comment on this calibration


 node name
Phaethontes     Look for this name in NCBI   Wikipedia   Animal Diversity Web
  recommended citations Smith and Ksepka, 2015
  node minimum age
56 Ma
OCP.DEK/GE 1087 was collected from Bed IIa, Ouled Abdoun Basin, from near Grand Daoui (Recette 4 + Sidi Daoui; see also Gheerbrant et al., 2003, figure 3), Morocco. This horizon can be constrained only to the level of the Thanetian stage. Tethyan phosphates of the Ouled Abdoun Basin (Oulad Abdoun of some authors) span the Late Cretaceous (Maastrichtian) to middle Eocene (Lutetian). These deposits have been extensively mined, and individual units are dated primarily based on biostratigraphy. No radiometric ages have yet been reported from the stratigraphic section yielding Lithoptila abdounensis. The holotype specimen was collected from an unspecified quarry but can be assigned to Bed IIa of the mining lithostratigraphical terminology (Office Chérifien des Phosphates, 1989; Gharbi, 1998), based on selachians identified in the matrix (Bourdon et al., 2005). As both the numerical age of Bed IIa deposits and the precise horizon from which the Lithoptila abdounensis holotype was collected remain uncertain, we conservatively suggest the entire span of the Thanetian (56.0–59.2 Ma; Gradstein et al., 2012; Walker et al., 2013) be included in the possible range of ages for this taxon. Following best practices for justifying minimum age constraints (Parham et al., 2012), the youngest possible age for the Thanetian, inclusive of error is used as a minimum: 56.0 Ma.
  node maximum age
0 Ma
None specified.
 primary fossil used to date this node 
OCP.DEK/ 1087
Lithoptila abdounensis, Bourdon et al. 2005
Location relative to the calibrated node: Stem

[show fossil details]
     Locality: Ouled Abdoun Basin, from near Grand Daoui
     Stratum: Bed IIa
     Geological age: Paleogene, Cenozoic

More information in Fossilworks   PaleoBioDB

  phylogenetic justification
Phylogenetic justification is based on analyses of morphological data (Bourdon et al., 2005; Smith, 2010). The analysis of Smith (2010) recovered 10 unambiguous cranial synapomorphies of Phaethontes, with four of these exhibiting no homoplasy on the most-parsimonious trees. The synapomorphies supporting Phaethontes, presented in the format: "Character(character state)", with boldface indicating no homoplasy in the character on the most-parsimonious trees, include: 29(1) Quadrate, orientation of the squamosal and otic condyles relative to the long axis of the skull: nearly perpendicular, angle between 75-90º; 50(1) Squamosal, relative length of rostral border of squamosal that joins zygomatic process and caudal wall of orbit: elongate and thin, with constant thickness throughout; 54(1) Squamosal/ Prootic, pila otica elongated, strongly protruding caudoventrolaterally, so that cotyla quadratica otici faces laterally: present; 64(1) Parasphenoid, lamina parasphenoidalis (‘basitemporal plate’) essentially flat and rostrolaterally bordered by marked osseous walls, tubercula basilaria well-developed: yes; 68(1) Dorsal tympanic recess, greatly enlarged, much longer than large, extending rostral to and between cotylae quadratica in a figure-8 shape: present; 72(1) Foramen nervi maxillomandibularis location relative to entrance of recessus tympanicus rostralis: caudal; 83(1) Cranium, elongate, concave, triangular lamina bordered by cristae (i) nuchalis transversae, (ii) nuchalis lateralis, (iii) otica dorsalis, and (iv) post zygomatica, status: present. Mayr (2015, p. 59) described an additional character supporting Phaethontes monophyly which is also present in OCP.DEK/GE 1087: "strongly developed and laterally prominent processus postorbitalis, which, in dorsoventral view, contributes to a marked semicircular concavity of the skull in the area of the fossa temporalis." Although laterally prominent postorbital processes are plesiomorphic for waterbirds (see Smith, 2010, character 47), the distinct shape of these processes in Lithoptila, Prophaethon, and Phaethon most likely represents a synapomorphy of Phaethontes. Additionally, there are several synapomorphies present in referred specimens of Lithoptila (Bourdon et al., 2008) that also support a relationship between Lithoptila and Phaethontidae (Smith, 2010). These include: 223(2) Humerus, relative location of muscle scar for insertion of M. pronator superficialis (= “m. pronator brevis”): only slightly posterior, and proximal to tuberculum supracondylare ventrale; 433(1) Tarsometatarsus, degree of development of area of origin for m. abductor digiti IV, and also passage/sulcus for joint tendon of m. fibularis longi and m. flexor perforans et perforatus digiti III on the lateral half of the plantar face of the tarsometatarsal shaft: well-excavated and distinct sulcus, distally extensive; 437(1) Tarsometatarsus, relative development of distal end of sulcus extensorius in area of foramen vasculare distale: sulcus extremely deep.
  phylogenetic reference(s)
Bourdon, E., Bouya, B., and Iarochene, M. 2005. Earliest African neornithine bird: A new species of Prophaethontidae (Aves) from the Paleocene of Morocco. Journal of Vertebrate Paleontology, 25:157–170.
Smith, N.D. 2010. Phylogenetic analysis of Pelecaniformes (Aves) based on osteological data: implications for waterbird phylogeny and fossil calibration studies. PLoS ONE, 5:e13354.
 tree image (click image for full size) 
tree image
Figure 3 from Smith and Ksepka (2015).