In:
PeerJ, PeerJ, Vol. 9 ( 2021-05-06), p. e11179-
Abstract:
Besanosaurus leptorhynchus Dal Sasso & Pinna, 1996 was described on the basis of a single fossil excavated near Besano (Italy) nearly three decades ago. Here, we re-examine its cranial osteology and assign five additional specimens to B. leptorhynchus , four of which were so far undescribed. All of the referred specimens were collected from the Middle Triassic outcrops of the Monte San Giorgio area (Italy/Switzerland) and are housed in various museum collections in Europe. The revised diagnosis of the taxon includes the following combination of cranial characters: extreme longirostry; an elongate frontal not participating in the supratemporal fenestra; a prominent ‘triangular process’ of the quadrate; a caudoventral exposure of the postorbital on the skull roof; a prominent coronoid (preglenoid) process of the surangular; tiny conical teeth with coarsely-striated crown surfaces and deeply-grooved roots; mesial maxillary teeth set in sockets; distal maxillary teeth set in a short groove. All these characters are shared with the holotype of Mikadocephalus gracilirostris Maisch & Matzke, 1997, which we consider as a junior synonym of B. leptorhynchus . An updated phylogenetic analysis, which includes revised scores for B. leptorhynchus and several other shastasaurids, recovers B. leptorhynchus as a basal merriamosaurian, but it is unclear if Shastasauridae form a clade, or represent a paraphyletic group. The inferred body length of the examined specimens ranges from 1 m to about 8 m. The extreme longirostry suggests that B. leptorhynchus primarily fed on small and elusive prey, feeding lower in the food web than an apex predator: a novel ecological specialisation never reported before the Anisian in a large diapsid. This specialization might have triggered an increase of body size and helped to maintain low competition among the diverse ichthyosaur fauna of the Besano Formation.
Type of Medium:
Online Resource
ISSN:
2167-8359
DOI:
10.7717/peerj.11179/fig-1
DOI:
10.7717/peerj.11179/fig-2
DOI:
10.7717/peerj.11179/fig-3
DOI:
10.7717/peerj.11179/fig-4
DOI:
10.7717/peerj.11179/fig-5
DOI:
10.7717/peerj.11179/fig-6
DOI:
10.7717/peerj.11179/fig-7
DOI:
10.7717/peerj.11179/fig-8
DOI:
10.7717/peerj.11179/fig-9
DOI:
10.7717/peerj.11179/fig-10
DOI:
10.7717/peerj.11179/fig-11
DOI:
10.7717/peerj.11179/fig-12
DOI:
10.7717/peerj.11179/fig-13
DOI:
10.7717/peerj.11179/fig-14
DOI:
10.7717/peerj.11179/fig-15
DOI:
10.7717/peerj.11179/fig-16
DOI:
10.7717/peerj.11179/fig-17
DOI:
10.7717/peerj.11179/fig-18
DOI:
10.7717/peerj.11179/fig-19
DOI:
10.7717/peerj.11179/fig-20
DOI:
10.7717/peerj.11179/fig-21
DOI:
10.7717/peerj.11179/fig-22
DOI:
10.7717/peerj.11179/fig-23
DOI:
10.7717/peerj.11179/table-1
DOI:
10.7717/peerj.11179/table-2
DOI:
10.7717/peerj.11179/supp-1
DOI:
10.7717/peerj.11179/supp-2
DOI:
10.7717/peerj.11179/supp-3
DOI:
10.7717/peerj.11179/supp-4
DOI:
10.7717/peerj.11179/supp-5
DOI:
10.7717/peerj.11179/supp-6
DOI:
10.7717/peerj.11179/supp-7
DOI:
10.7717/peerj.11179/supp-8
Language:
English
Publisher:
PeerJ
Publication Date:
2021
detail.hit.zdb_id:
2703241-3
Bookmarklink