Petroicidae Mathews, 1919

Nguyen, Jacqueline M. T., Hand, Suzanne J. & Archer, Michael, 2016, The Late Cenozoic Passerine Avifauna from Rackham’s Roost Site, Riversleigh, Australia, Records of the Australian Museum 68 (5), pp. 201-230 : 214-216

Family Petroicidae Mathews, 1919 –20

Genus et species indet.

Figs 12–13

Material. QM F57901 (AR19761), left humerus; QM F50576 (AR16065), right humerus; QM F36366, distal left humerus; QM F57931 , proximal left ulna.

Measurements (mm). QM F36366: preserved length 6.9, distal width>3.8, depth of condylus dorsalis 1.6. QM F50576 : preserved length ca 14.3, proximal width 4.7, length of crista deltopectoralis ca 3.6, mid shaft width 1.3, distal width>3.5, depth of condylus dorsalis 1.6. QM F57901 : preserved length 16.5, proximal width ca 4.5, length of crista deltopectoralis 2.8, mid shaft width 1.5, distal width 4.0, depth of condylus dorsalis 1.6. QM F57931 : preserved length 5.0, proximal width 2.6, length of proc. cotyla dorsalis 1.3.

Description and comparisons. Humerus. QM F57901 ( Fig. 12A,F ) is a near-complete humerus with several small, shallow punctures on the cranial and caudal shaft surfaces and condyles. QM F50576 ( Fig. 12D,I ) is also a wellpreserved humerus with breakage to the ventral parts of the proximal and distal ends and to the crista deltopectoralis. These two fossils are referred to Petroicidae because they possess the following combination of characters. (1) The fossa pneumotricipitalis II is shallow and clearly separate from the fossa pneumotricipitalis I. This fossa is restricted to a moderately deep excavation below the caput humeri. (2) The fossa pneumotricipitalis I is pneumatic and has few large foramina. (3) The crus dorsale fossae is about perpendicular with the long axis of the shaft. (4) The margo caudalis is short and very low. (5) The crista deltopectoralis terminates well distally of the crista bicipitalis. (6) The shaft is gently curved dorso-ventrally. (7) The distal end is well expanded ventrally (in QM F57901 ) and (8) dorsally from the shaft. (9) The sulcus humerotricipitalis is shallow. (10) The sulcus scapulotricipitalis is wide, shallow and ventrally bound by a distinct ridge. (11) In caudal aspect, the distal profile of the humerus between the sulcus humerotricipitalis and sulcus scapulotricipitalis is shallowly concave. (12) The proc. flexorius is truncate and extends a relatively short distance distally of the condylus dorsalis. (13) The proc. supracondylaris dorsalis is broad and has two apices.

QM F57901 and QM F50576 correspond in size to the humerus of the Lemon-bellied Robin Microeca flavigaster . They differ from extant petroicids studied as follows. QM F57901 is distinguished from Kempiella and Devioeca by its narrower distal end relative to the shaft width. The ventral portion of the distal end is broken in QM F50576 , but it can be differentiated from Kempiella and Devioeca in being relatively smaller in dorsal extent from the shaft. The fossil humeri also differ from Pachycephalopsis , Peneothello , Tregellasia and Eopsaltria because the distal end is less expanded dorsally from the shaft. They differ from Poecilodryas , Plesiodryas and Heteromyias in that the distal end is less expanded ventrally. The fossils further differ from Poecilodryas and Plesiodryas in having a shallower fossa pneumotricipitalis II and from Heteromyias in having a relatively narrower fossa m. brachialis. QM F57901 and QM F50576 differ from Amalocichla in having a less curved shaft and from Drymodes in possessing a comparatively longer crista bicipitalis. The fossils differ from Melanodryas because the proc. flexorius does not project as far distally, and from Monachella because the crista deltopectoralis terminates further distally relative to the distal edge of the crista bicipitalis.

The fossils are similar in overall morphology to species of Microeca ( Fig. 12B,G ) and Petroica ( Fig. 12C,H ) studied, but lack significant differences to allow confident generic identification. QM F50576 differs from QM F 57901 in having a slightly larger proc. supracondylaris dorsalis and a ridge on the dorsal surface of the shaft, proximally of the proc. supracondylaris dorsalis.

QM F36366 ( Fig. 12E,J ) is a distal humerus with breakage to the ventral portion. It is tentatively referred to Petroicidae because it shares character states 8–13 described above. This fossil humerus is similar in size to the corresponding bone of the Flame Robin Pet. phoenicea . It differs from Drymodes , Poecilodryas and Petroica in that the distal end is greater in dorsal extent from the shaft. QM F36366 differs from Kempiella , Monachella , Peneothello and Tregellasia in having a shallower fossa m. brachialis. The fossil differs from Devioeca in having a smaller proc. supracondylaris dorsalis, and from Plesiodryas in that the ventral apex of this process is blunt, not pointed. QM F36366 differs from QM F50576 and QM F 57901 in that the distal end is more dorsally expanded, and it has a smaller proc. supracondylaris dorsalis that does not protrude as far dorsally.

