Καρχαρίας
91.000.000 χρόνων
βρέθηκε στο Κάνσας!
Του Γιώργου Λεκάκη
Πρόσφατα ανακαλύφθηκε ένας
καρχαρίας, νέου τύπου, Cretodus Houghtonorum, ηλικίας 91.000.000 χρόνων, στην
περιοχή του Κάνσας των ΗΠΑ, μέρος του μακρύ καταλόγου των μεγάλων ζώων της
εποχής των δεινοσαύρων.
Οι ερευνητές εντόπισαν τα
ερείπια του εντελώς νέου είδους προϊστορικού καρχαρία στο Τιπτον / Tipton του Κάνσας,
το 2010.
Μπορεί να είχε μήκος περίπου 6,1
μ.!
Αλλά ήταν μάλλον αργός καρχαρίας.
 |
| Δόντι του καρχαρία του Κάνσας, 91.000.000 χρόνων! |
Ο Cretodus houghtonorum θα
ήταν ένας θεαματικός καρχαρίας.
Διατηρήθηκε σε ιζήματα που είχαν κατατεθεί σε
έναν αρχαίο ωκεανό, που ονομάζεται West’s Inland Waterway, που εκάλυπτε την
Βόρεια Αμερική κατά την Ύστερη Κρητιδική περίοδο (144.000.000 – 66.000.000
χρόνια πριν).
Το όνομα του είδους
houghtonorum είναι προς τιμήν των Keith και Deborah Houghton, των γαιοκτημόνων
του χωραφιού όπου βρέθηκε, που δώρισαν το δείγμα στο μουσείο για την επιστήμη.
ΠΕΡΙΣΣΟΤΕΡΑ για ΚΑΡΧΑΡΙΕΣ, ΕΔΩ.
Καρχαρίες Cretodus
crassidens, που έφταναν σε μήκος τα 6,8 μ., ευρέθησαν στην Αγγλία και στην
Βόρεια Αμερική.
Αυτό το ζώο γεννούσε μωρά, μήκους 1,2 μ. και γι’ αυτό, ίσως, "κατηγορείται" για καννιβαλιστική τάση.
ΠΗΓΗ: Kenshu Shimada &Michael
J. Everhart «A new large Late Cretaceous lamniform shark from North America, with comments on the taxonomy, paleoecology, and evolution of the genus Cretodus»,
DOI, Journal of Vertebrate paleontology, article: e1673399, 18 Nov 2019. ΑΡΧΕΙΟΝ ΠΟΛΙΤΙΣΜΟΥ, 19.11.2019.
ABSTRACT
We describe a partial skeleton of the Late Cretaceous shark, Cretodus,
collected from the Blue Hill Shale (middle Turonian) in north-central Kansas,
U.S.A.
It consists of 134 disarticulated teeth, 61 vertebrae, 23 placoid
scales, and fragments of calcified cartilage.
The scale morphology suggests
that Cretodus was a rather sluggish shark, and the vertebral morphology affirms
its placement into Lamniformes. With a strong tendency towards monognathic
heterodonty, the dental morphology indicates that the specimen belongs to a new
species, C. houghtonorum, sp. nov., increasing the total known species of
Cretodus to five.
The five species can be divided into three distinct groups:
the longiplicatus/semiplicatus-grade, gigantea/houghtonorum-grade, and
crassidens-grade. Cretodus, that successively evolved by broadening the tooth crown.
The individual of C. houghtonorum, sp. nov., is estimated to be about 515 cm in
total length (TL).
Our vertebra-based growth analysis suggests that the shark
was about 118 cm TL at birth and that the species had an estimated maximum
growth length of 684 cm TL. The large size at birth indicates that the
intrauterine cannibalism behavior of embryos seen in extant lamniforms had
already evolved by the Late Cretaceous. Where C. houghtonorum, sp. nov.,
preferred nearshore environments, the specimen co-occurred with isolated teeth
of Squalicorax and fragments of two dorsal fin spines of a hybodont shark,
circumstantially indicating that the individual of Cretodus fed on the much
smaller hybodont and was scavenged by Squalicorax.
Additional information
ACKNOWLEDGMENTS
We are indebted to K. and D. Houghton for allowing us access to their
land, providing logistical support during the digs, and the donation of the
specimen to the Sternberg Museum of Natural History. A local resident, G.
Pearson, initially introduced M.J.E. to the locality. The specimen was
discovered by another local resident, F. Smith, in conjunction with exploratory
work done by M.J.E. in 2010.
The assistance of G. Pearson and F. Smith with the
excavation is greatly appreciated. We thank especially C. K. Rigsby, A. C.
Nicholas, K. Gray, B. Karl, and J. Hickey (Children’s Memorial Hospital,
Chicago, Illinois) for assisting us with CT scanning of the vertebra-bearing
concretions; E. Bernard and K. Webb (NHMUK) for taking and supplying us the
photographs of the holotype of Cretodus crassidens; J. Pollerspöck
(www.shark-references.com, Stephansposching, Germany) for providing images of,
and additional information about, the holotype of C. semiplicatus; and L. E.
Wilson and C. Byrd (FHSM) for curating FHSM VP-17575, VP-19272, VP-19273, and
VP-19274 for the purpose of this study.
We also thank G. Guinot and M. Newbrey
for their comments on our manuscript that significantly improved the quality of
this paper. Financial support was made to K.S. by the Department of
Environmental Science and Studies and the Department of Biological Sciences of
DePaul University.
ΛΕΞΕΙΣ: Καρχαριας, 91.000.000 χρονια πριν, Κανσας ΗΠΑ, κρητωδης, δεινοσαυρος, 2010, Τιπτον, αρχαιος ωκεανος, Βορεια Αμερικη, Υστερη Κρητιδικη περιοδος, Αγγλια, καννιβαλισμος
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