Amazing Sawfish of the Past: A brief review of the fossil record of these intriguing animals

Amazing Sawfish of the Past: A brief review of the fossil record of these intriguing animals

All sawfishes are highly modified and elongate rays that swim like a shark and have a long snout with laterally-placed spines. The snout (called a ‘rostrum’) is actually an extension of the skull (known as the ‘chondrocranium’) and the lateral spines are called ‘rostral teeth’ by scientists. Like the rest of the skeleton of the sawfish, the rostrum is composed of cartilage, albeit reinforced with extra calcium. The rostrum and rostral teeth are used in food gathering. The sawfish uses the rostrum to stun prey, such as fishes and invertebrates, which it then sucks into its mouth positioned under the head. There is no cutting or tearing and sawfish can only consume fish and invertebrates that fit into the mouth whole.

The modern sawfish group (family Pristidae) first showed up in the fossil record between the beginning of the Cenozoic (about 66 million years ago) and the beginning of the Eocene (about 56 million years ago). The only exception is the nominal genus Peyeria, which first appeared during the upper Cretaceous (about 100 million years ago). However, the fossil material attributed to the genus Peyeria may actually represent another type of ray—a member of the sharkfin guitarfish family (Rhinidae) such as the bowmouth guitarfish (Rhina ancylostoma).

Living (extant) sawfishes include the following species:

The Knifetooth complex (one species):

  1. Anoxypristis cuspidata (knifetooth sawfish [western Pacific and Indian oceans])

The Smalltooth complex (three species):

  1. Pristis clavata (dwarf sawfish [western Pacific Ocean])
  2. Pristis pectinata (smalltooth sawfish [eastern and western Atlantic Ocean])
  3. Pristis zijsron (green sawfish [western Pacific and Indian oceans])

The Largetooth complex of sawfish has recently been combined into one species:

  1. Pristis pristis (largetooth sawfish [eastern and western Atlantic, eastern and western Pacific, and Indian oceans])

There were also several additional members of the modern sawfish group that are only represented as fossils:

  1. Anoxypristis mucrodens (fossils of Europe, North America, West and East Africa)
  2. Peyeria libyca (nominal species; fossils of northeast Africa including Egypt)
  3. Propristis schweinfurthi (fossils of North and West Africa)
  4. Pristis spp. (at least eight extinct species described; fossils of West and East Africa, Europe, and North America)

Prior to the modern sawfishes, a diverse group of sawfishes (family Sclerorhynchidae) lived during the Cretaceous epoch. Members of the Cretaceous sawfishes had a diverse array of rostral tooth morphologies, ranging from closely-spaced thin spines to widely-spaced massive barbed teeth on sturdy, widened bases. Although most species reached a modest size of not more than 1 meter in total length, fossil rostra measuring well over 1 meter in length have been unearthed in Cretaceous sediments of Morocco.

There are at least 20 genera of Cretaceous sawfishes, including the following:

  1. Ankistrorhynchus (fossils of Europe and North America)
  2. Atlanticopristis (fossils of South America)
  3. Baharipristis (fossils of East Africa)
  4. Biropristis (fossils of South America)
  5. Borodinopristis (a nominal genus of about three species [fossils of North America])
  6. Ctenopristis (fossils of West and East Africa)
  7. Dalpiaza (fossils of West Africa)
  8. Ganopristis (fossils of Europe)
  9. Ischyrhiza (fossils of North and South America)
  10. Kiestus (fossils of North America)
  11. Libanopristis (fossils of Middle East)
  12. Marckgrafia (fossils of West Africa)
  13. Micropristis (fossils of Europe and Middle East)
  14. Onchopristis (fossils of North America, Europe, West and East Africa, Asia, New Zealand)
  15. Onchosaurus (fossils of North America and West Africa)
  16. Plicatopristis (fossils of the Middle East)
  17. Pucapristis (fossils of South America)
  18. Renpetia (fossils of the Middle East)
  19. Schizorhiza (fossils of North America and Middle East)
  20. Sclerorhynchus (fossils of North America and Middle East)

Modern sawfishes and Cretaceous sawfishes evolved independently from the guitarfishes (Rhinobatidae). Thus, while both groups are commonly referred to as sawfish, and both share similar morphological characteristics, they are not closely related. Sawfishes should not be confused with the saw sharks (family Pristiophoridae), which are true sharks and therefore only distantly related to the sawfishes (which are rays, not sharks).

The rostral teeth of Cretaceous sawfishes are attached to the dermis of the rostrum via connective tissue. Their rostral teeth are thought to be continually replaced throughout the life of the animal in the same conveyer-belt fashion as are the oral teeth of all sharks and rays. In contrast, modern sawfishes have rostral teeth firmly embedded in sockets (called ‘alveoli’) and their teeth are not replaced if lost. Cretaceous sawfish rostral teeth are covered with an enamel-like coating along the cusp; this coating is lacking in modern sawfishes. Cretaceous sawfishes also differ from modern sawfishes in that they possess a long, whip-like caudal fin. Although the average fossil remains consist of isolated rostral teeth or oral teeth, some beautiful, fully articulated fossil skeletons have been unearthed in Lebanon quarries.

Sources:

Alroy, J. and M. McClennen. 2013. Paleobiology Database [online resource]. Accessed 06/10/13 online at http://www.paleodb.org/?a=displaySearchColls&type=view.

Faria, V.V., M.T. McDavitt, P. Charvet, T.R. Wiley, C.A. Simpfendorfer, and G.J.P. Naylor. 2013. Species delineation and global population structure of critically endangered sawfishes (Pristidae). Zoological Journal of the Linnean Society 167(1):136–164.

Seitz, J.C. 2013. Fossil Sawfish [online resource]. Accessed 06/10/13 online at http://www.fossilsawfish.com/.

Wueringer, B.E., L. Squire Jr., and S.P. Collin. 2009. The biology of extinct and extant sawfish (Batoidea: Sclerorhynchidae and Pristidae). Reviews in Fish Biology and Fisheries 19:445–464.

Authored by Jason C. Seitz of ANAMAR

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