A distal humerus that is considerably expanded dorsally (character state 8) was also observed in some species of Meliphagidae , Acanthizidae , Rhipiduridae and Monarchidae . QM F36366 can be excluded from Meliphagidae because it has a wider sulcus scapulotricipitalis relative to the width of the distal end, and the proc. supracondylaris dorsalis does not protrude as far dorsally as in meliphagids. In caudal aspect the distal profile of the humerus is less concave in QM F36366 than in meliphagids. The fossil can be excluded from Acanthizidae because the sulcus humerotricipitalis is deeper, and the proc. supracondylaris dorsalis is relatively longer but does not protrude as far dorsally. QM F36366 can be excluded from Rhipiduridae because it has a relatively wider sulcus scapulotricipitalis and the proc. supracondylaris dorsalis is not as set off dorsally from the distal end. It can be excluded from Monarchidae because the sulcus scapulotricipitalis is relatively wider and the condylus dorsalis is shorter with respect to the condylus ventralis.

Ulna. QM F57931 ( Fig. 13A–C ) is referred to Petroicidae because it exhibits the following character states. The proc. cotyla dorsalis is square and its proximal edge is located well distally of that of the cotyla ventralis, by a distance greater than one-third of the length of the latter. The cotyla ventralis is shallow; the ventral portion of the cotyla is near planar. In cranial aspect, the ventral edge of the tub. lig. collateralis ventralis is near parallel with the long axis of the shaft. In ventral view, the protuberance for attachment of the trochlea humeroulnaris projects beyond the caudal edge of the olecranon. On the caudal surface of the proximal end, there is a depression located ventrally of the impressio m. scapulotricipitis. In proximal view, the protuberance for insertion of M. scapulotriceps projects well caudally.

The fossil ulna is similar in size to the corresponding bone of Pet. phoenicea ( Fig. 13D–F ). It differs from those of extant species of petroicids studied as follows. QM F57931 differs from species of Microeca , Melanodryas , Heteromyias , Monachella , Petroica and Amalocichla examined in having a shallower cotyla ventralis. The fossil further differs from Microeca , Melanodryas and Heteromyias and from Drymodes and Pachycephalopsis in having a relatively shorter olecranon. It differs from Drymodes and Amalocichla in that the protuberance that bears the insertion scar for M. scapulotriceps projects further caudally. QM F57931 also differs from Amalocichla in having a depression situated ventrally of the impressio m. scapulotricipitis. This depression is deeper in the fossil than in Eopsaltria , Monachella and Petroica . The fossil further differs from Eopsaltria and Monachella in having a more prominent protuberance for attachment of the trochlea humeroulnaris.

Remarks. The Australasian robins ( Petroicidae ) are small to medium-sized, plump passerines, and comprise about 48 species in 19 genera (Dickinson & Christidis, 2014). The centre of diversity of petroicids is in Australia and New Guinea, but some species occur in Tanimbar Islands, New Zealand and the southwest Pacific islands (Schodde & Mason, 1999). Petroicids forage by pouncing on insects from an elevated perch or by catching insects on the wing (Schodde & Mason, 1999). In Australia, petroicid robins are predominantly found in wet to dry sclerophyll forests and woodlands, as well as arid scrub and mangroves. They occur in all bioclimatic zones, from rainforest to arid regions ( Higgins et al., 2002). The specimens described here add to the poorly known fossil record of Petroicidae in Australia, previously represented only by late Pleistocene remains of Petroica sp. from Cloggs Cave ( Baird, 1991a). Today, three species regularly occur in the Riversleigh region: the Hooded Robin Melanodryas cucullata , Buff-sided Robin Po. cerviniventris and Jacky Winter Microeca fascinans .

Figures

Figure 12. Humeri of (A,D–F,I–J) fossil Petroicidae gen. et sp. indet. compared with those of (B,G) Microeca fascinans AM O.65147 and (C,H) Petroica phoenicea AM O.60008. (A,F) QM F 57901 left humerus. (D,I) QM F 50576, right humerus. (E,J) QM F 36366, distal left humerus. (A–E) caudal view, (F–J) cranial view. Some distinguishing features of Petroicidae shown: 1, crista deltopectoralis terminates well distally of crista bicipitalis; 2, proc. supracondylaris dorsalis broad with two apices; 3, fossa pneumotricipitalis II shallow and separate from fossa tricipitails I; 4, sulcus humerotricipitalis shallow; 5, proc. flexorius truncate and only slightly extends distally further than condylus dorsalis; 6, fossa pneumotricipitalis I pneumatic; 7, margo caudalis short and very low; 8, sulcus scapulotricipitalis wide and shallow; 9, distal end well expanded dorsally and 10, ventrally.Arrows indicate tooth punctures. Scale = 2 mm.

Figure 13. Proximal left ulnae of(A–C) a fossil petroicid gen. et sp. indet. and (D–F) Petroica phoenicea AM O.60008. (A,D) cranial view, (B,E) caudal view, (C,F) ventral view. Some characteristic features of Petroicidae highlighted: 1, cotyla ventralis shallow; 2, proc. cotyla dorsalis square and its proximal edge is located distally of that of cotyla ventralis by a distance greater than one-third the lengthof the latter; 3, depression situated ventrally of the impressio m. scapulotricipitis; 4, protuberance for attachment of the trochlea humeroulnaris projects beyond the caudal edge of the olecranon. Scale = 2 mm.