Summarizing Compagno et al (2005: 286-87), in modern oceans Paragaleus includes four regionalized species (eastern Atlantic, Indian Ocean and western Pacific); they are small (< 1.5 m) and generally prefer the inner shelf of tropical waters. Most of the species are poorly known; however the Atlantic weasel shark. P. pectoralis (GARMAN 1906), is best understood. P. pectoralis is reported to inhabit shallow waters to 100m and feeds on cephalopods and small teleosts; they go on to note a singular reported occurrence from the NW Atlantic.
The combination of functional tooth-designs within the Paragaleus dentition is unique and diagnostic.
For pectoralis, in the upper quadrate (fig ) a symphyseal is followed by a reduced anterior, then teeth with a primary cusp and strongly cuspleted distal margin (Galeorhinus-like tooth-design). The first significant file is relatively upright, but in succeeding positions (fig ) the primary cusp becomes more & more distally directed -- primarily a cutting design. In the final half dozen positions (fig ), the mesial edge of the crown is nearly parallel to the jaw, serving a clipping function. In the lower quadrate, mesially-positioned files (half dozen or so) are awl-like clutching teeth (fig ). These rapidly gradate (over 2-3 positions) to the Galeorhinus-design (fig ) seen in the uppers then quickly morph into the clipping-like design as seen in the upper. Compagno (1988:258-61) often refers to the unique characteristics of this dentition-design as a diagnostic key.
In general, the Paragaleus dentition is of a clutching-cutting design displaying monognathic and dignathic heterodonty. According to Compagno (1988: 359), quadrate tooth counts range from 13-16. Mark Harris (pers. com 2006) notes that the number of lower anterior-type teeth relative to those of the lateral design might prove to be a specific diagnostic key.
To this author, complete tooth-design is problematic in that the poor availability of dentitions precludes a good study-set; however, there are characteristics that can be observed. Most importantly, the basal margin of the labial crown-face extends beyond the roots. This overhang is less dramatic than present in the triakids, and also lacks the folds characteristic of the triakids. The 'lateral' teeth noted as Galeorhinus-like above, have a primary cusp and distal cusplets; the actual cusplet count is dependent on tooth-position. In these files, the lower mesial cutting edge may be smooth or weakly serrate. Lower anteriors are T-shaped, often with a smooth cutting-edged shoulder; the distal shoulder becomes serrate as it nears the 'lateral' tooth-design positions. In lateral tooth-positions, lower teeth tend to reflect a mesially recurved cusp when compared with their upper counterparts. Compared with Galeorhinus the labial overhang is reduced and the tooth more labio-lingually compressed. A relatively strong nutrient groove with foramen is present.
The Fossil Record
Possibly due to the small size of these specimens (<10 mm), Paragaleus teeth have a poor fossil record.
Cappetta (1987: 118) includes a single fossil taxon -- Paragaleus pulchellus (Jonet 1966) from the Middle & Upper Miocene of Portugal and Middle Miocene of France. The author's tooth description appears to be largely based on extant material; however the included depiction of pulchellus (fig 101k) does reflect a labial overhang.
Case & Borodin (2000: 28) erected P. duplinensis for what they deemed to be Paragaleus-like crowns from the Lutetian of North Carolina. The description lacks detail and the figured specimens (pl 4, fig 34 & pl 6, fig 52-53) show no labial overhang and compare much better with teeth traditionally ascribed to the Physogaleus "secundus" bucket. There is no evidence at this time to accept this as a valid determination (see below).
Balbino & Cappetta (2000) erected P. antunesi for a large number of Paragaleus-like teeth from the Esbarrondadoiro Formation (Late Messian/Late Miocene) of Portugal. These teeth reflect all the propensities that might be expected for the genus and the figured teeth represent the expected tooth-positions. This determination appears totally valid and the paper an example of how a new taxon should be argued.
Purdy et al (2001: 141-42) reported this genus from the Pungo River Formation (units 1-5 = Lower-Middle Miocene) of North Carolina. They were reluctant to ascribe these teeth to a particular species due to the limited number of comparative recent jaws available. They noted that these teeth compared favorably with the Compagno (1988: 258) description of the genus. The lingual perspective crown-designs, as described in text and illustrated, are somewhat Paragaleus-like; but there are no comments or clear illustrations relating to a labial overhang (see below).
North American material
As noted above, the Paragaleus record in North America is very poor and sometimes questionable. Having collected and studied both reported sediments, a few comments might be appropriate. These observations are based on the published determinations, not an examination of the original source material.
Castle Hayne Formation (Middle Eocene, NC)
Case & Borodin (2000) is perplexing in that the figured holotype (pl 6, fig 53) and paratypes (pl 4, fig 34 and pl 6, fig 52) for Paragaleus duplinensis appear to represent a tooth-design normally ascribed to Physogaleus. Similar tooth-designs are included herein (fig.
