A middle Eocene mesoeucrocodylian (Crocodyliformes) from the Kaninah Formation, Republic of Yemen
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Date
2013-09-15
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Wydawnictwo Naukowe UAM
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Abstract
During the Cenozoic, the Arabian Plate separated from continental Africa and assumed a closer geographical
relationship with Eurasia. As such, the vertebrate fossil record of the Arabian Peninsula has great potential
for documenting faunal interchanges that occurred as a result of such tectonic events, with a shift from a primarily
Afro-Arabian fauna in the Palaeogene to a more cosmopolitan fauna in the Neogene. Understanding
of the sequence and timing of this faunal interchange has long been hampered by a lack of palaeontological data.
Recently recovered fossils from the Middle Eocene Kaninah Formation of Yemen constitute the earliest Palaeogene
record of continental vertebrates from the Arabian Peninsula, thereby offering a rare glimpse at the region’s post-
-Cretaceous fauna. Here we describe fossil materials from the Kaninah Formation, a collection of dental and postcranial
elements representing a mesoeucrocodylian crocodyliform of unclear affinities. The specimen exhibits ziphodont
tooth morphology along with a biserial paravertebral shield and polygonal gastral osteoderms, consistent
with certain mesoeucrocodylians (e.g., ziphodontan notosuchians). Yet the associated fragmentary anterior caudal
vertebra, although badly abraded, preserves morphology suggestive of procoely. This vertebral type in combination
with the dental and osteoderm morphology is much more taxonomically restrictive and consistent with
the suite of characters exhibited by atoposaurids, a finding that would significantly extend that clade through the
Cretaceous/Palaeogene boundary. Alternatively, given the relative paucity of information from the region during
the Palaeogene, the combination of characteristics of the Kaninah crocodyliform may reflect a novel or poorly
known form exhibiting previously unrecognised character mosaicism. We take a conservative approach, and refer
the Kaninah specimen to Mesoeucrocodylia, Atoposauridae (?) pending discovery of more complete material.
New fossils recovered from the Kaninah Formation raise unanticipated questions about the longevity of Mesozoic
clades, underscoring the role that the region may play in revealing novel occurrences, relictual forms, and evidence of
faunal dispersals from this critical interval in vertebrate evolutionary history.
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Keywords
Mesoeucrocodylia, atoposaurid, crocodyliform, Eocene, Kaninah Formation, Yemen
Citation
Geologos, 2013, vol. 19, 3, pp. 175-183
ISBN
978-83-232187-4-6