganui Beach, Chatham Island, New Zealand."

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