) to illustrate this observation. As a side note but very relevant: if the plate captions are to be believed, one of the Case & Borodin paratypes (fig. 34) is twice as large as the other teeth (fig 52 & 54); this is much larger than might be expected in Paragaleus.
With that said, their paper does include Paragaleus-like crown-designs (pl 6, fig 58-60) which are identified as Galeorhinus galeus. A similarly-designed tooth is included below (fig ); as can be seen, the labial crown base extends beyond the root and lacks folds. In addition, there are serrations on the mesial cutting-edge, a characteristic not associated with Galeorhinus. However, the strength of the mesial serrations is problematic giving these teeth a Galeocerdo-like tooth-design. Although large Galeocerdo (eaglesomei/latidens) are known from the fauna, there is a lack of ontogenetically transitional tooth-designs between these small teeth and the adult Galeocerdo specimens. The few available small "Paragaleus-like" teeth reflect no characteristics that cannot be attributed to a possible ontogenetic variability of Galeocerdo. Bill Heim (pers com Apr 2007) and I discussed this matter at length without arriving at a consensus -- a definite tooth-positional design is still required.
These specimens appear to display primitive hemigaleid characteristics and considering that Compagno (1988: 397) deemed Paragaleus as such, it would seem to be appropriate to consider the possibility of these teeth as Paragaleus based on lateral tooth-design; however additional tooth-positions are required to confidently determine if they represent Paragaleus, juvenile Galeocerdo or some other carcharhinid.
Pungo River Formation (Lower-Middle Miocene, NC)
The teeth as depicted by Purdy et al (2001: 141-42) appear to lack certain features normally associated with hemigaleids; most importantly, the root is rather thick, the distal cusplets look more like a serrate shoulder rather than running up the distal edge, the crown fails to crisply overhang the root and the tooth is rather large.
Rather than Paragaleus, these tooth-designs are more reminiscent of the recent taxon, Carcharhinus sealei. In the extant species, the mesial edge is serrate over a greater distance then these Lower Miocene specimens; however general tooth-design favors a sealei-like lineage for these teeth.
With that said, the Smithsonian collection includes a specimen which is arguably more Paragaleus-like in design. USNM 475447 (fig. ) has a much more labio-lingually compressed root, displays a crisper labial overhang and is sized in the range that might be expected for Paragaleus. The overall crown shape fits into the sealei design-envelope, but root characteristics are more reminiscent of a hemigaleid. The elasmo.com perspective is that convergent crown-designs may be masking the presence of two taxa, Paragaleus (scarce) and an early C. sealei-like species (uncommon).
Multiple perspectives, expertises and scarce specimens were required for this short webpage. Richard Chandler, Joy Herrington, Eric Sadorf and David Sanderson were kind enough to open their collections to the project, while Pat Young assisted in the imaging of specimens. Mark Harris opened his dentition collection and assisted in the definition of recent Paragaleus dentition-design; Bill Heim and Fabrice Moreau lent their knowledge of fossil carcharhinids.
Balbino, A. & Cappetta, H., (2000). Paragaleus antunesi (Hemigaleidae, Carcharhiniformes) a new shark species from the latest Miocene of Portugal. Tertiary Research 20(1-4): 1-6.
Cappetta, H., 1987. Chondrichthyes II: Mesozoic and Cenozoic Elasmobranchii. Handbook of Paleoichthyology, 3B. Gustav Fischer Verlag, Stuttgart and New York, 193 pp.
Case.G. & Borodin, P., 2000. A Middle Eocene Selachin Fauna from the Castle Hayne Limestone Formation of Duplin County, NC, Munchner Geowiss. Abh.. 39:17-32.
Compagno, L.J. 1988. Sharks of the Order Carcharhiniformes. Princeton University Press, 486 pp.
Compagno, L,, Dando & M., Fowler, S., 2005. Sharks of the World. HarperCollins, 368 p.
Jonet, S., 1966. Notes d'ichthyologie Miocene II: Les Carcharhinidae. Boletim do Museu e Laboratório Mineralógico e Geológico da Faculdade de Ciências. Universidade di Lisboa. 10:65-88.
Purdy, R., Schneider, V., Appelgate, S., McLellan, J., Meyer, R. & Slaughter, R., 2001. The Neogene Sharks, Rays, and Bony Fishes from Lee Creek Mine, Aurora, North Carolina. In: Geology and Paleontology of the Lee Creek Mine, North Carolina, III. C. E. Ray & D. J. Bohaska eds. Smithsonian Contributions to Paleobiology, No 90. Smithsonian Institution Press, Washington D.C. pp. 71-202.