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Gli squali fossili

Serratolamna

LANDEMAINE 1991
Extinct mackerel shark
Upper Cretaceous - Eocene
Ordine Famiglia
Lamniformes BERG 1958 Serratolamnidae LANDEMAINE 1991

Formerly placed in Cretolamna, three species are reported from Mid-Atlantic sediments. Serratolamna serrata (AGGASIZ 1843) is a Cretaceous species known from the Chesapeake, North Carolina and into Texas. Serratolamna lerichei (CASIER, 1946) is an Eocene species known from the Chesapeake and North Carolina, but included by Kent (1994) under Cretolamna. Kent notes a third species from the Eocene of the Chesapeake region and Mississippi - S. aschersoni (STROMER 1905). It would appear that these teeth may in fact be S. gafsana (see below).

The teeth from this genus can be best characterized as being an asymmetrical Cretolamna-type tooth with multiple cusplets. The crowns are smooth with a complete cutting edge. One to three cusplets are present with distal cusplets often outnumbering mesial. The roots have a V-shaped basal margin, weak nutrient groove and distinct foramen. In general, the cusp is an elongated triangle that is distally directed (anterior teeth are nearly erect).
 
Fig. 1 - Serratolamna serrata
from left to right: Anterior: 14 x 11,
anterio-lateral 13 x 14 & Lateral 9.5 x 11.5 mm
Peedee Formation, No. Carolina

Welton & Farish included a lateral tooth identified as S. serrata which looks very much like those of Cretolamna biauriculata maroccana ARAMBOURG 1935 and unlike other teeth of S. serrata. This is likely a dignathic variation, however this design is symmetrical with a significantly broader, shorter and erect cusp. (ref. C. biauriculata illustration). Figure 2 depicts a tooth from Castle Hayne (redeposited Cretaceous?) that shows differences with C. biauriculata illustrations (cusplets not splayed, small foramen) and the tooth image in the Cretolamna section.

Fig. 2 - Cretolamna biauriculata
or Serratolamna serrata
Lateral - 15.5 x 18.5 mm
Peedee Formation, No. Carolina

Serratolamna lerichei is a common tooth in Nanjemoy (Eocene) exposures of the Chesapeake region. Depending on tooth position and age, the teeth of this species can be readily identified or cloaked in "sand tiger homogeniosity". Teeth from mature individuals tend to have smooth crowns and two (the first triangular) cusplets on each shoulder. Juvenile teeth are more reminiscent of Carcahrias and /or Striatolamia, making identifications more difficult. [According to Steve Cunningham (pers. com.), figure 3 includes two ontogenetic variations of an upper anterior 2 tooth.]
 
Fig. 3 - Serratolamna lerichei Upper Teeth
Upper row from left to right
Ant 2 (15 x 11), Ant 2 (13 x 9.5) & lateral (10 x 11 mm)
Nanjemoy Formation (Eocene), Virginia
Fig. 4 - Serratolamna lerichei Lower Teeth
Upper row: Anterio-lateral (13.0 x 12.5 mm)
Lower row: Lateral (13.0 x 14.0 mm)
Nanjemoy Formation (Eocene), Virginia
Fig. 5 - Serratolamna lerichei
Upper: Upper lateral (9.0 x 12.0 mm)
Center: Lower, 1st Anterior (7.5 x 4.0 mm)
Lower: Upper posterio-lateral (6.5 x 10.0 mm)
Nanjemoy Formation (Eocene), Virginia

Uncommon in Nanjemoy (Eocene) exposures are the large teeth of Serratolamna gafsana. These have been often incorrectly identified in the past (including on this page) due to their identification as S. aschersoni in Case (1994). David Ward, when confirming Steve Cunningham's suggestion that these might represent S. gafsana, noted that the illustrations in Arambourg (1952) clearly show that the teeth of S. aschersoni have a shallow root and "bizarre" lateral cusplets. David went on to note that juvenile S. gafsana teeth are Carcharias-like with multiple lateral cusps, fine striations on the labial face.
 
Fig. 6 - Serratolamna cf gafsana
Lateral 22.0 x 18.5 mm
Nanjemoy Formation (Eocene), Virginia
From the collection of Michael Folmer

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